The capability and performance of anaerobic biological decomposition of malodorous compounds in kraft pulping wastewater were studied. The experimental apparatus used in this investigation was a bench-scale semi-batch anaerobic contact process of which a digester vessel was operated in regular sequence as a stirred digester and a stationary sedimentation tank. The results obtained from this experiment revealed that digesting anaerobic sludge could convert dimethyl disulfide (DMDS) to methyl mercaptan (MM) and that MM was partially decomposed into H2S. To maintain this anaerobic biodegradation of sulfur-containing malodorous compounds, the concentration of H2S in digester mixed liquor was required to be kept below about 5 mg/L. The conditions of temperature of 50 °C and pH of 6.5 were most suitable for the methane fermentation of the kraft pulping waste steam drainage and for the removal of the malodorous compounds. Scrubbing of the digester head space gas with the solution of sodium hydroxide removed not only H2S but also MM, so that a high removal rate of DMDS and MM was achieved. Unfortunately, dimethyl sulfide (DMS) could not be decomposed biologically, but it could be removed easily with a simple air stripping process. From these results, an effective process combined with anaerobic digestion for the economical prevention of odor nuisance was proposed.

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