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Methane Conversion at Struthers WWTP

Methane Conversion at Struthers WWTP

Methane Conversion at Struthers WWTP


The city of Struthers needed a cost-saving and innovative design to utilize the methane gas byproduct produced by its wastewater treatment plant.

Services Involved

  • Architectural Design
  • ARRA Funded
  • Bidding
  • Construction Administration
  • Construction Representation
  • Electrical Engineering
  • Environmental Planning/Engineering
  • Green/Energy Savings Aspects
  • Mechanical Engineering
  • Site Design


2012 Honor Award

American Council of Engineering Companies (ACEC) of Ohio

Methane Conversion at Struthers WWTP

In 2009, the City of Struthers received $5.4 million in funding assistance from the Ohio Environmental Protection Agency (OEPA) as part of the federal American Recovery and Reinvestment Act (ARRA) “Green Projects” stimulus program. The grant provided total funding for a project to utilize the methane gas produced as a byproduct of the primary digester at the 6.0 MGD Struthers Wastewater Treatment Plant (WWTP) to produce electricity to operate the plant. The project will save the city hundreds of thousands of dollars in future utility costs.


The city retained ms consultants to provide design, bidding and construction services for the plant modifications required to implement this innovative and cost-saving project. ms was instrumental in assisting the city with the ARRA funding application and the required support documentation.


ms completed the design of the modifications necessary to collect the methane gas produced in the primary digester. This required the demolition of the existing cover over the 50-foot-diameter primary digester, followed by replacement with a Siemens Dystor® gas holder system. This new cover consists of a fixed outer membrane and a flexible inner membrane that moves freely as it stores or releases gas generated by the anaerobic digestion process. In addition, approximately 300 feet of 6-inch gas pipeline was designed to transmit the gas to new generators.


ms prepared the design for the installation of two new 375 kw generators that can operate by either utility-supplied natural gas or plant-supplied methane gas. The paralleling switchgear rating is 1,600 amps, 480/277 volts, 3-phase, 4-wire. The generators will be housed in a new 50’ x 50’ building.


In addition to the new digester cover and the generators, the project team also designed the following improvements to the WWTP. These improvements will help to maximize the amount of gas that the sludge digester will produce.


  • A new sludge thickener, consisting of a flocculation tank, disk system, static mixers, discharge tank, disk drive and thickened sludge storage hopper. Included a new 45’ x 45’ building west of the existing east sludge storage tank to house the sludge thickener.
  • The replacement of the existing methane gas line and waste gas burner.
  • A floating aerator in the west sludge holding tank to assist with odor control.
  • The addition of two new 200 gpm rotary lobe secondary sludge pumps.


The design team also was required to provide a site design that would allow the new buildings to fit onto the limited available space at the WWTP site. The site design required relocating a parking area, site clearing and grading, and installation of new storm drainage for both the new buildings and the new parking area.


Upon approval of the final design, ms developed design plans and specifications, contract documents and cost estimates. The team supplied bidding assistance, which includes the distribution of plans and contract documents, a pre-bid meeting, responses to RFIs, issuance of addenda when required, assistance with the bid opening and tabulation, and a recommendation for award of the construction contract.


ms also supplied construction-phase services, including administration of the construction contract as the owner’s representative and onsite construction inspection to verify that work proceeded in accordance with the contract documents.

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