BACKGROUND: Low-pressure batch and continuous-flow microwave photoreactors were equipped with microwave powered quartz mercury electrodeless discharge lamps (Hg-EDLs). Photohydrolysis of aqueous mono-chloroacetic acid (MCAA) into hydroxyacetic acid and HCl was chosen as the model reaction to evaluate these photoreactors. The effects of operational parameters on the MCAA photolysis through a UV/MW process were investigated. RESULTS: Studies were carried out at relatively high MCAA concentration (0.1 mol L-1). The photoreaction course was monitored by the pH change in the solution. The MCAA conversion was optimized as a result of a trade-off between the thermal dependence of the photochemical quantum yield (which increases with increasing temperature) and the thermal dependence of the EDL light intensity of 254 nm line (which increases with decreasing temperature). The microwave photoreactors made it possible to study the temperature dependence of MCAA photohydrolysis. CONCLUSION: It was found that operational parameters (i.e. reaction temperature, quantum yield) had important effects on photoefficiency. Photohydrolysis of MCAA in the microwave photoreactors can be enhanced by the UV/MW system. The results of conversions (in 120 min) for the particular photoreactor set-ups show that the best reaction conditions for MCAA photolysis were obtained in the low-pressure batch microwave photoreactor (the conversion was 46% at 80 degrees C). (c) 2009 Society of Chemical Industry