Madison advances $223m consolidated biosolids and RNG project

Madison advances $223m consolidated biosolids and RNG projectThe Wisconsin utility has selected a Class A liquid biosolids alternative to address storage constraints and will bundle the upgrades with a transition to renewable natural gas to achieve economies of scale.

The district's preferred Class A liquid alternative carries a $107 million capital cost, part of a broader $184.1 million biosolids upgrade.

Consolidating the biosolids work with a $38.6 million heat and power improvement plan is expected to yield 10% to 15% in cost savings.

The energy component will replace aging cogeneration engines with a biogas upgrading system for pipeline injection.

To support the growing capital program, the district's Executive Director warned of an anticipated 12% service charge increase in the upcoming budget.

Madison Metropolitan Sewerage District (MMSD) is advancing a consolidated $223 million infrastructure program to overhaul its solids handling processes and transition its energy systems to renewable natural gas (RNG). During the commission's August 13 meeting, Planning Engineer Ana Uroic Stefanko presented the draft Biosolids Facilities Plan, which addresses mounting constraints in storage capacity, hauling, and available land application acreage. The district currently produces Class B liquid biosolids and utilizes approximately 7,000 acres for land application, but has struggled with weather-related storage challenges in recent years. After evaluating six alternatives ranging from $88 million to $215 million, the district identified a Class A liquid biosolids pathway as the preferred option. The selected process utilizes thermochemical hydrolysis—injecting steam and potassium hydroxide—to break down the biosolids. While maintaining the current Class B operations would require an $88 million baseline investment, the $107 million Class A alternative was chosen for its long-term operational benefits. Uroic Stefanko noted the process will reduce product volume, increasing the district's storage capacity to nearly 400 days without the need to construct a fourth storage tank. The resulting product will also feature lower nitrogen and higher potassium levels, allowing the district to increase application rates and reduce its required land footprint to roughly 5,500 acres while cutting hauling trips by two-thirds. When combined with $32 million in asset replacements and other process improvements, the total biosolids capital cost is estimated at $184.1 million. Commissioners also formally accepted the district's Heat and Power Improvements Facilities Plan, which carries a $38.6 million price tag. The selected alternative will replace aging cogeneration engines with a biogas upgrading system to condition, compress, and inject RNG directly into the natural gas grid, while decentralizing the plant's heating systems. Because the thermal and biosolids systems are highly interconnected, the district intends to bundle the two initiatives into a single mega-project. Staff indicated that delivering the projects together is expected to yield 10% to 15% in capital cost savings by avoiding duplicate construction mobilizations and mitigating inflationary risks. Design for the consolidated project is slated to run from 2027 through 2029, with construction scheduled for 2030 to 2032. The massive capital pipeline is already putting upward pressure on user rates. During the meeting, the Executive Director warned commissioners that customer communities should expect a service charge increase of approximately 12% in the upcoming 2027 budget to support capital projects and new reserve policies. The district is already ramping up major construction, having recently awarded a $90.9 million contract for Phase 2 of its Liquid Processing Improvements, with on-site work expected to begin next spring.