About grease interceptors

By Silvano Ferrazzo


Grease interceptors, or grease traps as they are often-misnamed, are frequently misunderstood and largely overlooked. After all, they are usually out of sight and therefore out of mind.

Grease interceptors are supposed to capture greasy wastewater and keep the facility in regulatory compliance without much hassle for the facility manager.

Historically, if the grease interceptor was installed inside the food prep area, such as a commercial kitchen, they were called “grease traps.” The term grease trap was often confused with plumbing traps installed directly in a sink drain, so code officials renamed them.

Grease removal devices (GRDs) or grease interceptors are now categorized into gravity grease interceptors (GGI), hydromechanical grease interceptors (HGI), which were previously called grease traps, and automatic or semi-automatic grease removal devices (AGRDs). This discussion will focus on GGIs and HGIs.

Owners, architects, and design engineers have options when choosing the best grease interceptor for any given project. Those options can be narrowed by space constraints, installation costs, performance requirements, maintenance costs, interceptor material, and ultimately regulatory compliance.

It is recommended that these choices be weighed with respect to the life cycle cost of the interceptor and total cost of ownership.


Separation and capture of pollutants

HGIs use hydromechanical separation, which is often achieved by means of flow control devices such as air entrainment and baffles, to separate the waste pollutants (fats, oil grease and food particles) from the incoming wastewater. This prevents those pollutants from discharging to the sewer and causing clogs and sanitary sewer overflows.

Conventional HGIs are typically smaller in volume in order to fit inside the kitchen. They tend to be less costly than the bigger gravity interceptors that are usually installed outside the building, but the smaller volume means more frequent maintenance to evacuate the collected pollutants, which can be more costly to the facility owner. Some of the newer large capacity HGIs reduce some of the higher maintenance costs by achieving larger holding capacities for the pollutants, to reduce pumping maintenance frequency.

GGIs achieve separation based on Stokes’ Law, which, simply put, means pollutants heavier than water such as food particles and sediment, among others, fall to the bottom of the wastewater. Pollutants lighter than water, such as food grease, rise to the surface of the wastewater. This is achieved by managing incoming wastewater flow and interceptor volume to ensure the wastewater is retained within the interceptor for a sufficient time to allow the pollutants to separate and become captured in the interceptor.

New engineered GGIs do this efficiently, and because of their usually larger size, they tend to require less frequent maintenance, saving the owner maintenance costs over the life of the facility.



The International Association of Plumbing and Mechanical Officials (IAPMO) released ANSI/CAN/IAPMO Z1001, Prefabricated Gravity Grease Interceptors, as an American National Standard (ANS) and National Standard of Canada (NSC) in October 2021. The binational standard is available in both English and French.

First published in 2007, this is the fourth edition of IAPMO Z1001 and the first to be published as an ANS and NSC. This standard supersedes the previous editions, last published in 2016. This is the first edition of this standard with both American and Canadian designation. The ANSI/CAN/ IAPMO Z1001 standard covers prefabricated gravity grease interceptors made of concrete, fiber-reinforced polyester (FRP), thermoplastic, or steel, and specifies requirements for design, materials, performance, testing and markings.

IAPMO received accreditation through the Standards Council of Canada (SCC) in 2018 for development of National Standards of Canada, thus accepting the responsibility for development of CAN/IAPMO-designated standards.

HGIs can be performance tested under PDI G-101 and ASME A112.14.3 test standards, which establish test apparatus and controlled testing criteria to allow comparison of performance

efficiencies of comparable interceptors. For example, in order for an HGI to be certified and accepted under CSA B481.1 it must be tested following the ASME A112.14.3 protocol, and separate and capture at least 90 per cent of the incoming grease.



Historically, HGIs have been made of steel, coated steel or stainless steel. Steel and coated steel are prone to corrosion, especially if the coating is scratched or damaged, due to the corrosive environment found inside a grease interceptor. More recent innovation by manufacturers now provides better corrosion resistant materials of construction, such as high-density polyethylene, polypropylene, plastic co-polymers, or fibreglass. These materials are all designed to withstand the corrosive environment found inside a grease interceptor.

Similarly, GGIs were often constructed of materials susceptible to corrosion, cracking and even structural failure, such as concrete, and even coated steel. Recent innovations by manufacturers now offer high corrosion resistance and structural durability with materials such as fibreglass and plastics. The construction material of construction can also impact installation costs. Interceptor buoyancy can sometimes mean the interceptor needs to be anchored in burial situations. In deep burial interceptor applications, we must take into account extra burial load and may require re-enforcement of the interceptor. All of these installation criteria impact the overall cost of the project.



Besides the method of separation and capture of pollutants, the other difference revolves around performance. HGIs, as stated above, must be tested and meet the minimum grease removal efficiency of 90 per cent. Some newer designs often exceed this minimum, so a buyer has the option to purchase a better performing interceptor, which will discharge less pollutants to the sewer and better protect the environment.

GGIs are not tested to the performance standards such as PDI G-101 or ASME A112.14.3, primarily because test equipment has not been designed to test the much larger capacities. However, some manufacturers have their GGI performance tested in real-life applications, at commercial kitchens of diverse facilities. By having effluent discharge from the interceptor tested at certified independent laboratories, real life performance can be determined.