Feasibility study of SCFAs production from microalgae during hydrogen fermentation

Abstract

In the present work, the feasibility of short-chain fatty acids (SCFAs) production from microalgae was investigated during hydrogen (H2) fermentation. The fermentation was conducted at various substrate concentrations ranging 2.5–100 g dry cell weight (dcw)/L by using anaerobic mixed cultures under mesophilic condition. It was found that H2 yield increased to 36 mL H2/g dcw as substrate concentration increased to 40 g dcw/L. However, a significant decrease in H2 yield was observed at substrate concentration of ≥60 g dcw/L. As substrate concentration increased, SCFAs concentration gradually increased, reaching 12,410 mg COD/L at 100 g dcw/L. However, in terms of SCFAs conversion efficiency, it increased from 17 to 34% (on chemical oxygen demand basis) with substrate concentration increase up to 10 g dcw/L. Acetate was the major product at 2.5 g dcw/L, but butyrate became dominant at substrate concentration of 5–60 g dcw/L. At 80 and 100 g dcw/L, lactate became the major product. H2 and SCFAs production rate were successfully described by kinetic models of Andrew's Eq. and Monod Eq., respectively. From the fermentation performance obtained, it can be concluded that microalgae could substitute the current attempt that acidifying sewage sludge to use as an external carbon source in denitrifier.