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Pilot-scale studies of the anaerobic digestion of combined wastewater sludges and mitigation of phosphorus release

University of British Columbia

The City of Penticton has operated a biological nutrient removal (BNR) treatment plant since 1991, in order to achieve lower phosphorus discharge limits into the Okanagan Lakes. Excess waste activated sludge (WAS) from the BNR process accounts for about 80% of total sludge wastage at the plant. Pilot-scale anaerobic digestion studies were conducted on-site at the Penticton wastewater treatment plant to investigate the influence of the codigestion of primary fermented sludge (PFS) and phosphorus rich WAS on the solubilization of phosphorus and on digester performance. Research was conducted in two phases: the first phase included the initial start-up of the digester and a control run of the digester using only PFS as feed at a 20 day HRT; the second phase used a combination of PFS/WAS (35/65 by volume) as feed at an HRT of 20 and 10 days. Anaerobic digestion of WAS resulted in a 70% release of the total phosphorus flow into the digester and about an 80% release of phosphorus previously removed during the BNR process. During the codigestion of PFS/WAS, HRT had no effect on the solubilization of phosphorus within the anaerobic digester. Addition of WAS to the anaerobic digester resulted in a significant reduction in volatile mass destruction and unit gas production, as well as a deterioration in the quality of the digester supernatant. During the codigestion of PFS/WAS, the digester operational efficiency, in terms of volatile mass destruction and unit gas production, decreased as HRT was reduced. However, ii HRT had no effect on the methane content of the anaerobic off-gas or the quality of the digester supernatant. Lab-scale studies demonstrated that chemical fixation of the digester effluent with lime, ferric chloride, or alum could produce high phosphorus removal efficiencies. In terms of overall effluent quality, ferric chloride, at a 2000 mg/L dosage, resulted in the highest removal efficiencies for orthophosphorus, COD, and TSS.

Thesis/Dissertation

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2009-01-15

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http://hdl.handle.net/2429/3665

Civil Engineering

University of British Columbia

UBCV

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