Performance Analysis of Photolytic, Photocatalytic, and Adsorption Systems in the Degradation of Metronidazole on the Perspective of Removal Rate and Energy Consumption

Abstract

The efficiency of the following systems: photolysis (UV-C only), photocatalysis with titanium-dioxide (UV-C/TiO₂), photocatalysis with granular-activated carbon (UV-C/GAC), and by adsorption on GAC, was assessed under different initial contaminant concentrations, i.e., 0.1–100 mg L⁻¹. The experiments were conducted in a batch photocatalytic reactor (1.9 L and 32 W UV power). It was found that UV-C/TiO₂ and UV-C/GAC systems showed fairly equal removal efficiencies under lower MNZ concentrations (0.1–5 mg L⁻¹) compared to higher concentrations at similar catalyst loading of 2.5 g L⁻¹. A decline in removal rate (based on first-order reaction) was observed with respect to increase in initial MNZ concentration in all systems. MNZ removal by adsorption on GAC was much lesser compared to UV-C only, UV-C/TiO₂, and UV-C/GAC systems. The adsorption data well correlated with the Freundlich model indicated that the adsorption was on the heterogeneous surface of the catalyst. The effectiveness of the systems were evaluated by calculating electrical energy consumed per order (E _EO). The lowest E _EO value was found to be for UV-C/TiO₂ (0.03 kWh m⁻³ order⁻¹) for the degradation of 0.1 mg L⁻¹ of MNZ compared to UV-C/GAC (0.06 kWh m⁻³ order⁻¹), UV-C only (0.15 kWh m⁻³ order⁻¹), and adsorption (0.44 kWh m⁻³ order⁻¹). The total organic carbon and nitrogen ion analyses have confirmed the mineralization of MNZ via aliphatic carboxylic acid compounds in the photocatalytic system. Overall, the photocatalytic system seems to be an energy-efficient treatment option for the removal of MNZ and similar other micropollutants.

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