The practical applicability of the double-skin sheet reactor (DSSR) for solar catalytic wastewater treatment has been checked at laboratory scale, in Hannover, and at the outdoor test-field of the Plataforma Solar de Almeria (PSA), in Spain, using dichloro acetic acid (DCA) as the standard test pollutant. This type of photoreactor has also been successfully used for the treatment of biologically pretreated industrial wastewater on laboratory and pilot plant scale. To analyze the experimental results, a first-order rate law in concentration and radiation density flux (assumed constant for each run) has been derived: R-V = k(3)(A(R)/V-R)(q) over bar(UV)(c), where k(3) is a lump kinetic parameter, A(R) is the illuminated reactor area, V-R is the volume of the photoreactor, (q) over bar(UV) is the time averaged radiation density flux of UV energy, and c is the concentration of the pollutant. It has been observed that the integrated form of this rate law fits fairly well the experimental data obtained with a model compound and solar energy, and that an expression derived from this rate can be used for an approximate scaling-up of a solar catalytic wastewater treatment plant.