Assessment of Fenton systems based on metabisulphite as a low-cost alternative to hydrogen peroxide

Here we show that a Fenton-like system based on zero-valent iron and metabisulphite (ZVI-MBS) is able to effectively degrade both ibuprofen (a non-steroidal anti-inflammatory drug) and its toxic product 4-isobutylacetophenone in 30 min at pH 3. Based on scavenging experiments, the main reactive species involved in the degradation process would be •OH and SO4•−, with SO4•− likely acting as •OH source. Compared to well-known ZVI-H2O2, ZVI-MBS loses performance considerably at pH > 3. Furthermore, differently from ZVI-H2O2 where the ZVI surface plays major role, dissolved Fe species are important in ZVI-MBS. In presence of MBS, it would thus be more convenient to add Fe2+ directly in the form of ferrous salts than to use ZVI as source of dissolved iron. Fe2+-MBS, similarly to ZVI-MBS, experiences considerable drop in performance above pH 3. MBS is much cheaper, more stable, and safer to operate than H2O2. However, the need to treat water at pH 3 has the important drawback that conductivity/salinity is increased by water acidification for treatment and neutralisation after treatment. That would be appropriate in most cases for water discharge, but could limit reuse of treated water in some fields such as irrigation.