Reduction of chlorine disinfection by-product formation: comparisonbetween dual-media filtration, micro-filtration and biofiltration

摘要

In Puerto Rico, high levels of DBPs have been problematic over the years for thePuerto Rico Aqueduct and Sewer Authority (PRASA), especially during and aftersevere tropical storms and hurricanes. A Pilot Plant Study approach wasproposed as part of the Action Plan adopted by Compania de Aguas de PuertoRico (CAPR-Vivendi) and PRASA to reduce formation of DBP's as well asmaintain compliance with current and future filtered water turbidity requirementsin the Metropolitan San Juan Water System. The advanced treatment pilot plantlocated at the Sergio Cuevas Water Filtration Plant was designed to evaluatetreatment processes and techniques necessary for meeting multiple drinkingwater quality objectives. The study completed its 5 phases of investigation inSeptember 2001 which included comparison between conventional flocculationand ballasted flocculation (ACTIFLO?) before the sedimentation step (phases 1and 2) and the comparison between dual-media filtration, micro-filtration andinter-ozonation coupled with inter-ozonation (phases 3, 4 and 5). Theinformation obtained through the last three phases of the study clearly indicatedthat ozonation coupled with BAC filtration not only helps minimize THM and HAAformation potentials but also provides good control of effluent turbidity andmanganese levels. This combination (ballasted flocculation + biofiltration) offersa superior finished water quality in terms of minimal organic content and low DBPformation potentials. Its implementation would however require specialmonitoring of bromate formation as a result of ozonation. Ballasted flocculationcombined with microfiltration offers a great barrier against suspended solids.