Aeration Study Optimization at the Deer Island Treatment Plant for the Greater Metropolitan Area of Boston, Massachusetts

The Massachusetts Water Resources Authority (MWRA) owns and operates the 1270 MGD Deer Island Treatment Plant (DITP) in Boston, Massachusetts. The MWRA contracted with Fay, Spofford and Thorndike (FST) Consulting Engineers to assist in the evaluation of the pure oxygen biological treatment process at the plant. This joint evaluation led to the following conclusions. Prior to the joint study, the final aerator in each aeration train was shut down, because sufficient oxygen transfer took place before the wastewater reached the last aeration stage. Next dissolved oxygen probes were installed in samplers that drew off the last stage. These probes allowed the operators to clearly see how much dissolved oxygen remained in the mixed liquor prior to entering the secondary clarifier. Dissolved oxygen profiles were done to further study the aeration characteristics of the system under various combinations of aeration stages being taken on and off-line. FST recommended that variable frequency drives (VFDs) and VFD-compatible motors be installed on two aerators in each train in order to reduce energy costs while maintaining sufficient oxygen transfer. Finally the oxygen feed system was successfully run in deck pressure mode in an effort to more efficiently deliver oxygen to the system. The overall avoided power demand of these efforts once completed is estimated to be nearly 10,000,000 kw-hrs, which is $900,000 annually at current power costs.