THOMASVILLE — A purchase approval for updated equipment should keep some important microorganisms functioning properly at the City of Thomasville Water Pollution Control Plant.

The Thomasville City Council recently approved a bid of $359,000 to RTD Construction for replacing outdated heat exchangers at the plant.

“It was a budgeted item in the sewer department budget,” Assistant City Manager Lynn Williams said Friday. “It will be paid for out of those funds. The total budgeted amount for the heat exchangers and any possible retrofit was $410,000.

“The bid came in at $359,000 and there will also be some engineering fees associated with the project, which should bring the total to around $409,000.”

Bill Gerber, director of water and wastewater treatment, said the heat exchangers were placed at the plant in the 1950s and have become obsolete.

He said they play an important role at the plant.

“What it does is heat up the contents of the digester — a large tank that decomposes the solids removed from the waste water treatment plant — and maintains that heat at about 95 degrees Fahrenheit,” Gerber said. “At that temperature, the microorganisms, or the anaerobes, can function properly.”

These “anaerobes” eat the organic material. The proper word is “oxidize.”

“Once finished, there will be nothing left in there to degrade, smell or cause problems,” Gerber said. “This process produces water, methane and carbon dioxide, along with reducing the volume of inert solids that can be easily and readily disposed of at the landfill.”

Most of the methane gas produced is used to provide fuel to the heat exchangers.

“It is a self-sufficient process,” Gerber said. “The heat exchangers run off the methane produced during anaerobic decomposition.”

The replacement equipment will have the same function as the old ones, along with having some additional safety equipment, he said.

These include waste gas burners to burn off excess gas not used to power equipment, traps to drain excess water out of the lines, and vacuum pressure regulators that sit atop the digester to keep it stable.

Jim Ridley, operation maintenance supervisor, explained the heat exchangers are constantly recirculating the tank’s contents to keep the temperature uniform and bring new food to the microorganisms.

He said it takes 45 to 60 days in the digester before the material is ready to be dewatered, or have the water pressed out of it. Then, the solids are ready to be disposed at the landfill.

“The heat exchangers run 24 hours and are self-sufficient but workers check operations daily,” Ridley said.

Preconstruction meetings are expected to begin this month, city staff said.

Plant staff look forward to upgrading the heat exchangers.

“This equipment is needed to maintain the proper temperature in the digester so solids adequately stabilize and are safely removed from the treatment system,” Gerber said. “Failure to do so would lead to permit violations and an adverse impact to the receiving stream.”