evaluacion filtrado fosforo lake george & nearby lakes

42 • SEPTEMBER 2008 • FLORIDA WATER RESOURCES JOURNAL

The St. Johns River is the largest river inFlorida, extending from southeast ofOrlando to Jacksonville and the

Atlantic Ocean. The lower St. Johns RiverBasin has exhibited issues associated witheutrophication, which has led to the estab-lishment of a Total Maximum Daily Load(TMDL) for Total Nitrogen (TN) and TotalPhosphorus (TP). Independent of the TMDL

process, the St. Johns River WaterManagement District (SJRWMD, district)has implemented the St. Johns River AlgalInitiative, which will limit the growth andnitrogen fixation from cyanobacteria (blue-green algae) in the river.

Algal initiative planning has determinedthat the TP load needs to be reduced by atleast 84 metric tons per year (MT/Yr) (93

tons per year) from current levels in the St.Johns River Basin (SJRWMD 2006) throughmultiple projects, including TP removal inLake George, which is the largest lake in theriver. To evaluate the feasibility of TP removalin Lake George, the district conducted a com-prehensive review of potentially viable andcost-effective Best Management Practices(BMPs), also referred to as managementmeasures, for reducing TP concentrations inthe lake.

The comprehensive review was the firststep in designing a potentially very largeregional surface water quality facility treating50 to 75 million gallons per day (MGD), or78 to 116 cubic feet per second (cfs). Thisarticle focuses on the results of this reviewand the components that were key to its suc-cessful completion. Each section presents akey component in the review of TP removalin Lake George and nearby lakes.

Project Area& TP Removal Goals

PPrroojjeecctt AArreeaaLake George is Florida’s second-largest

lake, with an area of approximately 73 squaremiles. It is part of the main stem of the St.Johns River north of Astor, as shown in

Methodology, Evaluation, & Feasibility Studyof Total Phosphorus Removal ManagementMeasures in Lake George & Nearby Lakes

Daniel L. Reisinger, Mary Brabham, Michael F. Schmidt, Patrick R. Victor, and Larry Schwartz

Daniel L. Reisinger, E.I., is a water resourcesintern in the Denver, Colorado, office of theconsulting, engineering, construction, andoperations firm CDM. Mary Brabham, P.E., isthe Middle St. Johns River Basin Program man-ager for the St. Johns River WaterManagement District in Altamonte Springs.Michael Schmidt, P.E., BCEE, is a vice presi-dent with CDM in the firm’s Jacksonville office.Larry Schwartz, Ph.D., P.W.S., is a CDM vicepresident in the firm’s Orlando office. PatrickR. Victor, P.E., is a CDM principal in theJacksonville office. This article was presentedas a technical paper at the 2008 FloridaWater Resources Conference in May.

Figure 1. Two large lakes, Lake Dexter andLake Woodruff, are located on a secondarychannel of the river upstream of Lake Georgeand were included in the evaluation of somemanagement measures.

The area surrounding Lake George, LakeDexter, and Lake Woodruff is largely in pub-lic ownership or divided into relatively smallindividual parcels. The district currently co-owns significant conservation lands on theeast shore of Lake George, referred to as theLake George Conservation Area and the NineMile Point area, which are shown as shadedareas in Figure 1. The land uses of the area arepredominately classified as wetlands, silvicul-ture (forested uplands), and agriculture (SJR-WMD 2000).

Lake George is surrounded by sandyhills between 20 and 80 feet NGVD(National Geodetic Vertical Datum of 1929).Stages in Lake George normally rangebetween 0 and 0.5 feet NGVD, but willincrease to two feet NGVD in large flowevents. The lake bottom is relatively uniformwith a mean depth of eight feet and a maxi-mum depth of 12 feet. The soils in the areaare generally hydrologic group B/D or D(poor permeability), except on the westernshore where they are almost entirely A soils(high permeable) (Lewis et al. 1987).

Eleven springs are located in the LakeGeorge tributary area, with three largesprings, Silver Glen, Juniper, and Salt Springs,discharging into Lake George on the westernshore (Stewart et al. 2006). Lake George is notaffected by marine salinity, but it is tidallyaffected and local sources of salinity haveallowed the lake to support a large number ofmarine species. Also shown in Figure 1, thesurrounding area has a large population ofBald Eagles—a threatened species in Floridathat is currently proposed for delisting.

SSuummmmaarryy ooff WWaatteerr QQuuaannttiittyy && QQuuaalliittyyStewart et al. (2006) performed exten-

sive hydraulic modeling of the Lake Georgearea that provides excellent information for aperiod of 1996 through 2004. Measured flowdata was available at the USGS flow gagelocated at the State Road 40 Bridge at Astor(USGS Gage 02236125) from 1994 through

the time of this study, 2007.Regular negative flows were recorded at

the Astor gage. Since treatment will occurregardless of direction, negative flows wereincluded in the possible treatment flow.Summary statistics for the gage as absoluteflows are shown in Table 1.

The nutrient and solids concentrationsare also measured at State Road 40 in Astor(SJRWMD Stations SJR40 and 20020012).The concentrations were found to be relative-ly low: less than 0.08 milligrams per liter(mg/L) of TP, less than 1.4 mg/L of TN, andless than 22 mg/L of Total Suspended Solids.Average seasonal and annual TP and TN con-centrations at Astor are reported in Table 1.These low concentration levels and the vari-ability by season have implications for thetypes of management measures that can beused cost-effectively and for potential effi-ciencies of treatment.

The variability of the water quantity andquality of Lake George provides significant

challenges for the removal of TP. Because ofthe large flow and lower concentration, rela-tively high treatment volumes will probablybe required to remove adequate TP mass. Therelatively low nutrient and solids concentra-tions are expected to be near or below thepractical limit of many standard technologies(e.g. wet detention, wetlands treatment), andinfiltration systems on the permeable soils onthe west side of the lake may cause nitrateimpacts in the springs..

TTPP RReemmoovvaall GGooaallLake George has potential for very large

TP removal facilities. The removal goal of 84MT/Yr was set for the overall St. Johns RiverAlgal Initiative, but the removal goal of indi-vidual projects will be decided based on acomparison of the potential projects in theinitiative. The establishment of a nonbindingTP removal goal was considered important tobe able to compare management measuresusing specific itemized costs.

The effect of phosphorus removal onLake George concentration was estimated byperforming a mass balance at Astor.Removing the total St. Johns River AlgalInitiative goal of 84 MT/Yr, resulting in anaverage annual concentration of 0.053 mg/Lin Lake George, would require at least 900MGD (1,395 cfs) to be treated, as shown inFigure 2. A lesser removal goal of 21 MT/Yr,resulting in an average annual concentrationof 0.072 mg/L in Lake George, would requiretreatment flow of at least 220 MGD (341 cfs).

Table 1 – Water Quantity and Quality in the St. Johns River at Astor, Florida

Figure 2 – Lake George Total Phosphorus Concentration as a Function of TP Removal

Continued on page 44

FLORIDA WATER RESOURCES JOURNAL • SEPTEMBER 2008 • 43

A goal of 5 MT/Yr was chosen by the dis-trict for the study, resulting in an averageannual concentration of 0.076 mg/L in LakeGeorge, which would require between 50 and75 MGD (78 cfs to 116 cfs) of treatment flow.This removal rate was chosen because itwould likely require several treatment unitsto be built, and if a higher goal was later cho-sen, the results could be scaled upward asnecessary.

Evaluation of PotentialManagement Measures

MMaannaaggeemmeenntt MMeeaassuurree RReevviieewwA lake management approach was taken

to determine possible management measuresfor phosphorus removal in Lake George.Using this approach, short-term and long-term measures with offline and in-lake treat-ment were considered.

Possible management measures weredetermined from lake management,stormwater control, and water qualityimprovement literature, relevant experts,and other implemented projects (both suc-cessful and unsuccessful). The U.S.Environmental Protection Agency (EPA)provides comprehensive review of lake andreservoir restoration and management tech-niques (EPA 1990), which was used as astarting point.

Because of the uncommon attributes ofLake George (e.g. large lake, variable flowrates, low inflow concentrations, in-stream,unregulated, and relatively shallow), manymanagement measures were not considered,as discussed with the district, since theyappeared not applicable or infeasible. Thefollowing nine lake management measures

considered applicable to the configurationand constraints of the project area wereevaluated:1. Aquatic plant harvesting (e.g. hydrilla or

water hyacinth)2. Chemical addition (e.g. ballasted floccula-

tion)3. Constructed wetland treatment4. Constructed water hyacinth treatment5. Diversion of water for reuse6. Dredging7. Fish harvesting8. Periphyton flowway treatment (e.g.

HydroMentia Algal Turf Scrubber orAquafiber)

9. Retention/infiltrationEach of the nine management measures

was reviewed for its benefits, challenges, rela-tive costs, relative time to implement, and ref-erences to publications used in order to veri-fy the applicability of the management meas-ure. Approaches that can be integrated for asynergistic benefit were also identified.

MMaannaaggeemmeenntt MMeeaassuurree SSeelleeccttiioonnDistrict and CDM representatives met to

discuss each evaluated management measureand to select three measures for furtherdetailed evaluation. A feasibility study was tobe conducted for each selected managementmeasure, which included the conceptualdesign, TP and TN removal capability, bene-fits, operation, and maintenance require-ments.

The feasibility of each managementmeasure was discussed until a consensus wasreached on whether or not the measure wasappropriate for further study. The majordecision criteria included its technical feasi-bility, cost, and the ability to permit the sys-tem. The three most promising managementmeasures were determined to be:

1. Aquatic plant harvesting2. Chemical addition3. Periphyton flowway treatment

Feasibility Studyof Management Measures

DDeettaaiilleedd PPllaannnniinngg ooff PPootteennttiiaallMMaannaaggeemmeenntt MMeeaassuurree PPrroocceesssseess

Detailed information on the configura-tion, sizing, nutrient removal, and byproductdisposal were determined in the feasibilitystudy. All analyses were performed at a plan-ning level of detail. The following paragraphssummarize each management measure andkey components.

Aquatic Plant Harvesting—Aquaticplant harvesting was considered, usingmechanical harvesters to remove TP and con-trol the population of invasive aquatic plants.Harvesters use a conveyor belt system toremove aquatic plants from the water, asshown in Figure 3. The feasibility study ofthis management measure focused on waterhyacinth, which is the main aquatic plantcontrolled in the Lake George area.

Harvesting was proposed to be themain method of control, with herbicidalspraying, which is the current populationcontrol method, as a secondary measure toassure very low water hyacinth populationsare maintained. Windrow composting in acontained site was found to be the mostfeasible method to dispose of harvestedwater hyacinth. The resulting compostcould be given away or sold, depending ondemand.

This management measure is a depar-ture from existing aquatic plant control inthe lakes; therefore, study efforts focusedon determining a feasible methods for har-

Figure 3 – Mechanical Harvester Removing AquaticPlants (Texas Aquatic Harvesting Inc. 2007)

Figure 4 – Bathymetry of Lake Dexter where DepthsLess than Three Feet Can Not Be Harvested


Continued from page 43



vesting.Large harvesters are limited to operating

in water depths greater than three feet.Bathymetric data for Lake George, LakeDexter, and Lake Woodruff indicate that largeareas of Lake Dexter and a significant portionof the near shore area of Lake George andLake Woodruff are less than three feet indepth, as shown for Lake Dexter in Figure 4.Based on the average standing crop of waterhyacinth, which was estimated from theacreage receiving herbicidal treatment(USACE 2007), no lake would have waterhyacinths at a harvestable depth in an averageyear.

Several methods to remove waterhyacinth from areas with less than two feet ofwater depth were evaluated. The most prom-ising method proposed is to chop thehyacinth using chopping boats to move thechopped material in windrows to deeperwater for harvesting. Chopping boats are typ-ically shallow-draft vessels with large pro-pellers affixed to the bow to chop the plantmaterial. The working area will be containedby turbidity-capturing geotextiles to reduceeffects of the chopping. The benefits of thismethod were provided by Weedbusters Inc.and include the following:� Widely used with proven feasibility.� Increases the efficiency of the harvesting

process.� May allow over five times more water

hyacinth to be collected per harvester.� Does not eliminate most submerged

aquatic vegetation or suspend sediment.The use of chopping boats and har-

vesters was considered feasible and was usedto determine TP removal, TN removal, andcosts.

Chemical Addition—Chemical additionof coagulants to a flow stream and subse-quent settling of formed floc can improvewater quality significantly. These processesare used widely in the water and wastewater

treatment process in controlled facilities.Because of the possibility of treating a largevolume of flow, patented or proprietary sys-tems, which generally reduce the footprint ofthe chemical addition system, were primarilyconsidered.

The ACTIFLO system that usesmicrosand ballast and settling plates toincrease overflow rates (the effective treat-ment system flow) is shown in Figure 5.Implementation of the ACTIFLO process wasevaluated in this study; however, other pro-prietary treatment systems may be equallyeffective.

The actual removal from chemical addi-tion systems can be estimated only by benchand pilot scale tests; therefore, the collectionand testing of a sample to provide an indica-tion of possible removal was the key compo-nent of the chemical addition feasibilityanalysis.

A water sample was taken from the inletof the St. Johns River to Lake George in April2007 and sent to Kruger Inc. for bench scale

ACTIFLO testing and chemical analysis. Atthe time of the testing, the St. Johns Riverwatershed was in drought condition and theriver exhibited low flow. The results from thewater sample indicated TP concentrations of0.064 mg/L, slightly below the seasonal aver-age, and undetectable quantities of ortho-phosphate.

The bench scale testing conducted byKruger Inc. evaluated TP removals associat-ed with various dosages of cationic andanionic polymers, ferric sulfate, and ferricchloride coagulants. The results, presentedin Table 2, show that ACTIFLO ballastedflocculation was able to remove at least 85percent of particulate TP, defined as the dif-ference between TP and dissolved TP, tolimit of detection for the measurementmethod. There were undetectable quantitiesof ortho-phosphate in the water, so one-third removal of ortho-phosphate was usedfor this study.

Periphyton Flowway Treatment—Periphyton flowways are constructed, biolog-ically based treatment systems that pass ashallow flow of water over a sloped mat ofperiphyton. Nutrients are removed from thewater biologically by the periphyton, whichare harvested to remove the nutrients fromthe system and encourage further growth ofthe periphyton.

These systems are differentiated fromperiphyton wetland systems by their flowcharacteristics. Flowways use shallow sheet-flow and higher velocity, although velocitieswould be considered low in most treatmentapplications. Periphyton flowways can beconceptualized as hydroponics-style horti-culture of algae.

Two proprietary periphyton flowwaysystems were evaluated: Aquafiber and

Figure 5 – ACTIFLO 35 MGD Modular Ballasted Flocculation System (Kruger 2007)

Table 2 – Bench Scale ACTIFLO Results for Lake George




HydroMentia. HydroMentia’s Algal TurfScrubber® (ATS) pulses a shallow flow ofwater over a bed of periphyton to removenutrients, which is shown in Figure 5.Included in the process are patented phos-phorus precipitation methods and biomassmanagement techniques.

Aquafiber has developed patented andtrade secret technologies, including a peri-phyton flowway system also using shallowsheet flow. The Aquafiber periphytonflowway system may include patented ozonetreatment to release nutrients bound inorganic matter, eliminate toxic compoundsfound in cyanobacteria, and destroy micro-invertebrates and their eggs.

HydroMentia and Aquafiber wereengaged to provide information for thisstudy. A detailed review of the ATS technolo-gy at Lake George was provided for the feasi-bility study by HydroMentia (Stewart E.A.2007). The report included the facility size,anticipated removal rates, and an estimatedcost per pound of phosphorus removed.

Aquafiber provided a short memoran-dum documenting the likely TP removalfrom a hybrid system of the periphytonflowway system and the company’s patent-pending, trade secret technology (Fagan2007). Aquafiber did not provide a cost esti-mate for this feasibility study.

The technical review of the documentprovided by HydroMentia found the facilitysizing, TP removal methodology, and coststo be reasonable. HydroMentia used the bestavailable data, results from the S-154 ATSfacility, to determine the periphyton growthrate and subsequent TP removal rate; how-ever, it was believed that this value may bedifferent in Lake George because of muchlower TP levels and environmental condi-tions, such as low bio-availability of nutri-ents, lower water temperatures, and solarradiation. Pilot testing was suggested todetermine a more accurate estimate of nutri-

ent removal.The HydroMentia ATS information was

considered to be acceptable and was used torepresent the periphyton flowway manage-ment measure in the feasibility study.

Feasibility StudyResults & Costs

RReessuullttss && CCoosstt ppeerr PPoouunndd ooff TTPP RReemmoovveeddThe conceptual specifications and asso-

ciated cost per pound of TP removed for eachmanagement measure is presented in Table 3.The sizing and TP removal for the feasibilitymanagement measures were based ondetailed planning using the best availableinformation. Each of the management meas-ures were evaluated based on approximately 5MT/Yr per year of TP removed from LakeGeorge and the St. Johns River; however, theexact removal varied by process.

Costs in Table 3 are based itemized costsfor each management measure, includingconceptual probable capital and operationalcost estimates of site preparation, pumps,and piping. Contingencies, engineering, sur-vey, permitting, mobilization, and discountrates were also included. These costs supple-mented the cost of the removal technology.

The cost of land was not included, since themajority of land was in public ownership. Allcosts were based on a 20-year design life andinclude 20 years of operation and mainte-nance.

DDiissccuussssiioonn ooff RReessuullttssEach management measure was evaluat-

ed in terms of feasibility and cost to make arecommendation for further study and ulti-mately, design and implementation.

Aquatic Plant Harvesting was estimatedto cost $240 per pound of TP removed. Thisprocess has a relatively higher level of uncer-tainty compared to the other alternativesbecause of a lack of data on the waterhyacinth population and disposal site condi-tions; therefore, a study of the Lake Dexterand Woodruff water hyacinth populationswas suggested. Harvesting water hyacinth inLake George was not suggested, based on thelong travel times and low density of waterhyacinths in the lake.

Chemical Addition using ACTIFLOcould provide high levels of TP removal on asmall footprint at an estimated cost of $350per pound of TP removed. It was recommend-ed that the ACTIFLO technology be consid-ered at sites other than Lake George, whichwould benefit from the ACTIFLO’s small foot-print. It was recommended that pilot testing ofboth the ACTIFLO system and potentialdewatering equipment be performed to betterdetermine phosphorus removal and operationand maintenance costs at a site near existingcommercial or industrial land uses.

Periphyton Flowway Treatment usingHydroMentia’s ATS provides relatively highlevels of phosphorus removal, and generatesa marketable byproduct (compost) at an esti-mated cost of $240 per pound of TPremoved. It was recommended that theAquafiber technologies also be considered forpilot testing

Figure 6 –HydroMentiaATS S-154

Basin Facility inOkeechobeeCounty, FL

(Stewart, E.A.2007)

Table 3 – Summary of Management Measure Sizing and Costs




Recommendations forFurther Planning & Design

Three management measures listed inTable 3 are recommended for further studythrough pilot testing:1. The harvest of water hyacinths should be

pilot tested in Lake Dexter.2. Periphyton flowway treatment should be

pilot tested in the vicinity of Lake George.3. ACTIFLO should be pilot tested in a pre-

dominantly industrial or commercial area.Because of the water quality fluctuations in

Lake George, pilot studies should be performedfor a period of at least one year to evaluate a fullrange of water quality and flow conditions. Thethree management measures are modular andcomplementary; therefore, they can be usedtogether if desired for additional removal.

References

• St. Johns River Water Management District(SJRWMD). 2006b. Lake George PRemoval Project MSJRB St. Johns RiverNutrient Discharge Reduction WBS2.3.30.00.08 (part of the SJR AlgalInitiative) Charter Document – 11/9/2006.

• St. Johns River Water Management District(SJRWMD). 2000. Elevation: SJRWMD 5

FT Contour (Line). Palatka, FL. St. John’sRiver Water Management District.http://www.sjrwmd.com/programs/plan_monitor/gis/docs/metadata/elev_5ft.htm

• Lewis et al. 1987. Soil Survey ofOkeechobee County, FL. Electronic Report.http://soildatamart.nrcs.usda.gov/Manuscripts/FL093/0/fl_okeechobee.pdf. AccessedFebruary 2007.

• Stewart, Joseph B., Sucsey, Peter, andHendrickson, John. “Meteorological factorsaffecting estuarine conditions within LakeGeorge in the St. Johns River, Florida”.Proceedings of the Seventh InternationalConference on Hydroscience andEngineering. Philadelphia, PA. September2006. http://hdl.handle.net/1860/732

• Hendrickson, J.C. and J. Konwinski. 1998.Seasonal Nutrient Import-Export Budgetsfor the Lower St. Johns River, Florida. FinalReport for Contract WM598, FloridaDepartment of Environmental Protection.109 pp.

• United States Environmental ProtectionAgency (EPA). 1990. “Lake and ReservoirRestoration Guidance Manual, SecondEdition.” Publication # 440490006,Electronic, NTIS # PB93-207926.

• United States Army Corps of Engineer(USACE). 2007. Unclassified Acreage,Herbicide Usage, and Man Hours for

Herbicidal Spraying of Lake George, LakeDexter, and Lake Woodruff, FL. ElectronicCommunication March 2007.

• Camp Dresser & McKee (CDM). 1999.“Renaissance Jar Testing.” Submitted to Mr.Jeff Hiscock of Mock Roos & Associates.

• Stewart, E.A. 2007. “PreliminaryEngineering Assessment for the Applicationof an Algal Turf Scrubber (ATS) forReduction of Nitrogen and PhosphorusLoads into Lake George, Florida.” Preparedby HydroMentia for SJRWMD: Ocala, FL.

• Fagan, William B. 2007. AquafiberApplication to Lake George. Letter to Mr.Daniel Reisinger of CDM. June 15, 2007. ��


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