FOG: Fats, Oils and Grease and the problems they create in our water system

What is it? Fats, Oils and Grease (FOGs) is in meats, salad dressing, gravies, sauces, fryer oil, butter and dairy products.

Why is it a problem? When FOGs are discarded down the kitchen sink or drain system it accumulates inside the sewer pipes, mixing with other solids and eventually clogging sewer lines causing backups into residences and businesses, endangering public health and requiring costly repairs and sewer line cleaning. These costs are borne by ratepayers and the homeowners or businesses that caused the backup.

Grease is a huge problem. Grease in a warm liquid may not appear harmful. But, as the liquid cools, the grease or fat congeals and causes nauseous mats on the surface of settling tanks, digesters, and the interior of pipes and other surfaces which may cause a shutdown of treatment plant units or messy backups in your home or business.

In the sewage collection and treatment business, grease is singled out for special attention because of its poor solubility in water and its tendency to separate from the liquid solution. Large amounts of oil and grease in the wastewater cause trouble in the collection system pipes and the wastewater treatment plant. It decreases pipe capacity and, therefore, requires that piping systems be cleaned more often and/ or some piping to be replaced sooner than otherwise expected.

Fat costs ratepayers money.

Air Release Valve (ARV)

The mechanism to the right is an ARV. The Force Main system has these at all of the high points of the pipeline. Valves are designed to release air pockets out of the line, so the pumps and piping will convey the liquids more effectively.

The grease makes its way into the small valve mechanism that is above the float. When air makes its way upward, the float is pushed upward, letting the air out. The problem with the grease is, the float and body of the ARV gets coated with grease, and then finally it plugs the valve all together.

When the valve plugs with grease, it does two things:
#1, it quits letting air out of the force main, which means the pumps have to work harder and longer to convey the sewage.
#2, and it let's water (sewage) bypass into a carbon canister which is only meant to be dry.   

Grease costs the Plant and ratepayers more money in worn pumps (having to work harder and longer), and higher costs for excessive maintenance to keep these valves operational.

F.O.G. in an ARV

Fouled Air Release Valve -Redwood Area

Vacuum Release Valve (VRV)

This photo is a red plastic float that opens and closes the This is a photo of the red plastic float that opens and closes the VRV assembly.

When the valves get fouled with grease, they let water (sewage) bypass into a carbon canister which is only meant to be dry. The carbon canister is a 55-gallon drum that is used to filter the air releases, and their odors that are emitted.

You Can Help

There are a number of ways you can help reduce the F.O.G. problem, both in your home and your business.

F.O.G. in a VRV

Red plastic float opens and closes the VRV assembly


  • Never pour greasy liquids down sinks or toilets.
  • Pour grease and cooking oil into a can, store it in the refrigerator and put it in the garbage can on the day of pickup.
  • Dry scrape and wipe food dishes, bowls and pans into the garbage can prior to washing, don’t use the garbage disposal.
  • Install a food strainer in kitchen sink drains and empty them into the garbage can.
  • Never pour grease or oil into sinks, floor drains, parking lots or streets.

Commercial businesses, Food Service Establishments (FSE’s)

  • Use a sealed grease dumpster or barrel to collect oils and grease for recycling.
  • Close the grease dumpster lid after use to keep the rain out.
  • Use a grease interceptor or oil/water separator.
  • Check and maintain interceptors regularly.
  • Clean interceptors and dispose of interceptor waste properly, not in the garbage can.

                                        Kitchen Best Management Practices

“Thank you” from your Public Works Crew