The Study On Biological Reduction Of Perchlorate By Combined Process Of Sulfur Autotrophic And Complex Three-dimensional Electrode Biofilm

High stability and mobility of perchlorate as a toxic pollutant results in theimpossibility of perchlorate removal from contaminated water through the regularwater treatment. Perchlorate has been widely used in rocket fuels, propellants,explosives, and some consumer products. Perchlorate can disrupt thyroid function byinterfering with iodine uptake. To date, Biological reduction and ion exchange （IX）are the most cost-effective technologies for treatment of ClO₄^-contaminated water.This study encultures firstly the sulfur-oxidizing, perchlorate-reducingenrichment culture, then investigates respectively the feasibility of sulfur autotrophicpacked-bed bioreactor and combined process of sulfur autotrophic and complexthree-dimensional electrode biofilm and put emphsis on effect of variable influentClO₄^-concentration and empty bed contact time （EBCT） on perchlorate removal bythe discussed techniques. With the analysis of the changer of biological and chemicalparameters during the period of operation, the optimal operating conditions anddesign parameters are obtained.The function of ClO3-and ClO2-accumulation doesn’t work and ClO₄^-cancompletely be reduced to Cl-in stoichiometry1:1during the sulfur-oxidizing,perchlorate-reducing enrichment culture. However, disproportionation of S0is thecause of the excess of SO₄^2-when the biological reduction of ClO₄^-happens. Throughbatch experiments, kinetic parameters qmaxand K of the monod equation is obtained.For perchlorate, the qpmaxand Kpwere0.43mg-perchlorate mg-DW^-1day^-1and6.63mg L^-1. In order to understand and assess the high competing ability of chlorate forperchlorate reduction, the kinetic parameters for chlorate in the the mixedsulfur-oxidizing autotrophic bacteria was determined. For chlorate, the qcmaxand K_c were0.41mg-chlorate mg-DW-1day-1and1.70mg L-1. Kc is lower obviously than Kp, so ClO3-has a preference over ClO4-in the process of reduction. When ClO3-remains, biological reduction of ClO4-is inhibited. The enrichment culture comprises of bacillus by SEM after83d.When EBCT is constant, performance of element sulfur autotrophic packed-bed bioreactor is discussed by the variable influent concentration of ClO4-. The data shows that within the range of influent concentration of ClO4-from60μg·L-1to200μg·L-1, the effluent concentration of ClO4-reaches the recommend regulation of18μg·L-1from US EPA after transition. This indicates that the bioreactor could tolerate the shock loading rate. When influent concentration of ClO4-is constant, performance of element sulfur autotrophic packed-bed bioreactor is discussed by the variable influent EBCT. The data shows that within the range of influent EBCT from18h to6h, the effluent concentration of ClO4-reaches the recommend regulation of18μg·L-1after transition. The change of pH caused by variable influent concentration of ClO4-and EBCT is helpful to the growth of microorganism and reaches the quality of drinking water. Besides, low ORP and DO also advance the biological reduction of ClO4-.When influent concentration of ClO4-is constant, performance of combined process of sulfur autotrophic and complex three-dimensional electrode biofilm is discussed by the variable influent EBCT. The data shows that within the range of influent EBCT from8h to4h, the effluent concentration of ClO4-reaches the recommend regulation of18μg·L-1after transition. Based on the electrochemical hydrogen and sulfur autotrophic packed-bed bioreactor, combined process of sulfur autotrophic and complex three-dimensional electrode biofilm is put forward. Influent concentration1mg·L-1of perchlorate is removed by cooperation of hydrogen and sulfur autotrophic microorganism. The removal efficiency is higher and the production of SO42-is lower than the regulated concentration of drinking water. The change of pH caused by variable influent concentration of ClO4-and EBCT is helpful to the growth of microorganism and reaches the quality of drinking water. Besides, low ORP and DO also advance the biological reduction of ClO4-.