This thesis describes a laboratory investigation of in-situ treatment of synthetic leachate representative of that generated by a municipal solid waste (MSW) landfill. The overall objective is to evaluate alternative designs and operating procedures for effective leachate collection in conjunction with efforts to accelerate waste stabilization (i.e. leachate recirculation). In the investigation five 15 cm (6) diameter PVC columns were packed with pea gravel and concrete of different sizes; geotextiles were also placed between the packed sections as filter-separators and promoters of bacterial growth. Synthetic leachate was continuously input to the top of the columns and circulated 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. Results indicate about a 97% decrease in COD from the synthetic leachate concentration entering the top of the column, and about 98 % conversion of the ammonia to nitrogen gas. COD depletion and methane production were not significantly inhibited by the denitrification process. Optimum Hydraulic Retention Time (HRT) for the nitrification-denitrification system makes it economically viable for its development at a landfill site. Gas production shows low CO2 values, decreasing the potential of clogging in the Leachate Collection System (LCS) and extending the Landfill Gas (LFG) networks life service by generating a less corrosive environment. The use of concrete as an alternative to the most commonly used natural gravel as leachate collection drains may not be a good option. During the experiment, the leachate that permeated the columns packed with crushed concrete, presented a higher pH than the leachate that permeated the natural stone. At the conclusion of the experiment noticeable weathering was observed when the columns where dismantled. Further studies are recommended until more conclusive evidence as to concrete performance is found. The overall results obtained from the experiment show that in situ passive treatment at landfills is viable.

This thesis describes a laboratory investigation of in-situ treatment of synthetic leachate representative of that generated by a municipal solid waste (MSW) landfill. The overall objective is to evaluate alternative designs and operating procedures for effective leachate collection in conjunction with efforts to accelerate waste stabilization (i.e. leachate recirculation). In the investigation five 15 cm (6) diameter PVC columns were packed with pea gravel and concrete of different sizes; geotextiles were also placed between the packed sections as filter-separators and promoters of bacterial growth. Synthetic leachate was continuously input to the top of the columns and circulated 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. Results indicate about a 97% decrease in COD from the synthetic leachate concentration entering the top of the column, and about 98 % conversion of the ammonia to nitrogen gas. COD depletion and methane production were not significantly inhibited by the denitrification process. Optimum Hydraulic Retention Time (HRT) for the nitrification-denitrification system makes it economically viable for its development at a landfill site. Gas production shows low CO2 values, decreasing the potential of clogging in the Leachate Collection System (LCS) and extending the Landfill Gas (LFG) networks life service by generating a less corrosive environment. The use of concrete as an alternative to the most commonly used natural gravel as leachate collection drains may not be a good option. During the experiment, the leachate that permeated the columns packed with crushed concrete, presented a higher pH than the leachate that permeated the natural stone. At the conclusion of the experiment noticeable weathering was observed when the columns where dismantled. Further studies are recommended until more conclusive evidence as to concrete performance is found. The overall results obtained from the experiment show that in situ passive treatment at landfills is viable.