A grease trap that smells is usually overdue. Grease and solids past 25 percent of capacity turn septic and give off a rotten-egg odor. Scottsdale's code names odor, an effluent pH below 5.0 and the 25 percent mark as reasons to clean, and requires use to stop if hydrogen sulfide reaches dangerous levels.
Why it smells
A trap works by holding wastewater still long enough for grease to float and solids to sink. Once the captured layers take up too much room, water rushes through, the grease and food scraps left behind rot, and the tank goes septic. The result is a sour, rotten-egg smell that comes up through floor drains and the trap lid.
When the codes say it is full
- 25 percent. Phoenix (Sec. 28-15) requires a full pump-out before combined grease, sludge and solids exceed 25 percent of the liquid volume. Chandler uses the same 25 percent rule of thumb.
- Odor. Scottsdale's cleaning triggers in IPC Section 1005.1 include when the captured grease and solids displace more than 25 percent of the interceptor volume, when a sample of the effluent has a pH below 5.0, when odor becomes a health issue or nuisance, and when the city decides a cleaning is necessary.
- Danger level. Section 1005.1.1 says when atmospheric hydrogen sulfide reaches the level OSHA calls immediately dangerous (100 ppm or above), immediate action is required, and if it cannot be fixed at once all use of the interceptor must stop until it is safe. If you smell strong rotten eggs and feel dizzy or sick, get out of the space and call for help.
What to do first
- 1Check the last pump-out date in your log. If it is past your schedule, book service now.
- 2Dip-test the trap to see the depth of the grease cap and solids compared with the tank depth.
- 3Have it fully pumped and cleaned. Skimming and pouring the water back is prohibited in Phoenix and Scottsdale.
- 4Inspect the parts. A cracked baffle or missing lid seal lets odor out even after a cleaning.
What not to do
Do not reach for enzyme or bacteria additives. Phoenix prohibits them in place of physical cleaning, and Chandler bans them in grease devices, because they only loosen grease that hardens again downstream. See are enzyme grease treatments allowed.
Smell in the dining room that keeps coming back after a fresh pump-out points to something else, like a dry floor drain trap or a vent problem. Start with why does my restaurant smell like sewer. For setting a pump-out interval, read how often should a restaurant grease trap be pumped, and for what backs up when a trap is ignored, commercial kitchen drain overflowing.
To keep the smell from coming back, see how to control odor from a trap or interceptor. If it is spilling over, see why a grease trap keeps overflowing.