Remediation Of Soil Pollution By Low Temperature Degradation Strains With Enhanced P-nitrophenol

P-nitrophenol(PNP)is a nitroaromatic compound used in human life and production in pesticide,medicine,and the rubber industry,etc.It has a stable physical and chemical properties and is highly toxic.P-nitrophenol will enter the environment through infiltration,adsorption and diffusion.The main repair methods of p-nitrophenol are adsorption method,chemical method and bioremediation.Microbial remediation has the characteristics of in-situ remediation,environmental protection,and economy,and gradually becoming a research hotspot.At present,the optimal growth temperature of p-nitrophenol degrading bacteria is about 30?,so its degradation ability is limited in the process of groundwater and soil pollution remediation in low-temperature areas of Northeast China.In this study,low temperature p-nitrophenol degradation bacterium was isolated,and its degradation characteristics and kinetics were studied.The response surface method was used to optimize the low temperature degradation conditions.Based on this,soil simulated remediation and degradation experiment were carried out at low-temperature.The following conclusions can be drawn based upon the investigations:(1)A low-temperature degradation strain of p-nitrophenol was isolated from farmland soil contaminate by methyl parathion pesticide.The strain was identified as Pseudomonas by 16S DNA.At low temperature,p-nitrophenol could increase the cell membrane permeability and became a moderately hydrophobic cell.The single-factor experiment results showed that the maximum degradation concentration of p-nitrophenol at low temperature were 303.77 mg/L.The strains was suitable for survival under alkaline conditions,and the optimal degradation p H was 8.00,and the optimal initial inoculation concentration was 225.92 mg/L.0.5%Na Cl,0.8%glucose and 1 g/L NH₄NO₃could promote the degradation of p-nitrophenol.(2)Multiple regression equation was obtained through response surface optimization experiment,and it was found that p H had great influence on the degradation of nitrophenol by strain.At 10?,optimal degradation conditions were p H 8.12,1.80 g/L NH₄NO₃,the optimal initial inoculation concentration was 224.00 mg/L,the maximum degradation rate of p-nitrophenol at 52.51 mg/L was predicted to be 79.85%at 52 h.The degradation rate of p-nitrophenol was verified to be 80.95%,which was close to the predicted value.At optimized conditions,the inhibitory degradation kinetics of the strain was in line with the Haldane model,with a fitting R²value of 0.990,a maximum specific growth rate of 0.2151/h,a half satiety coefficient of 5.35 mg/L,and an inhibition coefficient of 134.21 mg/L,indicating that the growth inhibition effect of p-nitrophenol concentration was 134.21mg/L.(3)Compared with 30?,the removal rate of p-nitrophenol was lower under low temperature,but the combined effect of biological stimulation and biological enhancement was better.In the process of remediation,the soil moisture content and p H gradually decreased,which was consistent with the degradation of p-nitrophenol..At the same time,p-nitrophenol had a great influence on soil enzyme activity,which was positively correlated with dehydrogenase and negatively correlated with catalase and urease.Biological stimulation of soil acidification would reduce soil dehydrogenase activity,and the two were significantly negatively correlated.Biofortification had little impact on the environment during degradation of p-nitrophenol,but biostimulation had great impact on soil p H and enzyme activity.Therefore,the substance and content of biostimulation need to be further studied.