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Effect of enzymes on anaerobic digestion of primary sludge and septic tank performance

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Abstract

Enzyme additives are believed to improve septic tank performance by increasing the hydrolysis and digestion rates and maintaining a healthy microbial population. Previous studies reported mixed results on the effectiveness of enzymes on mesophilic and thermophilic digestion, and it is not clear whether enzymes would be effective under septic tank conditions where there is no heating or mixing, quantities of enzymes added are small, and they can be washed out quickly. In this study, batch reactors and continuous-flow reactors designed and operated as septic tanks were used to evaluate whether enzymatic treatment would increase the hydrolysis and digestion rates in primary sludge. Total solids, volatile solids, total suspended solids, total and soluble chemical oxygen demand, concentrations of protein, carbohydrate, ammonia and volatile acids in sludge and effluent samples were measured to determine the differences in digestion rates in the presence and absence of enzymes. Overall, no significant improvement was observed in enzyme-treated reactors compared with the control reactors.

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Acknowledgments

This study was funded by Natural Sciences and Engineering Council of Canada (NSERC) under the Discovery grant program. The authors thank NSERC and Clearford Industries Inc. for providing an Industrial Postgraduate Scholarship for James Diak who was a Masters student at Carleton University at the time of this study.

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Correspondence to Banu Örmeci.

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Diak, J., Örmeci, B. & Kennedy, K.J. Effect of enzymes on anaerobic digestion of primary sludge and septic tank performance. Bioprocess Biosyst Eng 35, 1577–1589 (2012). https://doi.org/10.1007/s00449-012-0748-7

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  • DOI: https://doi.org/10.1007/s00449-012-0748-7

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