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Khoei, Shiva

University of British Columbia

Anaerobic digestion (AD) has become a common bioconversion approach for recovering resources and energy from biomass in wastewater treatment plants. Thermophilic anaerobic digestion (TAD) offers a wide range of possible applications due to its high ability for energy production, fast hydrolysis rate, and high potential for pathogen elimination. The accumulation of volatile fatty acids (VFAs), which occurs due to the accelerated fermentation rates in TAD, contributes to digester failure by reducing methanogenic activity as a result of a pH reduction. A recently identified method of electron transfer, known as direct interspecies electron transfer (DIET), involves bacteria directly transferring electrons to methanogens. The addition of conductive materials can improve methanogenesis activity and encourage DIET between bacteria and methanogens. In addition, the adsorption capacity of these materials increases stability of ADs by adsorbing inhibitory compounds, such as VFAs and ammonia. In this study, the effects of powdered (<0.075 mm) biochar on TAD was investigated using biochemical methane potential (BMP) assays. The assays had substrate-to-inoculum ratios (SIR) of 2.2 and 4.4 g-volatile solids (VS)/g-VS and biochar dosing of 6 g/g-total solids (TS) inoculum. Initially, BMP assays (Scenarios 1,2 and 3) were performed to evaluate the role of biochar in increasing methane production and shortening the lag period using various substrates and inocula. Adding biochar enhanced the methane production rate compared to controls at SIR 4.4 g-VS/g-VS by 94% and 75% in assays utilizing acidified mixed sludge (MS) substrates at 70ºC, and 55ºC, respectively. All controls at higher organic loading rates experienced acute inhibition with lag phases from 12-52 days, while assays with biochar generated methane from day 4. In scenario 4, BMP assays using acidified substrate acclimated at 55ºC were conducted to reveal the potential of biochar in improving AD stability. Results indicated that biochar-supplemented digesters reduced the accumulation of VFAs, which the adsorption potential of biochar could cause. In addition, up to 14 mg of ammonia as a determinative inhibitory factor was removed by one gram of biochar. Biochar presents great potential to tackle VFA accumulation, abbreviate lag phase and increase methane rate, particularly at high organic loadings.

Text

2022-12-01

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83335

Civil Engineering

University of British Columbia

UBCO

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