WASTEWATER REUSE: SOUTH FLORIDA'S ANSWER TO A SUSTAINABLE 21ST CENTURY
Abstract:According to a projection by the U.S. Bureau of the Census, the United States must find water for an additional 2.5 million people each year over the next 50 years. That is equivalent to adding a city the size of San Diego to the nation each year. Hence, water supply adequacy promises to be one of the country's primary resource issues for the hope of a sustainable 21st century.
Historically water rich areas of the country, such as South Florida, can expect to see significant population increases. [The Census predicts 5 million more people in the state over the next 25 years]. Due to this significant population growth, coupled with natural climatic variability and the water demanding task of Everglades restoration, South Florida water utilities are facing some of the largest and most challenging water supply issues they have ever seen. Rather than praying for rain, utilities are being asked to find synergistic solutions to water supply, wastewater effluent disposal and reuse issues. Several programs are leading the push down this path, including the Comprehensive Everglades Restoration Program (CERP) and the proposed Regional Water System Availability Rule.
During the dry season, Southeast Florida water suppliers currently depend on an estimated 500 million gallons of water per day from the Everglades to sustain their primary drinking water source, the Biscayne Aquifer. In turn, low dry season water levels have disturbed the Everglades ecosystem, and the State of Florida has committed billions of dollars to reversing these impacts through programs such as the CERP. The CERP has been described as the world's largest ecosystem restoration effort, and includes restoring natural flows of water, water quality, and more natural hydro-periods within the remaining natural areas. This plan is intended to result in a sustainable South Florida by restoring the ecosystem, ensuring clean and reliable water supplies and providing flood protection.
As a result of the CERP, the South Florida Water Management District (SFWMD) coded the Regional Water Availability Rule which limits water supply demands from the Everglades and Loxahatchee River Watershed to levels that existed prior to April 2006. The rule affects water suppliers in urban areas along the District's lower east coast, including Monroe, Miami-Dade, Broward and Palm Beach Counties. As a result of this rule, cities needing additional water supplies will be required to seek sources that are not dependent upon the Everglades for recharge. These alternative water supply solutions include conserving water, recycling wastewater, or finding new water sources such as the deeper and more brackish Floridan Aquifer or seawater. However, since millions of gallons of treated wastewater are being dumped into the ocean or injected deep into the ground, regulatory agencies are highly encouraging a more sustainable approach focusing on wastewater reuse as the primary alternative water supply option. Therefore, this paper will focus on a few of the more advanced cutting edge initiatives that will apply state of the art dual membrane technology for challenging applications such as indirect potable reuse that would recharge the Biscayne Aquifer, and spray irrigation using brackish water sources. Three of these initiatives that will be reviewed in this paper include:
City of Plantation Advanced Wastewater Treatment (AWT) Pilot
Miami Dade County Central District Wastewater Treatment Plant Water Reclamation Facility (CDWRF)
Miami Dade County South District Wastewater Treatment Plant Water Reclamation Plant (SDWRP)
As an ongoing regional effort to finding alternative water supplies, the City of Plantation and the SFWMD entered into a cooperative agreement to evaluate recharging the Biscayne Aquifer with highly treated reclaimed water through canal infiltration. The work associated with this project included an economical desk-top evaluation of the potential process treatment schemes capable of meeting the required effluent water quality. This evaluation was completed and the following process schemes were selected and designed to be piloted to meet the anticipated effluent requirements for surface water discharge, specifically TN < 1.5 mg/L and TP < 0.02 mg/L. Other non-regulated parameters were also evaluated such as algal growth potential, toxicity, microconstituent destruction and hormonal impacts of the treated wastewater.
MBR Scheme: Primary effluent, membrane bioreactor (MBR), reverse osmosis (RO), and UV disinfection.
Conventional Treatment Scheme: Nitrified secondary effluent, denitrification filter, ultrafiltration (UF), RO, and UV disinfection.
RO Scheme: Nitrified secondary effluent, UF, RO, and UV disinfection.
Based on pilot results all three pilots schemes are potential viable options for satisfying the stringent regulatory limits.
Miami Dade County, Florida is embarking on one of the largest water sustainability programs in the country. Ultimately the program envisions over 100 mgd of alternative water supply projects, primarily composed of wastewater reuse projects. The majority of the wastewater projects will likely incorporate dual membrane technology for indirect potable reuse. Two of the initial projects are the CDWRF and SDWRP.
The CDWRF will provide over 2 mgd of advanced side-stream treatment from the Central District Wastewater Treatment Plant, which currently treats an annual average flow of 143 mgd. Most of the reuse for the project will be spray irrigation with a possible industrial use as cooling water for cooling towers. Since this facility and its service areas are located very close to the Atlantic Ocean, there are high chloride concentrations in the treated wastewater effluent. This is the result of salty groundwater infiltration of the sewage collection system. As a result, dual membrane technology will be needed for chloride reduction. This project is aimed at replacing existing potable water demands with highly treated wastewater in lieu of potable water.
The SDWRP is envisioned to take highly treated wastewater (approximately 30 mgd) and recharge the Biscayne Aquifer. The goal of this project is to use treatment technologies similar to the Orange County Groundwater Replenishment Facility which include microfiltration and reverse osmosis membrane filtration to remove solids and dissolved constituents. Also an ultraviolet light – advance oxidation process will be used to destroy microconstituents such as pesticides, herbicides, hormones, antibiotics and other compounds of concern. The SDWRF will be one of the largest ground water recharge facilities in the country and will be the model for determining the feasibility of groundwater recharge as a solution to water supply issues in South Florida.
The purpose of this paper is to share some of South Florida's vision for a sustainable 21st century. Several of the innovative programs will be reviewed including key issues associated with the different technologies and regulations for wastewater reuse.
Document Type: Research Article
Publication date: January 1, 2008
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