Photocatalytic Nanofiltration Reactors

Heterogeneous photocatalysis permits to meet stricter environmental limits by using green chemistry concepts. Drinking, industrial and waste water, which are often polluted by toxic organic species, can be treated by complete degradation of organic pollutants to small and non‐noxious species, without using chemicals and avoiding sludge production and disposal. Photocatalytic Membrane Reactors (PMRs) are hybrid processes coupling heterogeneous photocatalysis and membrane separation. The membrane allows the confinement of photocatalyst and pollutants in the reaction environment while operating in continuous. In particular, Nanofiltration (NF) membranes enable the retention of larger recalcitrant molecules in the reactor while the small and non-noxious photodegradation products permeate through the membrane. Some basic principles of heterogeneous photocatalysis are presented, then the most important factors affecting the performance of PMRs are summarized, as reactor configuration, photocatalyst type/amount, light source, feed and membrane characteristics. System configurations with suspended or immobilized photocatalyst are discussed evidencing their effects on system performance. Some laboratory applications of PMRs on pollutants as 4-Nitrophenol, humic acids, patent blue dye (also at high concentration) in batch and continuous membrane photoreactors, using NF membranes are described evidencing how the use of these systems can give improved purification of various types of waters without producing sludge and saving chemicals. It is expected that these hybrid processes could be considered particularly when plant upgrading is planned and, especially, if sunlight energy can be used for irradiation.