BIODEGRADATION OF N-HEXADECANE BY ENTERIC BACTERIA ISOLATED FROM AN OIL-FIELD WASTEWATER TREATMENT PLANT

Four biosurfactant-producing bacteria strains with high n-hexadecane degradation efficiency were isolated from activated sludge in a sequential batch reactor (SBR) in Weizhou terminal oilfield wastewater treatment plant, designated SBR14, SBR27, SBR28, and SBR45. Strains SBR14 and SBR45 were identified as Leclercia adecarboxylata, while strains SBR27 and SBR28 were identified as Enterobacter sp, based on 16S rDNA sequence analysis. The strains maintained growth activity under the following conditions: n-hexadecane concentration of 0.05-1% (v/v), salinity of 5-100 g/L, and pH of 5.0-9.0. Under optimal conditions: salinity of 15-25 g/L, pH of 6.0-7.0, inoculation amount of 5%, and a temperature and shaking speed of 37 C and 160 rpm, respectively, the hexadecane (0.3%, v/v) degradation rate of each strain reached 93.74%, 65.66%, 73.27%, and 87.79% respectively, after 16 days of incubation. The crude products of these four strains were extracted, and the purified products were analyzed by thin layer chromatography and Fourier transform infrared spectroscopy. The products were identified as phospholipids biosurfactant, with yields of 0.564, 0.605, 0.435, and 0.657 g/L, for strains SBR14, SBR27, SBR28, and SBR45 respectively. The growth of strains agrees with the Logistic model, exhibiting specific growth rates of 0.1375, 0.254, 0.145, and 0.066 d(-1), respectively. Meanwhile, hexadecane utilization followed the first order reaction kinetics model, with half value periods of 5.874, 10.046, 7.967, and 6.729 days, respectively.