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Effect of biochar and wood ash amendment on biochemical methane production of wastewater sludge from a temperature phase anaerobic digestion process

University of British Columbia

Methane production is limited during anaerobic digestion (AD) due to complex molecular structure of organic waste and inhibition of archaea by by-products generated from mineralization of organic matter. In British Columbia, biochar and wood ash are waste products of bioenergy produced from forestry residues. Recent studies have found that addition of biochar to AD increases methane production through direct interspecies electron transfer and biofilm formation, attenuation of inhibition and buffering effect. The objective of this study was to compare the effects of local biochar and wood ash in granular (0.85-4.75 mm) and powdered (< 0.075 mm) form on the biochemical methane production (BMP) of AD of municipal sludge from the Lulu Island wastewater treatment plant (WWTP) in Vancouver, British Columbia (Canada) in batch bioassays. Powdered biochar at dosage of 0.8-3.7 g/g-volatile solids (VS)-substrate achieved the highest improvement in rate of methane production with 192-461% increase from controls, in the first 16 days. This increase was followed by an early stationary methane production phase and a reduction of total methane yield ranging from 9 ± 4% at the lowest dosage to 25 ± 1% at the highest. Results indicated that the early plateau could be caused by adsorption of volatile fatty acids (VFAs) by the biochar. There was generally no significant difference in total methane yield from granular biochar at dosages up to 2.2 g/g-VS-substrate, however, at 3.7 g/g-VS-substrate there was a 16 ± 3% reduction. Methane production rates from wood ash (under the propriety name of ZMM® T-Carbon) amended assays were either not significantly different from controls except at a granular dosage of 2.2 g/g-VS-substrate, where production rates were better than controls. Thus, ZMM® T-Carbon may contribute essential nutrients and be beneficial only under high organic loading rate. Granular ZMM® T-Carbon was effective at reducing ammonia nitrogen by up to 14%. Evidence from BMP colonization test and scanning electron micrograph images demonstrated that syntrophic bacteria and methanogenic archaea colonized the surface of the granular char media. Future research should investigate the VFA adsorption capacity of various biochar types.

Text

2020-02-26

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73613

Civil Engineering

University of British Columbia

UBCO

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