Enhanced In Situ Bioremediation Of Chlorophenols-Contaminated Groundwater

Chlorophenols (CPs) are made up of phenol with 1-5 chlorine atoms. There are 19 compounds according to different stations and amount of chlorine atoms on phenol. Chlorophenols are representative organic chemicals in persistent organic pollutants (POPs). Most of Chlorophenols have high toxicity, bioaccumulation, carcinogenic and transmissibility. The recent research showed that some kinds of CPs are endocrine disturbing chemical or potential endocrine disturbing chemical. If humans and organisms were exposed to low dose CPs chronically, their endocrine system would be disturbed.Chlorophenols brought many pollutions of groundwater as they were produced and used widely since 1930, as a result Chlorophenols became popular contaminations in groundwater. Because of the biorefractory charicristic, Chlorophenols existed in environment in a long time and the periods of degradation were long. Owing to the complexity, invisibility and difficulty to restore of the groundwater pollution, once the groundwater was polluted, the process of natural recovery and purification would take a long time. It was necessary to find an economical and efficient remediation method for it.The treatment of chlorophenols-contaminated groundwater abroad were mainly pump-and-treat technology and bimetallic catalytic reduction based on PRB. The cost of pump-and-treat technology was high, and the effect on the environment was great.Catalytic reduction technology could dechlorinate part of chlorophenols and the products were phenol and other chlorophenols with a few chlorines, but it was incapable of reach innocent treatment by the root.Therefore, Chlorophenols in the groundwater is taken as the target substance, and its economic and efficient remediation method is studied in this paper. The disciplinarians of transfer and conversion for chlorophenols in the media of aquifer were studied by series of experiments. The filtration, identification and characteristic of degradation of the microorganisms that could degrade chlorophenols effectively were researched in the condition of low temperature and oligotrophic. The electron acceptors were added and the microorganisms for degradation in advantage were injected to enhance in situ remediation of chlorophenols- contaminated groundwater. Then the consecutive reaction system of chemistry and biology was applied to enhance in situ remediation more effectively.Compared with the prevenient studies, the innovations of this work were:1. Four strains were screened which can degrade chlorophenols with high efficiency in low temperature, and they had good effect on bioremediation while they were applied to chlorophenols-contaminated by the method of injection. It offered a prior condition for in situ bioremediation for chlorophenols- contaminated groundwater.2. According to the biorefractory characteristic of chlorophenols , PRB the application of PRB reaction system for pretreatment of chlorophenols in groundwater was studied,so t chlorophenols were easier to be degraded by microorganisms. It was combined with microbe injecting and electron acceptor sending in order to shorten the cycle for remediation and reach thorough productions.The transfer and conversion of chlorophenols in underground environment have definite disciplinarian, while the biodegration of indigenous microorganisms and the absorption- desorption of the aquife rmedias to chlorophenols were the major factors that impacted the transfer and conversion.Batch experiments showed that the process of chlorophenols adsorption by the sandy aquifer material was fitted to Freundlich adsorption isotherm and the second-order kinetics. The ability of adsorption reduced along with the increase of the the degree of chlorination.The adsorption constant Kd of 2,4-DCP, 2,4,6-TCP and PCP in sandy material was 5.659, 2.507 and 2.104 respectively. The ionic strength and pH value affect the adsorption of chlorophenols on the sandy soil obviously, and the adsorbance increase along with the increase of ionic strength and the decrease of ph value. The mechanisms of the adsorption of CPs onto sandy aquifer material can be summarized as the corporate effect of hydrophobic separation, ligand exchange and electrostatic interaction. The experiment of natural decay showed that the velocity of natural decay for the indigenous microorganisms to degrade chlorophenols in groundwater was slow. The rate constant of the biodegradation of 2,4-DCP, 2,4,6-TCP and PCP were 0.0065 d-1, 0.0054 d-1 and 0.0038d-1 respectively, and the half life were 106.6d, 128.4d and 182.4d respectively. The simulated experiment of the transfer of chlorophenols in groundwater showed that the migration rate on transverse direction of 2,4-DCP, 2,4,6-TCP and PCP were 2.57, 2.25 and 1.60 respectively and the effects of indigenous microorganisms on the degradation of chlorophenols were weak.Four strains were screened from activated sludge of sewage disposal plant in Jilin chemical factory and pollution discharge port of pesticide factory in Jilin City which can take chlorophenols as the sole carbon source in low temperature. They were identified to be the Pseudomonas sp. and Microbacterium oxydans. According to the physiological and biochemical characteristics, identification system of bacteria Biolog and the analyses of homology by 16s rDNA. Characteristics of CPs-degrading bacterium show that under the optimum conditions the removal efficiency for 2,4-DCP and 2,4,6-TCP were above 90%, this was higher than that of PCP, and removal efficiency of b2 and j3 were better than h and z, and the mixed strains degradation rate were higher than single strain. The degradation of three kinds of chlorophenols by microorganism b2 accorded to first-order dynamics, and the degradation of three kinds of chlorophenols by microorganism J3 accords to secondary dynamics.Column simulation experiment showed that the rate of natural attenuation was very slow especially for PCP, added electron acceptor such as Fe3+, K2SO4 and NaNO3 could stimulate the indigenous microbe to degrade chlorophenols to a certain extent. The rate of degradation for 2,4 -DCP ,2,4,6 - TCP and PCP reached 23%, 16.5 % and 13% respectively after 29 days while the half lives were reduced by 31.3 d, 20.1 d and 46.5 d respectively. The treatment effect of the injection of Bacteria High-Effectively Degrading chlorophenols in low temperature were better than that of addition of electron acceptor,and the rate of degradation for 2,4 -DCP ,2,4,6 - TCP and PCP reached 37.2 %, 28.8 % and 27.9 %respectively after 29 days while the half lives were reduced by 34 d, 64.2 d and 81.7 d respectively comparing with the addition of electron acceptor. The rate of degradation for 2, 4 -DCP, 2,4,6 - TCP and PCP were 83.9 % , 67 % and 51.6 % respectively after 29 days when the electron acceptors and microorganisms high-effectively degrading chlorophenols were both injected ,and the half lives were 11.5 d, 15.6 d and 24.7 d respectively while they were reduced by 29.8 d, 38.5 d and 29.5 d respectively comparing with the injection of microorganisms high-effectively degrading chlorophenols. The biomass in groundwater in this condition was in the same order of magnitude as the biomass in the condition that microorganisms high-effectively degrading chlorophenols were injected solely, but it was over one order of magnitude than the biomass when the electron acceptors were added solely. Above results proved that the microorganisms high-effectively degrading chlorophenols which were screened were adapted to the change of conditions after they were injected into groundwater and they accelerated the degradation of chlorophenols in groundwater.The seepage tank was used in the lab to simulate the pollution of groundwater, the combination of PRB filling with Fe0 as the active media and injecting microbe were adopted to remediate the contaminated groundwater. The results showed that The results showed that the concentration of chlorophenols became lower obviously after PRB reacting region and the products were lower chloric, so the groundwater was easier treatmented by the microorganisms. The microbial biomass of the injection well where microorganisms high-effectively degrading chlorophenols and electron acceptors were in injected and other three sample connections in down stream increased obviously. The rate of removal of chlorophenols presented the trend of increase and the rate of removal reached 93.5 %, 89.3 % and 87.6 % respectively. It proved that the microorganisms injected into groundwater had definite capability of transfer, and they could keep definite advantage in the competition to aborigines microbial while they had superior activities for degradation.The technology on bioremediation of environmental pollution had wide prospect in application and development.Although the technology on bioremediation in internal locale wasn't mature enough, it would became the engineering technique which most had capability in the region of ecological environment protection as the studies were specialised continually and the subjects such as microecology, molecular genetics were combined effectively.