THE MILLBRAE RESULTS OF SIMULTANEOUSLY MITIGATING UPWARD SPIRALING ENERGY COSTS AND MODERNIZING ITS WASTEWATER TREATMENT FACILITIES

This manuscript reports on the first 12 months of full-scale operation of a grease-receiving/combined heat and power (CHP) system at the Millbrae publicly owned treatment works (POTW). The paper focuses on the receipt and preconditioning of inedible kitchen grease (IKG) through the new system and the performance of POTW anaerobic digesters when the slurry resulting from IKG processing is fed into them. In 1993, the Millbrae facility began electronically recording wastewater solids processing data, such as the number of hauled loads, the wet ton weight of biosolids, polymer use relative to filter cake density/weight, electricity produced and bought, and digester stability. Comparison of these historical performance data with results since Millbrae began feeding IKG into its wastewater anaerobic digesters shows that the resulting benefits are far greater than anticipated. These data indicate that the feeding of grease into the Millbrae wastewater anaerobic digesters steadily and substantially increases the amounts of biogas produced, improves the stability of digester operations, improves sludge dewaterability, and decreases the volume of biosolids disposed of by a surprising 36%.