Identifying The Feasibility of Canal Recharge for Indirect Potable Reuse: The Plantation Experience
- Enrique Vadiveloo, Richard Cisterna, Robert Harris, Tony Greiner, Paul Pitt, Ron Latimer, Paul Vinci - Hazen and Sawyer, P.C.,
- Hank Breitenkam - City of Plantation, Florida
- Jose Lopez - South Florida Water Management District
- Kevin Alexander - Separation Processes, Inc
- Zhi Zhou, Andrew Salveson - Carollo Engineers
Due to significant population growth, coupled with natural climatic variability and the water de-manding task of Everglades restoration, South Florida water utilities are facing some of the larg-est and most challenging issues they have ever encountered. Rather than praying for rain, utilities are being asked to find synergistic solutions to water supply focusing on wastewater effluent dis-posal and reuse issues. As a result, South Florida utilities are seeking alternative sources of water. As part of this effort, the City of Plantation and the South Florida Water Management District entered into a cooperative agreement to evaluate the feasibility of recharging the drinking water supply by discharging tertiary-treated wastewater to a surface water body. The East Holloway Canal (EHS), which is part of the Old Plantation Water Control District, was identified as a potential point of recharge to the potable water supply and ultimately the underground aquifer. However, due to the sensitivity of the receiving surface water body, the treated effluent would be required to meet several key criteria; stringent nutrient limits (TN < 1.5 mg/L and TP < 0.02 mg/L), microconstituent removal/destruction , zero toxicity impacts on aquatic organisms, and any hormonal effects. The relatively unique water quality concerns associated with this effort results in the need to evaluate, through desktop modeling and on site pilot testing, viable treat-ment technologies. Primary goals of this pilot testing program were evaluating potential treatment technologies and assessing the feasibility of discharging reclaimed water into the EHC near the City of Plantation Wastewater Treatment Facility (CP WWTF) based on anticipated effluent water quality requirements.
Materials and Methods
Two process treatment schemes were pilot tested:
1) Process Scheme 1: Primary effluent from the CP WWTF was treated using a Membrane Bioreactor (MBR), Reverse Osmosis (RO) and Ultraviolet (UV) disinfection. The bioreactor was configured for both biological nitrogen and phosphorus removal.
2) Process Scheme 2: Nitrified secondary effluent from the CP WWTF was treated using, de-nitrification (sand) filters (DNF), Ultrafiltration (UF), RO and UV disinfection.
The flow through the pilot system was approximately 10 gpm. Nutrient levels were measured be-fore and after each treatment unit and at different test conditions to demonstrate compliance with effluent criteria. The removal of microconstituents by these processes and effluent toxicity tests were quantified through five sampling events at three locations in each treatment train: UF effluent, RO influent, and RO effluent. The following were key parameters evaluated over a period of approximately one year: pH, total nitrogen (TN), total phosphorus (TP), total suspended solids, biochemical oxygen demand, total dissolved solids, particle size distribution, concentrations of selected microconstituents (32 were analyzed), chronic definitive testing on the waterflea (Ceriodaphnia dubia) and the fathead minnow (Pimephales promelas), E-Screen with MCF-7 cells, yeast estrogen screen, and fathead minnow (Pimephales promelas) vitellogenin and steroid assays.
Results and Discussions
The pilot testing was completed in April 2008 and it successfully demonstrated that both process schemes are a viable option for potential full-scale implementation with regards to nutrient re-moval. Both treated effluents consistently met the anticipated TN and TP effluent limits under varying test conditions. However, based on the results, it was evident that chemical and biological nutrient removal technologies alone were not sufficient to meet the stringent nutrient limits and that the use of RO membrane technology is essential for this type of project.
The results of the microconstituent analyses in the RO influent and RO permeate are shown in Figure 6. A sampling of the results is shown in Figure 6, which shows that the RO membranes effectively removed the majority of the microconstituents.
The results of the toxicity testing identified several issues regarding the toxicity of RO effluent on aquatic organisms. Specifically, the effects of the type of pretreatment (antiscalant and chlor-amines) used on the RO system and the re-stabilization/re-mineralization of effluent needed prior to discharge. These effects will be key issues for full-scale implementation. The endocrine dis-ruptor assays performed using the RO permeate exhibited no hormonal effect on the aquatic or-ganisms. The results of the toxicity and endocrine disrupter assays will be detailed in the techni-cal paper and presentation at the conference. The purpose of this paper is to share the results of this pilot project with the municipal community and review key issues associated with canal re-charge, and surface waters in general, for indirect potable reuse.
For a copy of the full paper, please contact the author at email@example.com
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