CuO/SBA-15 catalyst for the catalytic ozonation of mesoxalic and oxalic acids. Water matrix effects

• Catalytic ozonation of organic acids using CuO/SBA-15 as catalyst was studied.
• The effect of inorganic anions on the ozonation process was determined.
• The non-catalytic process was severely affected. Catalytic ozonation was almost unaffected.
• Under non-catalytic ozonation in STP effluent, oxalic acid was depleted by precipitation.
• Under catalytic ozonation in STP effluent, oxalate was depleted by ozone oxidation.

The depletion of mesoxalic and oxalic acids, two of the main by-products of wastewater ozone treatment, was studied in non-catalytic and catalytic ozonation using copper oxide supported on mesoporous silica SBA-15 as catalyst. The influence of the main inorganic anions present in natural and STP effluents (bicarbonates, sulphates, chlorides and phosphates) was also studied. The non-catalytic reaction rate was strongly dependent on the presence of inorganic anions and it was also almost inhibited by the presence of particulate material. Catalysed ozonation not only accelerates organic acid depletion, but was almost unaffected by the presence of these inorganic anions, or by the presence of suspended solids. The efficiency of catalytic and non-catalytic ozonation for depletion of both acids was studied in a real STP effluent. The depletion of mesoxalic acid was considerably slowed down in non-catalysed reactions, whereas under catalysed conditions it was not affected. Oxalate depletion was dominated by the formation with calcium of an insoluble salt, the precipitation equilibrium of which reversed only in the presence of a catalyst.