Abstract
Taguchi statistical design, an orthogonal array (OA) method, was used to study the impact of the COD/SO42− ratio, hydraulic retention time (HRT) and linoleic acid (LA) concentration on sulfate (SO42−) reduction in an anaerobic sequencing batch reactor using glucose as the electron donor. Based on the OA, optimum condition for maximum SO42− reduction was evaluated. Increasing the COD/SO42− ratio and HRT caused decreasing SO42− reduction while increased SO42− reduction was observed with increasing LA concentration (1 g L−1). In control (not fed LA) cultures, higher SO42− reduction (87% ± 3%) was observed at a low COD/SO42− ratio of 0.8. This indicates that increasing SO42− reduction was observed at increasing SO42− loading rates. In general, results from this study reveal that limiting the substrate concentration with high SO42− levels (low COD/SO42− ratio) favors high SO42− removal. Surface plots were used to evaluate the significant interactions between the experimental factors. Accuracy of the model was verified using an analysis of residuals. Optimum conditions for maximum SO42− reduction (97.61%) were observed at a COD/SO42− ratio of 0.8 (level 1), 12 h HRT (level 1) together with 1000 mg L−1 LA addition (level 3). In general, the Taguchi OA provided a useful approach for predicting the percent SO42− reduction in inhibited mixed anaerobic cultures within the factor levels investigated.
Highlights
The sulfate ion (SO42−) is found in natural environments such as sediments, seawater and areas rich in decaying organic matter
The Taguchi method is based on orthogonal array (OA) providing a systematic, simple and efficient approach [35]
This method provides an approach which allows for a realistic arrangement of the experimental data sets with the understanding system, parameter, and tolerance designs [35]
Summary
The sulfate ion (SO42−) is found in natural environments such as sediments, seawater and areas rich in decaying organic matter. Sulfate is released in effluents from many industries such as pulp and paper processing, coal powered power plants, edible oil industries, tannery operations, molasses fermentation and mining [1,2]. Effluents generated from these industries contain other sulfur species, which include thiosulfate, sulfite, sulfide and dithionite [3]. Minerals, such as iron and zinc are converted to reduced metal sulfides These sulfide compounds are oxidized with the release of metals ions and SO42− (Reactions (1) and (2); Table 1). Dissolution of heavy metals from metal oxides and carbonates results in the formation of metal and SO42− containing wastewater known as acid mine drainage (AMD) [4,5,6]
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