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

Towards an economy of value preservation | By Niels Faber


The realisation of a circular economy has thus far unfolded under the assumption that it would fit within existing economic arrangements. In practice, we witness many circular initiatives struggling to give shape to their ambitions, let alone develop to maturity. These past months, various material recycling organisations terminated their activities, seeing virgin alternatives from other parts of the world flooding the market at prices against they cannot compete. If the transition towards a circular economy (i.e. an economy of value preservation) is to be taken seriously, a new perspective on value in our economic system seems unavoidable, as the rewriting of the rules of the economic game. At this moment, current perceptions of value stand in the way of this transition both at micro as well as macro levels. Several contours for a collective exploration of new directions of value and economic configuration that foster circular transition will be addressed.

Searching Innovation for the Common Good | By Cees Buisman


In his key note he will conclude after a life of innovations that it is impossible that humanity will stay within the save planetary boundaries with innovation only. We should be more critical about the behaviour of the rich population in the world and more critical about new innovations that prove to be dangerous, like the PFAS crisis shows at this moment. In his keynote he will investigate how to look at the world that can stay within the save planetary boundaries, how should we change ourselves? It is clear if we only talk about the words of science and systems we miss the essential words of how we should cooperate and change ourselves. And his search for coherent save innovations. Which innovations will be save and will lead to a fair and sustainable world? And will lead to a world we want to live in.

Future-fit economic models: What do they have in common – how can they join forces? | By Christian Felber


There is a growing number of new sustainable, inclusive, cohesive, participatory, just and humane economic models. A possible next step in the discourse about them is the comparative analysis in order to find out key commonalities, potential synergies, and “requirements” for a future-fit economic model. The author and initiator of the Economy for the Common Good provides an overview of these „new sustainable economic models“ and compares them according to underlying values, principles, and practical ways of implementation. The keynote addresses the cooperative spirit of the conference and prepares the ground for its public highlight on the eve of June 3rd, the round table with representatives of diverse future-fit economic models.

The era of postgrowth economics | By Matthias Olthaar


The scientific debate on whether economies should always continue to grow increasingly becomes a political and societal debate. On the one hand further growth for the most affluent countries seems neither possible nor valuable, but on the other hand there is still lack of understanding and knowledge what a non-growing economy should look like and could best be governed. In this lecture we discuss various policy measures that can be realistically implemented, take into account government finances and aim at a higher quality of life despite a non-growing economy.

Democratic principles for a sustainable economy | By Lisa Herzog


Democracy is under pressure, and less and less able to stir the economy into a sustainable direction. Therefore, to stabilize democracy and to make possible the socio-ecological transformation of the economy, democratic principles need to be implemented directly in the economy. This is not only a matter of morality, but also has practical advantages. Democratizing the economy can increase legitimacy and take advantage of the “knowledge of the many” to accelerate the transformation. Democratic practices, especially deliberation, allow bringing together different forms of knowledge, which is crucial for the local implementation of principles of social and ecological sustainability. This talk explores what this idea means in more concrete terms, from democratic participation in the workplace to the democratization of time.

Market, state, association, and well-being. An historical approach | By Bas van Bavel


Over the past decades, markets have conventionally been seen as the best instrument to stimulate economic growth and enhance prosperity and well-being. The automatic link between markets and economic growth is increasingly questioned, however, as well as the automatic link between economic growth and enhancement of well-being. This has led to attempts to capture well-being development more directly than through GDP per capita figures and has produced a more variegated picture of well-being growth. Also, this has led to a shift of focus to other coordination systems than the market, as primarily the state but increasingly also the association. Analyses of the historical record suggest that especially the latter could be a vital component in future well-being.