Destin Water Users Inc. (DWU) is a member-owned utility that provides its customers with drinking water and wastewater reclamation services. Located on the sugar-white beaches of Northwest Florida’s Emerald Coast, DWU’s service area is bound on three sides by the Gulf of Mexico and the Choctawhatchee Bay. 

DWU operates under a voluntary no discharge permit. To avoid discharging treated wastewater into the Gulf or the Bay, the utility was faced with finding ways to dispose of wastewater effluent on the land’s surface. Dedicating hundreds of acres to an effluent spray field was not economically viable. With overwhelming support from the community, the goal became 100 percent effluent reuse. 

In 1985, DWU became one of the first utilities in Florida to save reclaimed water for beneficial reuse. Its first customer, Indian Bayou Golf Course, still irrigates its greens with the utility’s reuse water. 

Today, reuse water customers include two golf courses, the City of Destin, resort communities and business, and hundreds of homes. DWU serves a resident population of 20,000 and as many as 60,000 in peak tourist season. The 6 mgd (design) George French Water Reclamation Facility handles the heavy seasonal load. 

When it rains … 

As sunny as most days are, the area still gets its share of rain — nearly 100 days a year. But in Florida’s panhandle, coastal sands create a xerophytic landscape, so sandy soil does not retain water. When it rains, water seeps into the ground and filters through the porous silica sand. There is virtually no absorbent media to retain it or slow it down. 

In wet weather, DWU stores reuse water. Its three storage tanks hold 2 million gallons each — about two days’ demand for irrigation water. When the tanks are full, excess water is pumped onto the plant’s rapid infiltration basins (RIBS) or to a sandy subsurface location under the soccer and softball fields at the city’s sports complex. 

But General Manager Richard Griswold and his team of engineers believe that is a waste of resources. So Destin Water plans to store reuse water in an Aquifer Storage and Recovery (ASR) project. After nearly a decade of planning, design and construction, it is operational, but not yet permitted. 

“This uniqueness brings challenges,” says Paul Reese, plant operations manager, referring to the Florida landscape. “The Florida Department of Environmental Protection (DEP) is demanding more stringent standards for the ASR water than for drinking water. Total trihalomethane (TTHM) level is one of those challenges.” 

TTHMs in effluent 

TTHMs are carcinogens, strictly regulated in public drinking water supplies. With the ASR project, DWU’s wastewater effluent is pumped directly into an aquifer. And the state DEP has imposed stricter standards on the storage of this water than water that is sent directly to the surface for irrigation. 

The national drinking water standard is 80 μg/L as an annual running average. “Our wastewater permit requires that treated water being pumped into the ASR well does not exceed 80 μg/L in a single sample,” Reese says. “That’s our permit and we will do what it takes to meet it.” 

One idea to inhibit TTHM formation was to reduce the impact of photo-oxidation between chlorine and the available total organic carbon compounds (TOCs) in the effluent water. 

“It was simple: If you want to prevent sunburn, look for shaded cover,” Reese says. So, with the help of Pat Schipani and his crew from Tri-State Enclosures, DWU built a screen room around the high-level chlorine contact chamber that provides 80 percent UV shading. Since then, TTHMs rarely exceed 40 μg/L. 

Side benefits 

Step inside the chlorine contact chamber screen room on a hot day and the first thing you notice is how much cooler it is inside — as much as 15 degrees F. Protected by shade cloth overhead and surrounded by Super Screen walls, DWU operators appreciate the protection from sun, wind, insects and dust. 

“We have almost no algae growth in the chlorine contact chamber now,” Reese says. 

The screened enclosure has another benefit. Monica Autrey, engineering manager, calculates that the sunscreen protection should reduce chlorine dosage by about 15 percent — a welcome relief to the budget. 

“The screen room should pay for itself in about five years,” Autrey says.