Cow's milk contains quite high levels of minerals: about 0.7-0.8% on average. Much of this mineral content follows the whey and ultrafiltration permeate.
The purpose of whey demineralization is to make whey products more suitable for human consumption, some of the typical products/processes being:
- Whey-based products for infant formulas
- Whey-based beverages
- Whey used for lactose production
- Whey used as a skim milk replacer in ice cream
- Demineralization of whey prior to ultrafiltration to improve plant performance
- Demineralization of whey/permeate prior to production of products containing hydrolized lactose.
SPX FLOW's in-depth knowledge and active involvement in the world's whey processing industry, combined with proven experience in project management of capital projects, makes SPX FLOW the ideal partner for the design and installation of state-of-the-art demineralised whey processing equipment.
SPX FLOW has experience in the design and installation of a number of different processes for de-mineralisation of whey.
- Ion exchange
Each technology has a particular application and the selection of the most appropriate process depends on the required end-product properties, plus economic factors.
Ion exchange is the most mature of the demineralisation technologies. It has the ability to remove almost all of the minerals present in whey and permeate.
The operation principle is that whey is first passed over a bed of resin, which is initially saturated with ions. Here sodium, potassium, calcium are chlorides and sulphates are exchanged so that the minerals in the whey are replaced by H+ and OH ions.
A wide range of base polymers may be used in ion-exchange resins depending on the physical and chemical requirements of the system.
Once a resin is saturated with ions from the whey and has exhausted its capacity, it may be regenerated and returned to its original form.
The most common systems are those in which the resin is packed in columns or a simple system of a continuously-stirred reactor tank.
As all the systems are essentially batch operations, it is necessary to have two or more systems operating in parallel when continuous production is required.
Electrodialysis is generally used for applications where low levels of demineralisation are sufficient since power consumption at high levels of demineralisation is excessive. In practice, levels of demineralisation of about 50% are viable.
Construction and operation
The basic electrodialysis module is made up of pairs of channels which come together to form a stack or module. At the end of the stack are two electrodes that create the electron driving force over the stack.
The operation principle is that whey is fed to alternate flow channels with a brine solution, typically hydrochloric acid, being fed into the remaining channels.
The product can be processed in three ways:
- batch wise - feed is recirculated until the required level of demineralisation is reached
- continuous - feed is passed once through a series of modules to achieve the required demineralisation
- feed and bleed - feed is recycled continuously around the module with raw whey being fed in and demineralised whey being bled off.
Nanofiltration is a membrane filtration process using a special type of reverse osmosis membranes which reject the lactose in whey, but have excellent salt passage properties for monovalent salt when applied to whey and permeate.
With such membranes, it is possible to concentrate whey using higher flux rates than in ordinary reverse osmosis processes and simultaneously remove monovalent salts. The disadvantage is a small loss of lactose.
The level of demineralisation obtained for various types of whey depends on how much the volume is reduced through water removal. The demineralisation process can be further improved by the addition of water during the concentration stage. This process is known as diafiltration.
Since whey and permeate usually have to pass through a concentration stage before further processing, the nanofiltration option becomes very attractive becausesome demineralisation is obtained "free of charge". Some of the uses of nanofiltration are:
- conversion of salt-cheddar whey to whey with a normal composition instead of disposal
- pre-concentration and partial demineralisation of sweet whey as a pre-treatment for ion exchange or electrodialysis, thereby improving the total operation economy
- concentration and partial demineralisation of whey permeate prior to lactose production
- partical demineralisation of the mother liquor resulting from lactose production.
In comparison to ion exchange or electrodialysis, the advantages of nanofiltration are: reduced consumption of chemicals, less electrical consumption, and a considerable reduction in effluent. Using nanofiltration, it is possible to obtain some demineralisation levels (50%). Nanofiltration represents a unique opportunity for the dairy industry in relation to whey processing and a large number of plants have been installed since the process was introduced in the mid-1980s.
The basic concept is that lactose is crystallised and mixed with whey protein concentrate (WPC). By using WPC-80 and edible lactose of specific compositions, a mixed powder with a composition corresponding to more than 90% demineralisation of the whey powder is obtained. This method is especially suitable if the manufacturer is already producing WPC. Lactose can either be manufactured by crystallisation or it can be purchased as low-cost, edible lactose powder. One of the main advantages of this method is that the minerals are removed without using ion-exchange resins, and the very substantial effluent discharge problems that these involve. Compared with electrodialysis, the advantage is a considerable reduction in electricity consumption. Moreover, both ion-exchange systems and electrodialysis use considerable amounts of water.
- SPX FLOW's global experience as a supplier of APV processing technology and equipment for whey products is a key factor in our ability to deliver cost-effective solutions tailored to individual customer requirements.
- We offer an enormous range of resources to the dairy industry in process engineering, equipment manufacturing, project management - for both large and small projects - and world-class development facilities.
- APV's nanofiltration and crystallisation systems have reduced consumption of chemicals, electricity, and significantly reduced effluent in comparison to ion-exchange or electrodialysis.