Microbiological Mechanisms for Nitrogen Removal Using Anaerobic Fermentation Liquid from Spent Mushroom Substrates as a Carbon Source

In wastewater treatment, a low C/N ratio highly inhibits the bioremoval of nitrogen, and commercial external carbon sources are widely used. In order to obtain an economical substitute, fermentation broth of spent mushroom substrates (SMS) was employed here as a carbon source for denitrification in a sequencing batch reactor (SBR). During the domestication process, the SMS fermentation broth-feeding treatment presented comparable nitrogen removal ability (74.44%) with a commercial carbon source group (77.99%). Rhodobacter, Lactobacillus and Pseudomonas were the dominant bacteria in the fermentation broth, and Saccharomycetales Gymnopilus dilepis was the dominant fungi. At the early domestication stage, the relatively high concentration of fermentation broth led to a much lower abundance of typical nitrate reductase genes than the control group. Furthermore, extracellular polymeric substance (EPS) formation was observed in the broth-feeding sample. The microbial structure dynamic was investigated, which showed a high influent effect when 20% fermentation broth was added. As domestication proceeded, similar dominant species in the control and broth-feeding treatments were observed. Overall, SMS fermentation broth can be used as a promising substitute to replace a costly commercial carbon source.