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UBC Theses and Dissertations

Design of bioreactor for reducing sulphate in cattle drinking water Li, Winton

Abstract

A 5 litre laboratory-scale upflow anaerobic sludge blanket (UASB) bioreactor was constructed and operated for approximately one year to reduce sulphate in water using an agricultural byproduct, silage, as carbon source. The purpose of this water treatment system was to test the suitability of the UASB design to treat simulated ground water with high sulphate concentrations destined to be used as cattle drinking water. The UASB reactor design was selected after performing an extensive literature review of all available sulphate-reduction processes. A previous MASc project (Amber Brown, 2007) demonstrated the suitability of silage as a carbon source for sulphate reducing bacteria and, furthermore, in this thesis, fate of the organic compounds in the silage leachate during sulphate-reduction was determined. Six particular tests were performed in order to quantify the type of organics in the feed and effluent: chemical oxygen demand (COD), total organic carbon (TOC), total carbohydrates, total alcohols, total phenols, and selected organic and volatile fatty acids (VFA). The reactor ran continuously for approximately one year with a constant silage leachate feed COD concentration of 10,000 mg L₋−¹, and sulphate feed concentrations varying from 2,000 to 3,200 mg L−¹. The flow rates for each feed stream were maintained at ~0.5 mL min−¹ for silage leachate and ~1 mL min−¹ for sulphate feed for most of the experiment. The sulphate reduction rates (SRR) ranged from 368 to 845 mg L−¹ d−¹ and the amount of organics consumed was between 80-90%. Sulphide levels in the UASB bioreactor were consistently high for most of the experiment, ranging from 600-800 mg L−¹. When the sulphate feed concentration was increased to a maximum of 3,282 (± 27.22) mg L−¹, the sulphide concentration within the bioreactor reached a maximum of 1,273 (± 473.5) mg L−¹. A sulphide stripping column was introduced midway through the experiment in an attempt to reduce the sulphide concentration in the system. Short-term results were promising, however, prolonged sulphide removal in the system could not be maintained due to operational problems. Interestingly, during the last month of operation, despite the high sulphide levels, the SRR was at its highest with an upward trend.

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