Nuclear Power Plant Non-Radioactive Oily Wastewater: A KHC Plus CDOF Train Built for Oil Below 1 mg/L
A newly built nuclear power plant faces a purification problem that has nothing to do with radioactivity but everything to do with oil: a stream of non-radioactive oily production wastewater that must be cleaned before it joins the plant-wide network. The water carries petroleum substances - transformer oil, lubricants from mechanical equipment and similar sources - with oil concentrations between 500 and 2000 mg/L, plus suspended solids at about 100 mg/L. Both the influent quality and the flow rate fluctuate, and under shock loads the oil content rises significantly.
How the Plant Collects and Routes the Water
The collection logic is deliberately redundant. Non-radioactive oily wastewater from the nuclear island, the conventional island and other equipment is gathered and conveyed to an equalization tank in the oily production wastewater treatment area. A lift pump then sends it to the oil-water separation unit for primary separation. The separated effluent flows into an intermediate buffer tank, from which a second lift pump delivers it to precision filtration equipment for advanced treatment.
Water that meets the standard is discharged to the plant-wide production wastewater pipe network, with an emergency connection able to divert flow to a tank-type discharge monitoring tank. Non-compliant effluent returns to the equalization tank for re-treatment. Waste oil separated from the water is routed to a storage tank for temporary holding. Should the oil-water separation unit fail, or the influent flow overload the system and push the equalization tank level past the alarm value, an emergency drainage pump starts automatically and discharges the wastewater to the production wastewater system. The small amount of sludge generated during treatment can be returned to the equalization tank and removed periodically by manual cleaning.
Against this arrangement stands a hard acceptance target: the treated effluent must meet oil ≤1 mg/L and suspended solids ≤10 mg/L.
The Treatment Train SINOKLE Put Forward
To solve the purification problem, SINOKLE combined its core technologies with rich project experience in a mature and reliable train: pretreatment filter, then KHC high-efficiency coalescing oil-water separator, then CDOF ozone advanced catalytic oxidation unit. After the pretreatment stage, the oily wastewater first passes through the filtration units, which remove part of the suspended solids, and then enters the high-efficiency coalescing oil removal unit. The coalescing cartridges inside effectively aggregate emulsified oil droplets ranging from 0.1 to 20 micrometers, achieving thorough removal of emulsified oil and safeguarding effluent quality.
The coalescer effluent is boosted by an ozone dosing pump into the high-efficiency ozone injection and reaction unit. This reaction module combines ozone catalytic oxidation with dissolved-air flotation: residual organics are further oxidized and decomposed, while the converted insoluble matter is carried upward by microbubbles to form a scum layer that is removed at intervals. After multi-stage catalytic ozone oxidation, the oil concentration in the wastewater can be reduced to below 1 mg/L.
Backwash, Control and Layout
The filter units are backwashed with hot water based on differential-pressure signals, and the backwash wastewater is discharged separately. The whole system operates fully automatically under PLC or DCS control - simple to operate and requiring little maintenance. The unit is designed for a treatment capacity of 10 m³/h and mainly consists of one coalescing oil separator, two filter units and one CDOF ozone advanced catalytic oxidation device, which includes the CDOF reactor and an ozone generation skid. The system adopts a modular skid-mounted design with a compact layout covering only about 26 square meters.
Why the Train Holds Under Shock Loads
Successful operating experience from many similar projects at home and abroad shows that the scheme delivers stable and reliable effluent quality and can effectively handle extreme treatment demands under shock loads. The reasons are structural rather than lucky. The equalization tank decouples collection from treatment, so flow peaks arrive as a level signal rather than as a hydraulic surge. The KHC coalescer separates by density and coalescence, both of which tolerate the swings in droplet size that shock loads produce. And the CDOF stage treats what remains by oxidation, a mechanism whose removal rate does not collapse when the incoming emulsion gets tighter.
For a nuclear plant, that redundancy is the point: a wastewater stream that must never compromise the production network is handled by a train in which each stage protects the next, the automated fallbacks are already wired in, and the acceptance figures of oil ≤1 mg/L and suspended solids ≤10 mg/L are met by design rather than by operator vigilance.
The Nuclear-Specific Constraints Behind the Layout
What makes this project distinctive is not the oil - refineries see far worse - but the environment around it. In a nuclear plant, even the non-radioactive systems are engineered to the same discipline as the rest of the island: every stream must have a defined path, every failure mode a defined fallback, and every effluent a defined monitoring point. That is why the train carries an emergency connection to the tank-type discharge monitoring tank, why non-compliant effluent loops back to the equalization tank instead of being released, and why the emergency drainage pump is triggered by level rather than by operator judgement. The wastewater engineer's job here is as much about guaranteeing containment paths as about removing oil.
The modular skid layout serves the same discipline. One coalescing oil separator, two filter units and one CDOF device with its ozone generation skid can be delivered, installed and commissioned as discrete blocks within the 26 square meter envelope, and any block can be isolated for maintenance without dismantling the train. For a plant that will operate for decades, that serviceability - together with the automated hot-water backwash and PLC or DCS control - is what keeps the lifetime cost of the wastewater system predictable.