2025

Nieminen Joona; Soto-Salcido Luis; Moradi Mohammad Reza; Pihlajamäki Arto; Mänttäri Mika

Conversion of an End-of-Life (EoL) desalination spiral wound membrane into a nanofiltration element was investigated. The reconditioning treatments were first optimized in laboratory scale experiments and the main objective of this study was to upscale the chosen treatment to a spiral wound element. The effects of the treatments were evaluated with model substance filtrations, and the performance of the reconditioned element was shown by filtering municipal wastewater effluent with it. The EoL element was first alkali-cleaned and then subjected to a 10-hour oxidation by 13 000 ppm sodium hypochlorite solution, which transformed it into an ultrafiltration-like intermediate. Based on the preliminary small-scale experiments, the element was then coated with 3 bilayers of PDADMAC (poly(diallyldimethylammonium chloride)) and PSS (poly(styrene sulfonate)), and an element with 17 L m-2 h-1 bar-1 pure water permeance, 88% MgSO4 retention, 8% NaCl retention and 320 Da molecular weight cut-off value was obtained. The reconditioned EoL element was then used to purify municipal wastewater effluent. For instance, phosphorus concentration was reduced by more than 95% and several emerging pharmaceutical micropollutants, such as diclofenac, were simultaneously removed by more than 80%. From 1000 L of wastewater, 950 L of permeate was collected, and it was pure enough even to fulfil several potable water limit values. The reconditioned EoL element did not show notable signs of fouling during the testing. The results indicate that waste spiral wound membrane elements can be feasibly converted to well-functioning elements with a straightforward methodology.