Effect of process parameters on photodegradation of Acid Yellow 36 in a hybrid photocatalysis–membrane distillation system

Photocatalytic membrane reactors (PMRs) seem to be a very promising method of solving problems concerning separation of photocatalyst as well as products and by-products of photodegradation from the reaction mixture. In the presented studies an anatase-phase TiO2 was applied for degradation of Acid Yellow 36 (AY36) in the PMR coupling photocatalysis and direct contact membrane distillation (DCMD). The effect of different process parameters such as dye concentration, reaction temperature and photocatalyst loading on the effectiveness of degradation of AY36 was investigated. Moreover, in order to compare the effectiveness of AY36 photodegradation during photocatalysis alone and the hybrid process, additional experiments without application of MD were conducted. The addition of TiO2 to a feed did not affect the permeate flux, regardless of the process conditions applied. The flux remained constant and equal to the maximum permeate flux during about 400 h of experiments. The highest decolorization of AY36 solution during hybrid process was observed at the highest photocatalyst loading applied (0.5 g TiO2/dm3). The increase of the reaction temperature from 313 to 333 K resulted in an increase of the photodegradation rate of AY36. After 5 h of the hybrid process the effectiveness of dye degradation calculated on a basis of AY36 mass in a feed solution amounted to 31, 36 and 42% for the reaction temperatures of 313–333 K. Similar results were obtained when photocatalysis was conducted in the MD installation but with disconnected MD module. It was found that an improvement of AY36 photodegradation could be achieved by a decrease of initial dye concentration. Comparing the results obtained in a conventional slurry photoreactor and in the PMR and taking into account both, the rate of azo dye degradation and the quality of the product, it could be concluded that more beneficial configuration seems to be the PMR.