NASHUA – The failure of the Wastewater Treatment Facility’s egg-shaped anaerobic digester forced city officials to shut down this key solid waste processing piece for about a month this summer and instead haul sludge to the Manchester wastewater treatment plant and other facilities until repairs were made.

It was among a series of equipment failures that took place at the Sawmill Road facility in the last year. Others included the failure of five sludge storage tanks, the commercial boilers that heat the plant’s main building and the destruction of the plant’s non-potable water system by flooding last winter, according to state and city documents.

The plant’s estimated 30 workers have been using space heaters in the main offices to keep warm since the commercial boilers broke down at least one month ago, Nashua Public Works Director Lisa M. Fauteux said last week.

“We have been working diligently to get them replaced as quickly as they can,” she said of the boilers that failed sometime between a month to several months ago.

“There are two offices without heat and we have space heaters. Nobody is working in the cold,” Fauteux said.

City and state environmental officials stressed the equipment
breakdowns–particularly the primary anaerobic digester–never resulted in effluent being released into the Merrimack River that did not meet federal and state standards. Nor did they result in violations of the facility’s federal and state permits or threaten to shut the plant down.

Rather, state officials said they questioned whether the plant was on a timely schedule for maintenance and repair to ensure the seamless operation of a facility that runs around the clock.

“You can’t stop the flow from coming to the wastewater treatment plant unless everyone stops flushing their toilets. It’s very important that all equipment is maintained with redundancies so, if a necessary piece goes down, there is a back up for it,” DES Wastewater Engineering Bureau compliance supervisor Tracy L. Wood said.

“I had concerns about whether proper operations and maintenance were being performed,” added Wood, who inspected the plant Aug. 8.

While the primary anaerobic digester – often known by its nickname “the egg” – is critical to the facility’s solid waste management, its failure in July was not a “catastrophic” event since the plant shifted to back-up procedures to deal with it, Fauteux said.

“We couldn’t feed the egg until it was operational. It’s a very important part of our system, but it’s not a point that we couldn’t bypass easily. The sludge didn’t go to the egg. It went directly to other facilities that are regulated to take the material and we were never in any violation of our permit,” she explained.

Fauteux said the wastewater treatment plant, like many others built in the 1970s and 1980s, is experiencing “normal wear and tear” which requires adherence to a regular replacement and repair schedule. The digester began operating in 2000.

Still, she acknowledged she was not told the digester was failing.

“I did not know about it. Would I have pushed up some of the replacement of some of the parts? I probably would have had I known,” she said.

Sludge left at the bottom of the clarifying tank after undergoing primary and secondary treatment is fed into the anaerobic digester where bacteria feeds on it in a heated environment, reducing the volume and resulting in Class B biosolids, Fauteux said. The city contracts with Casella Organics to haul away the biosolids for land application.

According to the DES’ Sept. 5 Notice of Findings letter to the city, the digester’s two mixing pumps were not working at the time of Wood’s Aug. 8 site visit and “had been down for at least 20 days.” One replacement mixing pump was on site, but yet to be installed. The other had been ordered, but “there was a long lead time” for it to arrive, the state wrote.

The digester’s heat exchanger also had failed on July 23 and – without heat – workers stopped feeding it sludge on July 25, Fauteux wrote in her response to the state’s letter. A replacement heat exchanger was ordered but – given the long lead time to get the part – the city rented a temporary heat exchanger.

While the digester was shut down, workers replaced the failed mixer and installed the temporary heat exchanger, Fauteux told the state. They began feeding the digester sludge again on Aug. 22, she said.

While the digester was inoperable, the plant sent “raw sludge” to other landfills through its contract with Casella Organics, Fauteux wrote.

“When it became evident that the treatment plant could not process all the sludge we were producing and that we could not maintain an acceptable inventory within our system, we worked with Casella Organics for a different solution. At that time, it was suggested we truck liquid sludge off site,” Fauteux wrote.

Fauteux said the Manchester Wastewater Treatment Plant agreed to take “liquid loads of sludge to help us maintain an acceptable inventory until our digester was back online.”

The city and DES decided the plant could return to producing Class B biosolids on Sept. 9, she said.

Fauteux said it cost $11,505 to haul the sludge from Nashua to the Manchester Wastewater Treatment Facility. She stressed this is not an additional cost to the city since the city must pay to have its Class B biosolids trucked away. Manchester took the sludge at no cost, Fauteux said.

Other equipment failures already have been addressed. As of Oct. 14, the five sludge storage tanks that failed were repaired. The city still is waiting for its replacement boiler to arrive. They are among 13 areas of the plant’s operation that DES addressed in its letter to the city.

The destruction of the plant’s internal water system resulted from flooding that occurred last winter. The system was used for cleaning equipment and flushing toilets only. The plant now is using city water for these projects, she said.

State DES and city public works officials met on Nov. 7 to discuss the state findings and the city’s response to them, Wood said. DES spokesman James Martin said the city has been “extremely cooperative and extremely responsive” in addressing the issues.

The city must provide the state with quarterly reports that will detail equipment in need of repair, timetables to do it, update to its operating procedures and a staffing evaluation. The first report is due Jan. 15.

Fauteux would not discuss whether Mario Leclerc’s early retirement as superintendent of the wastewater treatment plant was related to the equipment breakdowns documented in the DES site visit on Aug. 8 and Sept. 5 Notice of Findings to the city.

In a letter dated Sept. 24, Leclerc wrote he was retiring from the position he held for 10 years effective immediately. His retirement came five days after the Board of Public Works met in non-public session to discuss an unspecified “personnel matter.”

“The only thing that I am going to say about Mr. Leclerc is that he retired,” Fauteux said.

David A. Simmons took over as superintendent of the wastewater treatment facility on Monday, Dec. 8.

“He has tremendous expertise,” Fauteux said, noting Simmons brings more than 35 years experience.

“It’s going to mean great things to the operation of the plant and all the staff. Certainly, he will make sure everything is updated in a timely fashion and we continue to be in compliance with our permits,” Fauteux added.

Kathryn Marchocki can be reached a 594-6589 or kmarchocki@nashuatelegraph.com. Also, follow Marchocki on Twitter (@Telegraph_KMar).