Trap grease is the malodorous waste grease which restaurants trap before it goes down the sewer. Today, those restaurants pay people to take it away, so trap grease is essentially free. It hasn't been exploited like yellow grease, which is recycled vegetable oil. Now a company called Fry-o-Diesel is attempting to use trap grease to produce biodiesel. The company is headed by Nadia Adawi and her business associate Michael Haas. Haas call the grease the "the foulest, ugliest" and most chemically challenging crude biodiesel feedstock he has ever brought into his lab. However, that didn't scare him off, and the scientist's decade of experience with low-value biodiesel feedstocks has brought a lot to the table for Fry-o-Diesel.
According to the National Renewable Energy Laboratory (NREL), a grease trap works by slowing down the flow of warm greasy water and allowing it to cool. As the water cools, the grease and oil separate and float to the top of the grease trap. The cooler water with less grease continues to flow down the pipe to the sewer. The grease is trapped by baffles, or deflectors, which cover the inlet and outlet of the tank, preventing grease from flowing out of the trap.
The grease, which turns solid at room temperature, must be collected in the trap, or else it congeals on the walls of sewer pipes and restricts flow, explains Debra McCarty, deputy commissioner of the Philadelphia Water Department. To prevent sewer blockage and backflow, food service providers are required by city laws to have their grease traps cleaned out at specific intervals. This service is usually performed by private businesses, such as septic tank service companies, for about 5 cents per pound, according to NREL. By creating value for what is currently a waste product, Fry-o-Diesel's plan could help both restaurateurs and the city, McCarty says, explaining that grease traps might be cleared more routinely if collecting and disposing of the unsavory material becomes easier and less costly.