A Rational Analysis on Key Parameters Ruling Zerovalent Iron-Based Treatment Trains: Towards the Separation of Reductive from Oxidative Phases

Abstract

The development of treatment trains for pollutant degradation employing zerovalent iron has been attracting a lot of interest in the last few years. This approach consists of pre-treatment only with zerovalent iron, followed by a Fenton oxidation taking advantage of the iron ions released in the first step. In this work, the advantages/disadvantages of this strategy were studied employing commercial zerovalent iron microparticles (mZVI). The effect of the initial amount of mZVI, H2O2, pH, conductivity, anions and dissolved oxygen were analysed using p-nitrobenzoic acid (PNBA) as model pollutant. 83% reduction of PNBA 6 µM into p-aminobenzoic acid (PABA) was achieved in natural water at an initial pH 3.0 and 1.4 g/L of mZVI, under aerobic conditions, in 2 h. An evaluation of the convenience of removing mZVI after the reductive phase before the Fenton oxidation was investigated together with mZVI reusability. The Fenton step against the more reactive PABA required 50 mg/L of H2O2 to achieve more than 96% removal in 15 min at pH 7.5 (final pH from the reductive step). At least one complete reuse cycle (reduction/oxidation) was achieved with the separated mZVI. This approach might be interesting to treat wastewater containing pollutants initially resistant to hydroxyl radicals.

Use of Fluorescence Spectroscopy and Chemometrics to Visualise Fluoroquinolones Photodegradation Major Trends: A Confirmation Study with Mass Spectrometry

“…The latter component was also found in a previous work, where a mixture consisting of enrofloxacin, ofloxacin and sarafloxacin (another commercial fluoroquinolone, whose fluorescent fingerprint is comparable to ENRox-like) was photolysed under simulated sunlight at neutral pH in ultra-pure water, detecting sarafloxacin-like component scores (i.e., fluorescence intensity) increment, indicating that the formed by-products from the three parent pollutants were emitting in this region [ 13 ]. When employing more oxidative conditions, e.g., photo-Fenton [ 22 ], a comparable component to ENRox-like was also found, but exhibiting a global maximum shift of 15 nm towards shorter wavelengths (blue shift) instead [ 12 , 14 ].…”