Greenhouse gas emissions from advanced oxidation processes in the degradation of bisphenol A: a comparative study of the H2O2/UV, TiO2 /UV, and ozonation processes

To estimate greenhouse gas (GHG) emissions and degradation rate constants ( k obs ) from H 2 O 2 /UV-C, TiO 2 /UV-C, and ozonation processes in the degradation of bisphenol A (BPA), the laboratory scale experiments were conducted. In the H 2 O 2 /UV-C process, the fastest degradation rate constant ( k obs = 0.353 min −1 ) was observed at 4 mM of H 2 O 2 , while the minimum GHG emission was achieved at 3 mM of H 2 O 2 . In the TiO 2 /UV-C process, the fastest rate constant ( k obs = 0.126 min −1 ) was achieved at 2000 mg/L of TiO 2 , while the minimum GHG emission was observed at 400 mg/L of TiO 2 . In the ozonation process, GHG emissions were minimal at 5 mg/L of O 3 , but the degradation rate constant kept on increasing as the O 3 concentration increased. There were three major types of GHG emissions in the advanced oxidation processes (AOPs). In the ozonation process, most of the GHG emissions were generated by electricity consumption. TiO 2 /UV-C process accounted for a significant portion of the GHGs generated by the use of chemicals. Finally, the H 2 O 2 /UV-C process produced similar GHG emissions from both chemical inputs and electricity consumption. The carbon footprint calculation revealed that for the treatment of 1 m 3 of water contaminated with 0.04 mM BPA, the H 2 O 2 /UV-C process had the smallest carbon footprint (0.565 kg CO 2 eq/m 3 ), followed by the TiO 2 /UV-C process (3.445 kg CO 2 eq/m 3 ) and the ozonation process (3.897 kg CO 2 eq/m 3 ). Our results imply that the increase in removal rate constant might not be the optimal parameter for reducing GHG emissions during the application of these processes. Graphical abstract .