Piloting Alternative Technologies for Indirect Potable Reuse in Florida
- Tara Fishbain, Ben Stanford, Enrique Vadiveloo, Phil Cooke - Hazen and Sawyer
As growing demand taxes existing drinking water supplies and rising wastewater effluent standards lead to more advanced wastewater treatment, planned indirect potable reuse is becoming a feasible scenario for more utilities. A majority of planned 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 full advanced treatment (FAT) technology, to ensure maximum removal of known and unknown contaminants.
In southeast Florida, specifically, recent legislation will require many utilities to begin elimination of their ocean outfalls and to institute an increase in water reuse. As a result, the City of Hollywood, FL, is performing an indirect potable reuse pilot study investigating the advanced treatment of secondary wastewater for groundwater recharge to the Floridan Aquifer. Since this study is focusing on recharge options to a brackish receiving water body (TDS > 500 mg/L), alternative treatment processes using ultrafiltration, ion exchange, ozone and ultraviolet light (UV) based AOPs, as well as biofiltration, are being examined as an alternative to the FAT approach of RO and UV AOP.
Due to the relatively high total dissolved solids (TDS) levels of the Floridan Aquifer (around 3000 ppm), any drinking water applications require nanofiltration (NF) or RO membrane treatment to achieve potable quality. This aspect of the aquifer allows the utility to consider potable reuse schemes where RO or NF membranes are not incorporated at the reuse facility, thereby deviating from the FAT approach. The avoidance of RO membranes in the reclamation scheme could save the City upwards of $100 million (US) in capitol expenses, in addition to the savings from operation and maintenance of a high pressure membrane system.
A primary concern of the local regulatory agency is the potential for trace organic contaminants (TOrCs, also referred to as emerging contaminants) to enter the environment and water supply. Therefore, multiple pilot treatment schemes are being operated to evaluate the formation/removal of nitrosamines and other TOrCs by these processes. This paper will provide an overview of the project, data on selected TOrC and nitrosamine removal, and regulatory concerns and perspectives from a local, state and national level.
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