Insights into the removal of terbuthylazine from aqueous solution by several treatment methods

摘要

This paper reports the removal of the s-triazine herbicide terbuthylazine (TBA) from aqueous solution by various treatment methods including adsorption onto activated carbon (AC) and multiwalled carbon nanotubes (MWCNT), UV254 photolysis, UV254/H2O2, single ozonation, O-3/H2O2, catalytic ozonation (AC, MWCNT and TiO2 as catalysts) and some solar driven processes such as TiO2 photocatalytic oxidation and photo-ozonation. TBA was adsorbed onto AC and MWCNT following a pseudo-second order kinetics and Freundlich isotherm. Rapid small scale column tests showed that TBA could be removed from solution by adsorption onto AC better than atrazine. The UV254/H2O2 treatment resulted in excellent removal of TBA primarily due to the oxidation capability of hydroxyl radicals (k(HO)(center dot) = 3.310(9) M-1 s(-1)) generated from H2O2 photolysis. As the H2O2 initial concentration was increased from 5 to 50 mg L-1 the HO center dot exposure per UV fluence (R-HO center dot,(UV)) increased, making the process more efficient. Single ozonation also allowed complete removal of the herbicide though the process was slow (k(03) =15.4 M-1 s(-1) at pH > 4). The ozonation process could be greatly accelerated by the enhanced generation of HO" through O-3/H2O2 and O-3/AC processes, which also led to more efficient processes in terms of ozone utilization. Commercial TiO2 (TiO2-P25) and lab prepared anatase TiO2 (TiO2-cat) nanoparticles catalyzed the removal of TBA by solar photocatalysis. In contrast, a lab prepared MWCNT-TiO2 composite was not useful as catalyst in solar photo-oxidation processes because of the HO center dot scavenging nature of the MWCNT used as support. A mechanism for TBA degradation by O-3 and HO center dot has been suggested after TBA degradation intermediates identification. (C) 2016 Elsevier Ltd. All rights reserved.