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

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.

Two-stage anaerobic process benefits removal for azo dye orange II with starch as primary co-substrate.

Two-stage anaerobic system (S1: R1 (acidogenic phase) + R2 (methanogenic phase)) and the one-stage control (S0) were established to investigate the effect of phase separation on the removal of an azo dye orange II, i.e., Acid Orange 7 (AO7), with starch as the primary co-substrate. Although final AO7 removal from two systems showed no statistical differences, the first-order rate constants for AO7 removal (kAO7-) and sulfanilic acid (SA) formation (kSA) were higher in S1. Kinetic analysis showed that kAO7- and kSA in S1 were 2.7-fold and 1.7-fold of those in S0, respectively, indicating the benefit of phase separation to the AO7 reduction. However, this benefit only appeared in the period with influent AO7 concentrations higher than 2.14 mM. Otherwise, this advantage would be hidden due to the longer HRT (5 d) and sufficient electron donor (1.0 g starch L-1). Within S1, R1 only contributed about 10% of the entire AO7 removal, and kAO7- in R1 (0.172 h-1) was much lower than in R2 (0.503 h-1). The methanogenic phase rather than acidogenic phase was the main contribution to AO7 removal, because the influent of R2 had more available electron donors and suitable pH condition (pH 6.5-7.0) for the bio-reduction process.