Development of a Continuous Photo-catalytic/Ozonation System: Application on Amido Black Removal from Water

ABSTRACT

A continuous system for photo-catalytic/ozonation was designed at laboratory scale and evaluated for water treatment using Amido Black 10B dye (AB) as a pollutant model. The effect of single ozonation (O₃), photolytic ozonation (UV/O₃) and combined photocatalytic/ozonation treatment (UV/O₃/TiO₂) were investigated. TiO₂ nanocatalysts films were coated on stainless steel grids (AISI 304) by Atomic Layer Deposition technique (ALD) at 350 °C. An experimental hydrodynamic study of the designed reactor was conducted based on dry and total pressure drop. Three flow regimes were observed by increasing the total pressure drop against gas load factor (Fs). Depollution experiments conducted on the developed reactor showed that reaction rates and efficiency of studied processes were dependent on the studied operational parameters (initial dye concentration, ozone dose, pH). The maximum AB dye ([AB]₀ = 100 mg. L⁻¹) conversion efficiency, using the designed (UV/O₃/TiO₂) system, was about 40.3% of initial TOC and 100% AB color removal was achieved within 10 min at an optimal ozone dose of 132 mg. L⁻¹. A significant improvement in AB removal using UV/TiO₂/O₃ process (k_overall = 0.056 min⁻¹, 40.3%) compared to O₃ alone (k_overall = 0.032 min⁻¹, 26.87). Results shows also that the addition of tert-butanol (TB), as radical scavenger ([TB] = 0.2 M and 0.4 M), greatly affects the reaction mechanisms of a photocatalytic ozonation process within 5 min of reaction, by decreasing the Amido Black conversion from 99.67% ([TB] = 0 M) to 74.63% and 31.35%, respectively, in presence of 0.2 M and 0.4 M of tert-butanol. The remarkable decrease in AB removal rate observed in the presence of a radical scavenger expresses that there was an obvious enhancement of hydroxyl radical OH• generation due to the synergetic effect between ozone and photocatalytic processes.

Graphical abstract

KEYWORDS:

• Ozonation
• catalytic ozonation
• photocatalytic ozonation
• photocatalysis
• continuous reactor
• sieve plates
• TiO₂
• amido black

Acknowledgments

This research was financially supported by the Tunisian Ministry of Higher Education and Scientific Research under an objective contract. The authors wish to acknowledge the facilities and support provided by the Department of Green Chemistry, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli, Finland.

Disclosure statement

No potential conflict of interest was reported by the authors.