Sustainable membrane-based process for valorisation of cork boiling wastewaters

Cork boiling wastewaters were processed by nanofiltration (NF) in order to concentrate phenolic compounds, whose tanning power allows their application in the leather tanning process as a retanning agent, and to produce a permeate suitable for reuse in the cork boiling operation, according to the International Code of Cork Stopper Manufacturing Practice. Four commercial polymeric membranes were selected and tested at laboratory scale: NTR7450, Desal-DK, NF90 and NF270. The feed volume reduction factor (VRF) was defined to be equal to seven or higher, and the operation was carried out in a batch mode at 15 bar and 25 °°C. The performance of the different membranes was evaluated determining membrane permeability and rejection coefficients for several pollutant indicators: total organic carbon (TOC), colour, absorbance at 254 nm and salt content. Two membranes were selected to perform pilot-scale studies, NF270 and NF90, based on their performance in this process. The results obtained in the laboratory and pilot-scale studies permitted the development of a mass balance model, which was calibrated with experimental data. Additionally, a technical and economical evaluation study was performed, which showed that the process proposed in this work is viable for industrial application.