Fats, Oils, Greases
Fats, oils, and grease are collectively referred to as "FOG" in the world of wastewater treatment. FOG can come from a variety of sources, cooking meat, dairy products, or salad dressings. FOG becomes liquid when heated, making it easy to wash down the sink; however, as FOG cools down, it hardens, congeals, and aggregates. This is problematic for sanitary sewer collection systems as the collection and eventual build-up of FOG leads to blockages in the sewer collection system.
Check out the Regional District of Central Okanagan's video on fats, oils and greases.
Solids & Grit
Solids and grit are another problem that have to be dealt with in the wastewater collection system. Solids can come from a variety of sources, including food scraps, packaging, or any other substances that should be composted, recycled, or thrown into the trash. Grit refers to small solids that can easily go down the sink with liquids, examples include coffee grinds, eggshells, or seeds. Solids and grit cause many problems for wastewater collection systems as they build up in the collection system, especially where FOG is present, and contribute to sewer main blockages.
Wet wipes should never enter the sewer system - not even if they are labelled "flushable". These disposable wipes should be placed in the garbage after use.
Garburators (food grinders) are not permitted to be connected to the Districts' sanitary sewer system. Garburators introduce excess solids to the sewer system, which can lead to costly backups. Food scraps should be collected using sink strainers and disposed of in the compost or trash.
Grease Traps/Interceptors
What are they?
Grease traps are small, engineered containers with baffle walls inside to help slow the rate effluent discharged to the sewer system. The slowed effluent allows solids and grit to settle to the bottom of the grease trap, while fats, oils, and grease float to the top. The effluent leaving the grease trap is relatively clear.
Grease interceptors serve the same purpose as grease traps; however, they are much larger and are designed to handle larger effluent flows. While grease traps are typically found under sinks or built into the floor of businesses, grease interceptors are constructed outside, underground, and are accessible by manholes.
Who needs them?
Any commercial business or home occupation that is likely to discharge FOG, grit, flammable substances, or other material that may interfere with the sanitary sewer system is required to install, monitor, and maintain a grease trap or interceptor/ Examples include:
- Commercial kitchens (including bakeries and coffee shops).
- Dry-cleaning establishments.
- Service stations, vehicle repair garages, and car wash bays.
- Concrete and aggregate washing plants.
- Laboratories.
Where should they be installed?
Grease traps are most effective when installed immediately downstream of the point of entry to the sewer system (i.e., under a sink). When grease traps/interceptors are installed too far away from where wastewater is discharged, they have the potential to cool, harden, and create blockages in your internal plumbing.
Grease traps typically should not be installed downstream of a dishwasher, as FOG becomes liquid when heated, which can flow through traps into the sewer system until cooled. FOG and food scraps should be scraped into the compost/garbage or wiped with paper towel or used citrus fruits before being placed in the dishwasher.
How should they be installed?
Grease traps must be sized and installed by a licensed plumber. A sampling "T" is required to be installed downstream of the grease trap/interceptor (refer to Appendix A). Use of a cleanout in the upstream process piping is recommended to make cleaning and maintenance easier.
It is important that effluent entering grease traps/interceptors not be combined with general wastewater (i.e., water from toilets). Enzymes or surfactants that break down FOG are only temporarily effective and should not be used as they will congeal further down in the sewer system.
Maintenance of Grease Traps/Interceptors
Image courtesy of the Capital Regional District
Grease traps are to be cleaned regularly to ensure the combined depth of FOG floating on the top and grit/solids at the bottom of the grease trap should never exceed 25% the wetted height. Additionally, effluent leaving traps should not exceed the required chemical or biological parameters as outlined by the Sanitary Sewer Regulations and Rates Bylaw 1176, 2022 [PDF/404KB] (section 10).
The frequency of grease trap cleanings can vary from once a day to monthly, depending on the nature of the restaurant. Grease interceptors are much larger; therefore, cleanings can vary from weekly quarterly or bi-annually.
Grease should be disposed of by the contractor doing the cleaning. If the cleaning is being done in-house it can be placed in the garbage. Maintenance logs are required to record all cleanings, repairs, or any calibration performed on grease traps. Maintenance logs are to be kept onsite for a minimum of three years and the District can request to review the log at any time. View a sample maintenance log.
Further Reading
