Increasing Biological Phosphorus Removal: Texas Case Study

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1 Increasing Biological Phosphorus Removal: Texas Case Study Leon Downing, Ph.D. Theodore W. Chan, P.E. David R. Jackson, P.E., BCEE Leonard E. Ripley, Ph.D., P.E. Freese and Nichols, Inc. Tod K. Maurina City of The Colony

2 Outline Introduction to The Colony 20 Upgrade Biological Phosphorus Removal Process evaluation Potential and limits for EBPR at The Colony Next steps

3 Located in North Texas on Lewisville Lake ~40,000 people (20 census data) ~3.5 MGD wastewater flow

4 20 Upgrades IFAS units to boost nitrification Influent/RAS pumping improvements Headworks upgrades

5 20 Upgrades Plant initially design for nitrification Shortly before bid, phosphorus monitoring was added to the permit Wanted to maximize biological phosphorus removal Minimize chemical addition and increased sludge production

6 Phosphate Accumulating Organisms (PAOs) PAOs: Anaerobic (starvation) DO ~ 0.0 mg/l NO 3 ~ 0.0 mg/l rbbod + stored P PHB + P i PAOs PAOs: Aerobic (cakewalk) DO > 2.0 mg/l NO 3 > 10 mg/l BOD + oxygen + P i cells + CO 2 PHB + oxygen + P i cells + stored P P i - Release P i Uptake Readily Biodegradable Carbon Substrate Organic & Inorganic Carbon Substrates WAS

7 Phosphorus Removal Anaerobic swing zones incorporated at the head of each aeration basin Provisions to use the WAS wet well as a denitrifying reactor Modified Johannesburg Process

8 Phosphorus Removal Sludge Holding Tank RAS Wet Well Aerobic Zone Headworks AB B AB A Anoxic/Anaerobic Zone Anaerobic Zone

9 Process Evaluation Fast-tracked EBPR design included a provision to evaluate the process after operating Historical data How was the plant operated? What effluent phosphorus concentrations are achievable? Intense field sampling

10 PHOSPHORUS (mg/l) Historical Data 6 Modified Johannesburg Process May- Jun- Aug- Oct- Dec- Feb- Apr- Jun- Aug- Oct- Dec- Feb- Apr- Jun- Aug- Oct- Dec- MONTH EFFLUENT 7 per. Mov. Avg. (EFFLUENT)

11 Historical Data Sludge Holding Tank RAS Wet Well Headworks AB B X X X X AB A X X X

12 PHOSPHORUS (mg/l) Historical Data 6 Modified Johannesburg Process A-A-O Process May- Jun- Aug- Oct- Dec- Feb- Apr- Jun- Aug- Oct- Dec- Feb- Apr- Jun- Aug- Oct- Dec- MONTH EFFLUENT 7 per. Mov. Avg. (EFFLUENT)

13 PHOSPHORUS (mg/l) Historical Data May- Jun- Aug- Oct- Dec- Feb- Apr- Jun- Aug- Oct- Dec- Feb- Apr- Jun- Aug- Oct- Dec- MONTH INFLUENT 7 per. Mov. Avg. (INFLUENT)

14 Historical Data Sludge Holding Tank Designed as an aerobic tank Headworks AB B RAS Wet Well To reduce BFP volume throughput, anaerobic decant introduced AB A

15 Historical Data PAOs: Anaerobic rbbod + stored P => PHB + P i PAOs PAOs: Aerobic (cakewalk) DO > 2.0 mg/l NO 3 > 10 mg/l BOD + oxygen + P i => cells + CO 2 PHB + oxygen + P i => cells P i - Release P i Uptake Readily Biodegradable Carbon Substrate Soluble and Particulate Carbon Substrates WAS

16 Historical Data Process operation impacted effluent phosphorus Modified Johannesburg Process produced lower effluent P A-A-O less effective, decreased anaerobic contact or rbbod availability? Operation of sludge holding tank. What are the process limitations?

17 Field Sampling Identify the cause of EBPR limitation Limited rbbod Nitrate inhibition in first anaerobic zone Develop recommendations to improve EBPR

18 Field Sampling Measured several parameters on separate days ORP Nitrate Ammonia DO rbbod Total phosphorus Two Sampling Days Day 1: A-A-O Day 2: Modified Johannesburg Process

19 ORP (mv) Field Sampling: A-A-O 200 Anaerobic-1-A Anaerobic-2-A Aerobic-A Aerobic/oxic Anoxic/denitrification Anaerobic -150 Basin Length

20 Field Sampling: Modified Johannesburg Process Basin Length

21 Field Sampling Modified Johannesburg Process resulted in more favorable EBPR conditions Phosphorus uptake still limited rbbod content: averaged 55 mg/l Influent P: averaged 11 mg/l rbcod:p ratio: average 5 Ideal ratio: 7 to 10 Not enough food for the PAOs

22 Total Phosphorus (mgp/l) Limitation of EBPR Permit 0 Influent Phosphorus Modified Johannesburg A-A-O Modified Johannesburg w/anaerobic Holding Tank

23 Next Steps Small, tight system does not give sufficient rbbod for removal below 1 mg/l Chemical polishing to meet 1 mg/l permit Supplemental rbbod Fermentation of primary sludge Acetate addition

24 Acknowledgements City of The Colony WWTP Staff Jason Fulco Daemeon Stovall

25 Questions?

A Review of the Current State of Knowledge on Phosphorus Removal

A Review of the Current State of Knowledge on Phosphorus Removal Sam Jeyanayagam, Ph.D., P.E., BCEE Senior Associate Malcolm Pirnie sjeyanayagam@pirnie.com Phone: (614) 430-2611 OWEA Conference 16 June