Search

Zeolites are potentially a more robust desalination alternative as they are chemically stable and possess the essential properties needed to reject ions. This work proposes to use zeolite membranes for desalination of saline recycled wastewater for the possibility of avoiding the costly pre-treatment needed for polymeric reverse osmosis membranes. The MFI-type zeolite membrane was developed on a tubular α-alumina substrate by a combined rubbing and secondary hydrothermal growth method. The prepared membrane was characterised by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and single gas (He or N 2 ) permeation, and underwent desalination tests with saline wastewater under different conditions. When saline wastewater was fed at 7 MPa to the zeolite membrane it showed a salt rejection of 80% based on electrical conductivity (EC) and a flux of 4 L m −2 h −1 . A 254 (organics absorption at the wavelength of 254 nm measured by a HACH DR5000 spectrophotometer) removal exceeded 90%. Slightly lower salt removal and A 254 results were observed when operating at a lower pressure of 3 MPa. During batch concentration runs on the saline wastewater, the EC of the feed water increased from the initial value of 1770 µS cm −1 to 3100 µS cm −1 over the 48 h test time which indicates that a 43% water recovery was achieved. EC reduction remained >70% and flux was maintained at around 2 L m −2 h −1 throughout the test period, indicating that the membrane resisted organic fouling. Chlorine stability studies showed that a long-term (7 days) strong hypochlorite clean did not significantly alter the flux or rejection confirming the chemical stability of zeolite membranes. Overall, the zeolite membrane showed excellent chemical resilience and produced a desalinated product suitable for reuse applications (e.g. irrigation, residential or industrial). Fluxes, however, need to be improved to be competitive with current polymeric membranes as do rejections for higher purity water applications.

Ceramic fibers and whiskers have been used for modification of toughness because they increase fracture energy due to their high elastic modulus and strength. The mechanism of this increase is well known to be pull-out, crack deflection and a bridging mechanism. This study focused on the increase in toughness, strength and thermal shock resistance when using ceramic fibers in a gas filter for high temperatures. The basic systems studied were clay bonded SiC-mullite and Al 2 O 3 -mullite with carbon black (to improve filtering efficiency). The Al 2 O 3 -mullite system showed lower porosity (2745%) and higher strength (131 kg/cm 2 ) than the same system fired in air. The strength was higher than for the SiC-mullite system with the same treatment because of the high sintering rate. Also, the hot strength at 1000 °C was higher than for the SiC-mullite system. Strength degradation was only 14% and 5% after thermal shock tests. Resistance to thermal shock was better than the Al 2 O 3 -mullite system owing to better thermal shock resistant raw materials (like SiC) and the fibrous microstructure. Both systems fired in air showed broader pore size distributions than when fired in a coke bed.