Clarifiers Getting Old? The City of Warren’s Experience in Replacing Final

Clarifiers

Trevor Wagenmaker, P.E., Hubbell, Roth & Clark Todd Schaedig, P.E., City of Warren.

January, 2017

Background

City of Warren is the 3rd largest City in Michigan with a population of 135,000

Home to the General Motors Tech Center

Background

City of Warren WWTP is a 54 MGD Tertiary Plant with a peak wet weather flow of 180 MGD

Secondary Treatment System includes eight (8) 100 foot diameter secondary clarifiers.

There are two banks of four clarifiers each, with a splitting box for each back of clarifiers

Background

Four (4) of the eight clarifiers were constructed in the 1950’s and had not been rehabilitated since

Background

There were in extremely poor condition

Flow Split Structure

The flow split structure was also failing

Summary of Problems

Clarifiers only had 10 feet of sidewater depth which limited performance (10 State Standards recommended depth is 12 feet)

Generally poor settling performance due to configuration of effluent weirs and lack of baffling

Constant breakdowns in clarifier mechanisms and steel degradation to the point of yearly failures

Summary of Problems (cont.)

No SCADA control or monitoring of any electrical components

Ice problems in the winter with the scum beach/scum arm freezing

Concrete degradation of the tanks increasingly bad Flow split structure was very difficult to operate with

no gate operators and limited access

Study Phase

Option of Total Replacement versus Partial replacement Costs were much higher for total replacement Base slab was in good condition Pipes were in good condition

How increase sidewater depth of tanks to 12 feet? This would require either raising flow split structure

approximately two feet or lowering clarifier base slab Backwater affects to aeration tanks were a concern

Study Phase (cont.)

How maintain treatment during construction? Reconstructing flow split structure would eliminate

existing piping connections to all four clarifiers Performance Enhancements Influent flow dissipation. Numerous options by different

manufacturers, LA-EDI Effluent flow baffling Effluent In-board Launders Stamford Baffles

Study Phase

Performance enhancement options Resolve ice issues for scum arm Torque monitoring for clarifier drive (SCADA) Algae control on effluent weirs/launders Brushes Effluent trough covers

Automatic control for flow split structure gates Roadway thru the area

Demolition

Walls and mechanism were removed

Construction Process

Base slab was extended/thickened.

Construction Process

New taller walls, reconnection of pipes.

Construction Process

Grout floor topping removed and replaced, new concrete effluent launders.

Temporary Flow Bypass System

Maintain flow to two clarifiers while flow split structure was being reconstructed

Temporary Flow Bypass System

Routed temporary pipe to influent of clarifiers

Galvanizing Operation of Steel Clarifier Mechanism

Galvanizing of new clarifier mechanism steel components eliminates need to field paint

Construction Process

Clarifier mechanism installed.

Flow Split Structure

• Resealed floor opening to effluent chamber below

Flow Split Structure

• Rebuilt walls, new automated gates to each clarifier

Site Improvements

New roadway thru site

Algae Brushes

Effluent Stamford Baffles

Dual Suction Header Sludge Withdrawal

Influent Flow Dissipation

Torque Monitoring

SCADA Improvements

Costs

Total Project Cost $5,460,393.94 Study of Alternatives $32,000.00 Project Design $247,400.00 Geotechnical Investigation $5,954.18 Construction Cost $4,989,170.76 Materials Testing $13,801.96 Construction Administration $98,960.00 Controls Manufacturing and Programming $59,427.04 Project Inspection - Performed by Plant Staff - Estimated

Savings $150,000

Questions