Conference on Environmental Science and Technology

Nanofiltration (NF) has undergone rapid development and has found numerous applications in recent years. Among them, the separation of multivalent ions (e.g. hardness) from various wastewaters and industrial process streams is still its main application. This paper reports on the cross-flow nanofiltration process in a fully automated laboratory pilot NF unit for the treatment of two real industrial wastewaters (samples A and B), aiming to produce high quality water for reuse in the production process and also to reduce fouling/scaling of the membrane. Samples A and B had moderate inorganic and organic content (pH 6.9-8.2, eC 1.9-2.5 mS/cm, 11-150 mg/L COD, 17-146 mg/L Ca2+, 11-13 mg/L Mg2+, 156-249 mg/L SO42-, 99-472 mg/L Na+, 16-227 mg/L K+, 119-316 mg/L Cl-) and originated from a steel and a pulp and paper industry, respectively. A series of filtration experiments were conducted in batch mode under various key process parameters such as initial pressure, cross-flow velocities and water recovery, testing different commercial hollow fiber membrane modules. Under optimal experimental conditions, encouraging results were obtained as high removal percentages of divalent cations (Ca2+, Mg2+) and rather moderate rejection rates of monovalent ions (Na+, K+, Cl-) were reported, followed by a rather low fouling tendency of the membranes as shown by the transmembrane pressure (TMP) temporal variation. In addition, optimization of the process was achieved with the aim of maintaining water productivity, increasing solute recovery (high selectivity towards divalent ions) and reducing energy requirements. The study is part of the CORNERSTONE project funded by the European Union. Horizon Europe under Grant Agreement No. 101138504.