What is a grease trap?
Kitchen grease from households and commercial kitchens enter wastewater disposal systems causing build-up, which eventually leads to blockages, damaged equipment, and expensive repairs.
For this reason, a grease trap is used to intercept fats, oils, and grease (FOG) from entering the wastewater system. Also known as grease interceptor (or grease recovery/ management device, or grease converter, or grease catcher), this plumbing device is designed to eliminate or reduce FOG and allow clear water to flow.
Why are grease traps needed?
Wastewater systems and treatment facilities cannot handle a large volume of FOGs discharged by commercial operations such as school cafeterias, restaurants, hotels, bakeries, and cafes.
Grease released from food preparation cools down to solidify at normal temperature in the pipes. Over time, this solidified grease accumulates around the pipes and overwhelms the system, causing blockages in the pipes and sewers.
The accumulation of FOGs in the sewer pipes leads to several sewage-related problems such as:
- Blocked pipelines can lead to the release of untreated sewage into the environment, also known as sanitary sewer overflows (SSOs)—causing serious problems for the municipalities, the environment and human health.
- Even if accumulated FOGs do not cause blockages and SSOs, it can disrupt the flowing rate of wastewater.
- Rotten smells emanating from the pipelines.
To avoid these problems, grease traps are installed in municipal sewer systems, particularly at locations that prepare food. In fact, all commercial premises engaged in the cooking, preparation or sale of food are required to install and regularly maintain grease traps.
How does a grease trap work?
When wastewater flows into a grease trap, the flow rate is reduced, which cools warm or hot greasy water. As a result, grease, which is less dense than water, floats to the top of the grease interceptor and separates from the wastewater and the FOGs are trapped in the grease interceptor.
The solids in wastewater settle to the bottom while the separated clear wastewater will escape out under an outlet baffle. Many grease traps will also have strainers to collect the solids that settle at the bottom of the grease trap.
For grease traps to function properly, they need to need to be emptied or cleaned when the sludge and grease reach 25% of the tank level, usually every 2 to 4 weeks.
However, using a biological grease treatment fluid in the system helps break down the FOG and increases the time required for pumping and cleaning out the trap to up to 8 weeks.
Types of grease traps
There are three main types of grease traps:
Passive hydromechanical grease trap
This is a manual grease interceptor and is one of the most common types of grease traps used in smaller operations. The hydromechanical grease trap is small enough to sit under the sink, or in the floor of the kitchen. Larger-sized hydromechanical traps can be used for bigger wastewater systems too.
Passive hydromechanical grease traps have a low initial investment, making it ideal for small establishments. However, the trap needs to be cleaned and pumped frequently, almost once a week, thus increasing the maintenance cost.
Automatic grease trap
Also known as Automatic Grease Removal Units (AGRUs), these grease removal devices passively separate the grease from the wastewater just like the hydromechanical devices.
However, automatic grease traps have an additional motorised mechanism that automatically re-heats the FOGs and skims it out into a collector bin. This process is automated on a schedule depending on the volume of FOG produced, thus reducing the need for manual inspection to check on grease levels.
These traps have a higher initial cost but are more efficient and reduce the cost of frequent cleaning and pumping, thus having a lower long-term running and servicing cost.
Gravity grease trap
Gravity grease traps, also known as Gravity Grease Interceptors (GGI), are large grease interceptors usually made from concrete, fibreglass, steel, or plastic.
They work on the same principle as the hydromechanical grease traps, but have a larger capacity, often holding about 1800 litres of liquid. This means they are better for high-flow operations.
However, these traps only hold a small capacity of FOGs and thus need to be pumped out regularly (approximately every 90 days) by a specialist grease management service company.
Gravity grease traps usually need replacement every 15 years, as they degrade and cannot work efficiently. Because these grease traps are installed underground, replacement is a costly process that requires expensive machinery and labour.
Maintenance of grease traps
Regular maintenance of grease traps involves removing the FOGs from the top and the solids from the bottom of the interceptor, as well as scraping and washing down the all the sides of the trap.
This is usually done by specialist grease trap service providers that help businesses with scheduled cleaning and maintenance, determined by the size and capacity of the device, usage, and how much FOG is collected.
Regular servicing and maintenance of grease traps reduces various problems associated with blocked pipelines, blockages, and foul odour. It also reduces interruptions in business operations, as well as reduces the risk of grease fires due to build-up.