From Rags to Riches lift station ragging solutions

Presented by:Craig B Anderson, P.E., Principal Engineer

Murray, Smith & Associates, Inc.

PACIFIC NORTHWEST CLEAN WATER ASSOCIATION2010 CONFERENCEOctober 24-27, 2010

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Presentation Overview

Background– New household products– Collection system impacts

Case Study (Glenwood Lift Station)– History– Options Evaluated– Solution Effectiveness– Return on Investment

Other Mitigation Options Conclusion

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BackgroundNonwoven technologies developed in 1940s and 1950s

Limited commercial products until 1990s

New product development and rapid growth starting in 1990s

2010 slow down (saturation)

Flushable/”Green”solutions VF

D US

E

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Background

Life at home made easier, but at a cost….

– Increased sewer back-ups (service lines)

– Increased Sewer Rates (O&M)

– Lift stations

– WWTP

– Collection System

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Glenwood Lift Station (Boise)

Problem StatementFacility built in 1976 (good condition)

Critical Facility/Location

High and increasing levels of pump maintenance

Gravity service potential in <10 years

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Glenwood Lift Station (Boise)

Glenwood Lift Station

West Boise WWTP

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Glenwood Lift Station (Boise)

75 ft

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Glenwood Lift Station (Boise)

OPTIONS EVALUATED

• Do Nothing• Operational Changes• Impeller Retrofit (Delta Impeller)• Grinder• Pump Replacement

• Grinder Pump

• Helical Impeller

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Glenwood Lift Station (Boise)

OPTION REFINEMENT

• Do Nothing• Operational Changes• Impeller Retrofit• Grinder• Pump Replacement

• Grinder Pump

• Helical Impeller

(80 man-days a year)

(no effect)

(low cost, but capacity decrease)

(City decision to not evaluate)

(moderate initial cost & City experience)

(initial option – collection system concern)

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Glenwood Lift Station (Boise)

OPTION EVALUATION

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Glenwood Lift Station (Boise)

OPTION EVALUATION

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Glenwood Lift Station (Boise)

SOLUTION EFFECTIVENESS

• Installed in early 2007• No ragging/problems since installed

• 2 year simple payback (45% ROI)

• PW break even at only 24% O&M reduction

• PW break even with replacement every 2 ½ years

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Other Options

Rag Removal– Regular Pump Maintenance (Do nothing)

– Public Education

– Screening

– Grinder

– Product (rag) development

Lift Station Modification– Operation (VFD low flow point & pump sequencing)

– Modified Pump Types (grinder and helical)

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Public EducationTheory of removing rags from waste stream by education

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Public Education

Success based on customer ownership of problem

• Local lift station

• Increasing sewer rates

If no ownership, then education can result in……

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Operation

VFD Setting

• Increase minimum flow point

Pump Cycling

• Return to on/off control

• Make sure motors protected

Combination

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OperationPump Cycling

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Modified Pump/Impeller TypesGrinder Pumps

• Standard for some City’s in Southern Idaho

• Higher HP

• Can be favorable with downstream re-ragging

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Modified Pump/Impeller TypesHelical Impellers

• Passes rags (no breakdown)

• Comparable HP

• Specify hardened impeller and volute

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Conclusions

Lift station ragging conclusions: Do Nothing costs can be significant

Multiple solutions (facility specific)

Evaluate City Standards for flow-paced facilities

Acknowlegements• City of Boise/CH2M HILL

• City of Nampa/Pharmer Engineering

• Pump Suppliers (Vaughan, Wemco & Hayward Gordon)

Questions/Discussions