Aeration of the teuftal landfill: Field scale concept and lab scale simulation
Introduction
The Teuftal landfill, located in the Swiss canton Bern, is the largest sanitary landfill in Switzerland. For more than 40 years both, municipal solid waste (MSW), construction and demolition waste, bottom ashes, flue gas cleaning residues as well as industrial waste are disposed of at different landfill sections. Untreated MSW has been landfilled between 1973 and 2000 on an area of approximately 12 ha. This section of the landfill which contains approx. 3.2 million tons of waste (approx. 2.1 million tons dry matter) is hereafter referred to as bioreactor. Based on the available records regarding the landfilled waste materials it can be assumed that the amount of organic carbon in the fresh MSW was in a range of 18–20% based on dry mass. Since 1 January 2000, landfilling of organic waste is prohibited in Switzerland (Schweizerischer Bundesrat, 1990). Consequently, the bioreactor has been covered with biologically non-reactive waste (slightly contaminated soil) during the past 16 years.
Between 1982, when landfill gas (LFG) collection started for the first time, and 2013 a total of approx. 256 million m3 LFG at an average methane concentration of 45% (average CO2 concentration: 32%) has been collected from the bioreactor and used for combined electrical and thermal energy production. Since 1996 the collected amounts of LFG declined significantly down to hourly mean values well below 100 m3/h in 2013. At the same time, analysis results for leachate samples taken directly out of the most reactive zone of the bioreactor still exhibited significant concentrations particularly for ammonium-nitrogen (NH4-N, up to 1500 mg/l) and dissolved organic carbon (DOC, up to 600 mg/l).
In order to diminish long lasting PCC associated with severe costs and monitoring efforts (Heyer et al., 2005, Laner et al., 2012), the landfill operator in cooperation with the Hamburg University of Technology decided to biologically stabilize the bioreactor by means of a combined in situ aeration and moisturization approach. According to Heyer et al. (2005) the net costs for investment and operation of aerated landfills range from € 1.1 to € 3.0 per m3 of aerated waste material. However, the investment made during and for the aeration will pay out through reduced expenditures for long term leachate and LFG treatment as well as monitoring. It is expected, that total cost reductions of at least 10–25% are possible as regards closure and aftercare measures. In December 2014 the aeration started at a section of the bioreactor containing approx. 30% of its total waste volume. There, landfill aeration using horizontal gas and leachate drains for air injection and off-gas extraction is carried out for the first time in full scale. The applied technology differs significantly from other approaches previously reported for landfills in Switzerland (Bachofner et al., 2010). Section 2 provides an overview on the technical concept applied for biological stabilization of the bioreactor. The stabilization processes is currently ongoing. First intermediate results from this field scale study are provided whilst final results will be presented at a later date. Sections 3 Material and methods, 4 Results and discussion present the set-up and major findings from lab scale simulation tests which have been conducted in parallel to the field scale study.
Section snippets
In situ aeration
Under consideration of site specific conditions it was decided to implement a large scale in situ aeration trial on Section 3 of the bioreactor. This section covers an area of approx. 4.8 ha and contains approx. 557,000 m3 of MSW. Based on an estimated wet waste density of 1.2 ton per m3 and a measured average moisture content of 35.5% (wt), the total amount of dry waste in bioreactor Section 3 is calculated to approx. 431,100 tons.
The aeration is realized using the existing horizontal gas and
Solid waste samples
The landfill section undergoing the accelerated bio-stabilization (Section 3 of the bioreactor) has been filled since 1986. Of particular interest for the combined aeration and moisturization approach, however, is the central zone where waste has been deposited until the year 2000. This zone exhibited a height of approx. 35 m and contains approx. 557,000 m3 MSW which has been subject to intensive bio-degradation processes under the prevailing anaerobic conditions for the last 16–28 years.
In April
Characterization of solid waste samples
Solid waste samples derived from Section 3 of the bioreactor have been analyzed in view of their specific state of bio-stabilization. Table 2 summarizes the results of both chemical-physical as well as biological investigations of the solid waste samples taken at the Teuftal landfill.
Analytical results presented in Table 2 clearly demonstrate the significant heterogeneity of the landfilled solid waste material. Particularly high standard deviations of more than 50% of the mean value have been
Conclusions
At the Teuftal landfill in the canton Bern, Switzerland, biodegradable waste (MSW) has been deposited between 1973 and 2000. Today, 16 years after the completion of MSW deposition, the average waste age at the bioreactor is approx. 29 years. In the course of microbial decomposition under the prevailing anaerobic conditions, a significant share of bio-available organic carbon contained in the landfilled wastes has already been converted. This is reflected by both a total of 242 million m3 of
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