Wastewater administrator outlines Class A power project: new digesters, methane recovery and $200M+ cost estimate

Mark Heinser, administrator of the wastewater department, briefed the council on a multiyear Class A power project at the wastewater plant that would replace aging systems, broaden digestion capacity and capture methane for on‑site electricity generation.

Heinser began by reviewing a 2013 consent decree with the EPA and Tennessee: over the last 13 years the city pursued collection-system rehabilitation, pump‑station work and tank construction to address chronic overflows and is now on track to finish stipulated projects about six months early. He said the result has been elimination of chronic overflows and a 90–95% reduction in overall overflows.

At the plant, Heinser proposed decommissioning a 45‑year‑old cryogenic oxygen plant that costs roughly $1 million a year to run, and retrofitting aeration tanks with IFAS (integrated fixed‑film activated sludge) and blowers that city staff can operate and maintain. "We don't have to have that oxygen," he said of the old system, arguing IFAS will boost treatment without new tank volume and reduce reliance on specialized contractors.

On biosolids, Heinser said the city produces roughly 70,000 tons a year today and expects the project to reduce that to about 7,000–10,000 tons of dried, Class A product. The plan calls for four new anaerobic digesters, methane recovery and a drying system that could produce a biochar‑type product with little odor and potential market value.

Heinser reported a two‑phase schedule: Phase 1 ("early works") to prepare the site and deploy six generators (expected delivery December 2026) and Phase 2 to build the digesters and the remaining generators over multiple years. He projected liquid‑process upgrades at $70–80 million and biosolids processing at $130–150 million; funding would combine a down payment of saved funds and low‑interest loans, with a target cash‑on‑hand floor of $30 million.

Heinser also highlighted potential operational savings: capturing methane and converting it to electricity could materially reduce the plant's energy bills (currently cited near $3–4 million annually). He estimated the first phase could cut electricity costs by close to $100,000 per month if performance meets projections. He noted EPB and TVA support the project in principle, and that similar systems exist elsewhere.

Councilmembers asked technical and financial questions: how dissolved oxygen will be measured (Heinser: "dissolved oxygen meters"), whether effluent oxygen levels will be similar under IFAS (Heinser: "roughly the same"), marketability and price ranges for dried biosolids (Heinser quoted web‑search figures of $600–$1,300 per ton and mentioned possible carbon‑credit values around $130/ton), and contractor risk for the dryer. Heinser said dryers are contracted services and the city can change contractors if performance fails; in a worst case the city would still have a better, less‑odorous Class B product to continue field application.

Heinser closed by stressing the project's resilience and long‑term planning value, saying the combined upgrades would extend plant life 40–50 years and position Chattanooga for growth. Council asked for follow‑up data on costs, projected rate impacts and commercialization options for dried biosolids.