Graduate Thesis Or Dissertation
 

Co-treatment of Municipal Wastewater and Landfill Leachate in an Activated Sludge Sequencing Batch Reactor

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  • A year-long bench-scale treatability study was performed to assess the feasibility of using an activated sludge sequencing batch reactor (SBR) to treat a mixture of domestic wastewater and landfill leachate. A 50/50 (v/v) of domestic wastewater and landfill leachate was treated in a 1 L SBR operated on a 12 hour cycle with a hydraulic retention time (HRT) of 4 days, mean solids retention time (SRT) no less than 25 days, and an average mixed liquor volatile suspended solids (MLVSS) of 2500 ± 500 mg/L. The combined influent had high chemical oxygen demand (COD) and total ammonia nitrogen (TAN), with average concentrations exceeding 1500 mg/L and 450 mg N/L respectively. The combined influent had a carbonaceous biochemical oxygen demand (CBOD₅) to COD ratio of 40 ± 10%, a TAN to COD ratio of 26 ± 7%, and also showed seasonal variability in pollutant loadings due to changes in rainfall. The SBR was capable of meeting effluent targets for 5-day carbonaceous biochemical oxygen demand (CBOD₅) and TAN, which were 10 mg/L and 5 mg N/L respectively, at loadings of up to 100 mg CBOD₅/L-d and 140 mg N/L-d. However, during the first 8 months, CBOD₅ removal was less consistent, with effluent values often above 20 mg/L, after which time effluent CBOD₅ was consistently below 20 mg/L. Filtration reduced effluent CBOD₅ by 50%, suggesting that a significant fraction was association with particulate matter. Nitrification performance was inconsistent during the first 7 months of operation, with accumulation of both TAN and NO₂-N, although good nitrification performance was eventually attained with complete nitrification of TAN to NO₃-N and almost 100% TAN removal. The decreased nitrification performance was most likely related to factors such as excess ammonia loading, aeration intensity, and free ammonia, rather than other inhibitory substances in the landfill leachate such as metals or organics. Aeration adjustments under different loading scenarios showed that the extent of nitrification was highly affected by aeration intensity, with improved nitrification observed with increased aeration. Increased aeration resulted in the complete nitrification of TAN to NO₃-N with effluent TAN and CBOD below target values for a combined influent of 67% landfill leachate and 33% wastewater. Denitrification was achieved only with the addition of methanol, which could provide another option for nitrogen removal in the SBR if reduction of NO₂-N or NO₃-N is needed. Average phosphorus removal in the SBR was approximately 10%. Based on mass wasting of reactor sludge, the reduction in phosphorus corresponded to normal microbial uptake and not to the presence of phosphorus accumulating organisms (PAOs). Metals analysis showed effluent manganese to be consistently below the preliminary target value of 5 mg/L and that reactor solids contained regulated heavy metals at concentrations well below the EPA ceiling limits for land application. Volatile organics and pesticides selected as additional preliminary target pollutants were either well below target limits or were not detected at all in the SBR effluent, although additional data may be needed to further verify whether these contaminants would be an issue in terms of effluent requirements.
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