Natural Wastewater Purification - Freezing

Lappeenranta University of Technology Is Using the Freezing Technology in the the Extractive Industry Requiring Seven Times Less Energy than Evaporation

Microbiologists rarely wash their jeans. The reason is because they know how to keep the color looking new without getting odors - they freeze their pants.

Freezing can even work in more extreme scenarios, like with waste water.

When waste water freezes, it is purified through the formation ofa cleanerlayer of ice. Then the clean layer of ice can be removed from the rest of the waste water, and the remaining waste water is more concentrated, which can be treated as needed with a lot less outside processing. Energy is required only for breaking the ice and transporting it from the waste water pool.

The most practical application is leaving waste water from mines to freeze in special pools and then removing the cleaner part by breaking the ice. Then the treated waste water would be recycled, or undergo further treatment using membrane filtration, reducing the amount of fresh water that is used.

Themethodis being developed at the LappeenrantaUniversity of Technologyfor the extractive industry, which produces large amounts of waste water. The freezing of water - crystallization - requires seven times less energy than its evaporation. Equipment developed by LUT chemical technology researchers includes a winter simulator which makes it possible to study how the temperature of cooling air affects freezing. The simulator has been used to study the growth rate of the layer of ice that emerges, and the degree of purity when salt solutions of different concentrations are used. Last winter researchers also took samples on the ice of Lake Saimaa.

"We took samples of both the lake water and the ice and we examined the amount of impurities that they contained. The result was that the lake water contained about ten times more impurities than the ice. Another finding in the research was that the slower the layer of ice grows, the cleaner the ice is. Therefore, the purity of the ice is directly dependent on its rate of growth," says Chemtech Professor Marjatta Louhi-Kultanen, who is specialized in the study of crystallization. According to Professor Louhi-Kultanen, future research will be aimed at an extensiveexaminationof different types of waste water pools and the purity of their layers of ice and the implementation of freezing experiments with waste water samples in mining areas.

Source: Science20

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• Treatment
• Water Distillation
• Purification
• Technology