Model reactor for photocatalytic degradation of persistent chemicals in ponds and waste water

A laboratory scale flow-through model reactor for the degradation of persis tent chemicals using titanium dioxide (TiO2) as photocatalyst immobilized o n glass beads is presented. In the test system with a volume of 18 L contam inated water is pumped to the upper part of the floating reactor and flows over the coated beads which are exposed to UV-radiation. The degradation of two dyes of different persistance was investigated. Primary degradation of methylene blue did not fit a first order kinetic due to coincident adsorpt ion onto the photocatalyst and direct photolysis, resulting in a half-life of 6 h. A filtrate of a green algae suspension accelerated the colour remov al. in contrast, reactive red 2 was degraded only by photocatalysis; neithe r adsorption nor direct photolysis led to a colour removal. The course of p rimary degradation followed a first order kinetic with a half-life of 18 h and a rate constant of 0.04 h(-1). Analysis of the degradation products ind icated mineralization by detection of NO2- and NO3-, accompanied by a decre ase of pH and an increase of conductivity. A successful adaptation of the m odel reactor (scale 1:10) to dimensions required for surface waters and was te water treatment plants would be a cost-efficient and environmentally sus tainable application of photocatalysis for the treatment of industrially po lluted water and could be of relevance for third world contries, particular ly those favoured by high solar radiation. (C)1999 Elsevier Science Ltd. Al l rights reserved.