Evaluation of a submerged membrane vis-LED photoreactor (sMPR) for carbamazepine degradation and TiO2 separation

A hybrid submerged membrane photoreactor (sMPR) combining a photoreactor irradiated with visible-light-emitting diode (vis-LED) and a submerged hollow fiber PVDF microfiltration (MF) membrane module was investigated in a continuous flow-through mode. A global carbamazepine (CBZ) photocatalytic degradation rate constant at steady state was achieved at (19.4 +/- 235) x 10(-3) min(-1) with hydraulic residence times (HRTs) in the range of 30-300 min using a visible-light responsive C-N-S tridoped TiO2 (T0.05-450). An alkaline pH condition was favorable for the CBZ photocatalytic degradation. The inhibitory effects of inorganic anions on the CBZ photocatalytic degradation followed the order of silica > phosphate > nitrate > bicarbonate > sulfate > chloride. The net effect of humic acid (HA) on the CBZ degradation depended on the three competitive phenomena: (i) HA as an electron shuttle promoting the generation of center dot O-2(-) while reducing the electron-hole recombination, (ii) HA competing with CBZ for the active sites of the photocatalyst, and (iii) HA contributing to the light attenuation in the photoreactor. The MF membrane realized effective separation of T0.05-450 as the turbidity of permeate water was <0.1 NTU. A steady-state transmembrane pressure (TMP) was achieved after its increase in the first 2 h due to the deposition of TiO2 cake layer on the membrane surface. NaOH (pH = 11) and 0.5 mM EDTA (pH = 11) solutions were efficient for cleaning the membrane surface fouled by HA. For the long-term operation of the sMPR system, the reduction of CBZ photocatalytic degradation efficiency could be attributed to the decrease of the photocatalyst dosage in the suspension, and the aggregation and deactivation of TiO2 particles during the prolonged operation. (C) 2012 Elsevier B.V. All rights reserved.