Anaerobic digestion coupled with three-dimensional iron-carbon electrolysis for enhanced treatment of wood-vinegar wastewater and bacterial structure changes

Abstract As one of novel organic wastewater with high chemical oxygen demand (COD), WV-WW treatment has gained more and more attention. Acetic acid is the most abundant organic substance in wood vinegar wastewater (WV-WW) and thus it can be reused by anaerobic digestion (AD), which is significant for energy recovery and environmental sustainability. However, some refractory components are contained, some of which show toxic or inhibitory effects on AD. Therefore, the performance of batch AD from WV-WW with gradient organic loadings (1, 2, 4, 6, and 8 g COD/L) was studied. And it was found that the microbial activity was initially inhibited by 38.2% at 4 g COD/L. The inhibitory effect was gradually aggravated with increasing the organic loading. Subsequently, the WV-WW with 4 g COD/L was pretreated by three-dimensional iron-carbon electrolysis (3D-ICE) before AD. The cumulative methane production could be increased to 244.3, 291.9 and 344.2 mLCH4/g COD under different electrolysis conditions. The COD removal rates reached 62.4%, 66.8% and 70.8% which were 31.3%, 35.7% and 39.7% higher than that of the contorl, respectively. The microbial community was analyzed by high-throughput sequencing. The increased abundance of dominant bacteria, such as Kosmotoga, which was associated with fermentation and hydrolysis, indicated the positive effect of 3D-ICE. For archaeal communities, the enrichment of acetotrophic methanogens implied that the main methanogenic pathway was shifted from hydrogen-consuming methanogenesis to acetic acid-consuming methanogenesis. Therefore, 3D-ICE coupled with AD could be an effective method to recover energy from WV-WW.