Study On Biological Degradation Of 2-Chlorophenol By Photosynthetic Bacteria

Chlorophenols (CPs) are categorized as non-biodegraded organic compounds which are widely used, large-volume produced, highly toxic and exhibit fair chemical and thermal stability. Due to their discharge into the environment without being appropriately disposed, CPs have posed great threat to natural ecosystem and human health by enrichment through the food chain. Treatment of water containing CPs by microorganism is considered economical as well as free of secondary pollution. In this work a complicated study was taken to evaluate the degradation efficiency and influencing factors of the process---degradation of 2-chlorophenol (2-CP) by photosynthetic bacteria (PSB).From different places such as shallow substrate sludge in downstream side of the sewage pipeline of pesticide factory, nearby paddy rice field, soil under the tree in the Northeastern University campus, a strain of photosynthetic bacteria named PSBA was obtained through separation, selection and acclimatization. Followed by morphologic observation as well as physiological and biochemical experiments, it was initiatively identified as Rhodopseudomonas palustris sp.By toxic experiment (i.e. dehydrogenase activity experiment), we drew the conclusion that acclimatization could effectively reduce the sensitivity of PSB to 2-CP. The safety concentration (i.e.LOEC) of acclimatized PSB, before-acclimatized PSB and multiple lake bacteria were 50mg/L,25mg/L and 25mg/L respectively procured from standard method for assessment of toxicity of chemicals on aquatic organism. In addition,96h-EC50 for those three samples---331.13 mg/L,188.36 mg/L and 167.49mg/L individually were obtained by applying probability unit method, which was verified by x2 test. In a word, PSB performed higher tolerance than multiple lake bacteria and this character was further fortified by acclimatization. The results also indicated that 2-CP could not act as sole carbon source and energy for PSBA and the degradation process could proceed by virtue of co-metabolism mechanism.Conditional optimization experiments presented that when the oxygen was provided, temperature set at 35℃, intensity of illumination at 30001x, initial pH at 7, 2-CP concentration at 50mg/L,2.0g/L citric acid as co-metabolism carbon source, 2.0g/L yeast extract as nitrogen source, inoculum concentration of 2-CP at 10% (volume) and reaction time at 96h, the degradation efficientcy were up to 56.05%. In addition, dosing of CO2 had no positive effect on 2-CP degradation.In conclusion, as-selected PSB (PSBA1) enjoyed fairly strong ability to endure 2-CP after acclimatization and it displayed relatively strong ability to degrade 2-CP, which shed the light of the prospect of application microorganism to dispose non-degradable and toxic organic compounds.