Microbial Degradation Of1,4–dioxane

1,4-dioxane was used as solvents, wetting agents, dispersing agents, stabilizers of1,1,1-trichloroethane and other chlorinated solvents, and byproduct in the surfactantsproduction process. Because of the stability of structure and its extensive use, itcaused widespread concern. The main objective of this laboratory research was tocarry out the microbiological method to remove the target pollutant1,4-dioxane.Included in this study were investigating the biodegradability and effectivness of1,4-dioxane removal by different environmental microorganism. Through the study ofmicrobial metagenome and transcriptome, the reaction system was analyzed by thechange of the structure and function of microbial communities and the correlationwith the degradation of pollutants. All of that gived the theoretical basis for practicalapplication of microbial remediation technologies in the restoration field of1,4-dioxane-contaminated environments.The main contents and results of this studywere as follows:(1) The simulation experiment that removal of1,4-dioxane by the natural soilsample carried out about15weeks, but1,4-dioxane degradation was not observed.Then, changing the experimental conditions and metabolic substrates tetrahydrofuranadded for11weeks, the degradation has not yet observed in the experimentalconcentrations.(2) The activated sludge sample from the sewage treatment plant was capable ofreducing1,4-dioxane via cometabolic degradation in the presence of tetrahydrofuran(THF). Biodegradation of1,4-dioxane began when THF concentrations in batchexperiments became relatively low. After THF degraded to below the detection limit,1,4-dioxane was no longer degraded, however, continuously adding THF,1,4-dioxane can continue to be degraded and the initial concentration of90mg/L of1,4-dioxane can be reduced to below the detection limit.(3) The removal rate of1,4-dioxane increased with the increase of THFconcentration, however, the degradation rate of1,4-dioxane had little effect by THF concentration after THF concentration reached a certain value. When THFconcentration was10mg/L, the degradation rate of1,4-dioxane was2.17mg/L/day. With the increase of the concentration of THF,1,4-dioxane degradation rateincreased. But when THF concentration was60mg/L or more, the degradation rateof1,4-dioxane basically stabled at5.22mg/L/day.(4) The analysis of the structure and function of microbial community showedthat1,4-dioxane degradated resulted from the interaction of a variety of bacteria andmany enzymes.Throughout the whole reaction, the gene abundance ofoxidoreductases was the most and had a greatest change. Monooxygenase, such asammonia monooxygenase, tetrahydrofuran monooxygenase and methanemonooxygenase enzymes presented in the degradation process. The phylogenicanalysis of the changes in microbial communities indicated that the typical1,4-dioxane degradation bacteria such as Flavobacterium and Pseudomonas wereprevalently existent. The composition and the abundance of specific microbialcommunity and monooxygenase played an important role in1,4-dioxanebioremediation, and can be used as a symbol of1,4-dioxane degradation inenvironment.