Caring foryour GreaseTrapA Presentation by theAustin Water Utility’sOffice of IndustrialWasteDecember, 2003

Given the prevalence of solids and fats, oils and greases (FOG) in thewastewater from commercial food establishments, preventing sanitarysewer overflows related to these discharges requires careful attention.

A grease trap is designed to physically separate grease and solids from kitchenwastewater. As wastewater enters a trap the water slows and the grease particles,which are lighter than water, coalesce and float towards the top of the tank. The heaviersolid particles settle at the bottom. The trap outlet is located near the middle of the tankto prevent the grease and solids from passing through the tank. The longer thewastewater stays in the trap, the better the separation. As the layers of grease andsolids increase (thicken), the retention time in the tank is reduced, separation is lesscomplete and grease & solids are allowed to pass through to downstream plumbing.

All kitchen fixtures located in food prep or clean up areasshould be plumbed to the grease trap.Examples include: 2and 3-compartmentpot sinks, prepsinks, dishwashers,floor drains, trenchdrains, floor sinks,disposers, wokstoves and tiltkettles. Hand sinks,mop sinks anddrains forcondensation onlymay bypass the trap.

Make sure you and your staff are aware ofthe Do’s and Don’ts of proper greasemanagement in your kitchen.TCEQ Poster GI-290This poster is available from the Texas Commission on Environmental Quality (TCEQ)Small Business & Local Government Assistance

By trapping theFOG and solidsnormally found infood prepoperations, thegrease trap standsas the last line ofdefense againstpotential sewerblockages,overflows and theensuing fallout.

A properly sized grease trap is critical. A trap that is too smallwill not be able to remove the FOG and solids efficiently.

The undercounter greasetraps like thisone are nolongerapproved. Thesmallest sizedgrease trapapproved forinstallationtoday is 100gallons.A trap that is too large may be just as problematic.Oversized traps may become stagnant, causing odorproblems and/or corrosive conditions that drasticallyshorten the trap’s useful life.

The design of the trap is as important as its size. Note theshort distance between the inlet and the outlet. This oldstyle cylindrical trap is no longer approved for installationbecause of its poor performance.

Note the flow diverter on inlet side of this new installation.This helps to eliminate channeling effects or “short circuiting.”

Here, the baffle wall and piping can be seen. Proper bafflinginsures that the flow is evenly spread throughout the tank.

This is what a 1000 gallon interceptor looks like after installation.

A grease interceptorshould not beconfused with the oilrendering containershown to the right.This container holdsthe old fryer oil (alsoknown as yellowgrease) and ishauled off-siteperiodically.Do not put old fryer oil into kitchen sinks and drains!

The City periodicallysamples the discharge fromeach individual commercialfood establishment as a partof the Surcharge Program.As a part of this program,wastewater charges aredetermined for eachparticular establishmentbased on the quality of thewastewater discharged. Assuch, the inadequate controlof FOG and solidsdischarges can result in veryexpensive utility bills for anindividual establishment.

Maintenance RequirementsThe FOGs and solids must beremoved regularly in order forthe grease trap to workproperly.The Austin City Code specifiesall grease traps must becompletely emptied andcleaned by a licensed hauler atleast once every three monthsor more frequently if, beforethree months, the grease andsolids in the trap’s finalcompartment accumulate to50% or more of the wettedheight of the trap.

The perfect clean-outfrequency will vary foreach business. Mostgrease traps should bepumped at least onceevery 30 to 45 days.Ask your grease trapmaintenance serviceprovider to take periodicgrease and sludge layermeasurements todetermine the rightfrequency for yourbusiness.

Enzymes, Bacteria & Other AgentsThe Austin City Codeprohibits the use of enzymes,bacteria and/or other agentsthat would cause thecontents of a grease trap topass through the grease trap.There is no substitute forregular cleaning andpumping!

Documentation RequirementsThe Austin City Code specifies that grease trap wastemanifest records must be made available for up to thepast three years in which the facility has been in business.

It is important that you do not treat your sinks and drains like agarbage can.Garbagedisposerstend to getabused andcan overloada greaseinterceptorwith solids,making itmuch lessefficient andrequiring it tobe pumpedout morefrequently.

A neglected trap may resultin: Much higher utilitysurcharge fees, Expensive plumbingrepairs and clean-upcosts, Fines of up to 2,000 foreach violation, Loss of business duringservice interruption, Environmental impacts,and A public relationsbacklash if neighborsare adversely effected.

Grease trapsdo not lastforever. Ifthe trap is notpumped andcleaned outregularly,acids willform as thegrease turnsseptic.These acids are very destructive and over time can causebaffles, piping, and tank walls to simply crumble apart. Noticethe black lines on tank wall of the trap shown above. This isexposed wire rebar.

Grease traps are very expensive to install and/orreplace. Making sure they are cleaned and pumpedout on a regular schedule is very important.Propermaintenancewill protect thewastewaterlinesdownstreamfrom greasebuild-up andpotential seweroverflows andit will ensure along healthylife for yourgrease trap.

the grease trap to work properly. The Austin City Code specifies all grease traps must be completely emptied and cleaned by a licensed hauler at least once every three months or more frequently if, before three months, the grease and solids in the trap's final compartment accumulate to 50% or more of the wetted height of the trap.