Over the last few years, lots of information and explanations about methane and our sewer plant have been researched and shared in the newspaper, at public meetings and via social media.
Shweta Sagun Sawant recently looked at whether a generator that reuses methane was an option. As a SUNY New Paltz electrical engineering graduate student and intern for the Village’s Environmental Policy Board, Sawant completed a methane-to-energy study for our sewer plant and deserves enormous credit and thanks.
In 1999, the Village installed a well-intentioned but imperfect dual-fuel system using methane from the plant and heating oil to warm sludge during its dewatering process. Sludge needs to be heated during anaerobic digestion, a biological process that breaks down organic solids. Anaerobic digestion is different than aerobic because aerobic uses oxygen and anaerobic is oxygen-free and requires heat. Think of the temperature needed in your stomach for digestion. Similarly, our sewer plant’s anaerobic digester works best when sludge is at 98 to 105 degrees.
Unfortunately, the volume of methane at our plant was not large enough for the conversion system to work efficiently and we still needed a significant amount of heating oil to heat sludge. Additionally, the methane was corroding the plant’s mechanicals. A small 100-pound cylinder of propane was used to keep the equivalent of a pilot light on so the methane could be used. There has never been any propane or natural gas used to heat sludge to foster anaerobic digestion. Only heating oil and methane have been used.
After less than 10 years of use, the dual-fuel system failed and was not replaced. The plant shifted to burning methane without using its energy. By burning methane, bonds in the oxygen and methane come apart, the atoms rearrange, and then re-bond to form water and carbon dioxide.
This continued until 2016 when the secondary digester’s mixer and floating cover broke down. Without a functioning floating cover, the plant was simply releasing methane directly into the atmosphere and not able to burn it so it could be converted to water and carbon dioxide. We needed to more responsibly handle the plant’s methane emissions. In response, the Village Board authorized investing approximately $850,000 in various new equipment for the plant.
Methane is collected on top of the roof next to the secondary digester well above where any flood water has ever reached. If there was no power because of a flood, methane would burn until it ran out. The bacteria making the methane will still keep off gassing even if the plant’s power and pumping stops — just like an old landfill. The amount of methane will only diminish with time and as sludge in the digester cools.
In an emergency when there isn’t power at the sewer plant, sludge would not be getting fed into the digesters. No power would be troublesome because it would not only mean our sewer plant was offline, but floods or stormwater infiltration — big problems in their own right — are completely different challenges facing the sewer plant and are unrelated to figuring out how to manage methane.
We made an important step in the right direction by burning methane again. The non-profit Environmental Defense Fund has reported that methane does not linger as long in the atmosphere as carbon dioxide, but methane is problematic because it traps more than 80 times more heat in the atmosphere than carbon dioxide during its first twenty years after release.
The study examined whether electricity could be generated from the methane. The focus was on whether the equipment exists and could work reliably at our low-level of expected methane production. It was discovered that a simple process where methane is burned to generate electricity for something like lights might make the most sense. The goal was to investigate a straightforward solution without the complexity of the 1999 dual-fuel system.
Next steps will require a costs versus benefits analysis. How much will it cost to meter the relatively small amount of methane that our sewer plant produces? This information is needed to see what type of methane-to-electricity equipment may be considered. Once that is known we can then explore whether it makes financial sense to buy a generator that runs on methane.
Harnessing methane for electricity could be an excellent outcome but given the costs, right now there appears to be
It is important to note that taxpayers do not directly fund sewer plant operations or its capital improvements. Per state law, these are the responsibility of ratepayers based on their demand from the utility. Grants from the state have also been used to purchase new plant equipment. There are ratepayers using our sewer plant in the Village and in the Town outside the Village. Village property taxes do not pay for our sewer plant.