The S-154 Algal Turf Scrubber® (ATS) single-pass demonstration was conducted in the Lake Okeechobee Watershed for the South Florida Water Management District to evaluate ATS treatment as a stand-alone load-reduction process. The project followed the earlier S-154 WHS-ATS demonstration and was designed to isolate ATS performance under single-pass operation using source water pumped directly from the L-62 Canal.
The project used three parallel ATS floways operated at different linear hydraulic loading rates. This allowed HydroMentia to evaluate the relationship between hydraulic loading, phosphorus loading, and nutrient load reduction under comparable source-water and environmental conditions. The results helped establish the importance of linear hydraulic loading rate in ATS design and influenced later HydroMentia floway designs.
Project Summary
Facility: S-154 ATS Demonstration
Location: S-154 basin / L-62 Canal, Lake Okeechobee Watershed, Florida
Technology: Algal Turf Scrubber® / attached-algae floway
Scale: Three (3) independent floways, each 300-foot-long by 5-foot-wide
Floway Slope: 1.5%
Average Inflow: approximately 34,000 GPD to the South floway; approximately 62,000 GPD to the North floway; approximately 136,000 GPD to the Central floway
Influent TN: 1.85 mg/L during the May 11, 2004 to December 5, 2004 monitoring period
Influent TP: 333-336 µg/L during the May 11, 2004 to December 5, 2004 monitoring period
Status: Demonstration completed
Operating Period: May 11, 2004 to December 5, 2004
Source Water: L-62 Canal / S-154 basin runoff
Operating Context: Lake Okeechobee Watershed phosphorus source-control demonstration; single-pass ATS operation; phosphorus load-reduction optimization; linear hydraulic loading rate evaluation
Application: Phosphorus and nitrogen load reduction, attached-algae biomass production, hydraulic-loading comparison, harvest-based nutrient recovery, and ATS design model development
Operating Context
The S-154 ATS demonstration was developed during the operation of the two-stage S-154 WHS-ATS system. In developing the two-stage WHS-ATS, initial emphasis had been on reducing effluent phosphorus concentrations toward the Lake Okeechobee 40 ppb target. As the Lake Okeechobee Watershed program increasingly emphasized pollutant load reduction and treatment cost, HydroMentia proposed a separate single-pass ATS study to evaluate phosphorus removal as a function of hydraulic loading and nutrient loading.
Three ATS floways were isolated from the existing S-154 ATS infrastructure on the 1.5% sloped floway. Each floway received water directly from the L-62 Canal, rather than receiving water after water hyacinth pretreatment. The floways were operated in parallel so that source-water quality, slope, climate, and operating environment were generally comparable. The principal intentional difference among the flowways was linear hydraulic loading rate.
The South floway was operated at the lowest loading rate, the North floway at an intermediate loading rate, and the Central floway at the highest loading rate. This created a direct comparison of ATS performance across a range of hydraulic loading conditions.
Hydraulic Loading Comparison
The three single-pass ATS flowways were each approximately 5 feet wide and about 300 feet long, with the North floway slightly longer because of site conditions. During the adjusted period of record, the South floway operated at an average linear hydraulic loading rate of approximately 4.7 gpm/lf. The North flowway operated at approximately 8.5 gpm/lf. The Central flowway operated at approximately 18.8 gpm/lf.
Because all three flowways received the same source water and operated under the same general environmental conditions, the comparison provided a useful field-scale evaluation of the relationship between LHLR and nutrient-removal performance.
Performance Summary
The single-pass S-154 ATS demonstration showed that higher linear hydraulic loading substantially increased areal nutrient load reduction.
The South floway, operated at the lowest LHLR of approximately 4.7 gpm/lf, received influent total phosphorus averaging approximately 336 µg/L and reduced effluent total phosphorus to approximately 250 µg/L. The mean phosphorus areal removal rate was approximately 25 g/m²-year.
The North floway, operated at an intermediate LHLR of approximately 8.5 gpm/lf, received influent total phosphorus averaging approximately 336 µg/L and reduced effluent total phosphorus to approximately 249 µg/L. The mean phosphorus areal removal rate was approximately 47 g/m²-year.
The Central floway, operated at the highest LHLR of approximately 18.8 gpm/lf, received influent total phosphorus averaging approximately 333 µg/L and reduced effluent total phosphorus to approximately 258 µg/L. The mean phosphorus areal removal rate was approximately 92 g/m²-year.
Although percent phosphorus removal was similar among the three flowways, the higher hydraulic and nutrient loading applied to the Central floway produced substantially greater phosphorus mass removal per unit area. This distinction was important because the project objective was pollutant load reduction, not simply the lowest effluent concentration.
Nitrogen removal showed a similar pattern. The South, North, and Central flowways removed total nitrogen at approximately 181, 332, and 722 g/m²-year, respectively. As with phosphorus, the highest-loaded floway produced the greatest areal load reduction.
Operational Significance
The S-154 ATS demonstration was one of the most important early HydroMentia studies for defining the role of linear hydraulic loading rate in ATS performance. The project showed that, within the tested range, higher LHLR increased nutrient load reduction even though effluent concentrations did not decline proportionally.
This result helped clarify a key ATS design principle: for load-reduction applications, treatment effectiveness should be evaluated using areal nutrient removal rates and total mass removal, not only effluent concentration or percent reduction. A system operated at higher hydraulic loading may produce similar percent removal while removing more phosphorus and nitrogen per unit of treatment area.
The project also helped move HydroMentia’s design approach away from very low-flow concentration-polishing assumptions and toward higher-flow ATS operation for watershed-scale load reduction. This design lesson influenced later ATS projects where linear hydraulic loading rates of approximately 20 gpm/lf or higher became a central design consideration.
Biomass Production and Nutrient Recovery
The S-154 ATS flowways produced attached algal biomass that was harvested periodically by hand. The algal community was dominated by filamentous green algae, including Cladophora, Hydrodictyon, and Rhizoclonium, with associated diatoms.
Measured algal production during the adjusted period of record was approximately 11.7 dry g/m²-day for the South floway, 11.9 dry g/m²-day for the North floway, and 14.2 dry g/m²-day for the Central floway. The Central floway, which operated at the highest LHLR, had the highest measured biomass production and the highest nutrient areal removal rates.
The project also evaluated nutrient accountability in harvested biomass. Phosphorus accountability through harvested biomass was strongest in the lowest-loaded South floway and lower in the higher-loaded flowways. The report identified harvest-induced sloughing and uncollected fine solids as possible contributors to differences between nutrient removal calculated from water quality and nutrient recovery measured in harvested biomass.
Design Lessons
The S-154 ATS demonstration provided several important design lessons for later ATS applications.
Linear hydraulic loading rate is a critical design variable for ATS load-reduction systems.
Higher LHLR can substantially increase phosphorus and nitrogen load removal per unit area.
Percent removal and effluent concentration should not be interpreted without considering hydraulic loading, nutrient loading, and areal removal rate.
Single-pass operation avoids the elevated-pH and reduced-carbon limitations associated with immediate recycle of ATS effluent.
Harvesting and solids recovery need to account for both captured biomass and fine solids or sloughed material that may escape during or after harvest.
The project helped support development of ATS design modeling by providing field data across three different hydraulic-loading conditions under similar source-water and environmental conditions.
Photographs
S-154 ATS single-pass demonstration flowways in the Lake Okeechobee Watershed. Three parallel 5′ wide ATS flowways were operated on the 1.5% slope at different linear hydraulic loading rates to evaluate phosphorus and nitrogen load reduction from L-62 Canal / S-154 basin runoff.
Reports and Publications
Technical report: S-154 Pilot Single Stage Algal Turf Scrubber® Final Report — March 2005
The 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 time-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 WHS-ATS, Egret Marsh ATS, Osprey Marsh ATS, STA-1W ATS, and other full-scale and pilot-scale systems.