Study On PCBs-degrading Enzyme Preparations And Remediation Of The PCBs Polluted Soil

Polychlorinated biphenyls (PCBs) are the most representative organic chemicals in persistent organic pollutants(POPs). PCBs are made up of a biphenyl nucleus with 1¹0 chlorine atoms. The properties of PCBs that made them valuable for industrial applications include thermal, chemical inertness, non-flammability and high dielectric. PCBs are non-biodegradable and lipophilic. PCBs have low-to-moderate toicity. Study on animals show conclusive evdience that PCBs are carcinogenic. In water, PCBs concern- trations are generally higher near human activity and near shorelines. PCBs attach strongly to soil and may remain there for several years. PCBs have become one of the important global environmental problems.With the rapid economic development these years, electrical and electronic waste(e-waste)has become the fastest growing stream among all the solid waste around the world. In China, the amounts of e-waste increases rapidly in recent years; these e-wastes can be sourced both domestically discarded products and imported waste. The demand for materials is on the increase with expanding economy. Recycling materials from e-waste is an effective way to obtain scarce industry raw materials. There are about 80% to 90 % of substances in e-waste are valuable and reusable. The demand for recycled materials and the potential economy benefit are promoting the development of disassembly industry of e-waste in littoral. provinces in China. E-waste contain high-concerntration of PCBs. There are many homelike small workshop engaged in appliances dismantling by methods of theory integration with practice, such as incineration, crash, acid extraction, direct discharge,etc. Solid wastes that remain after disassembling imported unusable electrical appliances constitute a serious pollution source of environment. It was concluded that it is imperative to study on ecological rehabilitation of PCBs polluted soils. These are national strategies.Therefore, in this paper PCBs were determined as target compounds, study on the efficient methods to treat PCBs polluted soil.Considering the serious and wide pollution, many countries poured a large sum lots of manpower, material and money to seek the control and eliminate methods. According to the principles of treatments, the treatment of PCBs can be summerized as physical, chemical and biologic technology. Though the microorganism only act on low concentration waste and the biodegradation rates depend on many environmental factors. But the in-situ bioremedation of contaminated soil is an environmentally sound, high-efficiency and economical way. Bioremediation used for the remediation of contaminated soil and sediments will be the subjects of future research. It is difficult that the indigenous microbes competed with the foreigener microbes after is was inoculated into the soil for the remediation of contaminated soil. Degradation of PCBs For thest reasons, it were selected the enzyme preparation from the microbe in this experiment.This paper consists of five parts: 1. Isolation and identification of PCBs-degrading bacterium. 2. The PCBs-degrading activity of the three strains and conditions of the enzyme's production. 3. enzymatic properties of the PCBs-degrading enzyme. 4. enzymatic degradation of Aroclor1260 mechanism. 5. In-situ remediation of the PCBs-polluted soils by the PCBs-degrading enzyme and the PCBs-degrading strains. The main results of the present study can be summized as followed:1. After enrichment culture and domestication, three strains capable of utilizing PCBs as sole carbon source for growth were screened for their high degradable abilities, and they were from the deep sea sediments of southern Yellow Sea and the soils long-term polluted by PCBs of a certain factory of Jilin. They were preliminarily identified according to their phylogenetic analysis and physiological and biochemical characteristics, strain B2.6 belonged to the Bacteria Proteobacteria Gammaproteobacteria Vibrionales Vibrionaceae,Vibrio,Vibrio splendidus, strain P1 belonged to the Bacteria Proteobacteria Betaproteobacteria Burkholderiales Alcaligenaceae Alcaligenes, strain P2 belonged to the genera Bacteria Proteobacteria Gammaproteobacteria Pseudomonadales Pseudomonaceae Pseudomonas Pseudomonas fluorescens.2. Through the degradation experiment, the optimal enzyme production conditions which are the optimal degradation conditions of odd and mixed strains were got. The condition of PCBs-degrading enzyme production of strain B2.6 were: the temperature increased above 20℃, the concentration of NaCl was 150 g·L^-1, PCBs was the carbon source for growth, the optimal nutrition source was 20 g·L^-1 beaf extract, pH value was between 7 and 9, the inoculation amount was 4 mL, the medium volume was below 100 ml per 250 ml flask, the PCBs concentration below 0.8 mg·L^-1, PCBs degradation could reach 80 % at 72 h, the highest ratio was 98.72 %. The condition of PCBs-degrading enzyme production of the mixed strains P1 and P2 were: the temperature increased above 20℃, PCBs was the carbon source for growth, the optimal nutrition source was 20 g·L^-1 protein peptone, pH value was between 6.5 and 7.5, the inoculation amount was 4 mL, the medium volume was below 100 ml per 250 ml flask, the PCBs concentration below 0.6 mg·L^-1, PCBs degradation could reach 75 % in 7 d, the highest ratio was 98.27 %. 3. Through the experiment of enzymatic degradation of Aroclor1260 mechanism, following phenomena were ovserved, reductive dechlorination of Aroclor1260 occurred in the experiment by the three strains. The extent od dechlorination were 87.97 % and 78.31 % respectively. The highly chlorinated PCB congeners were degradated into the lightly PCB congeners.4. Enzymatic properties of the three strains had been studied. The PCB- degrading enzyme of strain B2.6 was a kind of induction enzyme and intracellular enzymes. The PCBs-degrading enzyme formation was the model of continuous synthesis. The relative enzyme activity reached to the maximum at constant period (48h). The optimal pH value was 6 to 8, and the PCB- degrading enzyme woule be relativly stable. The univalent ions of main group, such as Na⁺ and K⁺ could enhance the activity of PCBs-degrading enzyme. The bivalent ions of main group such as Mg²⁺,Ca²⁺had little influence on the activity of PCBs-degrading enzyme, while the transitional metal ions, such as Co²⁺, Mn²⁺, Cu²⁺, Fe²⁺ and Fe³⁺ may inhibit it in a certain degree, even reduce 50 %. The activity was almost lost inder the presence of metallic ion was chelated by EDTA. The optimal temperature and concentration of NaCl for the PCBs-degrading enzyme were 25℃to 35℃and 50 mg·L^-1. The reaction rate increased linearly with with the increasint enzyme amounts. The results showed that the reaction rate is first order reaction with respect to the concentration of PCBs-degrading enzyme from the kinetics plot. Modified Michaelis-Menten equation was used as model to carry out the regression analysis with experimental data, kinetic equation of PCBs-degrading by PCBs-degrading enzyme and the important kinetic characteristic parameter had been determined. Vm was 0.6075 mg/L·min, Km was 1.48 mg·L^-1.The PCB-degrading enzyme of the mixed strains P1 and P2 was a kind of induction enzyme, including intracellular and extracellular enzymes. The PCBs-degrading enzyme formation was the model of Synchronization synthesis. The relative enzyme activity reached to the maximum at increasing period (30 h). The optimal pH value was 4 to 7, and the PCBs-degrading enzyme woule be relativly stable. The univalent ions of main group, such as Na⁺ and K⁺ had little influence on the activity of PCBs-degrading enzyme, The bivalent ions of main group such as Mg²⁺, Ca²⁺, the transitional metal ions such as Cu²⁺, Co²⁺ could enhance the activity of PCBs-degrading enzyme. While the transitional metal ions, such as Mn²⁺, Fe²⁺ and Fe³⁺ may inhibit it in a certain degree. The activity was almost lost inder the presence of metallic ion was chelated by EDTA. The optimal temperature and concentration of NaCl for the PCBs-degrading enzyme were 25℃to 35℃and 5 mg·L^-1. The results showed that the reaction rate are logarithmically related to the concentration of PCBs-degrading enzyme from the kinetics plot. The reaction rate and the concentration of PCBs are found to be approximately cubie polynomial relationship..5. The preliminary study on in-situ remediation of the PCBs-polluted soils under different concerntration of nutrition sources, soil moisture, soil tempreature and soil porosity contents were evaluated in this paper by the simulative experiments in laboratory. The concerntration of Aroclor1260 in the soil was 3.15μg·g^-1. It indicated that the concentration of the polluted soil decreased slightly which depend on degradation itself, the concentration was between 3.146μg·g^-1 and 3.149μg·g^-1 in 20 days. The degradation was 26.03 % at 20 d under the conditions of 60 % of field capacity, room temparature (below 10℃, minimum is 0℃), 0.5 g·kg^-1 beaf extract, undisturbed soil, the salt concerntration 0.2 g·kg^-1. When 1 g·kg^-1 beaf extract were added to PCBs polluted soils, the Aroclor1260 degradation was 42.94 % at 20 d. The Aroclor1260 degradation went up to 89.21 % at 20d under the soil temperature was30℃. The Aroclor1260 degradation decreased from 42.94 % to 19.45 % at 20 d. The degradation was 42.19 % at 20 d when the soil stirring was once per day. When 1 g·kg^-1 salt content were added to PCBs polluted soils, the Aroclor1260 degradation was 38.97 % at 20 d. Effect of treatment by PCBs-degrading enzyme was better than treatment by strain B2.6. The Aroclor1260 degradation reached to 41.95 % in the first day and did not increase in the following 20 days.Bioremediation of the polluted emvironment should be involved to degrading many fractory ogranic compounds and controlling environmental pollutants in China in the future, It is of great significiance and has promising wide market prospect. In the 21th century, bioremediation will become the most valuable and vital biological engineering technology in the field of ecological environmental protection with the development of microbal ecology, molecular genetic and other diciplines.