Essential and potentially dangerous

Essential and potentially dangerous

By Rory Macnamara

Using these two words in one sentence for grease traps and grease interceptors is not normally a good thing. But each word has a significant meaning on its own and if not properly installed and maintained properly, the danger can become great.

These products are Food, Oils and Grease (FOG) removal units that keep these ‘cloggers and potential fire hazards’ out of the drainage line. Essentially used in the food sector kitchens with an application in industrial places as well depending on the output.

Drainage Installation is defined in SANS 10252-2 standard as “an installation that is vested in the owner of a site and that is situated on the site and is intended for the reception, conveyance, storage or treatment of sewage, and that may include sanitary fixtures, traps, discharge pipes, drains, ventilation pipes, septic tanks, sewage treatment works, or mechanical appliances associated therewith.”

Now for all this stuff above to flow freely as it needs to be moved fast, it makes sense that FOG must not enter the drainage system. The result otherwise means that all this stuff will appear in the toilets, basins, showers, and any other outlet offering the path of least resistance.

Let us now look at the meaning of each product before going into what the standard says.

Grease Traps Feature Image

Selection of grease traps. Photo by Grease Traps

GREASE TRAPS – these are small FOG removal units that are used where the flow of water and residual grease from the kitchen is low. They are customised to operate in a low water pressure environment with a flow rate as specified in the standard. Generally, the size of the trap is a small iron box to as big as a mini fridge. Installed generally beneath the sink in the kitchen.

Maintenance of these units, because of the relative smallness if them, require regular emptying and cleaning. The frequency depends on the FOG generated in the kitchen. With the frenetic pace that a kitchen operates normally such cleaning should be done during the closed period to be done correctly. This not only enables the trap to work efficiently for years but avoids the danger of fire.

GREASE INTERCEPTORS – these are the large units, generally used in large-scale food establishments and places where large amounts of grease are generated. These units are designed to operate in high pressure water environments. Being considerably large these units are installed outside an establishment usually underground.
Because the unit is far larger than traps, they can gather more FOG over a longer period, again dependant on the amount of grease generated.

In both cases the local authority may well have by laws addressing these products so always wise to check with them.

SANS 10252-2 Water supply and drainage for buildings. Part 2: Drainage installations for buildings.

Whilst no standards exist for either product, provision is made for them in this standard, which is compulsory, making the installation directions compulsory.

Section 4.3 Provision of grease and light-liquid interceptors.

4.3.1 a grease interceptor shall be provided to take the discharge from any sanitary fixture or appliance where the discharge of such a fixture or appliance could contain grease, fat, or vegetable oil,

  1. where such discharge will drain directly to a French drain, or
  2. in quantities that could
    1. Cause an obstruction to the flow in any drain, or
    2. Interfere with the efficient operation of any sewerage treatment or disposal system.

Basic grease seperatorBasic grease separator. Photo by Kessel

4.3.2 Provision of light-liquid interceptors

A light-liquid interceptor shall be provided to take the waste-water discharge from

  1. Any sanitary fixture or appliance in a building where such a discharge could contain unacceptable levels of liquid that could,
    1. Affect the flow in any drain, sewer, or
    2. interfere with the efficient operation of any sewage treatment of disposal system, and
  2. any paved area upon which light-liquids or washing water contaminated with such liquids can fall. Such area shall slope at a gradient of at least 1 in 200 from all sides towards a floor drain gulley, which shall discharge to the light-liquid interceptor.

5.2.7 Grease interceptors any grease interceptor required for a given building or commercial establishments shall serve only that building or establishment. any grease interceptor shall be so located that it is easily accessible for inspection and cleaning purposes, and that intercepted FOG can be removed hygienically. The location shall be such that,
a. there will be no need to use ladders or to move bulky objects to check or service it, and
b. it is possible to completely empty and clean the interceptor. Unless otherwise approved, a grease interceptor situated below ground outside a building shall not be located within 1.0m of any building foundation or property boundary. all parts of the grease interceptor, including the inlet and outlet sockets, shall be easily accessible for cleaning purposes. The interceptor shall be fitted with a removable lid or a manhole cover that permits easy and effective removal of grease, fat, solid matter or fine sludge, and that seals airtight. Any grease interceptor shall be vented to prevent it from becoming air locked. The design and construction of the interceptor shall be such that the air space above the separation compartment is ventilated through the inlet pipe. Only wastewater that requires separation shall be discharged into a grease interceptor or sludge trap. Water and wastewater that promotes the process of separation may also be discharged through such a trap.

5.2.8 Light-liquid interceptors. Access to the automatic closure valves of light-liquid interceptors fitted with such valves shall be secured by a seal. the air space of the light-liquid interceptor shall not be ventilated, but the outlet pipe from the interceptor shall be ventilated with a vent pipe that has a diameter at least half that of the outlet pipe. -liquid interceptors shall be covered in a tight and traffic safe manner. Covers shall.

  1. be non-flammable.
  2. not be secured. And
  3. permit the removal of fine sludge and light liquids. it shall not be possible.

  1. to draw wastewater off through the outlet pipe to such an extent that the separated light liquid reaches the outlet pipe, and\
  2. for the intercepted light liquid to flow back into the inlet pipe. only wastewater that requires separation shall discharge into a light-liquid interceptor, and the interceptor shall discharge into a drain. Liquid entry into the interceptor shall be through a floor drain or floor channel and a sludge trap. The sludge trap shall be.

  1. installed before the liquid enters the interceptor, to retain substances capable of precipitating, and
  2. so designed and installed that it can be easily cleaned when necessary.

It must be noted that most clauses are accompanied by a commentary and diagrams that explain flow rates, flow through and other points that explain the clause in more detail. It is important to refer to the commentaries as it is important to have the full SANS 10252 -2 document available from

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