Coconut shell ash enhances short-chain fatty acids production from anaerobic algae fermentation.

[Display omitted] • Coconut shell ash enhanced SCFAs production from algae. • Coconut shell ash promoted solubilization, hydrolysis and acetogenesis. • Coconut shell ash increased alkalinity to tolerate higher acidic environments. • Coconut shell ash enriched microbes related to hydrolysis and acetogenesis. This study proposed a novel method to enhance short-chain fatty acids (SCFAs) production from anaerobic algae fermentation by using coconut shell ash. The maximum SCFAs production was 683.0 mg COD/g VS at the ash dosage of 1.2 g/g TS, which was about 1.4-folds that of the control, and the enhancement of acetate production was the main path for the promotion of SCFAs. Coconut shell ash increased the pH and alkalinity of digestate, thereby reducing the use of alkaline reagents and being more resistant to acidic environments. Coconut shell ash promoted the processes of solubilization, hydrolysis and acetogenesis, and enriched hydrolytic microorganisms (e.g., Candidatus Microthrix) and acidifying microorganisms with acetate as substrate (e.g., Caldilinea and Proteiniphilum). Anaerobic fermentation residue with ash containing inorganic elements has the potential to be used as fertilizer, making this waste-control-waste strategy with more economic and environmental benefits for potential practical applications. [ABSTRACT FROM AUTHOR]