Fe0 inhibits bio-foam generating in anaerobic digestion reactor under conditions of organic shock loading and re-startup

Bio-foaming during the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) is a major cause of unstable reactor operations, especially under high organic loading rates (OLRs). Here, we used two 40-liter anaerobic reactors to deal with the actual organic fraction of municipal solid waste at OLRs of 5 and 7.5 kgVS/m(3)/d and tried to inhibit bio-foam generation by dosing with Fe-0. One of reactors had 400 g of Fe-0 added before operation and additional 200 g of Fe-0 was added when the operating conditions changed; the other one was the control reactor with no Fe-0 dosing. The results show that bio-foam was generated in the control reactor at an organic shock loading of 10 kgVS/m(3)/d and re-startup at 5 kgVS/m(3)/d, while the reactor containing Fe-0 operated normally. Due to the surfactant attributes of volatile fatty acids (VFAs), the probability of bio-foam generation was positively correlated with the effluent's degree of surface activity (SA) induced by VFAs, which is a parameter representing the foaming potential. Because VFA biodegradation was enhanced in the reactor with added Fe-0, at the position of Fe-0 accumulation, the SA was decreased by 49.7-59.2%. Furthermore, the effect of Fe-0 dosing on inhibiting bio-foam was evaluated by comparison with traditional commercial anti-foam agents. The results suggest possible reasons for bio-foam generation in OFMSW AD and suggest the reasonable usage of Fe-0 to inhibit bio-foam formation. (C) 2019 Published by Elsevier Ltd.