Development of a water treatment process reducing chlorinous odor and infection risk assessment of the treated water

摘要

To better control chlorinous odor in tap water, we assessed the performance of the combination of oxidationrn(ozonation or advanced oxidation processes, AOP) and ion-exchange treatment. In this process, hydrophilic neutralrnfraction (a major DOM fraction) is converted to ionic species, and these ions and ammonium ion are effectivelyrnremoved during ion-exchange processes. We found that each treatment process (e.g., oxidation alone or ionrnexchange alone) was effective for the reduction of chlorinous odor to some extent, but the combination of AOPrn(ozone/vacuum ultraviolet treatment) at a high ozone dose and ion-exchange (both cation and anion) was mostrneffective. The chlorinous odor formation potential was reduced to approximately 30 TON from more than 100rnTON. Also, DOC and ammonium ion were effectively removed with this process. The effectiveness of this processrnwas also confirmed in continuous mode with plot-scale experiment. Furthermore, this process was also assessedrnform the viewpoint of microbial safety. The model water treatment process reducing chlorinous odor was supposedrnto consist of coagulation-sedimentation, rapid sand filtration, AOP, cation exchange, anion exchange and chlorinerndisinfection treatment. Since the C.jejuni is one of the major causes of waterborne disease in Japan, it was selectedrnas the target pathogen when conducting quantitative microbial risk assessment (QMRA) to estimate the infectiousrnrisk of the treated water. The over-all removal efficacies by six treatment steps were estimated to be the medianrnand mean values of 14.96 log10 and 13.25 log10, respectively. The mean value of the yearly infection risk wasrnestimated to be 1.59 × 10~(-10) infection/person/yr, which was far below the acceptable yearly risk of infection of 10~(−4)rninfection/person/yr. The sensitivity analysis shows that the AOP treatment was the critical control point among therntreatment steps. The pathogen completely inactivated by AOP treatment is extremely important to stably producernsafe drinking water.