Biodegradation Of Organochlorine Pesticides And Remediation Of Contaminated Sediments

Organochlorine Pesticides (OCPs) are typical persistent chlorinated pollutants, which are recalcitrant to degradation and highly toxic to living organisms, particularly when accumulated through food chains. Thus, developing novel techniques to remediate the sites contaminated with OCPs has been a continuous effort in environmental science and technology. Microbial remediation and activated carbon stabilization are the promising treatment techniques for OCPs pollution control.In this research, an Enterobacter sp. strain LY402, which was isolated previously to degrade polychlorinated biphenyls (PCBs), was explored to degrade 14 OCPs, includingα-HCH,β-HCH,γ-HCH,δ-HCH, HCB, p,p'-DDE, o,p'-DDT, p,p'-DDD, p,p'-DDT, aldrin, heptachlor, dieldrin,α-chlordane andβ-chlordane. Cyclodiene pesticide (dieldrin) and chlorinated benzene pesticide (DDTs) were chosen to evaluate the degrading versatility of the strain LY402. Moreover, retrievable activated carbon fiber felt (ACFF) was applied to extract dieldrin and DDTs from the simulated aqueous solutions and sediments, and then treated by the chemical method. The results are as below:(1) The aerobic degradation of the OCPs mixture in solutions by the resting LY402 cells was studied, which degraded 72.2% of the total OCPs at the initial concentration of 2.8 mg/L at 30℃within 7 d. The strain has strong degradation capacity for 12 OCPs, while not forβ-HCH andδ-HCH. The sequence of two kinds of OCPs degradation is heptachlor> aldrin>β-chlordane>α-chlordane>dieldrin for the hexachlorocyclopentadiene pesticides and p,p'-DDD >p,p'-DDE>HCB>p,p'-DDT>α-HCH>γ-HCH>o,p'-DDT for the chlorinated benzene and derivative pesticides. It was found that the pesticides consist of cyclodiene or benzene structures are more likely to be degraded than the ones consist of cyclohexane structures, which might be related with the structure of OCPs and toxic inhibition. Moreover, about 72, 61.3 and 46.7% of the total OCPs at the initial concentrations of 4.2, 7 and 14 mg/L were degraded within 8 d, respectively.(2) Aerobic degradation of dieldrin and DDTs by the strain LY402 was systematically studied. The best environmental factors for the biodegradation were 30℃-40℃and pH7. The effects of the concentrations of the pesticides on their biodegradation were investigated. About 94.8,83,40.4 and 34.5% of dieldrin were consumed within 7 d for the initial concentrations of 0.5,2,5 and 10 mg/L, respectively, and about 95.1,64.5,57.7 and 55.5% of p,p'-DDT were consumed within 5 d for 0.5,2,5 and 8 mg/L, respectively. Moreover,88, 57.3,39 and 13.3% of∑DDT were degraded within 10 d for 1,5,15 and 30 mg/L, respectively. High concentrations of DDTs pose negative effect on their biodegradation. The effects of additional nutrients on the biodegradation of dieldrin and DDTs were also studied. It was found that yeast extract and peptone could improve the biodegradation of these pesticides. Significant release of inorganic chloride was observed during the degradation of dieldrin. An unknown metabolite was detected by GC-ECD in the degradation of p,p'-DDT, but the metabolite could not be identified by GC-MS because of its low accumulation level.(3) ACFF effectively removed dieldrin from the aqueous phase. The optimal pH of the solution for dieldrin adsorption was determined to be around 6. The adsorption process obeyed the second-order kinetic model. Freundlich isotherm was better in describing the behavior of dieldrin adsorption onto ACFF.(4) ACFF also removed DDTs from three laboratory-spiked sediments. The ACFF-mediated desorption process of DDTs from the sediments included rapid and slow phases. At the end of 332 h of adsorption, the removal of∑DDT from 7-d aging HR, LR, QR sediments spiked with 8 mg/kg∑DDT were 41,28.9 and 6.7%, respectively. Lower removal of DDTs by ACFF occurred with longer aging time of the spiked sediments, higher hydrophobicity of contaminants, higher organic carbon contents in the sediments, and lower initial spiking concentrations. Moreover, the adsorption ability was enhanced by increasing the amount of ACFF, as well as by its sequential replacement.(5) The OCPs adsorbed onto ACFF were degraded by Fenton's reagent. After 1.5 h of the Fenton's reaction, the adsorbed dieldrin, p,p'-DDE, o,p'-DDT, p,p'-DDD and p,p'-DDT were significantly degraded, and the degradation percentages of the total OCPs was 60.6%. These results suggested that the Fenton method was expected to regenerate the ACFF.In conclusion, Enterobacter sp. LY402 has strong degradation capacity for OCPs. ACFF is the optimal adsorbent for extracting dieldrin and DDTs from the contaminated water and sediments, and the Fenton oxidation could effectively degrade the same OCPs adsorbed onto the ACFF, suggesting that the coupling method could potentially be applied for the remediation of OCPs-contaminated water and sediments.