Studies On The Screening Of Degradation Bacteria From Coking Wastewater By Composite Mutagenesis And Their Degradation Properties

Coking wastewater,like other types of wastewater,belongs to the high concentration of refractory organic wastewater.If not treated,it will cause serious pollution to the environment.The organic components of coking wastewater include phenols,fats,benzene and heterocyclic compounds.Inorganic components include cyanide,thiocyanide,ammonia nitrogen,sulfide,etc.In this study,the degradation strain of coking wastewater was screened,of which the survival and degradation ability was improved by composite mutagenesis,and its degradation performance was also studied.The following conclusions were obtained:(1)From coking wastewater sludge,m-cresol was selected as the only carbon source to obtain a strain named Z2.One strain of potassium thiocyanate degradation bacteria was screened by activated sludge dilution coating plate method and named J4.Preliminary wastewater degradation tests were conducted on these two strains,and the results showed that the COD degradation rate was 38.6% and 40.0%,and the ammonia nitrogen degradation rate was 36.8% and 34.0%,respectively.Z2 was identified with 16 S r RNA and matched in NCBI,and the similarity between strain Z2 and Pseudomonas reached100%.(2)Strain Z2 was subjected to UV-DES combined mutagenic treatment.First,Strain Z2 was treated by diethyl sulfate with a volume fraction of 1% for 20 min.Then,15 W UV lamp was applied to illuminate Z2 for 20 s.Three highly effective strains C,D and G were screened.All of them improved the degradation ability of COD and ammonia nitrogen in coking wastewater,among which strain C had the best degradation effect,with COD degradation rate reaching 50.5% and ammonia nitrogen degradation rate reaching45.8%.The genetic stability test was conducted on strain C.After 5 passages,the degradation rate of m-cresol was maintained at 98.1%,so the strain C had good genetic stability.(3)The mutagenesis strain C was subjected to single-factor tests including temperature,pH,and external carbon and nitrogen sources to obtain the optimal growth conditions.Orthogonal tests were used to optimize the degradation conditions such as inoculum,rotational speed and liquid loading.The optimal growth conditions of strain C were obtained as follows: pH of 7 and 28?,and the optimal external carbon source was sucrose,and the optimal external nitrogen source was ammonium sulfate.Optimum degradation conditions of strain C are 200 rpm,4% inoculum dose,50 mL loading.The results showed that COD degradation rate reached 64.9% and ammonia nitrogen degradation rate reached 59.2% during this optimal condition.(4)The mutagenesis strain C and degrading KSCN strain J4 were tested for degradation of wastewater by mixed strains,and the optimal combination of the two strains was selected through different inoculum ratio.The results showed that when strain C: strain J4 is 2%: 4%,the degradation rate of wastewater reached the highest COD degradation rate of 66.8%,ammonia nitrogen degradation rate of 66.7%.(5)The growth kinetics and degradation kinetics of strain C were investigated,and the results showed that the growth kinetics of strain C was consistent with the Logistic model.And the degradation kinetics was consistent with the first-order exponential rate model..