Nanocelluse-Coated Membranes And Ion Exchange Polishing For Sustainable Water Reuse In Steel Manufacturing

The steel industry is among the most water-intensive industrial sectors, generating large volumes of complex wastewater that require advanced treatment for reuse. This thesis, carried out within the framework of the R3VOLUTION project, a European Union-funded initiative targeting Zero Liquid Discharge (ZLD) in water-intensive industries, evaluates an integrated treatment train designed for process water recovery at the CELSA steel plant: nanocellulose-coated nanofiltration (NF) membranes and ion exchange (IX) polishing. Two bio-based nanocellulose membranes developed by VTT Technical Research Centre (Finland) were tested at pilot scale on synthetic and real steel-plant wastewater. Rejection performance, permeate flux, and ion selectivity were assessed under varying transmembrane pressures. In parallel, a reverse osmosis (RO) stage was simulated using DuPont's WAVE software with a BW30 PRO-4040 membrane, and the resulting brine was used as feed for IX polishing trials with two iminodiacetic chelating resins: Lewatit® MDS TP 208 and MonoPlus TP 208. Results show that the VTT membranes exhibited rejection values far below commercial NF benchmarks, with sulphate reaching a maximum of ~23% and monovalent ions displaying negative rejection due to Donnan exclusion. RO simulation confirmed optimal performance at 10 bar, with ion rejection exceeding 99%. IX polishing achieved near-complete removal of Ca²⁺ and Mg²⁺ over 45 hours, confirming resin suitability for protecting downstream electrodialysis with bipolar membranes (EDBM). These findings contribute to the design of scalable water reuse systems for the steel sector.