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Influence of temperature phased anaerobic digestion on stabilization of municipal wastewater sludge Nazyab, Bita


Wastewater sludge has the most significant volume among all the constituents that are removed through wastewater treatment, and the annual cost of treating and disposing it accounts for more than half of the overall operation cost of a wastewater treatment plant (WWTP). Among all methods for treating the sludge, anaerobic digestion is the most popular process for its ability to reduce the pathogens and odor potential, save energy by producing methane-rich biogas, as well as reduce the biosolids volume for disposal. Although anaerobic digestion is the most favorable option for the treatment of sludge, it still has some aspects that can be improved. Emerging sludge treatment technologies are currently being studied to reduce the digester volume required and enhance the biogas production in anaerobic digestion. This study investigated the effect of temperature phased anaerobic digestion (TPAD) on treatment of municipal sludge generated by Lulu Island WWTP (BC, Canada) and compared it to conventional single-stage mesophilic anaerobic digestion (AD) currently implemented at the Lulu Island plant. A total number of five lab-scale digesters were operated according to the following scenarios: single-stage mesophilic AD (control), TPAD1 (acid/methane phase temperatures of 55/38°C), TPAD2 (acid/methane phase temperatures of 70/38°C). The systems were operated at three overall sludge retention times (SRTs) including 30, 20, and 15 days. The acid-phase of TPAD systems were able to improve the hydrolysis of sludge significantly and the acid phase of TPAD2 (70°C/2-d SRT) achieved the highest soluble to total chemical oxygen demand (COD), protein, humic acid and sugar ratios. Overall, anaerobic digestion benefited considerably from TPAD in terms of methane yield, pathogen removal and dewatering rate of biosolids. Relative improvements (over control) in solids removal and methane yield increased considerably by gradually decreasing the SRT from 30 to 20 and 15 days. TPAD1 system achieved the maximum methane production and pathogen destruction and it generated Class A biosolids according to Organic Matter Recycling Regulation of British Columbia at all operating SRTs, while the biosolids produced from the other digestion systems (control and TPAD2) could not meet the criteria for Class A and was classified as Class B.

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