Biosurfactant Production From Low-Cost Substrates for The Degradation of Selected Emerging Pollutants

Abstract

Emerging contaminants are widely detected in water, wastewater and aquatic environment. On account of their environmental and human-related effects, increasing the tendency towards wastewater treatment technologies. Bioremediation techniques are increasingly used to decontaminate the pollutants from the environment due to their eco-friendly nature, economic and degradation effectiveness. The present study focused on the role of biosurfactant produced by Pseudomonas aeruginosa (MTCC 1688) and Bacillus licheniformis (MTCC 429) for the removal of ibuprofen (IBU), triclosan (TCS) and ketoprofen (KETO) from wastewater. It was carried out in three stages i) Biosurfactant production by Pseudomonas aeruginosa (MTCC 1688) using crude sunflower oil (10 to 100%), sucrose and ammonium bicarbonate (1 to 10 g/L) and Bacillus licheniformis (MTCC 429) was used in the combination of crude sunflower oil (10 to 50%), glycerol and ammonium bicarbonate (1 to 10 g/L) for the optimized biosurfactant by Box-Behnken Design (BBD). Further characterization of the optimized biosurfactant was carried out by FTIR, NMR and LC-MS and comparison with the commercial biosurfactant. The experimental investigation on biosurfactant screening and its stability was carried out ii) Application of produced biosurfactant for the removal of IBU, TCS and KETO from domestic wastewater from Surathkal region, Karnataka, India and its detection by HPLC method. iii) The possible degradation metabolites were identified using LC-MS method and pathways of IBU, TCS and KETO was proposed. Firstly, biosurfactant production was performed by both the organisms. Pseudomonas aeruginosa showed the optimized biosurfactant with maximum reduction in the surface tension of 41 mN/m, biosurfactant yield of 11.2 g/L, emulsification index of 50% (in diesel and benzene) and foaming activity of 30% for the combination of crude sunflower oil (10%), sucrose (5.5 g/L) and ammonium bicarbonate of 1 g/L. Critical micelle concentration (CMC) is the surfactant's minimal concentration was found to be at 10.5% and 10 mg/L respectively for liquid and dry biosurfactant. The optimized biosurfactant showed higher stability at neutral to basic pH with high temperature and salinity concentration which showed the reduction in surface tension with a greater emulsification index. BBD statistical model was found to be significant for the responses of biomass and surface tension with having the regression coefficient of 0.9912 and 0.9907 respectively for Pseudomonas aeruginosa produced biosurfactant. ii Bacillus licheniformis showed the optimized biosurfactant with a maximum reduction of surface tension from 72 to 48 mN/m, biosurfactant yield of 7.8 g/L, oil displacement of 5 cm and emulsification index of 62.5% in coconut oil for the combination of crude sunflower oil (10%), glycerol (1 g/L), and ammonium bicarbonate (5.5 g/L). Bacillus licheniformis produced biosurfactant that showed higher stability at basic pH and high temperature, and salinity conditions. A statistical validation experiment was performed to check the accuracy of the model, the predicted values are good in agreement with that of experimental values obtained for the response of surface tension and an insignificant statistical model was found for the response of biosurfactant yield. Characterization studies (Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) and Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (LC-ESI-MS)) was performed for Pseudomonas aeruginosa and Bacillus licheniformis produced biosurfactant. For Pseudomonas Species, it revealed that it belongs to category of rhamnolipid type of glycolipid biosurfactant. Bacillus species falls under the category of iturin type of lipopeptide group of biosurfactants after the characterization studies and was compared with the commercial biosurfactant. Based on the results, it can be concluded that, the produced biosurfactant was well in agreement with commercial biosurfactant. Secondly, the pollutants were extracted by solid-phase extractor (SPE) from wastewater and analyzed by HPLC method, which showed linearity for the calibration curve with R2 close to one for IBU, TCS and KETO. The raw domestic wastewater sample showed the initial concentration of 4.36, 0.356 and 0.312 ppm of IBU, TCS and KETO during the summer season influent sample and 0.137 ppm of IBU was found in the influent sample during the rainy season. For rainy season sample, no TCS and KETO was found in the influent and effluent sample. Further, the removal of 98.74% and 99.68% of IBU at 36 h and 6 h was achieved in the influent sample during the summer season by Pseudomonas aeruginosa produced biosurfactant at 100% (crude biosurfactant) and 10.5 % (at CMC). Complete removal of TCS was achieved in 16 h by crude biosurfactant of Pseudomonas sp. and KETO removal was found to be 91.7% and BDL was obtained at 1 h for the summer season sample. iii The application of Bacillus licheniformis produced biosurfactant showed the IBU removal of 99% at 12 h and 30 min respectively with the use of crude biosurfactant (100%) and 14% (at CMC) for the influent sample of summer season. During the rainy season, it was found that the 84.7% and BDL of was reported at 1 h of treatment period using 100% and 14% of biosurfactant usage for the summer season sample. TCS removal was found to be 100% at 16 h (100% biosurfactant) and KETO removal was achieved to be 97.7% and BDL in 4 h and 30 min by crude biosurfactant and 14% of biosurfactant for the summer season influent sample. Thirdly, the degradation metabolites of IBU, TCS and KETO was proposed based on the LC- MS method. During the triclosan degradation, the toxic metabolite of methyl triclosan was found by the use of both biosurfactant produced by Pseudomonas aeruginosa and Bacillus licheniformis and further, it was degraded into a non-toxic by-product of 5-chloro-2-(2,4- dichlorophenoxy)phenyl 2- hydroxy acetate. The fifteen intermediates (I178, I176, I208, I192, I210, I225, I302, I296, I344, I370, I340, I22, I238, I265, and I297) of IBU were found during treatment by Pseudomonas aeruginosa produced biosurfactant and several KETO metabolites (K222, K299, K210, K165, K226, K242 and K240) are detected by the use of both biosurfactant for the treatment of wastewater. Hence it can be concluded that biosurfactant usage at CMC condition performed better with higher removal rate of contaminants than the 100% crude biosurfactant by both the organisms. The biodegradation of IBU, TCS and KETO by using both biosurfactants was achieved with the non-toxic metabolites. Hence, the present study investigation proves that the proposed biosurfactants were effectively suitable for the removal of IBU, TCS and KETO from domestic wastewate.