Recent developments in the coupling of photoassisted and aerobic biological processes for the treatment of biorecalcitrant compounds

A general strategy to develop combined photochemical and biological system for biorecalcitrant wastewater treatment is proposed. For the development of this strategy, the following points were taken into account: the biodegradability of initial solutions, the operation mode of the coupled reactor, the chemical and biological characteristics of the phototreated solutions, the evaluation of different photoassisted advanced oxidation processes, the optimal conditions of both photochemical and biological processes, and the efficiency of the coupled reactor. The strategy to couple photochemical and biological processes is illustrated by case studies of four different biorecalcitrant pollutants. Three kinds of combined systems were developed using either photo-Fenton, Fe3+/UV, or TiO2 supported on glass rings for the photocatalytic pretreatment and in all cases immobilized biomass for the biological step. The advantages of the each coupled system are discussed and beneficial effects of such two-step treatments were found. However this strategy is not a universal solution. Chemical, biological, and kinetic studies must be always carried out to ensure that the photochemical pretreatment increase the biocompatibility of the treated wastewater. Some field experiments using solar reactor indicated that a coupled photochemical-biological treatment system at pilot scale is a possible way to achieve the complete mineralization of the biorecalcitrant pollutants. (C) 2002 Elsevier Science B.V. All rights reserved.