Fabrication of low-cost ceramic microfiltration membranes with the addition of fly ash to kaolin-natural zeolite structure for greywater treatment
摘要
In this study, low-cost tubular ceramic microfiltration membranes were fabricated by extrusion using kaolin, natural zeolite, fly ash, and α-alumina for laboratory-scale greywater treatment. Fly ash content (5–20 wt %) was evaluated to tune membrane permeability, porosity, and mechanical behavior while avoiding crack formation. Among the fabricated membranes, kaolin–natural zeolite–fly ash (K–Z–F, 75–10–15) and kaolin–α-alumina–fly ash (K–Al–F, 80–10–10) showed the most favorable balance between permeate flux, COD reduction, and mechanical stability. The optimized membranes had average pore sizes in the microfiltration range (1.06–1.14 µm) and porosities of 33.07–41.26%. During 60 min greywater microfiltration at 1 bar and 25 °C, the K–Z–F (75–10–15) membrane achieved a permeate flux of 632.29 ± 3.63 L m⁻2 h⁻1 with 86.69 ± 0.18% COD removal, while the K–Al–F (80–10–10) membrane achieved 91.50 ± 0.03% COD removal with a permeate flux of 559.80 ± 15.53 L m⁻2 h⁻1. The COD decrease is interpreted as the combined removal of suspended and colloidal organic matter, oil/fat droplets, adsorption on aluminosilicate surfaces, and dynamic cake-layer filtration, rather than size exclusion of dissolved COD alone. The treated permeate satisfied the investigated Iranian discharge/reuse limits for the measured parameters; however, the study was based on single-source kitchen greywater and short-term filtration. Direct laboratory raw-material-and-energy costs, calculated using the complete furnace program, were estimated as 2.22 $ m⁻2 for K–Z–F (75–10–15) and 4.27 $ m⁻2 for K–Al–F (80–10–10). These values should not be interpreted as full industrial production costs because labor, equipment depreciation, maintenance, membrane replacement, infrastructure, and scale-up losses require pilot-scale techno-economic assessment.