Synergistic Degradation Of Propionic Acid By Sulfate-reducing Bacteria In UASB

Anaerobic biological treatment process is widely used in the field of industrial high-concentration wastewater treatment with the characteristics of high efficiency, low consumption and safety. Propionic acid accumulation is the main factor which results in reactor acidification and even the failure of anaerobic process. At present, there is no effective method with low cost and industrial application to eliminate the propionic acid accumulation. In this paper, propionic acid was the sole carbon source, the maximum organic loading rate (OLR) of UASB reactor in propionic acid degradation was investigated. Sulfate reducing bacteria (SRB) was cultured to eliminate propionic acid accumulation. The carbon sulfur ratio was the key factor in the synergistic degradation of propionic acid, which was discussed. The influence of SRB on microbial community in UASB was analyzed by using high-throughput sequencing technology.When propionic acid was used as the sole carbon source, the maximum propionic acid OLR was 1.13 kgCOD/(kgVSS-d) with maximum propionic acid concentration of 5500 mg/L. Acetic acid concentration was less than 105 mg/L with increasing OLR, and acetic acid did not accumulate in UASB. The optimal carbon sulfur ratio was 6 in the experiment, when the minimum propionic acid concentration dropped to 483 mg/L and the removal efficiency was 91.22%. When carbon sulphur ratio decreased from 10 to 1, the acetic acid concentration in UASB increased to 975 mg/L, which incidated that acetic acid accumulated. When S2- concentration was higher than 41 mg/L, methane producing bacteria (MPB) was inhibited. When S2-concentration was higher than 97mg/L, SRB was inhibited. The percentage of electron flow for sulfate reducing increased gradually from 2.99% to 43.22% when carbon sulphur ratio reduced from 10 to 1.High throughput sequencing results showed that the species of methane bacteria increased while the percentage of methane filamentous bacteria decreased, and the diversity of anaerobic microorganism increased with sulfate addition.