Ozone Oxidation Pathways in Wastewater Treatment Explained
Ozone (O₃) is a powerful oxidant and disinfectant that also decolourises and deodorises, and it plays an important role in wastewater treatment. The ozone oxidation technologies commonly used in plants fall into the following categories:
Single ozonation
Ozone reacts with pollutants in water mainly through two mechanisms: direct oxidation and indirect oxidation.
Direct oxidation relies on the ozone molecule itself and is selective. It mainly breaks large organic molecules into smaller fragments, markedly improving biodegradability, although its overall reduction of total organic carbon is relatively limited.
Indirect oxidation, by contrast, drives ozone decomposition to produce highly reactive hydroxyl radicals (·OH) that then react with organics. Hydroxyl radicals are regarded as the ideal oxidant in advanced oxidation processes: their action is non-selective and can rapidly, even completely, mineralise a wide range of refractory organics, effectively lowering organic carbon in the water.
Combined ozone processes
Because single ozonation has limitations — some stubborn organics are hard to degrade completely or fully mineralise, for example — many combined processes pairing ozone with other technologies have been developed. These combinations exploit both the strong oxidising power of ozone and the strengths of the partner technology, raising overall treatment performance.
Ozone-biological activated carbon: ozone pre-oxidation cleaves complex organics into easily biodegradable small molecules and raises dissolved oxygen, after which the biological activated carbon unit adsorbs and biodegrades them.
Ozone-coagulation: ozone destroys hydrophilic substances and converts them into hydrophobic ones, greatly improving subsequent coagulation and sedimentation.
Ozone-activated carbon adsorption: ozone breaks down the structure of large molecules and reduces their size, making them easier for activated carbon to adsorb and raising adsorption capacity.
Ozone-activated sludge: the main aim is to improve wastewater biodegradability and prepare it for biological treatment.
Ozone-membrane treatment: ozone is often used as post-treatment for ultrafiltration membranes to optimise effluent quality.
Ozone-ultrasonic treatment: ultrasonic cavitation works synergistically with ozone oxidation to improve the removal of complex organics.
The industry also uses O₃/H₂O₂ (hydrogen peroxide) combined oxidation, UV-catalysed ozonation, and combinations of ozone with aerated biological filters.
Catalytic ozonation
This technology introduces a catalyst into the ozonation system to raise reaction rate and treatment efficiency. Common catalysts include metals and their oxides and activated carbon. Catalytic ozonation falls mainly into the following types:
Photocatalytic ozonation: ultraviolet light is used as the catalytic energy source to strengthen ozone decomposition and oxidising power.
Homogeneous and heterogeneous catalytic ozonation: the two differ mainly in the form of the catalyst and how it is supported; they are an important current research direction.
The ozone oxidation technology family offers wastewater treatment plants a wide range of options for tertiary treatment; the choice should be optimised for the specific water quality and treatment target.
