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Algae Removal from a Facultative Lagoon System Using Dissolved Air Flotation

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Algae Removal from a Facultative Lagoon System Using Dissolved Air Flotation Algae Removal from a Facultative Lagoon System Using Dissolved Air Flotation J. Patrick Pierce, P.E. Environmental Treatment Systems, Inc. Facultative Lagoon System • Designed for 1.5 MGD • Discharging 1.15-1.35 MGD • Serving a population of 15,000 Site Prior to DAF Installation A) Control Building for Lift Station Pumps B) Gaseous chlorine and sodium bi-sulfite building C) Chlorination/de-chlorination contact chamber D) Outfall from the facultative lagoon system to lift station E) Future location for DAF installation F) Final discharge magnetic flow meter G) Lift station pumps Background • The Plant’s existing wastewater treatment infrastructure consisted of: • 52 Acre Facultative Lagoon System (1960) • Upgraded with Curtain Baffles in 1980’s • Aerators Added to Lagoons at Same Time to Increase D.O. Levels • Chlorine Contact Chamber added in 2007 • Plant Still Unable to Meet NPDES Permit • Malcolm-Pirnie (Arcadis, U.S.) Contracted to Evaluate Additional Treatment Options Background • The issue and next step: – Excessive algae growth in the lagoon system is causing a violation of their TSS and cBOD5 discharge limit per their NPDES permit – Consulting engineering firm reviewed five (5) different technologies to remove the algae • Mechanical Filtration • Coagulation – Flocculation • In-Pond Removal Methods • Granular Media Filtration • Dissolved Air Flotation Background Final evaluation and testing for solutions • Bench scale Precipitation and Sedimentation • Bench scale Precipitation and Filtration • Bench scale Precipitation and Flotation Conclusion: • Bench-scale testing on all technologies showed DAF to be the best overall choice for algae removal • Commission a pilot test with chemical flocculation followed by DAF to remove algae from the lagoon effluent DAF Pilot Study Goals Evaluate the treatment performance of a DAF system for the removal of algae Evaluate from biologically treated wastewater prior to disinfection and final discharge. Determine the approximate chemical consumption requirements using a Determine DAF system. Determine a chemical program that would be effective and economical for Determine flocculation prior to flotation. Approximate Approximate the amount of solids generated using a DAF system. Confirm Confirm the initial design parameters of the system. Aid Consulting Engineer in developing the process design for a full-scale Develop DAF system for algae removal. DAF Overview DAF Process Overview Top Skimmer Flotation Cell Contact Chamber System Effluent Discharge Chamber & Weirs Whitewater Injection Ports & Valves Bottoms Removal Float/Skimmings Chamber Air Dissolving Pipe Rotameter Air Eductor (ADP) Pilot DAF System Setup on Site Algae Laden Effluent in Chlorine Contact Chamber Pilot Study 2009 Methodology • November 10-12, 2009 • Samples collected twice daily • Total TSS tests run – six (6) • Skid mounted Small DAF with • Two mix tanks & • Chemical feed components o Single flocculent used in the study: cationic polymer @ 5 ppm DAF Pilot Study Operating Conditions & Results Flocculent Influent Effluent Influent Effluent Total Solids Test # Flow Flocculent Removal Removal 1 Dosage cBOD5 cBOD5 TSS TSS Produced GPM Charge ppm mg/L mg/L % mg/L mg/L % lbs/hr 1 15 Cationic 5 - 4 - - 8 - - 2 15 Cationic 5 - 3 - - 14 - - 3 15 Cationic 5 21 3 85.7 93 11 88.2 0.62 4 15 Cationic 5 15 3 80.0 62 10 83.9 0.39 5 15 Cationic 5 15 3 80.0 58 6 89.7 0.39 6 15 Cationic 5 13 4 69.2 49 12 75.5 0.28 Study 15 N/A 5 16 3 78.7 66 9.8 84.3 0.42 Average 1 Total solids are on a dry matter basis. Pilot Study TSS Removal Data Influent TSS 120 Effluent TSS Influent Sample 100 Not Taken 80 60 40 Total Suspended Solids, mg/L Solids, Suspended Total 20 0 1 2 3 4 5 6 Pilot Test Number Full-Scale DAF System – Design Parameter Units Design Notes/References Forward Flow MGD 1.5 Design flow based on peak flow to lagoon system Total Suspended mg/L 300 Design maximum Solids Solids Mass Loading lbs/hr 156 Calculated Recycle Pressure psi 90 Typical range is 80-100 per ETS design Air Solution Rate SCFH 120 By design Recycle Rate gpm 150 N/A Recycle % 18 15% to 25% is typical for ETS designs Flotation Surface Area ft2 240 By design Based on pilot DAF Test Hydraulic Loading gal/min/ft2 4.3 Typical ETS design range is 2-6 gal/min/ft2 Low based on typical ETS designs; low TSS effluent requirement and hydraulic loading Solids Loading lbs/hr/ft2 0.65 dictated the DAF unit size as well as pilot operating data Air to Solids Ratio lbs/lbs 0.057 0.006 to 0.070 (WEF MOP-FD-3, 1994) Process Flow Diagram of the Full-Scale DAF Algae Removal System Full-Scale Algae Removal DAF Unit Installed on Site Full-Scale DAF in Operation Comparison of Pilot-Scale and Full-Scale DAF Performance TSS Influent Effluent cBOD Influent TSS Effluent TSS 5 Removal cBOD5 cBOD5 Removal mg/L mg/L % mg/L mg/L % Average Before DAF 97 61 37.1 61 25 59 Unit Installation Average During Pilot 66 1 9.8 84.3 2 16 1 3 78.7 2 Study Average After DAF Unit 147 29 80.3 107 12 88.8 Installation • NPDES Permit requires removal efficiencies of 65% for TSS and 85% for carbonaceous BOD5. 1 Influent sampled at pilot DAF Unit; all others at headworks of lagoon 2 Removal is based solely on pilot DAF Unit performance which is used for TSS removal since no coagulants were used Operational Data Before and After the DAF Unit Installation 2013 2014 MONTH INFLUENT EFFLUENT INFLUENT EFFLUENT cBOD5 cBOD5 cBOD5 cBOD5 TSS (mg/L) (mg/L) TSS (mg/L) (mg/L) TSS (mg/L) (mg/L) TSS (mg/L) (mg/L) January 72 110 52 17 173 142 17 6 February 67 88 60.5 18.5 76 102 30 15.5 March 76 117 27 16.5 68 74 19 17.5 April 122 108.5 73 28.5 57 47 21 9.5 May 112 128 59 30 100 75.5 43.5 15.5 June 27 73 80 42.5 126.5 62.5 26 9.5 July 151 144.5 71 38.5 223 143 50 23.5 August 85 114 76.5 24.5 68 115.5 40 11.5 September 87 84.5 82 28 N/A N/A N/A N/A October 83 98.5 40.5 24 335 182 23.5 7.5 November 116 119 55 20.5 N/A N/A N/A N/A December 165 95.5 56 15.5 242 127.5 20 8.5 AVERAGE 97 107 61 25 147 107 29 12 * TSS and cBOD5 readings are resultant monthly averages from two samples. ** N/A results indicate months of no discharge from the lagoon and therefore no samples were recorded. Issues After DAF Unit Installation • Variation in Influent Total Suspended Solids – Seasonal Algal Blooms – Heavy Rain Events • Variation in Polymer Dosing – Attempts to Reduce Usage = Carryover in Effluent – Changing Polymer Vendors • DAF Float Pumping – Float Material Too Thick to Flow to Sump – Submersible Grinder Pump Not Positive Displacement Conclusion • Full scale system is operating as anticipated • System is allowing the City to meet NPDES Permit Requirements of 65% and 85% removal Acknowledgements Charles H. Starling III, P.E. BCEE – ARCADIS U.S.,Inc. 5 N. Conception St., Suite 200 Mobile, AL 36602 Charles C. Ross, P.E. – Environmental Treatment Systems, Inc. 4310 McEver Industrial Drive, Acworth, GA 30101 G. Edward Valentine – Environmental Treatment Systems, Inc. 4310 McEver Industrial Drive, Acworth, GA 30101 .
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