Degradation Of Atrazine And 2, 4-D By Nanoscale Fe₃O₄ And Microorganism Integrated Treatment System

Atrazine and 2,4-Dichlorophenoxyacetic acid (2,4-D) are most commonly used organochlorine pesticides, which are of strong toxicity and difficult to biodegraded. Degradation of atrazine and 2,4-D by a combination of nanoscale Fe₃O₄ and microorganism were stuided. The Fe₃O₄ would eliminate the toxicity by reductively transform the electron-withdrawing chlorine groups to chlorine ion. Then the bacteria was employed combination with the nanoscale Fe₃O₄ to degrade atrazine and 2,4-D. The combination mechanism was revealed by analysis the relationship between bacteria and nanoscale Fe₃O₄. The experiment results will provide the theory for remediation of pesticide pollution in farmland as well as provide a new method for fast degradation of residual in soil. The main research contents and results were as follows:1. A bacterium was isolated from activated sludge by enrichment using atrazine as sole source of carbon and nitrogen, which was identified as Ochrobactrum sp. The bacteria could degrade atrazine and 2,4-D efficiently by microbial co-metabolism. The atrazine and 2,4-D provided carbon and nitrogen sources for promoting microbial growth. The degradation rates of atrazine and 2,4-D were 31.8% and 64.2% respectively in 7 days.2. Reductive degradation of atrazine and 2,4-D by nanoscale with microscale Fe₃O₄ were studied. The results indicated that the 34.4% atrazine and 37.3% 2,4-D would be degraded by nanoscale Fe₃O₄ in 7 days, and 25.6% atrazine and 28.6% 2,4-D by the micro-scale Fe₃O₄, respectively. The removal efficiency by Fe₃O₄ nanoparticles was prior to Fe₃O₄ microparticles. Nanoparticles had the large surface, which could increase the expose to atrazine and 2,4-D which would enhance the reductive degradation of atrazine and 2,4-D.3. The degradation of atrazine and 2,4-D by a combination nanoscale Fe₃O₄ with microorganism were studied, and the factors influenced degradation rate were investigated by the batch experiments. The results showed that degradation rates of atrazine and 2,4-D with a combination of nanoscale Fe₃O₄ and microorganism were much higher than that separate nanoscale Fe₃O₄ or microorganism. There were significant synergistic effects between nanoscale Fe₃O₄ and microorganism for the degradation of atrazine and 2,4-D. The degradation rates of atrazine and 2,4-D increased with increases the initial concentration of atrazine and 2,4-D from 0 to 10 mg·L^-1, and increases the dosage of nanoscale Fe₃O₄ from 0 to 200 mg·L^-1, as well as increases the microbial inoculation amount from 0 to 12 mg·L^-1. The optimum reaction conditions for the removal of atrazine and 2,4-D were as follows: the solution pH at 3.0, the initial concentration of atrazine and 2,4-D with 10 mg·L^-1, the inoculation amount 12 mg·L^-1 of microorganism, and the dosage 200 mg·L-1 of nanoscale Fe₃O₄. The residual rates of atrazine and 2,4-D were reduced to 54.0% and 35.7% after 7 days. As a result, a combination of nanoscale Fe₃O₄ and microorganism could accelerate the dechlorination of atrazine and 2,4-D compared to the individual use.4. The combination mechanism between nanoscale Fe₃O₄ and microorganisms could be described as follows: the Fe₃O₄ nanoparticles could stimulate the growth of microorganisms, and intermediates of reductive dechlorination by Fe₃O₄ would be further degradation by microorganisms. The results showed that the growth OD₆₀₀ value of microorganisms was 3.69 in a combination of nanoscale Fe₃O₄ and microorganism, and 3.01 in a single system. The presence of naoscale Fe₃O₄ was obviousely beneficial to the growth of degrading bacteria. The 40.2% of 2,4-D and 48.35% of 2,4-DCP would be degraded by nanoscale Fe₃O₄ in 5 days, accordingly, the growth OD₆₀₀ value of microorganisms were 3.40 and 3.55 respectively. The intermediate of 2,4-DCP was more apt to degradation than 2,4-D.5. The degradation of atrazine and 2,4-D in soils by combined nanoscale Fe₃O₄ with microorganisms were studied. The results showed that atrazine and 2,4-D degradation in soils could be described by first-order kinetic equation. The degradation rates varied with different soils. The half-lives (t1/2) of atrazine were 50.6 d, 157.5 d and 173.3 d in red soil, alfisol and vertisol, respectively. When adding nanoscale Fe₃O₄ and the microorganism, the half-lives were 27.0 d, 60.8 d and 50.6 d, respectively. The half-lives (t1/2) of 2,4-D were 48.8 d, 73.7 d, and 108.3 d in red soil, alfisol and vertisol, respectively. When adding nanoscale Fe₃O₄ and the microorganism, the half-lives were 34.3 d, 31.6 d, and 39.6 d, respectively. The results suggested that the combination of nanoscale Fe₃O₄ and microorganism could accelerate the degradation of atrazine and 2,4-D in soils, which might be a effective method for the cleanup of organochlorine pesticide residues.