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Iowa City approves $28.2M bid package for wastewater digester upgrade and renewable natural gas system
Summary
The City Council approved plans and a bidding schedule for a multi‑phase rehabilitation of the wastewater treatment plant digester complex, including a renewable natural gas system expected to produce revenue and cut energy use. The project is budgeted at about $36.2 million with an estimated payback of 12–15 years.
The Iowa City Council on June 3 approved plans and directed staff to solicit bids for Phase 1 of a rehabilitation of the city’s wastewater treatment plant digester complex, a project that includes production of renewable natural gas (RNG) and upgrades to aging infrastructure.
The vote clears advertisement of a $28,200,000 construction package for work the city estimates will total about $36,200,000, including interconnection and technical costs. The city expects about $3 million in Inflation Reduction Act rebates after the system is operating and a projected net revenue of about $1 million a year from tipping fees and gas sales, the project team told the council.
Why it matters: the rehabilitation replaces 20‑plus‑year‑old digester equipment, reduces the plant’s electrical use and aims to convert waste gas into pipeline‑quality natural gas that will be sent to MidAmerican Energy. City staff and consultants said the upgrade will both reduce greenhouse‑gas emissions associated with flaring and create a new revenue stream to offset operating costs.
Consultant Randy Wirtz summarized the plan and timeline, saying the digester work includes new mixing systems, stainless‑steel covers on tanks and a new sludge‑processing building sized to accept fats/oils/grease (FOG) and high‑strength waste. “We’re expecting the bid costs to be in the neighborhood of 28,200,000,” Wirtz said. He said the RNG equipment will be containerized and the pipeline interconnect to MidAmerican will be approximately a half‑mile of small‑diameter, high‑pressure line.
Ben Clark, civil engineer with the city’s engineering division, presented the formal project resolution to open the public bid process. Clark told the council the planned construction timeline runs from July through November for the advertised contract, with RNG contracting and pipeline work extending into 2027 and final project completion expected around June 2028.
City staff emphasized parts of the original scope were “descoped” to reduce cost but that the building and connections will be sized so additional equipment can be added later. Wirtz said the work could roughly double the plant’s gas production by accepting high‑strength waste and FOG from commercial generators and by installing screening and storage systems that increase recoverable gas.
On finances, a city staff member noted the project will be financed from the wastewater fund (rate‑supported debt and a state loan are planned). “We are issuing revenue bonds… and there will be debt, but it will only be wastewater funds to pay back that debt,” the staff member said.
Opponents did not appear at the hearing; several council members praised the project’s technical approach and the potential for both environmental benefit and revenue. Council approved the resolution to advertise the $28.2 million contract and set the bid opening for July 2025; the council later voted to award the contract after bid review.
The project team said equipment orders already placed in 2024 were timed to qualify for federal rebates and that the city will begin an RFP process in late 2025 or 2026 to secure a gas‑marketing (broker) agreement; RNG injection is forecast to begin in mid‑2027 with full completion in 2028.
Ending: The city will advertise the contract in July; staff expect to return to council in early August for contract award and to bring back RNG contracting terms in the months ahead.
