Dissertation Defence: Evaluation of Various Carbon Cloth as Biomass Support Media for Bioaugmentation of Anaerobic Digestion of Municipal Sludge

Vikas Kumar, supervised by Dr. Cigdem Eskicioglu, will defend their dissertation titled “Evaluation of Various Carbon Cloth as Biomass Support Media for Bioaugmentation of Anaerobic Digestion of Municipal Sludge” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering.

An abstract for Vikas’ dissertation is included below.

Examinations are open to all members of the campus community as well as the general public.

Please email cigdem.eskicioglu@ubc.ca to receive the zoom link for this defence.

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ABSTRACT

The disposal of municipal sludge is a growing global environmental issue due to its high levels of organic pollutant and pathogens. Anaerobic digestion is a widely adopted process for treating municipal sludge that reduces pollutants and produce biogas as a source of renewable energy. However, the complex structure of sludge and the difficulties retaining slow-growing archaea in bioreactors, leading to low organic conversion efficiency and lower biogas yield in anaerobic digestion. To address these issues, the present research focuses on developing a side-stream bio-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 surface to attract and retain beneficial cultures; a novel bio-incubator reactor development with activated carbon cloth; and an effective bio-augmentation strategy to transfer microbial cultures from the bio-incubator to a Control reactor (conventional digester without activated carbon cloth). To synthesize high-performance activated carbon cloth, two methods were implemented: a two-step activation process (acid pretreatment followed by 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, it reduced the available 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, activated carbon cloth braided ropes were used for the development of a continuous-flow bio-incubator reactor, with a packing density of 1.48 gram activated carbon cloth per gram volatile solids of substrate, determined from the preliminary assays. The bio-incubator system with braided carbon cloth ropes produced a continuous supply of active microbial culture for bio-augmentation of the Control reactor for process improvement. Finally, different bio-augmentation strategies, pellet bio-augmentation and liquid bio-augmentation, were tested to transfer anaerobic cultures from the bio-incubator system to the Control digester. Pellet bio-augmentation outperformed the liquid bio-augmentation with 33 and 88% daily biogas increases at digester hydraulic retention times of 20 and 10, respectively, with a 2% increase in methane percentage of biogas compared to the Control reactor. Also, the pellet bio-augmentation strategy enhanced the Control digester’s resilience to stress induced at higher organic loads and can be retrofitted to existing wastewater treatment plants.