Membrane distillation and freeze crystallisation treat salt-streams containing organic pollutants

Over the last three years, research has been conducted within TKI Energy and Industry to determine whether membrane distillation and freeze crystallisation are capable of treating salt-streams of 1-10 m3 per hour, with the aim of further concentrating the brine and producing clean water and clean salt. Such waste streams are generated by different industrial processes, for example, in the chemical industry. The Orpheus (Organic Pollutants Handling during Effective concentration of Unsaturated Salt-streams for re-use) project was carried out by the partners Nouryon, Vito, Cool Separations and KWR, and was coordinated by ISPT.

Impact of pollutant type

Vito tested membrane distillation on a lab scale. The type of pollutant appears to have a strong impact on the effectiveness of membrane distillation: some components remain entirely behind in the concentrate, while others can be found in the distillate. In addition, surface-active substances render the membrane permeable so that no further separation takes place.

KWR tested freeze crystallisation. For this technology as well, the degree of separation depends on the organic pollutants present.

Pilots and economic comparison

A successful pilot was carried out with each of the technologies using brine from operating situations. KWR drew on the results as inputs for an economic comparison, which showed that the cost-price of the (residual) heat needed to run the membrane distillation process is the key parameter in determining which of the two technologies is more interesting economically.

The possibility of processing brines that are polluted with organic components renders feasible the reuse of the water, and sometimes the salt, while the processing of the concentrated salt-stream becomes more cost-effective.