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Grease traps and interceptors

What are they?

Grease traps are used primarily in mechanical workshops and food industry kitchens. Their function is always the same: to remove solids and fats, oils and greases (FOG) from liquid effluent streams.

A typical grease trap has three parts:

  1. A solid particle interceptor – also known as a sludge catcher;
  2. A grease/fat interceptor – called the ‘stilling tank’ where FOG in dirty water is prevented from rising to the surface; and
  3. A small sampling chamber – where the improved quality of the cleaned effluent can be observed.

Grease traps are rated on their flow performance. For example:

  • Small users such as households and sandwich bars will use traps rated at 1.5lt per second;
  • Medium-sized restaurants and food production lines often use traps rated at 4.5lt per second; and
  • Food courts, dairies, cheese factories, etc. will use a trap rated at 11lt per second.

How grease traps work

The aim of a grease trap is to improve the discharge quality of the effluent prior to it entering the municipal sewer, and to allow an operator to remove solids and grease from the effluent stream with ease.

Well designed grease traps usually have three chambers. The first chamber is equipped with perforated solids retention baskets into which the inflowing effluent arrives. The second chamber, between two baffles, slows the liquid permitting the oils to float to the surface (since oil floats on water) where microorganisms - both latent and added - degrade the floating scum from the underside, improving the quality of the effluent. When there is excessive fat in the effluent a scum will form and is liable to steadily thicken with the increased daily volumes. This fat scum should be removed carefully to avoid dripping and discarded in an approved fashion (BIO-SYSTEMS can provide an established protocol for this task). The third chamber is narrow and allows for visual inspection and sampling.

In many cases grease traps receive effluent from both floor drains and sinks. Dirty water flows through the particle interceptor (perforated sieve baskets) where small solids such as metal swarf, scraps of meat and vegetable solids are caught in the chamber baskets – these should be emptied into disposal bags twice a day before the rubbish putrefies and becomes unpleasant to handle. The grease interceptor trap should be situated sufficiently far away (down-line) from the under sink particle interceptor to allow the temperature of the dirty water to drop to below 40oC, preventing the biomass of bacteria in the stilling tank from being damaged.

Common grease trap problems

Oil overload is a frequent problem plaguing industrial grease traps. Modern fuels, lubricants and catering oils are highly complex compounds and pose even more of a problem because they are difficult to degrade and take a long time to break down. The result? Congested, slimy drain pipes and sulphurous, foul odours. This is also true of effluent in the food and catering industry where modern ‘trans fats’ often accumulate and cause blockages unless dealt with correctly and timeously.

The BIO-SYSTEMS solution

Our microbial blends ensure that the biodegradation of floating FOG and sludge in grease traps is efficiently and effectively controlled. The quality of effluent migrating to the third chamber will not only be improved – thus lessening the load on municipal conveyance and treatment plants – the grease trap will be cleaner, healthier and free from unpleasant odours.

Mechanical areas


  2. BIO-SYSTEMS L1800

  3. Hard Surface Degreaser (HSDG)

  4. Spill-SorbTM Absorbents

Food industry

  1. DrainFlow 60 (DF60)
  2. Dop-a-Day
  3. BIO-SYSTEMS B220 and B220R. B220 is the parent of FogFree and is supplied for improving the quality of large industrial effluent systems where high grease loadings are experienced.
    These include most meat and fish processing plants, as well as manufacturers of soups, confectionary, synthetic bread spreads, etc. B220R is a specialist pack designed for easy application into grease sumps and effluent pump station wet-wells. Read more about BIO-SYSTEMS B220R.
  4. BIO-SYSTEMS L2120
  5. FogFree (FF). FogFree is a DIY product compiled and marketed for use in food industry kitchen grease traps in medium-sized factories, hotels and restaurants. Safe and easy to use, it is compounded from a complex mixture of natural microbial powders that have been blended to degrade FOG in kitchen drain interceptors and grease traps.
    FF is particularly suited for use in the stilling tanks of traps where it has time to proliferate to a viable biomass that will feed on the FOG, breaking it down to natural gasses and water. There is no residue other than inherent, inorganic molecular radicals. For most catering effluent, FogFree is the answer.
    Just one 25g soluble pouch per week will maintain the average busy restaurant or supermarket trap in good working order. The dosage must be increased proportionately under heavy (peak season) loads.
  6. AirMix Aerators/DAF Units

Grease trap before treatment  Grease trap before treatment   

Grease trap after treatment  Grease trap three weeks after initial treatment



  1. BIO-SYSTEMS B560 - cannery and winery waste
    B560 is a dry micronutrient powder blend specially selected for organic processing wastes. It provides a complete formulation for maximum biological activity and reacts with fruit, vegetable and wine waste to produce biological enhancers. B560’s aerobic and facultative anaerobic microorganisms help to establish a biomass that provides greater resistance to the effects of organic inhibitors present in the effluent. As a result, it is able to perform more effectively than the naturally-occurring biomass. B560 is packaged in unique water soluble pouches to make dosing hassle and mess free.
  2. BIO-SYSTEMS B570 - pulp and paper (timber) mills
    B570 is a microbial powder blend that degrades paper and pulp waste. It is used in paper and card, and timber mills. The range of microorganisms selected for the B570 products are chosen for their cellulose degradation abilities under both aerobic and anaerobic conditions. To ensure optimal performance of these organisms under the toughest conditions, they are blended together with ‘high potency’ nutrients and stimulants. The production of enzymes – including a complex of cellulases, hemicellulases, amylases and lipases – provide the capacity to degrade extra cellular polymers (which cause foaming) and suppress the growth of the filamentous organisms by affecting the structure of the filaments.
  3. BIO-SYSTEMS B570 and BIO-SYSTEMS B560 products are both also excellent at degrading sugar mill effluent.

Click on the BIO-SYSTEMS Product table for a complete list of products. Also see our Grease trap case history.

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