Microbiological risk from non-potable reuse of greywater treated by anaerobic filters associated to vertical constructed wetlands

Abstract

The objective of this research was to evaluate the performance of a greywater treatment plant, composed of an upflow anaerobic filter followed by a vertical constructed wetland, and to assess the microbial risk resulting from the non-potable reuse of its effluent. The microbial risk posed by selected pathogens (rotavirus, Campylobacter spp. and Cryptosporidium spp.), through the ingestion of aerosols during toilet flushing or garden irrigation, was investigated using the QMRA approach. According to the Brazilian water reuse technical standards, the monitored greywater treatment plant was not able to consistently produce reclaimed water with satisfactory quality for reuse. Moreover, although the treatment plant produced an effluent that achieved the USEPA recommended level of 10-4pppy for the risk of infection posed by Campylobacter spp. and Cryptosporidium spp., the risk posed by rotavirus was above this threshold. The monitoring data and the QMRA outcomes showed that a post-treatment, including sand filtration and chlorination, was essential to produce reclaimed water presenting a risk of infection below 10-4 for all evaluated target pathogens. The QMRA was very useful to evaluate and compare different levels of treatment applied to greywater reuse, based on similar assumptions. It was also concluded that the use of E. coli does not appear to be appropriate to assess the risk of infection in greywater reuse systems.