Treatment of lipid-rich wastewater using free and immobilized bioemulsifier and hydrolytic enzymes from indigenous bacterial isolates.
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2017
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Abstract
The production and discharge of raw and poorly treated lipid-rich wastewater increase yearly due to rapid urbanization and industrial growth. This results in severe environmental and health hazards by affecting the normal operations of ecosystems. Biological approach involving synergistic application of low cost bioemulsifier and hydrolytic enzymes is an efficient, cost-effective, sustainable and eco-friendly technology for the treatment of high strength lipid-rich wastewater. Therefore, the main objective of this study was to investigate the potential of a mixture of free or immobilized bioemulsifier and hydrolytic enzymes (protease and lipase) in the reduction of pollutants present in dairy and poultry processing wastewater. Glycoprotein bioemulsifiers and hydrolytic enzymes were produced extracellularly by submerged fermentation from indigenous Acinetobacter sp. and Bacillus aryabhattai, respectively. Optimization of bioprocess parameters, using response surface methodology, revealed a 4.4- and 7.2-fold increase in protease and lipase production, respectively. The bioemulsifier from strain AB9-ES (XB9) and strain AB33-ES (YB33) formed stable emulsions only with edible oils with highest emulsification indices of 79.6 and 67.9%, respectively obtained against sunflower oil. The emulsifying activity of the bioemulsifiers was stable over broad range of temperature (4-121 ºC), moderate salinity (1-6%) and pH (5.0-10.0). Comparative study of biochemical profiling of both free and immobilized hydrolytic enzymes showed no change in the optimum temperature and pH of both enzyme preparations for maximum activity. However, in comparison to free enzymes, the immobilized enzymes recorded enhanced stability over the investigated pH and temperature ranges. Kinetics properties revealed enhanced enzyme-substrate affinity and increased catalytic efficiency of the immobilized enzymes when compared to soluble enzymes. In addition, the immobilized enzymes were more stable when stored at 4 and 25 °C and reusable for more than five consecutive cycles. These hyper-active and highly stable bioproducts were utilized in cocktail in both soluble and entrapped form for the batch biodegradation of pollutants present in lipid-rich wastewater. Biodegradability of the wastewater was assessed by measuring the reduction of COD and lipid content at time intervals under varying incubation conditions. In dairy wastewater treated at 37 °C without pH adjustment, maximum COD (60.51 and 65.19%) and lipid (47.98 and 63.53%) reduction efficiencies were recorded at 120 h using free and immobilized bioproducts, respectively. However, under these conditions, maximum COD (86.44 and 93.65%) and lipid (51.62 and 69.06%) removal efficiencies of poultry processing wastewater were observed at 120 h when treated with free and immobilized bioproducts, respectively. At temperature of 50 °C and pH 8.0, there was enhanced reduction of organic pollutants, with maximum COD (65.96 and 77.52%) and lipid (55.22 and 71.12%) removal efficiencies obtained in dairy wastewater at 72 h when using free and immobilized bioproducts, respectively. In the case of poultry processing wastewater, optimum COD (90.29 and 94.72%) and lipid (63 and 76.66%) removal was recorded at 72 h when treated with free and immobilized bioproducts, respectively. Reusability studies suggest that the immobilized bioproducts could be reused for up to six and seven times for the treatment of dairy and poultry processing wastewater, respectively. Findings from this study suggest the efficient, cost-effectiveness, sustainability and synergistic application of the developed immobilized bioemulsifier and hydrolytic enzymes in the removal of pollutants present in dairy and poultry processing wastewater.
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Doctoral Degree. University of KwaZulu-Natal, Durban.