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Combined treatment of landfill leachate and domestic sewage

University of British Columbia

Leachate generation from a sanitary landfill site often causes a serious pollution problem. Amongst the various options available to the engineer, collection and subsequent treatment of leachate is gaining wide acceptance. This study investigated the feasibility of treating leachate in combination with domestic sewage. Conventional activated-sludge units were operated at SRT's of 5, 10 and 20 days. A continuous-flow reactor and two fill-and-draw reactors, each with a reactor volume of 5 L, were operated at different organic loadings and temperatures. One fill-and-draw system was fed once a day, while the other was fed the same amount of food in two feeding operations. The organic loadings applied corresponded to sewage: leachate mixtures of 80:20 and 60:40, by volume. The temperatures studied were 22° C (average room temperature), 10° C, and 6°C. Leachate used in the experiment was collected, in one sampling, from a landfill site, while sewage was collected on a weekly basis from the UBC pilot-plant influent feed tank. The COD of the landfill leachate was 3530 mg/L, whereas the average COD of the domestic sewage was 275 mg/L. The first set of steady-state runs were conducted with a sewage: leachate ratio of 80:20, corresponding to an average influent feed COD of approximately 800 mg/L. COD removal efficiency ranged from 85.7 percent to 92.8 percent, for all the conditions investigated. Settling properties of the biomass, as reflected by the effluent suspended solids and SVI, improved as the sludge age was increased from 5 days to 20 days. However, due to endogenous respiration, cell lysis occurred in all the systems during the 20-day SRT and this caused the average effluent COD to increase. The continuous-flow system experienced the largest increase in the effluent COD since it was in an endogenous respiration state at all times. At the higher SRT's, the once-a-day system was found to be more efficient in treatment as compared to the twice-a-day system, while at the lower SRT, the reverse was true. The second set of steady-state runs, with a 60:40 sewage: leachate ratio and an average influent COD of approximately 1200 mg/L, performed better in terms of COD removal efficiency. The continuous-flow reactor performed best at the 20-day SRT with a treatment efficiency of 95.0 percent. At the 5-day SRT, however, the once-a-day system produced the best quality effluent (93.3 percent COD removal). The biomass continued to show good settling properties for all the conditions studied. However, in the fill-and-draw systems, at the 20-day SRT, sludge bulking was observed due to the low F/M ratios. This was reflected by the increased SVI values as well as the effluent suspended solids. Frequent sludge settling problems were encountered at the lower operating temperatures of 10° C and 6°C. A decrease in the treatment efficiency, with temperature, was clearly indicated for all three systems. At 10° C, the continuous-flow system was least efficient due to a high organic loading (72.7 percent COD removal). However, at 6°C, all three systems performed poorly, indicating system failure at that temperature. Aerobic treatment of a combined sewage: leachate waste stream was found to be feasible, even at high organic loadings. A detailed study of the settling characteristics indicated that settling is governed by the following parameters : food/microorganism (F/M) ratio, organic loading, mixed-liquor suspended solids (MLSS), and temperature. In this study, most of the steady-state runs indicated a properly settling sludge.

Text

2010-05-24

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http://hdl.handle.net/2429/24942

Civil Engineering

University of British Columbia

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