Biological Treatment Of Perchlorate-contaminated Water

The discovery of perchlorate, ClO₄^-, in a large number of ground and surface water supplies, resulted in perchlorate being added to the U.S.EPA's candidate contaminant list of drinking water, is gaining increasing attention all over the world duo to its interference with the function of the thyroid gland as well as its potential health impact at low-dose exposure. Bioremediation is proved to be an attractive option for treating perchlorate-contaminated water because of its high efficiency and low expense and minimal impact on water quality, and it has been successfully used for removing high level of perchlorate in the field. Under the anaerobic surroundings, bacteria reduce the perchlorate to innocuous chloride iron with the degradation via the sequence: ClO₄^-→ ClO₃^-→ ClO₂^-→Cl^- + O₂. Transformation of perchlorate to chlorate, ClO₃^-, is the rate-limiting step with complete conversion to chloride. Perchlorate reducing microorganisms(PRMs) are ubiquitous in the natural environment, and apply to perchlorate remedation through enrichment.In our experiments, the potential of bioremedication to treat perchlorate-contaminated water was investigated. All enrichments and growth of mixed cultures were performed in anaerobic medium. Parameters affecting perchlorate removal were mensurated by batch experiments using the bottle-point method. Simultaneous removal of perchlorate was also conducted through domesticated sludge packed column. Results indicate:1 , The potential of mixed microorganisms to reduce perchlorate was increasinglyimproved, removing 50 mg/L perchlorate from primitively twelve days to 24 hours after domestication.2 , Acetate is found an effective electron donor and carbon source, while glucose andantiscorbutic vitamin(Vc) inhibit the growth of PRJVIs. Under the optimal conditions with domesticated sludge 1.0 g, acetate concentration 1.2 g/L, AAM 20%, pH 8.0, C/N ratio 20, T 40℃ and perchlorate was rapidly reduced to non-detectable levels within 24h.3 -. Nitrate and dissolved oxygen inhibit perchlorate reduction by obtaining electron prior to perchlorate, meanwhile, dissolved oxygen decreases active ability of enzymes (perchlorate reductase and chlorite dismutase ) to effect perchlorate reducing efficiency.4> Fe(0) can not reduce perchlorate alone. It is not a suitable energy source for PRMs and has no obvious effect on perchlorate bioreduction. Fe( II) inhibits perchlorate bioreduction due to the decrease of pH.5^ The complete conversion of perchlorate to chloride was demonstrated by a stoichiometric ratio 1.0. The intermediates were not found to accumulate in solution.6, Mixed culture packed-bed bioreactor can remove perchlorate from water effectively. Biomass generation was found after a period of time and perchlorate reduction efficiency was obviously accelerated. The minimal staying-time for reducing perchlorate completely with acetate 0.29 g/L were 6 h.