CDOF vs. Conventional Oxidation Processes: A Comparison
In wastewater treatment, ozone catalytic oxidation is widely used for refractory wastewater thanks to its strong oxidizing power. Conventional tank-type ozone catalytic oxidation and the innovative CDOF (swirl dissolved-ozone flotation unit) process, as two mainstream technical routes, differ significantly in structural design, process efficiency, safety and stability. This article compares them from multiple dimensions and analyzes their respective core strengths and weaknesses.
In terms of structure, the conventional process uses an open tank design consisting of an ozone contact oxidation tank and an intermediate tank. Inside the tank, components such as aeration discs, supporting layers and catalyst bed layers are arranged in functional layers, requiring complex auxiliary facilities. This decentralized structure results in a large footprint, requires additional auxiliary equipment such as off-gas destruction devices, and involves long construction periods.
Fig. Conventional tank-type ozone oxidation system
CDOF process adopts an integrated design of enclosed pressurized vertical tanks. Its core is a skid-mounted unit composed of a main reaction tank, a secondary reaction tank, a jet dosing device, etc. The structure is compact with few auxiliary facilities, greatly saving floor space and shortening the construction period.
Fig. CDOF ozone advanced catalytic oxidation flotation integrated system
Process efficiency is where the two differ most.
Conventional oxidation tank process: the microbubbles produced by the aeration discs readily coalesce and grow to 1-3 mm, so only a small amount of ozone contacts the inner surface of the catalyst to generate hydroxyl radicals (·OH), resulting in low ozone utilization. To ensure treatment performance, the wastewater residence time must be as long as 90 min, and ozone consumption is enormous.
CDOF process: jet technology cuts the ozone-containing gas into micro/nano bubbles, and the pressurized environment enables rapid ozone dissolution; dissolved ozone contacts the catalyst fully, greatly improving ·OH conversion efficiency. With the coordinated action of the main and secondary reaction tanks, the total residence time is only 15 min—less than 1/6 of the conventional process—and ozone consumption is only 1/4-1/3 of conventional, significantly reducing operating costs.
In terms of safety, stability and ease of operation and maintenance, the shortcomings of the conventional process are particularly prominent.
Conventional ozone oxidation tank: the open tank design allows ozone to escape easily; untimely off-gas treatment can easily cause equipment corrosion and personnel safety risks; fixed-bed catalysts are prone to caking and blockage, the backwash interval shortens with running time, and backwashing is ineffective, making it difficult to guarantee long-term stable compliance; moreover, operation is mostly semi-automatic or manual, with high labor costs.
CDOF process: enclosed pressurized operation achieves zero ozone leakage, making the site environment friendly and safe; the floating-bed catalytic design, combined with the cleaning and agitation of the catalyst by micro/nano bubbles, together with automatic backwashing 1-2 times per week and acid-washing regeneration once a month, effectively prevents catalyst caking and blockage and ensures long-term stable operation; supported by a fully automatic DCS/PLC control system with intelligent optimization and early warning, no manual intervention is required and maintenance is easy.
