When FOG is 'FROG' (Fats, Rocks, Oils and Grease): A Pilot Study on Sludge Degritting and FOG Screening

East Bay Municipal Utility District (EBMUD) processes high-strength waste, which includes fats, oil and grease (FOG), food waste and other organics at their Main Wastewater Treatment Plant as part of their resource recovery program. FOG and waste feedstocks typically include a fair amount of grit, rocks and other unwanted debris that are difficult to separate and remove. These unwanted materials cause excessive operational and maintenance problems and grit build-up in the digesters. EBMUD and Brown and Caldwell designed a pilot study to assess the feasibility and performance of available screening and degritting equipment on blended sludge, and to develop design criteria for a full-scale facility. A double disc pump, sludge screens (5-mm and 10-mm), and a cyclone-classifier were evaluated on 5-percent blended sludge. In addition, screens were evaluated on FOG deliveries. This paper documents the key findings from the equipment evaluation and presents the recommendations made for the full-scale facility.