ESTIMATING THE SAFETY OF WASTE-WATER RECLAMATION AND REUSE USING ENTERIC VIRUS MONITORING DATA

The reliability of wastewater reclamation and reuse to meet a given an nual risk of infection, considering the variability of enteric virus c oncentrations, has been investigated. Two concepts related to the reli ability and safety of wastewater reclamation and reuse are presented. The first is reliability, defined as the probability that the risk of infection from enteric viruses in reclaimed wastewater does not exceed an acceptable risk. The second is based on the expectation of the acc eptable annual risk in which the exposure to enteric viruses may be es timated stochastically by numerical simulation. To assess the potentia l risks associated with the use of reclaimed wastewater in various reu se applications, four exposure scenarios were tested: golf course irri gation, food crop irrigation, recreational impoundments, and groundwat er recharge. Past monitoring data on enteric virus concentrations in u nchlorinated secondary effluents in California were used. Because ente ric virus concentrations in unchlorinated secondary effluents were fou nd to vary over a wide range, characterizing their variability was fou nd to be extremely important. The reliability criterion of meeting the less than 10(-4) annual risk of infection (less than or equal to one infection per 10 000 population per year) at least 95% of the time was used to assess the safety of using reclaimed wastewater in the four d ifferent exposure scenarios. The methodologies used in this study shou ld be refined, based on a larger enteric virus database developed usin g standardized field and laboratory protocols.