1. Field of the Invention
This invention relates to a water-containing alkaline cleaning formulation containing potash lye for equipment used in the food industry.
The invention also relates to a process for cleaning equipment used in the food industry with an alkaline cleaning formulation which is regenerated by membrane filtration, the permeate being recycled.
It is known that equipment used in the food-processing industry, for example tanks, pipelines, bottling plants and the like, can be cleaned with alkaline cleaning solutions. These cleaning solutions or liquors essentially consist of a 2% soda lye containing added cleaning enhancers, for example defoamers and emulsifiers. In principle, potash lye could be used instead of soda lye because it produces the same cleaning result. However, soda lye is used for reasons of cost. Only where low outside temperatures prevail is potash lye added in small quantities to the soda lye in order to lower the crystallization point of the cleaning concentrate. However, the potash lye always makes up considerably less than 20% by weight of the hydroxide total.
The alkaline cleaning solutions often contain an addition of ethylenediamine tetraacetic acid (EDTA) in the form of its disodium salt because EDTA--as the only complexing agent in aqueous alkaline cleaning solutions--is capable of dissolving mineral soils, such as calcium and magnesium salts, for example in the form of limescale, milk scale, beer scale and the like.
In recent years, an integrated cleaning and disinfecting technique known as cleaning in place (CIP) has been successfully applied. The corresponding fully automatic cleaning systems clean all storage tanks and pipelines automatically after each production cycle. The cleaning formulation and cleaning process according to the invention are particularly suitable for use in the CIP process.
2. Discussion of Related Art
It is known that wastewater pollution by spent cleaning solutions can be reduced and the economy of the cleaning process improved by regenerating the spent cleaning solution in membrane filtration units. To this end, part of the cleaning solution is transferred from a collecting tank to a buffer tank and pump-circulated from there through a membrane system in which it undergoes crossflow filtration. One such regenerating process is known from WO 95/27681 A1. The permeate consisting of water and soda lye is returned to the collecting tank for the cleaning solution. The organic soils collect in the buffer tank of the membrane filtration unit and are periodically removed for disposal as waste. Since, in cases where EDTA-containing cleaning solutions are used, any introduction of EDTA into the wastewater should be avoided on account of the poor biodegradability of this compound and its ability to remobilize heavy metals in the environment, Israeli patent application IL 109 249 proposes recovering the EDTA from the concentrates collecting in the buffer tank by acidic precipitation. However, the addition of EDTA to the cleaning solutions affects the performance of the nanofiltration unit which is reflected in distinctly reduced flow. In addition, in the case of cleaning equipment for the dairy industry and in the case of EDTA-free cleaning solutions, it is known that the concentrate can be freed from the alkaline constituents by diafiltration and subsequently used as an animal feed or animal feed supplement. Diafiltration is necessary to reduce the sodium content of the concentrate which is too high for its use as an animal feed. Unfortunately, the large volume of wastewater accumulating in the diafiltration process and the high cost of diafiltration are disadvantages.
The problem addressed by the present invention was to provide an alkaline cleaning formulation and a process for cleaning equipment used in the food industry of the type mentioned at the beginning which would enable cleaning to be carried out far more economically than in the prior art.