Degradation of Reactive Black 5 in a submerged photocatalytic membrane distillation reactor with microwave electrodeless lamps as light source

A novel submerged photocatalytic membrane distillation reactor (SPMDR) was developed and microwave electrodeless lamps were applied as the source light. Reactive Black 5 was used as a model dye with an initial concentration of 400 mg/L. The effects of TiO2 dose and feed temperature on the photodegradation efficiency and permeate flux were first investigated. The highest degradation rate was observed at 2.0 g/L TiO2 and 65 degrees C. The permeate flux decreased by 15.8% when the TiO2 dose increased from 0.5 to 6.0 g/L. The permeate flux of the SPMDR in the presence of 2.0 g/L TiO2 was higher than the pure water flux using conventional heating, which confirms the enhancement of microwave irradiation to the membrane distillation mass transfer. The SPMDR achieved a high color (100%) and TOC (80.1%) removal efficiency after 300 min reaction. The byproducts identified in the feed included aliphatic acids (formic, acetic and maleic) and inorganic ions (SO42-, NH4+ and NO3-). The SPMDR produced high quality water because dye, TiO2 and inorganic ions were completely retained in the feed side. Formic and acetic acids were detected in the permeate side with amounts of 0.08 and 0.25 mg (i.e., 1.83 and 5.29 mg/L), respectively. Scanning electron microscope (SEM) images showed that a loose TiO2 cake layer was formed on the membrane surface, which decreased the membrane porosity and contact angle to some extent. However, the module efficiency, porosity and contact angle could be largely recovered after 30 min of washing with distilled water. (C) 2013 Elsevier B.V. All rights reserved.