Research Of Bacteria Screening And Degradation Characteristics Based On Drilling Wastewater Treatment

Drilling wastewater,which contains high oil content and high Chemical Oxygen Demand(COD),is an industrial wastewater produced during the drilling process.It is harmful to the soil and groundwater if it discharges to the environment without any treatment.Currently,the traditional methods has a lot of deficiencies,as chemical reagents used in the chemical treatment process,which have a secondary pollution to the environment.Thus,treatment of drilling wastewater by biological method is important to protect the environment of the drilling site.The objectives of this study are treat the drilling wastewater through biological method.A highly oil-degrading mixed strains named B4-53 were obtained through natural selection and mutation breeding.The optimum strains culture conditions,degradation conditions,basic reaction kinetics of mixed strains,and the COD degradation rate were studied.The main research work and results are as follows.8 groups of mixed strains which can degrade diesel were obtained through natural selection.However,low diesel degradation rate limits its performance,thus the microbial degradability was optimized by means of domestication.The domestication period is 15 days.The degradation rate of the mixed strains of B4 increased from 27.3% to 40.7% in three days.A highly oil-degrading mixed strains named B4-53 was obtained through UV mutagenesis and screening.The diesel degradation rate reached to 76.7% after 3 days.The growth and degradation characteristics of mixed strains were studied by changing the culture parameters such as pH,temperature,inoculum concentration,shaking speed,and NaCl concentration.The conditions of pH 6-8,temperature of 24-36 ?,inoculum concentration of 15-20%,rotating speed of 140-160r/min were optimal for growth,while the pH of 7,the temperature of 32?,inoculum concentration of 20%,rotating speed of 160 r/min was optimal for degradation.This study also explored the effects of different diesel concentrations on the degradation characteristics of B4-53.The results show that the diesel with a concentration of less than 2000 mg/L can be degraded by mixed strains of B4-53.When the concentration of diesel was 100 mg/L,the diesel degradation rate can reach to 93.0%.Based on the above results,the biochemical reaction kinetics of diesel degradation by mixed strains was studied.The results show that the maximum relative growth rate ?max was 0.09 h-1,the half-saturation constant Ks was 0.20 g/L,the maximum cell yield Y*x/S was 0.015,and the cells maintain constant m was 0.268 h-1.Organic matter degradation experiments show that the optimal degradation conditions were the pH of 7,the temperature of 34 ?,aeration rate of 100mL/min.In the optimal conditions,the degradation rate of COD in wastewater reached to 87.9%.