Biodegradation Of Polychlorinated Organic Compounds In Natural Sediments

p,p'-DDT and Diuron are two typical chlorinated organic compounds in the environment. They are listed as Persistent Toxic Substance by US EPA due to their toxicological and ecotoxicological impact on the humans and biota.Their environmental transformation and fates are of great concern because their significant toxic effect to the health of human beings. In the current study,the biodegradation of p,p'-DDT and Diuron in sediments was investigated under natural conditions.Their biodegradation kinetics was also studied.The main conclusions were as followed:(1) During the Anaerobic-aerobic incubation,the effect of small molecular acid on the biodegradation of p,p'-DDT in two sediments of different carbon contents(f_oc=3.25%and f_oc=0.41%) was investigated.During anaerobic incubation,K_a=-0.0621week^-1;during the aerobic incubation,K_a-a=-0.0621week^-1.The results showed that comparing to the anaerobic incubation,the anaerobic-aerobic incubation enhance the biodegradation of p,p'-DDT. During the aerobic incubation,the biodegradation efficiency of p,p'-DDT increased by 5% in the sediment with low organic matter content where the biodegradation efficiency increased only by 1%in the sediments with high organic matter content.The sediments with low organic matter content can enhance the biodegradation of p,p'-DDT in both the anaerobic incubation and the anaerobic-aerobic incubation.(2) During the anaerobic incubation,the citric acid inhibited the biodegradation of p,p'-DDT at first and then enhanced the biodegradation of p,p'-DDT.After 17 weeks of the anaerobic-aerobic incubation added with citric acid,the degredation rate were 84.7%and 59%respectively in two sediments with low and high organic matter contents.Oxalic acid inhibited the biodegradation of p,p'-DDT in sediments in both the anaerobic incubation and the anaerobic-aerobic incubation.(3) The effect of the black carbon contents(0%,0.1%,0.2%,0.5%,1%) in the sediments on the biodegradation of Diuron in the presence of Pb was studied.The results showed that the biodegradation rate of Diuron decreased as the black carbon contents increased in BC400 and BC500.(4) Metal ion enhanced the biotransformation rate of Diuron when the black carbon content is 5%in the current experiment.The biodegradation half-live increased by 20.5 d when the content of BC500 is 1.0%.The results showed the black carbon could inhibit the biodegradation of Diuron with more micropore structures and larger specific surface area. The absorption of Diuron in the micropores of soil and black carbon could make it unavailable for biodegradation thus slowed the biodegradation rate.(5) The effect of Fe⁰,β-cyclodextrin and HA on the bio-remediation of p,p'-DDT was investigated.The degradation of p,p'-DDT in the "Fe⁰+microorganisms" systems are mainly anaerobic.The adding of Fe⁰ enhanced the degradation of p,p'-DDT.The adding ofβ-cyclodextrin inhibited the biodegradation of p,p'-DDT and the degradation rate decreased as the contents ofβ-cyclodextrin increased.The reason for this decrease of degradation rate was that p,p'-DDT could easily format macromolecular complex withβ-cyclodextrin which made p,p'-DDT bio-unavailable.The adding of HA inhibited the degradation of p,p'-DDT. Compared with the adding amount of 0.5 g/kg,the degradation rate of p,p'-DDT decreased by 8.2%when the HA content is 2.5 g/kg.