QMRA-based reliability analysis to assess the performance of an ultrafiltration plant

In the drinking water treatment industry, it is becoming increasingly important to evaluate the reliability of different water treatment processes. This paper extends the use of quantitative microbial risk assessment (QMRA) as part of a reliability analysis, to assess the capacity of alternative water treatment technologies to minimize risk of microbial infection. The approach is demonstrated, in the Canadian context, for an ultrafiltration (UF) technology used for the removal of the protozoon Cryptosporidium spp., for which the removal is quantified using real operational data. The performance of the UF facility is compared with that of reference conventional trains, for which the removal performance is reported in the literature. The UF physicochemical process appears to reliably provide water with lower levels of Cryptosporidium spp. than the conventional trains. However, many issues such as the time scale at which the removals are measured and the methods used to establish the removal for different technologies impose moderation on the strength of this conclusion.