Making Cogeneration Pencil Out: Anaerobic Co-Digestion of Grease Trap Waste
At the end of 2006 the City of Millbrae, California completed a $5.5 million wastewater treatment plant improvement project at no additional cost to the City’s ratepayers. The project improved cogeneration facilities, provided an automated grease trap waste receiving station, improved digester heating, replaced the aging main electrical switchgear, and enhanced digester mixing. Costs for the project were not passed on to rate payers because the overall project is self-funding, which means that the savings and revenue generated by the project will be used to pay the debt service for the improvements. For the term of the loan, the City will spend the same amount of money it does each year for operations, except now a portion of that money will pay for plant improvements rather than paying for utility-purchased power. The project would not have been financially viable if grease trap waste receiving were not included. Grease trap waste receiving resulted in an increase in digester gas production and added revenues from tipping fees.