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Following are a list of terms, acronyms and definitions that are applicable and commonly used in the Fats, Oils and Grease industry.

What does Net-Zero mean?

The US Department of Energy has a common definition for 'net zero' energy buildings:  "An energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy."

Grease Interceptor:

A plumbing appurtenance or appliance installed in a sanitary drainage system to intercept, [retain & facilitate the proper removal of] non-petroleum fats, oil, and grease (FOG) from [commercial, industrial & institutional] wastewater [applications, prior to discharging to the public (or private) drainage network]”

Grease Trap:

Commonly confused with “Grease Interceptor” the term ‘grease trap’ was correctly applied to early products in the industry that included a water seal to prevent the passage of foul odor passing back upstream under normal drainage system operation conditions. As products developed it was acknowledged that the inclusion of a water seal was detrimental to the function of the interceptor and significantly increased the risk of the contents of the interceptor being drawn under a siphonic effect (negative air pressure) in the downstream system. All FOG Control devices are now defined as Interceptors as identified below. The term ‘Grease Trap’ is still commonly used as a generic descriptive reference in the field by numerous stakeholders.

What are the generic types of Grease Interceptor

HGI – Industry abbreviation for Hydromechanical Grease Interceptor. An HGI is designed to use managed flow, air entrainment and specifically designed features to provide an enhanced level of separation efficiency, to significantly remove non-petroleum FOG (Fats, Oil and Grease) from a transitional flow of waste water in foodservice applications. HGI’s are performance tested for efficiency of grease separation based on National Standards. Performance must be a minimum of 90% efficiency, the most effective units removing in excess of 98% of the FOG.

GGI - Industry abbreviation for Gravity Grease Interceptor. A GGI has a minimum of 350USG capacity and operationally averages 1200 to 1500USG of liquid capacity. No flow control device. Separation of FOG is based on capacity and retention time of water (minimum 30mins to exchange volume). There are currently no performance Standards for GGI’s. Industry accepted efficiency/ performance suggests around 80% however higher efficiencies are reported operationally. (Note: there can be huge variation in performance depending at what point in the maintenance cycle the test samples are being taken)

GRD – Industry abbreviation for Grease Removal Device. Designed firstly as an HGI, a GRD uses a heat source and a timed or sensor based skimming (or draw-off) device to remove accumulated FOG from the separation chamber into an external container for collection and disposal. These units require daily maintenance for management of food solids. Prone to issues with odor as the contents are artificially heated to keep FOG in an optimal state for removal by the associated mechanical devices.

SI – Solids Interceptor: Typically, a standalone device installed upstream of a Grease Interceptor to prevent excess food solids and debris from accumulating in the interceptor. Food solids take up liquid volume that ultimately reduces the effectiveness of the GI.

Air Entrainment:

Mixing of air with influent using a flow control device. Air and grease are attracted to each other, the air wanting to separate from water more easily than grease. Because they become mixed together the air increases the efficiency of separation.

Active FOG Removal Device:

Phraseology adopted by a specific manufacturer to describe their technology as having a differentiated method/mode of function compared with a generic GRD.


Authority Having Jurisdiction.

Regulatory and/enforcement responsibility who has jurisdiction over the respective elements of local or regional codes/ordinances and their implementation. The ultimate ‘power of veto’ enforceable by law.


American Society of Mechanical Engineers. Publishers of ASME A112 Series of standards for plumbing products. This portfolio of standards was recently sold to a consortium between CSA and ICC. This will lead to eventual harmonization of the texts with the CSA standards.


American Society of Plumbing Engineers. Professional organization for Plumbing Design Engineers.


American Society of Testing and Materials: Technical organization who based on consensus process generate technical requirements top validate properties and performance of materials. ASTM standards are referenced in the writing of product standards to define material performance.

Black Water:

Industry term for wastewater that contains all sanitary waste and discharge


Biological (or Biochemical) Oxygen Demand is the amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in a given water sample at a defined temperature over a specific time period.

Brown Grease:

Accumulated FOG within a GI that is contaminated with kitchen drainage water, food solids, chemicals, detergents and naturally occurring bacteria. This material is typically removed by a third party licensed hauler at a cost to the FSE. Brown grease is substantially considered a waste product. Conversion to bio-diesel is possible but relatively costly. Waste from HGI’s and GGI’s is in this category.


Chemical Oxygen Demand - an indicative measure of the amount of oxygen consumed by reactions in a measured solution. COD is usually expressed in mass of oxygen consumed divided by the volume of solution (mg/l). A COD test can be used to identify the amount of organics in a water sample.


Canadian Standards Association. Standards writing organization for the Canadian market. CSA B481 Series of Standards covers Hydromechanical Grease Interceptors.


Combined Sewer Overflow. A combined sewer receives both sanitary and surface wastewater. These systems are more prone to overflow particularly in high rainfall events which can overload systems particularly where restrictions exist due to FOGS accumulation, for example.


Drainage Fixture Units. A numeric factor applied in drainage system design to quantify the load producing effect of waste water being discharged. Values are attributed by fixture based on reference tables in model plumbing code such as UPC and IPC.

Drain Period or Drain Down Time:

A multiplier applied to the sizing method published by PDI g101 and adopted few exceptions. Once the volumes of the know fixtures have been calculated and the 0.75 capacity factor has been applied, a decision for either 2 min or 1 min drainage period is made. Applying a 2 minute drain period as a multiplier to the sum of the flow rate reduces the size of the grease interceptor in half typically making it of a smaller footprint and lower capital cost. IMPORTANT. Realize that by reducing the size of the GI, the grease capacity is also decreasing too and this will mean that maintenance is required on a basis that is twice as frequent as using the 1 minute approach. Some AHJ’s do not allow use of the 2 minute factor.


Generically this is waste water discharge that las passed from associated fixtures into the drainage/sewer system. In direct reference to a GI this waste water will typically containing little to no FOG, as it is relative to the water being discharged out of the interceptor.

Flow Control Device (FCD):

Commonly associated with HGI’s (see Hydromechanical Grease Interceptors) a flow control manages the rate of flow entering the interceptor and entrains air to the flow to enhance separation efficiency. All PDI (Plumbing & Drainage Institute) Approved Grease Interceptors are approved with and need to be installed with an FCD.

FCD (FOG Control Device):

An alternate definition of FCD also exists as ‘FOG Control Device’. This appears in some Ordinances and is used as a generic description for all types of interceptor or device used to manage FOG.


Fats, Oils and Grease. Organic (Non-Petroleum) materials with a specific gravity in the range of 0.90 to .92 making them 8-10% lighter than water and therefore able to be separated by flotation.


Fats, Oils, Grease and Solids. As above but including the presence of food solids and other operational debris present in FSE wastewater discharge (Grease Interceptor ‘Influent’)


Food Service Establishment. Can be Commercial (restaurant, café, etc), Institutional (School, Hospital, Nursing Home, etc.) or Industrial (Food production/manufacturing)


Gallons Per Minute (US). Common unit of measure to define flow rate of Hydromechanical Grease Interceptors.


International Association of Plumbing & Mechanical Officials. www.iapmo.org Certification, Code and Standard writing body.


International Code Council. Publishers of International Plumbing Code (IPC)


Evaluation Service. Laboratory and technical evaluation service to verify code compliance of products.


International Plumbing Code. Model Plumbing code written and published by ICC. IPC is reference in approx. 60% of the US market.


Waste water containing uncontrolled and variable levels of FOGS based on the nature and practices of the foodservice operation.


Pig Fat. Used as the basis of performance testing in the PDI/ASME test method. Lard is insoluble (will not dissolve) in water, with a specific gravity of 0.917 at 77° F, with a dielectric constant of 2.1 at 176° F. It becomes liquid when heated at between 97° to 107° F. Lard is used as it provides a stable, specifiable and readily available test media that is representative of FOG characteristics


National Pollutant Discharge Elimination System. Federally enforced via the USEPA and administered by the respective State authority.


National Sanitation Foundation. Third party testing, certification and standards writing organization. www.nsf.org


Plumbing & Drainage Institute. Manufacturers association with technical expertise in Grease Interceptors and Water Hammer Arresters. PDI maintains and publishes PDI G-101.


Term applied in wastewater regulatory sector to describe all elements that occur within a wastewater system upstream of the treatment facility.


Publicly Owned Treatment Works. Water treatment equipment/facility receiving volume wastewater discharge from a municipal wastewater drainage/sewer system.


Parts per Million. Means of quantifying concentration of contaminants or constituents in another body of liquid. A range of 100-350ppm is common in the regulatory environment pertaining to FOG.


Sanitary Sewer Overflow. Sewer dedicated to carrying sanitary wastewater (blackwater) from its source to a wastewater treatment facility. Systems operate under gravity flow and may include pump/lift stations where distance or topography requires. SSO’s occur when a blockage occurs in the system causing waste to flow back upstream or be discharged at the lowest/weakest point in the system.

TSS - Total Suspended Solids

Defined as the dry-weight of particles trapped by a filter. TSS is a water quality parameter used to assess the quality of wastewater after treatment in a wastewater treatment process.


Turbidity is a measure of the light-transmitting properties of  water as a result of the presence or absence of both suspended and colloidal material. Suspended solids and colloids cause turbidity (cloudiness) in water. Turbidity is the degree to which a transparent liquid scatters light.

UPC: Uniform Plumbing Code.

Model Plumbing code written and published by IAPMO. UPC is reference in approx. 35% of the US market


Necessary element of an operational drainage system to allow air to enter the system behind/upstream of a wastewater discharge allowing it to move through the drainage system as intended. A vent also allows exchange of air within a plumbing system, releasing gaseous odors to atmosphere.


Waste Water Treatment Plant. Typically operated by municipality or serving a number of Municipalities operated by a county/regional responsibility.

Yellow Grease:

Used oils from an operational FSE that are not contaminated with any significant water or foreign waste material – i.e. in waste terms it is “clean”. This material has a value to the FSE typically representing an income of $1500-2000 annually (subject to market fluctuations). FOG from some high performance GRD’s can depending on local definition, fall in this category.