Screening Of High Efficiency Strains By Compound Mutagenesis And Study On The Treatment Of Coal Gasification Wastewater

Coal gasification refers to the conversion of coal into clean energy containing hydrogen and carbon monoxide at a certain temperature and pressure.Coal gasification is of great significance in improving China's air environment and reducing pollution.However,the coal gasification wastewater(CGW)with high pollution produced by the coal gasification process is difficult to deal with.In general,chemical oxygen demond(COD)and ammonia nitrogen of CGW,which contains organic compounds such as phenols,polycyclic aromatic hydrocarbons and heterocyclic compounds containing nitrogen,oxygen and sulfur,is about 5000 mg/L,500 mg/L.The treatment and utilization of CGW can greatly alleviate the pollution of the environment.In this paper,a strain was screened from coal gasification sludge.And the degradation ability of the strain was improved by compound mutation.The adaptability of the strain in the possible complex environment was studied.The following conclusions are obtained:(1)In the sludge of CGW,3 strains named R,X and Y respectively,were screened by phenol as the only carbon source.The degradation performance of the 3 strains was preliminarily measured,and it is shown that COD degraded by R,X and Y decreased from 1000 mg/L to 500 mg/L,550 mg/L,600 mg/L and ammonia nitrogen decreased from 500 mg/L to 270 mg/L,350 mg/L,350 mg/L respectively,thus,the results shows that strain R is the best among R,X and Y.16 S rDNA sequencing was carried out for the strain R,and the sequence was matched in GenBank.The strain R was identified as Bacillus subtilis by phylogentic analysis.(2)The strain R was mutated by diethyl sulfate(DES)-UV compound mutagenesis.The steps are as follows: First,Strain R was mutated by 1% DES solution for 10 minutes.Then strain R was irradiated with ultraviolet light for 30 s.Finally,3 effective strains were screened out,named R1,R2 and R3 respectively.The COD and ammonia nitrogen degradation ability of all strains increased to a certain extent,but the R1 degradation effect was the best.Degrading wastewater for 72 h,the results showed that: the COD decreased to 200 mg/L,ammonia nitrogen reduced to 200 mg/L,COD and ammoniadegradation rate reached 80% and 60% respectively.The degradation rate of mutation were increased by 30% and 14% than before.The genetic stability test of strain R1 was carried out.After 5 passages,the COD degradation rate of strain R1 was maintained at80%,and the ammonia nitrogen degradation rate remained at 60%,which indicates that the degradation ability of strain R1 had good genetic stability.(3)The single factor test of temperature,pH and external carbon source was selected to optimize the growth conditions of strain R1.The orthogonal experiment was used to optimize the degradation conditions(temperature,pH,inoculation amount).The test results show that: The optimum growth conditions for strain R1 are as follows,30?,pH=7,and the most suitable carbon source is sucrose.The optimal conditions for degradation of wastewater by strain R1 were determined as follows: 30?,pH=7,and inoculation volume of 5%.Under this condition,the COD of the wastewater reduced to120 mg/L and the ammonia nitrogen content was 120 mg/L.The COD degradation rate of strain R1 increased by 8% and the ammonia nitrogen degradation rate increased by16% compared with before the optimization.(4)The adaptability of strain R1 in different environments was studied.The effects of highly concentrated ammonia nitrogen and phenol solution on the growth of strain R1 were studied.The activity of superoxide dismutase(SOD)of strain R1 in different environments was determined.When the concentration of ammonia nitrogen and the concentration of phenol in the wastewater increased,the bacterial concentration of strain R1 decreased but the activity of SOD increased.When the ammonia nitrogen of the wastewater reached 800 mg/L,the strain R1 still had some adaptability.After degradation of 24 h,the concentration of bacteria was 1.69 g/L.Compared with the normal concentration of ammonia nitrogen,the concentration of the bacteria decreased by35%.The active activity of SOD was 653.5 U/ml,and the activity of SOD was increased by 33.78%.When the concentration of phenol in the wastewater reached 400 mg/L,the concentration of the bacteria reached 0.67 mg/L after the strain R1 degraded the wastewater for 24 h.Compared with the normal concentration of phenol,the concentration of the bacteria decreased by 81.35%,but the activity of SOD reached 692.7U/ml,and the activity of SOD was increased by 33.14%.Those results shows that Strain R1 could endure the phenol concentration of 400 mg/L and the ammonia nitrogen concentration of 800 mg/L.