Background Mercury electrodeless discharge lamps (Hg-EDLs) coated with titania in the form of thin films were used to generate UV/Vis radiation when placed in a microwave field. Effects of additional operational parameters (i.e. initial MCAA concentration, reaction temperature, and the presence of inorganic anions) on the photocatalytic degradation of aqueous mono-chloroacetic acid (MCAA) in a microwave field are discussed. Results Studies were carried out in atmospheric or low-pressure batch type microwave photocatalytic reactors. The photocatalytic process was monitored by the change in concentration of Cl in the solution. Coupled UV/MW irradiation led to effective photodegradation at higher MCAA concentration at an optimum value of 0.15 mol L1. Photocatalytic reaction of MCAA was favoured at higher temperature mainly owing to thermal dependence of the Hg-EDL light intensity on the 366 nm line. Inhibition of MCAA photodegradation was observed in the presence of CO32 and SO42 anions, whereas the effect of NO3 was negligible. Conclusions It was found that additional operational parameters had important effects on photocatalytic efficiency in a microwave field. The MCAA photodegradation process with titania-coated Hg-EDLs can be enhanced in the TiO2/UV/MW system. (c) 2012 Society of Chemical Industry