Cleaning of spiral-wound membrane filtration systems with lower chemical use
New opportunities to streamline CIP – without compromising on food safety
Membrane filtration is one of the key technologies in the production of lactose-reduced products, high-protein products, plant-based alternatives to milk-based products, and baby food among many other foods.
Effective cleaning of filtration systems is an important part of the manufacturing of these products to ensure the highest food safety. At the same time, sustainability is high on the agenda.
A shorter, optimized cleaning of the membrane filtration systems can make a key difference; both for the bottom line and for the environment. In addition to extending the production time, a shorter cleaning process also extends the life of the membranes, since cleaning is what wears them out the most.
“It has now become possible to shorten the cleaning time by using fewer steps in the procedures, partly because new and even more advanced enzyme-based cleaning agents have entered the market. The exact procedure depends on which applications are run on the membrane filtration system,” says Jacob Jacobsen, Application Technologist, Tetra Pak.
For the cleaning of membranes, one of the benefits of enzymes is that they usually extend membrane life considerably compared to chemicals as e.g. chlorine.
Enzymes or chemicals?
Some countries and dairies still prefer chemicals such as chlorine for cleaning membrane filtration systems, primarily due to traditions and economics.
Chemicals such as chlorine and hydrogen peroxide break down proteins and at the same time have a disinfectant effect. Enzymes cut proteins into smaller pieces and thus remove fouling, but they do not act as a disinfectant. Nevertheless, there is generally no need for the disinfection of membranes except in a few cases when problems occur.
Historically, chlorine has been used extensively to clean membranes because it is inexpensive, breaks down proteins, and removes bacteria effectively.
“From our vast experience, we know that chlorine reduces the life of spiral-wound membranes, while it is harmful to the environment. It is also more difficult to dose as it is consumed during the cleaning process, so more must be added along the way. In addition, minimal chlorine residues can potentially be traced in the finished products in the first production runs after a chlorine step,” says Jacob Jacobsen.
Enzymes have taken over as the preferred cleaning agent in large parts of the world because they are more environmentally friendly, degrade proteins very efficiently, and generally extend membrane life considerably compared to e.g. chlorine cleaning. In addition, it is easier to predict the cleaning time with enzymes and to dose these. The activity of the enzymes is completely stopped using acid in the subsequent cleaning step. The use of membranes that can withstand higher temperatures and higher/lower pH has also made it easier to phase out the use of chemicals.
Accurate dosing of CIP chemicals is one of several important elements in the more sustainable cleaning of spiral-wound membrane filtration systems.
Reuse water and save energy
A shorter and more efficient CIP means not only longer production time and lower energy consumption, but also lower water intake. And there are more water savings to be made.
“Many large dairies simultaneously clean the excess permeate water from the filtration of milk and whey with an additional filtration system, a so-called reverse osmosis polisher, and reuse the water for cleaning. This means large savings on water intake, and there is an increasing focus on this in dairies around the world due to increasing water shortages. Even smaller dairies can advantageously install a polisher,” says Jesper Kjeldal, Senior Sales Manager, Tetra Pak.
New methods to enable the recovery of the heat from the cleaning water are also on the drawing board.
“When we rinse a membrane filtration system, we use 10°C cold tap water or water from the permeate tank on the polisher. This water is heated with steam for approximately 10 minutes to 50°C to be used for cleaning. It is possible to recover the heat from the hot outgoing rinsing water to heat the incoming cold rinsing water,” says Jesper Kjeldal.
In this way, the heat is not flushed out into the sewer and lost but is used as a heating medium for the cold rinsing water. Cleaning with preheated water ensures a more efficient and shorter rinse. The reduced time needed for heating can be converted into production time.