Kinetic study of the degradation of rhodamine B using a flow-through UV/electro-Fenton process with the presence of ethylenediaminetetraacetic acid.

An UV enhanced electro-Fenton (EF) process was conducted in a flow-through system to remove rhodamine B (RhB) in the presence of ethylenediamine tetraacetate (EDTA). The process was denoted as UV/EDTA/EF where EDTA formed complexes with iron ions, thus keeping them soluble at high pH values. The process was very efficient as it could initiate the fast reduction of FeIII to FeII and thus the decomposition of H2O2. The influence of Fe dose, the ratio of EDTA:Fe, aeration rate, flow rate, current, initial RhB concentration and pH on the RhB removal in the UV/EDTA/EF process was investigated. The best RhB removal was obtained as 89.9% at [Fe]0 = [EDTA]0 = 0.2 mM, current = 50 mA, aeration rate = 20 mL min-1, flow rate = 7 mL min-1, pH = 7 and [Na2SO4]0 = 0.05 M. The degradation of EDTA during the process was also studied. Radical scavenging experiments indicated that OH was the dominant radical for RhB removal. While, the photolysis of FeIIIEDTA was mainly responsible for EDTA degradation. RhB and EDTA removal in different systems was compared. The stability test proved that in the presence of EDTA, the UV/EF process could remove RhB with high efficiency in the first two runs. While, the efficiency dropped remarkably after EDTA's complete depletion. The mechanisms of the UV/EDTA/EF process were proposed. UV/EDTA/EF conducted in the flow-through system was able to efficiently remove RhB as well as EDTA in a wide pH range and proposed as a promising approach for wastewater treatment.