Role of sulfur in the treatment of organosulfur aqueous waste by water plasma.

Organosulfur pollutants in industrial aqueous waste pose significant challenges to wastewater treatment processes, due to their toxicity and odorous nature. Water plasma is a novel alternative for aqueous waste treatment, with the advantages of high capability and high energy efficiency. The role of sulfur in aqueous waste treatment by water plasma is studied by coupling thermodynamic calculations and experiments. The treatment of highly concentrated organosulfur aqueous waste is demonstrated with a novel water plasma torch, using dimethyl sulfoxide as a model compound. Decomposition rates exceeding 98% with organic carbon removal rates over 97% are achieved at dimethyl sulfoxide concentrations up to 66 g/L. Notably, this process attains high energy efficiencies of up to 26 g/kWh. Syngas produced from the process mainly consist of hydrogen, carbon monoxide, carbon dioxide, and a small portion of sulfur dioxide. Sulfate is identified as the main sulfur-containing product in the liquid effluent. The strong temperature gradient in the downstream region inhibits the formation of sulfite and hydrogen sulfide, resulting in sulfur trioxide formation in trace amounts. The existence of sulfur trioxide in the downstream region promotes the oxidation of carbon monoxide. The role of sulfur-containing species in different regions of water plasma is discussed in detail based on experimental results and calculations. The comparison with other methods highlights water plasma's distinct advantages of superior capability and energy efficiency.