Surface water treatment by the nanofiltration method

Studies concerning the removal of natural organic matter (NOM) from surface and tap water by nanofiltration are presented. The separation and transport characteristics of nanofiltration membranes were determined. The degree of NOM coefficient and water hardness removal from surface water and a reduction of water hardness were studied. The content of organic matter, both in the feed and the permeate, was estimated by the determination of total organic carbon (TOC), colour, turbidity, chemical oxygen demand (CODMn) and the absorbance in ultraviolet at a wavelength of 254 nm. The investigations demonstrated the complete removal of humic acids determined as the UV254 absorbance, and a high removal of colour (93.3%), TOC (93.5%) and turbidity (85.5%).

1. The studies performed to determine the transport and separation characteristics of the NF membrane using the model solutions of various salts demonstrate that the retention coefficient was in the range of 90–99% for sulphates, about 82% for carbonates, whereas the monovalent salt were rejected by 40–55%. 2. The studies demonstrated that the organic pollutants determined as TOC were removed from the surface water in 93.5%, whereas UV254 absorbance (indicating the presence of humic acids) in 100% and the CODMn in 85.9%. 3. The studies showed a significant retention of inorganic carbon (62.8%), electrical conductivity (68.4%) and a reduction of total hardness by 85.2% and turbidity by 85.5%. 4. The treatment of surface water with low initial turbidity but a high value of TOC by NF is associated with a gradual plugging of the NF membranes. However, flushing the membranes with RO permeate allowed recovery of the initial flux. 5. Nanofiltration was found to be an efficient process for surface water treatment. The obtained permeate meets standards of drinking water quality as far as the investigated indicators of contamination are concerned.