Dealing with discharges: How Sarasota County works to protect water quality
The first approaching storm of the 2020 hurricane season could mean trouble for the state’s wastewater treatment plants. The Bee Ridge Water Reclamation Facility (WRF) in Sarasota County has been a concern. The plant has dealt with the issue of stormwater inflows during the rainy season, leading to discharges into local waterbodies. Though this has never been intentional, the lack of capacity to take on the additional load from rain events has made it a recurring problem. A long-term plan has been created to enhance the capacity of the Bee Ridge WRF so that overflows are an issue of the past. The plan, available on Sarasota County Government’s website, details some of the main changes coming to the plant by 2025.
We sat down with David Sell, Sarasota County’s Facilities and Lift Stations Operations Manager, to get the latest updates on the facility’s ongoing improvements.
Bee Ridge WRF discharges
Question: There are some misconceptions that the water discharged at the Bee Ridge WRF is sewage, but it is not. What exactly is the water?
We treat about 7 million gallons at the Bee Ridge plant during a normal day. Our flow went up to about 11 million a day during this last rainy period*. So we get about a third more rainwater that comes in during the rainy season. The water that is discharged is a mixture of rain and treated wastewater or reclaimed water.
*David was referring to the 10 inches of rain we received over the first 6 days of June.
Question: Wow, that is a lot of rainwater coming into the system. Once the system is overwhelmed where does the water go?
Since 2013, when we have gotten too much flow and we couldn’t get rid of the reclaimed water, the pond at the Bee Ridge Plant fills up and discharges through an overflow structure and into a wetlands area, which eventually flows through Phillippi Creek (Figure 1). We’re not permitted to do that. We’re not supposed to do that, but if there’s nowhere for the water to go that’s what happens.
Question: We understand that two new deep wells are being created to help keep water from moving off-site. When will this be complete?
March of 2021. Each of the deep wells will take 18 million gallons a day. So, that’s a total of 36 million gallons a day we could put down those two deep wells. The total capacity of the plant will be 18 million gallons a day. So the theory is there’s enough capacity to have all the wastewater we treat plus the 30% additional rainwater to be placed down one well. The second well then will just be for backup.
Nutrients in the discharged water
Question: There was a lot of concern over the nutrient load in the wastewater. Are there folks who monitor the nutrient levels being discharged when this occurs?
We monitor nutrients in the plant all the time. When water goes over the overflow structure, we monitor at the weir where it’s going over and we go downstream in one of the drainage canals. We take samples right by the corner of McIntosh and Bahia Vista, where the water flows under the bridge. We monitor the water there, which is probably a couple miles downstream from where it enters the system. We take samples there three times a week during these periods of overflow.
Question: What is the range of the nutrient levels being discharged due to flooding?
Total nitrogen leaving the plant on a normal day is around 12 milligrams per liter (mg/L). Typically, when we measure it downstream, we get around 2 milligrams per liter (mg/L).
(Note: this exceeds the 1.65 mg/L threshold as stated in the for streams in West Central Florida. However, currently the segment where the Bee Ridge WRF discharges is not impaired for nutrients. Although the northern segment of Phillippi Creek, which Bee Ridge WRF does not directly discharge, has been impaired for nutrients.)
Solutions to the problem
Question: Is Sarasota County doing anything right now to address the concerns of high total nitrogen discharges to surface waters?
We did a pilot test to remove some nutrients and reduce the total nitrogen in our treated wastewater. It doesn’t bring it to AWT standards (3 mg/L), but it reduces the nutrients. The pilot seems to be going well. So, we’ll do temporary improvements before we get to the complete AWT process to lower the nutrients in the water.
Question: Can you tell us more about this pilot project?
It’s an improvement to the biological process we currently use. Essentially, we are adding recycle pumps and a basin to retreat the water. The process is called Modified Ludzack-Ettinger (MLE). Through MLE an anoxic (or oxygen-free) basin is added to complete the nitrogen cycle (Figure 2). In the anoxic basin, microorganisms use the oxygen from nitrate (NO3–) reducing it to nitrate (NO2–) and further to N2 and N2O gas (Figure 3). The gas goes into the air completely removing nitrogen from the water.
Question: MLE is currently in use or it’s going to be in use?
It is currently in use in one of the basins at the plant. This basin was a part of the pilot test to make sure it would work before we put it into all of our basins. Our pilot shows positive results, it seems to be working well in that one basin. There will be a project to put it in the rest of the basins.
Question: Tell us about the changes to total nitrogen (TN)?
Total nitrogen coming out of the other basins runs about 12 milligrams per liter (mg/L). Coming out of the pilot basin is running around 5 milligrams per liter (mg/L).
By the end of 2025, the Bee Ridge Water Reclamation Facility will move to Advanced Wastewater Treatment (AWT), a process that further removes nutrients from treated water. Treated wastewater will contain nitrogen at 3 mg/L or less when the treatment process is enhanced to AWT standards. If you would like to learn more about Advanced Wasterwater Treatment (AWT) then check out our blog on Advanced wastewater treatment (AWT).
Thank you, David, for taking the time to talk to us. The plan for improvement sounds robust and we look forward to seeing the designs for the new AWT plant and the completion of these projects.
Author’s notes: David’s conviction for making things better was apparent. That really goes for everyone that I have met at Sarasota County’s wastewater treatment facilities — genuine people working really hard to ensure quality disposal of a product that everyone creates but no one really wants to think about.