Comparison of treatment trains for indirect potable reuse and use of quantitative microbial risk assessment (QMRA) to evaluate reliability of pathogen removal: Zoo Miami case study

Abstract

Wastewater and reclaimed water contain various microorganisms such as bacteria, viruses, and protozoa that can cause waterborne diseases in humans and animals. Zoos and animal conservation parks utilize reclaimed water for various purposes which may contain pathogens harmful to human and animal health. The goal of this study was to assess the treatment performance of two treatment trains for indirect potable reuse (IPR) and perform quantitative microbial risk assessment (QMRA) to evaluate the reliability of pathogen removal at a proposed advanced water treatment facility at the Zoo Miami. A review of advanced treatment and disinfection technologies relevant for reclaimed water production and pathogen removal was conducted as a part of this study. DPRisk was used to perform QMRA for four reference pathogens selected as model organisms for two IPR treatment trains (TT1 and TT2). Public health risk estimates for pathogens including Adenovirus, Cryptosporidium, Giardia, and enteric viruses indicated that the risk of infection was below the EPA's target daily threshold of 2.7 × 10−7 and annual risk threshold of 10−4 without failure analysis. With failure analysis, both treatment trains met the daily risk goals for each of the reference pathogens approximately 99 % of the time. Adenovirus demonstrated the highest probability of infection with a mean annual risk of infection for TT1 of 6.65 × 10−9 in the absence of failures but reached a maximum of 7.34 × 10−2 with failure analysis. TT2 resulted in higher risk estimates compared to TT1 with a mean annual risk of infection of 2.10 × 10−8 without failure and a maximum of 8.37 × 10−2 with failure analysis. The results of the failure analysis demonstrate the benefit of treatment redundancy in potable reuse system design and highlight the importance of online process monitoring to rapidly identify off-spec or treatment failure events to protect public health. With this information, stakeholders can better understand treatment requirements and microbiological risks to inform potable reuse planning, design, and risk management.