Pharmaceutical Wastewater at 6000 mg/L COD: What a CDOF Train Delivered in Inner Mongolia

The pharmaceutical industry keeps people alive and, in the process, produces an effluent that is genuinely difficult to treat. Its wastewater carries refractory organics, heavy metal ions and biotoxic substances; discharged untreated, it damages ecological balance in ways that are slow to reverse and hard to attribute.

At one large pharmaceutical enterprise, the arithmetic was blunt. Wastewater COD exceeded 6000 mg/L, far above the national discharge standard, and the conventional treatment process in place could not close the gap. That is the situation the ozone catalytic oxidation process developed by SINOKLE was built to answer.

Why Biological Treatment Alone Cannot Get There

Biological processes work on what bacteria can metabolise. Pharmaceutical wastewater contains a large share of molecules that bacteria either cannot break down or break down slowly enough that the hydraulic retention time is never sufficient. At the Inner Mongolia site, the conventional biological train removed only about 15% of the incoming COD, which is close to the amount removed by dilution and settling rather than by oxidation.

The other obstacle is toxicity. Biotoxic compounds suppress the very organisms the process depends on, so the plant becomes less effective exactly as the load rises. A process that attacks those molecules chemically, before or alongside biology, changes the shape of the problem.

What CDOF Puts Together

The core of the SINOKLE technology is the CDOF process, cyclonic dissolved-ozone flotation, which integrates three technologies — ozone advanced oxidation, cyclonic flow and dissolved air flotation — into one treatment system. The integration is the point: oxidation creates particles and colour bodies, flotation removes them, and sharing a vessel means the second step does not have to wait for a pump and a tank.

The key lies in multiple catalytic oxidation, which runs homogeneous and heterogeneous paths at the same time. Homogeneous catalysis adds metal ions that accelerate ozone decomposition in the liquid phase. Heterogeneous catalysis uses porous carriers to hold the active phase, which improves both catalyst stability and activity. Working together, the two paths lower the reaction activation energy, speed up ozone self-decomposition and raise the hydroxyl radical concentration — and hydroxyl radicals are the species that actually attacks the refractory fraction.

The cyclonic element handles mixing. Ozone has to meet the pollutant in the liquid, and a swirl field produces the interfacial contact that a bubble column does not. The dissolved air flotation element then exploits ozone own gel-breaking and demulsification effects to reduce coagulant dosage and improve effluent quality, which is a saving that shows up on the chemical invoice rather than in the discharge report.

The Catalyst Is Where the Performance Lives

The process competitiveness rests on a heterogeneous ozone catalyst developed in house. After a long series of formulation adjustments and process optimisation, the R&D team settled on a composite of highly active precious metals and transition metals as the active components, with particle size controlled below 10 nanometers through nanotechnology. That size is what produces the specific surface area, and specific surface area is what produces reaction rate.

Combined with stable carrier materials and special additives, the catalyst achieves efficient oxidation at low ozone concentration — the operating condition that keeps the power bill down — while offering a long service life and a low loss rate. In simulated operating tests, COD removal exceeded 80%, colour removal approached 100%, and service life went well beyond the industry average. The catalyst itself is silica-alumina based.

Engineering Choices Around the Vessel

Under pressure, ozone dissolves rapidly and disperses highly uniformly through the wastewater, which shortens reaction time dramatically compared with conventional technology. The footprint is one-third of traditional processes or less, and in a pharmaceutical plant hemmed in by clean rooms and utility corridors that is often the constraint that decides the project.

The unit runs fully automated in closed pressurised mode. That reduces manual intervention, eliminates the risk of ozone leakage, and produces no harmful by-products during treatment — the three conditions that let an ozone plant sit inside a facility with strict air quality requirements rather than at the far end of a fence.

The Inner Mongolia Result

The case that validates the process is the same site where biological treatment was managing 15%. After adopting the CDOF route, retention time dropped to 45 minutes and the brown, high-concentration, high-colour, biotoxic raw water came out clear, transparent and compliant. COD fell below 200 mg/L, suspended solids below 20 mg/L, and the B/C ratio rose from below 0.1 to 0.37.

That last figure is the one a process engineer should look at first. A B/C ratio of 0.37 means the effluent is now treatable by biology, so the oxidation stage is not carrying the whole duty permanently — it is opening the door for a cheaper downstream step. The 45 minutes matters for the same reason: at that retention time the unit is small enough to be affordable, and small enough to fit.

Over several months of continuous industrial operation, catalyst activity loss stayed below 5%. That is the number that separates a working catalyst from a laboratory result, because a catalyst that loses activity in weeks turns an operating cost into a consumable habit.

What the Case Establishes

Three things are now demonstrable rather than claimed. Ozone catalytic oxidation can take a pharmaceutical effluent from a COD above 6000 mg/L to below 200 mg/L in a single pass at realistic retention time. It can do so without generating a secondary waste stream that has to be dealt with elsewhere. And the economics hold in continuous operation, not only in a pilot.

For the wider field of industrial water pollution control, that is a useful reference point. The pharmaceutical sector is where the hardest molecules concentrate, so a process that works there has a credible claim on landfill leachate, coal chemical wastewater and the other streams that resist biological treatment.