The Carlisle Mosquito Online

Friday, July 13, 2007


Watching over wastewater operations

School Building Committee members Bill Risso, Lee Storrs, Wendell Sykes and School Business Manager Heidi Zimmerman met recently with Hoyle, Tanner and Associates (HTA), the engineers who designed the school's new Wastewater Treatment Plant, to resolve some operating issues. Before the plant's one-year warranty expired at the end of April, the school sent a letter to HTA detailing items that needed to be fixed.

The school now has a plan to manage electricity and propane heating costs at the plant, which began operating in the spring of 2006. During its first winter of operation the facility used about twice as much electricity and propane as projected.

The 800-square-foot building is heated with propane to a minimum temperature for the biological system to work. At the same time, ventilating fans run to exchange outside and inside air to minimize methane gas emissions in the plant to comply with state Department of Environmental Protection safety regulations. The air exchanges reduce methane build-up for the operator's health, and prevent a potential gas explosion inside the building. The number of air exchanges per hour has been reduced to save energy costs, while still meeting ventilation safety requirements. A fan timer will be installed to automate the air exchanges.

A recent inspection of bearings in the Rotating Biological Contactor (RBC) unit showed no problem, though the school asked an independent contractor to check the bearings after hearing noise in the unit. A sensor in the ultraviolet light intensity reader now needs to be cleaned with a different solution, while installing a humidistat to control humidity in the plant is still under discussion with HTA.

The school plans to deduct the cost of the additional controls installed from the final invoice to be paid to HTA, according to Zimmerman. The school also met with Weston and Sampson, the engineering firm that handles maintenance for the wastewater plant, to ensure the operator is clear on plant operations and will not modify the new energy-saving settings.

During the summer months there is limited flow from the school, except for summer camps. To promote bacterial growth that is necessary for the plant to operate, Micro-C, a new chemical, and a sugar additive were recently added to the system.

Last summer, the operator from Weston and Sampson had effluent from the Middlesex School septic tank added to Carlisle's wastewater system to "seed" the tank and help promote bacterial growth. After the plant started operating last year, there was not a lot of growth on the RBC unit by the end of the school year. School Buildings and Grounds Supervisor David Flannery said the Weston and Sampson operator explained to the Building Committee that adding seed sludge is a common practice in the first year of operation in order to start up the system.

The Building Committee did not learn that the seed sludge was added until after it was done, and has since told the operator not to put effluent into the system again, in order to minimize any risk from outside additives. The school will continue to work with Weston and Sampson to monitor how the system works this summer with the new chemical and sugar additives.

The school must maintain adequate flow to the system to comply with state Department of Environmental Protection (DEP) regulations. However the operator has told the Building Committee that the state agency is aware of and understands the problems that schools have maintaining RBC systems during the summer months when flow rates plummet.

Daily maintenance

The licensed operator from Weston and Sampson visits the plant daily from Monday to Friday to take samples, run tests, check equipment, add chemicals when necessary, and record plant data in a log book. Weston and Sampson must provide the school with a monthly report on plant operations and a copy is sent to the state DEP to comply with its regulations. The company also has sludge and solids removed from the tanks, as needed.

In the first three years of the wastewater plant's operation, the Building Committee plans to continue with the outside contractor and to draw on their experience in operating the plant successfully. At a later time the school will consider sending a town employee to an area college for training to become a licensed plant operator.

Zimmerman said the school recently negotiated a new $55,100 annual contract with Weston and Sampson, the same price as last year's contract. Other anticipated annual costs for the wastewater system during the current fiscal year are: electricity $10,000; propane heat $11,000; equipment and building maintenance $2,000; and telephone $900.

2007 The Carlisle Mosquito