The Powell Creek Algal Turf Scrubber® (ATS) pilot was implemented for Lee County, Florida, to evaluate attached-algae treatment for nutrient reduction and recovery from surface waters associated with the Powell Creek By-Pass Canal in North Fort Myers. The pilot was located near the Caloosahatchee River / Estuary, where source-water conditions were influenced by both urban stormwater runoff and tidal exchange with estuarine waters.
The Powell Creek pilot was unique because the source water changed substantially over daily and seasonal cycles. During low-tide and runoff-dominated periods, the system treated freshwater stormwater runoff from the surrounding urban watershed. As tides rose, estuarine water backed into the canal and introduced brackish or saline conditions to the ATS floway. The pilot therefore provided important data on ATS performance under euryhaline conditions, where conductivity and salinity varied widely over time.
The pilot evaluated attached-algae treatment under source-water conditions influenced by both stormwater runoff and tidal exchange with the Caloosahatchee Estuary.
Project Summary
Facility: Powell Creek Algal Turf Scrubber® Pilot
Location: North Fort Myers, Lee County, Florida
Technology: Algal Turf Scrubber® / attached-algae floway
Scale: 500-foot-long by 1-foot-wide pilot floway
Floway Slope: 1.0%
Design Inflow: 28,000 GPD
Influent TN: 0.95 mg/L during the December 4, 2008 to December 10, 2009 monitoring period
Influent TP: 139 µg/L during the December 4, 2008 to December 10, 2009 monitoring period
Status: Pilot testing completed
Operating Period: October 25, 2008 to December 10, 2009
Status: Pilot testing completed
Source Water: Powell Creek By-Pass Canal
Operating Context: Urban stormwater runoff; tidal backwater influence; Caloosahatchee River / Estuary watershed; euryhaline source-water conditions
Application: Total phosphorus reduction, nitrogen reduction, biomass recovery, conductivity/salinity response evaluation, and full-scale ATS performance projection
Owner / Sponsor: Lee County, Florida
HydroMentia Role: Pilot system design, installation, operation, monitoring, harvesting, data evaluation, ATSDEM modeling, full-scale performance projection, and final reporting
Operating Context
The Powell Creek ATS pilot was located on the west bank of the Powell Creek By-Pass Canal on Lee County right-of-way property in North Fort Myers. The pilot intake was located upstream of the Caloosahatchee River / Estuary confluence, where source-water quality was affected by watershed runoff, tidal exchange, seasonal rainfall patterns, and estuarine backwater movement.
This operating setting made Powell Creek different from many earlier ATS pilots. Rather than treating a relatively consistent freshwater source, the system received water that shifted between freshwater stormwater runoff and brackish or estuarine conditions. Conductivity varied both seasonally and over shorter tidal cycles. These conditions provided an opportunity to evaluate whether ATS treatment could sustain algal turf development and nutrient removal under large and recurring changes in salinity.
The pilot was operated for a full annual period from December 2008 through December 2009. This longer duration was important because it allowed evaluation across seasonal changes in rainfall, temperature, runoff, conductivity, nutrient concentrations, and biological community development.
Operational Significance
The Powell Creek pilot is significant because it demonstrated ATS operation under tidal-influenced, euryhaline source-water conditions. The facility tested whether a managed attached-algae system could maintain treatment function when source water alternated between freshwater urban runoff and estuarine backwater influence.
This was an important boundary-condition test for ATS technology. The algal turf community had to respond not only to changes in nutrient concentration and seasonal temperature, but also to repeated conductivity shifts associated with tidal exchange and stormwater dilution. The pilot therefore provided data relevant to estuarine tributaries, coastal stormwater systems, tidal canals, and urban watersheds where salinity is not constant.
The final report indicated that conductivity varied widely over the operating period, but there was no clear evidence that conductivity changes alone caused a sustained deleterious effect on overall system performance. This finding was important because it suggested that ATS systems could potentially be applied in tidal or brackish settings, provided that full-scale design and operations account for tidal hydraulics, salinity variability, biofouling, and source-water management.
The project also reinforced the importance of communication between watershed maintenance activities and biological treatment system operation. Lee County applied glyphosate within the watershed on several occasions during the operating period. The report did not identify clear evidence that those applications significantly affected algal turf productivity, but it recommended coordination with system operators when herbicide applications are planned near a treatment-system intake.
Performance Summary
The Powell Creek pilot was operated at a linear hydraulic loading rate of approximately 18 gpm per linear foot of floway width, resulting in a mean flow of approximately 25,728 gallons per day. The system operated as a 500-foot-long by 1-foot-wide mobile pilot floway, with pulsed flow delivered from a surger at the head of the floway.
During the annual monitoring period, the average total phosphorus areal removal rate was approximately 19.80 g/m²-year based on influent/effluent water-quality calculations. When phosphorus removal was calculated from harvested algal biomass, the areal removal rate was approximately 20.80 g/m²-year. The close agreement between water-quality-based and harvest-based phosphorus calculations indicated strong phosphorus accountability for the Powell Creek pilot.
Mean influent total phosphorus concentration was approximately 139 ppb, with mean effluent total phosphorus concentration of approximately 110 ppb. Total phosphorus mass removal was approximately 19% based on water-quality calculations. Ortho-phosphorus, the more directly biologically available form, represented a large portion of the incoming phosphorus load and was removed at a higher percentage than total phosphorus.
For nitrogen, mean influent total nitrogen concentration was approximately 0.95 mg/L, with mean effluent total nitrogen concentration of approximately 0.87 mg/L. The water-quality-based total nitrogen areal removal rate was approximately 46.75 g/m²-year, while the harvest-based nitrogen recovery estimate was approximately 71.37 g/m²-year. The difference between those estimates suggested that nitrogen dynamics were affected by additional processes, likely including nitrogen fixation within the algal turf community.
The system was harvested 28 times during the monitoring period. Total wet harvest was approximately 5,078 pounds, with an estimated dry harvest of approximately 411 pounds. The harvested biomass averaged approximately 0.55% phosphorus and 1.90% nitrogen on a dry-weight basis.
Full-Scale Projection
The Powell Creek final report used pilot performance data to calibrate and verify ATSDEM model projections for full-scale implementation. The modeling evaluated a potential 6.2-acre ATS facility on Lee County property contiguous to the Powell Creek By-Pass Canal.
Based on ATSDEM projections, a 6.2-acre full-scale Powell Creek ATS facility was projected to remove approximately 1,118 pounds of phosphorus per year and approximately 4,125 pounds of nitrogen per year from the Powell Creek / Caloosahatchee River system.
The report also projected that biomass harvested from the 6.2-acre facility would total approximately 1,218 wet tons per year, with an estimated annual yield of approximately 122 tons of compost. Initial biomass management concepts included windrow composting, with potential future evaluation of additional biomass uses.
Lessons Learned
The Powell Creek pilot demonstrated that ATS treatment can be evaluated and operated under complex tidal-influenced source-water conditions. The system maintained algal turf development and measurable nutrient removal even though conductivity and salinity varied widely across daily and seasonal cycles.
The project also showed the value of full-year pilot testing. Because the source water was affected by seasonal rainfall, tidal exchange, runoff conditions, and estuarine backwater movement, a shorter pilot would not have provided a complete picture of system behavior. The full annual operating period allowed Powell Creek performance to be evaluated across a broad range of environmental conditions.
From a technology-development perspective, Powell Creek helped expand ATS experience beyond freshwater agricultural and lake-water applications. The project provided evidence that coastal and estuarine tributary systems may be suitable for ATS application, but that full-scale design must account for tidal water-level changes, conductivity variability, pumping hydraulics, biofouling, seasonal runoff, and coordination with watershed maintenance practices.
Photographs
Photographs of the Powell Creek ATS pilot show the mobile pilot floway, Powell Creek By-Pass Canal source-water setting, pulsed-flow operation, algal turf development, harvesting activities, and monitoring infrastructure.
Additional photos included in Powell Creek Final Report_Appendix B.
View Powell Creek 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
The Powell Creek ATS pilot is documented in HydroMentia’s final report prepared for Lee County, Florida.
Technical report: Powell Creek Algal Turf Scrubber® Pilot Final Report — December 4, 2008 through December 10, 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 Lake Lawne In-Lake ATS, Santa Fe ATS, Suwannee River Regional ATS Assessment, Falls Lake ATS, S-154 ATS, Egret Marsh ATS, Osprey Marsh ATS, PC-South/Osprey Marsh ATS, NYCDEP Rockaway ATS, Maryland Port Administration Algal Flow-Way, and other full-scale and pilot-scale attached-algae treatment systems.