Removal Of Perchlorate From Drinking Water In An Ion Exchange Membrane Bioreactor

A systematic study on removing perchlorate from drinking water in an ion exchange membrane bioreactor has been carried out. Three aspects are discussed, including influent ClO4- concentration, influent section width and hydraulic retention time. The optimal operating conditions and design parameters are gained by analyzing the changes of the indexes in the operating process. Scanning electron microscopy (SEM), polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and Cloning are used to analyse the succession of microbial community structure changes and the dominant bacteria of the species are determined by DNA sequencing.Studying the performance of the ion exchange membrane bioreactor by changing the influent ClO4- concentration when the hydraulic retention time is fixed. The results show that the effluent ClO4- concentration raises with the increase of influent ClO4- concentration, while the ClO4- removal rate decreased. When the influent ClO4-concentration is in the range of 29.30-104.24μg/L, the effluent ClO4- concentration is from 0.04μg/L to 19.00μg/L. The effluent ClO4- concentrations meet the U.S. Environmental Protection Agency standards required 18μg/L except the 49th day and the 51th day. With the increase of influent ClO4- concentration, the ClO4- flux shows an increasing trend. In the initial stages of the influent ClO4- concentration increase, the ClO4- concentration in the anaerobic bioreactor, the effluent Cl- concentration and the effluent conductivity increase suddenly. As the operating time increases, the ClO4-concentration in the sludge supernatant decreases and keeps below 10μg/L; the effluent Cl- concentration declines slowly and finally stabilizes at about 90mg/L; the effluent conductivity decreases gradually and finally stabilizes at about 279μs/cm.In the same operating conditions, the performance of the ion exchange membrane bioreactor is investigated by changing the influent section width. The results show that the effluent ClO4- concentration and ClO4- flux raise and the effluent Cl- concentration reduces when the influent section becomes more wider. The effluent conductivity is related to the dimension of water flowing chamber.The widder the influent section, the more obvious the effluent conductivity fluctuations. The ClO4-concentration in the sludge supernatant increases with the influent section becoming more wider. In the operating process, the anaerobic reactor has a temporary accumulation of perchlorate. And the accumulative perchlorate is reduced to less than 4μg/L after 2-8days.The impact on performance of the ion exchange membrane bioreactor is tested through changing the hydraulic retention time when the influent ClO4- concentration keeps in a certain value. The effluent ClO4- concentration, the ClO4- flux, the effluent Cl- concentration and the effluent conductivity have a upward trend with the decrease of HRT. In the initial stages of HRT shorten, the ClO4- concentration in the anaerobic bioreactor increases all of a sudden. With the augment of operating time, the ClO4-concentration in the sludge supernatant decreases or reaches a steady state, keeping below 2.0μg/L generally.The microbial community structures of the ion exchange membrane bioreactor are studyed at different influent ClO4- concentrations by SEM, PCR-DGGE and Cloning. The results show that a distinct change of the microorganism form takes place with the operating time increasing. During the entire operation, bacilli and cocci as the major species involved in the changing process. Comparative profile of DGGE bands and the phylogenetic tree show that during the operation the microbial diversity is well and complex changes have taken place in communities.α,β,γ,δ-Proteobacteria, Bacteroidia, Actinobacteria and Clostridia are the main bacteria in the system. And the dominant member in the reactor is Proteobacteria. Although the microbial community structure change largely, there are some strains such as Desulfovibrio alaskensis strain Jlac, Devosia sp. 1_C16₂7, Mesorhizobium temperatum strain SDW 018 and Delftia acidovorans isolate As3-4 maintain a superior position in the whole operation. They can be noted as the main strains of the perchlorate-reducing bacteria.