New study: Freeze crystallization cleans wastewater efficiently

In wastewater purification, natural freeze crystallization is an ecological alternative to, for instance, chemical treatment methods. Industry can take advantage of natural climate conditions to implement energy efficient purification processes.

In areas where temperatures naturally drop below the freezing point of water, it is possible to employ natural freezing in wastewater treatment. The method relies on the fact that ice crystals are naturally resistant to impurities. In other words, when wastewater freezes, the ice layer generated is significantly cleaner than the water itself.

This topic was investigated by Post-doctoral Researcher Emil Kurvinen and his research group at LUT University.

"The study indicates that ice contains up to 65-90% less impurities than the original water," Kurvinen explains.

Surprisingly efficient water purification in a naturally cold climate

WINICE, a joint research project of LUT University and Aalto University, has investigated natural freezing. The project collected ice and water from wastewater treatment basins in the Terrafame mine in Sotkamo and Vapo's peat treatment areas in Suursuo and Konnunsuo, South Karelia.

Samples were also taken from the southern part of Lake Saimaa, in Taipalsaari, for reference values on the mechanical strength and purity of ice.

"Wastewater purification has been studied a great deal from the perspective of controlled freezing. In a naturally cold climate, freezing purifies wastewater in basins with surprising efficiency," Kurvinen elaborates.

"Finding out that nature has this type of separation or purification ability makes me wonder what else it could be harnessed for – especially if the freezing process is controlled," he adds.

Eco-friendly industrial purification method

In Finland, the stakeholders that stand to gain most from purification by freezing are the chemical and mining industries. According to Kurvinen, the method has the potential to contribute to wastewater treatment because it can reduce the amount of wastewater that requires other treatment techniques.

"When we let wastewater freeze first, we can naturally separate the cleaner part – the ice."

In the study, the research in natural conditions was preceded by a freeze crystallization study on saline solutions with a special winter simulator. Read more.

More information:

  • The Wastewater Management by Natural Freeze Crystallization and Ice Separation (WINICE) consortium included the following professors and their research groups: Marjatta Louhi-Kultanen (LUT & Aalto), Pentti Kujala (Aalto) and Aki Mikkola (LUT). WINICE was a three-year project (2015–2017) and was connected to the ARKTIKO programme of the Academy of Finland.
  • The WINICE project coincides with the JÄPÄ project on wastewater purification solution based on ice crystallization (Teollisen jäteveden puhdistaminen liikuteltavalla ratkaisulla). The JÄPÄ project is funded by the New Business from Research Ideas programme of Business Finland.
  • The study on the purity of naturally frozen ice and its mechanical strength in Finnish wastewater basins in 2017 is presented in the following article: https://www.sciencedirect.com/science/article/abs/pii/S0043135418306936. The article was published in the Water Research journal, which has a National Publication Forum rating of 3.