Sustainable tuning of pozzolan microfiltration membranes using walnut shell additives: A response surface methodology investigation

Abstract

• Walnut shells are used as a pore-forming agent in pozzolan-based membranes. • RSM is applied to optimize walnut shell content and sintering temperature. • The membranes show high porosity and good water flux. • A trade-off between porosity and mechanical strength is observed. • Up to 98% turbidity removal from textile wastewater is achieved. This study investigates the fabrication and characterization of flat ceramic membranes prepared by dry pressing using natural pozzolans and walnut shell powder as a bio-additive. Raw materials were characterized by XRF, XRD, FTIR, and TGA/DSC. A response surface methodology was applied to optimize walnut shell content (5–15 wt%) and sintering temperature (850–1050°C). Under optimal conditions, the black pozzolan membrane showed 45.25% porosity, 16.12 MPa mechanical strength, 5000.11 L.h −1 .m −2 water flux, and 1.37 μm average pore size. The red pozzolan membrane exhibited 44.74% porosity, 15.05 MPa strength, 3850.50 L.h −1 .m −2 flux, and 0.99 μm pore size. In textile wastewater treatment, modified membranes achieved >99% turbidity removal, >93% COD removal, >89% TOC removal, and >85% BOD₅ removal. These results demonstrate that walnut shell–modified pozzolan membranes provide a cost-effective, sustainable, and efficient solution for microfiltration of industrial effluents, although performance depends on wastewater characteristics.