Regulation of volatile fatty acid accumulation from waste: Effect of inoculum pretreatment

Mechanism of dielectric barrier discharge plasma technology to improve the quantity of short-chain fatty acids in anaerobic fermentation of waste active sludge

The mechanism of improving the anaerobic fermentation performance of waste active sludge by using dielectric barrier discharge (DBD) plasma pretreatment technology was investigated. The maximum accumulation of short-chain fatty acids (SCFAs) was observed on the 7th day of anaerobic fermentation when the DBD power was 76.50 W, which was 1726.70 mg COD/L, 1.50 times of the control group. The ratio of acetic acid in DBD group was 9.30% higher than that in the control. Further mechanism research indicated that DBD pretreatment can destroy the structure of extracellular polymer substances and release organic substances such as protein and polysaccharide. The dissolved organic matter analysis indicated that the DBD technique could increase the release of biodegradable organics (eg., tyrosine proteins, soluble microbial by-products), thus accelerate the biotransformation of organic substance. Bacterial community structure analysis showed that the increase in the abundance of Firmicutes and Bacteroidetes and the decrease in the abundance of Proteobacteria in DBD group were beneficial to the accumulation of SCFAs. Besides, further archaeal analysis indicated that the decrease of Methanosaeta sp. and Methanosarcina sp. abundance in the DBD group facilitate acetic acid accumulation. This study demonstrated that the DBD technique can be used as an effective and potential pretreatment method to improve sludge anaerobic fermentation performance.

Enhanced volatile fatty acids accumulation in anaerobic digestion through arresting methanogenesis by using hydrogen peroxide

Volatile fatty acids (VFAs) can be accumulated as a final product of anaerobic digestion via arresting methanogenesis. Herein, hydrogen peroxide (H₂ O₂ ) was studied to inhibit methanogenesis for enhancing VFA accumulation with glucose as a substrate. The addition of 0.06 wt.% H₂ O₂ significantly reduced methane production and led to a VFAs concentration of 1233.1 ± 55.9 mg L^-1 , much higher than 429.3 ± 5.6 mg L^-1 in the control that did not have H₂ O₂ addition. The dominated VFAs with H₂ O₂ were acetic acid and propionic acid. A low H₂ O₂ dosage of 0.03 wt.% produced 466.3 ± 3.9 mg L^-1 more VFAs than that of O₂ addition at the similar (theoretical) dosage, but when the dosage was relatively higher, the VFA accumulation with O₂ addition became more than that with H₂ O₂ addition, likely because of stronger oxidation of VFAs by the overly added H₂ O₂ . A hypothetical mechanism for H₂ O₂ inhibition suggests that at a low H₂ O₂ concentration the inhibition is mainly toward methanogenesis to limit their consumption of VFAs and a high H₂ O₂ concentration starts to inhibit hydrolysis and acidogenesis and/or oxidize VFAs. Those results encourage further exploration of H₂ O₂ -based arresting methanogenesis for VFAs production.