Investments in wastewater treatment help protect water quality in Manatee County
By Darcy Young, Director of Planning and Communications, Sarasota Bay Estuary Program
Direct permitted wastewater discharges to Sarasota Bay ceased several years ago, but maintaining this no-discharge status – and keeping up with a rapidly growing population – requires local utility departments to make regular investments in wastewater infrastructure. Manatee County Utilities Department’s (MCUD) Southwest Regional Water Reclamation Facility (SWRWRF) is one of the largest treatment plants in the Sarasota Bay watershed, processing about 13.3 million gallons of wastewater per day. As a water reclamation facility, SWRWRF stores the treated wastewater effluent, or reclaimed water, after processing. MCUD then distributes the water to reclaimed water customers, including residential developments, golf courses, schools, farms, and others that use the water for irrigation. Reclaimed water infrastructure reduces pressure on stressed potable water sources by substituting “recycled” water for uses like irrigation that don’t require drinking water quality. In some areas of the United States, lawn irrigation accounts for 30 to 50 percent of all drinking water use, so this is no small problem.
However, reclaimed water use comes with challenges. Regional wastewater treatment plants differ in their capacity to remove nutrients from effluent. Depending on each plant’s treatment level, nutrient levels in the effluent can vary significantly. Reclaimed water customers are mostly unaware of the nutrient levels in the reclaimed water they use for irrigation. This often leads them to unnecessarily add fertilizer to their landscapes, not knowing that reclaimed water is already enriched with nutrients. This unwitting practice raises the likelihood of excess nutrients entering stormwater conveyances and groundwater. Through these pathways, reclaimed water may exacerbate poor water quality conditions and lead to algae blooms in surface waters like Sarasota Bay. A $24.9 million upgrade to the SWRWRF in early 2017 improved the plant’s ability to remove nitrogen from effluent by more than 40%. Today, total nitrogen levels in the plant’s effluent average less than 8 milligrams per liter. By upgrading the plant’s ability to remove nitrogen, Manatee County reduced the amount of nitrogen that reclaimed water customers applies to their landscapes. Ongoing efforts to educate reclaimed water customers about nutrient levels in the reclaimed supply should further reduce nutrient inputs to surface waters. An innovative pilot project in Lakewood Ranch to reduce nutrients in reclaimed water before delivery to customers is also promising.
Storage capacity is the second major challenge that reclaimed water use poses to surface water quality. In the wet season, there is less demand for reclaimed water as irrigation needs decrease. Yet wastewater still needs to be treated, and utilities must find something to do with it. Under Florida statute, utilities discharging to specific waterbodies in southwest Florida must ensure that the effluent contains an average of less than 3 milligrams of nitrogen per liter and less than 1 milligram per liter of phosphorus. This regulation ensures that wastewater discharges do not add excessive nutrients to protected waterbodies such as Sarasota Bay. In order to avoid discharging treated wastewater that does not meet this standard, wastewater plants must either store their reclaimed water or dispose of it. Water reclamation facilities like SWRWRF have large lakes that store reclaimed water before delivering it to customers. The entire MCUD system has 1.2 billion gallons of capacity for reclaimed water storage.
When storage capacity is reached, usually during the wet season when there is little demand for irrigation, utilities must dispose of the water. In southwest Florida, the most common way to dispose of excess reclaimed water is to inject it underground. The key is to have enough disposal capacity. Without enough disposal capacity, utilities run the risk of discharging to surface waters during wet weather, which may constitute a violation of state statute. In early 2018, MCUD completed construction of a Class V recharge well at the SWRWRF that increased MCUD’s overall disposal capacity by 15 million gallons per day. This well and other recently-completed wells across the MCUD system have eliminated surface water discharges that are attributable to inadequate storage and disposal capacity.
These recent investments in the SWRWRF ensure reclaimed water availability, reduce the impact of reclaimed water use, and improve MCUD’s ability to avoid wastewater discharges. These actions are consistent with managing nutrient load impacts to Sarasota Bay as outlined in SBEP’s Comprehensive Conservation and Management Plan. Continued investment in wastewater treatment, storage, and disposal will help protect Sarasota Bay’s natural resources and water quality into the future.