Alternative Technologies for Indirect Potable Reuse: A New Paradigm
- E. Vadiveloo, T. Fishbain, J. Page, P. Cooke, B. Stanford, D. Hernandez - Hazen and Sawyer
Rising wastewater effluent discharge standards have led to more advanced wastewater treatment while growing demand has taxed existing drinking water supplies, making planned indirect potable reuse a feasible scenario for more utilities. A majority of planned indirect potable reuse schemes currently in operation or planned to be employed in the U.S. make use of advanced oxidation processes (AOPs) and reverse osmosis (RO), the fully available treatment (FAT) technology, to ensure maximum removal of known and unknown contaminants. An indirect potable reuse pilot study in the Southeastern US is investigating the advanced treatment of wastewater for groundwater recharge to a brackish aquifer using ultrafiltration, ion exchange, ozone and ultraviolet light (UV) based AOPs, as well as biofiltration. Since this study is focusing on recharge options to a brackish receiving water body, these treatment processes are being examined as an alternative to the FAT approach of RO and UV AOP. However, in addition to low nutrient limits (Orthophosphate < 0.01 mg/l), the regulatory community is still concerned about the potential for trace organic contaminants (TOrCs) entering the environment and water supply. Therefore, multiple pilot plants are being operated to evaluate and validate the formation and removal of nitrosamines and the removal of other TOrCs by these processes.
Since Florida currently does not have TOrCs regulations, California’s Title 22 Groundwater Replenishment Reuse Draft Regulation which focuses on log removal for indicator compounds from nine functional groups, was used to determine the efficacy of the different treatment schemes.The City owns and operates a reclamation facility that uses an open ocean outfall to discharge secondary effluent. Recently enacted legislation requires the City to begin a process to eliminate its ocean outfall and to increase water reuse. Floridan Aquifer recharge has been identified as an option to meet the over 20 mgd of reuse required. Due to the relatively high total dissolved solids (TDS) levels of the Floridan Aquifer (around 3,000 ppm), any drinking water applications require RO membrane treatment to achieve potable water quality. This aspect of the aquifer allows the utilities that surround the Floridan Aquifer to consider indirect potable reuse schemes where RO membranes are not incorporated at the reuse facility, thereby deviating from the FAT approach. The pilot operated for over ten months and results demonstrated adequate TOrCs oxidation without the use of RO membranes.
The avoidance of RO membranes in the reclamation scheme could save the City upwards of $100 million (US) in capital expenses, in addition to the savings from operation and maintenance of a high pressure membrane system. This approach may also reduce the carbon footprint of the overall system. This paper and presentation will provide an overview of the project, data on TOrC removal, nitrosamine formation an orthophosphate removal through each process, and the presence/removal of regulated and unregulated contaminants.
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