Passive treatment of municipal landfill leachate in a granular drainage layer

This paper describes a laboratory investigation that simulates in situ treatment of leachate representative of that generated by a municipal solid waste (MSW) landfill. The objective of the investigation is to demonstrate that recycle of leachate and treatment within a leachate collection system (LCS) coupled with a nitrification reactor can provide significant decreases in leachate chemical oxygen demand (COD) and ammonia concentration. In the investigation five 15 cm (6 in.) diameter polyvinyl chloride (PVC) columns were packed with drainage media of various sizes consisting of natural gravel and (or) crushed concrete (washed and screened). Geotextiles were placed between the various media as filter-separators and to promote bacterial growth. Synthetic leachate was continuously fed into the top of each column and recirculated from the bottom at rates representative of operating field conditions. For each column, effluent was discharged to a nitrification reactor before recirculation. The tests were conducted under anaerobic and unsaturated conditions in the columns. The results obtained from the experiment show that in situ treatment at landfills using this approach is viable. A 97% decrease in COD and about 98% conversion of the ammonia to nitrogen gas was observed. The denitrification process did not significantly inhibit COD depletion or methane production. Further, the biogas produced contained only a small fraction of CO2, which could suggest a potential benefit in terms of decreasing the potential of clogging in the LCS and extending the service life of a landfill gas (LFG) collection network by generating a less corrosive environment.