Abstract:To ensure the availability of clean water for humans into the future, efficient and cost-effective water purification technology will be required. The rapidly decreasing quality of water and the growing global demand for this scarce resource has driven the pursuit of high-performance purification materials, particularly for application as point-of-use devices. This review will introduce the main types of natural and artificial contaminants that are present in water and the challenges associated with their effective removal. The efficiency and performance of recently developed materials for water purification, with a focus on activated carbon, carbon nanotubes and graphene will be discussed. The recent advances in water purification using these materials is reviewed and their applicability as point-of-use water purification systems discussed.

The performance of activated carbon water filters, with respect to the breakthrough of dissolved organic matter (DOM) and dangerous trihalomethanes (THMs) from supplied water, has been analysed by fluorescence spectroscopy. Fluorescence spectroscopy has been demonstrated as a viable technique to monitor carbon filter performance, using the fluorescently active DOM species as an indicator. Due to the relationship between DOM and THMs, where DOM is the precursor for THM formation during the chlorine treatment of water, fluorescence spectroscopy can be used to predict the breakthrough of both species from activated carbon filters. In order to establish a versatile measurement technique, the most appropriate fluorescence excitation and emission wavelengths for detecting the DOM in water were firstly determined. These fluorescence measurement parameters were then applied to effluent water samples from carbon filters, over a total filtrate volume of 4,200 L. The total THM concentration in filtered water samples was determined by headspace gas chromatography (HSGC), with the fluorescence and HSGC results showing a high degree of correlation for the amount of DOM and THM respectively. Importantly, this correlation is observed for both of the determined fluorescence measurement parameters, highlighting the validity and versatility of this technique.

An electrically-regenerated electrosorption process known as carbon aerogel CDI has been developed by Lawrence Livermore National Laboratory (LLNL) for continuously removing ionic impurities from aqueous streams. A salt solution flows in an unobstructed channel formed by numerous pairs of parallel carbon aerogel electrodes.Each electrode has a very high BET surface area (2.0-5 .4x1 OGft2 lb-i or 400-1100 m2 g-') and very low electrical resistivity (<40 mQ cm). BET surface areas of 1.3x107 ft2 lb-' (2600 m2 g-') have been achieved with thermal activation.After polarization, anions and cations are removed from the electrolyte by the imposed electric field and electrosorbed onto the carbon aerogel. The solution is thus separated into two streams, concentrate and purified water. Based upon thk analysis, it is concluded that carbon aerogel CDI may be an energy-efllcient alternative to electrodialysis and reverse osmosis for the desalination of brackish water (< 5000 ppm), provided that cell geometries and aerogel properties are c&efi.dly tailored for such applications. The intrinsic energy required by this process is approximately Q?72, where Q is the stored electrical charge and V is the voltage between the electrodes, plus losses due to parasitic electrochemical reactions, electrical resistance and pressure drop. The estimated requirement for desalination of a 2000 ppm feed is estimated to be -0.53-2.5 Wh gal-' (0.50-2.4 kJ L-'), depending upon voltage, flow rate, cell dimensions, carbon aerogel density, recovery ratio and other parameters. These estimates assume that 50-70'%0of the stored electrical energy is reclaimed during regeneration (electrical discharge). The possibility of such low power requirements for desalination of brackish water (BW), as well as the possibility of energy storage and recovery, may. make this process attractive for such applications. Though the intrinsic energy requirement for desalination of sea water (SW) are also relatively low, this application will be much more difficult. Additional work will be required to determine the suitability of carbon aerogel CDI for desalination of streams that contain more than 5000 ppm total dissolved solids (TDS). Applications at 2000 ppm will require the construction of electrochemical cells with extremely tight, demanding tolerances. At the present time, the process is best suited for streams with relatively dilute impurities, as recently demonstrated during a field test at LLNL Treatment Facility C.