Mineralization of Acid Red 1 azo dye by solar photoelectro-Fenton-like process using electrogenerated HClO and photoregenerated Fe(II)

Abstract

The degradation of Acid Red 1 (AR1) azo dye by solar photoelectro-Fenton-like (SPEF-like) process involving continuously electrogenerated hypochlorous acid (HClO) and photoregenerated Fe(II) to yield hydroxyl radicals, has been studied. The assays were made in a flow plant included a filter-press cell equipped with a Ti|Ir-Sn-Sb oxide anode, to oxidize Cl- ion to HClO, and a stainless-steel cathode. The cell was coupled to a compound parabolic collector (CPC) photoreactor, in series with a reservoir containing 6 L of solution. The influence of the added Fe2+ concentration, current density and initial AR1 content over the performance of the SPEF-like process was systematically studied. The best treatment for 0.196 mM AR1 solutions in 35 mM NaCl and 25 mM Na2SO4 at pH 3.0 was achieved in the presence of 0.40 mM Fe2+ under a current density of 15 mA cm-2, which yielded total color removal at 120 min and 74% COD decay at 480 min, with 25% of average current efficiency and 0.076 kWh (g COD)-1 of energy consumption. The SPEF-like process was compared with anodic oxidation with electrogenerated active chlorine (AO-HClO), electro Fenton-like (EF-like) and photoelectro-Fenton-like (PEF-like) processes, and it was found that the oxidation power decreased in the sequence: SFEF-like > PEF-like > EF-like > AO-HClO. Ion-exclusion HPLC analysis of electrolyzed solutions revealed the formation of maleic and oxalic acid as final short-chain linear carboxylic acids.