Increasing CHP Productivity While Reducing Biosolids Volume and Climate Changing Gasses

Abstract

This manuscript reports the first 30 months performance of POTW anaerobic digesters when feeding the pre-processed slurry produced from combining inedible kitchen grease (IKG) composed of fats, oils, and greases (FOG) with anaerobically digesting sewage solids to produce biogas for a combined heat and power (CHP) system. In 1993, the Millbrae facility began recording electronically 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 those of the first thirty months shows surprising results that yield benefits far greater than anticipated. These data indicate feeding pre-processed IKG into the Millbrae wastewater anaerobic digesters steadily and substantially increases the amounts of biogas produced, decreases the volume of biosolids disposed of by a sustainable 32%, improves the stability of digester operations, and improves biosolids dewaterability.

Employing Energy Management Planning to Achieve Net Zero Energy in Wastewater Operations

“…York reports: "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%." (York, Magner et al 2008;York and Magner 2009) The reported electricity production from its 250 kW cogeneration system was about 4,000 kWh/day, which is an energy yield of a high 2,500 kWh/MG. Nevertheless, this was between 60 and 80 percent of the electrical requirements of Millbrae.…”