GAC-sand dual media filters (GSFs) could be used as rapid filters in drinking water treatment.Particle counts and size distribution, heterotrophic bacteria (HPC) in the effluent and the disinfectioncharacteristics, trihalomethanes (THMs) and trihalomethane precursors were used to evaluate effluent safety.GSFs had stable removal efficiencies on particles during stable operations, and better removal efficiency couldbe got on larger particles. Extended subfluidization wash after the traditional backwash was an effectivemethod to improve removal efficiency on particles during filter ripening period, while no effect was found onHPC control. Bacteria could be removed by the filters, while there were chances for more bacteria existed inthe effluent than that of influent. There was little microbial risk in the effluent when judged by HPC afterdisinfection. GSFs could effectively remove THMs, while better removal efficiencies could be achieved onTHM precursors. There were chances for the desorption of previously adsorbed THMs when the concentrationin the influent was low, while the concentration in the effluent was much less than the maximum contaminantlevel in national standard. In sum, more attention should be paid to the bacteria in the effluent, especially whenthere were pathogens in the raw water and during filter ripening period.
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