Research On Microbial Remediation Of DDTs-PAHs In Co-Contaminated Farmland Soil

With the rapid development of social economic.the acceleration of urbanization process and the improper use of chemical pesticides have resulted in organic contaminated farmland soil.And the contaminated by organochlorine pesticides and polycyclic aromatic hydrocarbons have became the focus problem.In this study,dichlorodiphenyltrichloroethanes(DDTs)and polycyclic aromatic hydrocarbons(PAHs)co-contaminated farmland soil was investigated,Through screening and identifying the high efficient DDT-degradation bacteria,optimizing the degradation conditions.The field experiment was conducted to research on microbial remediation of DDTs-PAHs in co-contaminated farmland soil,and surfactant-enhanced microbial remediation measures.The microbial degradation mechanism of DDTs-PAHs,and the effect of remediation measures on soil microorganism were cleared.The main results were showed as follows:(1)With the method of enrichment culture using DDT as the sole carbon,a high efficient DDT-degrading strain named DC-1 was isolated from DDTs and PAHs co-contaminated farmland soil from the Shenyang North New Area of China(The degradation rate of 10 mg·L-1 DDT at 5 days was 78.5%).After the morphological,physiological and biochemical characteristics,and 16S rDNA sequence analysis,this strain was identified as Arthrobacter globiformis.The broad-spectrum analysis of substrates were showed that strain DC-1 had good broad-spectrum degradation.Besides the high efficiency degradation of DDT.DDE and DDD,and it also had good degradation effect of PAHs.Up to now,it was the first time to investigate A.globiformis as DDTs-PAHs degrading bacteria.The optimum growth and degradation conditions of strain DC-1 were determined:DDT concentration 10 mg·L-1]?temperature 30??pH 7.0?7.5?inoculation size 10%and peptone as carbon source.Under the action of strain DC-1,the DDT degradation rate within 24 hours was up to 84.7%.and the PAHs degradation rate within 168 hours was 32.9%.(2)Through field experiments,the degradation effect of DDTs with strain DC-1,N,PN-1 on the remediation of DDTs-PAHs in co-contaminated farmland soil was compared.Strain DC-1 treatment and mixed bacteria PN-1 treatment were confirmed as appropriate microbial remediation of DDTs-PAHs in co-contaminated farmland soil.After 150 days of incubation,the highest degradation rate of DDTs and PAHs with strain DC-1 in soil were up to 52.1%and 21.9%,which were 48.5%and 15.6%higher than the control treatment(CK);The degradation rate of DDE and high ring PAHs with strain DC-1 in soil were 61.5%and 17.3%,which were 57.3%and 12.5%higher than CK.The degradation rate of DDTs and PAHs by mixed bacteria PN-1 in soil were 43%and 23.7%,which were 39.4%and 17.4%higher compared with CK;The degradation rates of DDE and high ring PAHs by mixed bacteria PN-1 in soil were 44.2%and 18.1%,39.9%and 13.3%higher compared with CK.(3)The appropriate microbial remediation of DDTs-PAHs in co-contaminated farmland soil by surfactants was developed.When the concentration of RL was applied at 5 mg·kg-1 soil(RL-5),the degradation effect of DDTs and PAHs in soil was the best.The highest degradation rate was up to 64.3%and 35.6%,which were 12.2%and 13.8%higher than single strain DC-1 treatment;They are 36.9%and 19.8%higher than RL-5 treatment alone;And they are 60.7%and 29.3%higher than CK;The degradation rates of DDE and high ring PAHs in soil were 75.4%and 32.5%,which were 13.9%and 15.2%higher than single strain DC-1 treatment.The effect of SDBS-Tween 80 enhanced strain DC-1 and mixed bacteria PN-1 on biodegradation of DDTs and PAHs with 100 mg kg-1soil was relatively good:The highest degradation rates of DDTs in soil were 61.0%and 57.8%,and for DDE in soil were 73.1%and 63.0%;The highest degradation rates of DDTs in soil were 29.0%and 35.6%,and for high ring PAHs in soil were 25.0%and 30.6%.(4)Through plasmid extraction,plasmid elimination and competent cell transformation molecular biology experiments proved that the degrading function encoding gene of strain DC-1 was carried in the form of plasmid DNA.Through GC-MS analysis,the degradation products of DDT were identified as DDD,DDE,DDMU,DBP and PAA;The degradation products of benzo[a]pyrene were identified as phenanthrene and pyrene.The degradation pathways of DDT and benzo[a]pyrene were speculated.The enzyme activity experiment and MPN method showed that under RL-5 enhanced strain DC-1,soil catalase and invertase enzyme activity peak values were 7.1 mL·g-1·20 min-1 and 238.7 mg· g-1·day-1,respectively;The number of DDTs and PAHs degraders were up to 6.14 and 6.51 log10 CFUs·g-1 dry soil,respectively;And it was significantly higher than that of single RL-5 treatment and strain DC-1 treatment.The high throughput sequencing showed that compared with RL-5 treatment alone,the dominant degrading bacteria abundance of DDTs and PAHs,such as Arthrobacter sp.,Sireptomyces sp.,Sphingobacterium sp.,Chryseobacterium sp.and so on increased significantly.And they promoted biodegradation of DDTs and PAHs in soil.