Abstract
Removal of sulfanilic acid (SA) from water is an urgent but still challenging task. Herein, we developed a low pressure electrochemical membrane filtration (EMF) system for SA decontamination using RuO2-TiO2@Ti/PVDF composite membrane to serve as not only a filter but also an anode. Results showed that efficient removal of SA was achieved in this EMF system. At a charging voltage of 1.5 V and a electrolyte concentration of 15 mM, flow-through operation with a hydraulic retention time (HRT) of 2 h led to a high SA removal efficiency (80.4%), as expected from the improved contact reaction of this compound with ROS present at the anode surface. Cyclic voltammetry (CV) analysis indicated that the direct anodic oxidation played a minor role in SA degradation. Electron spin resonance (ESR) spectra demonstrated the production of •OH in the EMF system. Compared to the cathodic polarization, anodic generated ROS was more likely responsible for SA removal. Scavenging tests suggested that adsorbed •OH on the anode (>•OH) played a dominant role in SA degradation, while was an important intermediate oxidant which mediated the production of •OH. The calculated mineralization current efficiency (MCE) of the flow-through operated system 29.3% with this value much higher than that of the flow-by mode (5.1%). As a consequence, flow-through operation contributed to efficient oxidation of SA toward CO2 and nontoxic carboxylic acids accounting for 71.2% of initial C. These results demonstrate the potential of the EMF system to be used as an effective technology for water decontamination.
Highlights
Sulfanilic acid (SA) is one of the most widely-used sulfonated aromatic amines in the production of azo dyes, dyeing auxiliaries, food coloring, pharmaceuticals perfumes and pesticides (Chen et al, 2012; El-Ghenymy et al, 2012)
The TiO2 and RuO2 particles were dispersed on the surface of titanium mesh uniformly, and coating polyvinylidene fluoride (PVDF) layer onto RuO2-TiO2@Ti electrode surface had no significant influence on the conductivity of resultant composite membrane
At a charging voltage of 1.5 V and an electrolyte concentration of 15 mM, flow-through operation with a hydraulic retention time (HRT) of 2 h resulted in a high SA removal efficiency (80.4%)
Summary
Sulfanilic acid (SA) is one of the most widely-used sulfonated aromatic amines in the production of azo dyes, dyeing auxiliaries, food coloring, pharmaceuticals perfumes and pesticides (Chen et al, 2012; El-Ghenymy et al, 2012). The resulting water contamination calls for the development of cost-effective treatment technologies. Low-pressure membrane filtration, e.g., microfiltration (MF) and ultrafiltration (UF), offers an attractive technology for water/wastewater due to its small footprint, and high efficiency in removing bacteria and colloidal/particulate matter (Zimer et al, 2016). Low-pressure membrane filtration is incapable of removing low molecular weight organic matter, e.g., SA, due to the size exclusion effects. The combination/integration of other robust technologies with low-pressure membrane filtration process is needed to address this concern
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