MIDDLEBURY — Many humans believe 20 years old is the gateway to their prime.

Not so for municipal wastewater treatment plants, which pretty much age in dog years. Middlebury’s plant is marking its 20th birthday this year — not with a big party and imminent adult status, but rather a senior citizen-like list of aches, pains and parts in need of updating or replacing.

The town has hired the Montpelier engineering firm of Tata & Howard to diagnose the Middlebury wastewater treatment plant’s (MWTP) deficiencies and to propose fixes to keep the critical piece of infrastructure humming for another two decades. The plant receives and treats waste from hundreds of local homes and scores of businesses — including AgriMark/Cabot, Porter Medical Center, Middlebury College and Otter Creek Brewing — all crucial to Addison County’s employment scene.

Tata & Howard launched its study of the MWTP in 2018, and is expected to deliver its findings in around a month, according to plant Superintendent Bob Wells. Recently Wells provided the Independent with a peek at some of Tata & Howard’s early findings, including proposed solutions that he said could total upwards of $18 million.

“The plant is getting old,” he said. “You’ve got parts and pieces that are obsolete. We have a hard time finding (replacement parts), and it reaches a point where you have to go with after-market stuff, or see how you can (modify) things just to make them work.”

Case in point — what Wells called a “comb and rake” assembly that is part of the plant’s septage receiving equipment. Waste haulers pull up, connect their trucks to the system, and unload their septage cargo into what is essentially a big box. The material is run through the comb-and-rake assembly, which removes anything larger than a quarter-inch in diameter.

Wells recalled an episode where the teeth in the rake got bent, and couldn’t be replaced because of their vintage. So he and his staff trimmed the bent teeth in order to keep the unit in service.

“Everything changes, even just a little bit,” he said of wastewater technology. “But it makes a big difference when (replacement parts) don’t fit in properly.”

Another part of the plant that’s been causing problems: The ultra violet (UV) disinfection system that emits an intense light that destroys potential disease-causing organisms in the wastewater prior to its discharge into the Otter Creek. Wells said some of the computer boards within the UV system are becoming obsolete and harder to find.

It’s clear the current UV setup can’t be tweaked to coax more life out of it, officials said.

“It has to be replaced completely,” Wells said.

He’s looking at two replacement options right now: returning to a chlorination/dechlorination system as a means of treating wastewater, or investing in a new UV setup.

He’s leaning toward the former.

“It’s a lot simpler and less expensive to run, it’s tried and true, and 20 years down the road, nobody is going to say, ‘Oh, you can’t find a pump to get the chlorine to the chlorine chamber,’” Wells said of the chlorination/dechlorination method.

By contrast, he believes a new UV system would become outdated in relatively short order.

Other areas of the plant that need updating, according to Wells and Tata & Howard, include:

•  Tweaking the dewatering and pasteurization systems. Officials are considering a screw/fan press to replace the current Komline dewatering presses, in an effort to more effectively deliquefy waste coming into the plant. The solid, pasteurized byproduct of the wastewater treatment process is currently spread on farm fields, Wells noted.

“A lot of those components are failing,” Wells said. “We’re still able to produce a class ‘A’ biosolid, but that system needs to be replaced, too.”

•  Adding a primary clarification system to the sewage treatment process. “Primary clarifier” equipment uses gravity to remove solids from the wastewater. After preliminary treatment, the wastewater is introduced into a sedimentation tank or clarifier and the solids are allowed to settle to the bottom.

“Primary clarification can take off 30-40% of your organic load in the process,” Wells said.

•  Updating the septage receiving station to include a grit-removal unit and a bypass if something goes wrong with the main septage intake conduit.

The MWTP is currently the only facility in the county that accepts septage, so haulers would be in a pickle if that outlet was interrupted for any length of time.

“This isn’t about making money, because it doesn’t — it’s break even,” Wells said. “We want to make sure we’re there for the public.”

•  Adding a “pre-thickening” unit to further extract liquid from the incoming waste before it’s pumped into the plant’s digester.

•  Introducing an anaerobic digestion system that would produce enough methane to heat the plant building, digester and sludge dryer. This would also require replacement of the 20-year-old boilers, according to Wells.

“When this process gets upgraded, we’re going to be cutting our electrical expenses here quite a bit,” he said.

A bond will be required to pay for the MWTP overhaul, Wells said. The payback on that note would be generated by an increase in the town’s sewer rates. The good news is, Middlebury this year will retire the original 20-year bond that paid for the sewer plant. Plans call for the sewer rate to continue to reflect that $400,000 annual payment in order to build up savings to draw down the new bond when it is ultimately pitched.

“There’s no sense dropping the rate, just to say we’re going to raise them back up again,” Wells said.

Wells said the MWTP upgrades could be phased in to soften the financial impact to ratepayers, and to ensure continuity of service during the project.

“When you talk about full plant upgrade, it’s a huge disruption and it’s also runs the risk of environmental impacts,” Wells said. “Can you meet your permit when you’re under construction?”

Wells hopes to retire in around five years, at which time he hopes to leave the next generation of MWTP operators a user-friendly facility.

“Just finding staff willing to step into these roles is becoming difficult,” he said of wastewater treatment. “There aren’t a lot of people knocking on the door.”

Reporter John Flowers is at [email protected].