The S-154 WHS-ATS demonstration was conducted in the Lake Okeechobee Watershed for the South Florida Water Management District to evaluate a two-stage managed aquatic plant treatment system for phosphorus reduction from S-154 basin runoff. The facility combined a Water Hyacinth Scrubber (WHS) system as the first treatment stage, followed by Algal Turf Scrubber® treatment as the second stage.
The project was operated under two distinct objectives. During the initial concentration-reduction phase, the system was operated to evaluate whether the combined WHS-ATS process could reduce total phosphorus concentrations toward the Lake Okeechobee 40 ppb target. During this period, ATS effluent was recycled back to the ATS influent to increase hydraulic loading and treatment contact within the available ATS floway length. The project later shifted to load-reduction optimization, with higher external inflow, reduced treatment surface area, and elimination of ATS recycle.
Project Summary
Facility: S-154 WHS-ATS Demonstration
Location: S-154 basin / L-62 Canal, Lake Okeechobee Watershed, Florida
Technology: Water Hyacinth Scrubber followed by Algal Turf Scrubber® treatment
Scale: WHS: Two (2) cells at 1.25 acres each (2.5 acres total) at mean depth 3.5 feet; ATS: Two (2) floways at 300-foot-long by 182-foot-wide each (2.5 acres total)
Floway Slope: 1.5% and 2.0%
Average Inflow: approximately 0.43 MGD during concentration-reduction operation; approximately 0.84 MGD during load-reduction operation
Design Inflow: 500,000 GPD
Design ATS Recycle: 4.6 MGD
Influent TN: approximately 2.36 mg/L during concentration-reduction operation; approximately 1.86 mg/L during load-reduction operation
Influent TP: approximately 476 µg/L during concentration-reduction operation; approximately 279 µg/L during load-reduction operation
Status: Demonstration completed
Operating Period: 2003–2004
Source Water: L-62 Canal / S-154 basin runoff
Operating Context: Lake Okeechobee Watershed phosphorus source-control demonstration; concentration reduction; load-reduction optimization; evaluation of WHS-ATS process sequencing
Application: Phosphorus and nitrogen reduction, biomass harvesting, process optimization, hydraulic-loading evaluation, and design support for future managed aquatic plant treatment systems
Operating Context
Lake Okeechobee had been identified as an impaired water body, with excessive phosphorus loading recognized as one of the major threats to lake water quality. The S-154 basin, draining through the L-62 Canal, was part of the broader Lake Okeechobee Watershed source-control effort. The S-154 WHS-ATS demonstration was implemented to evaluate whether managed aquatic plant systems could provide cost-effective nutrient reduction from agricultural and basin runoff waters.
The facility used two biological treatment processes in series. The first stage consisted of two 1.25-acre water hyacinth treatment units operating in parallel. These units cultivated water hyacinths for nutrient uptake and biomass harvest. The second stage consisted of two 1.25-acre ATS floways, with 1.5% and 2.0% slope, that received water from the WHS units. The ATS floways used shallow pulsed flow across sloped, lined treatment surfaces supporting attached algal turf growth. Periodic biomass removal provided the physical mechanism for long-term nutrient recovery.
The original operational objective emphasized effluent concentration reduction. The target was influenced by the Lake Okeechobee 40 ppb total phosphorus concentration goal. Because the available ATS floway length was limited, ATS recycle was used during the early phase to increase hydraulic loading and treatment exposure across the ATS surface.
Operational Phases
The project is best understood as two operating phases.
During the concentration-reduction phase, from January 27, 2003 to November 3, 2003, the system was operated to reduce effluent total phosphorus concentrations. The two-stage system received approximately 117.47 million gallons of L-62 Canal water during this period, with an average external inflow of approximately 0.43 MGD. Influent total phosphorus averaged approximately 476 µg/L, and influent total nitrogen averaged approximately 2.36 mg/L.
During this phase, a major portion of ATS effluent was recycled back to the ATS influent. This approach increased hydraulic loading and flow energy across the ATS surface, but it also created an important design limitation. Immediate recycle of ATS effluent returned water that had already been exposed to photosynthetic carbon uptake. As a result, recycled water could enter the ATS with elevated pH and reduced carbon availability, affecting algal productivity and demonstrating that hydraulic energy and carbon chemistry must be considered together.
During the load-reduction optimization phase, from November 2003 through October 2004, the operating objective shifted from achieving the lowest effluent concentration to maximizing nutrient load removal. External inflow was increased, the active treatment area was reduced, and ATS recycle was eliminated. During this phase, average external inflow was approximately 0.84 MGD, influent total phosphorus averaged approximately 279 µg/L, and influent total nitrogen averaged approximately 1.86 mg/L.
This second operating phase helped show that nutrient-removal performance depended strongly on hydraulic loading, nutrient loading, process area, and operating objective. It also provided the technical basis for evaluating ATS as a stand-alone load-reduction process, which led directly to the separate S-154 ATS single-stage floway study.
Performance Summary
During the concentration-reduction phase, the S-154 WHS-ATS system reduced total phosphorus from a flow-weighted mean influent concentration of approximately 476 µg/L to a mean effluent concentration of approximately 79 µg/L. Total phosphorus removal averaged approximately 84 percent during this period. The system did not consistently achieve the 40 ppb target, but it produced substantial concentration reduction from a relatively high-phosphorus surface-water source.
During the load-reduction phase, the system was operated at higher hydraulic loading and with reduced process area. Influent total phosphorus averaged approximately 279 µg/L, and effluent total phosphorus averaged approximately 167 µg/L. Total phosphorus removal averaged approximately 47 percent, while the areal phosphorus removal rate increased compared with the concentration-reduction phase.
The results demonstrated an important distinction between optimizing for effluent concentration and optimizing for pollutant load removal. Lower effluent concentrations required longer exposure and more conservative loading, while higher load reduction favored increased hydraulic and nutrient loading within the limits of the biological system.
Nitrogen dynamics were more complex because the L-62 Canal water had a low nitrogen-to-phosphorus ratio, and nitrogen was supplemented during portions of the project to support phosphorus uptake and aquatic plant productivity. The system increased the nitrogen-to-phosphorus ratio in the effluent and also improved dissolved oxygen concentrations.
Operational Significance
The S-154 WHS-ATS demonstration was significant because it documented both the value and limitations of a two-stage managed aquatic plant treatment train. The WHS front end provided substantial nutrient removal, while the ATS stage provided additional polishing, organic phosphorus treatment, dissolved oxygen improvement, and biomass recovery.
The project also produced one of the most important ATS design lessons from the early Lake Okeechobee work: recycle can increase hydraulic loading and treatment exposure, but immediate recycle of ATS effluent can also return elevated-pH, carbon-depleted water to the ATS inflow. Under those conditions, carbon availability can become limiting even where nutrient concentrations remain adequate.
The later shift to load-reduction optimization helped redirect design thinking away from simply achieving the lowest effluent concentration and toward optimizing areal nutrient removal, hydraulic loading, and treatment cost. That shift directly supported the subsequent S-154 ATS single-stage study, where three independent ATS flowways were operated in parallel at different linear hydraulic loading rates.
Lessons Learned
The S-154 WHS-ATS project showed that process objectives must be clearly defined before performance is interpreted. The same facility produced different results depending on whether it was operated for concentration reduction or load reduction.
The project also demonstrated that the volume of water entering the treatment facility and the volume of water moving across the ATS surface were not the same during the recycle phase. External inflow from the L-62 Canal defines the facility treatment rate, while ATS recycle increased internal hydraulic loading across the ATS floway.
For future ATS designs, the project supported several key lessons:
Recycle should be used cautiously where photosynthetic carbon uptake can elevate pH and reduce carbon availability.
Load-reduction optimization may require higher hydraulic loading and different treatment-area assumptions than concentration-polishing operation.
WHS and ATS unit processes should not be compared only by total mass removal without accounting for where each process sits in the treatment train and the nutrient load each process receives.
ATS performance should be evaluated in relation to linear hydraulic loading rate, influent nutrient concentration, carbon availability, pH, and harvestable biomass recovery.
Photographs
View S-154 WHS-ATS photo gallery
Additional facility photographs are available in HydroMentia’s Facebook photo archive. Facebook may require visitors to sign in to view the complete gallery.
Reports and Publications
Technical report: S-154 Pilot WHS-ATS Aquatic Plant Treatment System Final Report — 2005
The linked report was prepared as formal project technical documentation under an approved Quality Assurance / Quality Control plan and was submitted to the sponsoring agency for technical review, comment, revision, and final acceptance.
Influent and effluent water quality monitoring used automated composite samplers operated on a flow-weighted interval basis. Analyses included total nitrogen, total phosphorus, and individual nitrogen and phosphorus species, providing a robust basis for evaluating ATS performance.
Additional reports and publications related to Algal Turf Scrubber® technology and facility-scale applications are available in HydroMentia’s ATS Library.
Related Projects
Related HydroMentia ATS facilities and demonstrations include S-154 ATS, Egret Marsh ATS, Osprey Marsh ATS, STA-1W ATS, and other full-scale and pilot-scale systems.