I’ve taught environmental courses for high school, college and the general public. I often begin such a course with two questions: 1. (pointing at an electric outlet), “Where does your electricity come from?”; and 2. (pointing at a bathroom), “Where does it go when you flush the toilet?” It’s surprising how few otherwise educated citizens can answer confidently.

This column explores both questions, as they apply to the town of Middlebury.

Until the 1960s, question 2’s answer was simple: Middlebury dumped raw sewage directly into Otter Creek. There followed a series of increasingly effective wastewater treatment plants that reduced the pollution going to Otter Creek. In March 2025, Middlebury voters approved a $50 million bond for upgrades to the treatment plant and related infrastructure.

Middlebury’s wastewater treatment plant has two products: treated water that’s discharged to Otter Creek, and dried sludge. The goal is to produce the Environmental Protection Agency’s Class EQ (Exceptional Quality) biosolids, which are approved for widespread use including land application as fertilizer. Among other requirements, Class EQ biosolids must be at least 90% solids — and that means removing nearly all the water that constitutes the bulk of our sewage.

Sewage treatment starts with mechanical removal of large objects, followed by settling to remove some solids, then biological processes where bacteria digest waste to reduce its oxygen-depleting effect. Next, chemical treatment removes harmful pollutants such as phosphorus and other nutrients. The result is a wet sludge that’s about 99% water. Electrically powered mechanical de-watering — similar to the spin cycle in your washing machine — increases the solids content to about 20%. A final drying step brings the solids content up to the desired 90%. Our current plant uses lime to dry the sludge. Lime is expensive and its production (which takes place in Canada) is energy intensive and produces climate-changing greenhouse gases.

The upgraded treatment plant’s sludge processing will still begin with mechanical de-watering, but will then use high-temperature heating for the final drying. This choice is driven in part by the possible need to later add pyrolysis treatment, which destroys “forever chemicals” and other contaminants that survive conventional sewage treatment.

Unfortunately, the choice of high-temperature heated drying rules out less energy intensive drying methods, including possible use of heat pumps. The sludge dryer that’s being proposed for Middlebury’s treatment plant heats mineral oil to some 400 degrees Fahrenheit and circulates the oil through a screw-like device that moves initially wet sludge through the dryer until it emerges as a dry, usable biosolid.

Where to get the energy for heated sludge drying? Natural gas and electricity are our two choices. The Middlebury Energy Committee and the engineering firm Wright-Pierce, consultants on the treatment plant upgrade, are both attempting to compare costs and greenhouse gas emissions associated with the two energy sources, and the Energy Committee is taking a careful look at those numbers that Wright-Pierce has made available.

There are still many unknowns — detailed specifications of the drying equipment, its energy requirements, special rates we might get from Green Mountain Power, future cost increases for gas and electricity, etc. Under current conditions, using electricity would increase operating costs for the treatment plant, and that would result in a modest increase in ratepayers’ sewer bills.

But in the future it could go the other way, with electricity ending up cheaper. We face real challenges in trying to project costs over the next 20 years because it’s nearly impossible to predict how electricity and gas prices will change over two decades. If both increase at the same rate, then we would spend less money if we went with gas. However, some models suggest that the cost of electricity may not increase as rapidly as that of gas, and that the price of gas may fluctuate widely because it’s a global commodity — as is happening with the price of oil in today’s tumultuous world. So in the long term, Middlebury ratepayers might or might not see larger sewer bills if we went with electricity.

Why would we choose electricity? Because using gas would result in a many-fold increase in climate-warming greenhouse emissions as compared with electricity.

In 2021 the Middlebury selectboard established this goal: “That emission of carbon dioxide-equivalents as a result of Town operations be reduced by 80% compared to 2018-2019 fiscal year levels, in or before fiscal year 2029-2030.” In 2026 we are still far from achieving that goal, and adopting gas-based sludge drying for our wastewater treatment plant would make its achievement virtually impossible.

Why would I, personally, want to pay a modestly higher sewer bill that might result from the choice of electricity over gas? Because I’m concerned that climate change is causing irrevocable damage to our planet — including climate-exacerbated flooding right here in Vermont, where we rank fourth in per-capita spending on climate-related disasters. I’m willing to pay more for sewage treatment as part of my personal share in mitigating climate change, and I would be proud of my town for doing its small part in the effort to slow global warming. Given the unpredictability of future energy costs, it’s hard to quantify possible increases for ratepayers. If the “green” solution — electric sludge drying — turns out to be more expensive, how much more would you be willing to pay on your quarterly sewer bill to avoid emitting thousands of tons of carbon dioxide?

We in Vermont are blessed with a progressive electric utility, Green Mountain Power, whose generation entails very little greenhouse emissions. That’s the reason for the mantra “Electrify Everything,” which is driving the move to cold-climate heat pumps, electric vehicles, and other technologies that replace fossil fuels with electricity. Shouldn’t that include the way we treat our sewage?

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Rich Wolfson is Professor of Physics and Environmental Studies, Emeritus, at Middlebury College. He is the author of the textbook “Energy, Environment, and Climate” and serves on Middlebury’s town Energy Committee.