A review of the photodegradability and transformation products of 13 pharmaceuticals and pesticides relevant to sewage polishing treatment

Many xenobiotics are only partially treated by conventional wastewater treatment plants. Photodegradation is one promising solution currently being investigated to improve their removal from effluents. We present an in-depth review of the photodegradation kinetic parameters of selected pesticides and pharmaceuticals and assess whether the data available in the literature are applicable to polishing treatment processes under sunlight. We made a thorough inventory of literature data describing the photodegradation of pesticides and pharmaceuticals in water, the laboratory, pilot plants, and in situ conditions. To this end, we built a database compiling results on photodegradation experiments from 70 scientific publications covering 13 xenobiotics commonly found in secondary effluents. Special care was taken to compile reliable data on photolysis kinetic parameters (half-life and kinetic rate constant) and removal efficiencies. We also include a comprehensive description of experimental operating conditions and an up-to-date inventory of known phototransformation products. As practical outputs we (i) propose a classification for the xenobiotics according to their photodegradability: fast-, medium- and slow-photodegradable, (ii) compare kinetic parameters in direct and indirect photodegradation conditions, and (iii) list 140 phototransformation products formed by direct or indirect photodegradation. We conclude by identifying gaps in the literature that need to be filled to adapt these available results to the conditions of polishing processes.