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Pathogen Removal by Secondary and Advanced Water Reclamation for Water Reuse
AuthorTeel, Lydia Rochelle
Civil and Environmental Engineering
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As water scarcity compels regions to implement more sustainable water reuse practices, alternative options such as potable water reuse have proven to provide many water management benefits. Most potable reuse treatment systems are based on membrane technologies that are energy intensive and produce brines whose disposal is a challenge in inland regions. Ozone-biological activated carbon (ozone-BAC) based advanced water treatment technologies are emerging as an appealing alternative; although, there is uncertainty regarding the reduction of waterborne pathogens. Common pathogen log reduction requirements have been modeled after California Department of Drinking Water’s 12-10-10 log reduction value (LRV) for enteric virus, Cryptosporidium and Giardia, respectively, based on raw wastewater to potable reuse finished water. The objective of this research is to investigate LRVs of pathogens that can be achieved in secondary biological treatment and ozone-BAC based treatment systems and to assess the applicability of employing drinking water pathogen guidelines for potable reuse applications. Pathogen LRVs through these processes are not fully established and understood; therefore, this research demonstrates pathogen and bacterial indicator removal and how process factors can affect treatment. A pilot-scale ozone-BAC based treatment train was operated at two water reclamation facilities in Reno, Nevada, USA over a two-year period. Virus, Cryptosporidium, Giardia and bacterial indicators were monitored across individual and combined treatment processes, while Cryptosporidium and Giardia were measured across secondary biological treatment at two full-scale water reclamation facilities. Pathogen removal/control barriers investigated at full scale and pilot scale include secondary biological treatment, coagulation/flocculation/clarification/granular media filtration, ozonation and ultraviolet disinfection. Literature and drinking water guidelines suggest the pathogen barriers are capable of meeting 12-10-10 LRV for virus, Giardia and Cryptosporidium. However, the low presence of specific pathogens in the wastewater prevented a comprehensive numerical demonstration of LRVs at each pathogen barrier. Monitoring criteria based on literature, including turbidity, specific ozone dose, ultraviolet transmittance, ultraviolet dose, and surrogate sampling was developed to demonstrate the efficacy of each pathogen barrier. Results from this study indicate that applying drinking water pathogen reduction guidelines for potable reuse applications in ozone-BAC based treatment systems is valid.