New integrated photocatalytic-biological flow system using supported TiO2 and fixed bacteria for the mineralization of isoproturon

The photodegradation of isoproturon (IP) was performed using TiO2 supported on glass rings in a 1.5 l coaxial rector. After 60 min of phototreatment, IP was completely eliminated and about 80% of dissolved organic carbon (DOC) remained in solution. This efficiency of photodegradation was compared with that using the suspended catalyst in solution and the results indicated that the catalytic activity of TiO2 is not reduced when it is immobilized. The durability of the supported TiO2 was also tested. It was found that after 300 h of photodegradation experiments, its activity was not affected. The chemical nature of the phototreated solution was assessed following the evolution of the initial compound, the organic carbon, and the formed ions, as well as the toxicity and the biodegradability. These analyses demonstrated that the solution resulting from the phototreatment of IP is biologically compatible and its complete mineralization can be performed by biological means. In this way, for the mineralization of an IP solution, a combined photochemical and biological flow reactor was used operating in semi-continuous mode at laboratory scale. This coupled system employs TiO2 supported on glass rings in the photocatalytic reactor and bacteria supported on biolite in the biological part. In this combined system, 100% of the initial concentration of IP and 95% of DOC were removed. Finally, some field experiments under direct sunlight were carried out at the Plataforma Solar de Almerı́a (PSA), Spain. The photocatalytic oxidation of IP was performed in homogeneous and heterogeneous solutions and two different reactors were compared: a medium concentrating radiation system (Helioman, HM) and a non-concentrating radiation system (compound parabolic collectors, CPC). The degradation rates obtained in the CPC are around 5 times more efficient than the HM collectors. However, in both systems 100% of the initial concentration of IP was removed. The possibility of coupling a CPC photoreactor with a biological system at field pilot scale employing supported TiO2 and fixed bacteria for the treatment of real bio-recalcitrant wastewater is also suggested.