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The Environmental Protection Agency (EPA) is fining majors cities for sanitary sewer overflows (SSOs). These overflows result in raw sewage discharging into streams, rivers, and bays. They are caused by fats, oils, and greases (FOGs) that clog and block underground pipes, like cholesterol clogs our arteries. More needs to be done to prevent SSOs. Pollution, unsanitary conditions, and fish kills are the consequences of these SSOs.

Grease buildup in sewers is a major cause of SSOs. Controlling the FOG's discharged from food service facilities is very important in preventing these buildups. Many jurisdictions are reviewing standards associated with their pretreatment program. Many have found current practices insufficient in removing adequate amounts of FOGs.

The purpose of this experiment was to study different variables in food service facilities and how they affect the separation times of FOGs. It will address the issue of how the type of FOG, the temperature of water, and especially soap affects the rate of separation. Current standards do not address these issues.

Test samples were evaluated in 500ml graduated cylinders. Variables evaluated included temperature (85°F, 120°F, 155°F), type of soap (liquid Dawn detergent, liquid Sisco detergent, powdered Cascade detergent), and type of FOG (liquid vegetable oil, solid vegetable shortening, solid animal fat). The samples were shaken and then let sit for twenty-four minutes. Oil/water interface readings were taken at one, two, eight, twelve, and twenty-four minutes.

There were a few major findings in this experiment. It was first concluded that, as an emulsifier, soap affected the separation rate significantly. The solutions with soap took twenty-four minutes to separate to 84%, while the solutions without achieved that level of separation in less than one minute. The different soaps tested only affected the rate discreetly, and the different FOG's reacted somewhat differently to each other. The one interesting result was the affect that the solid vegetable shortening had on the separation rate. The solution took a significantly longer time to separate when this FOG was used.

Several recommendations came out of this work. First, testing criteria that includes soap should be developed to evaluate grease interceptors and traps. Next, retention times need to be adequately addressed and increased to consider the effects from soaps. Finally, local codes should be adapted to properly size grease interceptors based on flow rates and retention times.

The purpose of this experiment was to study separation times not addressed by current standards. The study clearly showed the addition of soap affects separation times. Since the elimination of soaps is unlikely in commercial kitchens, changing the required retention times of interceptors should be the focus of future municipal code changes. A few municipalities have done this, but more should follow. Detailed studies should confirm and elaborate on the work started here and ultimately reduce the amount of buildup and blockages in sanitary sewers.
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Document Type: Research Article

Publication date: 2004-01-01

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