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Michigan Water Environment Association Annual Conference

June 26, 2012 Dennis J. Benoit, P.E., Hubbell, Roth & Clark, Inc.

Petoskey WWTP Headworks Improvements

Problem Statement: 40 Year Old WWTP

Headworks Badly in Need of Improvement

Original Design

Influent Flume for Flow Monitoring

Wastewater Grinding

• Originally Comminutor

• Replaced with “Muffin Monster” in 2002

Aerated Grit Channel

• Bucket Elevator with Horizontal

Auger Conveyor

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40 Year Old WWTP Headworks Badly in

Need of Improvement

Horizontal Auger

Wet Grit

Huge Odor Issues

Manual Transfer Of Grit Was

Very Labor intensive

Wet “Sloppy” Grit

Problems with Original Headworks

Grinding Never works Flawlessly!

Numerous Cases of Screened

Material “Reweaving”

Odors

Minimal Ventilation

Wet Grit

Grit Required Manual Handling from Auger to Dumpster

Waste Hauler Refused Acceptance Due to Free Liquid

• Rectified with Visquine-Lined Dumpster

• Hauling three 12 CY Dumpsters per week at one point

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Problems with Original Headworks

Corroded Equipment

Grit Chain Replaced on Numerous Occasions

Bucket Elevator Jams

Criteria for Headworks Revisions

Fine Screening

• ¼ inch opening size desired

• Washer/Compactor to Reduce Organics in Screenings

• Reuse Existing structure if Possible to Minimize New Land

Aerated Grit Removal

• Requested by Operators to “Freshen” Waste

Clean, Dry Grit

• Free of Organics

• Reduce Moisture to Minimize Disposal Costs

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Criteria for Headworks Revisions

(Continued)

Capture Odors and Treat

• Indoor Housing for Grit Dumpster For Weather

Protection and Odor Containment

• Carbon Contactor on Building Ventilation

• Energy Recovery Due to Significant Ventilation

Volumes

Air to Air Contactors Recover Energy

Criteria for Headworks Revisions

(Continued)

Foul Air Streams To Aeration Blowers

• Foul Air From Wastewater Channels

• Aerated Tank Off-gas Routed To Aeration Tanks

• This Required A Duct From Headworks Building To

Administration Building And Modified Air Filter Inlet Boxes

• An Existing Foul Air Duct From A Biosolids Holding Tank Was

Also Connected

• The Duct Included A Fresh Air Inlet Prior To Blowers For

Blending

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Project Highlights

Bid in July 2011

Estimated at $2.52M

Low Bid at $2.64M

Expectation Was Closer To $2.2m

• Value Engineering Reduced Project Cost To 2.27m

• Sloped Grit Tank Floor

Reduced Undermining Potential of Main Electrical Feed

Duct

• Lowered West Half of Building Two Feet

Made Channels More Accessible

• Deleted OC Unit, One Grit Pump, Aeration Blower, Other Items

Construction Start September 2011

Underground Construction

• Main Duct Bank Underpinning

• Utility Location Conflicts

• Relocations of…

Sludge Line

Biogas Line

Chlorine Solution Lines

Others

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Construction (Continued)

Plant Bypass

• Plan Detailed on Construction Drawings

• Modified by Contractor Based on Available Equipment

• Grit Removal using Precast Concrete Tank and Used

Grit Removal Equipment Including:

Pump

Cyclone

Grit Washer (Auger Type)

• Contractor Constructed Temporary Building to House

Equipment Throughout Winter

Bypass Infrastructure

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Bypass and Pouring New Grit Tank

New Grit Tank

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Dumpster Room Footings

and New Structure Floors

Building Walls and Interior Channel Floors

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Exterior Building and Setting ERV

Fine Screen and Washer Installation

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Foul Air Ducting to Blowers

Interior Building Finishes

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Interior Building Finishes (Cont.)

Highlights of Project

Reuses Existing Channel Structure

In Place Bypass Saved Extensively

Fine Screening Reduces Downstream Maintenance

Screenings Washer Compactor Reduces Odor

Potential of Screenings

Clean Grit Washer Minimizes Grit Volume as Well as

Odor and Moisture Content

Extensive Savings on Grit Disposal Costs

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Highlights of Project (Continued)

Existing Aeration Blowers:

• Provide Rolling Air For Grit Tank

• Pull Foul Air From Channels and Tanks

• Control Valve Regulates Air Flow

Unique Approach to Odor Control

LED Light Fixtures Save Energy

Energy Recovery Ventilation System Saves

Energy

Lessons Learned

Fine Screening Operation

• Developing a mat on the screen is beneficial to screenings

removal.

• Putting the screenings into a Washer Compactor with Similar size

openings can be counterproductive.

Screenings Odors

• Probably the most significant source of odor in the room

Grit Removal

• Plant Effluent Water used for counter current washing.

• Produces very clean grit.

• Steep Auger used on washer produces very dry grit.

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Lessons Learned (Continued)

Aeration

• Air Use For Aerated Grit Is Minimal (Using About 50 CFM

Versus 110 CFM Manufacturer’s Recommendation)

• Control Valve Is Used To Regulate The Air Flow To Grit

Tank

• Routing Air Flow Supply To Aeration Blowers Can Keep

Influent Channels Under Negative Pressure.

Old and New Building

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Screenings and Grit Handling Area

Equipment Room

Grit Pumping /Control Area

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Dumpster Area

Staff Acknowledgments

Sherrie Elliott - Public Works Supervisor

Steve Keel – Crew Leader

Mike Robbins - Director of Public Works

Dan Ralley – City Manager

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Thank You!

Any Questions??