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TRANSCRIPT
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Bill McConnell
NEWEA Annual Conference January 28, 2015
PresentaFon Outline
• Background • Nitrogen Removal Requirements • OperaFons and Performance EvaluaFon • DescripFon of Improvements • QuesFons
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Background
• Bucklin Point WWTF – East Providence, RI – Owned by NarraganseR Bay Commission – Operated by United Water
• Serves – Central Falls – Cumberland – East Providence – Lincoln – Pawtucket
• Combined CollecFon System
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
History – Bucklin Point WWTF
• 1952 – Constructed as Primary Plant • 1973 – Upgraded to Secondary Treatment
– 46 mgd secondary capacity – 67 mgd wet-‐weather capacity
• 2006 – Upgraded to nitrogen removal & 116 mgd wet-‐weather capacity
• 2014 – Further upgrade for improved nitrogen removal
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Design Flows
Influent • Average Dry Weather 23.7 mgd • Maximum Month 31 mgd • Peak Hour 116 mgd • Max to biological treatment 46 mgd • Max wet weather treatment 70 mgd
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Bucklin Point WWTF Prior to 2006 Upgrade
• Preliminary Treatment – Screens – Aerated Grit – Pre-‐aeraFon – Flows in excess of 67 mgd diverted to discharge without treatment
• Primary Treatment • Secondary Treatment
– AeraFon – Clarifiers
• DisinfecFon
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Nitrogen Removal Design (2006)
• Year-‐round nitrificaFon • DenitrificaFon within exisFng tankage
– No new bioreactor volume or clarifiers required • Tanks converted to MLE • First cell of each aeraFon tank converted to three
cell anoxic – First two cells sized for selecFon – Third cell sized for nitrate removal – Target Effluent TN of 8 mg/L
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Modified Ludzack-‐Ehnger Process (MLE)
Internal Recycle
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
MLE Process Design Criteria
Design Flow (maximum month) 31 mgd
# of bioreactors 4
Total anoxic volume 2.4 MG
Total aerobic volume 9.7 MG
Design temperature (minimum month) 11 deg. C.
Design MLSS concentration 3,200 mg/L
Design aerobic SRT 8.7 d
Total internal recycle pumping capacity 64 mgd
Total recycle ratio (IR + RAS) 3.25
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Changing Effluent TN Goals
• At start of 1997 FaciliFes Plan – Ammonia limits only
• 5.4 mg/L June through October • 15.8 mg/L November through May
• Subsequent to approval of FaciliFes Plan – RIDEM indicated N removal likely
• 8 mg/l TN probable • 5 mg/L TN being considered
• During construcFon RIDEM noFfied NBC – 5 mg/L TN monthly average May – Oct
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Permit ModificaFon
• Permit modificaFon requiring average monthly TN limit of 5 mg/L from May through October
• Required engineering analysis of upgraded plant performance to determine if average monthly limit of 5 mg/L was aRainable
• If not, start faciliFes planning process
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Effluent TN VariaFon
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
EvaluaFon of AlternaFves
• The WWTF could not meet the average monthly 5 mg/L TN concentraFon limit in the MLE configuraFon
• At Bucklin Point, the size of the anoxic zones limited the ]performance of the MLE process, such that increasing the IR rate will not improve nitrogen removal.
• Process improvements will be required to meet the average monthly 5 mg/L TN limit
• ImplementaFon of 4-‐stage process was recommended
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Conclusions of EvaluaFon
• The following alternaFves were evaluated: – 4-‐stage process – IFAS – MBR – Biologically acFve filters (BAFs)
• 4-‐stage BNR process recommended: – ConsideraFon of seasonal TN limit – ImplementaFon of swing zones – Compliance with no new tankage
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
4 Stage BNR Process
Supplemental Carbon (if/when needed)
Internal Recycle
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
MLE and 4-‐Stage Process Process Design Criteria
Criterion MLE 4-stage
Design temperature (minimum month) 11 deg. C. 16 deg. C.
Design aerobic SRT 8.7 d 5.6 d
Pre-anoxic volume 2.4 MG 2.4 MG
Main aerobic volume 9.2 MG 5.8 MG
Post-anoxic volume --- 2.8 MG
Reaeration volume --- 0.6 MG
Supplemental carbon usage (available) no yes
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Process Model: MLE configuraFon, 11 deg C
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Process Model: MLE configuraFon, 16 deg C
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Process Model: 4-‐stage configuraFon, 16 deg C
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Process Model: 4-‐stage configuraFon, 16 deg C., 100 gpd of supplemental carbon
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Bioreactors
1.1 0.5 1.5 2.0 DO setpoint (mg/L)
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Bioreactors
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Swing Zone Details
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Internal Recycle
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Blower Improvements
• 2 new 300-‐HP, 6000 icfm turbo blowers
• Replace 1 600-‐HP, 12,000 icfm blower
• Improved turndown and DO control
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Carbon Storage and Feed System
• Glycerin-‐based supplemental carbon
• Max usage 270 gpd
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Effluent Total Nitrogen Results
First bioreactor switched to 4-‐stage on 8/1/2013
All bioreactors operaFng in 4-‐stage on 5/5/2014
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
Achieving 5 mg/L TN with no New Tankage at Bucklin Point
QuesFons?
Acknowledgements Terry Cote, NBC Tom Ciolfi, United Water Many others as well