Miami-Dade's Reuse Pilot Program – Investigates the Limits of Technologies to Meet Ultra-low Levels of Nutrients and Micropollutants

Biscayne Bay is a shallow subtropical estuary that is an important natural and economic resource to the region. As a result, Miami-Dade Water and Sewer Department has embarked on an ambitious program to reuse their effluent to revitalize the coastal wetlands that ultimately discharges to Biscayne Bay. Historically, the groundwater and surface water flows to Biscayne Bay have been dramatically altered and the total impact of these manmade changes is not fully understood. However, it is recognized that the freshwater flows necessary for a healthy estuarine system have been altered to the point of causing ecological impact. The Biscayne Bay Coastal Wetlands Project was thus selected as one of the components of the Comprehensive Everglades Restoration Plan (CERP) which was approved by Congress as part of the Water Resource Development Act of 2000.The South District Wastewater Treatment Plant (SDWWTP) has an average annual daily flow (AADF) permitted capacity of 425,859 cubic meters per day (m3/day) (112.5 million gallons per day (MGD)) and discharges its effluent via a series of deep injection wells. The existing treatment processes at the facility include screening, grit removal, pure oxygen activated sludge process, secondary clarification, and standby chlorine disinfection prior to deep-well injection.A number of stakeholders have participated in the overall decision making process. These stakeholders have included regulatory agencies, the federal government (National Park Service), and environmental organizations, and have been involved with the development of this project from the project onset. Major steps were identified at the beginning of this project, and with the concurrence from the stakeholder's the treatment technologies to be tested, flow streams, and monitoring and sampling plans were developed.In summary, the pilot program investigated various treatment technologies to provide additional treatment of the SDWWTP secondary effluent to further reduce CBOD5, TSS, nitrogen and phosphorus, selected micropollutants and other pollutants to accepted levels as agreed upon by the various stakeholders, in addition to providing disinfection. This pilot program became more important with the impending numeric nutrient criteria that are proposed by the USEPA for the state of Florida.The pilot plant was designed to treat a nominal flow of 114 m3/day (0.03 MGD), and consisted of three alternative and distinct treatment process flow schemes:Process Flow Train A — MBR (biological nitrification/denitrification, chemical phosphorus removal, and membrane filtration), advanced oxidation (Peroxide/UV and Peroxide/Ozone were both tested) and effluent stabilization.Process Flow Train B — MBR (biological nitrification/denitrification, and membrane filtration), reverse osmosis, advanced oxidation and effluent stabilization.Process Flow Train C — MBR (biological nitrification/denitrification, chemical phosphorus removal, and membrane filtration), reverse osmosis, advanced oxidation and effluent stabilization.The pilot program was designed and constructed to meet certain regulated parameters, namely total nitrogen (TN) and total phosphorus (TP). The target nutrient limits that were set for this program were 0.25 mg/L for TN and 0.005 mg/L for TP. In addition, a selected group of micropollutants, and priority pollutants were sampled. To determine the effectiveness of the individual treatment technologies in meeting the water quality goals, individual flow streams were monitored and sampled, along with the effluent from the overall process flow streams.The objective of this pilot program was to evaluate treatment benefits to determine if the effluent can be reused to rehydrate the Biscayne Coastal Wetlands. The demonstration plant takes into account the existing secondary process at the SDWWTP and the proposed high level disinfection (HLD) facilities. This paper will present the results of Miami-Dade's ambitious pilot program, which will include:The development of this pilot program, including water quality and scientific goals, and the stakeholders input process; andThe performance and effectiveness of the individual advanced treatment technologies, as well as the individual flow streams for the high level removal of nutrients to ultra low levels, priority pollutants, micropollutants, and other water quality parameters of interest.