Enhancement of short-chain fatty acids production from microalgae by potassium ferrate addition: Feasibility, mechanisms and implications

Abstract

Anaerobic fermentation of microalgae was always hindered by its rigid cell wall structure. This paper reports a novel technique, i.e., adding potassium ferrate (K2FeO4) into microalgae fermentation systems to enhance short-chain fatty acids (SCFAs) production. The results showed that the maximum SCFAs production and acetic acid proportion were 732.6 mg COD/g VS and 54.6% at a dosage of 112.8 mg Fe(VI)/g VS, which were 168% and 208% of those in the control, respectively. Mechanism studies revealed that K2FeO4 effectively destroyed surface morphology and cell structure, and thus facilitated microalgae solubilization, providing a large number of biodegradable substrates for subsequent SCFA production. Although K2FeO4 inhibited all the microbial activities relevant to hydrolysis, acidification and methanogenesis processes to some degree, its inhibition to methanogens was much severer than that to other microbes. Illumina MiSeq sequencing analyses revealed that K2FeO4 addition increased the relative abundance (from 9.45% to 50.4%) of hydrolytic and SCFAs-forming bacteria.