Water Reuse: Why Purple is the New Green in Florida

By Clayton McCormack, PE

Landscape irrigation is a growing application for reclaimed water in residential areas such as the Sandy Pines Development in Palm Bay, FL

As our population grows, our demand for water is increasing along with the quantity of wastewater that requires disposal. Sometime in the future, our water demand will exceed our available fresh water supply. Agencies who regulate water use in Florida believe some regions in the state are nearing this point. As an example, there is a 2013 moratorium looming that would limit any increased withdrawal of groundwater in Central Florida, including the Orlando area. Recognizing the need to effectively manage water resources, the State of Florida actively promotes the use of highly treated wastewater effluent or reclaimed water for beneficial use. The goal of the five Water Management Districts is for communities to beneficially use 100% of their treated wastewater effluent. Reclaimed water provides a consistent alternative water supply for many uses that do not require higher quality potable, or drinkable water, thereby conserving potable quality raw water sources. For example, 400,000 gallons of groundwater used daily to irrigate a typical golf course can supply drinking water to 1,450 homes. Irrigating the golf course with reclaimed water would preserve the higher quality water source to meet potable water demand.

Typical reclaimed water applications include agricultural irrigation, landscape irrigation of public and residential areas, industrial activities like process cooling, groundwater recharge, non-potable urban uses such as fire protection and toilet flushing, and indirect potable reuse. Reclaimed water supply pipelines are increasingly being installed in residential and commercial developments to supply irrigation water. Reclaimed water pipelines, sprinkler heads, meter boxes, and other irrigation equipment are color-coded purple to distinguish reclaimed water pipes from drinking water systems.

For wastewater to be reused, specific treatment and monitoring requirements must be met to protect public health. The Florida Department of Environmental Protection requires reclaimed water to receive secondary biological treatment, filtration and high level disinfection. The total suspended solids concentration must be reduced to a maximum of 5.0 mg/L before disinfection. High-level disinfection requires that at least 75% of all samples collected for fecal coliform be less than the detection limit and that no single sample exceeds 25 fecal coliforms per 100 mL. In many cases, these standards far exceed requirements for the discharge of treated wastewater effluent to a surface water. In addition, on-line instrumentation must continuously monitor the quality of treated wastewater. Increased state certified treatment plant operator staffing requirements are also required for plants that produce reclaimed water.

Wade Trim has helped several clients plan for the expansion of their reuse system or design treatment facilities to produce reclaimed water. We helped the City of Palm Bay prepare a Reuse Master Plan that shows how the number of residential reuse customers in the community will be increased to meet regulatory requirements of the St. Johns Water Management District. Twenty-six neighborhoods were surveyed to gauge their interest in using reclaimed water for irrigation. Based on the results, the City targeted 12 neighborhoods to supply reclaimed water to over the next 10 years. In a manner similar to a water study, Wade Trim projected the reclaimed water demand for each area and developed a hydraulic model of the current and proposed reuse distribution system. The model became a tool to develop the list of Community Investment Program projects necessary to construct the needed reuse infrastructure.

Reclaimed water used for irrigation must not contain contaminants that could damage vegetation. This is a concern for the North Key Largo Utility Corporation’s wastewater treatment plant where the treated effluent contains elevated concentrations of salts due to seawater infiltration into the collection system. For reuse, the water must be further treated using reverse osmosis to remove excess salts that could damage vegetation. Wade Trim designed a 300,000 gallon per day reverse osmosis treatment system that will allow treated wastewater effluent to be used for golf course irrigation.

In Florida, approximately 600 million gallons of highly treated wastewater effluent is being beneficially reused every day. Florida’s proactive approach is conserving our limited water resources for drinking water needs and maximizing the beneficial use of reclaimed water.

Clayton McCormack, PE, has extensive experience designing wastewater treatment facilities for municipalities. He can be reached in our Palm Bay, FL, office at 321.728.3389 or cmccormack@wadetrim.com.

Originally published in Innerview Vol. 22, No. 3, 2008

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