Wafting odors, increasing operational efficiency, and making the most of captured methane prompted another upgrade proposal for the Montpelier Water Resource Recovery Facility at a city council meeting last month. The $16.4 million project aims to capture methane produced by the plant’s waste treatment and use it to power a new dryer at the plant. While potentially reducing odors, the dryer project will reduce the amount of material hauled to the landfill in Coventry, Vt. It also will produce biosolids containing PFAS that may be distributed for land application.
The project will be on the ballot as a bond vote during Town Meeting Day, March 1, 2022. If passed, the $16.4 million debt will be paid through water and sewer usage rates over 20 years. However, Kurt Motyka, Montpelier’s public works deputy director and engineer, said the upgrades could improve efficiency at the plant such that the facility operates on a break-even basis. The project is one of four separate bond votes that will be on the Montpelier ballot this year. Public hearings to discuss the bond votes and the city budget are scheduled for Jan. 12, and Jan. 20, both at 6:30 p.m. either in person at city hall or online. Find out more here.
Motyka presented information about Phase II to the city council along with Chris Cox, water resource recovery facility chief operator, and Colin O’Brien, a project manager for the environmental engineering firm Brown and Caldwell.
Upgrades to the wastewater plant (“Phase I”) were completed in June 2021, Motyka said, which allowed the plant to accept food scraps and brewery waste (“high-strength organic waste”), resulting in increased methane production. As a result, the plant has been able to replace oil with methane to heat the facility in winter. But last summer, when more septage came into the facility, excess methane required flaring. So, Motyka said, the team searched for a way to put that methane to better use.
The team considered various technologies, said O’Brien, and settled on “an indirect-fired belt dryer” as the best use for excess methane. O’Brien noted that the team sought the safest and most efficient solution.
A hot-water belt dryer, explained Motyka in an interview, is like a pizza oven: waste travels through the heated dryer along a belt, then onto a second belt, where it travels back. The dryer spurs evaporation, producing dried granules containing 10% water (as opposed 75% water, as with the plant’s current process).
O’Brien said the belt dryer’s waste processing will yield “class A material” that can be put to beneficial reuse. Class A materials, according to the U.S. Environmental Protection Agency (EPA), are considered free of pathogens and can be used without restriction.
Class-A biosolids can be used as soil amendments and greenhouse gas storage because they carry carbon into the soil, Cox said. Locations for such uses might include mine reclamation and superfund sites, he noted.
Another benefit of the belt dryer, said O’Brien, is its automation. “One really important thing for the WRRF staff was that we can run this automated. The rest of the plant is very automated, so you can dewater your sludge currently without anybody being there. The operators have the availability to log into a laptop and view the plant’s current operations.” O’Brien added that this solution has minimal impact on current staffing needs.
The belt dryer project requires a new building and new hot water boiler, which would replace an existing dual-fuel boiler, O’Brien said. Space in the current dewatering building can accommodate a pump that moves solids to the new dryer building. The belt dryer would also reuse existing hot water boilers at the site, O’Brien noted.
Cox said the granules produced by the dryer could be a marketable commodity. “The goal is to sell this product, right from the start.” He said the biosolids could potentially be sold within a 30-mile radius, and a third-party resource management company would handle the biosolid management at first. But, Cox said, “If a robust-enough market for the material is established, the city will eventually be able to manage their own product and reduce costs further.”
In a subsequent interview, Motyka noted that other plants the team visited during their research did not sell the product, but simply gave it away. Motyka also said that the Phase II budget did not account for biosolid sales, and if the biosolids do go to market, it would be through the managing company, not by the city.
Savings in Reduced Trucking
Cox pointed out that “Another benefit is reduced solids disposal volume and associated reduction in trucking.” The plant’s current process creates waste containing about 70% water that must go through the plant’s treatment process, Motyka had explained in an earlier interview, with the remaining solids heading back to the landfill.
Because of that, Cox said, the plant currently produces about 3,800 tons of solids per year, but with the new dryer, output may reduce to 1,300 tons. Such a change would mean a 78% reduction in carbon dioxide emissions from trucks transporting material, Cox said. He noted, “This dryer aligns with core functions of the resource recovery facility.”
Despite these reductions in emissions, methane, which replaces oil as a heat source at the plant, is a powerful greenhouse gas in its own right. According to the National Oceanic and Atmospheric Administration, methane is 28 times better at retaining infrared radiation than carbon dioxide. Motyka noted, however, that virtually no methane releases from the plant; instead, it heats the building or gets flared.
Cox said the upgrades will reduce smells, addressing a directive from the Vermont Department of Environmental Conservation, which requires the city to control odors emitted by the plant.
Phase I upgrades brought the plant’s dewatering building up to code, Motyka said. This increased air circulation (moving air into and out of the building), which led to a higher heating demand. Motyka noted that by connecting dewatering equipment to odor control, air exchanges could be reduced (along with oil consumption). In other words, the Phase II plans that alleviate odors will make the building smell better, so they won’t need to exchange air as frequently, resulting in energy and cost savings.
Cox said the facility’s anaerobic digester currently works at 50% capacity, but at the projected 80% capacity, it will produce enough methane so little other fuel will be required to heat the building. Furthermore, less ventilation to the outside could help lessen the odors neighbors have experienced.
The overall cost for the Phase II project is $16.4 million, with the capital, engineering, construction, and final design cost at $11.6 million; the secondary clarifiers and associated costs at $1.8 million; and the odor control needs at about $3 million. Motyka noted the equipment for Phase II should be paid off in about 19 years total. In 10 years, Motyka said, the anticipated budget with the belt dryer in place would be $848,000.
“Now is a great time to do a big project,” Motyka said. “There is more funding than I’ve ever seen in my 15 years here at the city.” Potential funding sources include U.S. Department of Agriculture grants and funding through the Clean Water State Revolving Fund and the American Rescue Plan Act of 2021.
The team considered other possibilities to use the plant’s excess methane, Motyka said, including combined heat and power. But this would be tough to fund via grants, and would need to be completed by December 2023 because of the terms of the associated power sale agreement. Thus, the team arrived at its decision that the belt biosolids dryer was the best option.
“Our recommendation is to proceed with final design on the biosolids dryer,” Motyka said at the meeting. “The economics and long-term price stability and renewable opportunities that it presents, we feel like that’s the best project. We also advise that we include the secondary clarifiers and the odor control.” He added that the team suggested moving forward with submitting grant applications, planning for bond warning, and, if legally permitted, perhaps combining with the East State Street ballot item.
What about PFAS?
City councilor Lauren Hierl expressed concern about PFAS and other contaminants in biosolids, and asked about their removal. O’Brien responded that both the EPA and DEC have requirements regarding how PFAS must be handled, and PFAS chemicals can occur in both the effluent (fluid) and biosolids that emerge from the plant. Technology is available to remove PFAS from liquid, he said, but not in biosolids, “EPA has not sanctioned a method that is acceptable to test or treat biosolids. There’s a lot of technologies out there currently that have claims, but those aren’t sanctioned, approved treatment disposal methods by EPA.” However, he said, drying is a first step in finding ways to deal with PFAS in the biosolids.
As Motyka noted in an interview, PFAS chemicals are widespread and found virtually everywhere, but they exist in higher levels in the landfill leachate the plant accepts than in other materials. The city council plans to stop accepting landfill leachate within one year unless leachate gets treated to drinking water standards, said Motyka. The biosolids dryer would not be online and functional before this deadline, he noted; it would likely take two years or longer to complete Phase II.
“The PFAS levels in the biosolids I don’t think can be confirmed reliably based on our current testing methods,” said Motyka in an interview. A 2019 report by Waterbury firm Weston and Sampson for the Vermont Department of Environmental Conservation found that concentrations of five chemicals, under the umbrella of PFAS, in sludge solids from around Vermont averaged 22 to 27 parts per billion. However, the report indicated an average of just over 35 parts per billion of these PFAS in class-A biosolids, the type of material the proposed Montpelier belt dryer would yield. Motyka said “(t)he drying process would not increase PFAS levels, so I’m not sure how valid these numbers are for Montpelier.”
The current EPA limit for PFAS in drinking water is 70 parts per trillion. Vermont’s drinking water standard is 20 parts per trillion. Pyrolysis, a potential means of eliminating PFAS from waste, is not currently being considered in Montpelier, said Motyka in the interview. The process has not yet approved by the EPA; plus, it’s expensive and, he said, would probably be on a regional rather than local basis.
In the end, Montpelier Mayor Anne Watson expressed her approval. “This seems like a really promising project,” adding her hope that pyrolysis could address PFAS concerns moving forward. Others echoed her approval.
“What Chris (Cox) and I like about the project is we are using renewable energy to create a renewable material that is otherwise landfill,” said Motyka.