Screening Of Degradating Bacteria For 2-methyl-4-chloropphenoxyacetic Acid And Its Application For Bioaugmentation Treatment Of Simulated Wastewater

2-methyl-4-chlorophenoxyacetic acid(MCPA)is a hormone-selective herbicide.It is widely used all over the world due to its high efficiency and low price.Due to its mobility,it is easy to transfer in the soil stucture and enter the aquatic system which may possess certain toxicity to aquatic organisms and pollute groundwater.A large number of previous studies have shown that MCPA has biological toxicity and low biodegradability.Wastewater containing MCPA can cause serious harm to the water ecological environmengt and human health after its inappropriate discharge into the environment.Therefore,to isolate a high efficient MCPA degrading strain and investigate its bioaugmentaion technology in treating MCPA containing wastewater is of great importance.In this paper,a highly effective MCPA degradating strain F-2 was isolated from an activated sludge collected from a pesticide manufactory in Jiangsu province in China.Through the morphological and biochemical characteristics,the strain F-2 was identified to be the genus Pseudomonas according to the sequence analysis of 16S rRNA sequence.The strain F-2 was aerobic and its optimal growth temperature was 25?-35?.The favorable pH condition for cell-growth was determined as pH5.0-9.0.Specially,Strain F-2 could adapt to a wide range of NaCl concentrations and it grew best with using the glucose as the carbon source and ammonia sulfate as the nitrogen source.The results of degradation characteristics for strain F-2 in liquid inorganic salt medium showed that the optimum pH for the degradation of MCPA by strain F-2 was pH6.0-8.0 and the optimum temperatures was 25-35?.The strain F-2 strains showed tolerance to high salt concentration.The degradation kinetic was studied using the Lao Mai equation and results showed that the maximum degradation rate was 18.43 mg·h-1·L-1.The degradation products of MCPA by the strain F-2 were analyzed by HPLC-MS and two metabolites were identified including 2-methyl-4-chloro-phenol and 5-chlorosalicylic acid.Therefore,the pathway of CPA degradation was proposed:Firstly,deacetylating reaction happened on MCPA molecule and produced 2-methyl-4-chloro-phenol.Secondly,the methyl group in 2-methyl-4-chloro-phenol was oxidized to form a carboxyl group and produce 5-chlorosalicylic acid.Lately,5-chlorosalicylic acid was oxidized and finally entered tricarboxylic acid cycle and was completely mineralized.In the immobilization experiment,the specific surface area of the prepared immobilized bead was 23.31 m2·g-1,while the specific surface area of the ordinary sodium alginate bead was 3.98 m2·g-1.MCPA degradation efficiency for immobilized bacteria was greatly improved.Compared with the free bacteria,the immobilized bacteria could tolerate higher substrate concentrations and could adapt to a wider range of pH and temperature levels.The immobilized bacteria also had enhanced resistence to heavy metals.After applying the laboratory-scale SBR reactor,high-throughput sequencing analysis was performed for the samples of the initial sludge,the sludge during the degradation process,and the degradation-stable sludge.Results showed that the immobilized bacteria in the reaction system promoted the succession of microbial communities in the system.The genus Pseudomonas had relatively better environmental adaptability and eventually became a dominant genus in reaction system.