Removal of thiocyanate from synthetic wastewater using TiO ₂mediated photocatalytic degradation process

The present work investigated aqueous phase thiocyanate (SCN^-1) removal using the titanium dioxide (TiO₂) assisted photocatalytic degradation (PCD) process. Preliminary results showed that use of 15 W UV lamp yields much higher SCN^- removal efficiency as compared to 8 W UV lamp, considering which further PCD work was conducted using the 15 W UV lamp. Results from the present studies also showed that SCN^-1 removal at 4 h reaction time increases with an increase in pH, i.e., pH 12 > pH 7 > pH 4, with 92% substrate removal noted at pH 12. The reaction intermediates analysis results indicated that at pH 4 most SCN^-1 that is removed from the aqueous phase is converted into CN^-1 that actually showed a constant increase with time. Furthermore the SO4^2--S formation results at pH 4 also followed the overall SCN^--S portion removed. Though the pH 7 reaction intermediates formation findings showed a significant SO₄^2-, CN^- and OCN^- production, however the CN^- results showed reaching a plateau, with somewhat smaller values compared to respective pH 4 data. Nevertheless the CN^- formation results at pH 12 first showed an increase that was followed by a decrease. Also the OCN^- species accounted for most SCN^--N removed at pH 12 and 4 h reaction time. The present results indicated that with a careful control of process pH the PCD technology can yield high SCN ^- removal efficiency under a varying set of conditions.