Enhancing the anaerobic bioconversion of complex organics in food wastes for volatile fatty acids production by zero-valent iron and persulfate stimulation

The addition of zero-valent iron (ZVI) and ZVI & persulfate (PS) were efficient approaches to enhance the production of volatile fatty acids (VFAs), especially butyric acid, from food wastes (FW) during anaerobic fermentation. The maximal concentration of VFAs was increased from 1256 mg COD/L in the control reactor to 8245 mg COD/L with ZVI addition, and it was further improved to 9800 mg COD/L with the PS/ZVI treatment. An investigation of the mechanisms revealed that both the ZVI and PS/ZVI treatments improved the bioavailable substrates in FW and enhanced the bioconversion efficiency of fermentation substrates, especially proteins and lipids. The provision of a sufficient amount of bioavailable substrates was advantageous to the enrichment of the functional bacteria that are responsible for the production of VFAs. Additionally, the microbial activity and key metabolic enzymes involved in the biological VFAs generation processes were stimulated in the ZVI and PS/ZVI-added reactors, which jointly contributed to high-rate VFAs yields.

Promoting the anaerobic production of short-chain fatty acids from food wastes driven by the reuse of linear alkylbenzene sulphonates-enriched laundry wastewater

An efficient attempt to improve the anaerobic fermentation of food wastes (FW) via the reuse of linear alkylbenzene sulphonates (LAS)-enriched laundry wastewater was reported. The production of short-chain fatty acids (SCFAs) from FW was enhanced by approximate 6-folds with high proportions of butyric and valeric acids at appropriate LAS level. Mechanism investigations demonstrated that the solubilization of macromolecule organics in FW was effectively improved by surface tension reduction. The hydrolysis and acidification processes during FW fermentation were accelerated and enhanced with the stimulation of microbial activities (higher activities of hydrolases and ATP concentrations). Also, the abundances of anaerobic microorganisms responsible for SCFAs production were enriched. Metatranscriptomic analysis indicated that the encoding genes involved in the metabolism of fermentation substrates for SCFAs production were highly expressed in LAS-added reactors. It was the simultaneous increase of bioavailable substrates and metabolic activities that contribute to the efficient SCFAs production in LAS-added reactors.