Authors: Dipl.-Ing. Dipl.-Wirt.Ing. Christoph Bröcker CDM Consult GmbH Am Umweltpark 3-5 D-44793 Bochum Telefon +49 234 68775 418 Email: Website: www.cdm-ag.de Dipl.-Geol. Martin Burger uve GmbH für Managementberatung Kalckreuthstr. 4 D-10777 Berlin Telefon +49 30 31582 500 Email: m.burger@uve.de Website: www.uve.de

Improvement Of Long-Term Behaviour And Energy Efficiency Of Municipal

Waste Landfills (DEPO+

Process)

Authors: Bröcker, Christoph, CDM Burger, Martin, uve

1 SUMMARY The decrease in the extraction of landfill gas in the past years has caused a decline in the revenues from landfill gas utilisation. Practice shows that there is still a great organic potential in municipal landfills but the existing gas extraction systems in their present state are not suitable to tap into this potential, especially in the deep areas of landfills. Concrete results from long-term monitoring and ongoing gas extraction tests prove that the upgrade of standard gas wells to so-called DEPO+

wells facilitates the use of this gas potential and provides the basis for a substantially higher gas yield and an optimised efficiency in the existing landfill gas utilisation.

Sometime in the future the economic use of the landfill gas will no longer be feasible. At this point it will be possible to use the upgraded gas wells to initiate a targeted aerobic in situ stabilisation. This action accelerates a further decomposition of the carbon compounds within the landfill and results in a reduction of the aftercare costs. The method proposed is the DEPO+ process, developed and offered by CDM Consult GmbH (holder of patent rights). The application of the DEPO+ process

optimises gas formation and extraction, thus facilitating a highly economical use of the landfill gas. Furthermore, the extraction of the landfill gas accelerates the decomposition of the carbon compounds inside the landfill. The emissions decrease substantially and the long-term behaviour of the landfill is improved. A cost benefit analysis shows that the necessary investment for the upgrade of the gas wells will be amortised within a financially acceptable period by the increased revenues from the resulting landfill gas utilisation. This fulfils the economic requirements for the licence application and a technically efficient implementation of an in situ stabilisation.

2 SITUATION, MOTIVATION AND TARGET The length of after-care periods is usually determined by the long-term leaching processes within the landfill body. According to some prognoses they can last between approx. 130 and 200 years, based on the threshold value for ammonium of appendix 51 of the German wastewater ordinance (see Ramke 2004). Among other influences, the long-term behaviour of municipal landfills is determined by the change of the biologically degradable mass in the landfill. The collection and energetic utilisation of the methane content of the landfill gas represents a considerable contribution to the protection of our climate and environment. Ideally, this utilisation should also be viable from an economic point of view.

The aim of measures for the acceleration of biological decomposition processes is to minimise the emissions within a reasonable period of time, if possible within one generation. The gas path should be focussed upon, because more than 90% of the biologically degradable organics can be discharged from the landfill along this way (Henken-Mellies 2008). The key factor for the quality of the material reduction is the dischargeable amount of carbon per unit of time. This carbon load derives from the volume flow and the concentration of carbonaceous gas. The higher the volume flow and/or the concentration of carbonaceous gas, the quicker the targeted discharge will be achieved. Therefore, the organic decomposition is focussed on in the anaerobic phase. Measurements show that landfill gas usually contains +/- 90 % carbonaceous gas (mainly methane and carbon dioxide), whereas exhaust gas from the aeration has a content of approx. 30 % (CO2) of carbonaceous gas. The material balance indicates that in terms of figures more than three times as much organic material can be discharged via the gas path under anaerobic conditions as under aerobic conditions, with the same volume flow. However, due to the considerably higher growth rate of the aerobic micro-organisms, which are responsible for decomposition, aerobic biological reactions are much quicker than anaerobic reactions, so that the results of the processes are similar (see Hohenschurz-Schmidt 2009). 3 THE DEPO+ PROCESS

The most decisive factor for the quality of the degasification of a landfill is the gas collection system. The requirements for a successful gas extraction can only be met by using an efficient collection system (deep action, range). The optimisation of both the degasification system and its operation leads to an increase of the quality and quantity of the landfill gas. The following aerobic in-situ stabilization results in a far-reaching material reduction of biologically degradable carbon in the landfill body and therefore meets the criteria for a release from after-care obligations. The DEPO+ process

aims at the optimal material carbon reduction of the landfill body, resulting in an early release of the landfill from after-care obligations. The priority of the energetic utilisation of the landfill gas according to the German landfill ordinance (DepV 2009) places the activation of biologically degradable organics and their discharge as high-energy biogas in the anaerobic phase foremost, before the aeration of the landfill body is performed by a targeted over-extraction.

Figure 1: Flow behaviour and range – comparison of classical standard gas wells and depth-filtered gas wells of the DEPO+ process

Figure 1 shows the different mechanism of a single depth-filtered gas well compared with a classical gas well with filters from top to bottom. Experiences won during the operation at several sites show that if a landfill is deeper than 15 m and the deposit has many layers, it can be more effective to upgrade depth-filter wells on several extraction levels. Figure 1 also shows the extraction radiuses at the landfill top in relation to the flow behaviour. The range of depth-filtered gas wells mainly depends on the depth of a landfill and the extraction flow. At several landfill sites the range of the extraction radiuses could be improved from approx. 15 m to more than 40 m. The gas extraction is operated on the basis of the following principle: The gas wells extract landfill gas of different qualities and quantities as they occur. Key parameters, observed during the activation of the decomposition processes in the landfill are, besides methane and oxygen, the negative pressure as evidence of the effectiveness of the extraction, typical landfill gasses (such as CO2, CO, H2S) as well as the temperature as evidence of the effectiveness of the biological decomposition processes. Figure 2 illustrates the different phases A (extraction during the utilisation of energetically usable landfill gas), B (extraction during the aerobic in situ stabilisation) and C (intermittent extraction at the end of the landfill degasification), the extraction rates and the forecasted gas concentrations.

Figure 2: Schematic course of gas flow and gas concentration during anaerobic degasification phase (phase A), followed by presentation of course during the aerobic in situ stabilisation (phase B) and during the intermittent operation at the end of the landfill extraction (phase C) Depending on the degree of decomposition of the biologically available organics, the extraction of the landfill targets the generation of energetically usable landfill gas. The adjustment of a suitable extraction flow in this phase guarantees an efficient emission control of the landfill. In Phase A the inverse direction of the flow ensures that the condition

of the landfill body remains anaerobic to enable an optimized energetic utilisation of the landfill gas. Figure 3 shows the main benefits of the supply of landfill gas for an economical utilisation in the first phase of decreasing landfill gas quantities and qualities, if the DEPO+ process

is applied.

Figure 3: Effects of the application of the DEPO+ process

in the anaerobic phase

The black line shows the classical mode gas prognosis. In comparison to this classical approach, the actual quantity of landfill gas collected varies between 30 and 50 % - as shown by the black dotted line. The difference between these two curves shows us the gas that is not utilised with the classic method – a part of this amount can be allotted to the surface emissions during the operating period. The rest of this gas is lying dormant in the landfill in the form of biologically disposable mass due to microbial inhibition and can be activated by the DEPO+ process

. This is symbolised by the green arrow and by the blue line and shows us the additional economically utilisable gas potential.

The red line symbolises the point where the gas can no longer be economically utilised. As shown, the DEPO+ process

Figure 3 lengthens the period of time before this point is reached,

allowing the utilisation of gas that would otherwise be lost (see “Otherwise not energetically utilisable gas potential”). The technical operational concept must provide for a permanent maximum organic discharge, if possible for the generation of electricity. As soon as these requirements can no longer be met, phase B starts with the aerobic in situ stabilisation. The required extraction rate depends on the reaction of the landfill and is adjusted step-by-step under permanent monitoring. The increased extraction and the resulting decomposition of biogenic mass leads to a reduction of the methane concentration while the oxygen concentration increases. The aerobic front seeps through the landfill step-by-step from the outside to the inside (see Figure 4).

Figure 4: DEPO+ process

, organic decomposition in the aerobic in situ stabilisation phase B

Generally, it must be observed that, due to oxidation with the atmospheric oxygen during the aeration process, landfill fires are possible. The DEPO+ process

Figure 4 accounts for this

danger (please comp. ) in Phase B by: • introducing oxygen via the landfill top and therefore over the largest area possible, • keeping the introduction velocity very slow, guaranteeing a high capacity, • raising the temperature only slightly (35 - 40 °C) and therefore reducing the risk of

dehydration. Upon reaching stationary conditions with the above mentioned concentrations in the exhaust gas, the plant will be operated intermittently (Phase C). The aim is to identify the time at which only minor methane quantities are produced. The intermittent operation usually starts with a rest phase, followed by an up-time, followed once again by a rest phase and so on. The criteria for stopping the intermittent operation, resp. the end of the whole project, is defined by the time, at which the methane concentration does not exceed a certain maximum value after a predefined rest phase (please see Figure 2). 3 PRACTICAL EXPERIENCES FOR PHASE A The following examples demonstrates the significance of the DEPO+ process for the targeted municipal waste landfill with low emissions. Because of the importance of the optimized degasification under anaerobic conditions, the selected example focuses on phase A. In regard to the effectiveness of the depth-filtered gas wells under “aerobic” conditions (phase B), which was tested and proven during the test and also permanent operation, please compare the findings of Kanitz and Forsting (2004). 3.1 Initial Situation and Target At the following landfill the gas quantities were permanently decreasing, causing a parallel decrease in the profits of the electricity generation. Additionally, the planned development of an industrial site in the oldest landfill section 1 required the acceleration of the settlement of the landfill. Therefore, the application of the process aims to achieve an optimal and accelerated material discharge of biogenic degradable organics, involving an increase of energy yield during the anaerobic operation and the early anticipation of settlement. The key features of the landfill can be found in Bröcker & Rambadt (2010).

3.2 Procedure Prior to the upgrade of the gas wells a pre-investigation regarding the present condition (technical status, inventory of gas quantity and quality, etc.) was conducted on three selected gas wells as part of the depth-zoned measurements. On the basis of the analytical results two gas wells in section 1 and one in section 2 were upgraded on a trial basis and afterwards tested in extensive gas extraction tests regarding their improved effectiveness. The gas regime was monitored during the extraction test at the upgraded wells and two nearby wells in section 1 (please see Figure 5).

Figure 5: General layout and sectional view incl. location of the samplings and the measured minimum ranges The execution of gas extraction tests on the test wells proved the effectivity of the DEPO+ process

. The comparatively low under pressure of 1 to 5 mbar allowed the converted test wells to be easily reconnected to the degassing system, without having to make any changes during the suction process.

The appreciable increase of methane and the resulting energy won from the investigated wells led the landfill operator to the decision to first convert all the wells in the oldest section of the landfill, before deciding whether to instigate the optimisation of the wells in the remaining landfill sections.

0

10

20

30

40

50

60

Nov 09 Dez 09 Jan 10 Feb 10 Mrz 10 Apr 10 Mai 10 Jun 10 Jul 10

Time

[Vol

.-%]/[

°C]

0

20

40

60

80

100

120

140

160

180

[m³/h

]

CH4 Vol.-% Flow m³/h CH4 m³/h

Prior conversion of gas wells:38 Vol.-% Methane, Flow 35 m³/h

Frost period:13.12.2009 - 12.03.2010

Cool weather:until 26.05.2010

Sep 08

Figure 6: Overview of the development of collected gas quantity in section 1 Figure 6 shows the development of the total gas quantity in section 1. The comparison of the conditions before the conversion in 2008 (gas flow = 35 m³/h with a methane content of 38 Vol.-%) and in December 2009 (gas flow = 165 m³/h and CH4 = 43 Vol.-%) shows that the quantity of utilisable energy was increased by over 400% within one year. External influences, such as the unusually long winter period in 2009/10 (see Figure 6) leading to decreased gas productivity, meant a lower amount of collected gas in the middle term. By July 2010 the amount of collectible gas had recovered significantly (present gas flow approx. 150 m³/h). The gas prognosis models predict a total increase of the amount of collectible gas by 200-300% in comparison to the initial situation. Further practice examples of in situ stabilisation, also in aerobic form, are to be found in the following literature: (Bröcker 2008), (Bröcker & Rambadt 2010), (Hohenschurz-Schmidt 2009), (Kanitz & Forsting 2004), (Kanitz & Pauluweit 2007). 4 ECONOMIC FEASIBILITY 4.1 Costs On the basis of recent test results at different landfill sites the landfill bodies bear an additional gas collection potential, which will generally be usable and economically profitable through electricity generation by the upgrade of existing standard gas wells according to the DEPO+ process

.

The expected amortisation time of the necessary investment for the conversion of the gas wells under consideration of additional profits of the energy input e.g. energy utilisation and the operational costs (combined heat and power plant) is less than 2 years (applicable for energy revenue of 5 to 7,67 Cent/kWh). 4.2 Benefit The operator of the landfill must differentiate between the short-term, medium-term and long-term ecological and economical benefits (please compare Table 1).

Table 1: Economical and ecological benefit – short-term, medium-term and long-term – by the application of the DEPO+ process

Period Economical Benefit Ecological Benefit Short and medium term Additional revenue by

energetic landfill gas utilisation Carbon discharge / high-level reduction of emissions

Long term Reduction of after-care expenses Shortening of after-care period

Landfill with low emissions

Cost benefit analyses of landfill sites show that the optimised operation of the DEPO+

wells generates higher revenues in Phase A that can compensate the operation costs in Phases B and C.

LITERATURE Bröcker, C. (2008): Practical experience with in situ stabilisation measures when using the DEPO+ process®

, 3rd Practical Experience Conference, 2008 - intermediate storage - landfills - post-closure maintenance, Conference volume, 2nd and 3rd December 2008, pages 239 - 251, publisher: Matthias Kühle-Weidemeier in the Culliver Verlag.

Bröcker, C. (2009): Accelerating of biological decomposition processes and increasing of the methane yield taking as example the Alsdorf-Warden landfill, International Conference of Experts on Biological and Landfill Gas; organiser: DAS – IB GmbH, in Weimar on 28.04.2009, pages 79 - 92, publisher: DAS-IB GmbH. Bröcker, C., Rambadt K. (2010): Subsequent use of the Alsdorf Warden landfill using an optimised gas collection system, International Conference of Experts on Biological and Landfill Gas, organizer DAS – IB GmbH, Düsseldorf on 04.05.2010, pages 67 - 84, publisher: DAS-IB GmbH. Bröcker, C. (2009): Increasing the energy efficiency and improvement of long-term behaviour of municipal waste landfills by the application of the DEPO+ process®

, booklet series of the Deutsche Gesellschaft für Geowissenschaften from 2009, volume 64 ISEG 2009 10th International Symposium on Environmental Geotechnology and Sustainable Development, September 7th – 11th 2009 Bochum, Germany, pages 30 - 37, publisher: Deutsche Gesellschaft für Geowissenschaften e.V. (DGG)

Henken-Mellies, W.U. (2008) in situ stabilisation of municipal landfills – how? – how long? – what is the success? Seminar of the VKS im VKU society „shut down landfills“, Organizer Obladen und Partner, Berlin. Hohenschurz-Schmidt, R. (2009): Practical experience with the DEPO+ process®

taking as an example the Alt Duvenstedt landfill (Rendsburg-Eckernförde district), event of the ANS, DWA, VKS societies from 05. to 06.05.2009 in Minden entitled "Landfill conferences - operating, shutting down and post-closure maintenance of landfills“

Kanitz, J. & Forsting J (2004): Innovative degassing concepts for municipal landfills – energetically utilisation and aerobic in situ stabilisation. 15th Nuremberg Seminar on

Landfills, organiser: LGA-Grundbauinstitut, publisher Dr. U. Henken-Mellies, pages 131 – 146 Kanitz, J., Pauluweit, N. (2007): Results on the remediation of the gas wells in progress at the Wernsdorf landfill of the Berlin Stadtreinigungsbetriebe, 3rd Leipzig Conference of Experts on Landfills NN (2009): German landfill ordinance (Deponieverordnung 2009) Ramke, H.-G. (2004): Considerations on estimating the post-closure maintenance period for landfills, 15th Nuremberg Seminar on Landfills, organizer: LGA-Grundbauinstitut, publisher Dr. U. Henken-Mellies, pages 147 – 175 References/information on the use of the DEPO+ process®

www.cdm-ag.de on the CDM home page