Potential use of solar photocatalytic oxidation in removing emerging pharmaceuticals from wastewater: A pilot plant study

A pilot plant was used to evaluate the potential of solar photocatalytic processes in the treatment of wastewater containing emerging contaminates. Four groups of commonly used pharmaceuticals (antibiotics, estrogens, acidic, and neutral) were selected as model compounds and were treated with different combinations of solar advanced oxidation processes including solar-photolysis, homogenous solar oxidation with ferric ions, heterogeneous solar oxidation with titanium dioxide, and solar ozonation. Oxidation experiments were performed in Doha, Qatar (25.2854°N, 51.5310°E) under natural sunlight and at ambient temperature, in a semi-batch photo-reactor. Treatment performance was evaluated based on the efficiency of the processes in removing the target compounds and in mineralizing the organic content of the aqueous solution. The improvement in biodegradability and the reduction in the toxicity of the aqueous solution before and after the treatment were also evaluated. The results show that solar photolysis and solar oxidation with ferric ions are not effective in removing or mineralizing aqueous solutions containing the selected contaminates, while solar-driven oxidation processes with ferric ions, titanium dioxide, and ozone rapidly removed these pharmaceuticals from the wastewater and to some extent decreased the organic carbon content of the solutions. The removal efficiencies with solar photolysis and solar oxidation with ferric ions did not exceed 12.7% and 28.3%, respectively. Adding H2O2 to solar oxidation with ferric ions or utilizing TiO2 increased the percentage removal to the range 80-96%. Ozonation and solar ozonation processes removed 90-100% of the pharms in very short time. Performance indictor analysis showed that combining solar photocatalytic oxidation process with ozonation significantly improved the removal performance, increased the degree of mineralization, reduced the chemical requirements, and reduced the demand for ozone and energy. The kinetic profile of the combined processes is higher than that of the single oxidation process; thus, the combined oxidation processes is recommended for efficient treatment. The oxidation processes with their effective degradation capacity improved wastewater biodegradability and reduced its acute toxicity.