Consultants recommend anaerobic digestion plus thermal drying as preferred biosolids option for Carlisle plant

At a March 5, 2025 workshop of the Carlisle Borough Council, consultants from Dannon Plumbing presented a study of options to replace the borough—s nearly 40-year-old lime slurry stabilization system at the Carlisle Wastewater Treatment Plant and identified anaerobic digestion with thermal drying as their preferred alternative.

The consultants said the current lime stabilization process has been reliable but creates nuisance odors, recurring equipment failures and a large hauling demand: the process requires more than 7,000,000 gallons of Class B liquid biosolids to be hauled each year—about 1,200 tanker loads. "The main goal for the study was to develop a plan that is affordable, cost effective, energy efficient and environmentally sound that will last you guys 25 years," Ben Briston, senior project manager with Dannon Plumbing, told council members.

The report evaluated four alternatives: continuing the current post-lime treatment; autothermal thermophilic aerobic digestion (ATAD); anaerobic digestion with thermal drying; and thermal drying with pyrolysis.…