The STA-1W Algal Turf Scrubber® (ATS) pilot was implemented for the South Florida Water Management District to evaluate attached-algae treatment for additional phosphorus reduction and recovery from Stormwater Treatment Area 1W effluent in the Everglades ecosystem. The pilot was located along the STA-1W effluent canal, west of Cell 5B, and was operated for a full 12-month monitoring period from August 2008 through August 2009.
The STA-1W pilot differed from many other ATS projects because it treated water that had already passed through a large wetland treatment system. The source water therefore had comparatively low phosphorus concentrations, and the project focused not only on phosphorus load reduction, but also on whether ATS treatment, combined with fine solids recovery, could help reduce outflow phosphorus concentrations toward the low levels required for Everglades protection.
Project Summary
Facility: STA-1W Algal Turf Scrubber® Pilot
Location: Stormwater Treatment Area 1W, Palm Beach County, Florida
Technology: Algal Turf Scrubber® / attached-algae floway
Scale: 1200-foot-long by 1-foot-wide pilot floway
Floway Slope: 0.5%
Design Inflow: 29,000 GPD
Influent TN: 2.52 mg/L during the August 13, 2008 to August 13, 2009 pilot monitoring period
Influent TP: 35 µg/L during the August 13, 2008 to August 13, 2009 pilot monitoring period
Status: Pilot testing completed
Operating Period: August 13, 2008 to August 13, 2009
Source Water: STA-1W effluent
Operating Context: Everglades restoration; post-STA treatment; low-phosphorus polishing; phosphorus recovery
Application: Total phosphorus reduction, organic and ortho-phosphorus evaluation, nitrogen assessment, biomass recovery, 10-micron solids recovery simulation, and ATSDEM model verification
Owner / Sponsor: South Florida Water Management District
HydroMentia Role: Pilot system design, floway extension, installation, operation, monitoring, harvesting, phosphorus accountability analysis, 10-micron solids recovery evaluation, ATSDEM calibration and verification, and final performance reporting
Operating Context
Stormwater Treatment Areas are large constructed wetland systems used to reduce phosphorus loads entering the Everglades Protection Area. The STA-1W ATS pilot was developed to evaluate whether ATS technology could provide an additional phosphorus-reduction and nutrient-recovery tool for waters already treated by STA-1W.
The project setting changed the treatment objective. Earlier ATS evaluations often focused on maximizing cost-effective phosphorus load reduction from higher-nutrient waters. At STA-1W, the pilot treated Post-STA effluent, where phosphorus concentrations were already low. As a result, the project placed additional emphasis on achieving the lowest possible outflow phosphorus concentration, with particular attention to the Everglades 10 ppb total phosphorus criterion.
The original pilot concept included a shorter floway, but the project was revised to provide a 1,200-foot-long floway sloped at 0.5%. The longer floway was intended to better evaluate phosphorus concentration reduction and provide field data relevant to a potential full-scale Post-STA ATS polishing facility.
Operational Significance
The STA-1W pilot is significant because it tested ATS technology under one of the most demanding nutrient-polishing conditions evaluated by HydroMentia: treatment of low-phosphorus wetland effluent in the Everglades ecosystem. Rather than treating nutrient-rich agricultural runoff or wastewater, the system was asked to remove additional phosphorus from water already treated by a large-scale wetland treatment system.
This made STA-1W an important boundary-condition project for ATS technology. The pilot evaluated whether a managed attached-algae community could continue to grow, remove nutrients, and recover phosphorus when influent total phosphorus concentrations averaged only tens of micrograms per liter.
The project also tested a critical treatment concept: the use of fine solids recovery as a polishing step after ATS treatment. Because algal turf systems can convert dissolved or biologically available phosphorus into harvested biomass and small suspended organic particles, downstream solids recovery may be important when the treatment goal is the lowest possible effluent phosphorus concentration. The STA-1W pilot therefore evaluated both ATS treatment alone and ATS treatment with simulated 10-micron effluent solids recovery.
The pilot also provided one of the more important datasets for ATSDEM calibration and verification under low-phosphorus field conditions. After calibration, ATSDEM projections for effluent phosphorus concentration, phosphorus areal removal rate, and effluent nitrogen concentration were in close agreement with 12-month field data.
Performance Summary
The STA-1W ATS pilot was operated for 12 consecutive months. The system consisted of a 1,200-foot-long by 1-foot-wide floway, with mean quarterly linear hydraulic loading rates of approximately 18.9, 14.7, 14.5, and 12.9 gpm per linear foot for Quarters 1 through 4, respectively.
For ATS treatment alone, including the start-up period, mean influent total phosphorus concentration was approximately 35 µg/L and mean effluent total phosphorus concentration was approximately 24 µg/L. This represented a total phosphorus concentration reduction of approximately 33.3% over the 12-month project period. The total phosphorus areal removal rate for ATS treatment alone was approximately 3.1 g/m²-year.
The project also evaluated the effect of 10-micron solids recovery by filtering weekly grab samples to simulate the performance of a fine microscreen polishing process. For the 10-micron solids recovery evaluation period, mean influent total phosphorus concentration was approximately 31 µg/L and mean filtered effluent total phosphorus concentration was approximately 15 µg/L. This represented a total phosphorus reduction of approximately 49.9%. The ATS with simulated 10-micron solids recovery achieved outflow total phosphorus concentrations of 10 µg/L or less in 7.9% of weekly samples and 11 µg/L or less in 26.3% of weekly samples.
The 10-micron solids recovery evaluation indicated that a measurable portion of residual effluent phosphorus was associated with fine particulate organic material. This supported the concept that microscreening or a similarly effective fine solids recovery process could be an important final polishing step for Post-STA ATS applications.
Nitrogen was not the primary treatment target for Everglades compliance, but the project also evaluated nitrogen dynamics. Mean influent total nitrogen was approximately 2.52 mg/L and mean effluent total nitrogen was approximately 2.39 mg/L, representing a smaller overall total nitrogen reduction. Nitrogen dynamics were more complex than phosphorus dynamics, with differences between water-quality-based and harvest-based nitrogen calculations suggesting the influence of additional biological processes.
Biomass Harvesting and Solids Recovery
The STA-1W pilot generated a substantial dataset on biomass harvesting, solids content, and nutrient recovery along the length of the 1,200-foot floway. Harvested material was collected and weighed in 300-foot segments to evaluate how productivity and nutrient content changed with distance from the influent surge box.
Periphyton growth was observed within the first week of operation in the upper portion of the floway, and substantial algal turf was observed throughout the monitoring period except where temporary flow interruptions affected the community. Harvested biomass characteristics varied along the length of the floway, with nutrient content generally decreasing downstream as phosphorus concentrations were reduced.
The project also reinforced the importance of harvest frequency and standing crop management. As with other ATS systems, treatment performance depended on maintaining an active algal turf community through periodic biomass recovery, while avoiding excessive standing crop, senescence, tissue sloughing, and solids carryover.
ATSDEM Model Verification
A major purpose of the STA-1W pilot was to verify ATSDEM projections under site-specific Post-STA conditions. The pilot dataset was used to calibrate and verify ATSDEM model parameters related to algal turf productivity, phosphorus uptake, water temperature, linear hydraulic loading rate, standing crop, tissue nutrient content, and effluent nutrient concentrations.
After calibration, the ATSDEM model produced results that were in close agreement with field performance. The model projected a 12-month average effluent total phosphorus concentration of 22 µg/L, compared with 22 µg/L in the field data. The projected phosphorus areal removal rate was 3.34 g/m²-year, compared with 3.43 g/m²-year in the field data. The projected effluent total nitrogen concentration was 2.36 mg/L, compared with 2.37 mg/L in the field data.
This close agreement made STA-1W an important ATSDEM verification project. It demonstrated that field pilot data could be used to refine model assumptions for low-phosphorus applications and support evaluation of potential full-scale ATS polishing systems.
Lessons Learned
The STA-1W pilot demonstrated that ATS treatment can remove and recover phosphorus from low-phosphorus Post-STA effluent. Although areal removal rates were lower than those observed in higher-nutrient waters, the project showed that attached-algae treatment could continue to function under nutrient-polishing conditions.
The project also demonstrated that fine solids recovery can be important when the treatment objective is to minimize outflow total phosphorus concentration. Simulated 10-micron solids recovery substantially improved effluent phosphorus results, suggesting that full-scale Post-STA ATS systems should include an effective final solids recovery or polishing process when very low phosphorus concentrations are required.
From a technology-development perspective, STA-1W was important because it helped define the relationship between ATS treatment, phosphorus accountability, fine particulate organic phosphorus, and model-based design for Everglades applications. The project also provided field verification that ATSDEM could reasonably project performance under low-phosphorus Post-STA conditions.
Photographs
Photographs and figures from the STA-1W ATS pilot show the project location, pilot floway layout, floway cross-section, algal turf development, harvesting activities, 10-micron solids recovery context, and STA-1W / Everglades treatment setting. Additional project photographs may be added as available.
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
The STA-1W ATS pilot is documented in HydroMentia’s final performance report prepared for the South Florida Water Management District.
Technical report: STA-1W Algal Turf Scrubber® Pilot Final Performance Report — August 13, 2008 through August 13, 2009
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 ATS, Egret Marsh ATS, Osprey Marsh ATS, PC-South/Osprey Marsh ATS, Santa Fe ATS, Suwannee River Regional ATS Assessment, Falls Lake ATS, Lake Lawne In-Lake ATS, Powell Creek ATS, NYCDEP Rockaway ATS, Maryland Port Administration Algal Flow-Way, and other full-scale and pilot-scale attached-algae treatment systems.