Effect of temperature on fermentative VFAs production from waste sludge stimulated by riboflavin and the shifts of microbial community.

Abstract

Fermentative volatile fatty acids (VFAs) production from waste activated sludge (WAS) under moderate temperature is a promising way for resource and energy regeneration in municipal wastewater treatment plants (MWTPs). In this study, the effect of temperature on VFAs production and the associated microbial community from riboflavin-assisted WAS fermentation were investigated. Three fermentative reactors under 25, 35 and 55 °C were operated for 30 days, respectively. The results indicated that riboflavin enhanced VFAs production from WAS fermentation under moderate temperatures (25 °C, 35 °C), increasing conversion of organic matters to bioavailable substrates for the subsequent acidification process. Although a small dosage of riboflavin (1.0 ± 0.05 mM) hardly inhibited the methanogenic process, it could mediate the electron sink for VFAs under lower temperatures. This in turn increased the accumulation of acetic and propionic acids (up to 234 mg/g of volatile suspended solids) and their proportions relative to the total VFAs, being efficient electron donors and carbon sources for nutrient removal in MWTPs. Furthermore, microbial communities were shifted in response to temperature, and riboflavin stimulated the special fermentative bacteria under room temperature and mesophilic conditions. The study suggested a feasible and eco-friendly method to improve VFAs production from crude WAS at a relatively lower temperature.