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 that 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 6L 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 0.196mM AR1 solutions in 35mM NaCl and 25mM Na2SO4 at pH 3.0 was achieved in the presence of 0.40mM Fe2+ under a current density of 15mAcm-2, which yielded total color removal at 120min and 74% COD decay at 480min, with 25% of average current efficiency and 0.076kWh (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.