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UBC Theses and Dissertations

Temperature phased anaerobic sludge digestion with high pressure homogenization pretreatment Wahidunnabi, Abdullahil Kafi Md.


Management of municipal waste sludge has been a concern as it represents more than half of the total operation and disposal cost of a wastewater treatment plant (WWTP). Among different sludge disposal alternatives, anaerobic digestion has become an attractive option for its ability to generate methane-rich biogas, nutrient-rich fertilizer from organic waste as well as to reduce the sludge volume for final disposal. Recently, endeavors have been made to increase biogas and reduce digester volume requirement by emerging waste pretreatment (disintegration) techniques. This study investigated advance anaerobic digestion involving temperature phased anaerobic digestion (TPAD) coupled with high pressure homogenization (HPH) pretreatment as a new disposal option for the municipal sludge generated by WWTP in Kelowna (BC, Canada). The study began with preliminary examination of thickened waste activated sludge (TWAS) solubilization due to HPH pretreatment at different pressure (6,000 and 12,000 psi) and chemical dose (0.009 to 0.036 g NaOH/g total solids). Homogenizing pressure was found as a statistically significant factor (p-value < 0.05) for enhancing solubilization of particulate chemical oxygen demand (COD) and biopolymers in TWAS and particle size reduction of TWAS. A pretreatment with chemical dose of 0.009 g NaOH/g total solids and pressure of 12,000 psi was selected for digester studies. Upon acclimation of anaerobic inocula, a total number of twelve lab-scale digesters were operated under scenarios including single-stage (control), TPAD, and HPH coupled with TPAD (HPH+TPAD) at sludge retention times (SRTs) of 20, 14 and 7 days. Overall, mesophilic digestion was found to be benefited significantly from pretreatments. Relative (to control) improvements in methane yield and COD removals increased noticeably as SRT was shortened from 20 to 14 and 7 days. HPH+TPAD system was found to achieve maximum methane production and COD removals. Both TPAD and HPH+TPAD systems produced nearly Class A biosolids according to organic matter recycling regulation (OMRR) of British Columbia (BC), at 20 d SRT while digestates from all systems were qualified as Class B. Energy analysis indicated that all the digestion scenarios attained positive energy balance with HPH+TPAD system operated at 20 d SRT producing maximum net energy of 72.4 to 79.2 GJ/d.

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