Algae Removal from a Facultative Lagoon System Using Dissolved Air Flotation. J. Patrick Pierce, P.E. Environmental Treatment Systems, Inc.

Transcription

1 Algae Removal from a Facultative Lagoon System Using Dissolved Air Flotation J. Patrick Pierce, P.E. Environmental Treatment Systems, Inc.

2 Facultative Lagoon System Designed for 1.5 MGD Discharging MGD Serving a population of 15,000

3 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

4 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

5 Background The issue and next step: Excessive algae growth in the lagoon system is causing a violation of their TSS and cbod 5 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

6 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

7 DAF Pilot Study Goals Evaluate Evaluate the treatment performance of a DAF system for the removal of algae from biologically treated wastewater prior to disinfection and final discharge. Determine Determine the approximate chemical consumption requirements using a DAF system. Determine Determine a chemical program that would be effective and economical for flocculation prior to flotation. Approximate Approximate the amount of solids generated using a DAF system. Confirm Confirm the initial design parameters of the system. Develop Aid Consulting Engineer in developing the process design for a full-scale DAF system for algae removal.

8 DAF Overview

9 DAF Process Overview Effluent Discharge Chamber & Weirs Top Skimmer System Flotation Cell Contact Chamber Whitewater Injection Ports & Valves Bottoms Removal Float/Skimmings Chamber Rotameter Air Eductor Air Dissolving Pipe (ADP)

10 Pilot DAF System Setup on Site

11 Algae Laden Effluent in Chlorine Contact Chamber

12 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 5 ppm

13 DAF Pilot Study Operating Conditions & Results Test # Flow Flocculent Flocculent Dosage Influent cbod 5 Effluent cbod 5 Removal Influent TSS Effluent TSS Removal Total Solids Produced 1 GPM Charge ppm mg/l mg/l % mg/l mg/l % lbs/hr 1 15 Cationic Cationic Cationic Cationic Cationic Cationic Study Average 15 N/A Total solids are on a dry matter basis.

14 Pilot Study TSS Removal Data Influent TSS 120 Effluent TSS Total Suspended Solids, mg/l Influent Sample Not Taken Pilot Test Number

15 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 Solids mg/l 300 Design maximum Solids Mass Loading lbs/hr 156 Calculated Recycle Pressure psi 90 Typical range is 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 ft By design Hydraulic Loading gal/min/ft Solids Loading lbs/hr/ft Based on pilot DAF Test Typical ETS design range is 2-6 gal/min/ft 2 Low based on typical ETS designs; low TSS effluent requirement and hydraulic loading dictated the DAF unit size as well as pilot operating data Air to Solids Ratio lbs/lbs to (WEF MOP-FD-3, 1994)

16 Process Flow Diagram of the Full-Scale DAF Algae Removal System

17 Full-Scale Algae Removal DAF Unit Installed on Site

18 Full-Scale DAF in Operation

19 Comparison of Pilot-Scale and Full-Scale DAF Performance Influent TSS Effluent TSS TSS Removal Influent cbod 5 Effluent cbod 5 cbod 5 Removal Average Before DAF Unit Installation Average During Pilot Study mg/l mg/l % mg/l mg/l % Average After DAF Unit Installation NPDES Permit requires removal efficiencies of 65% for TSS and 85% for carbonaceous BOD 5. 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

20 Operational Data Before and After the DAF Unit Installation MONTH INFLUENT EFFLUENT INFLUENT EFFLUENT TSS (mg/l) cbod 5 (mg/l) TSS (mg/l) cbod 5 (mg/l) TSS (mg/l) cbod 5 (mg/l) TSS (mg/l) January February March April May June July August September N/A N/A N/A N/A October November N/A N/A N/A N/A December cbod 5 (mg/l) AVERAGE * TSS and cbod 5 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.

21 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

22 Conclusion Full scale system is operating as anticipated System is allowing the City to meet NPDES Permit Requirements of 65% and 85% removal

23 Acknowledgements Charles H. Starling III, P.E. BCEE ARCADIS U.S.,Inc. 5 N. Conception St., Suite 200 Mobile, AL Charles C. Ross, P.E. Environmental Treatment Systems, Inc McEver Industrial Drive, Acworth, GA G. Edward Valentine Environmental Treatment Systems, Inc McEver Industrial Drive, Acworth, GA 30101