Abstract

Abstract Anaerobic treatment of a bleached chemithermomechanlcal/ thermomechanical BCTMP/TMP (2:1 by volume) effluent obtained from Quesnel River Pulp Co. was studied on a laboratory scale at 35°C. The experimental apparatus consisted of upflow anaerobic sludge bed (UASB) acidogenic reactors followed by hybrid upflow anaerobic sludge bed/fixed-film methanogenic reactors. Under anaerobic conditions, sulphite and sulphate are reduced to sulphide, presenting problems of toxicity, odour, corrosion and reduced methane yields, and treatment efficiencies. The fate of these compounds was examined under various hydraulic retention times and sulphur management strategies, including: (i) pH control; (ii) inhibition of the sulphur reducing bacteria via molybdenum addition; and (iii) stripping hydrogen sulphide dissolved in the reactor liquor by recycling hydrogen sulphide-free off gas. Controlling the pH of the acidogenic reactor from 5.5 (uncontrolled) to 8.0, in order to shift the formed sulphide species to the less toxic ionic form, appeared to be ineffective in promoting wastewater treatment efficiency. Molybdenum addition to the wastewater, tested at levels from 0.1 to 1.0 mM, was effective at 1.0 mM in retarding sulphide formation. Hydrogen sulphide stripping, using scrubbed and recycled off gas, appeared to be the most effective means of sulphur management for this type of wastewater under these conditions.

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