Photocatalytic nanofiltration reactors

Potable, industrial, and wastewaters are often polluted by toxic organic species.Environmental laws are now very severe and they will become more and morerestrictive in coming years; in addition, various directives suggest the use of greenchemistry concepts and clean technologies to protect the environment. Classicalmethods (e.g. adsorption on active carbon, chemical oxidation, aerobic biologicaltreatments [1, 2]) to clean up waters, before sending them to rivers or to munici-pal drinking water supplies, usually transfer pollutants from one phase to another,thus creating further waste streams.Methods such as those involving photocatalytic reactions allow in many casesa complete degradation of organic pollutants to small and non-noxious species,without using chemicals, avoiding sludge production and its disposal.In conventional approaches used to design photoreactors, the non-degradedmolecules or their by-products remain in the final effluent with the result thatthe process can be relatively inefficient; furthermore, the photocatalyst is usuallyemployed in suspension, so its recovery and recycle is another problem. Th seproblems can potentially be overcome by coupling photocatalytic and membranetechniques. Indeed, membrane separation processes, thanks to the selectiveproperty of membranes, have already been shown to be competitive with otherseparation processes with regard to energy costs, material recovery, reductionin environmental impact, and achievement of integrated processes with selectiveremoval of some components [3-5]. In particular, nanofiltration (NF) mem-branes enable the retention of larger recalcitrant molecules in the reactor whilethe small and non-noxious molecules resulting from photodegradation passthrough the membrane.