Proposed Reuse Projects to Expand Environmental Water Supply in the Everglades
The Comprehensive Everglades Restoration Plan (CERP) was envisioned as a multidecadal effort to achieve ecological restoration by reestablishing the hydrological characteristics of the historic Everglades ecosystem, where feasible, and to create a water system that simultaneously serves the needs of both the natural and human systems of South Florida (NRC, 2010). The conceptual plan (USACE/SFWMD, 1999) included 68 different project components focused on restoring the quantity, quality, timing, and distribution of water in the ecosystem. The largest component of the budget for this $13 billion project is devoted to water storage, including conventional surface water storage reservoirs, in-ground reservoirs, aquifer storage and recovery, and seepage management. To provide sufficient water supply to meet anticipated future environmental, urban, and agricultural water demands in South Florida, the comprehensive plan included two water reuse projects in Miami-Dade County, which together would treat more than 200 million gallons per day (MGD; 760 million m3/d). In the preliminary project concept, the reclaimed water would be used for aquifer recharge to enhance urban water supplies and reduce seepage out of the Everglades. Additionally, reclaimed water could be provided to Biscayne Bay National Park to help meet freshwater flows to support ecosystem needs. However, the plan acknowledged the high costs of such treatment to support ecological needs and noted that other potential sources of water would be investigated before water reuse was pursued.
Pilot projects were planned to assess the “cost effectiveness and environmental feasibility of applying reclaimed water to sensitive natural areas” and to “identify treatment targets consistent with preventing degradation to natural area,” among other objectives. A pilot plant was constructed by Miami-Dade County that included several different wastewater reclamation treatment trains (e.g., with and without reverse osmosis; ozone vs. ultraviolet/advanced oxidation processes), and trace organic chemical data were collected for several months. However, the pilot project was halted in 2011 before the planned toxicity testing was initiated because of general concern about the economic feasibility of the larger ecological restoration project (Jim Ferguson, Miami Dade County Water and Sewer Department, personal communication, 2011).
receiving water bodies. However, the level of toxicant exposure and dilution within the receiving systems are key considerations when assessing toxicity. The individual constituents may arise from industrial, household, or wastewater treatment plant applications. For instance, chlorine is often used as a disinfection chemical to reduce pathogen load and disease risk in wastewater. Low levels of chlorine may cause toxicity in the receiving stream or form chlorinated byproducts capable of causing ecotoxicity. Organic chemicals in wastewater have the potential to deplete the receiving aquatic system of oxygen, thus impacting aquatic life. Suspended solids from wastewater can block sunlight, thus reducing the photosynthetic capability of aquatic plants. Reduction in sunlight penetration may reduce plant life, as well as vertebrate and invertebrate populations. All of these stressors singularly or in combination may affect aquatic life, which includes macroinvertebrates, fish, plants, and amphibians (Sowers et al., 2009; Brix et al., 2010; Slye et al., 2011). Ecological assessments of wastewater effluent-dominated surface waters have shown that aquatic life can be sustained in these types of waters; however, site-specific factors may influence the aquatic life in various locations (Brooks et al., 2006; Slye et al., 2011).
Many studies associated with municipal effluents have been focused on standard measures of water quality, such as pH, temperature, total nitrogen and phosphorus, dissolved oxygen, and the impact of the effluent on the receiving system (Howard et al., 2004; Kumar and Reddy, 2009; Odjadjare and Okoh, 2010). Regulatory agencies, such as the U.S. Environmental Protection Agency (EPA), have developed guidance documents and criteria for many of these water quality parameters on a site-specific or ecoregion basis. Further, the EPA created the National Pollutant Discharge Elimination System to prevent aquatic life impacts associated with these traditional forms of wastewater pollution. As information on new classes of environmental contaminants arise, standard methods for assessing risk (e.g., whole effluent toxicity [WET] testing) may be unable to detect the subtle changes associated with these compounds. For instance, there have been recent reports of treated wastewater causing severe lesions and developmental alterations in amphibians, which are not common sentinel testing organisms in the WET testing paradigm (Sowers et al., 2009; Keel et al., 2010; Ruiz et al., 2010).
Because stressors may be different between each reuse scenario, basic information on the effects of potential ecological stressors in treated wastewater are described in this chapter.