Dosage-Dependent Toxicity of Universal Solvent Dimethyl Sulfoxide to the Partial Nitrification Wastewater Treatment Process

Laboratory-scale bioreactors were used to study the effect of dimethyl sulfoxide (DMSO) on the start-up, pollutant removal efficiency, and microbial community of nitrification (basic wastewater treatment process). The partial nitrification start-up time with 1 and 2% DMSO addition was 14 and 20 days, and reactor with 3.5% DMSO addition did not start up successfully until 42 days. When the DMSO concentration was above 2%, it had a significant inhibitory effect on the nitrification process. Although the abundance of Nitrosomonas increased from 9.7% (the control) to 11.9% (3% DMSO), the specific oxygen uptake rate of ammonia-oxidizing bacteria decreased from 0.64 to 0.08 mg O2/(gMLSS·min). The principal component analysis results indicated that when the DMSO concentration exceeded 2%, the microbial community was significantly different from that at a low concentration. The key classes of Blastocatellia and Clostridia under low concentration DMSO changed to Actinobacteria and Acidobacteria under high DMSO content environment. LC–MS analysis revealed that DMSO was degraded in the reactor, and a large amount of methanesulfenic acid was generated. Apparently, the widely used biological solvent DMSO was toxic to microorganisms at high concentration, and the concentration should be less than 2% when using DMSO as a solvent.