Valorization of Field-Spent Granular Activated Carbon as Heterogeneous Ozonation Catalyst for Water Treatment.

Developing sustainable cost-effective strategies for valorization of field-spent granular activated carbon (s-GAC) from industrial water treatment has gained much interest. Here, we report a cost-effective strategy for the regeneration of s-GAC as an adsorbent in a large-scale drinking water treatment plant and used as an efficient and durable ozonation catalyst in water. To achieve this, a series of samples is prepared by subjecting s-GAC to thermally controlled combustion treatments with and without pyrolysis. The catalytic performance of the optimized sample is evaluated for oxalic acid degradation as the model pollutant under batch (>15 h) and continuous flow operations (>200 h). The partially deactivated catalyst upon reuse is restored by thermal treatment. Electron paramagnetic resonance and selective quenching experiments show the formation of singlet oxygen (1O2) during catalytic ozonation. The GAC-ozonation catalyst is efficient to minimize the formation of chlorinated disinfection by-products like trihalomethanes and haloacetic acids in an urban wastewater effluent.

Graphitic Carbon Nitride as Visible-Light Photocatalyst Boosting Ozonation in Wastewater Treatment.

Light can boost ozone efficiency in advanced oxidation processes (AOPs), either by direct ozone photolysis with UV light or by using a photocatalyst that can be excited with UV-Vis or solar light. The present review summarizes literature data on the combination of ozone and the g-C3N4 photocatalyst for the degradation of probe molecules in water, including oxalic, p-hydroxybenzoic and oxamic acids as well as ciprofloxacin and parabens. g-C3N4 is a metal-free visible-light photocatalyst based on abundant elements that establishes a synergistic effect with ozone, the efficiency of the combination of the photocatalysis and ozonation being higher than the sum of the two treatments independently. Available data indicate that this synergy derives from the higher efficiency in the generation of hydroxyl radicals due to the efficient electron quenching by O3 of photogenerated conduction band electrons in the g-C3N4 photocatalyst. Given the wide use of ozonizers in water treatment, it is proposed that their implementation with g-C3N4 photocatalysis could also boost ozone efficiency in the AOPs of real waste waters.