Grease trap

Common wastewater contains small amounts of oils which enter into septic tanks and treatment facilities to form a floating scum layer.

Large amounts of oil from food preparation in restaurants can overwhelm a septic tank or treatment facility, causing the release of untreated sewage into the environment.

High-viscosity fats and cooking grease such as lard solidify when cooled, and can combine with other disposed solids to block drain pipes.

The most common are those specified by American Society Of Mechanical Engineers (ASME), utilizing baffles, or a proprietary inlet diffuser.

[1] Passive grease traps are generally smaller, point-of-use units used under three-compartment sinks or adjacent to dishwashers in kitchens.

These units, made of concrete, fiberglass, or steel, have greater grease and solid storage capacities for high-flow applications such as a restaurant or hospital store.

Interceptors require a retention time of 30 minutes to allow the fats, oils, grease, and food solids to settle in the tank.

[citation needed] A third system type, hydromechanical grease interceptors (HGIs), has become more popular in recent years as restaurants open in more nontraditional sites.

The upfront cost of these units can be higher, but kitchen staff can handle the minimal maintenance required, avoiding pumping fees.

[citation needed] Restaurant and food service kitchens produce waste grease which is present in the drain lines from various sinks, dishwashers and cooking equipment such as combi ovens and commercial woks.

[8] For these reasons, depending on the country, nearly all municipalities require commercial kitchen operations to use some type of interceptor device to collect grease before it enters sewers.

[9] Where FOG is a concern in the local wastewater system, communities have established inspection programs to ensure that these grease traps and/or interceptors are being routinely maintained.

[10] It is estimated 50% of all sewer overflows are caused by grease blockages, with over 10 billion US gallons (38,000,000 m3) of raw sewage spills annually.

This attacks mild steel and concrete materials, resulting in "rot out", On the other hand, polyethylene has acid-resisting properties.