Settled Sewage. Tap Water. CaO. Pond Effluents 23 M 95 M

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1 Algae Removal from Wastewater Treatment Pond Effluent by Dissolved-Air Flotation Dr. Yakup Nurdogan CDM, N.E. 1 st Street Bellevue, WA nurdogany@cdm.com September 14, 2009 Presentation Outline Dr. William J. Oswald HRP pioneer Experimental HRP system Selection of colonial algae species in HRP Microscopic photos of colonial algae Micractinum and Scenedesmus Advanced dissolved air flotation system DAF clarification results DAF vs. sedimentation clarifier HRP vs. Activated Sludge Conclusions 1

2 Dr. William J. Oswald Pioneer of HRP Technology Dr. William J. Oswald s Handwriting! 2

3 Experimental HRP System Paddle-Wheel Mixing of HRP 3

4 Plan View of Two 1,000 m 2 HRP Settled Sewage East Pond Tap Water 8 CaO 23 M Pond Effluents Paddle Wheel West Pond 95 M Symbiotic Relationship Between Microalgae and Bacteria in HRP Organics plus O 2 Bacteria New Cells O 2 CO 2 NH 3 New Cells Algae Sunlight 4

5 Algae Abundance in Ponds Ponds in the USA (Oswald, 1976) Rank Richmond HRPs in This Study, Chlorella 1 Micractinium Ankistrodesmus 2 Scenedesmus Scenedesmus 3 Ankistrodesmus Euglena 4 Chlorella Chlamydomonas 5 Chlamydomonas Oscillatoria 6 Euglena Micractinium 7 Oscillatoria Factors Affecting the Selection of Algal Genera in HRP Parameters Micractinium Scenedesmus Chlorella Motile Algae Pond Depth, cm > 50 Hydraulic Detention Time, days > 10 Organic Loading mg COD/L/day > 500 Mixing Type P. Wheel P. Wheel Pump None Linear Mixing Velocity, cm/sec Pond ph Pond Water Temperature, ºC

6 Linear Mixing Velocity in HRP vs. Paddle-Wheel RPM 40 Linear Mixing Velocity (cm/sec) cm Depth 39 cm Depth Paddle Wheel Tip V V = 0.53 V Channel Paddle Wheel Speed (rpm) Micractinium 6

7 Micractinium Scenedesmus 7

8 Bioflocculating Scenedesmus Cells Micractinium and Scenedesmus 8

9 Autoflocculated Micractinium Micractinium Solids in 1-hr Settling Test 9

10 Pilot DAF Unit Advanced DAF - Rotating Inlet and Outlet Inlet Flow Clarified Water Outlet At the pressure release valve (1) The clarified water, near the bottom, is absorbed air is released into the water. removed by slotted outlet pipes (5) attached The water flows in at the exact center, to the wall of the moving center part. Clean through a rotary joint (2) and into water flows into the center section (6) and the distribution duct (3). overflows over the telescopic weir (7)

11 Advanced DAF - Outlet and Spiral Float Scoop Single Scoop Double Scoop Triple Scoop An Elevated 33-ft Diameter DAF Unit for 2,400 gpm Flow 11

12 A 70-ft Diameter DAF Unit for 11,800 gpm Flow Klett Unit vs. SS Concentration 250 SS Concentration (mg/l) y = 2.6x 8.8 (R = 0.97) Optical Density (Klett Unit)

13 Alum Coagulation 100 SS Removal Efficiency, (%) Micractinium Scenedesmus Optimum ph: Alum Dose (mg/l) Ferric Chloride Coagulation 100 SS Removal Efficiency, (%) Micractinium Optimum ph: FeCl 3 Dose (mg/l)

14 Effect of DAF Underflow Rate on Effluent SS Concentration 60 DAF Effluent SS Concentration (mg/l) Alum Ferric Chloride Nalco s Utrion Underflow Rate (gpm/ft 2 ) Effect of DAF Underflow Rate on SS Removal Efficiency 100 DAF SS Removal Efficiency (%) Alum Ferric Chloride Nalco s Utrion Underflow Rate (gpm/ft 2 ) 14

15 Effect of DAF Recycle Ratio on Effluent SS Concentration 60 DAF Effluent SS Concentration (mg/l) Alum Ferric Chloride Nalco s Utrion Recycle Ratio 0.8 Effect of DAF Recycle Ratio on SS Removal Efficiency DAF Effluent SS Removal Efficiency (%) Alum Ferric Chloride Nalco s Utrion Recycle Ratio

16 Advanced DAF vs. Sedimentation Clarifier Costs for 7.5 MGD flow Items Advanced DAF Sedimentation Clarifier Diameter 44 ft 112 ft Depth 2 ft 7 ft Detention Time 3 min 110 min Sludge Consistency 2 3% % Power Consumption: Feed Pump 44 KW Feed Pump 44 KW Recycle Pressure Pump 51 KW Scraper 12 KW DAF Drive 3 KW Compressor 1 KW Total: 99 KW 56 KW Equipment Cost: $512,000 $1,344,000 Operational Cost: 3 c/1000 gal 8 c/1000 gal *Cost of chemical remains the same for equal clarification HRP vs. Activated Sludge Parameters Raw Sewage HRP System Secondary Treatment Conventional Activated Sludge System Phosphorus Removal Nitrogen Removal BOD, mg/l % Removal COD, mg/l % Removal SS, mg/l % Removal PO4-P, mg/l % Removal NH4-N, mg/l % Removal

17 Conclusions DAF is an efficient and reliable method for algae harvesting from HRP. DAF effluent SS concentrations were 30 mg/l or better when chemical coagulants were used without any polymer. The optimum DAF underflow rate: gpm/ft 2 to achieve a DAF effluent SS concentration of 30 mg/l. The optimum recycle ratio: greater than 55-65% to achieve a DAF effluent SS concentration of 30 mg/l. Optimum coagulant dosages obtained by jar test settling are not optimum for flotation. Conclusions Micractinium is easier to flocculate than Scenedesmus. Optimum coagulant dosages based on the jar test settling: Nalco s Utrion-8109: 45 mg/l Ferric chloride: 80 mg/l Alum: 150 mg/l for Micractinium and 250 mg/l for Scenedesmus species. DAF float solids concentrations were % by wt without any polymer usage. Polymer addition will improve the clarification by reducing coagulant dosages required and increase float solids concentrations. 17