Microbiome re-assembly boosts anaerobic digestion under volatile fatty acid inhibition: focusing on reactive oxygen species metabolism.

The accumulation of volatile fatty acids (VFAs) in anaerobic digestion (AD) systems resulting from food waste overload poses a risk of system collapse. However, limited understanding exists regarding the inhibitory mechanisms and effective strategies to address VFAs-induced stress. This study found that accumulated VFAs exert reactive oxygen species (ROS) stress on indigenous microbiota, particularly impacting methanogens due to their lower antioxidant capability compared to bacteria, which is supposed to be the primary reason for methanogenesis failure. To enhance the VFAs-stressed AD process, microbiome re-assembly using customized propionate-degrading consortia and bioaugmentation with concentrated digestate were implemented. Microbiome re-assembly demonstrated superior efficiency, yielding an average methane yield of 563.6±159.8 mL/L·d and reducing VFAs to undetectable levels for a minimum of 80 days. This strategy improved the abundance of Syntrophomonas, Syntrophobacter and Methanothrix, alleviating ROS stress. Conversely, microbial community in reactor with other strategy experienced an escalating intracellular damage, as indicated by the increase of ROS generation-related genes. This study fills knowledge gaps in stress-related metabolic mechanisms of anaerobic microbiomes exposed to VFAs and microbiome re-assembly to boost methanogenesis process.

Biogas liquid digestate grown Chlorella sp. for biocrude oil production via hydrothermal liquefaction.

Microalgae can not only purify and recover the nutrients from wastewater, but also be harvested as wet biomass for the production of biocrude oil via hydrothermal liquefaction (HTL). Chlorella sp. cultivated in the ultrafiltration (UF) membrane treated anaerobic digestion (AD) liquid digestate of chicken manure was used as the feedstock in this study. The present study characterized the products and investigated the elemental migration during HTL of Chlorella sp. fed with AD effluent wastewater (WW) and BG11 standard medium (ST) in 100mL and 500mL reactors under different operational conditions. Results showed that the highest oil yield of WW (38.1%, daf) was achieved at 320°C, 60min and 15% TS in 500mL reactor, which was 14.1% higher than that of ST (33.4%, daf) at 320°C, 30min and 20% TS in the same reactor. WW had a similar carbon and hydrogen distribution in the four product fractions under HTL conditions compared with ST. 43.4% and 32.4% of carbon in WW11 and ST11 were released into the biocrude and aqueous phase in 500mL reactor, respectively. As much as 64.5% of the hydrogen was transferred to the aqueous phase. GC-MS results showed that the chemical compounds in the biocrude oil from WW consist of a variety of chemical constituents, such as hydrocarbons, acids, alcohols, ketones, phenols and aldehydes. These two biocrude oils contained 17.5% wt. and 8.64% wt. hydrocarbons, and 63.7% wt. and 79.8% wt. oxygen-containing compounds, respectively. TGA results showed that 69.3%-66.7% of the biocrude oil was gasified in 30°C-400°C. This study demonstrates the great potential for biocrude oil production from microalgae grown in biogas effluent via HTL.

Co-digestion of chicken manure and microalgae Chlorella 1067 grown in the recycled digestate: Nutrients reuse and biogas enhancement.

The present investigation targeted on a sustainable co-digestion system: microalgae Chlorella 1067 (Ch. 1067) was cultivated in chicken manure (CM) based digestate and then algae biomass was used as co-substrate for anaerobic digestion with CM. About 91% of the total nitrogen and 86% of the soluble organics in the digestate were recycled after the microalgae cultivation. The methane potential of co-digestion was evaluated by varying CM to Ch. 1067 ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10:0 based on the volatile solids (VS)). All the co-digestion trials showed higher methane production than the calculated values, indicating synergy between the two substrates. Modified Gompertz model showed that co-digestion had more effective methane production rate and shorter lag phase. Co-digestion (8:2) achieved the highest methane production of 238.71mL⋅(g VS)-1 and the most significant synergistic effect. The co-digestion (e.g. 8:2) presented higher and balanced content of dominant acidogenic bacteria (Firmicutes, Bacteroidetes, Proteobacterias and Spirochaetae). In addition, the archaea community Methanosaeta presented higher content than Methanosarcina, which accounted for the higher methane production. These findings indicated that the system could provide a practicable strategy for effectively recycling digestate and enhancing biogas production simultaneously.

Anaerobic co-digestion of chicken manure and microalgae Chlorella sp.: Methane potential, microbial diversity and synergistic impact evaluation.

Anaerobic digestion (AD) is a promising alternative for livestock manure management. This paper presents the experimental results obtained through a batch experiment by using chicken manure (CM) and microalgae Chlorella sp. as co-substrates. The effect of co-digestion was evaluated by varying CM to Chlorella sp. ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10: 0 based on the volatile solids (VS)). The major objective of this study is to evaluate the feasibility and synergistic impact of co-digestion of CM and Chlorella sp. Enhanced 14.20% and 76.86% methane production than CM and Chlorella sp. mono-digestion respectively was achieved in co-digestion at the ratio 8:2. In addition, the co-digestion at the ratio 8:2 showed significantly higher methane yield than the weighted average of the individual substrates' specific methane yield (WSMY), indicating strong synergy effect. The Illumina Miseq sequencing analysis showed that the AD process suppressed the acetoclastic methanogenesis Methanosaeta content; but partly enhanced hydrogenotrophic methanogenesis Methanosarcina, Methanospirillum and Methanobacterium, which was responsible for the methane production. The pre-treated microalgae was then introduced at the optimal ratio 8:2 to estimate the effect of pre-treatment of microalgae on AD process. However, the pre-treatment exhibited no positive effect.