Behind the PhD degree: Ruben Halfwerk

Big steps should be trivial for the tall PhD candidate Ruben Halfwerk – though the scale of his research and personal learning growth surprised most. Learn more about the fun he had on the way and his studies in the microscopic lactose crystal structure applied to the factory floor.

The person behind the science, the science behind the person

Odd-sounding ideas

True innovative ideas will be ridiculed – that is one of Cees Buisman’s key takeaways after being Wetsus’ scientific director for twenty years. You could say that ridicule, and odd-sounding ideas, may be a measure of success in that sense — a feature you need in the field of water technology.

Ruben Halfwerk is an innovator. Originally a thermal engineer, he is a true water technologist now that he has studied the crystallization of lactose, chemical equilibriums, whey solutions, and ice. Using a brine-based technique for a wildly different application in the dairy industry. Powered by perhaps half the energy of conventional state-of-the-art systems and Ruben’s will to better the world.

Roman ice

Many factories processing dairy produce waste streams full of milk sugar – lactose. Well, waste… there still is value in the compound. Usually, they can still get most of it out using big evaporators. But powering oversized kettles costs tremendous amounts of energy – bringing water to a boil. So, Ruben set out to solve this problem by flipping the thermometer. Given the right circumstances, you can achieve the same goals.

People encounter the same issue when salt and water need to be separated. Eutectic Freeze Crystallization (EFC) is what they use to resolve it, converting a solution into pure ice and salt crystals.

You probably have witnessed the physics phenomenon behind it already. In the winter, we here often salt the roads because a little bit of salt decreases the temperature at which ice forms. And the knowledge is at least as old as the Roman era. They already made ice cream through this.

Now, depending on how much salt is in the liquid water, on cooling down, one of two things will happen: first, ice forms, or otherwise, salt crystals form. It all concerns the freezing points of water or the solubility of salt and the combination of both. If water first crystallizes, leaving it as ice, the number of salt particles in the remaining water is higher, and this will, in turn, affect the total freezing point so that the subsequent drop in temperature again precipitates salt or ice again. This cycle will continue until a certain point – the eutectic point – is reached, in which both compounds will turn solid simultaneously. And since ice floats, they are easy to separate.

That EFC works for salty brines is nothing new. But in principle, it could work for other compounds, too.

Heat energy

And yes, a mixture of water and milk sugars – lactose – almost acts similarly. Proving that, of course, already was a big part of Halfwerk’s PhD. But the scientist decided to take it a step further: to the factory floor.

“I went from 1-liter solutions to 500 liters. In the heat of the summer, my student and I were sweating away in the hot factory hall of Cool Separations in Rotterdam. We only had a small time frame to make it work.”

And it did. Ruben managed to build a system that could churn out sixty kilograms of ice and sixteen kilograms of lactose. All continuously from a conveyor belt. And on top of all that, the system would cost 30-80% less energy than modern state-of-the-art evaporators. And if explored further from this conceptual design, yields of at least 80% and up to 95% of the input lactose can be achieved.


But to Ruben, there are many more memorable experiences. “I am glad I did my PhD in an institute that is not all about work. When there are times when the research is not going as you planned, you still have all your colleagues. We had a great group that went climbing, had dinner together, and went on short trips to the microbe museum Micropia.”

Let’s keep that going. Let’s keep changing the world while having fun too.

On June 2, 13:30hrs, Ruben Halfwerk will defend his thesis “Eutectic Freeze Crystallization of Lactose”. Location: De Harmonie, Leeuwarden