Recovering short-chain fatty acids from waste sludge via biocarriers and microfiltration enhanced anaerobic fermentation

Abstract

Short-chain fatty acids (SCFAs) could be harvested from waste sludge via anaerobic fermentation to offset the cost of waste sludge management. Recovering SCFAs from wastes could also help build a more sustainable society. The present study proposed an approach to recover SCFAs from wasted activated sludge via biocarriers and microfiltration (MF) enhanced anaerobic fermentation. Results show that biocarriers and MF membrane separation promoted SCFA production through different ways. The application of biocarriers alone increased the concentration of soluble organics and SCFAs by enhancing the disintegration and solubilization of sludge particles and enriching hydrolytic bacteria such as Christensenellaceae_R-7_group, Proteiniclasticum, and Proteocatella. The MF membrane alone promoted SCFA production due to the retention of organic matter and acidogenic bacteria such as DMER64 by the MF membrane. The fact that the MF membrane could hardly retain NH4+ and SCFAs was beneficial to the mitigation of ammonia inhibition and acid inhibition. Employing biocarriers and MF membrane separation at the same time achieved a considerable SCFAs concentration of 3500 mg/L and increased the concentration of soluble COD and SCFAs by 2 and 1.3 times, respectively, higher than either of them alone. In addition, biocarriers effectively alleviated the membrane fouling of the MF membrane and increased the membrane flux from 5 L/m2/h to 7 L/m2/h. This study shows the synergistic effects of biocarriers and MF on sludge anaerobic fermentation, and provides a cost-effective approach for SCFA recovery.