Why are grease traps important for sewage treatment plants?

If grease in excess of 50 mg/l is contained in the sewage stream, it will negatively affect the performance of your sewage treatment plant, regardless of the technology because the vast majority of sewage treatment plants are based on a combination of settlement/biological treatment, where a biofilm (bacteria and other microorganisms) consumes the biological content of the sewage in combination with settlement e.g. BOD and make it safe for discharge.

Grease more correctly referred to as Fats, Oil and Grease or ‘FOG’ for short is very difficult to break down and does not settle out well.  FOG will coat the biofilm making it impossible for the biofilm to access the oxygen it needs to breath.  Therefore, as the level of FOG in the sewage increases the growth and performance of the biofilm is negatively affected, eventually to the point where no biofilm can survive and there is little or no sewage treatment.  High levels of grease will also be contained in the effluent further increasing the BOD/SS content.  No to mention the pungent smell of high level of rancid grease!

This is why all premises with commercial cooking on site must have properly sized and maintained grease traps installed.  The first part being that the grease trap(s) remove FOG to a level of 10 mg/l and the second that they are regularly inspected and emptied as soon as they are full.  If there is more than one kitchen on the site each should have its own grease trap.

BMS, in our 37 years of business, have come across countless situations where either no grease traps or inadequate grease traps are installed and secondly even if the correct grease traps are installed, that they are not regularly inspected and emptied.

Not only does FOG have consequences for a Sewage Treatment System but it will also progressively block pipes forming ‘Fatbergs’, which will eventually mean expensive professional cleaning of the sewage pipes is required.  For this reason, it is recommended that everyone including residents in private accommodation do not put FOG straight down the drain!

Example of a Giant Fatberg blocking a pipe

The good news is that BMS have substantially improved the performance of many sewage treatment systems by installing properly sized grease traps (if not already in place) and working with the owners to ensure a proper maintenance regimen is in place.  As part of our sewage treatment solution BMS manufacture static grease traps to European EN1825 Standard.

A lot of people view removing grease as dead money but not doing so as described above is not only illegal but will have a lot of negative consequences.  Indeed, a lot of commercial establishments have been fined and even threatened with closure due to their poor grease trapping regimen, no to mention FOG causes blockages of the sewage pipes"!

Typical biofilm surface with high inlet Fats, Oil and Grease (note the grey greasy appearance with the absence of a biofilm compared to the healthy surface below)

BMS Rotor with healthy growth at large Irish Hotel after properly sized and maintained grease trap is resolved.

The use of heavy degreasers, enzymes and heating elements, in our experience causes more harm than good, as it typically only pushes the problem further down the pipes or indeed, into the sewage treatment plant, again with all the negative consequences as described above.

If there is a FOG problem at a site, the solving of this problem will definitely improve the performance of your sewage treatment plant, sometimes substantially.

Finally, if you need a sewage treatment solution for your hotel, restaurant, pub or tourist site, we have 36+ years’ experience producing effluent to the highest standards available worldwide e.g. BOD/SS < 5 mg/l, NH4 < 5 mg/l, TN < 10 mg/l & P < 1 mg/l.  However, one of the first places we will start is checking what grease trapping you have in place and what maintenance is being done!

BMS GT08 Grease Trap in operation at a large Irish Hotel with high function/wedding business (note the large amount of FOG trapped).  This is installed adjacent to the kitchen before entering the sewage stream.  The installation of this grease trap immediately solved a large grease problem at the BMS Blivet sewage treatment plant.  Please note that this is only maintained when the grease trap is checked regularly.

A bit about the company

BMS is a quality manufacturer of package products for wastewater and stormwater treatment. BMS started in 1986 and has exported products to over 50 countries around the world.  It is a third generation family business with huge expertise in wastewater and stormwater.
BMS also manufacture a full range of products for surface water and wastewater treatment including our pioneering next generation RBC system the Aerotor, which forms part of our world leading Blivet package sewage treatment plant, a ‘one stop shop’ for all surface water products from design to installation including attenuation, interceptors, holding tanks (incl. chemical resistant), hydrobrakes, rainwater harvesting tanks & vortex silt/oil/debris separators, fully fitted pumping stations, our plug & play vehicle wash water recycling system; the Recyclone and much more.  Please see our enclosed Company & Product Profile for a full summary or View our full product/services catalogue at this link

BMS also can provide a Free Design Service for Sewage Treatment, Pump Stations or Surface Water and a full O&M, Repair, Advice and Testing service for existing installations.  We also can do free CPD Presentations on Sewage Treatment/Surface Water Management at any location.  Let us know when suits.

We would be delighted to discuss any requirements you might have, and we are available to meet you at your convenience.  Please do not hesitate to contact us.