Plan for Milorganite processing calls for solar panels

MILWAUKEE, WISCONSIN - Solar energy would provide nearly all of the electrical power needed to transform sewage sludge into Milorganite fertilizer at the Jones Island wastewater treatment plant, under a proposal by the Milwaukee Metropolitan Sewerage District.

Four rows of photovoltaic panels would be installed atop the roof of the Milorganite plant this year at a cost of $198,000 if the proposal is approved by the sewerage commission. The south-facing panels would be visible to motorists on I-794 crossing the Hoan Bridge. Grants of $72,500 from We Energies and $35,000 from the state Focus on Energy program would pay 54% of project costs, sewerage district Executive Director Kevin Shafer said at a meeting of the commission's operations committee.

The committee recommended approval. The Milorganite plant would become nearly 100% self-sufficient for electrical needs, depending on cloud cover, if the solar panels are installed, Shafer said. By eliminating the need to buy electricity from We Energies, the project would pay for itself in 18 years, well within the expected 30- to 40-year useful life of the equipment, a preliminary analysis found.

Most of the energy consumed at the plant, however, comes from natural gas, which is burned to dry sludge in Milorganite production. Photovoltaic panels contain semiconductors that convert sunlight to electricity. The proposed 20-kilowatt system would generate about 24,130 kilowatt hours of electricity in a year, according to the preliminary analysis.

One kilowatt is 1,000 watts of electricity.The sewerage district already produces much of the electrical power needed to operate its South Shore wastewater treatment plant in Oak Creek. Methane released by microbes digesting sewage sludge is burned to generate electricity there.