Using pig manure to promote fermentation of sugarcane molasses alcohol wastewater and its effects on microbial community structure

•PM is an ideal candidate for co-digestion with MAW.•The optimal COD ratio of PM:MAW for anaerobic digestion is 1.0:1.5.•The structure and composition of bacterial communities varied in the early and late stage.•The type of main OTUs did not differ much among tanks with different ratios of PM to MAW, only the proportion is different. Molasses alcohol wastewater (MAW) is difficult to be bio-treated and converted into biogas. In this study, MAW mixed with pig manure (PM) in different ratios was co-digested. Biogas production, chemical oxygen demand (COD) removal and the structure of microbial communities were monitored in the process. Our results showed that under the optimal COD ratio of PM:MAW (1.0:1.5), CODremoval and biogas yield were the highest. And in fermentation tanks with different PM to MAW ratios, the structure and composition of bacterial communities varied in the early and late stage. Furthermore, the type of main bacterial operational taxonomic units (OTUs) have no differences, yet the relative abundance of OTUs varied. The current research showed that there was a good potential to the use of PM as a co-digested material to anaerobic treatment of MAW and provided references for further improving bio-treatment of MAW.