Aerobic Pretreatment of Grease Trap Wastes

As part of the Derry Township Municipal Authority (DTMA) septage receiving program, an aerobic grease pretreatment digester (AGPD) was constructed. The AGPD is a 40,000 gallon reactor designed to function as an aerobic grease trap waste pretreatment process for the 12,000 to 15,000 gallons per day of trucked-in grease trap wastes discharged at the DTMA Septage Receiving Station. The ADPD is operated as a simple fill and draw aerobic digestion pretreatment process.Two submersible chopper pumps supply the energy to alternately mix or aerate the reactor contents. The pumps also chop miscellaneous materials accompanying the grease trap loads. Physical mixing is accomplished by pumping the mixed liquor through the proprietary mixing nozzle system while the aeration is accomplished by using a venturi nozzle and draft tube. The unit is currently seeded with bacteria every twelve hours using two ECOBionics BioGenerators. In order to maintain a neutral pH during the process, a quicklime slurry is periodically added to the AGPD.This paper will present DTMA's work in the development and operation of a program for accepting and pretreating grease trap wastewaters. Additionally, the paper will present the results of a two month study in 2006 and supplemental study in 2007 on fats, oils, and grease (FOG) reduction as well as the operational problems experienced, equipment selection issues, and ongoing improvements to fine tune and improve the operation of the AGPD.