Influence of organic fouling and operating conditions on nanofiltration membranes to reduce phenol concentration in natural waters

Phenol is a product widely used in manufacturing and as a disinfectant for industrial and medical applications. The treatment of aqueous effluents polluted with phenol and phenolic species has deserved much attention in the last years due to the toxicity and low biodegradability of those organic compounds. Nanofiltration (NF) has a great potential to remove these contaminants. The main objective of this work is to study the influence on the rejection of phenol by a NF90 2540 NF membrane of various operating conditions: pressure (0.3, 0.4 and 0.5 × 10⁶ N/m²); phenol feed concentration (from 0.025 kg/m³ up to 0.150 kg/m³) and pH (from 5.9 to 11.5). The influence of organic fouling is also investigated. Results showed that when different phenol concentrations were compared at the same pressure, permeate fluxes decreased as phenol concentrations increased (from 20% for the highest phenol feed concentration tested to 10% for the lowest); when phenol concentration increased, phenol was probably adsorbed onto the membrane, which led to lower rejection values (from 78 to 59% rejection). Changes in the pH of the solution altered the phenol dissociation equilibrium and membrane rejection characteristics. The reduction in phenol rejection by organic fouling (maximum of 35%) was a consequence of the materials deposited onto the membrane, which led to the formation of a cake layer.