Compared to municipal wastewater, which primarily contains common pollutants like organic matter, nitrogen, and phosphorus, industrial wastewater often features complex contaminant compositions and is frequently accompanied by extreme conditions such as high temperatures, strong acids, and strong alkalis. Under these harsh conditions, traditional organic membranes such as polyvinylidene fluoride (PVDF) and polyethersulfone (PES) tend to struggle-they are prone to aging, deformation, chemical degradation, pore clogging, and even swelling-induced damage, leading to significantly shortened service lives. In contrast, inorganic ceramic membranes, typically made of alumina (α-Al₂O₃), offer inherent advantages including high temperature resistance, strong acid/alkali resistance, high mechanical strength, and resistance to hydrophobic pollutants. When combined with cross-flow filtration and backwashing techniques, they can effectively address the challenges posed by high-concentration pollutants. As a result, they demonstrate excellent separation performance and operational stability in scenarios such as oily wastewater, papermaking wastewater, and comprehensive industrial park wastewater. In this article, we systematically review the typical application scenarios of alumina ceramic membranes.
Filtration Principle of Alumina Ceramic Membranes
Alumina ceramic membranes are fabricated using high-purity α-Al₂O₃ (typically ≥99% content). Their microstructure generally exhibits a pronounced asymmetry, forming a "sandwich" structure consisting of a support layer, an intermediate layer, and a separation layer. The support layer is sintered from relatively large alumina particles, providing high mechanical strength and bearing the mechanical load. The intermediate layer has a pore size that lies between that of the separation layer and the support layer, serving as a connecting bridge and preventing the membrane layer from penetrating into the macroporous support during fabrication. The separation layer is typically only a few to several tens of micrometers thick, with a dense pore structure that directly determines the filtration accuracy.
Supported by this structure, the ceramic membrane achieves efficient separation via cross-flow filtration. When the feed liquid containing different particle size fractions flows across the surface of the separation layer at a certain velocity, the pore size acts as a sieving mechanism. Under the action of transmembrane pressure, the solvent (e.g., water) and some small-molecule solutes smaller than the separation layer pores pass through the membrane, enter the large pore channels on the support side, and are discharged as "permeate." Meanwhile, suspended particles, colloids, bacteria, macromolecular organics, and even emulsified oil droplets larger than the pores are retained on the outer surface of the membrane, forming a "retentate." Based on this principle, ceramic membranes can also be combined with surface modification or other technologies (such as adsorption and precipitation) to selectively remove specific components from industrial wastewater, such as heavy metal ions.