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Oily wastewater consists of fats, oils and greases together with a broad spectrum of dissolved organic and/or inorganic substances in suspension. It is regarded as one of the most hazardous wastewaters, causing serious environmental and health threats to the ecosystems, flora and fauna. The global increase in the discharge of oily wastewater coupled with stringent regulations for effluent discharge and incessant drive for re-use of treated wastewater necessitate the need for treatment of the wastewater. Conventional approaches employed in the past are inept for oily wastewater treatment due to low treatment efficiency and high operational costs, among others, hence the need for adoption of advanced technologies as promising alternatives to existing treatment systems for oily wastewater. Furthermore, the use of combined treatment processes is effective for the removal of hazardous pollutants present in high-strength oily wastewater. This review provides insights into advanced and emerging state-of-the-art technologies for safe and efficient treatment of industrial oily wastewater.

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a b s t r a c tThe combined use of free or immobilized bioemulsifier produced by Acinetobacter sp. and enzyme pool (protease and lipase) from Bacillus aryabhattai in the reduction of organic pollutants present in lipid-rich wastewater was investigated. Physicochemical characterization of the raw wastewater revealed high pollutant load in poultry processing wastewater in comparison to dairy wastewater. Biodegradability of the wastewater was assessed by measuring the reduction of COD and lipid contents at time intervals under varying process conditions. In dairy wastewater treated at 37°C without pH adjustment, maximum COD (61 and 65%) and lipid (48 and 64%) reduction efficiencies were recorded at 120 h using free and immobilized bioproducts, respectively. However, under these conditions, maximum COD (86 and 94%) and lipid (52 and 69%) 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 (66 and 78%) and lipid (55 and 71%) 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 and 95%) and lipid (63 and 77%) 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. This study suggests the efficient and synergistic application of the developed immobilized bioemulsifier and hydrolytic enzymes in the treatment of high fat-containing wastewater.

Lipases are enzymes that hydrolyze fats into fatty acids and glycerol at the water-lipid interface and are also involved in a variety of bioconversion reactions in non-aqueous and micro-aqueous environments. In this study, we optimized the culture conditions for extracellular lipase production by an indigenous lipase-producing bacterial strain isolated from lipid-rich wastewater, using response surface methodology. The studied isolate was identified as Bacillus aryabhattai SE3-PB by polymerase chain reaction and analysis of 16S rDNA. Sunflower oil was found to induce maximum lipase production. Face centered central composite design revealed that temperature (40 C), pH (7.6), inoculum volume (2.8%, v/v), agitation (193 rpm) and inducer oil concentration (2%, v/v) significantly influenced lipase production at the respective optimum conditions. The coincidence of observed lipase production (264.02 ± 1.94 U/mL) with predicted lipase yield (265.82 U/mL) coupled with a high correlation coefficient (R 2 ¼ 0.9919, P < 0.01) confirmed the validity of the model. A 7.2-fold increase in lipase production was obtained in the optimized medium compared to the basal medium. These findings provide the first report on lipase production and optimization by B. aryabhattai SE3-PB and suggest a rational choice of optimum processing conditions for commercial lipase production by B. aryabhattai SE3-PB.

In this study, two indigenous bacterial strains (Ab9-ES and Ab33-ES) isolated from lipid-rich wastewater showed potential to produce bioemulsifier in the presence of 2% (v/v) olive oil as a carbon source. These bacterial strains were identified as Acinetobacter sp. Ab9-ES and Acinetobacter sp. Ab33-ES by polymerase chain reaction and analysis of 16S rRNA gene sequences. Bioemulsifier production by these strains was found to be growth-linked. Maximum emulsifying activities (83.8% and 80.8%) were recorded from strains Ab9-ES and Ab33-ES, respectively. Bioemulsifier yields of 4.52 g/L and 4.31 g/L were obtained from strains Ab9-ES (XB9) and Ab33-ES (YB33), respectively. Fourier-transform infrared spectroscopic analysis revealed the glycoprotein nature of the bioemulsifiers. The bioemulsifiers formed stable emulsions only in the presence of edible oils. Maximum emulsifying activities of 79.6% (XB9) and 67.9% (YB33) were recorded in the presence of sunflower oil. The bioemulsifiers were found to be stable at a broad range of temperature (4-121 °C), moderate pH (5.0-10.0) and salinity (1-6%). In addition, bioemulsifier XB9 showed maximum emulsifying activities (77.3%, 74.5%, and 74.9%) at optimum temperature (50 °C), pH (7.0), and NaCl concentration (3%), respectively. On the contrary, YB33 demonstrated highest activities (73.6%, 72%, and 61.2%) at optimum conditions of 70 °C, pH 7.0, and NaCl concentration of 5%, respectively. Findings from this study suggest the potential biotechnological applications of the bioemulsifiers, especially in the remediation of oil-polluted sites.