Water treatment using electrodeionization Ultrapure water for the beverage industry

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Hydronomic Makkah

At Makkah Water in Saudi Arabia, a new water treatment system from Krones will go into operation in mid-2021. This particular Hydronomic contains a first: With a total dissolved solids (TDS) value of less than 0.1 milligrams per liter, the resulting water is more pure than any other in the beverage industry. The combination of the Krones Hydronomic and an electrodeionization (EDI) module makes it possible. Dirk Scheu is one of Krones’ sales specialists for water treatment solutions. He rediscovered this system and developed it further for the Makkah Water project.

Mr. Scheu, how does electrodeionization work?

EDI removes ions and ionizable substances from water to the greatest extent possible, almost completely demineralizing the water. The EDI module combines a continuously regenerating mixed-bed ion exchanger with ion-selective membranes. Basically, the water is split, then the ions that need to be removed are separated out, and the remaining H+ and OH- ions react to form the purest possible, deionized water.

How did Krones combine its Hydronomic water treatment system with EDI technology?

Before the water reaches the EDI module, two Hydronomic systems do important prep work: First, the water is ultrafiltered by the Hydronomic UF, which uses state-of-the-art membrane technology with hollow fibers (pore size 0.02 micrometer). Then, in the reverse osmosis (RO) module, mineral salts in the water are removed down to a TDS value of 5 to 10 milligrams per liter.

The next step is EDI, which further reduces the TDS considerably, to less than 0.1 milligrams per liter. This ultrapure water is often even less conductive than the target of 0.1 microsiemens per centimeter. The completely demineralized water is ideal for remineralization according to the customer’s recipe in a Hydronomic MDS.

So electrodeionization completely demineralizes water?

Yes. But not only that. In addition to mineral salts, the process also removes CO2. So the treated water has a pH value of 7, which is neutral. Therefore, there is no need to add sodium bicarbonate (NaHCO3), which means the water produced can have either very low or even no sodium.

What are the benefits of using an EDI module for continuous operation?

There are many. For one, you can operate 24/7. Because, unlike conventional mixed-bed ion exchangers, regeneration of the resins here uses electrical energy instead of acids and caustic chemicals – and it occurs continuously during production. By contrast, if you wanted to run a conventional mixed-bed exchanger around the clock, you would need at least two systems to bridge the regeneration cycles.

Also, as long as the feed water doesn’t exceed the maximum values*, the EDI module can be connected immediately downstream of the first RO system. Thus, no additional high-pressure pump is needed as would be the case when connecting two RO modules (the common approach). The great advantage there is that it saves energy. In our project, energy consumption in the EDI stage for the MPure36 – SB developed in collaboration with MEGA comes to 0.088 kilowatt hours per cubic meter.

Which beverage producers might want to consider integrating EDI?

An additional EDI module makes sense wherever the quality of the raw water tends to fluctuate. This is especially important when producing still table water, where the mineral composition of the water must not deviate from the figures printed on the label by more than 20 percent. When the content of the raw water itself already varies by +/- 15 percent before remineralization, there’s very little wiggle room for adding minerals back. EDI eliminates these variations. With it, the water is always demineralized to the same degree, and the quality of the treated water is therefore independent of the water coming from the RO system. When adding minerals afterward, the dosing can be kept closer to the minimum, thus saving costs on the rather expensive minerals. It saves on raw materials. In other words, the same amount of minerals can yield more product. Thus, using an EDI module can reduce consumption of the expensive, ultrapure minerals used to make table water by five to ten percent.

EDI can also be of interest to producers of alkaline water. Here, too, the consistent quality and resulting pH value of 7 provide the perfect basis for then producing water with a pH of 9, which is becoming increasingly popular.

What outputs can be achieved by combining Hydronomic and EDI?

EDI can cover the same spectrum as the Hydronomic. It can treat up to 120 cubic meters of water per hour, with the option of variable product volumes. The system is always precisely calibrated to the quality of the raw water and the requirements of the final product.

The water treatment solution developed for Makkah Water is one of the biggest Krones has built to date. It operates at up to 3 x 110 cubic meters of water per hour and is therefore around three times the size of our conventional Hydronomic systems.

* FCE < 20 µS/cm, where FCE (Feed water Conductivity Equivalent) is calculated as follows: Conductivity + mg/l CO2*2.66 + mg/l SiO2*1.94

Electrodeionization in detail

Electrodeionization uses resins for continuous ion exchange. After reverse osmosis (RO), the water is split into H+ and OH ions. These ions are then captured by the resins and pulled toward the electrodes (anodes or cathodes, respectively). While the ions that are to be removed are captured in the concentrate (C) channels and flushed out of the system, the remaining H+ and OH ions can react. The result is ultrapure, deionized water that is ready to have the desired minerals added back.