Nanofiltration: a Final Step in Industrial Process Water Treatment
We report here a proposed process water treatment design guide: selection of nanofiltration membrane, membrane test for model solutions and test for pre-treated industrial process water. We also suggest a complex evaluation method, which can help in decision-making process. Membrane selection experiments showed that high flux coupled with high enough rejection is favored to shorten treatment time and perform acceptable rejection. The effect of composition was studied during constant total salt concentration and it was revealed that the DL membrane had stable flux and high rejection. In case of pre-treated industrial process water a more complex effect could be observed: the counter ions present in the feed solution, moreover the complexing agents as well as other properties of the feed could lower the membrane’s rejection, simultaneously decreasing the flux. Nanofiltration though still showed advantages, which allowed its implementation into an existing industrial scale technological chain. At a recovery rate of 0.2-0.5 all the environmental requirements could be fulfilled, and the permeate leaving the technology could be fed into the city sewer system.