Decree of the Government of the Russian Federation No. 644 "On Approval of the Rules for Cold Water Supply and Drainage Regulations..." sets the maximum allowable concentration of fats in wastewater at 50 mg/dm3. As can be seen from the explanation to the table of pollutant substances given in the Resolution, this MAC for fats is set, first of all, to prevent their negative impact on sewage systems.
As mentioned above, while the discharge of polluted wastewater directly into a water reservoir or land is completely prohibited by environmental legislation, maximum permissible concentrations for various pollutants, including fats, are established for the discharge of wastewater into the sewer system. Thus, it will only be illegal to exceed the established volumes of effluents and concentrations of pollutants in them. The collection and analysis of samples for their compliance with the standards is carried out by specialists of accredited laboratories, according to the results of their activities, issuing to the customer a final table in which the concentration of all hazardous elements is indicated.
The essence of their work is to retain the fat floating on the water surface by means of a number of separator partition, which are installed across the flow of wastewater. In the very first section sedimentation - sinking of trash and the heaviest fractions caught in the trap to the bottom - takes place. Further, when passing through the system, the speed of flow of liquid slows down and its temperature decreases. The main part of the fat thus passes to the unemulsified state - it stratifies, thickens and collects on the walls of the trap, forming first a film, and then a dense fat mass. Water, in its turn, through the outlet pipe enters the next stages of purification and disinfection or, if they are not provided, and the MAC is not exceeded, it enters the sewage system. Since the tank of the grease trap is hermetically sealed to prevent leakage or spread of odors, the thickness of accumulated grease is usually monitored by a special sensor that, when a certain critical point is reached, signals the need for cleaning. In case the grease trap is not cleaned in time, fermentation and putrefaction processes start in the accumulated mass, with the appearance of the accompanying unpleasant smell. Also these deposits tend to harden over time, which significantly complicates their pumping, and sometimes even makes it impossible without additional measures to liquefy the consistency of the formed solid masses of fat products
If you stop keeping up the maintenance of the device at all, it can be fraught not only with a decrease in the efficiency of its work, but also with a complete cessation of operation, up to the probability of an accident, with the logical entry of large volumes and high concentrations of oil waste into the sewage system. This will lead to a shutdown of production and economic activity of the enterprise until the elimination of the failure, which usually takes considerable time and entails significant costs. In the case of an accidental discharge of contaminated wastewater, the picture will be complemented by a large fine and an unscheduled inspection of the organization. Grease traps vary greatly in their type, capacity, size and materials used in production. For example, while household grease separators, due to their small size, can simply be installed under the sink, the production ones require special mounting inside the workshop or taking them out of the perimeter of the room. All this depends on the specific activities of the enterprise and the available logistical capabilities. For a large producer of fat and oil waste with considerable concentrations of the pollutant the fat separator can be a complex of tanks and reservoirs buried in the ground. Multistage structures, in addition to the presence of mechanical methods, also involve biological purification systems, as some of the fat may still not be captured by the grease separator, but it exceeds the maximum allowable concentration. In some cases, for additional separation of fats at the enterprises more complex method of flotation is also used, but it requires a special flotation unit, the use of which exclusively for fighting oil and fat contaminants is ineffective and expensive, so in most cases the standard grease trap is enough. Pumping grease out of a small grease trap is done manually with a compact pump , while cleaning a large industrial grease trap is done with a sewage truck through a drainage connection and should be done at least twice a year.