Montague, Massachusetts
Montague Water Pollution Control Authority
Re-engineering the Montague 1.80 MGD municipal wastewater treatment plant so that it operates in a cycled air-ON / air-OFF mode has reduced effluent total-Nitrogen to less than 8 mg/L, reduced electrical consumption by 7%, and reduced sludge production by 35%.
Without automation, in a manual mode, the dual train aeration tanks are operated as follows. Influent flow is split equally to the two, parallel plug-flow aeration tanks. For a period of eight hours, one of the two aeration tanks is aerated while the other is not. All of the return activated sludge (RAS) is pumped to the non-aerated tank; the aerated tank does not receive any RAS. At the end of every cycle air is turned on in the anoxic tank, turned off in the aerobic tank, and RAS is pumped the other aeration tank. The mixed liquor concentration is 5,500 mg/L.
Automating the valve operations and installing new in-line instrumentation will cost $75,000 and will allow the process to be optimized. More frequent cycling is envisioned. The circa-1982 treatment plant contains two parallel rectangular primary treatment tanks, parallel aeration tanks equipped with step-feed capabilities, two 50-foot diameter (12 feet deep) circular clarifiers, and chlorine disinfection. Primary and waste activated sludges (WAS) are thickened in a gravity thickener. Dewatered cake is trucked off-site for final disposal.
Pumping RAS to the aeration tank only when it is in the anoxic mode increases the velocity of the flow through the anoxic tank to three times that of the flow through the aerobic tank. Because of this, the aerobic hydraulic retention time is three times the hydraulic retention time in the anoxic tank, approximating the ratio of aerobic and anoxic tank sizing that is standard for Modified Ludzack-Ettinger (MLE) Process designed facilities.
Data Summary. Typical effluent quality is as follows. BOD: <10 mg/L. TSS: <10 mg/L. total-Nitrogen: 7-8 mg/L, total-Phosphorus: 0.6-1.0 mg/L.
The MontagueTM Process provides better treatment, sustainably, with O&M savings. EPA Region 1 recognized Montague’s innovative efforts by presenting staff with the 2010 Wastewater Treatment Plant Excellence Award.