Transcript No Slide Title

WRF Facilities Plan
- Gary McGill
MSD WRF
Facilities Plan Study
Asheville, NC
March 21, 2007
Agenda
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Scope of Work
Summary of Findings
Conclusions and Recommendations
Detailed In-house Evaluation
Implementation Plan
Scope of Work
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Process Evaluation
Collect and review historic and current plant
data and NPDES effluent standards, project
future loadings and effluent standards.
 Evaluate existing and projected
flows/loadings and performance of the
plant unit liquid and solids processes.
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Physical Facilities Assessment
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Conduct physical facilities evaluation of all
liquid and solids processes
Process Evaluation
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Plant Overview
Summary of Historical Data
Process Performance
Flows and Loads
Detailed RBC Capacity Evaluation
Recommendations
Physical Facilities Assessment
Facility Evaluation Criteria
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Description of Facility
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Function
History
Detailed Description
Controls
Lighting
Safety
Special Issues
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Facility Operation and
Performance
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Normal Operation
Performance History and
Current Issues
Probable Future
Performance
Facility Evaluation Criteria (continued)
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Facility Maintenance
Routine Maintenance
 Maintenance History, Costs, and Current Issues
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Recommendations for Future Service
Issues
 Options
 Recommendation
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Detailed In-House Evaluation
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Grit and Grease Removal
Rotating Biological Contactors (RBCs)
Intermediate Clarifier
Secondary Microscreens
Grit and Grease Removal Existing Facilities
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Capacity
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Operation
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40 MGD average/65 MGD peak
Modified during high plant flows (frequency and duration)
Restore operation to intermittent and sequential design
Performance
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Replace air piping/diffusers
Restore process control
Add classifier capacity
Grit and Grease Removal
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Measure of Performance
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Grit and grease pass-through to RBC basins
Objectives
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Prevent migration of grit and grease to RBC process
Prolong useful life to defer improvement costs for more
critical improvements
Rotating Biological Contactors
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Hydraulic and biological loading imbalance
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Primary concern is age
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Existing piping arrangement between basins
Future flow division to basins
20 +/- years in service
25 year average expected useful life
Mechanical failures due to metal fatigue
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Random locations
Unpredictable
Rotating Biological Contactors
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Short-term plan to replace individual units
Method of existing unit removal/new unit
installation
 Lack of continued availability of square shafts
 Obsolescence of air-driven units
 Logistics of installing mechanical-driven units
 Concurrent air-driven/mechanical driven operation
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Rotating Biological Contactors
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Long-term plan to replace entire RBC process
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Phased within existing RBC basins
Relocate existing operable units to failed locations
Decision-making process
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Process performance monitoring throughout plant
Correlate with plant influent conditions (quantity and
quality)
Correlate RBC performance with other treatment
process performance
Intermediate Clarifier/Pumps
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Initial purpose
Current over-performance/erratic loading
Performance sensitivity
Performance stress testing
 Effluent compliance
 Additional secondary clarification in RBC Basin 3
 Potential abandonment of intermediate clarifier
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Intermediate Clarifier/Pumps
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Existing pumping arrangement
Complex
 Inefficient
 Potential effluent contamination
 Safety hazard
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Secondary Microscreens
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Performance failure – very little suspended
solids removal
Corrosive environment
Chlorine injected prior to microscreens
 Inadequate building ventilation
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Secondary Microscreens
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Operation and maintenance costs
18 existing units
 5 units out of service due to irreparable mechanical
problems
 9 units with chain and sprocket problems
 6 units with wheel or grid problems
 All units with significant metal corrosion problems
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Secondary Microscreens
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Replacement is eminent
Total barrier vs. conventional filtration vs. other
 Site space considerations
 Use existing building
 Correlate with enhanced disinfection
 Correlate with other intermediate and secondary
clarification issues
 Concurrent on-site equipment pilot testing (AquaAerobics and Kruger)
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Recommended Improvements
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Short term Improvements
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Grit and grease removal
 Add
classifier capacity, replace air piping and
diffusers, improve control
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Repair/replace out-of-service RBCs
Develop plan to replace air-driven RBCs
with mechanically driven RBC
Replace intermediate pumps with electric
motor driven pumps
Pilot test cloth filtration to replace
secondary microscreen
Recommended Improvements
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Medium term Improvements
Replace secondary microscreens with
selected alternative technology
 Evaluate the need for additional
intermediate clarification - Conduct
stress testing of clarifiers
 Consider a plan to convert RBC Basin 3
into clarifiers
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 RBC
capacity loss will need to be mitigated
Recommended Improvements
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Long term Improvements
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Consider alternative processes to meet
wastewater needs beyond 2020
 Activated
sludge
 Moving Bed Biological Reactor
 Others