Home News and Features New Technology Proposed to Treat Capital City Wastewater 

New Technology Proposed to Treat Capital City Wastewater 

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Image of brick building with pipes and a dome.
Montpelier's Water Resource Recovery Facility. Photo by Lauren Milideo.
Montpelier’s wastewater treatment plant upgrades may include a high-temperature gasification system and drum dryer, as well as odor-reduction systems. The $16.4-million price tag for these upgrades will likely increase because of higher than projected labor and other costs, but the city is receiving nearly $3 million in federal infrastructure grants. 

In a presentation at the Oct. 26 city council meeting, Kurt Motyka, the interim public works director, described a shift in how waste will be processed. The new plan moves from the belt dryer solid waste treatment described at the December city council meeting, to a drum dryer — a method that uses high temperatures onsite to dry solid waste and reduce its volume, meaning far less solid waste will be transported from the Montpelier plant to the Coventry landfill. The change is significant; from the current two 40-yard dumpster containers of waste per week to two a year, Motyka noted. 

Another part of the plan includes an emerging technology not widely used in the United States: a gasification process to destroy per- and polyfluororakyl substances (PFAS) in the waste. A 2021 EPA research brief about technologies to destroy PFAS refers to gasification (and another related solid-waste treatment, pyrolysis) as “emerging treatment technologies.” The brief notes that much remains to be learned about the long-term use of gasification, which requires significant up-front investment.

While drum dryers are common in treatment plants across the country, Motyka noted that only one other plant used this gasification process in the United States. That system was used for a year and data collected on it, and that same gasification unit is now on its way to a different plant to be installed there, Motyka said in an interview. One other gasification unit is planned in the country, Motyka said.

An engineering report about options for handling solids at the plant was submitted last June, and Motyka noted in an interview that as the engineering team moved through the report process, it became clear that “PFAS would be a big issue for the state” in coming years. The gasification system heats these hard-to-destroy chemicals to temperatures (typically 800 to 1650 degrees C) that destroy them by breaking the carbon chains they contain. And, Motyka said, “it was essentially the same capital cost.”

 This led the report to identify the gasification system as “the better alternative,” Motyka said in an interview. His Wednesday presentation noted that “air emissions” from the plan were “being evaluated,” and he noted in the interview that the plant would need an air-quality permit for the gasification unit. 

“I do anticipate there will be some very specific air-quality requirements,” he said.

The selected process uses methane to get started, Motyka explained, but from there, uses energy within the solids themselves to sustain the drying process. 

The proposed system would also house a self-contained odor control unit, Motyka said at the meeting. This follows complaints from residents about odors emanating from the plant, and an air-quality violation last November as a result of the plant’s odor. The high-strength organic waste (i.e., food- , brewery- , and dairy-derived waste believed to be causing stronger odors) peaks during the summer months, Motyka said. He noted a technical memo from engineering firm Brown and Caldwell indicated that most of the odor was coming from the first blend tank, which sees 10 times the high-strength waste loadings of the other locations at the plant. 

The plan for updating odor control at the plant’s Area One (from which most odors originate) would include an odor removal system in which bacteria consume odor-causing particles, followed by carbon filtration, removing 99% of odors, Motyka said. This would cost about half a million dollars, plus the cost of site work, he said. The plant’s Area Two plan would involve a carbon-scrubbing mechanism, which would cost about $150,000, Motyka said. 

Motyka announced at Wednesday’s meeting that Montpelier had received a USDA Rural Development grant for $3.251 million, and an American Rescue Plan Act grant for $1.275 million. A low-interest USDA loan for about $15.9 million. The USDA grant is to be applied in part to the plant’s Phase II project per a city-issued press release. The ARPA money will go toward part of the East State Street Reconstruction Project, the release said. The city is also awaiting word on additional grant funding up to about $1.5 million. Motyka noted at Wednesday’s meeting that with the $16.4 million bond passed earlier this year, the city remains in a good position.

Meanwhile, the plant continues to hold off on accepting leachate from the Coventry landfill, Motyka said, with leachate last accepted at the plant in April. The plant stopped accepting leachate following a high E. coli count found in plant effluent, and workers later determined that leachate in the water was lessening the effectiveness of the plant’s ultraviolet disinfection system, Motyka explained. 

Casella Waste Management, which operates the Coventry landfill, has chosen a PFAS treatment technology for the leachate, Motyka said at the meeting, and is hoping to have the system by July in time to meet a deadline that the city council had set in order to continue accepting the landfill’s leachate. Motyka noted that permitting and equipment delays left this date in question, however. 

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