The City of Lynnwood

Centrifuge or Screw Press?

To Incinerate or not to Incinerate

a Best Practice Review

Agenda

• The City of Lynnwood

• Lynnwood Wastewater

Treatment

• Evaluation Process

• O&M Cost Comparison

• Summary & Questions

The City of Lynnwood

• Population over 35,000

• Fourth largest City in Snohomish County and twenty-

ninth largest in Washington State.

• The city is a mix of urban, suburban, small city,

crossroads, and bedroom community

• 16 miles north of Seattle – the city covers 7.8 square

miles

• Scriber Lake, Hall Lake and Swamp Creek all run

through Lynnwood

• Central Washington University and Edmonds

Community College have locations in Lynnwood

Lynnwood Wastewater Treatment

• Lynnwood provides sewer service to approximately 35,000 people

with:

• 104 miles of sewer mains

• 6 lift stations

• 1 Wastewater Treatment Plant (WWTP)

• The Lynnwood WWTP treats sewage for 90% of Lynnwood plus a

portion of Edmonds north of Olympic View Drive

• The facility has a rated capacity of 7.4 MGD and an average flow

of 5 MGD.

• Peak flow has reached 20 MGD during severe storm weather

• The 36” diameter outfall into Browns Bay goes out approximately

1000 feet and is 120 feet deep

• 8,000-10,000 pounds of dried solids are incinerated daily

Lynnwood WWTP Biosolids

Handling Challenges

Dewatering

• The existing Centrifuges at end of life and

require significant capital investment

• High risk of failure and cost of sludge

hauling

• Funds allocated in CIP for new centrifuges

• High O&M costs, maintenance burden

Lynnwood WWTP Biosolids

Handling Challenges

Incineration

• New EPA air quality regulations for

wastewater incineration

• Annual emissions testing

• High risk of failure and cost of sludge

hauling

Dewatering Evaluation Process

• Why screw press?

• Tour facilities with existing installations

• Define performance requirements

• Sludge sampling, signed performance guarantees

• Evaluation matrix to determine manufacturer

Lynnwood Wastewater Treatment

Evaluation Process

• Project team selected 3 screw press manufacturers

• Project team developed performance specification

• Each manufacturer signed the performance spec

• An evaluation matrix was developed by project team in

order of City priorities and drivers

• The manufacturers were scored and the equipment was

selected

Screw Press Matrix

Centrifuge vs Screw Press

O&M Cost Comparisons

**Ongoing dryer evaluation

O&M Costs Centrifuge Screw Press

O&M 26,000$ 1,000$

Energy Use 11,000$ 1,140$

Total Annual O&M Costs 37,000$ 2,140$

Incineration vs. Drying

• Incineration – challenges

• Risk of increasing EPA restrictions

• Sludge hauling

• 24/7 operation

• O&M Costs

• Rock formation

• Drying Benefits

• Fits limited WWTP real estate

• Reduced Sludge Hauling Risk

• Natural gas vs. diesel fuel

• Reduced O&M costs

• Marketable waste product

**Ongoing dryer evaluation

Incineration vs. Drying

O&M Cost Comparisons

**Ongoing dryer evaluation

O&M Costs Incinerator Dryer

Ash/Sludge Hauling 50,000$ 70,000$

Staff Overtime Cost 6,000$

Sand Replacement & Downtime Cost 4,000$

Emissions Testing (annual) 40,000$

Annual Incinerator Down Time & Associated

Hauling Costs 235,000$

Dryer Annual Maintenance 5,000$

Total Annual O&M Costs 335,000$ 75,000$

Project Goals – Phase 1

Replace Centrifuge with Screw Press• Limit City’s risk

• Stretch CIP funding

• Replace end of life equipment, energy savings

• Increase system reliability

• Reduce annual energy consumption and O&M costs/labor

• Reduce project management burden on City staff

Energy Savings Performance Contracting

• City gets what they want

• Reduced burden on City staff

• Guaranteed maximum price

• Maximize grant/incentive dollars

• Leverage CIP funding to optimize cash flow

Laying the foundation of partnership

• Lynnwood selected Trane because Trane partnered with the

City to make it the City’s project

• Design Build Construction

• Lynnwood involved throughout design to shape the project

through equipment/consultant selection and driving

solutions

• Guaranteed Maximum Cost and Guaranteed Minimum

Savings (known max budget before project starts)

• City maintains control over the project

Questions?