Maureen O Shaughnessy. Prince William County Service Authority

Transcription

1 Maureen O Shaughnessy Prince William County Service Authority

2 Facility Description Overview Operational Flexibility Liquids: Nitrogen Removal Power Solids Summary

3 Featherstone Pump Station H.L. Mooney Advanced Water Reclamation Facility (AWRF) Ferric Lime MeOH RAS Preaeration Screening & Grit Removal Landfill Equalization Basins To Atmosphere Primary Clarifiers CEPT Activated Sludge Nitrogen Removal Polymer Secondary Clarifiers Denitrification/ Final Filters Ultraviolet Irradiation Cascade Aeration Neabsco Pump Station Hypochlorit e Odor Control Gravity Thickenin g Effluent to Neabsco Creek Sludge Holding Polymer Centrifuge Dewatering Fluidized Bed Incinerator Lime Ash Settling Drying Ash Landfill 1/28/2015

4 H.L. Mooney Plant Solids Incineration Biological Treatment Ash Flow Equalization Screens and Grit Primary Settling Filters UV Cascade Aeration

5 HL Mooney AWRF Recent Changes Expansion from 18 to 24 MGD Enhanced Nutrient Removal Total effluent nitrogen from 8 to 3 mg/l (Annual) Total P remains at 0.18 mg/l (Monthly) Lower QL for CBOD5 2 mg/l MACT Sewage Sludge Incinerator (SSI) Rule Mercury and Cadmium

6 Upgrades to achieve 24 mgd and Regulatory Requirements New Screens and Grit removal New step-feed BNR basins & secondary clarifiers Denitrification filter expansion and methanol addition automation Gravity thickener expansion Dewatering expansion 3 rd centrifuge & pump Chemical systems for nutrient removal Electrical upgrades Control upgrades new Supervisory Control and Data Acquisition (SCADA) Incinerator New Mercury Scrubber and WESP

7 Defining Flexibility of Design Designs that can adapt when external changes occur Wikapedia for Engineering Flexibility Flexibility is a complex, multidimensional concept that refers to an organization's ability to respond to uncertainty in its environment. De Groote X. The flexibility of production processes: a general framework. Management Science. 1994;40(7): Operational flexibility is the ability to change or react with little penalty in time, effort, cost or performance. Upton DM. The Management of Manufacturing Flexibility. Calif Manage Rev Win. 1994;36(2):72 89.

8 Flexible and Robust Flexibility Ability to respond to change by taking appropriate action (Mandelbaum, 1978) Modular capacity Designs that can adapt to external changes Thought to have lower present cost, however adding flexibility can increase present cost. Robustness The innate capacity to function well in more than one state (Mandelbaum, 1978) Large, reserve capacity Designs that endure external changes. Thought to have higher present cost and lower future cost Prevention rather than cure Increase System Robustness by containing Flexible elements

9 Liquids Treatment Filters Biological Treatment

10 H.L. Mooney ENR Process Primary Effluent Lime Internal Nitrate Recycle Methanol Anoxic Zones 1-3 Swing Zone 4 Aerobic Zones 5 9 Aerobic Zone 10 Swing Zone 11 Aer. Zone 12 Process Air 1) 4-Stage Bardenpho Effluent TN < 3 mg/l Primary Effluent Lime Methanol Internal Nitrate Recycle Return Activated Sludge Waste Activated Sludge to Gravity Thickeners Anoxic Zones 1-3 Swing Zone 4 Aerobic Zones 5 9 Aerobic Zone 10 Swing Zone 11 Aer. Zone 12 Process Air 2) MLE Process - Effluent TN < 8 mg/l Return Activated Sludge Waste Activated Sludge to Gravity Thickeners

11 Denitrification Filters

12 Denitrification Filters 1) Denitrification Filter: with methanol 2) Conventional Filter - without methanol Two ChemScan units - Operate side by side - Reduce risk: - Methanol overdose - Permit violation - CBOD5 QL 2 mg/l

13 Liquids Operational Flexibility Design Conditions: 24 mgd MLE + Denitrification Filters Current Operating Conditions: 4-stage Bardenpho + Conventional Filters - Simpler to operate one control point for nitrogen - Reduces risk of permit violation due to methanol overdose - Simpler filter operation

14 Liquids Treatment Test Train

15 Test Train Modifications Try alternative configurations before implement in other tanks Change NRCY rate and/or intake? Install NH3 probe (ISE?) DO = high setpoint from model NH3 reading controls DO setpoint Can mixers be run during aeration? NH3 reading controls DO setpoint Reduce methanol feed Install DO probe (LDO?) NH3 reading controls DO setpoint Evaluate low DO mixing options for this zone (rolling aeration) DO = high setpoint from model

16 Stand-by Generators 2.5 MW each 2 diesel generators each can operate plant 2 power feeds into the plant from separate substations A third generator for UV Disinfection Note: both feeds have been lost and generators were needed!

17 Solids Treatment FBI Full load: 2200 to 2800 dry pounds per hour (up to 45 dry tons/day) Existing Emission Controls: Venturi and Impingement tray scrubber

18 Solids Treatment Upgrade for MACT SSI Ammonia(NO x ) not installed WESP (Cd) Caustic Addition (SO 2 ) Mercury Scrubber

19 Biosolids Changes BTU/lb increasing - capacity

20 Solids Flexibility FBI Backup FBI down for maintenance ~1 month/year 2011 Landfills rejected hauled dewatered cake due to ODORS Approach: Expanded Options for Solids Regulatory: Added land application of lime stabilized solids to our VPDES permit by piloting a Bioset Lime Stabilization Unit External Options: Added more destinations to reduce reliance on large landfills Off-site incineration at Hopewell Regional Facility Local Prince William County Landfill MOU Discussions with local composting facilities

21 Centrifuge Dewatering H.L. Mooney AWRF Solids Management Off-site Incinerator Dewatered Cake Current Incinerator Backup Incineration Ash (~90% wt reduction) Landfill Disposal Alternate Incinerator Backup Lime Stabilization Biosolids (Class B, Class A) Land Application Other Process? (future evaluation)

22 Summary Regulatory and capacity changes lead to 12 years of construction projects affecting all aspects of the plant. Implemented flexible operational strategy: Uncertainty in regulatory environment Uncertainty in flows, loads, rate of growth Expanded solids options in permit and building a menu of destinations. Uncertainty in future regulations affecting incineration Many options increase reliability beyond that of individual off-site destinations

23 Thank you! Maureen O Shaughnessy moshaughnessy@pwcsa.org