CDOF in Industrial Service: Catalytic Ozone, Flotation and the Cost Case

Why the process exists

Industrial wastewater treatment keeps running into the same three complaints: efficiency is low, cost is high, and the process creates a secondary pollution problem while solving the primary one. Oxidation answers the first complaint because it destroys pollutants rather than transferring them to a sludge, but conventional ozone oxidation answers it expensively. The CDOF process — cyclonic dissolved ozone flotation — was developed by SINOKLE to close that gap by putting oxidation and separation in the same vessel and letting each one improve the other.

Three technologies in one shell

CDOF, short for Cyclonic Dissolved Ozone Flotation Unit, integrates multiple ozone catalytic oxidation stages, cyclonic separation and dissolved gas flotation into a closed loop of oxidation, demulsification and separation. Through a patented catalyst, ozone is converted into highly active hydroxyl radicals (OH) instead of reacting only as molecular ozone, which raises oxidation efficiency 2-5 times over conventional methods. The practical consequences are visible in the schedule and the layout: reaction time falls from 60 minutes to 5-10 minutes, and equipment footprint drops to 1/10 of a conventional process line.

A landfill project in Zhejiang

The clearest demonstration of the oxidation stage is a landfill leachate project in Zhejiang, where CDOF achieved COD removal above 80% and brought effluent COD from 1,500 mg/L down to below 200 mg/L. The more important number for the plant, though, is the biodegradability ratio: B/C rose from 0.22 to 0.37, which is what turns a leachate that a biological system cannot digest into one that it can. Oxidation here is not the final step, it is the step that makes the following biological step possible.

A petrochemical project in Xinjiang

Operating cost is where ozone processes usually lose the argument, and it is where the catalytic route changes the arithmetic. In a petrochemical wastewater project in Xinjiang, at an ozone dosage of 100 ppm, COD removal exceeded 90% and oil content fell from 35 ppm to 2.3 ppm. Oily sludge generation dropped by more than 90%, and the site saved over RMB 1 million per year in hazardous waste disposal costs alone. The ozone consumption figure behind those numbers is 1/8-1/4 of what a conventional process would need for the same duty, because the catalyst keeps the oxidant from being wasted on reactions that go nowhere.

Leachate in Shenzhen and the stability question

A landfill leachate project in Shenzhen tested a different claim: whether the process holds its performance when the feed moves. Effluent quality met China's Class I-A national standard on a stable basis, and system operating stability improved by 300% against the plant's previous line, which had been repeatedly upset by water-quality fluctuations. That improvement is the one operators value most, because an effluent that complies on a good day and fails after rain is not compliance at all.

Closed operation and what it prevents

CDOF equipment uses a fully closed pressurised design with an integrated intelligent control system, and it runs unattended and fully automatic. Ozone leakage is effectively nil, which removes the secondary pollution risk that makes ozone systems difficult to site near occupied buildings. Micro-bubble flotation also cuts flocculant dosage and the chemical residue that comes with it, so the sludge stream is smaller and cleaner at the same time.

The catalyst is the process, not an accessory

Most of what separates CDOF from a plain ozone contactor sits in the catalyst. The patented formulation converts dissolved ozone into hydroxyl radicals on its surface, and it also complexes with organic molecules, which makes them easier to attack than the same molecules in bulk solution. Two consequences follow. The oxidant is spent on pollutants instead of on itself, which is where the utilisation and dose-ratio figures come from. And the reaction route changes: partial oxidation that would otherwise stop at short-chain acids and stall continues further, so the residual COD after treatment is lower rather than merely chemically different. A plant that buys the vessel and substitutes a cheaper catalyst gets the vessel and none of the numbers.

Where it has already run

The process has been applied to oil-produced water, landfill leachate, pharmaceutical wastewater, dye wastewater and other difficult streams. In diphenylguanidine wastewater, it broke through the bottleneck of poor results and high cost that conventional processes had hit, and cut the operating cost for the enterprise by more than 50%. In oily wastewater at heavy-oil power plants, its compact design and high treatment capacity fit a site where plot space is the limiting factor.

Where it does not fit

Ozone oxidation is a poor choice for bulk organic load, and no catalyst changes that economics; it belongs downstream of biological treatment, not in place of it. Streams with very high salinity need the materials question answered first, because a pressurised ozone vessel in a chloride-rich environment is a corrosion problem before it is a process problem. And where the pollutant is a metal or a salt rather than an organic, oxidation has nothing to attack.

How to evaluate a CDOF proposal

Ask for the ozone dosing ratio rather than the removal percentage, because the ratio tells you what the plant will spend per unit of COD destroyed. Ask for the B/C shift, not only the COD drop, if a biological stage follows. Ask what happens at 60% of design flow, since ozone systems are often tuned at one point and left there. And ask for the catalyst replacement interval in writing, because that single line decides whether the operating savings survive year five.