Electro-catalytic microfiltration membranes electrochemically degrade azo dyes in solution

Abstract Azo dyes and Chlorinated Organic Compounds (COCs) like trichloroethylene (TCE) are environmental contaminants found in textile industry effluents and groundwater sites respectively. Both compounds are carcinogenic to humans and hazardous to the environments they contaminate and are difficult to treat by conventional wastewater processes. In this study, electrocatalytically active nanocomposite membranes were fabricated and evaluated for their ability to remove azo dyes. Nano zero-valent iron (nZVI) particles were grown and stabilized within a network of dispersed single and double-walled carbon nanotubes (SW/DWCNTs), and this mixture was filtered onto the surface of a microfiltration polyethersulfone (PES) support membrane to form a porous, conductive, reactive surface nanocomposite. These catalytic surface nanocomposites were tested as a cathode alongside a graphite anode with -2 V applied for their ability to remove methyl orange (MO) dye in both a batch system and a continuous dead-end filtration system. In a well-mixed batch, it was found that complete removal of 0.25 mM MO (7.5 mMoles in 30 mL) by the charged membranes occurred within 2–3 h of operation. The performance of these nZVI-SW/DWCNT cathodes alongside controls suggests that the application of an applied current regenerates the spent reactivity of the embedded iron nanoparticles. Systems using nZVI-SW/DWCNT membranes achieved ∼ 87 mol % removal of methyl orange and demonstrated a 2.7 times greater removal rate than batch tests of analogous parameters, and 1.6 times greater than other continuous tests using membrane surface composites that lacked nZVI. Furthermore, the application of voltage to the membrane thin film surface composite increases the transmembrane flux through system, allowing for increased throughput at a given feed pressure. The results of these experiments show promise in the continuous removal of contaminants from wastewaters through reductive degradation, such as azo dyes and chlorinated organic compounds. Continuous regeneration of nZVI reactivity on a membrane surface offers substantial advantages over single-use approaches for the treatment of azo dyes and COCs in solution.