Adsorption And Degradation Of Bensulfuron-methyl In Soil By The Charcoal Enriched With Consortia Of Degradation Bacteria

The application of immobilized microorganism technology has become the hotspot that more and more scholars are studying in. It shows the broad prospects for development, while it is widely used in industry, agriculture, medicine, environment protection and energy exploration etc. On the foundation of our country soil environment background, the adsorption and degradation of bensulfuron-methyl in soil by immobilized microorganism on charcoal is studied, the aim of which is to develop a new approach to enhance the degradation of organic contamination. The main items as following:1. Aerobic domestication of the sludge from the pesticide factory disposal plant is carried on, from which two strains are isolated growth on bensulfuron-methyl as carbon and nitrogen source. Two bacteria are screened by using streak plate, marked as red and yellow strain. The physiological and biochemical of the two strains are identified. Furthermore, phylogenetic tree of two strains is established. Combined with physiological and biochemical characteristics of strains, red strain is initially identified as Serratia sp. Yellow strain is identified as Bacillus aerogenes, both of them belong to Gammaproteobacteria.2. The study of the two strains on degradation characteristic of bensulfuron-methyl indicate that 2 strains have the highly effective degradation ability, the rate of which can in 2 days achieve above 20%, in 7 days can achieve about 60%. Degradation ability of bensulfuron-methyl by red strain is higher than by yellow strain, which can achieve 54% in 72 hours. The most suitable growth condition of the strain show that it is suitable for acid environment and optimum value of pH is about 6.0. In the acidic highly condition, bensulfuron-methyl hydrolysis is quick, and microbial degradation can not play a major role. However, in the alkaline environment, growth of the strain is restrained and bensulfuron-methyl is also difficult to hydrolyze.3. Adsorption-desorption of bensulfuron methyl on two types of soils treated with charcoal different in particle size were studied using the batch equilibration technique, which focus on the effect of charcoal amendment on adsorption-desorption of bensulfuron methyl in soils. The results show that the adsorption-desorption isotherms of bensulfuron-methyl in charcoal and soils fitted the Freundlich equation (r>0.93). Charcoal showed a great adsorption capacity for bensulfuron-methyl, and the smaller the particle size of charcoal, the higher the adsorption of bensulfuron-methyl. The amendment of charcoal improved adsorption of bensulfuron-methyl in the soils. The adsorption of bensulfuron-methyl in the soils increased with the increasing rate of charcoal amended. Desorption of bensulfuron methyl from charcoals and the soils displayed significant hysteresis, which was shown by the higher adsorption slope (1/nads) compared to the desorption slope (1/ndes). The hysteresis was closely related with the initial concentration of bensulfuron-methyl and the content of charcoal in the soils, and the hysteresis index (H) increased with the increasing rate of charcoal amended. This research suggests that charcoal can be used as artificially added adsorbent to efficiently control the pesticide in the soil from leaching.4. By laboratory incubation experiment, the degradation of bensulfuron-methyl in soil was studied. The degradation of bensulfuron-methyl was conducted with initial concentrations of 20 mg/kg in soils by red strain and immobilized red strain, 28 days later, when adding immobilized microorganism, free microorganism into paddy soil, the residual concentration of bensulfuron-methyl is 6.30 mg/kg, 7.95 mg/kg separately. The residual concentration of bensulfuron-methyl in sterilized and non-sterilized natural soil is 11.04 mg/kg, 10.54 mg/kg separately. When adding immobilized microorganism, free microorganism into yellow-brown soil, the residual concentration of bensulfuron-methyl is 8.13mg/kg, 8.96 mg/kg separately. The residual concentration of bensulfuron-methyl in sterile and non- sterilized natural soil is 11.13 mg/kg, 11.03 mg/kg separately. It shows that the degradation rate of bensulfuron-methyl can be enhanced by adding immobilized microorganism in soil. The effect of degradation of bensulfuron-methyl by immobilized microorganism is better than by free microorganism.Bensulfuron-methyl degradation in soils can be described by first-order kinetic equation. The research shows that adding immobilized microorganism into soil can decrease the half-time of bensulfuron-methyl in soils. The half-life of bensulfuron-methyl in non-sterilized paddy soil is 59 days. By adding free microorganism, the half-life (t1/2) of bensulfuron-methyl is 37 days. By adding immobilized microorganism, the half-life (t1/2) of bensulfuron-methyl is 26 days. The half-life of bensulfuron-methyl in non-sterilized yellow brown soil is 53 days. By adding free microorganism, the half-life (t1/2) of bensulfuron-methyl is 42 days. By adding immobilized microorganism, the half-life (t1/2) of bensulfuron-methyl decreased to 29 days.