UV/TiO2 photocatalytic oxidation of recalcitrant organic matter: effect of salinity and pH

Abstract

Photocatalytic oxidation processes have interest for water treatment since these processes can remove recalcitrant organic compounds and operate at mild conditions of temperature and pressure. However, performance under saline conditions present in many water resources is not well known. This study aims to explore the basic effects of photocatalysis on the removal of organic matter in the presence of salt. A laboratory-scale photocatalytic reactor system, employing ultraviolet (UV)/titanium dioxide (TiO₂) photocatalysis was evaluated for its ability to remove the humic acid (HA) from saline water. The particle size and zeta potential of TiO₂ under different conditions including solution pH and sodium chloride (NaCl) concentrations were characterized. The overall degradation of organics over the NaCl concentration range of 500-2,000 mg/L was found to be 80% of the non-saline equivalent after 180 min of the treatment. The results demonstrated that the adsorption of HA onto the TiO₂ particles was dependent on both the pH and salinity due to electrostatic interaction and highly unstable agglomerated dispersion. This result supports UV/TiO₂ as a viable means to remove organic compounds, but the presence of salt in waters to be treated will influence the performance of the photocatalytic oxidation process.

Hybrid Processes Combining Photocatalysis and Ceramic Membrane Filtration for Degradation of Humic Acids in Saline Water

“…In order to elucidate the role of TiO 2 catalyst and UV light as well as their combined effects on the HA degradation, experiments were performed for 2 h with different experimental conditions (UV, TiO 2 , and UV/TiO 2 ) using an initial HA concentration of 20 mg/L at pH 7.5. Previous research [ 26 ] has shown that TiO 2 concentrations of 0.5 and 1 g/L resulted in significant HA removals of up to 83% using HA solution of 20 mg/L with an initial TOC concentration of 7 mg/L which is similar HA concentration as used in this work. Therefore, these TiO 2 concentrations were again used in this work.…”

“…More importantly, the combination of photocatalytic oxidation process with physical separation of TiO 2 via a ceramic membrane filtration was explored. This study is an extension of our previous work where the influence of salinity on the removal of HA using UV/TiO 2 photocatalytic process alone was examined [ 26 ]. The purpose of this study is to evaluate the potential for the hybrid process under ideal conditions prior to exploring on municipal wastewater.…”

Performance of Hybrid Photocatalytic-Ceramic Membrane System for the Treatment of Secondary Effluent

“…Our previous work described the influence of experimental variables such as solution pH, salinity and TiO 2 dose on the removal of a model HA solution using TiO 2 /UV photocatalytic oxidation process and ceramic membrane filtration [8,24]. These studies showed that relatively high removal of TOC and UV absorbance, removal of HA fouling potential and the complete recovery of TiO 2 slurry using this hybrid system were achieved.…”

“…Membrane filtration is not only able to separate suspended catalysts, but can also enhance the effluent quality by selective separation at the molecular level if small pore size memranes are used [6]. Furthermore, semiconductor photocatalysis is able to mineralize compounds causing membrane fouling and thus improve the consistency of the membrane’s operation [4,7,8]. …”

“…In particular, this hybrid process was used to improve membrane flux and minimise fouling, as well as recovery of the TiO 2 catalyst [8,9]. For example, Lee et al observed that there was a significant flux decline occurred when a mixture of humic acid (HA) and TiO 2 without UV irradiation was applied during ultrafiltration (UF).…”