COMBINED TREATMENT OF LANDFILL LEACHATE AND DOMESTIC SEWAGE IN A SEQUENCING BATCH REACTOR

A study was undertaken to examine the feasibility of biologically trea ting a combined waste stream of landfill leachate and municipal sewage . The ratio of sewage to leachate was 9 to 1 by volume. The combined w aste had an avenge BOD5 430 mg/l, COD 1090 mg/l, and TKN 133 mg/l (80% of which was in the form of ammonia). A laboratory-scale sequencing b atch activated sludge reactor was used to carry comparative performanc e evaluations of biological treatment, including nitrification and den itrification. The SBR reactor was operating in daily time cycles emplo ying the following sequential operation phases: filling phase, anoxic phase, aeration reaction phase, settling phase, and drain phase. In pa rticular, the anoxic and aeration periods were tailored in order to de velop conditions conducive to desired nitrification and denitrificatio n. During the reaction period, the process was operated under an exten ded aeration mode with the MLSS concentration being around 3500 mg/l. The results indicated that successful biotreatment of combined leachat e and sewage was possible, with the treated effluent being low in BOD5 and COD. The system was capable of BOD5 removal efficiencies exceedin g 95%. Furthermore, nitrate removal during the anoxic phase was approx imately 99% due to denitrification. However, the overall nitrogen remo val during a full cycle was about 50%. The inclusion of an anoxic peri od right after the aeration phase enhanced the nitrogen removal effici ency, yet this phase required the addition of an external carbon sourc e to the reactor due to the low concentration of biodegradable carbon, and at the same time the process became less efficient in BOD removal . (C) 1997 IAWQ. Published by Elsevier Science Ltd.