Research On Biostimulation And Bioaugmentation About Degradation Of Pesticide Adjuvant Contaminated In Soil/Groundwater

Pesticide and chemical pollution sites have the characteristics of high pollution degree,wide range,fast pollutant migration speed,complex and diverse types,etc.,which pose a serious threat to the ecological environment and human health,and have become an environmental problem that needs to be solved urgently.The study aimed at a pesticide adjuvant contaminated site in the Yangtze River Delta,and took typical pesticide adjuvant pollutants benzene,toluene and trichloroethylene(TCE)as the research objects to explore the means of biostimulation—that is,nitrogen sources,phosphorus sources and different carbon sources.The effect of dosing on the degradation effect of pollutants in soil and groundwater was determined,and the optimal biostimulant and proportion were determined.At the same time,on the basis of the development of high-efficiency bio-enhanced inoculants,combined with the optimal proportion of bio-stimulants,the bio-enhancing agent was discussed.The effect of means combined with biostimulation technology on composite polluted soil/groundwater,The main research results obtained are as follows:(1)Using emulsified vegetable oil,sodium acetate,ammonium sulfate,and dipotassium hydrogen phosphate as biostimulants in soil/groundwater media,the pollution conditions of benzene and toluene pollution,TCE pollution and the coexistence of three pollutants were discussed.And determined the best biostimulant and its ratio.The results showed that the addition of biostimulants significantly improved the degradation efficiency of pollutants in soil/groundwater within the 40-day experimental period,and all four biostimulants had significant effects on the degradation of pollutants in soil/groundwater.As far as carbon source biostimulants are concerned,the long-term biostimulation repair performance of emulsified vegetable oil is better than that of sodium acetate and requires less nitrogen source.The optimal dosage of biostimulant in 300 mg/kg benzene,300 mg/kg toluene and 100 mg/kg TCE compound polluted soil is 2000 mg/kg emulsified vegetable oil,200 mg/kg N and 20 mg/kg P,the mass ratio is vegetable oil:N:P=100:10:1,the degradation rates of the three pollutants are(76.87±1.07)%,(77.48±1.13)%,(61.55±5.17)%;300 mg/L benzene,300 mg/L toluene and 100 mg/L trichloroethylene compound polluted groundwater,the optimal dosage of biostimulant is 2000 mg/L emulsified vegetable oil,200 mg/L N and 20 mg/L P,mass The ratio was vegetable oil:N:P=100:10:1,and the degradation rates of the three pollutants were(92.66±2.26)%,(92.95±1.21)%,and(67.62±2.80)%,respectively.During the biostimulation process,the volatilization rate of benzene was faster and the residual amount was large.It is speculated that TCEs are mainly degraded by aerobic mechanisms,simultaneously the small amount of DCE and VC detected indicated the existence of the anaerobic reductive dehalogenation pathway in the degradation process of TCE under the action of biostimulation.(2)Three degrading bacterial groups Be,Te and T with benzene,toluene and TCE as the target pollutants were screened and domesticated from the soil of the contaminated site,and the Be and Te bacteria were mixed and domesticated to obtain the target pollutants with benzene and toluene.Biodegradation bacteria group B was obtained,and Be,Te and T bacteria groups were mixed and domesticated to obtain degrading bacteria groups B-T with benzene,toluene and TCE as target pollutants.The results showed that the Be and Te bacterial groups could achieve complete degradation of 1000 mg/L benzene and 1000 mg/L toluene respectively within 18 days,and the T bacteria group using sodium acetate and emulsified vegetable oil as codegradation substrates could achieve 400 mg within 21 days./L TCE is completely degraded,B bacteria can achieve complete degradation of 1000 mg/L benzene and toluene within 15 days,and B-T bacteria can achieve 1000 mg/L benzene,1000 mg/L toluene and 200 mg/L within 18 days.Complete degradation of LTCE.Combined with Cl-material balance calculation,it can be seen that more than 55% of TCE in the T bacteria group degradation experiment was degraded by biological action,while more than 75% of TCE in the B-T bacterial group degradation experiment was degraded by biological action.It shows that benzene and toluene are good co-degradation substrates for TCE degradation;(3)The 16 S rRNA gene sequencing results of the five bio-enhanced inoculants showed that,at the genus taxonomic level,differences in the types of pollutants would induce great changes in the bacterial community structure.The abundance of the dominant bacteria in the single pollutant-degrading bacteria group decreased significantly under the combined pollution condition.Compared with Be,Te,and T bacteria,the relative abundances of Leifsonia and Rhodococcus in B bacteria were significantly increased,while the relative abundances of Stenotrophomonas,Chryseobacterium,Bordetella,and norank_f__JG30-KF-CM45 in B-T bacteria were significantly increased,indicating that the above The genus played an important role in the co-degradation of benzene & toluene and the co-degradation of benzene,toluene and TCE,respectively;(4)Using B-T bacteria as the bio-enhanced bacterial agent,combined with the optimal dosage and dosage ratio of biostimulants,the effects of single and combined effects of benzene,toluene and TCE under compound pollution were explored in soil/groundwater media.The degradation efficiency of pollutants is different,and the optimal dosage of bio-enhanced bacterial agents in different media under the combined action is determined.The results showed that the 30-day soil/groundwater pollutant degradation rate of the bio-enhanced inoculants alone did not exceed 50%,which was much lower than that of the bio-stimulation group and the combined action group,indicating that the degradation efficiency of the bio-enhanced inoculants was in the environment lacking nutrients.It is obviously limited and difficult to use alone.Compared with the single action,the combined action of bioaugmentation and biostimulation has a higher degradation efficiency of pollutants and achieves better results in a shorter time.Under the optimal dosage and ratio of biostimulants within 30 days,the optimal dosage of bio-enhanced bacterial agents in the composite contaminated soil of 300 mg/kg benzene,300 mg/kg toluene and 100 mg/kg TCE was 1.5 ml/100 g dry soil,the degradation rates of pollutants were(92.74±0.53)%,(93.95±0.92)% and(86.92±2.07)% respectively;300 mg/L benzene,300 mg/L toluene and 100 mg/L TCE compound polluted groundwater When the dosage of bio-enhanced bacterial agent was 1ml/100 ml of groundwater,the degradation rates of pollutants were(94.57±0.40)%,(95.62±0.47)% and(90.17±0.48)%,respectively.In addition,based on the detection of the intermediate products formate and glyoxylic acid,it is speculated that a considerable part of benzene,toluene and TCE can be degraded by aerobic co-metabolism through hydrogen oxidation under the mediation of enzymes such as toluene dioxygenase(TDO).