Study On Silkworm Excrement Immobilized Degrading Microorganism Preparation In Diuron Residue Bioremediation

Diuron is a moderetely toxic and broad-spectrum phenylurea herbicide which is easy to be adsorbed on organic matter.Given the accumulation of diuron in the environment and its potential hazards,there is an urgent need to degradate the residual in environment safety and non-target animals.This study developed an environmentally friendly microbial preparation of Arthrobacter globiformis D47 assisted with silkworm excrement,to enhance the availability of diuron efficiently degrading bacteria and promote the bioremediation of diuron residue.The field application conditions were studied to provide a theoretical basis for the industrialization and practical application of degrading bacterial preparations.The main results of this study were list as following:1.Defining the substrate specificity of A.globiformis D47.The High Performance Liquid Chromatography(HPLC)conditions of 17 pesticedes were confirmed.Inoculating with 1%bacterial solution in LB Media,the degradation rates of diuron,linuron,chlorotoluron and isoproturon with initial concentration of 10 mg/L were 100.0%at 25?for 6 d;the degradation dates of Initial concentration of diuron between 0.5-20 mg/L reached 100.0%after 4 d.the strains D47 has degradative effect on Mesotrione,carbofuran,tricyclazole,beta-cypermethrin and deltamethrin with the initial concentration of 9.7,4.3,18.2,19.8,20.3mg/L,the degradation rates were 100.0%,98.0%,42.2%,50.4%,61.1%respectively.The strain has a wide degradation spectrum,which lays a foundation for soil pesticide residue degradation.2.Diuron was bound with silkworm excrement by sorption progress,It indicates that the adsorption mechanism of silkworm excrement to diuron is caused by surface adsorption and internal electron transfer or electronic sharing which was well fitted in pseudo kinetics.The adsorption of diuron on silkworm excrement was a non-monolayer comprehensive adsorption by using the Langmuir and the Freundich models.3.With immobilized microorganism technique,the immobilization degradation ability of silkworm excrement-degrading bacteria preparation was tested.The concentration of the strain D47 was 2.2x10~9 CFU in the carrier.Inoculating with 1%bacterial solution,the degradation rate reached 100.0%of the preparation for 6 d with 10 mg/L.the degradation rates were 91.4%?95.5%?92.3%?93.6%after 14 d resbectively with initial concentration of 1?5?10?20 mg/L.The preparation of silkworm excrement-degrading bacteria can effectively degradate diuron.4.The effects of pH,soil moisture content,formulation dosage,and different soil types on the degradation rate of the formulations were studied.When the pH value is between 7~8,water content is 50%,and dosage of the preparation is 5%,the effect of preparation on the residual degradation of diuron in soil is optimal,which provides the technical basis for field experiment.5.This study also confirmed the effects of microbial preparations on degrading diuron in farming field.In the Paddy field,100 g/667m~2,150 g/667 m~2,300 g/667 m~2 of 80%diuron wettable powder was applied,the degradation rates were 89.7%,96.9%,and 92.9%,respectively.there was no significant difference of the three doses with the silkworm excrement-degrading bacteria preparation.When the dosage of the preparation was 40,80,160 kg/667m2 with 150 g/667m~2 of 80%diuron WP,the final residue concentrations decreaced 3.6?4.3 and 4.3 mg/kg,respectively.The application of 80 kg/667 m~2 preparation to sugar cane field resulted in 97.5%after 40 days.The silkworm excrement-degrading bacteria preparation showed outstanding bioremediation of diuron in different medium such as normal saline and soil by the combination of silkworm excrement sorption and biodegradation.Under the combined action of the absorption of diuron from silkworm excrement and the biodegradation of D47,degrading bacteria preparations based on silkworm sand can efficiently degrade diuron in different media(solution and soil).The preparation with Silkworm excrement as carrier has potential applications for industrialized remediation of pesticide residues in soil after further optimization.