Aquifer Recharge to Increase Supply: Miami-Dade Water Reclamation Plant

Client:: Miami-Dade Water and Sewer Department

Location:: Miami-Dade County, FL

Recent legislation has capped withdrawals from the Biscayne Aquifer - South Florida’s primary source for large quantities of safe drinking water. This places great stress on the utilities faced with quenching the thirst of Florida’s rapidly expanding population. Recent legislation will also limit wastewater effluent discharges via open ocean outfall. To address both issues, Hazen and Sawyer is currently designing the largest indirect potable reuse plant of its kind in the State of Florida. The first step in that design process was to perform a pilot study of the technologies used to reclaim the wastewater effluent.

Project Outcomes and Benefits

The finished plant will contribute 21 mgd of recharge to the Biscayne Aquifer, significantly increasing the available drinking water supply.
The design reclaims and beneficially reuses wastewater effluent in a healthful and safe manner.
In addition to the development of the treatment process, including the pilot testing, Hazen and Sawyer is involved in developing the regulatory standards for implementation and long term operation of the project, paving the way for additional, much-needed reuse projects in the state.

The pilot plant was constructed on the wastewater treatment plant site to utilize the exact effluent that would be treated in the future. Pilot scale deep bed sand filters and chlorine tanks were installed as part of the pilot project to provide effluent quality similar to that anticipated once the full scale system, which is under construction, is completed.
The completed pilot plant included all of the components to be designed in the full scale reclamation project.

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The main removal mechanism in this type of reuse treatment facility is the reverse osmosis (RO) system. A three stage configuration is being designed to remove several of the constituents in the effluent. These constituents, such as, nutrients like ammonia and phosphorous, as well as, emerging pollutants of concern, including pharmaceuticals and industrial compounds, are often present in very low concentrations.

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The reclaimed water from the South District Water Reclamation Plant will be conveyed to the area around the Miami Metrozoo and injected in to the Biscayne Aquifer at a rate of 21 mgd. This location was selected because it is upstream of the well field that supplies a portion of the County’s drinking water and will impact the strained “Regional System.”

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The water that is reclaimed and used to replenish the Biscayne Aquifer for drinking water will provide relief the “Regional System” by reducing the flow out of the South Florida Water Management District’s canal network, which ultimately impacts flow to and from the Everglades.

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The pilot plant was constructed on the wastewater treatment plant site to utilize the exact effluent that would be treated in the future. Pilot scale deep bed sand filters and chlorine tanks were installed as part of the pilot project to provide effluent quality similar to that anticipated once the full scale system, which is under construction, is completed.
The completed pilot plant included all of the components to be designed in the full scale reclamation project.
The main removal mechanism in this type of reuse treatment facility is the reverse osmosis (RO) system. A three stage configuration is being designed to remove several of the constituents in the effluent. These constituents, such as, nutrients like ammonia and phosphorous, as well as, emerging pollutants of concern, including pharmaceuticals and industrial compounds, are often present in very low concentrations.
The reclaimed water from the South District Water Reclamation Plant will be conveyed to the area around the Miami Metrozoo and injected in to the Biscayne Aquifer at a rate of 21 mgd. This location was selected because it is upstream of the well field that supplies a portion of the County’s drinking water and will impact the strained “Regional System.”
The water that is reclaimed and used to replenish the Biscayne Aquifer for drinking water will provide relief the “Regional System” by reducing the flow out of the South Florida Water Management District’s canal network, which ultimately impacts flow to and from the Everglades.

Hazen and Sawyer, in partnership with another national firm, is currently designing the largest wastewater reclamation plant of its kind in the State of Florida, for the Miami-Dade Water and Sewer Department. The 21-mgd South District Water Reclamation Plant (SDWRP) includes an advanced wastewater treatment approach that will provide indirect potable reuse water to replenish the Biscayne Aquifer via rapid infiltration.

In addition to the development of the treatment process, including the pilot testing, Hazen and Sawyer is involved in developing the regulatory standards for implementation and long term operation of the project. This project builds on an upgrade to the South District Wastewater Treatment Plant (SDWWTP) which adds High Level Disinfection (HLD) to the existing pure oxygen secondary treatment plant. Hazen and Sawyer is working with Department staff to provide program management, design and construction management services for the HLD project.

The SDWRP is adjacent to the SDWWTP and will treat secondary effluent from the SDWWTP to extremely high water quality levels since the receiving body is the primary drinking water source for South Florida residents. The first step in the treatment process will be strainers followed by microfiltration (MF) or ultrafiltration (UF) to minimize suspended solids from the secondary effluent. The RO treatment process at the SDWRP will remove organic carbon (TOC), total organic halides (TOX), and significantly reduce nitrogen and phosphorus to satisfy potable reuse and environmental application requirements. Microconstituents and emerging pollutants of concern (EPOC), like NDMA and pharmaceuticals will also be reduced by the process.

The final step in the SDWRP process will be an advanced oxidation process (AOP) to reduce the concentrations of the Microconstituents, or EPOC, that remain in the flow stream. The AOP step will actually include two separate components, ultraviolet light (UV) application and hydrogen peroxide (H2O2) addition, to form hydroxyl radicals (OH·) which oxidize most organic compounds. This type of AOP was selected given the relatively low concentrations of interfering compounds like alkalinity or other constituents in reduced states found in RO permeate.

Recharge Facilites
Several discharge facilities were evaluated for recharging the aquifer with 21 mgd of highly treated water from the SDWRP. In order to accomplish this, the treated effluent would need to percolate through moderately to highly permeable soil as it travels through the soil matrix. During the evaluation it was determined that the existing topography at the Metro Zoo lends itself to use of an existing moat that has been created around the MetroZoo. Hydrogeologic modeling indicated this approach prevented reuse water contact with protected areas in the vicinity of the recharge location.

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