Membrane screening for humic substances removal

To produce healthy drinking water is the main problem almost all over the world. The aim of this study is to find an efficient method to remove humic substances (HS) from water, because HS cause some types of cancer when they react with chlorine or other disinfection materials composing disinfection by-products, e.g. trihalomethans. Different membranes with a wide range of nominal molecular weight cut off (NMWCO), using different recycle flow rates and transmembrane pressures were investigated. The solutions were well-water with humic substances, model-solution with humic acid from Sigma-Aldrich GmbH and deionized water. The permeates and feeds in the case of modelsolution and natural well-water were analyzed measuring the UV absorbance on 254 nanometer. Based on the experiments, it can be established that the membranes with NMWCO ≤2 kDa are suitable for the removal of humic substances. The UF membranes with NMWCO >2 kDa were proper for model-solutions, but in the case of natural well-water the HS content of the permeates was higher than the limit value (3.5 mg/L). The measured HS values showed a moderate increase with an increase in the NMWCO of the membranes.

Based on the experiments performed with membranes in the range of NMWCO = 0.3–100 kDa the following conclusions were established: • In the permeates of NF membranes (NMWCO = 0.3–0.4 kDa) there was no HS to detect, so the rejection of the nanofiltration membranes was ~100%, but they have also removed all the other compounds (e.g. total hardness), which are important for the drinking water quality. Also the costs of the nanofiltration are higher, because of the higher pressure needs. • The UF membranes with NMWCO ≤2 kDa are suitable for the removal of humic substances, the rejections were ~83%. Also the costs of the ultrafiltration are lower than those of the nanofiltration, so these membranes seem to be optimal to produce the proper water quality. • The UF membranes with NMWCO higher than 2 kDa (5–15 kDa) are proper for modelsolutions, but for natural well-water the HS content of the permeates is higher than the limit value (3.5 mg/L).