Microbial elimination capacity of conventional water treatment for viruses, bacteria and protozoan (oo)cysts

Abstract

In the process of Quantitative Microbial Risk Analysis prescribed by the Dutch Drinking Water Decree quantitative information about the elimination capacity of water treatment is necessary. Site specific data can be collected by monitoring the removal of surrogates like bacteriophages, indicator bacteria and spores. Spores of sulfite-reducing clostridia may serve as surrogate for persistent protozoan (oo)cysts. But this is not possible for all locations or processes. Alternative strategies are pilot plant studies or literature reviewing. In the current paper the latter has been explored for conventional treatment. A standard method was developed to evaluate quantitative data from literature and applied to establish the Microbial Elimination Capacity (MEC) of conventional treatment and the individual processes, coagulation/floc-removal and rapid granular filtration. With these results QMRA can be performed for sites with no or debatable quantitative data on micro-organism removal by site specific processes. Further studies are necessary to develop a standard method to include the observed variation of MEC in the calculation of the uncertainty level of the infection risk level assessed in the QMRA-process.