Advances in ceramic membranes for water treatment

Porous ceramic membranes can offer a more robust and long-term alternative to polymeric membranes in aqueous microfiltration and ultrafiltration processes. Their superior chemical, thermal and mechanical properties mean that not only can they be operated under harsh conditions, they can also be backwashed and cleaned with strong cleaning agents as well as sterilized at high temperatures, offering reliable performance over long periods of time. These ceramic membranes are conventionally fabricated via multiple layer deposition steps on top of a membrane substrate followed by several heat treatment sessions to achieve the desired final selectivity for micro- or ultrafiltration. Because of the large number of steps required, conventional methods are time- and energy-consuming, contributing to the high capital costs of ceramic membranes. The combined phase-inversion and sintering technique is an emerging method for the fabrication of ceramic membranes and considerably reduces the number of steps required by eliminating the need to deposit layers on a substrate; thus, only one heat treatment step is required. Furthermore, it can produce membranes with a wide range of unique microstructures, which can be tailored for the application. The ability to produce much thinner hollow-fibre membranes can improve packing density considerably compared with the commonly used flat-sheet and tubular modules. This simpler fabrication cycle can potentially reduce the costs of ceramic membranes, but currently further research and development is required before commercialization of this method can commence. Potential applications of ceramic membranes for water treatment include the production of drinking water, treatment of municipal and industrial wastewater, treatment of produced water and use in the food and beverage industries. Successful implementation of ceramic membranes in these industries has been achieved with stable and long-term operation but the high capital cost of ceramic membranes remains the main deterrent to large-scale water treatment. However, anticipated cheaper ceramic membranes with higher packing densities of hollow-fibre configuration will increase applications in municipalities.