Enhancing blackwater methane production by enriching hydrogenotrophic methanogens through hydrogen supplementation.

Source diverted blackwater (i.e., toilet wastewater with or without food waste residuals) represents an ideal waste stream for bioenergy recovery through anaerobic digestion. However, due to the high free ammonia concentration contained in blackwater collected from water conserving toilets (e.g., vacuum toilets), CH4 recovery can be significantly reduced because methanogenesis is inhibited. Our current study evaluated the feasibility of enriching hydrogenotrophic methanogens (known to be more resistant than acetoclastic methanogens toward free ammonia inhibition) in anaerobic sludge with H2 supplementation for blackwater treatment. Our results demonstrated that hydrogenotrophic methanogens can be enriched by supplementing anaerobic sludge with H2 and CO2 in a volume ratio of 4:1 for 3 months. The dominance of hydrogenotrophic methanogens after 3-month enrichment was confirmed with quantitative PCR studies. It was observed that the hydrogenotrophic methanogen dominant anaerobic sludge significantly alleviated blackwater free ammonia inhibition, and led to enhanced biochemical methane production (BMP) (e.g., from 30% to 53%). Our current study offers a new treatment option for anaerobic treatment of wastewater with high free ammonia content.