Towards Valeric Acid Production from Riboflavin-Assisted Waste Sludge: pH-Dependent Fermentation and Microbial Community

The fermentative valeric acid production is a carbon-neutral method for the disposal of waste sludge in municipal wastewater treatment plants. To overcome the bottlenecks of energy-consuming and slow hydrolysis and acidification during the fermentation process, riboflavin was supplemented to enhance the biological redox reaction. The effect of pH (3, 5, 7, 9, 11) on the production of total volatile fatty acids (VFAs) and valeric acid from waste sludge, and on the shift of microbial community was investigated. The results indicated that the release of organic compounds and nitrogen, the production of VFAs and valeric acid, and the associated microbial community were pH-dependent in riboflavin-assisted sludge fermentation systems. Higher pH (9, 11) and shorter retention time (12 days) benefited the valeric acid production, which achieved to 190.8 (mg COD / g VSS), accounting for 76.6% of the total VFAs. Meanwhile, the solubilization of organics and ammonia was up to 43.7% and 38.4%, respectively. Alkaline condition in riboflavin-assisted fermentation system reduced the taxonomy categories and enriched the bacteria phyla of Firmicutes and the associated genera species, which were responsible for the acidification process related to valeric acid production. The study provided scientific insights into the recovery of valuable organic matter from waste sludge to achieve carbon-neutral and sustainable society. [GRAPHICS] .