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What’s This HWA Design Thing All About???

What’s This HWA Design Thing All About???. Design Capacity HWA Info from one POTW CITY OF GREENSBORO North Buffalo POTW. NORTH BUFFALO POTW. Design Flow: 16 MGD Current Flow = ~10.0 MGD Primary Treatment Secondary Treatment Trickling Filters Activated Sludge with Nitrification

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What’s This HWA Design Thing All About???

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  1. What’s This HWA Design Thing All About??? Design Capacity HWA Info from one POTW CITY OF GREENSBORO North Buffalo POTW

  2. NORTH BUFFALO POTW • Design Flow: 16 MGD • Current Flow = ~10.0 MGD • Primary Treatment • Secondary Treatment • Trickling Filters • Activated Sludge with Nitrification • Tertiary Treatment • Phosphorus removal • Chemical Addition/Precipitation • Effluent Sand Filters

  3. NB CURRENT MAHL CALCULATIONCBOD [Actual Removal/Actual Flow] NPDES Permit Limit: 8.0 mg/l (summer) Removal Rate: 98.8% (270 data points/MRE) Actual Flow: 14.2 MGD** 8.0 mg/l = 8.0 = 666 mg/l max. allowable 1.0-.988 .012 influent conc. 666 * 8.34 * 14.2 MGD = 78,952 pounds **DWQ required use of actual flow..flow has dropped since then. These are the approved headworks calculations from December 2003

  4. “DESIGN CRITERIA”NORTH BUFFALO POTW • From Hazen and Sawyer Engineers Original Design (~1980 Upgrade) • BOD = 196 mg/l • TSS = 245 mg/l • Total Phosphorus = 6.0 mg/l • NH3-N = 18.5 mg/l

  5. NB “DESIGN CRITERIA” per DWQMAHL CALCULATION: CBOD • Engineering Design BOD = 196 mg/l • Used BOD as CBOD • Engineering Design Flow = 16 MGD 196 * 8.34 * 16.0 = 26,154 pounds MAHL • Current Domestic BOD Loading: 27,615 lbs • 20 of last 24 monthly average influent concentrations exceeded 196 mg/l while resulting in average effluent CBOD of <2 mg/l • CAN YOU SPELL OVERALLOCATED?????

  6. NB CURRENT HWA CALCULATIONTSS [Actual Removal/Actual Flow] NPDES Permit Limit: 30.0 mg/l Removal Rate: 97.8% (271 data points/MRE) Actual Flow: 14.2 MGD 30.0 mg/l = 30.0 = 1363 mg/l max. allow. 1.0 -.978 .022 influent conc. 1363 * 8.34 * 14.2 MGD = 161,492 pounds **DWQ required use of actual flow..flow has dropped since then. These are the approved headworks calculations from December 2003

  7. NB “DESIGN CRITERIA”CALCULATIONS: TSS • Engineering Design TSS = 245 mg/l • Engineering Design Flow = 16 MGD 245 * 8.34 * 16.0 = 32,693 pounds [Current Domestic TSS Loading: 22,289] • Not overallocated now, but flow is only ~10.0 MGD • Domestic alone will use up the rest of the allocation

  8. IMPLICATIONS • Underestimating POTW Conventional Pollutant Capacities and Capabilities • Potential Over-Allocation With Just Domestic Loading! • Loss of Potential New Industrial Users • Potential Moratorium • “Domestic concentration” is rising due to newer plumbing fixtures • BOD Limits for All SIUs • North Carolina Local Limits Policy

  9. North BuffaloCurrent Loading Situation: DISMAL • Actual Influent CBOD Loading = 19,718 lbs • 213 mg/l * 8.34 * 11.1 MGD [24 mo. avg] • DWQ Design Loading = 26,154 lbs • 6436 lbs CBOD left…[“domestic” on paper is >MAHL] • BOD Limits for Everyone!!!! [75.4% “loaded”] • Actual Influent TSS Loading = 32,401 lbs • 350 * 8.34 * 11.1 MGD [24 mo. avg] • DWQ Design Loading = 32,693 lbs • Only 292 Pounds of TSS Left…but over 4 MGD of hydraulic capacity left… • TSS Limits for Everyone!!!! [~100% “loaded”]

  10. North Buffalo SUMMARY

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