Potable Reuse in Florida: How City of Plant City is Making it Happen

Carlyn Higgins, Paul Biscardi, Stephanie Ishii, and Andre Dieffenthaller

The City of Plant City (city) is a small, agricultural-based community on the eastern outskirts of the greater Tampa Bay area faced with both water supply limitations and effluent management challenges. The city launched an integrated water management plan, which includes increased water supply through potable reuse as part of its recommendations. To evaluate the feasibility of using treated wastewater effluent as a potential alternative source for drinking water, the city is conducting a potable reuse pilot study consisting of membrane filtration (MF), reverse osmosis (RO), and an ultraviolet/advanced oxidation process (UV/ AOP). The year-long pilot study demonstrated that the purified water quality met current and anticipated pending regulations.

The pilot study also identified several key design parameters for the full-scale potable reuse design. The city’s comprehensive public outreach program, aimed at educating and receiving feedback from the community, was successful in gaining support in favor of the city utilizing potable reuse as an alternative drinking water supply.

The city is known for abundant berry production and the annual Strawberry

Festival, which brings thousands to the area to engage in rodeo-like activities, listen to music from national headliners, and enjoy strawberry shortcake. The city also owns and operates an integrated water, sewer, and reclaimed utility. Plant City is projected to have significant population growth within the next 20 years, prompting increased water demand that will eventually surpass the existing water supply.

The city has limited expansion opportunity with its current groundwater potable supply due to the location within the Dover Plant City Water Use Caution Area and is faced with identifying alternative drinking water sources to satisfy increasing demand. Plant City intends to remain water secure, while also acknowledging the potential for mutually shared resources.

As a unified water management approach, the city developed a holistic project that incorporates stormwater treatment, mitigation of localized flooding, rehabilitation of a natural habitat park, and increased water supply through potable reuse. The overall program objectives are to increase water supply while providing restoration of hydrologically impacted wetlands and enhancing the beneficial reuse of high-quality reclaimed water.

Carlyn Higgins, Ph.D., P.E., is an engineer; Paul Biscardi, Ph.D., P.E., is an associate; Stephanie Ishii, Ph.D., P.E., is an associate; and Andre Dieffenthaller, P.E., is a vice president, at Hazen and Sawyer in Tampa.

As a part of the feasibility phase, the city evaluated potable reuse by investigating the effectiveness of technologies to further treat reclaimed water, with the goal of augmenting its drinking water supply.

Current regulations in Florida require a pilot to demonstrate performance for intended potable reuse. Florida has been a “hot spot” for testing of potable reuse, with more than a dozen Florida utilities having conducted pilots or demonstrations in the last decade. The city is unique, as it’s one of the few in Florida to pilot while still adhering to a set of draft Florida Department of Environmental Protection (FDEP) statewide potable reuse regulations. Continued discussions with FDEP have confirmed that the city is collecting the appropriate data for future permitted full-scale implementation. These discussions with FDEP will continue to help shape and finalize the statewide potable reuse rules.

Although the city has a smaller utility that may not have been originally thought of as being in the forefront of implementing a full-scale potable reuse process, it’s paving the way for potable reuse in Florida and providing an example of a small community’s holistic water management strategy for the future.

The pilot- and subsequent full-scale potable reuse facility is designed to treat reclaimed water to meet all regulated chemical and pathogen concentrations for drinking water, while also providing monitoring for unregulated contaminants. The city considered both membraneand nonmembrane-based potable reuse treatment types. Both treatment approaches have been studied and utilized at other pilotand full-scale facilities in Florida and the United States. Criteria in the potable reuse treatment selection included treatment efficacy, regulatory unknowns, waste stream disposal, operation and maintenance, and life cycle cost of the facility.

One of the first efforts included examining the city’s wastewater effluent water quality over time, which would determine appropriate treatment techniques. The average conductivity of the effluent was close to 900 microsiemens per centimeter (μS/cm) with seasonal variation, including concentrations as high as 1200 μS/cm, as shown in Figure 1. Elevated conductivity levels correspond to a total dissolved solids concentration of greater than 500 mg/L, which would constitute an exceedance of the secondary drinking water standard in Florida; therefore, the higher salt content in the source water drove the need for salt removal using high-pressure membrane technology, such as RO.

To permit a potable reuse treatment facility, the process train must reliably achieve a certain log inactivation of pathogens. Although the pathogenic log removal requirement for potable reuse treatment in Florida has not been finalized, the piloted unit process was chosen based on the draft FDEP regulations and other regulations from California and Texas. The log removal requirements for the membrane-based potable reuse treatment system, consisting of MF, RO, and UV/AOP, are shown in Table 1.

Using the credit given by other state regulations (i.e., California), the potable reuse process achieves log removal of 12, 12, and 15 for Virus, Cryptosporidium, and Giardia, respectively. The potable reuse treatment train provides barriers against both chemical constituents and pathogens to protect human health. This multibarrier train is recognized as a validated treatment approach for potable reuse and has been piloted elsewhere in the state of Florida. The RO-based technology approach is recognized by the U.S. Environmental Protection Agency (EPA) for potable reuse treatment, and has been implemented successfully and verified in potable reuse treatment facilities throughout the U.S., Europe, Africa, and Australia.

The pilot treatment was selected to treat water suitable for either indirect potable reuse (IPR) or direct potable reuse (DPR). The IPR consists of advanced treatment followed by a natural buffer, such as groundwater recharge or surface water augmentation; the DPR eliminates the natural buffer and sends treated water directly to the potable distribution system. Based on the finalization of the Florida regulation, additional treatment may be required for DPR.

To better characterize the near- and longterm implications of IPR versus DPR at the city, the pilot study was coupled with groundwater modeling to determine optimal location and sizing for recharge and withdrawal wells, should the aquifer be included as an environmental buffer. The potential of recharged water to not only supply the city, but also be shared with other local authorities in the area without the need for interconnecting infrastructure, may drive the project in the IPR direction. The purpose of the pilot, however, was to validate the current treatment; the terminus of the alternative water supply will be decided after the pilot has concluded.

The city’s pilot testing program was designed to achieve the following goals:

S Meet the regulatory requirements of the FDEP Florida Administrative Code 62-610.564, in its existing form and proposed draft form in the potable reuse rulemaking process.

S Establish preliminary design and operating criteria for the full-scale process.

S Provide an educational demonstration for public officials, regulators, schools, community groups, and the public.

S Provide operator training for operation and maintenance of the process.

A water quality sampling plan and treatment process operational guide were established to outline the procedure required to meet the piloting goals.

To achieve the pilot goals, an MF, RO, and UV/AOP pilot was procured and installed in series to represent advanced potable reuse treatment. Each pilot unit was prefabricated by a vendor and contains appropriate meters, gages, valves, instrumentation, etc., required to monitor and adjust performance. The pilots also have sample panels to appropriately collect samples as water goes through each treatment stage. The process mimics that of a potential full-scale purification facility, but is scaled down to receive only a fraction of the flow. In this application, the wastewater treatment plant diverts approximately 40 gal per minute

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(gpm) of wastewater effluent from the city’s sand filter effluent to the pilot process, which is 1/40th of the expected full-scale flows.

The process flow diagram of the pilot is shown in Figure 2 and images of the city’s pilot installation are shown in Figure 3.

As part of the pilot, water quality entering both the wastewater treatment facility and the pilot was closely monitored to identify seasonal trends and variability in character. Throughout the study, the pilot influent conductivity and temperature varied seasonally and did not have an impact on pilot performance; however, as the wastewater treatment facility receives flow from industrial users, it was important to closely observe the quality and quantity of their discharges to confirm they are within permitted limits and determine the potential impacts on the pilot.

Although the city currently monitors industrial waste flows, conductivity, and pH, additional parameters may be better suited to identify waste character changes. As result of the pilot, the city is intending to conduct a collection system investigation to further characterize unique sewer sheds to identify additional constituents for prioritized monitoring.

To achieve the goal of meeting FDEP requirements in existing and proposed draft form, water quality samples were taken consistently and analyzed for primary standards, secondary standards, and unregulated constituents, such as pharmaceuticals, pesticides, personal care products, per- and polyfluoroalkyl substances (PFAS), and other contaminants of emerging concern.

Table 2 presents pilot influent and treated water parameter water quality concentration, compared to their respective maximum contaminant levels (MCLs). Each constituent was present in the finished water at concentrations less than the existing or potential MCLs. Each constituent in the existing FDEP primary and secondary standards was sampled, which confirmed that the UV/AOP-treated water met the required water quality standards, and in many cases, several of the constituents were undetected. The current water quality data demonstrate that the MF, RO, and UV/AOP treatment train yields water quality in compliance with existing and anticipated future regulations.

A critical and important function of a pilot program is the investigation, documentation, and demonstration of performance of the individual and combined processes. The city’s potable reuse pilot was used to identify set points that would yield the most sustainable operation for potential full-scale design. Real-time data from each pilot unit were incorporated into a PowerBI dashboard, which displayed trends in performance. Operators monitored processes daily to facilitate informed decisions regarding set point changes for optimal performance. In addition to performance, the dashboard included monitoring the critical control points (CCPs) of the process, which are points that have a direct impact on the quality of finished water as it relates to public health. Performance data were used to validate that each process was operating as intended and producing adequate water quality, but they also have the capability to alert an operator if the system is not operating as intended, thus requiring corrective action.

For example, the RO process is a CCP and was validated through permeate water conductivity. Sensors on the pilot are constantly measuring RO permeate conductivity and sending data to the human-machine interface (HMI) every 10 minutes. The RO permeate conductivity was consistently below 30 µS/cm throughout the pilot study, but exceeded the limit once in June 2022, indicating a breach of performance. The breach was immediately investigated and determined to be due to a scaling event from a change in water quality from an industrial contribution to the wastewater treatment plant. As a result of this incident, the RO pilot experienced moderate scaling in the second stage of the process; the scaling was deemed primarily to be calcium phosphate and organics.

The pilot unit was restored to previous performance after conducting a clean-in-place procedure. The event further verifies the need to consistently monitor wastewater influent and effluent water quality, as well as performance, in each pilot process. This and other events from the pilot will be used to create operational bounds and alarms at a full-scale facility.

Table 3 presents preliminary design parameters, which were optimized based on performance. For example, continuously injecting a low dose of chloramines prior to

MF and RO treatment significantly improved biofouling and aligns with pretreatment strategies for potable reuse noted elsewhere; furthermore, operating at a RO recovery of 85 percent and flux of 11.4 gal per square foot per day (gal/ft2/d) was sustainable, and thus will guide the membrane surface area requirements for the full-scale treatment facility in the design phase. Preliminary criteria developed for fullscale implementation will contribute to the overall size, layout, and cost determination of the facility. Such design-based activities are planned to take place after the conclusion of the piloting period.

The city has engaged in a comprehensive public outreach program to educate the surrounding community about the future of its water supply. Public education and outreach efforts were developed with the goal of increasing public acceptance of potable reuse by educating stakeholders on the quality and safety of alternative potable water supplies. Components of the program included branding of the overall program, development of user-friendly graphics and educational materials, and hosting public tours to educate the community and gather feedback.

The branding effort encompassed the creation of a name, logo, and tagline to communicate the city’s availability of highquality recycled water accurately and succinctly. A creative brief was initially conceived, which documented information about the city to successfully produce a logo in accordance with its essence and community values.

Aligning with the city logo of “Preserving the Past, Embracing the Future,” the creative brief emphasized the city’s historic and patriotic roots. Once a logo was narrowed down to a few finalists, the city engaged in a staffwide survey to gain feedback regarding the logo that would best represent the community. The final logo

to brand the larger “One Water”-based effort is seen in Figure 4.

Important aspects within the logo are:

S The water drop shape representing the continuity of recycled water and its importance to the community.

S The upper “water wheel” logo representing the many uses for water in the community and the ability to expand those uses in the future. The feature creates a “hidden” star feature in the center as a nod to the city’s patriotic character.

S The lower waves representing the positive ripple effect that Plant City Water will have both locally and in the larger “One Water” effort.

S “Our Water, Our Future” tagline representing the city’s commitment to water independence.

The team developed a full campaign of supporting graphics and educational materials for public education and outreach. A series of easy-to-read and user-friendly signs were created and housed at the pilot to portray information regarding the motivation behind the city engaging in potable reuse, how water cycling works, and the piloted technology and individual process descriptions.

Figure 5 presents an example of the sign created for the MF process. Elements incorporated into the signs included a simple color scheme, basic process description and indicated treatment flow path, and fun facts to generate interest, arouse curiosity, and increase understanding of the process.

Touring efforts also took place and included the branding materials, demonstration models, and informative signage to engage and educate the local community about potable reuse. The city’s public outreach plan commenced with a ribbon-cutting ceremony to gather support and spread awareness of the efforts to continue to provide safe drinking water to the community. Along with materials used to educate the community, a survey was created to gather feedback on the public’s opinion of the city’s potable reuse efforts.

Multiple tours have occurred since the ribbon cutting, with each tour group encouraged to complete a short survey after the conclusion of the tour. Initial responses from the tour groups have been encouraging, with 100 percent of individuals in support of the city using recycled water to sustain its water supply. Delivering effective communication is critical to change public perception about the safety of the city’s water supply.

The MF-RO-UV/AOP process as applied to potable reuse treatment paradigms has been investigated for decades. The process consists of the most advanced and comprehensive water treatment technologies available for drinking water treatment. The city engaged in an integrated water management program, which includes investigating the feasibility of gaining alternative water supplies through potable reuse.

The city piloted a MF, RO, and UV/ AOP treatment train over a year-long study. Understanding that it’s important to verify that the pilot water quality performance meets regulatory requirements for drinking

water quality, the city monitored primary and secondary standards, as well as unregulated constituents, such as pharmaceuticals, pesticides, personal care products, and other contaminants of emerging concern.

Current data suggest that the piloted process meets current and anticipated future regulations. Frequent communication with regulatory bodies has provided assurance that the proposed treatment elements and approach will provide public health protection and environmental benefits. Initial public outreach methods have been successful, with the community in support of identifying additional potable supplies.

The city will pilot the potable reuse train through April 2023 to gain a full understanding of the process performance over a year of seasonal variation. Once the full suite of pilot data have been analyzed and reported, the design engineer will continue with the preliminary design of the full-scale facility. Post-treatment considerations, waste disposal, end use of the potable water, capacity, location, and cost elements will all be evaluated and determined at this stage in the facility design.

This project was jointly funded by the City of Plant City and the Southwest Florida Water Management District. The authors would like to thank Lynn Spivey, Hye Kwag, Mike Darrow, Patrick Murphy, and Tony Bauer of Plant City. The authors would also like to thank Arcadis and Dewberry for their support as subconsultants on the work, as well as Harn R/O, Xylem, and American Water Chemicals for providing pilot equipment and assistance. S

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