A hybrid photocatalysis–ultrafiltration continuous process for humic acids degradation

The successful operation of a hybrid photocatalysis–membrane separation process (in a laboratory-scale pilot system) is demonstrated for degradation of Humic Acids (HAs), which are typical refractory components of Natural Organic Matter (NOM). The Photocatalytic Membrane Reactor (PMR) employing an Ultrafiltration (UF) submerged module was operated in continuous mode with TiO2 catalyst concentration 0.75 g/L and UV-A radiant flux 15.1 J/s, treating feed water with HA concentrations 5.0 and 10.0 mg/L. Experiments carried out within a sufficiently broad pH range (approx. 3.5–7.0) exhibited satisfactory HA mineralization rates and rather high HA mineralization efficiencies; a near optimum pH at approx. 5.5 was identified. The overall process removal efficiency (comprising both HA oxidation and UF membrane rejection) was even higher, as a result of the synergistic effects of photocatalytic oxidation and membrane filtration. The degradation of HA aromatic rings, that diminishes the Disinfection By-Products (DBPs) formation potential, was also very high; the specific UV-A254 removal efficiency was greater than 95% in almost all cases studied. Concerning membrane filtration performance, the periodic backwashing employed, combined with the moderate membrane flux, effectively controlled membrane fouling thus permitting stable continuous operation with no wastewater stream.

► A novel system, coupling photo-catalysis with a submerged UF module, permits a steady state operation.
► Fouling is controlled by periodic backwashing with permeate, ensuring long-term operation with no reject stream.
► Successful operation of a laboratory pilot is demonstrated for the degradation of humic acids (HAs) in water.
► Degradation of HA aromatic rings (by >95%) diminishes the potential for disinfection by-products formation.