Environmental Management Guideline for the Palm Oil · PDF fileEnvironmental Management...

Environmental Management Guidelinefor the Palm Oil Industry

Department of Industrial Works Deutsche Gesellschaft fürTechnische Zusammenarbeit (GTZ) GmbH

Environmental Advisory Assistance for Industry

Environmental Management Guideline

for the Palm Oil Industry

THAILAND

PN 2000.2266.5-001.00

September 1997

IP-Institut für Projektplanung GmbH on behalf of GTZ

Environmental Management Guideline: Palm Oil Industry

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INTRODUCTION The Department of Industrial Works (Ministry of Industry) is implementing the project “Environmental Advisory Assistance for Industry”. This project is executed with support from the German Ministry for Economic Co-operation (BMZ) under the Thai-German Technical Co-operation Programme through the German consulting firm “IP-Institut fuer Projektplanung GmbH” under contract from “Deutsche Gesellschaft fuer Technische Zusammenarbeit – GTZ”. An important activity of this project is the introduction and preparation of industry sector specific environmental management guidelines. The guidelines for the palm oil mill industry are part of this activity and describe alternative methods for utilisation of residues and by-products, waste avoidance and minimisation and give recommendations on how to achieve, in the most cost-effective way, overall environmental management requirements. Sector specific effluent standards form the legal part of the guidelines. These standards can be achieved by implementing the described alternative environmental management methods. The content of the guidelines is the result of teamwork in the palm oil mill working group. This working group consists of representatives from the Department of Industrial Works, Department of Pollution Control, Federation of Thai Industries, The Palm Oil Mill Industry Association and the Prince of Songkla University (PSU). The PSU has been contracted as consultant for the development of the guidelines. Besides discussion and approval of the guidelines content, the working group also agreed on the effluent standards described for this industrial sector. The project implementing agency, Bureau of Industrial Environment Technology within the Department of Industrial Works, hopes that the introduced co-operative approach, which led to this guideline, will support both, the industry as well as the environmental control agencies, in applying cost effective environmental management. For further information concerning additional details please feel to contact the Bureau of Industrial Environment Technology at the Department of Industrial Works – Ministry of Industry - Bangkok. Bangkok – July 1997 Director Bureau of Industrial Environment Technology Department of Industrial Works Ministry of Industry


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CONTENT page Section I Effluent standards for the palm oil mill industry I.1 Minimum standards 5 I.2 Standard method of analysis 5 I.3 Explanation of the minimum standards 6 Section II Environmental management guidelines for the Palm Oil Mill Industry Chapter 1 Preface 7 Chapter 2 Scope of the Guidelines 8 Chapter 3 Palm oil industry of Thailand 9 Chapter 4 Review of palm oil production 10 4.1 Oil palm plantation 16 4.2 Review of “standard wet mill process” 4.2.1 Storage of FFB 4.2.2 Sterilisation 4.2.3 Bunch stripping 4.2.4 Digestion 4.2.5 Oil extraction and handling of residues 4.2.6 Oil purification 4.2.7 Treatment of settling tank underflow 4.2.8 Mass balance summary 4.3 Characteristics of residues 23 Chapter 5 Process integrated pollution prevention And control strategy (IPPCS) 5.1 Improvements in production technology 26 5.1.1 Plantation management 5.1.2 Quality of raw material 5.1.3 Prevention of oil loss 5.2 Utilisation of palm oil mill by-products 33 5.2.1 Utilisation of solid residues 5.2.2 Liquid residue Chapter 6 Review of appropriate techniques for wastewater treatment 6.1 Primary wastewater treatment 38 6.1.1 Segregation of waste streams 6.1.2 Oil separation 6.2 Secondary wastewater treatment 40 6.2.1 Effluent cooling 6.2.2 Anaerobic treatment systems 6.2.3 Aerobic treatment systems 6.3 Nitrogen Removal 47 6.4 Separation and handling of excess sludge 48


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6.5 Design example – pond treatment system 48 Chapter 7 Monitoring and control 7.1 In-plant control 55 7.2 Control by the authority 56 Chapter 8 Glossary and minimum requirements 8.1 Explanation of technical terms 58 8.2 Explanation of minimum effluent quality 60 8.2.1 Biochemical oxygen demand 8.2.2 Chemical oxygen demand 8.2.3 Suspended solids 8.2.4 Total lipophilic substances 8.2.5 TKN-nitrogen Annex-A Detail information of Thailand’s palm oil mills 63 Annex-B Economical aspects 68 Annex-C Members of DIW working team 71 Annex-D Literature 72


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SECTION I EFFLUENT STANDARDS FOR PALM OIL MILL INDUSTRY

I.1 Minimum standards

The described effluent standards apply to the discharge of treated wastewater from palm oil mills into natural watercourses at the final outlet of the plant or processing facility. The effluent sample has to be collected by the procedure described in a special regulation and has to be completely homogenised before analysis.

Table I.1: Effluent standards for palm oil mill industry

Parameter Unit standard

BOD5 COD

Suspended solids Oil & Grease 1)

Total Kjeldahl nitrogen (TKN) pH

Temperature

mg/L mg/L mg/L mg/L mg/L

°C

< 100 < 1,000 < 150 < 25 < 50 5 to 9 < 40

1) Total lipophilic substances (compare Guidelines chapter 8)

I.2 Standard method of analysis Table I.2 shows the methods of analysis to be applied in effluent control.

Table I.2: Standard methods of analysis related to minimum requirements for palm oil mill effluent (compare Guidelines chapter 8) are :

parameter methods 1 BOD5: biochemical oxygen demand 2. COD : chemical oxygen demand 3. SS : suspended solids

Parameters 1-5 must be analysed according to the Standard Method for Analysis of Wastewater of USA (APHA, AWWA, WPCF, 1989) [ 1]

4. O&G: oil and grease1) 5. TKN : total Kjeldahl nitrogen 6. pH Measure with pH meter at the point of

sampling 7. Temperature Measure with thermometer at the point

of sampling. 1) Total lipophilic substances


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I.3 Explanation of the minimum requirements

The given minimum standards differ significantly from general effluent standards of Thailand (1996). This is due to the specific conditions of the Palm Oil Mill effluent. These conditions and the reasons for the required standards are prescribed in the Environmental Guidelines for Palm Oil Mill Industry. Summarising this, it has to be recognized that after full biological treatment, even if this treatment achieves a very high efficiency, the remaining effluent still has relatively high concentrations of pollutants if compared with the general wastewater standard. This is due to the extremely high pollution load in the untreated raw effluent.


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SECTION II ENVIRONMENTAL MANAGEMENT GUIDELINES FOR THE PALM OIL MILL INDUSTRY CHAPTER 1 PREFACE In order to achieve the minimum environmental standards prescribed by National Law, the following Environmental Management Guidelines for the Palm Oil Mill Industry have been developed.

These Guidelines deal with all aspects of the production of palm oil (except the refining of the oil) including liquid and solid by-products/residues and effluents/wastes and consider possible emissions to the atmosphere. These Guidelines promote closed concepts for utilisation and disposal regarding the complex of all environmental media of this branch of industry. National Environmental Law states that the owner or processor of the palm oil mill has to reduce or eliminate the pollutants or to appropriately dispose of them. This leads to the priority of avoiding or utilisation of residues within the industry instead of treatment and disposal of created wastes offsite Furthermore these Guidelines prescribe measures which help to meet the defined minimum requirements and the general objective of reducing or eliminating the pollutants.


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CHAPTER 2 SCOPE OF THE GUIDELINES

At present, there are 49 palm oil mills in Thailand (see Annex A1) with mills using the “standard wet milling process” accounting for 85 % of the total production capacity. The mills using the “standard wet process” have the greatest impact on the environment. Therefore, the minimum environmental requirements together with the environmental management guidelines will deal only with those mills using the “standard wet process”. The refining process is not the subject of the guidelines.

The advice, recommendations and information regarding the utilisation of Palm Oil Mill by-products, for example by using good agricultural practices, could be applied to all types and sizes of oil palm plantations and in some aspects to other kinds of plantations and palm oil mills. The Guidelines aim to support the operating companies in their effort to meet the minimum requirements and avoid or reduce their pollutants. The oil mill should choose the combination of pollution prevention and control technology, which is found optimum for their specific conditions.


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CHAPTER 3 PALM OIL INDUSTRY OF THAILAND The oil palm plantation and the palm oil industry in Thailand is comparatively young. In 1979 oil palm plantation area was 155,000 rai (2.5 rai = 1 acre) and increased to 950,000 rai in 1993 with the production yield of 1,530,000 ton of fresh fruit bunches (FFB), valued at about 2,600 million Baht. More than 98% of the plantations are in Southern Thailand, particularly in the provinces of Krabi, Surat Thani, Chumporn, Trang, Satun and Songkhla (Table 4.1). The palm oil industry has developed very fast in recent years. In 1995 there were 49 palm oil mills in operation (Annex A1) with an overall production capacity of 405,000-t crude oil/year. Fifteen mills share about 60 % of the total palm oil production capacity, equal to about 250,000-t crude oil per year. Both, the plantations and the mills have a high potential for further optimisation in terms of agricultural & production technology. Because of the concentration of palm oil plantation & mills in Southern Thailand, this industry is of dominant importance in terms of work provision and generation of income to local people. Beside the main product - crude palm oil - the mills generate many by-products and liquid wastes, which may have a significant impact on the environment if they are not dealt with properly. During the study of “Oil Recovery from Palm Oil Mills Waste Water” [H-Kittikun, et al., 1994 [2]] it was observed that standard palm oil mills, for each 1 ton (fresh fruit bunch - FFB) used will generate liquid waste of about 1 t with a pollution load, related to 1 ton of FFB, of BOD 27 kg, COD 52 kg, suspended solids (SS) 13 kg and oil and grease 8 kg/t FFB respectively (see map in Annex A). Comparing the pollution load of the palm oil mill industry with domestic sewage, in average, the water pollution of the total palm oil mill industry is equal to the wastewater generated by around 3 million people per day - in terms of BOD5 (Annex A2 and map). Palm oil is an agro industrial product, which has been listed for free trade by Asian Free Tariff Area (AFTA). However, Thailand had to ask for suspension of free trade in palm oil for a period of time, to give the palm oil industry a chance to become more competitive with its neighbouring countries. Palm varieties, plantation management, extraction and refinery technology and utilisation must be developed further and improved to be competitive with other palm oil producers in South East Asia, namely Malaysia and Indonesia. Because of the rapid growth of the palm oil producing industry, the economic importance of palm oil production, as well as because of the subsequent impact of palm oil production on the environment, it was found necessary to implement special minimum environmental requirements for this industry. The environmental management guidelines describe methods of production management by the mill, through process integrated pollution prevention and control strategy (IPPCS) This production strategy aims at the maximum utilisation of residues and by-products as well as the minimisation of non-valuable residues resulting in optimum waste avoidance and raw material utilisation. In addition, the guidelines provide recommendations to meet environmental requirements, by describing the most cost-effective wastewater treatment systems for this branch of industry.


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CHAPTER 4 REVIEW OF PALM OIL PRODUCTION A schematic flow sheet, indicating the relationship between the oil palm plantation, the mill and the environment is shown in Figure 4.1 4.1 Oil palm plantation The palm oil is extracted from the pulpy portion (mesocarp) of the oil palm (Elacis quieensis). At present, the Tanera variety provides the highest content of oil in the Fresh Fruit Bunch (FFB) (oil content: 18 % w/w average, 21 % maximum, 16 % minimum). About 120 kg/t FFB are nuts, which include 60 kg/t FFB (5% of FFB) as kernels, which contain about 50 % oil resp.30 kg/t FFB. The overall oil content of the FFB may be between 20 % and 25 % including the kernel oil. All oil palm plantations in Thailand are located in the southern part. Map No.1 (Annex A) and table 4.1 shows the southern provinces and the oil palm regions.

Table 4.1 Oil palm plantation area [rai] (1993) [3]

Province oil palm plantation area - rounded figures -

flat area about 10 %3)

<5 % slope area about 5 %3)

Prachuab Khirikan

Chumporn1)

Krabi2)

Satun2)

Songkhla1)

Surat Thani1)

Trang2)

21,000

170,000

360,000

55,000

8,000

270,000

35,000

2,100

17,000

36,000

5,500

800

27,000

3,500

1,000

8,000

18,000

3,000

400

14,000

1,700

Summary Westcoast 448,000 45,000 22,500

Summary Eastcoast 450,000 45,000 22,500

Summary total 898,000 90,000 45,000

1) east coast 2) west coast 3) of total area estimated


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Figure 4.1 process flow sheet, oil palm plantation/oil mill


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Please note: the estimation of flat and 5% slope-land was made in order to approximate a realistic utilisation of liquid residues from palm oil mills. (See chapter 5.2.2 of the guidelines).

The palm trees are planted in rows as follows:

number of palms per rai 20 trees/rai distance between the rows: ~ 8 m distance between palm tree in the row: ~ 8 m The oil mills normally are situated in the neighbourhood of the plantations. The average distance to the mill is about 20 km. Nevertheless the average transportation time is about one (1) day. Sometimes, however, long distance transportation of up to 100 km (from Krabi-province to Surat Thani-province) has been reported.

The number and size of individual plantations and their part of the total planting area is shown in Table 4.2..

Table 4.2: oil palm plantations - rounded figures1993 [3]

type of oil palm plantation

area per site (rai)

number of sites total area in rai (rounded)

estates 62 430,000

large plantations 200 210 160,000

medium plantations 50 to 200 510 95,000

small plantations < 50 3,750 175,000

summary 860,000

If the average production of a medium size Palm Oil Mill is 25 tons FFB/h (or 400 t/d and 150,000 t/year), and 2 tons of FFB/(rai/year) are harvested, the average oil palm growing area per palm oil mill is calculated as 75,000 rai. The transport of the harvested fresh fruit bunches (FFB) from the plantation to the mill is mostly organised by the farmers and done with open lorries. In addition to oil palm plantations also rubber is grown in that area. The rubber growing area is shown in table 4.3, which was used for calculating the rate of utilisation of liquid palm oil mill residues (wastewater).


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Table 4.3: Rubber plantations (1993) [3] Province Area [rai]

Chumporn1) Krabi2) Satun2)

Songkhla1) Surat Thani1)

Trang 2)

Others

190,000 510,000 260,000

1,650,000 1,325,000 1,060,000 6,634,000

Summary 11,625,000

legend:1) east coast 2) west coast 3) estimated

number of rubber trees planted per rai: 70 trees/rai The main types of fertilisers needed are given in table 4.4. The demand is developed referring to the mean soil quality and estimates of crops-demand over a period of several years.

Table 4.4: Medium annual demand of fertiliser for oil palm and rubber trees (1993) [4]

type of crop fertiliser demand [g/(tree : year)]

N P K Mg B

young oil palms adult oil palms old oil palms

260 to 700 900 to 1280

» 1630

110 to 140210 210

60 to 320 420 to 560

560

14 to 70 140 210

100 80

100

mature rubber (older then 7 years)

470

230 540 80

N = Nitrogen P = Phosphorous K = Potassium Mg = Magnesium B = Boron The following Table 4.5 shows the amount of fertilising elements required per one rai (20 oil palms or 70 rubber trees planted per one rai)


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Table 4.5: Medium annual demand of fertiliser for oil palm and rubber trees per rai

type of crop fertiliser demand [kg/(rai year)] N P K Mg B

young oil palms adult oil palms old oil palms

5.2 to 14 18 to 25.6

> 32.6

2.2 to 2.6 4.2 4.2

1.2 to 6.4 8.4 to 11.2

11.2

0.3 to 1.4 2.8 4.2

2 1.6 2


32.9 16.1 37.8 5.6

the above table indicates that rubber plantations need much more fertiliser (related to P and K) than palm oil plantations.

Figure 4.2 shows the monthly rainfall values for the province Krabi in the West Coast of southern Thailand in correlation with the production of fresh fruit bunches. It shows clearly the peak production at the end of the rainy season (August).


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4.2 Review of “standard wet mill process” and its variations, the sources of residues and the mass balance The schematic flow diagram of the standard wet process is shown in Figure 4.3. This process is characterised by the application of gravity oil separation in a “settling tank”. (The following numbers given are derived from “PORIM-Standard-Sheet 1988" [6] and from research work of the Prince of Songkla University PSU during 1992 until 1994)[2, 7, 8, 9, 10, 11, 12]. The data are presented as rounded average figures. However, these figures may differ for each particular Palm Oil Mill, depending on the degree of applied internal recycling of liquid phases.

4.2.1 Arrival and storage of fresh fruit bunches (FFB) at factory

Soon after harvesting, the FFB must be brought to the mill. The FFB are unloaded on a ramp and put into containers of 2.5 to 3 t transport capacity. The time from harvesting until sterilising of the FFB should be as short as possible and not longer than 72 h. This is to avoid excessive production of free fatty acids by the natural enzymes present in the mesocarp. Palm oil of fresh fruits contains about 1 % free fatty acids (FFA). This content increases rapidly by ageing of the fruits with the value of oil decreasing respectively.

4.2.2 Sterilisation Sterilisation of the FFB is done batchwise in autoclaves of 20 to 30 t FFB capacity. Depending on that capacity 7 to 9 containers of FFB can be put into the “steriliser”. Sterilisation of FFB is done with the application of “live steam” under the following process conditions:

temperature: 120 - 130 °C pressure 2 bar total sterilising time per batch about 2 hrs. retention time (for sterilising) 45 to 60 minutes total steam consumption 200 kg/t FFB steam loss into air 75 kg/t FFB liquid residue about 150 kg/t FFB initial oil content about 180 kg/t FFB loss of oil about 0.5 kg/t FFB

Figure 4.3 Process flow sheet standard wet process with settling tank (palm oil milling)


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The FFB is sterilised in order to inactivate the natural enzymes which stops splitting of fat into free fatty acids (FFA) and the subsequent loss of oil.

In addition, the sterilising process loosens the fruit of the FFB, and softens the mesocarp, resulting in easier extraction of oil.

4.2.3 Bunch stripping

The containers with the sterilised bunches are emptied into a rotary drum threshers where the fruits are separated from the bunch stalk. The empty fruit bunches (EFB) are at present often separately stored for incineration to reduce the mass of residues and for simultaneous production of ash which has plant fertilising value.

This process step generates the following residues: EFB (solid residues) 200 to 230 kg/t FFB moisture content 150 kg/t FFB oil loss 4.5 kg/t FFB moisture evaporation 30 kg/t FFB liquid residues none

4.2.4 Digestion The separated fruits are discharged into vertical steam-jacketed drums (digesters). Here the fruits are treated mechanically by to convert them into a homogeneous oily mash. Hot water is added to the digester to facility homogenisation. This mash is subsequently fed into the oil extraction press. Process conditions: steam consumption 20 kg/t FFB hot water consumption 65 kg/t FFB moisture evaporation 30 kg/t FFB solid/liquid residues none

4.2.5 Oil extraction and handling of solid residues Extraction of palm oil is done by means of a continuous screw press system. The extracted oil phase is collected and is discharged to the purification section. The remaining press cake is transported to a separation system consisting of air classifiers and cyclones (depericarper or fibre separator) for recovery of the nuts and fibres. The nuts and fibres are dried during this separation process by hot air, which is indirectly heated by steam to a temperature of 135°C. Kernels are recovered from nuts in centrifugal crackers and are normally sold to kernel oil mills. Fibres and shells are sent to the boilers house and used as fuel. The screw press produces raw crude oil which contains a high concentration of suspended matter, resulting in difficulties in oil water separation and a high organic loading in the wastewater discharged from the palm oil mill.


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Products and residues of this process steps: raw crude oil (mixture of oil, water, fibres) 400 kg/t FFB oil content (PO) 170 kg/t FFB water content (steam, fruit water) 200 kg/t FFB non-oil substances (NOS) 30 kg/t FFB moisture evaporation 50 kg/t FFB solid residues total (mixture of fibres and nuts) 320 kg/t FFB kernels (incl. 30 kg PK/t FFB) 60 kg/t FFB shells 60 kg/t FFB fibres (the rest) 145 kg/t FFB moisture loss during 55 kg/t FFB separation of fibres liquid residues none 4.2.6 Oil purification: clarification and drying The production process described in chapter 4.2.6 and 4.2.7 take place in the so called “oil room”. 4.2.6.1 Screening of raw crude oil For improvement of the following separation steps of oil clarification, hot water is added to the raw oil and then passed through a vibrating screen (Johnson-Screen or Sweco-screen) to separate larger size solids as dirt, fibres and fragments of the pericarps from the liquid phase. The oil, after sieving, still contains small size solids and water. The large surface of these types of sieves result in intensive contact of oil with air which has a negative effect on oil quality due to oxidation of oil. Products and residues of this process step: raw crude oil 400 kg/t FFB solid residues very little* liquid residues none * depending on the efficiency of the sieve, solids are transferred directly back to the press 4.2.6.2 Separation of suspended solids from oil The conventional procedure for separation of oil from water and suspended solids is the “settling tank” method. The raw oil is heated either by the introduction of live steam or with closed steam heating coils which facilitates gravity separation. Depending on the applied settling tank surface loading rate and retention time, this procedure, however, has a low separation efficiency of about 50 % only. As a result, either the separated oil still contains a high concentration of suspended solids or the settled residue (settling tank bottom sludge) contains a high content of oil. Long retention times combined with high temperature also reduce the oil quality. To improve overall oil yield of the process, some mills switched from the settling tank procedure to a more efficient oil clarification system using a 3-phase centrifuge (decanter). This equipment, however, is not part of the original standard wet process. A more detailed description of this advanced oil separation system is given in chapter 5 of the guidelines (process integrated pollution prevention and control strategy).


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The separated oil floating on top of the settling tank is collected by a funnel system and sent to the oil purification system. The settling tank underflow is collected in the sludge tank and subsequently treated recovery of oil. Products and residues of the settling tank process step: hot water consumption up to 320 kg/t FFB raw crude oil about 95 kg/t FFB (mixture of around 90 % oil, 10 % water and very little amount of fibres) liquid watery residues up to 625 kg/t FFB (underflow: mixture of water, oil and non oily substances) process temperature > 95 °C surface loading rate 0.5 to 2 m/hr retention time 1 to 5 hr 4.2.6.3 Separation and removal of fine suspended solids from the oil The raw crude oil from the settling tank (top oil) is combined with recovered oil from the treatment of the settling tank underflow (see chapter 4.2.7). This results in a total crude-oil production of about 163-kg per ton of FFB processed. Centrifuges carry out this final oil purification (solids removal) step. For easy operation, these centrifuges are equipped with an automatic cake discharge and cleaning system Because of the low suspended solids content in the raw crude oil this process step does not generate large volumes of solid residue and, hence, has a very low impact on the environment. - Residues from this production process step are negligible 4.2.6.4 Oil drying and cooling The purified crude oil, after the centrifugation step, still contains water, which is removed by a vacuum evaporation system. Subsequently, the dried crude oil is kept in storage tanks and sold to an oil refinery. This process-step of crude oil drying has very little environmental impact. Products and residues of the drying step (estimated): steam consumption about 10 kg/t FFB (indirect steam) cooling water consumption 300 kg/t FFB pure crude oil 163 kg/t FFB process temperature 95 °C final oil temperature 40 °C cooling water (effluent) 300 kg/t FFB cooling water temperature 80 °C vapours (from drying) 10 kg/t FFB

4.2.7 Treatment of settling tank underflow (bottom sludge)

The bottom sludge from the “settling tank” is characterised by a high oil content (around 14 %), high concentration of organic substances (both in the dissolved form and as suspended


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solids) and water soluble substances. In addition, the water phase contains fine fibres and sand. In order to recover oil and to decrease the organic load of the liquid residue, the settling tank bottom sludge is further treated as described below.

4.2.7.1 Straining and desanding

In order to protect the equipment in the subsequent process steps (in particular centrifuges) against clogging, the bottom sludge is pre-cleaned by means of microstrainers/hydrocyclones. These “desanders” are frequently cleaned by discharging the accumulated solids to the drain, followed by the injection of fresh water. Desander washwater consumption is normally around 5 litre per ton of FFB

This process step results in solid residues: residues from micro-strainer negligible sand/water mixture 10 kg/t FFB washwater consumption 5 kg/t FFB

4.2.7.2 Centrifuging

The pre-cleaned settling tank bottom sludge is collected in a buffer tank (“sludge tank”) and then pumped to two-phase centrifuges (separators) for oil recovery. To improve oil separation it is common practice to add water to the bottom sludge to improve the oil separation efficiency, which is normally about 92 %. Water consumption is about 200 kg per ton of FFB processed. This water consumption figure includes equipment-cleaning washwater. Products and residues from the centrifugation step: raw crude oil recovered 78 kg/t FFB (by underflow-treatment) liquid residue < 742 kg/t FFB incl. suspended solids (NOS) 30 kg/t FFB incl. oil loss 7 kg/t FFB solid residue none Improved oil recovery efficiency can be achieved by using the decanter process in place of the settling tank - separator process. This process, using a three-phase centrifuge (decanter) in place of the settling tank system is described in detail in chapter-5 of the guidelines. The mass balance of the two different oil recovery systems is given in table 4.6 and 4.7 respectively.


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4.2.8 Mass balance summary

Tables 4.6.1 and 4.6.2 show output data of the different production processes applied in the “oil room”. Since steam consumption has been considered only in respect to the generation of polluted effluent, the total mass balance for steam in the production and utilisation areas (production of electricity etc.) is not included in the Table 4.6 and 4.7.

Table 4.6: Output-balance of “standard wet process” (settling tank and separator centrifuges (see flow sheet Figure 4.3 for comparison)

medium type of material individual mass

individual oil content

oil loss rel. to total loss

kg/t FFB kg/t FFB %

Solids EFB fibre shell kernel (incl. PK oil) centrifuge cake (oil separa-tion and purification)

230 145 60 60 0

4.5 5 0 0 0

26 30 0 0 0

Total 495 9.5 56

Liquids raw oil PO Washing/cooling water (except indirect cooling water) steriliser effluent underflow of settling tank after centrifugation (separator) with a suspended solid load of > 30 kg/t FFB

163 depending on

local conditions 150 742

0

0.5 7

0

3 41

Total 1055 7.5 44

gas/vapour water vapour 250 0 0

Total 250 0 0

Leakage process instability, breakdowns inefficient equipment

depending on local conditions

Total

Summary total 1800

oil loss 17 100


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Table 4.7: Output-balance of “standard wet process” with improved decanter process (compare flow sheet Figure 5.2)

medium type of material individual mass

individual oil content

oil loss rel. to total loss

kg/t FFB kg/t FFB %

solids EFB fibre shell kernel (incl. PK oil) centrifuge cake (oil separation and purification)

230 145 60 60

~ 20

4.5 5 0 1

30 33 0 7

total > 515 10.5 70

liquids raw oil PO washing/cooling water (except indirect cooling water) sterilizer effluent waterphase of separator after decanter centrifuge

165 depending on

local conditions

150 165

0

0.5 4

0

3 27

total > 480 4.5 30

gas/vapour water vapour 250 0 0

total 250 0 0

leakage process instability, breakdowns inefficient equipment

depending on local

conditions

total

summary total

> 1245

oil loss 15 100

4.3 Characteristics of residues It has to be emphasised that the entire palm oil milling process does not need any chemicals as a processing aid. Therefore, all substances found in the products, by-products and residues originate from the oil palm plantation. Considering wastewater treatment either for effluent utilisation or for discharge to a watercourse, the main characteristics of the final residues are described by the following substrates, which are quantified in table 4.8 and 4.9 respectively.


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- carbonaceous substrate as BOD5, COD or PE1) - nitrogen fixed in organic and inorganic TKN substances: - phosphorus (total phosphorus) P - potassium K - magnesium Mg 1) PE = population equivalents in respect to sewage (60 g BOD5/person/day)

Table 4.8: Average organic load of residues generated by the “standard wet process” consisting of settling tank and separator centrifuge

medium type of material

individual mass BOD5 BOD5 PE CO

D COD

SS SS oil oil

2) 1) 2) 3) 1) 2) 1) 2) 1) 2) solids EFB 230 - - - - - - - 20 4.5 fibre 145 - - - - - - - 34 5 nuts 100 - - - - - - - 0 04) sludge - centrifuges 0 - - - - - - - - liquids POME after

final 892 30 27 450 90 52 34 13 8 7.5

oil trap(mixed)

summary

1367 17

1) g/L 2) kg/t FFB 3) PE60 /tFFB 4) related to PO - = not determined


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Table 4.8: average nutrient content in the residues of Palm Oil Mills residue water

content (%)

N1) P1) K1) Mg1) kg /t of FFB 2)

solids

EFB EFB-ash fibre fibre/shell-ash sludge centrifuges if improved dec.proc.

60 0

20 0

720

8-

23-

20

0.6 17

0.1 17-66

8

24.1 450

2 170-250

20

1.8 36

0.4 40

4

230 4

145 50

30

liquids 4) POME after final oil trap (mixed) POME after anaerobic treatment POME after full biological treatment3)

0.2-1

~ 0.1-0.9

~ 0

0.1-0.3

~0.1-0.3

~ 0.1

~ 2

~ 2

~ 2

~0.5

~ 0.5

~ 0.5

settling tank: 892 improved decanter proc: 315 settling tank: 892 improved decanter proc: 315 settling tank: 892 improved decanter proc: 315

2) evaporation excluded 3) rough estimation 4) as kg/t FFB [1) kg/t dry residue for solids, kg/m3 for POME] (rounded figures) [2) these figures are to be verified by additional measurements]

Boron is not shown in the table because the few available analysis results of show only traces of this element in the residues. It is important to mention that biological treatment of POME does not influence the content of mineral substrates significantly.


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CHAPTER 5 PROCESS INTEGRATED POLLUTION PREVENTION AND CONTROL STRATEGY [IPPCS]

The principle of IPPCS is to manage the production process efficiently, such as: to improve the production yield, to improve product quality, to recover by- products and residues and to utilise as much of these residues as by-products as possible. Where this is either technologically or economically feasible, all residues should be minimised and the unavoidable residues are treated properly for disposal. IPPCS will help to save natural resources, reduce environmental pollution and will provide benefits to the producer by increasing production yield and reducing energy and waste treatment costs.

With respect to the existing state of the art of Palm Oil Milling, it is anticipated that there is a significant potential to develop IPPCS in the Palm Oil Mill industry. The following examples (table 5.1) may stimulate improvements in this direction [13, 14]. 5.1 Improvements in production technology 5.1.1 Plantation management Until there are new developments, the Tanera variety of oil palms will be used for oil palm plantation. Public institutes should make efforts to increase the quality of oil palms, especially for the special climate and soil conditions of Southern Thailand. There are activities to develop oil palms with fruits without any kernels [15]. The pre-nursery, main-nursery, small, adult and old palm must be managed differently, especially the fertilisation (See Table 4.4). 5.1.2 Quality of raw material Co-operation between the plantations and the palm oil mills needs to be developed with respect to the optimal timing of the harvest of the FFB and their utilisation in production. The time span between harvesting and processing at the mill has to be reduced to less than 72 hours. Utilisation of residues should be given more importance. Overripe fruits and aged FFB can result in oil loss due to oil splitting (formation of free fatty acids [FFA]) by natural enzymes, low quality crude oil and high organic loading in the mill’s effluent, as described in chapters 4.1 and 5.2 [15].


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Table 5.1 Pollution control in palm oil extraction process Processing step detail step prevention and control results

1. raw material handling 2. sterilisation 3. bunch stripping 4. oil extraction 5. oil separation

screw pressing filtration flotation and settling tank desanding sludge centrifuging

process within 24 hrs. control steam pressure and time should not mix steriliser condensate with wastewater from oil room fruit bunches still containing palm fruits should be collected and resterilized control the pressure to get maximum oil out of the fibre and minimise the cracking of palm seed vibrating screen is in good condition use steriliser condensate to mix with crude oil, separate oil as soon as possible examine the waste water wash the desander according to the time table use decanter check and wash the decanter according to the time table

easy to extract and provide better quality oil save energy and time easy to separate oil since contains low concentration of suspended solids increased oil yield minimised oil loss with fibre separates small fibre reduces the solid load in crude oil reduces water consumption improves oil separation reduces oil loss reduces oil loss reduces water consumption reduces solids in wastewater

6. final oil trapping steriliser condensate wastewater from decanter (or separator) washing and cleaning water cooling water from boiler and evaporator oil collection

separate from other wastewater add one more separator into the system save water and minimise usingdetergent collect this water for washing and cleaning, routine collectionor use automatic skimmer routine control and check the equipment maintenance and repair fast

easy to separate oil reduce oil loss reduce water consumption reduce emulsification reduce water consumption recovers good quality oil back to the process reduces equipment damage reduces oil loss through leakage and accident


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5.1.3 Prevention of oil loss in the production process

The mass balance of the standard wet oil milling process with settling tank (figure 4.3 and table 4.6) reveals an overall oil loss of about 10 % (17 kg/t FFB). About 56% of the oil lost is fixed to the solid residues (mainly to EFB and fibre). The other 44 % are discharged along with the liquid residues (mainly oil-room effluent). In addition, the mass balance shows that the oil room effluent is the main source of oil loss in liquid residues during normal operation. Oil losses due to process instabilities and leakage are not considered in the mass balance. However, they may be of great importance, depending on the quality of the process equipment and the efficiency at which the process is operated.

5.1.3.1 Oil loss prevention by improved process control and equipment maintenance

Oil losses due to process instabilities and leakage result in increased oil concentration in the mill’s effluent. The oil load in the effluent may double for these reasons, leading to total oil loss of 10 - 15 kg/t FFB. Examples for oil loss in the production process: steriliser: sub optimal process conditions lead to poor loosening of the fruits and oil loss to the EFB (if not controlled and recycled) settling tank: hydraulic overloading leads to poor quality oil and high oil load in the underflow excessive retention time leads to poor oil quality in terms of to FFA-content centrifuges (separator): clogged plates reduce separation efficiency and increase oil loss In addition, inefficient equipment (leaking steriliser, unsuitable type and opening sizes of sieves and filters, inappropriate type and outfit of centrifuges), defective machinery, leakage (by break down, leaking flanges, overflow of tanks) may often be the reason for extra oil losses. Prevention methods include improved process control and equipment maintenance (including tanks and pipes), and repair/replacement of worn-out or broken equipment without delay. 5.1.3.2 Oil loss prevention in the different process stages Measures taken to improve the process firstly should concentrate on those process stages, which produce the highest oil losses as shown in the mass balance: - screw press oil extraction including the subsequent press cake treatment - oil separation by settling tanks (oil room) - treatment of settling tank underflow (oil room)


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The other process steps may be optimised in a later improvement phase. Improved oil extraction The results of pilot tests carried out with oil mill effluent [2] indicate:

- the lower the amount of suspended solids in the water phase, the better the separation of oil, leading to improved sludge separation (fibre and cell material).

- the higher the oil concentration in the water/oil mixture the higher the separation efficiency through centrifugation.

The suspended matter in the liquid residues of the process (mainly consisting of fibres) which come from the screw press cake and the centrifuge cake, has a high absorption capacity of oil. At present, about 33 % of the oil lost is absorbed on these fibres (including the centrifuge sludge). As a result of these observations, it can be concluded that the screw presses should be improved to achieve better press efficiency and to minimise the fibre content (SS) in the liquid phase. Further investigations are required to conclude on the feasibility of using advanced extraction methods for oil recovery from the liquid residue, i.e. by the application of special solvents [6]. Improvements in screening/sieving The application of improved screening methods could lead to a reduction of suspended solids in the liquid phase, resulting in better oil separation and avoiding the formation of FFA by reduction of contact between the hot oil and the ambient air (oxygen). Suitable screening systems, for example rotating brush sieves should be tested and evaluated for their applicability. Improvement of oil separation The mass balance for the oil separation system using the combination settling tank / underflow-centrifuge indicates poor separation efficiency of 50 %. In addition, this process leads to poor oil quality (oxidation because of long retention time, up to 5 hrs, high temperature and large contact area) and produces large volumes of highly polluted effluent (dilution water for separation). A better alternative to this method is direct centrifuging of the screened/sieved raw oil (from the screw press) in a 3-phase-centrifuge (decanter) without any settling tank in between. This method is well known as the standard decanter process and has already been implemented in several palm oil mills and has been proven to be technologically and economically feasible. The schematic process flow diagram of the standard decanter system is shown in Figure 5.1. A comparison of this method with the settling tank process (see Figure 4.3), with respect to efficiency and effluent generation is shown in table 5.2.

Figure 5.1 process flow sheet,”improved wet process with standard decanter” (standard decanter process)


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Table 5.2: Comparison of oil separation systems: standard settling tank process vs. standard decanter process and improved decanter process

criteria unit “standard settling tank process” settling tank +

underflow-separator

“standard decanter process”

direct centrifuging (decanter)

“improved decanter process”

direct centrifuging (decanter + separator)

separation efficiency oil loss during separation reduction of SS of POME hydraulic load of settling tank centrifuge No.1 centrifuge No.2 volume of effluent

% kg/t FFB kg/t FFB

ltr/t FFB ltr/t FFB ltr/t FFB ltr/t FFB

95.3 7 0

720 820

- 892

95.9 7

10 to 20 -

395 -

315

97 5

> (10 to 20) -

395 165 315

Table 5.2 indicates that the capacity of the centrifuge required for direct centrifuging in the standard decanter process is only 50 % of the separator-centrifuge used in the standard settling tank process. This indicates a significant reduction in capital and energy costs if this type of oil separation process is used. In addition, the standard decanter process will be less complicated to operate (no settling tank, no diluting water, no recycling). Besides operating at a much smaller liquid (water) volume (40 to 60 % reduction) the standard decanter process also removes the majority of suspended material from liquid. This results in a reduced BOD load generated by the standard decanter process despite its higher BOD and oil concentrations [16, 17, 18].

Further optimisation of the standard decanter process is possible by installing a separator in series after the decanter. (centrifuge-separator process). This process is called the improved decanter process (see Figure 5.2 and Table 5.2). This process improvement leads to an extra oil recovery of about 2 kg oil per ton of FFB, and an increase of the total oil separation efficiency to about 97 %. This second stage separator/centrifuge will receive the water-phase of the three phase decanter at a comparatively low hydraulic rate of about 165 kg/t FFB. In addition to the improvement in oil in separation efficiency this separator/centrifuge further reduces the suspended solids contents and helps to stabilise the overall oil separation process.

Figure 5.2 process flow sheet, ”improved wet process with two stage centrifuge oil separation” (improved decanter process)


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5.1.3.3 General measures for effluent minimisation

Effluent minimisation of the effluent volume has many consequences, especially if it is achieved by a process of internal recycling. Therefore, this option has to be carefully evaluated for each individual case before implementation. The evaluation should concentrate on; - preventing natural water resources from pollution - up-concentration of substances in the process water, i.e. of components of the

introduced water (salts etc.) or concentration of fine suspended solids - increasing corrosiveness of the process water - formation of high concentrations of toxic substances Utilisation of recycling/reuse of process water could be possible in the following process steps: - water for the digester - washwater for the desanding equipment 5.2 Utilisation of palm oil mill by-products and residues

The quantities of by-products and residue from a palm oil mill are summarised as follows (compare Table 4.6): Solid residues: Empty fruit bunches 230 kg/t FFB Fibre 145 kg/t FFB Shell 60 kg/t FFB Decanter Sludge cake ~ 30 kg/t FFB (if decanter process is used) Liquid residues (if standard wet process with settling tank [Figure 4.3] is used): total ~ 900 kg/t FFB The description of various measures for utilisation of palm oil mill residues should give stimulating impulse to both scientific research and pilot projects supported by the government and to their subsequent full-scale application by the industry [14]. 5.2.1 Utilisation of solid residues 5.2.1.1 Empty fruit bunches (EFB) Empty fruit bunches present the bulk of solid residues (20% of FFB) generated by a palm oil mill. Returning EFB to the plantations (see Figure 4.1) utilising the EFB’s value as organic fertiliser (see chapter 4.3) and soil conditioner should be given first priority. Several possibilities of EFB application exist:

a) direct application of unconverted EFB on land. b) use of EFB as covering material to protect the soil against erosion, for

improvement of moisture retention in the soil surface and as a nutrient. The rate of benefit depends on the type of soil and the humidity conditions of the location. This approach suits in particular the dryer inland plantations and is useful during the dry season.

c) application as organic fertiliser. The usage of EFB under “good agricultural management practice” is shown in Table 5.3 (derived from Tables 4.5 and 4.9 and moisture content assumption of EFB of 60 %).


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Table 5.3: Average annual application of EFB for oil palm and rubber trees (per 1 rai with respect to the different fertilising compounds)

EFB application [tons/(rai year)]

crop N P K Mg

young palms adult palms old palms

1.1 to 3 3.8 to 5.3

» 6.8

6.2 to 7.2 11.7 11.7

0.08 to 0.4 0.6 to 0.75

0.75

0.3 to1.3 2.7 3.8


6.9 44.7 2.6 -

The above Table 5.3 indicates that the EFB utilisation rate is limited by its Potassium (K) value. Therefore, only 0.1 to 0.75 t EFB can be utilised per rai per year for an oil palm plantation and 2.6 t for a mature rubber plantation. However, exact figures concerning the actual availability of the EFB-substrate to the palm trees have not yet been developed and need further investigation.

However, there are disadvantages in the application of unconverted EFB as fertiliser. Firstly, its high specific volume, which results in comparatively high transport and distribution costs. Secondly, EFB attracts rodents and insects, both of which can cause damage to plantations.

d) EFB could be used as a substrate for mushroom cultivation. At present, a few farmers only practise this. Further research into mushroom cultivation would certainly help in terms of improving the viability of this option e) EFB may be used in the production of particleboard. This would add a significant value to this residue. f) The use of EFB as a fuel for boiler is constrained by its high moisture content and low heating value (dry EFB <10 MJ/kg). In addition, there are better solid residues available as fuel sources at the mills such as dried fibre and shells. Furthermore, incineration of EFB requires air pollution control in terms of removal of suspended particles (dust), SO2, CO, CO2 and NOx. These air pollution control systems are rather expensive, especially when compared to the size of boiler house. g) Incineration of EFB in order to reduce its volume and to recover the ash (as fertiliser) has the great disadvantage of generating excessive air pollution because of incomplete incineration. This method should not be applied because of the wastage of valuable carbon material, which can be useful for soil conditioning. An advantage of this method is the easier utilisation of the EFB fertiliser value. Because of the low volume of the incineration ash, which still contains the fertilisers present in the EFB, distribution of the fertilising compounds at the plantation is made much easier.

The conversion of EFB by i.e. by shredding into small pieces can significantly reduce the specific volume and improve substrate availability for the plants. The technical and economical feasibility of this method, however, has to be further investigated to establish its techno-economic soundness.


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5.2.1.2 Palm fibre Around 15 % of the FFB are palm fibres (see Table 4.6). The composition of palm fibre in respect to its fertilising substances is shown in Table 4.8. Fibres are used mainly as fuel for boilers (calorific value of dried fibres <5 MJ/kg). Other applications of palm fibre include its use as a substrate for enzymatic saccharification as animal feed with a 10-20% addition to the feed. Too large an amount of palm fibre (40 to 60%) could decrease the feed’s digestibility. Adding 5 to 6% NaOH (w/w) or urea and allowing 2 to 3 weeks fermentation can achieve an improvement in its quality. Addition of proteins such as fishmeal, soybean meal and molasses to the fibre will result in a higher palatability. 5.2.1.3 Shell Shells can be used as boiler fuel (calorific value of dried shells is around 17 MJ/kg). Therefore, the shells are often accumulating in the mill. A further possible use is the production of activated carbon, which should be further investigated. 5.2.1.4 Decanter cake For mills using decanter for oil separation or purification, the generated decanter cake can be utilised as a fertiliser like EFB. The acceptable annual soil application can be calculated using Tables 4.5 and Table 4.9. 5.2.2 Liquid residue (palm oil mill effluent - POME) The generation and characteristics of liquid residue (POME) is described in Chapter 4.2.8 and 4.3. Application of biologically treated POME for irrigation is a method used by many palm oil mills. The preconception that the utilisation of raw POME leads to soil deterioration because of its high concentrations of oil/grease, organic acids and nitrogen-compounds, may be the result of poor application resulting in overdose. Application of POME for irrigation purposes has to be carried out carefully, as overdose will result in nutrient imbalance and leads to undesirable chemical reactions in the soil. It has been reported that prolonged inadequate utilisation of POME may cause the accumulation of magnesium and inhibit the availability of the potassium. In this case, potassium may have to be added. The pH of the soil (pH 4.5 to 5.5) may also be increased. However, if application of POME is based on the following calculations the risk of accumulation will be minimised. The POME dosage should be based on the fertiliser requirement of the plants and not on the permissible hydraulic loading rate of the soil. Spillage of POME into ground water or into surface water must be avoided. Using this method, seasonal weather conditions have to be considered, in particular the rainy season (see Figure 4.3 of chapter 4.1) during which POME application is limited, requiring storage of POME. Most of the existing palm oil mills have sufficient storage POME capacity in their treatment ponds. POME as fertiliser. The amount of POME to be applied under “good agricultural management practices” is shown in Table 5.4 which is derived from Tables 4.5 and 4.9 and Annex B, Chapter 1.2; [14].


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Table 5.4: Average annual application of POME for oil palm and rubber trees (per 1 rai with respect to the different fertilising compounds)

POME application [m3 /(rai year)]

crop N P K Mg

young palms adult palms old palms

10 to 28 36 to 51

~ 65

11 to 13 21 21

0.5 to 4 4 to 7 ~ 7

0.5 to 4 ~ 6 ~ 8

mature rubber (older then 7

years)

66 81 23 -

Table 5.3 indicates that the utilisation rate is limited by the Potassium value (Mg is of the same order of magnitude). Therefore, only 0.5 to 7 m3 POME can be utilised per rai per year for an oil palm plantation and 23 m3 POME for a mature rubber plantation. This value may not be exceeded because of the possible harmful consequences to the soil, including bad-smell problems. The potassium demand must be calculated according to the needs of the plants for a period of more than one year, and up to three years depending on the type of soil. In summary, the volume of POME, which can be used for fertilising of oil palm, is limited by its potassium content resulting in a maximum application of approximately 7 m3/rai/year. This figure is derived using the following conditions: - Potassium (K)-demand 560 g/tree /year - trees/rai: 20 trees/rai - K-demand per rai: 11.2 kg K/rai /year - K-content of POME: 1.6 kg K/m3 - POME-dosage (= 11.2/1.6 ) ~ 7 m3/rai /year From Table 4.9 it can also be concluded that biological treatment has no significant influence on the permissible amount of POME to be used for proper fertilisation. Biological treatment does not significantly reduce the mineral content in POME. Considering the above conditions the following calculations can be made for analysing the feasibility for this type of POME utilisation in the plantations of Southern Thailand.


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Calculation for utilisation of the total POME of all palm oil mills Production capacity (for the year 1993) 1,530,000 tons FFB/year Case A: all palm oil mills use the standard wet process with settling tank (Figure 4.3)

specific amount of POME about 0.9 m3/t FFB resulting in a total annual quantity of about 1,400,000 m3/year calculated plantation area required about 200,000 rai available oil palm plantation area about 135,000 rai

necessary area required for other usage i.e. rubber plantations 65,000 rai

Case B: All palm oil mills use the improved decanter process (Figure 5.2)

specific amount of POME about 0.3 m3/t FFB resulting in a total annual quantity of about 500,000 m3/year calculated plantation area required about 65,500 rai available oil palm plantation area about 135,000 rai necessary area required for other usage i.e. rubber plantations none

One of the main biochemical processes taking place in the soil is the mineralisation of organic nitrogen. In the first conversion step the organic nitrogen is converted into ammonia. In a well-aerated soil, the nitrifying organisms subsequently convert ammonia to nitrate (via nitrite). Ammonia and nitrate are the only available compounds of nitrogen to the plants. The organic-N and ammonia-N are absorbed by the soil and not washed out into the ground water by the rain when dosage is accurate. The absorption capacity depends on the type of soil. Investigations in Malaysia show that POME used in a oil palm plantation increased the yield by 13 % without adding other fertiliser. Some palm oil mills in Thailand also adopt this method of POME application and found that palm tree growth and yield were clearly increased. Several systems are available for transporting POME from an oil mill to the plantation including its distribution on land as fertiliser. The most suitable method should be selected according to the local conditions including factors such as distance, type of roads, type of soil etc. Distribution by tankers or sprinkler systems can be used. Furrow irrigation and similar systems should be avoided because of the comparatively low volume of POME to be applied per rai. This method could lead to overloading of the land on which POME is applied. In order to establish practical and economically feasible methods for distribution of these small quantities onto land, it is highly recommended to initiate technical scale trials, which should be conducted over a prolonged period of time.


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CHAPTER 6 REVIEW OF SUITABLE WASTEWATER TREATMENT TECHNOLOGIES Treatment of palm oil mill wastewater has the following two main objectives:

- to adjust the existing insufficient quality of POME to a load level (i.e. oil and grease) suitable to the individual fertilising conditions; here partial treatment would be sufficient. This treatment will not significantly reduce the content of dissolved mineral substances.

- to meet the requirements for effluent discharge into surface waters; in this

case full treatment would be necessary. These guidelines provide only general information about available treatment technologies most suitable for POME. The supply of details of the selected treatment method for a particular palm oil mill will be the responsibility of the factory’s environmental engineering consultant. The decision for selection of the most suitable wastewater treatment system has to be based on the wastewater characteristics of the particular factory. Other factors which have to be considered are: flow rate pattern, available space and location of wastewater treatment plant, required degree of treatment, fixed and operating costs of treatment, type of operation method and experience of the operator. 6.1 Primary wastewater treatment

6.1.1 Segregation of wastewater streams As shown in the schematic process flow diagrams (figures 4.3, 5.1 and 5.2 respectively) a palm oil has the following effluent streams:

- high polluted effluent; i.e. effluent from steriliser and oil room - low polluted effluent; i.e. steam condensate and indirect cooling water from oil

dryer/cooler; boiler house discharge (except if it contains high concentrations of phosphorus or other inhibitors)

- sanitary effluent; i.e. toilet, bathrooms and canteen To minimise overall treatment costs the different wastewater streams should be collected and treated separately The highly polluted wastewater streams from a palm oil mill have different suspended solid contents, which influence the effectiveness of the pre-treatment system. The highly polluted effluent streams, therefore, should be further classified into two categories:

- low suspended solids content wastewater; i.e. steriliser condensate, and oil discharged from leakage

- high suspended solids content wastewater; i.e. oil room effluent Because of the significant difference in quality and treatability, the two waste streams should be collected separately as follows:

- combine all streams with little or no suspended solids (SS) - combine the remaining effluent streams with high SS concentration

- avoid recirculation of streams with high SS content with raw wastewater streams for oil recovery (i.e. never utilise the water phase of the centrifuge/separator for dilution purposes in the settling tank)


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6.1.2 Oil separation In order to make oil separation/recovery as efficient as possible, the different wastewater streams should be treated separately in gravity type oil separators. The removal/recovery of oil by means of gravity separator pre-treatment contributes to improved production yield and minimises the organic loading to the subsequent biological treatment system. Because of the high oil content in the raw wastewater, the remaining oil content in the pre-treated effluent will still be rather high at > 250 mg/l. However, these conditions have to be accepted and considered for the subsequent methods of effluent utilisation or treatment: 6.1.2.1 Low suspended solids content wastewater Since the oil in this type of wastewater is mainly in the free form, removal/recovery can be easily achieved in gravity type oil separators. The pre-treated wastewater could be recycled/reused in the mill. Design criteria for gravity type oil separator (oil trap): - the oil trap should be designed for the maximum flow rate - permissible surface loading rate: 2 to 6 m3/(m2*h) depending on results

from lab tests (separation speed) - accidental discharge of oil through leakage or equipment failure should be

considered in the design - installation of an automatic oil skimming device will help to recover good

quality oil Oil separation efficiency for this wastewater stream by gravity type oil trap is in the range of 60 to 90 %.

6.1.2.2 High suspended solids content wastewater These streams mainly originate from centrifuges in the oil room. Since this wastewater is generated by oil separation equipment using very high acceleration forces compared with the gravity oil trap, further oil removal by gravity separation will be marginal. However, installation of gravity type oil traps for this type of wastewater is recommended mainly as a safety device for cases of accidental oil discharge from equipment failure or other types of oil leakage. Design criteria: - the oil trap should be designed for the maximum flow rate (as litre/second). - permissible surface loading rate 0.5 m3/(m2*h) - for storage and thickening of settled solids the depth of the trap should be considered carefully. The trap should be divided into several compartments by either bottom baffles (for bottom sludge) or surface baffles (for detention of floating oil). - installation of an automatic oil skimming device will help to recover good quality oil Many physical and chemical oil recovery methods such as filtration, dispersed air flotation, dissolved air flotation (DAF) and chemical coagulation (testing different inorganic and organic flocculants) have been investigated at laboratory scale [2, 6, 7, 8, 9]. The findings, however, indicate very low oil recovery efficiency of these methods, resulting from the large high suspended solids concentration in combination with the formation of a stable oil/water emulsion in this particular type of wastewater [2, 7, 8, 9].


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6.2 Secondary wastewater treatment

The most appropriate secondary treatment method for palm oil mill wastewater is biological digestion. Preconditions are:

- mainly organic substances are to be treated - absence of substances toxic to biological decomposition; operational

difficulties for palm oil mills can be expected only in case of excessive oil discharge

If the anaerobically treated effluent is used for irrigation, no secondary treatment is necessary. However, if the final effluent is discharge to a public watercourse, secondary treatment in the form of an aerobic treatment step is necessary after anaerobic treatment. The principle of biological digestion is the utilisation of micro-organisms like bacteria, protozoa, algae etc., either under aerobic or anaerobic conditions, for the conversion of organic substrate. Anaerobic systems convert the dissolved organic substrate mainly into biogas (mixture of around 60 % methane CH4 and 30 % CO2). Only very little of the substrate is converted into biomass. The biomass must be separated as biological excess sludge (measured as volatile suspended solids [VSS]). Under normal operating conditions less than 0.3 kg VSS per kg BOD5 removed is formed. The organisms under aerobic conditions convert organic substrate dissolved in the effluent mainly into biomass and to some extent into gas like CO2 or N2, which is discharged to the atmosphere. Generation of excess sludge for the aerobic treatment methods is in the range of 0.2 to 0.8 kg VSS/kg BOD5, depending on the organic loading rate. The COD/BOD5-ratio of the filtered raw POME is about 1.8, indicating good biodegradability of the wastewater. However, the COD/BOD5-ratio of the unfiltered raw POME is in the range of 2 - 2.4 which suggests poor biodegradability. However this high COD/BOD5-ratio in the homogenised (unfiltered) raw POME results from the high suspended solids content (NOS= non-oily substances) which are of organic material (e.g. cellulose). These particles are only partially degraded by biochemical means during 5 days; however are oxidised biochemically during longer retention periods, as is the case in the actually used biological reactor (ponds) for POME-treatment. The optimum substrate to nutrient ratio (BOD5: N: P) for aerobic treatment of 100: 5: 1 is normally not given in the raw POME. But anaerobic micro-organisms need only a nutrient ratio of at 100/1.3/0.3, which can be achieved for POME. In fact there is normally a surplus of nutrient in POME available for anaerobic treatment. Because anaerobic treatment mainly reduces the carbonaceous material in the effluent the subsequent aerobic treatment will have no deficiency of N or P but may have a deficiency of carbonaceous substrate. Full-scale biological effluent treatment is ecologically less preferable as compared with the utilisation of the wastewater as fertiliser. Used as fertiliser all nutrients including the dissolved salts are recycled to the soil from were they are utilised by the oil palm. Biologically treated effluent still contains the majority of the dissolved inorganic substances like inorganic salts, which are not removable by this kind of treatment. After discharge of the biologically treated POME to the receiving water these substances are wasted to the aquatic environment.


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At present, different types of biological treatment systems are operated in palm oil mills, which use a combination of anaerobic and aerobic treatment methods. However, only limited information is available on design figures as well as operational experience with these treatment systems in palm oil mills. The following chapters give a summary of the available information.

6.2.1 Effluent cooling The optimum temperature for anaerobic treatment is 37°C. Since the POME has a temperature in the range 75-90°C, a cooling step is required prior to biological treatment. Temperature reduction through flow in a long channel or using a cooling pond is common practice in the palm oil mills. The channels have the advantage, that they can be constructed in such a way, that there is always sufficient flow, avoiding separation of oil and NOS as well as creating turbulence for good heat exchange. Because of the low hydraulic loading of cooling ponds fat and NOS will separate. These ponds, therefore, have to be cleaned regularly. The pond bottom construction as well as the inlet distribution systems and the shape of the pond have to be carefully designed. The pond depth should not exceed 1.5 m otherwise the cooling efficiency decreases. The hydraulic retention time of the cooling pond should be at least 1 day. If cooling towers are used for temperature reduction they must have a two cycle, counter current system (indirect cooling) in order to avoid clogging problems. Cooling towers have the best cooling efficiency of the systems applied.. Despite the high initial temperature of the effluent, biological decomposition (anaerobic) of POME already starts in the cooling system. This normally leads to acidifying processes which convert oil/grease into fatty acids and subsequently to short-chain organic acids by enzymatic reactions. As a consequence odour-generating substances are released, resulting in bad smell. Control of pH (at about 7-7.5) is important to avoid this problem. In order to improve effluent cooling, as well as to get some adjustment of the pH-value and to decrease the substrate concentrations in the initial part of the treatment system to moderate conditions, and to avoid settling of sludge, some parts of the anaerobically treated POME can be recycled back to the inlet of the cooling system. The optimum recycling ratio has to be established for each individual palm oil mill by experiment and should be between 30 and 70 % of the wastewater flow rate. Also the most suitable location at the treatment system from where recycling has to be carried out, has to be determined by trial to achieve optimum pH-control. In case of an anaerobic pond system uses a retention time of >100 days, not the final effluent should be recycled but recycling should be done from the spot where highly active anaerobic biomass (with methanogenic type bacteria) is available. The first third of the overall pond system may be optimal for recycling i.e. after 30 to 40 days retention time.

6.2.2 Anaerobic treatment systems

These systems have the following significant advantages over aerobic treatment methods:

- (almost) energy free operation - only moderate operational impact from high organic loads, except in the acidification

step of the system (which can be avoided) - low surplus sludge formation ( less than 0.3 kg TS/kg BOD5 removed)


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6.2.2.1 Anaerobic pond The anaerobic digestion system usually used in Thailand is the open pond system consisting of a series of several ponds. The advantages and disadvantage of the anaerobic pond system are shown in Table 6.1 [20, 21].

Table 6.1 Advantages and Disadvantages of Anaerobic Pond Systemz

Advantage Disadvantage 1. Simple construction 1. requires large land area (COD volumetric loading

between 1 to 5 [kg/m3*d]) 2. Simple operation 2. treatment efficiency of the system should be limited

to 60-70% of BOD5 removal in order to maintain adequate nutrient ratio (C/N/P) for further aerobic treatment required for river discharge

3. biogas can not be recovered 4. bad smell of H2S and organic acids, if over-loaded 5. needs regular desludging During design and operation of the pond system the volume requirements for collection of the settled primary sludge of the raw POME as well as the anaerobic excess sludge have to be considered. Sludge accumulation will result in reduced pond volume with subsequent reduction in pond retention time, increased COD-volume-load as well as reduced overall tre-atment efficiency. This impact of sludge accumulation in the ponds is discussed in more detail in chapter 6.5. The operational experience with pond systems shows the development of a thick scum top layer, which closes the pond surface area and hence minimises the rate of gas exchange between the reactor and the ambient air. If acidification in the first part of the pond can be avoided, there is very little development of odour from the ponds. Design considerations:

- suitable inlet- and outlet-construction for optimum flow distribution and avoidance of short-cut flow in the ponds

- watertight and firmly compacted embankments - if the system has more than single-stage ponds, the first stage should not exceed a

volumetric load of 5 kg COD/(m3*d); the pH in the first stage must be controlled, appropriate recycling has to be introduced

- appropriate sloped pond banks (1/1.5) - because desludging of the ponds is only possible by emptying, standby pond have to

be constructed The decision on whether to use this system depends on many factors. The main factors are land price, conditions of the surrounding area of the factory, such as density of population and communities who may be affected by possible air pollution. In addition the loss of unrecoverable biogas as a source of energy must be considered. However, the biogas is not an important source of energy for palm oil mill at present, because the energy produced by combustion of fibre and shell is sufficient for the factory. This may change if refinery activities are introduced, which require more energy.


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Table 6.2: design criteria for wastewater treatment by anaerobic pond BOD overall volumetric loading 1) 0.5-1.5 kg/(m3*d) (the first part of the plug flow system may be much higher loaded as the last part)

Depth of pond 3 to 5 m pH should be controlled by proper loading 6.7 to 7.4 Efficiency 1) (% BOD removed) 60-70 % (% COD removed) < 80 %

Excess sludge 0.1 to 0.32) kg/kg BOD5

1) should be limited in order to maintain an adequate nutrients-ratio for subsequent aerobic treatment

2) depending on the final BOD volume load and the content of slow biodegradable SS in the influent

6.2.2.2 Closed anaerobic digestion systems Palm oil mills have sufficient supply of energy from the use of solid residues (fibres and shells). This energy surplus as well as because of the simplicity and low investment and operation cost of the pond system, the closed anaerobic digester is at present not widely used in palm oil mills. Various systems of closed anaerobic reactors are available, such as: - one-stage-reactors and two-stage-reactors; with the first stage operating as acidification step (gas produced is mainly CO2) and in the second stage as methanogenic step (methane gas) Widely used types of methane-reactors are + completely mixed reactors + fixed bed reactors + upflow anaerobic sludge blanket reactors (UASB-reactor) Because of the presence of ammonia, magnesium and phosphorus in the POME, the possibility of magnesium-ammonium-phosphate formation in the digester has to be considered. This magnesium salt tends to precipitate under methanogenic conditions of the reactor which can clog fixed bed type reactors. If UASB-reactors are selected, the concentration of COD in the raw wastewater should not exceed 6,000 mg/L in the raw effluent. Higher COD loads will result in excessive gas formation, which will washout the biological sludge from the reactor and hence reduced treatment efficiency. To achieve operational stability in the anaerobic digester, intense fluctuation of organic loading has to be avoided. This can be achieved by using the cooling pond as equalisation tank, from where the raw effluent is fed continuously to the anaerobic reactor. The effluent recycle principle as discussed in chapter 6.2.1 is applied in closed completely mixed anaerobic reactors. This recycling is carried out either internally (by gas insertion or by mechanical stirrers) or by external means (via pumps and pipes). This principle activates the reactor by increasing the turbulence resulting in more intensive contact between substrate and micro-organisms.


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Screening of the raw wastewater is required to protect closed reactors from coarse solids. In addition, anaerobic reactors may generate excessive foam formation, which can be controlled by dosing antifoaming agents. The material used for reactor construction should be resistant to acid corrosion (especially in the gas phase). The energy content of the generated biogas in comparison to other energy sources: 1 m3 of biogas is equal to 0.7 litre fuel oil

0.8 litre petrol 2.7 kg dry firewood

For one cubicmeter of POME per ton of FFB, with a loading of 40 kg COD/t FFB the production of biogas will be around

7.2 m3 biogas / t FFB 7.3

equal to an energy value of 150 MJ / t FFB

Table 6.3: Advantage and disadvantage of closed anaerobic digester compared with anaerobic pond.

Advantage Disadvantage

1. High efficiency, depends upon the 1. High investment cost. COD volume loading 20 kg COD/m3.d , % removal > 50 3 kg COD/m3.d , % removal > 90 (Efficiency of the system should be limited in order to maintain adequate nutrients-ratio (C/N/P) 2. Requires small land areas. 2. High operating cost, requires

trained personnel for operating and maintenance

3. Can recover biogas . 3. Needs special safety system to (a( (average gas formation prevent explosions

0.4 L/kg COD removed) Caloric value: 20 to 25 MJ/m3 4. Less problem of bad smell. 4. Needs additional equipment for

recovery and storage of gas 5. No accumulation of sludge in the system, continuous desludging

For the design of a closed anaerobic digester the following Table 6.4 shows the main information, which have to be collected by the palm oil mill.


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Table 6.4: Data for the design of closed anaerobic digester Wastewater flow rate 1) m3/hr 1) m3/d BOD concentration 1) mg/l load 1) kg/d COD concentration 1) mg/l load 1) kg/d COD overall volumetric loading 3 to 10

kg/(m3.d) pH to be controlled by proper loading 6.7 to 7.4 (for adapted bacteria) Efficiency (% BOD removed) 60-70 % (% COD removed) < 80 % should be limited in order to maintain an adequate nutrients-ratio for subsequent aerobic treatment Biogas 0.4-0.6 l/kg COD removed Caloric value of gas around 20 MJ/m3

1) individual data of the palm oil mill 6.2.3 Aerobic treatment systems If the final effluent is used in the plantation as fertiliser, it may not be necessary to carry out further purification after the anaerobic treatment. However, if the treated wastewater will be discharged into a public watercourse, additional aerobic treatment is needed to achieve the prescribed effluent quality. Various aerobic treatment systems for palm oil mill wastewater are readily available in Thailand. The most widely applied system is the aerobic pond system whereas only few palm oil mills use the more advanced activated sludge system. Palm oil mills in Thailand do not use another possible treatment method, the trickling filter system. 6.2.3.1 Aerobic pond systems The various applicable aerobic pond systems, which differ in the type of the oxygen supply system (aeration system) and the design loading rates, are: facultative ponds (maturation ponds), oxidation ponds, aerated lagoons and polishing ponds. The oxygen supply of facultative ponds, oxidation ponds and polishing ponds is established by photosynthetic activities of algae and plants and by absorption of oxygen from the atmosphere. However, aerated lagoons are artificially aerated. The high temperature of the pond content does enhance the biochemical reactions, resulting in increased substrate removal even at the lower solubility of oxygen in water at increased temperature. The pond systems, including the anaerobic ponds, have the general advantage being very good adaptable to the surrounding environment of the treatment plant. The facultative ponds secure their oxygen supply mainly from algae. These ponds have an upper aerobic zone and a lower anaerobic zone. The depth of both zones varies from day to night depending on the intensity of photosynthesis. The liquid depth from bottom sludge to the pond surface should not exceed the range of 1.5 to 2.5 meters, which is the depth of the aerobic zone, which can normally develop during daytime. Because of the dark brown colour


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of the wastewater light penetration is insufficient for proper photosynthesis which makes this system not suitable for treatment of POME (even after anaerobic treatment). The oxidation ponds are shallower as facultative ponds and are supplied with oxygen through absorption from air. Depth of this type of pond is normally in the range of 1.0 - 1.5 meters. Because of the limited oxygenation capacity of this system the volume loading rate must be low [around 0.01 kg BOD5/(m3*d)]. This leads to land area requirement of 100 to 65 m2/(kg BOD5*d) and a retention time up to 40 days depending on the influent concentration. The aerated pond (lagoon) system needs electrical power for aeration. The relation of oxygen supply to organic load has to be > 1.5 kg O2/kg BOD5, leading to an energy requirement of around 1.1 kW/kg BOD5. The organic volumetric loading rate should be about 200 g BOD5/(m3*d). Aerated lagoons require much less area than other pond types (less than 3 m2/(kg BOD5*d) and have shorter retention times (1 to 10 days) depending on the in-fluent concentration. The aerated pond may have a water depth up to 6 m. Apart from economical reasons the applied depth depends on the quality of the embankment and the efficiency of the aerators. Normally a liquid depth not exceeding four meters is used. Aerated lagoons can be designed and operated in two methods i.e. complete mixed and partial mixed type. In the complete mixed mode, the sludge will leave the pond along with the treated effluent. Sludge sedimentation is carried out in a subsequent settling pond or in a clarifier (see chapter 6.4). In the partial mixed mode of operation, the aeration zone is separated from a quiescent zone in which the sludge is allowed to settle. The accumulated sludge has to be removed every five years. Both types of ponds (oxidation and aerated ponds) are stable in operation and BOD removal efficiency if they are properly loaded and - in the case of aerated ponds - well aerated. Under steady-state operation conditions these ponds have sufficient buffer capacity to cope with inlet load fluctuations. The polishing pond [22] can achieve its task to improve the final effluent quality only, if it is in aerobic conditions. The design parameters for polishing ponds are: volumetric loading rate 0.05 kg BOD5/(m3*d) maximum depth 1.5 m land area requirement approx. 0.03 m2/(kgBOD5*d). The oxygen is supplied by photosynthesis of algae and absorption from air. This type of oxygen uptake is possible because of the transparency of the effluent after extended treatment and because of the large surface area of the pond. The oxygen producing algae, however, cause high concentrations of suspended solids in the final effluent. Therefore separation/removal of thes solids is required to achieve the prescribed effluent standards. Construction of a stone/gravel filter embankment in the final part of the polishing pond will help to remove the suspended solids. The polishing pond may be used for fish production. This may give economical benefit and could minimise the growth of algae. Examples show a possible fish production yield of up to 15 t fish per hectare and year. However, fish production possibilities in polishing ponds at palm oil mills have to be further studied to arrive at proper design parameters. 6.2.3.2 Activated sludge process The activated sludge system has been used successfully since more than 50 years. The micro-organisms concerned in this system are bacteria, fungi, algae and protozoa. Bacteria


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play the most important role in the activated sludge process. In the activated sludge process the biological process of the aerated pond system are intensified by controlling the concentration of active biomass in the aeration tank. The suspended biomass is separated from the treated effluent in a final clarifier. The main part of the biomass (mixed liquor suspended solids – MLSS) is returned to the aerated tank. This stabilizes the biomass concentration in the aeration tank at the appropriate level of 3 - 7 g/L. This biomass concentration, which is much higher than under natural conditions in an aerated pond, leads to an accelerated digestion (removal) of organic substrate. The volumetric BOD load should not exceed 0.5 kg/(m3*d) to achieve the prescribed effluent quality. To achieve stabilized operating conditions in the activated sludge process, the biomass concentration should be kept at around 4 g/L. The depth of aeration tank is in the range of 2.5 to 5 m – typically around 4 m). These design figures result in a land area requirement of less than 1 m2/(kg BOD5*d). The supply of oxygen should be > 2 kg of oxygen per kg of BOD5, equal to an energy requirement of around 1.5 kW per kg BOD5 . In order to keep the biomass at a constant concentration in the aeration tank, the produced excess sludge has to be frequently withdrawn from the clarifier. Excess sludge generation under the above conditions for treatment of palm oil mill wastewater is about 0.4 kg sludge per kg BOD5 removed. The operation units of an activated sludge system are:

- Aeration tank - Sedimentation tank (final clarifier) - Return sludge pumping system - Excess sludge removal & treatment system

Special attention has to be given to the type of bacteria grown in the system. The growth of bacteria resulting in the so-called “bulking sludge” has to be avoided. There are several design possibilities to improve the operational stability of the treatment system, i.e. installation of “selectors” before aeration tank, implementation of “plug-flow” in the aeration tank instead of one-tank-completely- mixed- systems. 6.3 Nitrogen removal If river discharge is the chosen option, nitrogen removal can be necessary depending on the local situation. To be able to achieve this biochemically the treatment system has to be plan-ned in an appropriate manner.

Design Example (overall figures):

loading rate of raw wastewater: BOD5 30 g/L TKN 1 g/L BOD/N 100: 3

permissible BOD-efficiency of anaerobic reactor 60 % loading after anaerobic treatment:

BOD5 10 g/L TKN 1 g/L BOD/N* 100 : 10

At the above BOD/N-ratio almost all the nitrogen is absorbed by the micro-organisms for the production of biomass. As a result no nitrification and denitrification step is necessary. However, if high efficiency anaerobic ponds are used, about 30 % of the BOD-load have to


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be treated further aerobically to achieve the required overall BOD removal efficiency of 99.8 %. This requires an about 20 times higher power consumption and produces proportionally more excess sludge. 6.4 Separation and handling of excess sludge

Chapters 6.2.2.2 and 6.2.3.2 describe (design example given in chapter 6.5) the generation of excess sludge in anaerobic and aerobic treatment systems. In addition a very important part of the total sludge generation is the primary sludge developed by the suspended matter (fibres, cell material of fruits) of the raw influent which is not digested completely and thus accumulates at the pond bottom. In the pond systems this sludge has to be removed periodically, depending on the technical conditions of the particular plant (sedimentation ponds or zones, clarifier). If sludge is separated in a final clarifier, equipped with mechanical scraper devices, the excess sludge can be continuously removed. The dry solids content of the collected excess sludge depends on the sludge characteristic, the separation system used and the overall retention time of the sludge (sludge age) in the system. The sludge collected in a pond system has a much higher dry solids content as compared with sludge from high rate sedimentation tanks. Normally the sludge of a final clarifier, equipped with mechanical scrapers, will have a dry solids content of around 0.5 to 2 g/L . The collected sludge may be further thickened and subsequently dried in sludge drying beds or sprayed (as wet suspension) on land for use as fertiliser. The sludge collected from biological pond systems will be mineralised extensively, resulting in negligible mal-odor problems during handling. Therefore, utilisation of this sludge as fertiliser will give no nuisance to the neighbourhood. Landfilling at a domestic garbage site is another possibility for safe disposal of the dried from POME treatment systems. 6.5 Design example for palm oil mill effluent treatment by pond system

6.5.1 Example showing the impact of primary sludge (SS of POME) and anaerobic

excess sludge accumulation on the available pond volume and the subsequent treatment efficiency of the pond system: Primary sludge flow rate of POME: 400 m3/d content of SS in the raw POME: 30 g/L daily quantity of SS 12 t/d annual quantity of SS (250 d/y) 3000 t/y reduction by biodegradation (suggestion) 50 % remaining quantity of SS 1500 t/y water content of sludge (suggestion) 80 % annual volume of settled SS-sludge 7500 m3/y Excess sludge (anaerobic) content of BOD5 in the raw POME 30 g/L daily BOD5 load 10.8 t/d excess sludge (suggestion) 0.1 kg VSS/kg BOD5

daily 1 t/d annual (250 d/y) 250 t/y

annual volume (if 80 % water content) 1250 m3/y Total annual sludge volume about 9000 m3/y


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The conditions of biodegradation in the pond are illustrated in Figure 6.1. Sludge sedimentation takes place mainly in the silent zones of the ponds system. Sludge sedimentation is insignificant in the first part of the anaerobic pond system because of the high gas production resulting in high turbulence. Gas production slows down after about 40 days retention time after which sludge settling starts (see Figure 6.1). Total volume of the anaerobic pond has been initially around 30,000 m3, after one year of operation around 1/3 of the volume has been occupied by the sludge (mainly primary sludge - see diagram 6.1/6.2). The sludge-volume has been estimated considering 80 % water content. At reduced pond volume available for sedimentation, more anaerobic sludge is transported into the subsequent aerobic part of the pond system. This leads to in an increase of the organic load to the aerated lagoon, resulting in insufficient oxygen supply.

6.5.2 Example of the commonly used combination of anaerobic and aerobic ponds (BOD removal efficiency of the anaerobic part is considered to be 98 %, the aerobic pond is seen as oxygenation of the final effluent, which is utilised for irrigation) Some suggestions about the pond system - in addition to the information given in chapter 6.2.2.1: - because of the high BOD load of the raw effluent, the treatment system starts with

anaerobic ponds, followd by oxidation and polishing ponds. Each treatment step consists of a series of ponds, their number depending on the BOD loading rate and the actual shape and size of the ponds with respect to the particular local situation.

- the bad smell which may occur from overload conditions in the first anaerobic pond (acidification step) can be reduced by adjusting the pH to the range of 6 –7. This can be achieved by recycling the high pH water from the first third of the anaerobic pond back to the pond inlet.

The following Table 6.5 shows an example of loading rates to a number of ponds under anaerobic and aerobic conditions and the subsequent removal efficiency as well as the change of the COD/BOD-ratio during treatment. The aim of this type of treatment is to reduce the BOD and COD values as much as possible under anaerobic conditions, without considering elimination of Total-Kjeldahl-nitrogen. The pond no.3 and no.5 are mainly sludge retaining ponds. Figure 6.1 indicates the impact of retention time on treatment efficiency and shows the influence of sludge accumulation in the pond on BOD-removal efficiency.

6.5.3 Example of using the combination of anaerobic and aerobic ponds to remove BOD as well as TKN (BOD removal efficiency by the anaerobic pond is assumed as around 60 %, the aerobic pond system will oxidise one-third of the BOD load and absorb the influent TKN, which makes the final effluent suitable for river discharge) Table 6.6 shows an example of dealing with same load as described in chapter 6.5.2 but in addition considers the elimination of TKN. As in the previous example, two of the ponds (no. 3 and no.6) are mainly sludge collection ponds. The overall pond volume in this example is only around 2/3 of the size of the previous example. Significant in this example is the large number of aerated lagoons used. This results in the total elimination of BOD5 as well as TKN. Because of higher energy requirements for the supply of oxygen, this treatment systems has higher operating costs. A further difference to the previous example is the amount of excess sludge produced. In example 6.5.2 Table 6.5 - under anaerobic conditions - around 0,1 kg VSS/kg BOD5 are produced, in example 6.5.3 Table 6.6 the aerobic excess sludge is about 0.2 kg VSS/kg BOD or a total excess sludge generation of around 0.14 kg VSS/kg BOD5 . Excess sludge production for both examples is calculated as follows:


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example 6.5.2: 1*(0.96 * 0.1 + 0.04 * 0.2) = 0.104 kg VSS/kg BOD5 example 6.5.3: 1*(0.6 * 0.1 + 0.4 * 0.2) = 0.14 kg VSS/kg BOD5 Sludge production in example no.2 is about 35 % higher as compared with example no.1. Figure 6.2 indicates the impact of retention time on treatment efficiency and shows the influence of sludge accumulation in the pond on BOD-removal efficiency.


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Table 6.5 Example of biological treatment of palm oil mill wastewater (max. efficiency of anaerobic treatment)


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CHAPTER 7 MONITORING AND CONTROL

Environmental management systems in the palm oil mill will be successful if the IPPCS is implemented as desired and the wastewater treatment system functions properly. The owners of the palm oil mill must work in close co-operation with government authorities in monitoring and controlling the production process as well as the treatment plant. 7.1 In-plant control The owner or the plant manager is responsible for both, production process optimization and operation of the wastewater treatment. The operating personnel have to be qualified to run the various processes according to the operating instructions. They must understand the process as a whole as well as the interrelationship between each step [23].

The factory management should give special attention to the following measures: - Sustain measures to stabilise and improve processes + process development + improvement of operator and personnel skills + implementation of improved methods for control and monitoring. - Consider precautions for unexpected operational events + install appropriate sensors and alarm systems + install measures to prevent and contain leakage + train personnel - improve the management plan for by product utilization with regard to seasonal fluctuations

in oil palm plantation + implement regular analysis and monitoring of nutrients available in by-products and

nutrient deficiency in plantations + support farmers/plantations in fertilisation management + improve or install storage capacity for useable by-products - understand the type, quality and value of by-products and residues + provide equipment for flow measurement of the relevant streams of oil, sludge and

other liquid residues + actualise the mass balance of the factory + monitor characteristics and quantities of by products and residues + introduce measures to segregate or combine by products and residues + introduce measures to separate or combine treatment, storage or utilisation + reduce pipe leakage The success of IPPCS measures as well as effective process operation and the efficiency of the effluent treatment system should be regularly documented as follows: - efficiency of IPPCS-measures - operation of equipment - main operational parameters - effluent quality

- sludge handling figures Sampling must be done at sufficient frequency at the most important production process steps and at the wastewater treatment system. The in-plant control program should be discussed with the authority and should lead to a monitoring agreement. It is of great importance to evaluate all analytical data and investigate all irregular incidences. In Table 7 examples of measured and monitored parameters of an effluent treatment system are given, which have to be adopted for the requirements of each individual treatment plant.


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7.2 Control by the authority The authority’s personnel must have sufficient knowledge and understanding of the different production process steps of a palm oil mill and its wastewater treatment system. In addition, the officials should be capable to suggest and advise the plant manager and/or the mill’s owner in process optimisation. The authority must convince the plant manager to use and follow the environmental management guidelines, especially in terms of utilisation of by-products and residues, and operation of the wastewater treatment system. Monitoring of application of the guidelines has to be introduced at the authority concerned. It is advisable to introduce a checklist of monitoring activities for each individual plant to be controlled. This checklist should contain:

- general operation of the plant. - verification of in-plant monitoring and control. - data of sampling events, sampling conditions and results of analysis.

Sampling and analytical work should be carried out 3 - 4 times a year, depending on the reliability of plant operation.


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Table 7: example of listed parameters to be monitored during effluent treatment

operational step parameter unit

Final oil trap inlet outlet

flow rate COD (regularly) BOD5 (occasionally) SS temperature pH

m3/d

mg/L mg/L mg/L °C

Behind cooling system/after mixing tank if effluent is recycled before first anaerobic pond Recycled Total influent

flow rate of recycling temperature pH

m3/d

°C

In the anaerobic ponds sludge level % of depth

End of anaerobic part of treatment COD BOD5 SS settleable solids temperature pH

mg/L mg/L mg/L ml/L °C

Settling pond for anaerobic excess sludge Excess sludge removed

volume solid content

m3/month

g/L

In the aerated reactor (pond, activated sludge etc.) If recycling

VSS settleable solids sludge volume index O2 power consumption temperature flow rate

g/L ml/L ml/g mg/L kW/d

°C m3/d

Settling pond for aerobic excess sludge Excess sludge removed Result of treatment

sludge level volume solid content COD (regularly) BOD (occasionally) SS temperature pH

% of depth

m3/month

g/L

mg/L mg/L mg/L °C


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CHAPTER 8 GLOSSARY OF TECHNICAL TERMS MINIMUM EFFLUENT QUALITY REQUIREMENTS The minimum effluent quality requirements for the palm oil industry were decided with regard to

- the existing general discharge requirements prescribed by the Ministry of Industry (1996)

- the existing requirements of effluent sampling - the effluent standards applied for palm oil mills in neighbouring countries - the initial pollution load and type of raw wastewater generated by palm oil mills and

the treatment efficiency required to achieve the present effluent standards - the attainable treatment efficiency by applying the best available technique - the interrelation ship between the different effluent parameters

Selection of the parameters is based on the type of parameters already applied (BOD5, SS, oil & grease, temperature, pH) as well as on analytical reliability and simplicity (COD). With the inclusion of TKN an additional parameter has been introduced to reflect on eutrophication of receiving waters (TKN). 8.1 Glossary of technical terms 1) BOD5 (Biochemical Oxygen Demand) The BOD5 is the conventional overall sum-parameter for biodegradable organic carbonaceous substances in the effluent. BOD is measured in terms of the oxygen utilised by micro-organisms in degrading the organic matter within 5 days at an incubation temperature of 20 °C. During biodegradation other types of substances are also involved, such as nitrogenous (protein) and phosphorous (phospholipoids) substances. Their degradation not only unfolds N and P but also contributes to the measured BOD (for further details see the chapter on “suspended solids”) 2) COD (Chemical Oxygen Demand) The COD is another sum-parameter indicating the oxygen required to chemically oxidise organic matter in the wastewater. This chemical oxidation is carried out by using potassium dichromate (K2Cr2O7) under strong acidic conditions. An important indicator for biodegradability of the wastewater is the ratio of COD to BOD5. Because of biological decomposition of the organic substrate during treatment, the COD/BOD ratio is different in the raw effluent as compared with the treated effluent, as shown in Table 8. Table 8: The range of COD/BOD5-ratio in POME

Type of palm oil mill wastewater

range of COD/BOD5-ratio

Raw homogenised Raw filtered final homogenised final filtered

2 to 3 1.5 to 2

15 to 251)

> 101) 1) in case of total BOD-efficiency > 99,99 %


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The difference in COD/BOD5 ratio between the homogenised and filtered raw wastewater sample is because of the presence of suspended solids (e.g. cellulose material, which requires longer time for biodegradation as compared with dissolved organic matter). 3) Suspended solids (SS) The suspended solids can be measured by filtering a fixed volume of effluent through a glass fibre filter (Whatman GF/C), which is subsequently dried to a constant weight. The SS are included in the homogenised samples if analysed for BOD5 or COD. The total amount of suspended solids in the raw wastewater results from insoluble organic substances used or released during the production process (oil palm fibres, pieces of kernels or shells) as well as from inorganic material like sand. In the biologically treated effluent, the SS consists mainly of biomass. 4) Total lipophilic substances These substances are normally defined as oil and grease (O&G). As long as the requirements deal with raw effluent, this parameter mainly describes the content of palm oil in the raw effluent of a palm oil mill. Under normal operation conditions of extended biological treatment, the analysed O&G-concentrations are not only due to the “primary “ palm oil losses of the process but also result from the content of natural lipophilic substances (biomass) produced during biological treatment. The biomass contains about 10% of lipophilic substances, which contribute to this parameter. Other extractable substances are analysed due to the properties of the solvent used for chemical analysis. The analytical result of this parameter in the final effluent, therefore, does not precisely reflect oil discharge from the mill. The O&G is included in the BOD and COD values if homogenised samples are analysed. 5) Nitrogen (N) There are various forms of nitrogen existing in effluent. The most important N-parameter is Total Kjeldahl-nitrogen (TKN). Which describes the total amount of organic-N and ammonia-N compounds present in the wastewater. 6) pH The pH indicates the concentration of dissociated hydrogen ions in the water. 7) Temperature Excess effluent temperature will decrease the dissolved oxygen concentration in the water. However, biochemical reactions are accelerated at higher temperatures, resulting in quicker biological decomposition of organic waste.


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8.2 Explanation of minimum effluent quality requirements The Palm oil mills are one of the major agro-industries in southern Thailand. The main input material is fresh fruit bunches harvested in the oil palm plantations. The process of extracting oil from the palm fruits is a physical process. No chemicals are added. Because of the process water requirements the standard wet process generates high quantities of effluent. The palm oil mill effluent has unique characteristics, containing high concentrations of BOD and suspended solids. The concentration of Nitrogen containing compounds could be a limiting factor in aerobic biological treatment. The combination of anaerobic and aerobic treatment leads to balanced nutrient conditions.. Because of the extremely high load of organic material in the raw wastewater, it has to be accepted that even after full biological treatment the effluent still contains high concentrations of impurities. The final effluent quality therefore exceeds the existing effluent standards. The effluent quality requirements specified for palm oil mills were formulated based on data collected during recent surveys [PSU, 1995] of palm oil mill effluents. The recommended effluent standards are defined below. Sufficient safety margins have been incorporated in the standards to cope with common operational/efficiency fluctuations of biological treatment systems. Interrelation between various parameters has also been considered.

8.2.1 Biochemical Oxygen Demand - BOD5 The palm oil mills are allowed to discharge effluent, if their treatment systems include improved algae (SS) separation systems, at the end of the polishing pond. In this case the following requirements can be met. The recommended total BOD value originates from: - soluble organic matter < 50 mg/L - suspended solids as 0.31) * [SS] » 45 mg/L rounded summary < 100 mg/L therefore a BOD5 standard value of 100 mg/L is used

8.2.2.1 Chemical Oxygen Demand – COD The COD-value is derived from BOD5-value as follows: - COD due to dissolved matter: COD/BOD5 » 102) < 500 mg/L - COD due to SS: 1.83) * [SS] » 270 mg/L - COD to O&G: = 24) * [O&G] » 50 mg/L rounded summary < 850 mg/L therefore a COD standard value of 1,000 mg/L is used 1) very limited biodegradation of suspended solids [24] 2) estimated from ranges commonly known: COD/BOD5 see chapter 8.1 3) fully chemically degradable SS as average-composition, see [24] 4) fully chemically degradable O&G as average-composition [25]

8.2.3 Suspended Solids (SS)


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The polishing ponds should be the last step of treatment prior to river discharge after oxidation ponds. The formation of algae is not only unavoidable in the polishing pond but also required for oxygen supply and polishing purposes. On the other hand the algae removal efficiency is limited to the best available technology, economically affordable. therefore a suspended solids standard value of 150 mg/L is used

8.2.4 Total lipophilic substances (O&G)

O&G analysed in the final effluent (under good/normal working conditions) of the biological treatment plant does not result from the discharge of palm oil as such, but reflects the total concentration of lipophilic substances in the effluent (incl. algae and micro-organisms). The O&G-standard value is derived from the SS-standard, assuming that the total biomass reflected in the SS value contains is equal to a value of lipophilic substances of about 150/10 < 15 mg/L

therefore a O&G standard value of 25 mg/L is used 8.2.5 TKN-nitrogen In the raw effluent the nutrient to substrate relation ship is approximately BOD5 to N » 12 to 0.5 »100 to 4 The BOD/N ratio required for aerobic treatment is: BOD5 to N = 100 to 10 If the ratio of anaerobic to aerobic treatment capacity is correctly chosen, then most of the nitrogen compounds present in the raw water will be absorbed by the produced biomass. The remaining nitrogen compounds are oxidised in the aerobic ponds, including the polishing pond, if the recommended biological treatment system has sufficient capacity. The relatively high organic nitrogen content results from the nitrogen content of the biomass (about 30 % of SS) included in the SS (TKN ~45 mg/L= 150 x 0.3). therefore a TKN - N standard value of 50 mg/L is used It is of great importance that all palm oil mills follow the Environmental Management Guidelines. This will result in more widespread application of process integrated pollution prevention and control measures as well as in improved operational performance of the installed biological wastewater treatment systems.


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Annex A: Detail information of Thai palm oil mills Table A 1 Palm oil mills using “standard wet process” Table A 2 Palm oil mills using “dry press process” Map 1: Area under oil palm cultivation in Thailand, 1993 Map 2: Effluent generation of palm oil mills per day, 1993 Map 3: Average BOD load of palm oil mills per day, 1993


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Table A 1 Palm oil mills using standard wet process production capacity and investment

Name of palm oil mill Investment Mio Baht

Production cap. tons palm oil/year

Krabi Province

1. Thai Industry and Oil Palm Co.Ltd. 132.7 16,425 2. Siam Palm Oil and Industry.Co.Ltd. 120.0 18,000 3. United Palm Oil Industry Co.Ltd. N/A. 15,832 4. Srichalern Palm Oil Co.Ltd. 95.0 14,400 5. Asian Palm Oil Co.Ltd.

160.0 14,400

Chumporn Province 6. Chumporn Palm Oil Industry Co.Ltd. 175.8 24,000 7. Vichitphan Palm Oil Co.Ltd. 98.7 11,680 8. Sawee Palm Oil Industry Co.Ltd.

111.0 14,400

Trang Province 9. Trang Palm Oil Co.Ltd. 79.6 14,400 10. Abico Holding Co.Ltd. 70.5 22,464 11. Otago Company Co.Ltd.

97.0 12,000

Surat Thani Province 12. Southern Palm (2521) Co.Ltd. 50.0 32,671 13. Unipalm Industry Co.Ltd. 75.0 37,256 14. Prasaeng Palm Oil Co.Ltd. 51.0 21,600 15. Thai Tallow and Oil Co.Ltd.

40.0 34,587

Satun Province 16. Thai Development Palm Co.Ltd.

42.0 3,600

Songkhla Province 17. Pure Plant Oil Co.Ltd. 22.0 3,500


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Table A 2 Palm oil mills using dry pressing process production capacity and investment

Name of palm oil mill Investment Mio Baht

Production cap. tons palm oil/year

Krabi Province

1. Krabi Plant Oil Co.Ltd. 12.0 1,800 2. Trang Saengtawan Co.Ltd. 6.1 4,800 3. Sahagarn Palm Co.Ltd. 4.7 1,200 4. IPI Oil Palm Extraction Industry Partnership Co.Ltd.

14.0 8,000

Chumporn Province 5. Palm Oil Agriculture Co.Ltd. 45.7 6,430 6. D.P.Palm Oil Co.Ltd. 36.2 1,638 7. Thai Pearl Products Co.Ltd. . 6.1 3.500 8. Thai Palm Products Co.Ltd. 2.5 9,000 9. Mitr Chalern Plant Oil Co.Ltd. 11.0 1,800 10. POT Industry Co.Ltd. 11.5 5,700 11. Raumporn Palm Oil Industry 16.0 5,500 12. Udomchai Palm Oil Co.Ltd. 8.5 4,000 13. Laksana Lang Suan Partnership 5.0 2,000 14. Vijaksananon Partnership Ltd. 3.0 1,500 15. Coconut Oil Refining Factory 3.0 1,400 16. Nikom Lang Suan Co-operative Ltd. 16.2 1,824 Trang Province 17. Pure Plant Oil Co.Ltd. 34.0 2,880 18. Trang United Palm Oil Co.Ltd. 5,7 4,320 19. Trang Oil Co.Ltd.. N/A. N/A. 20. Trang Agriculture Partnership Co.Ltd. 6.2 1,200 21. Sihpa Hana Plant Oil Co.Ltd. N/A N/A 22. Surat Saengsiri Plant Oil Co.Ltd. N/A N/A 23. Thai Rungreung Co.Ltd. 19.5 370 24. Satun Industry Co.Ltd. N/A N/A 25. Gold Medal Palm Co.Ltd. N/A N/A Songkhla Province 26. Karnchanasin Plant Oil Co.Ltd. 2.1 180 27. Goodluck Plant Oil Co.Ltd. 5.5 36 28. Rungreungkit Co.Ltd. N/A N/A 29. T.C.K. Food and Fruit Co.Ltd. 15.0 2,400 30. Sinpattana Co.Ltd. N/A N/A 31. Tek Seng Factory 1.3 20 32. Hua Seng Plant Oil Factory 0.5 1,220


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Annex B: Economical aspects

1. Prices (year 1996) 1.1 fertiliser 1.2 operation costs 1.3 Investments 2. Methodological remarks 3. Example of financial calculation of alternative technologies for oil

separation


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ECONOMICAL ASPECTS 1. Prices 1.1 Fertiliser - Urea (46 % N) 7,4 Baht/kg - Rock phosphate (25 % P2O5) 1,6 Baht/kg - Triple superphosphate (45 % P2O5) 3,0 Baht/kg - Kieserite (27 % MgO) 6,0 Baht/kg - Potassium (60 % K) 4,2 Baht/kg - Borate (48 % B) 24,0 Baht/kg residue possible price1) fertiliser value ------------------------------------------------------------------------------------------------ EFB 120 Baht/t 8 kg N/t; 0.6 kg P/t; 24 kg K/t (60 % water cont.) (on dry weight) EFB-ash 3420 Baht/t 17 kg P/t; 450 kg K/t fibre 80 Baht/t 23 kg N/t; 2 kg K/t (20 % water cont.) (on dry weight) decanter cake (80 % water cont.) 100 Bath/t 20 kg N/t; 8 kg P/t; 20 kg K/t (on dry weight) POME 25 Baht/m3 0,6 kgN/m3; 0,2 kgP/m3; 2 kgK/m3 1) price represents the value of fertiliser content of the residue only 1.2 Operating Costs: parameter value source ____________________________________________________________ electricity 2 Baht/kWh Electricity supplier water consumption - river water 2 Baht/m3 calculation - boiler water 8 Baht/m3 calculation/supplier of conditioners transport costs 19 Baht/ton (see table 2.1.1) personnel costs 4000 Baht/month factory information fuel (transport) 8 Bath/L 1.3 Investment the guideline gives basic information concerning the process design of the required equipment as well as for the utilisation of residues and for wastewater treatment. By using this information it will be possible to estimate roughly the respective investment costs of the system.

2. Methodological remarks

The economic feasibility of different technological alternatives can be appraised and be analysed by calculating: - the amortisation period of capital invested (pay back period) - net present value of capital invested.


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The sensitivity analysis is an useful media to asses investment risks, which may be combined with the technological transfer of up to now unknown equipment. The pay back period indicates the required time, which is necessary to earn the invested capital. The period can be used as a risk indicator. Short pay back periods indicate that the return of invested capital is quick and attractive. The calculation should be done without using discounting factors, a statistic calculation using cumulative cash flow data is the most objective procedure to determine the pay back period. The pay back period as such, gives no information about the profitability of the investment. For this purpose the net present value has to be calculated, using a discounting factor of 15 %. The overall economic information consisting of pay back period and the net present value gives the best information about profitability of the investment. 3. Example of financial calculation on alternative technologies for oil separation This example is given in the Activity report PN 91.2070.5-01.100 “ Oil Recovery from palm oil mills waste water” of Technical Co-operation Royal Thai Government - Federal Republic of Germany, April 1994 which can be obtained from the Department of Industrial Works – Ministry of Industry.


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Annex C Members of the DIW palm oil mill environmental management guideline preparation team Mr. Issra Shoatburakarn DIW Mrs. Sukanya Bunpaesat DIW Ms. Boonsom Lewsrivilai DIW Mr. Sakchai Suriyajantratong DIW Prof. Dr. Poonsuk Prasertsan PSU Prof. Dr. Galaya Srisuwan PSU Prof. Dr. Aran H-Kittikun PSU Mr. B.Meyhoefer IP as German Long-term expert Mr. A.Krause IP as German Short-term expert


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Annex D: Literature (recommended for more detailed information) Source No. Author and title [1] American Standard methods for examination of water and wastewater APHA-AWWA-WPCF; 17th edition 1989 [2] H-Kittikun et al., Thai-German Project PN 91.2070.0-01.100: Executive Summary Report of PSU, April 1994 [3] No. 16/1994: Agricultural Statistics of Thailand [4] H.R. von Uexkull, Fertilizing for High Yicld and Quality T.H. Fairhust: “The Oil Palm”,International Potash Institute Worblaufen (CH) 1991, IPI-Bulletin No. 12 [5] Jantaraniyom T., Tongkum, P., Nilnond, C. and Eksomtramage, T.: Variation in

yielding potential of oil palm. 1995 Songklanakarin J. Sci&Technol. 17, 251-259 [6] Palm Oil Research Institute of Malaysia, 1985 “Palm Oil Factory Process Handbook Part 1" [7] Activity Report, Thai-German Project PN 91.2070.0-01.100: of STE- assignment: 16.04. to 16.05.1992 [8] Activity Report Thai-German Project PN 91.2070.0-01.100: of STE-assignment: 01.11. to 12.11.93 [9] Activity report PN 91.2070.5-01.100, April 1994 “Oil Recovery from palm oil mills waste water” [10] Asian Institute of Technology, Bangkok, Thailand, 1980 “Palm oil waste treatment study in Malaysia and in Thailand” [11] Royal Tropical institute, Amsterdam, The Netherlands, 1984, (Klöckner) “Thailand: Oil palm research and development in Thailand” [12] ESCAP-Environment and Development Series, United Nations, Bangkok, 1982

“Industrial Pollution Control Guide-lines; IV Palm oil industry” [13] A.N.Ma; S.C.Cheak and A.S.H. Ong; PORIM/ISP-conference, Kuala Lumpur, 1987

“Towards zero discharge from palm oil mill” [14] Activity report Thai-German Project PN 91.2070.0-01.100: for Seminar Surat Thani, April 1994 [15] M.Bockisch: Ulmer 1993, ISBN 3-8001-5817-5 “ Nahrungsfette und -öle” (Edible fats and oils) [16] W.Roge; A Velayuthan: The palm oil product technology in the eighties,

E.Pushparajah, Kuala Lumpur, June 1981 “Preliminary trials with Westfalia 3-Phase-Decanters for Palm Oil Separation” [17] Lim Chan Lok; PORIM/ISP-conference, Kuala Lumpur, 1987 “The application of decanters for palm oil clarification” [18] GTZ-report PN 81.2068.5-01.200, Stuttgart, July 1990 " Study on Waste in the Palm Oil Industry (Oil/Water separation)" [19] N.C. Thanh et al. Report No. 114, August 1980, Asian Institute of Technology

“ Palm Oil Wastewater Treatment Study in Malaysia and Thailand” [20] Chan Khoon San and C.F. Chooi "Ponding systems for POM effluent treatment" [21] Proceedings of JAW PRC-Conference, Lisbon 29.06.-2-07.87, Pergamon

Press, ISBN 0080355986 "waste stabilization ponds" [22] S. Sinnappa, International Conference on Water Pollution Control in

Developing Countries, Bangkok, February 1978 “Treatment Studies of Palm Oil Mill waste effluent” [23] Lim Kang Hoe and D.A.M. Whiting, The palm oil product technology in the eighties,

E. Pushparajah, Kuala Lumpur, June 1981 “Material Balances of a Palm Oil Mill Clarification Station”


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[24] Firk, W., D.te Heesen, B. and Klopp, R. 1991. Einflop von Festostoffen in Ablauf von Abwasserreiningungsanlagen auf die Gewaesserbe-schaffenheit. Korres pondenz Abwasser 38 Jahrgang p 811-813.

[25] Bucksteeg, W. 1959. Problematik der Bewertung giftiger Inhaltsstofte in Abwasser und Moeglichkeiten zur Schaffung gesicherter Bewertungsgrundlagen. Verlag R. Oldenbourg, Muenchen. p 1-5

Deutsche Gesellschaft fürTechniche Zusammenarbeit (GTZ) GmbH

- German Technical Cooperation-

GTZ Office BangkokTel: (662) 661-9273 (8 lines) Fax: (662) 661-9282Email: [email protected] Web: www.gtzth.org

Street Address: 193/63 Lake Rajada Building (16th Flr.) New Ratchadapisek Road, Bangkok 10110Postal Address: P.O. Box 11-1485 Nana, Bangkok 10112

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