Revealing the influencing pathways and mechanisms of inorganic salts on the catalytic ozonation of petrochemical wastewater

Abstract

The presence of inorganic salts poses a significant challenge to the effective removal of petrochemical wastewater during the catalytic ozonation. However, the mechanism by which inorganic salts influence the catalytic ozonation of actual wastewater remains unclear and controversial. This study investigated the effects of inorganic salts (Na₂SO₄ and NaCl) on the catalytic ozonation of petrochemical wastewater. The TOC removal rate decreased from 59.89% to 32.12%–35.80% as Na₂SO₄ concentration increased from 0 to 5–10 g/L, whereas increasing NaCl had a slight impact on the TOC removal efficiency. Similar trends were observed for the removal of UV₂₅₄ and fluorescent organic substances. This is attributed to the superior ozone mass transfer enhancement and ·OH generation, as well as weaker inhibition of the adsorption process exhibited by NaCl compared to Na₂SO₄. Enhanced ozone mass transfer and elevated ozone concentrations promote direct oxidation by ozone molecules, reducing both the content and proportion of macro-molecule (molecular weight > 3 kDa) matters in the effluent. Conversely, weakened adsorption impedes the mineralization of micro-molecule (molecular weight < 3 kDa) fractions, leading to an increase in their content and proportion in the effluent. Our findings demonstrate that inorganic salts influence catalytic ozonation through a complex interplay of enhanced ozone supply, stronger direct oxidation, higher radical production, and hindered pollutant adsorption. These insights may guide future process optimization and catalyst design to improve the catalytic ozonation of saline petrochemical wastewater.

Graphical abstract

Keywords

Catalytic ozonation / Inorganic salts / Petrochemical wastewater / Mass transfer / Adsorption

Highlight

	● Both Na2SO4 and NaCl hampered catalytic ozonation of petrochemical wastewater.
	● Inorganic salts promoted ozone transfer but inhibited pollutant adsorption.
	● Na2SO4 showed stronger inhibition and weaker promotion compared to NaCl.
	● The insights guide improved catalytic ozonation for high-salinity wastewater.

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