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Kumar, Vikas

University of British Columbia

Municipal wastewater sludge disposal is a growing global environmental issue due to high concentrations organic pollutants and pathogens. Anaerobic digestion is a widely adopted process for treating municipal sludge and producing biogas as renewable energy. However, the complex structure of sludge and the difficulties retaining slow-growing archaea in bioreactors, leads to low organic conversion efficiency and lower biogas yield in anaerobic digestion. To address these issues, the present research develops a side-stream incubator reactor system that grows a dense population of syntrophic bacteria and archaea, with attention to microbial syntrophy. The research is divided into three main parts: developing a high-performance activated carbon cloth that retains beneficial cultures; a novel incubator using carbon cloth; and an effective bioaugmentation strategy to transfer microbial cultures from the incubator to a Control reactor (conventional digester, baseline scenario). To synthesize high-performance activated carbon cloth, two methods were implemented: a two-step activation process (acid pretreatment and air calcination at 525 ± 25°C), and metal-impregnation of carbon cloth that incorporated nickel and/or iron nanometals. Although metal impregnation enhanced the electrical conductivity however reduced the surface area for microbial attachment. The activated carbon cloth had a 435-times larger pore size area than the commercial carbon cloth, leading to improved microbial colonization and methane production rates in preliminary biochemical methane potential assays. Next, the activated carbon cloth braided ropes were used in a continuous-flow incubator reactor, with a packing density of 1.48 g activated carbon cloth/g volatile solids of substrate, determined from the preliminary assays. The developed incubator system produced a continuous supply of active microbial culture for bioaugmentation of the Control for process improvement. Finally, two bioaugmentation strategies, pellet bioaugmentation and liquid bioaugmentation, were tested to transfer microbial cultures from the incubator system to the Control digester. Pellet bioaugmentation outperformed the liquid bioaugmentation with 33 and 88% daily biogas increases at digester hydraulic retention times of 20 and 10, respectively, with a 2% higher methane compared to the Control reactor. Also, the pellet bioaugmentation strategy enhanced the Control digester's resilience to stress induced at higher organic loads and can be retrofitted to existing wastewater treatment plants.

Text

2023-05-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/84643

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/