In industrial production, waste emulsions are inevitably generated during machining, metal cleaning, and cutting lubrication processes. Traditional chemical demulsification followed by biochemical treatment is widely used but has major drawbacks such as high chemical dosage, secondary pollution, and high operating costs. With the advancement of membrane separation technology, special ultrafiltration membranes have emerged as a breakthrough solution for waste emulsion treatment.
1. Transition from "Chemical Demulsification" to "Physical Separation"
Most domestic emulsion treatments still rely on chemical demulsification by adjusting pH or adding PAC and PAM to separate oil and water. However, this approach produces large amounts of chemical sludge and hazardous solids, while incurring high reagent costs.
By adopting the Dutch B&C special ultrafiltration membrane, the new "membrane concentration + physical demulsification + base oil recovery" process achieves efficient phase separation without chemical additives. Practical data show that:
- For waste emulsions with oil content of 1–3%, the concentrated liquid after membrane separation reaches 15–20% oil content;
- The ultrafiltration permeate has an oil content below 50 mg/L and a COD of 15,000–20,000 mg/L;
- After subsequent anaerobic–A/O–MBR biological and Fenton oxidation treatment, the effluent COD can be reduced below 500 mg/L, meeting reuse standards.
This "replacing chemicals with membranes" approach not only reduces secondary hazardous waste but also lowers the system's overall carbon footprint.
2. Integrated and High-Efficiency System Design
The process consists of five stages: pretreatment, special ultrafiltration membrane separation, anaerobic biological treatment, A/O + MBR biological treatment, and advanced oxidation (Fenton).
- Pretreatment: An oil separation tank and grating remove floating oil and suspended solids to ensure stable influent for the membrane system.
- Ultrafiltration Stage: Using an organic composite membrane with a design flux of 50 L/m²·h, the system operates in cycles to achieve concentration and demulsification.
- Biological Treatment: The UASB + MBR combination enhances biodegradation of high-COD wastewater.
- Terminal Oxidation: The Fenton process further removes refractory organics, ensuring water quality suitable for reuse.
This integrated approach-combining membrane pre-treatment, enhanced bioprocessing, and deep oxidation-embodies a forward-looking design philosophy for industrial wastewater systems.
3. Operational and Maintenance Insights
Operational experience shows that emulsion concentration significantly affects membrane flux. When the concentration is below 5%, the flux remains above 50 L/m²·h, but it gradually decreases as concentration increases. Regular chemical cleaning (every 1–2 weeks) restores flux and extends membrane life to approximately 2.5 years.
However, the increasing complexity of new emulsifiers in machining processes has made some emulsions more stable and harder to break. In such cases, evaporative devices are used to enhance oil recovery, indicating the need for future membranes with better anti-fouling and anti-emulsifier properties.
4. Achieving Both Economic and Environmental Benefits
In a hazardous waste treatment facility handling 25,000 tons of waste emulsion annually, this membrane-based process has demonstrated lower operational costs compared with chemical demulsification. The recovered base oil and reusable water contribute to a closed-loop recycling system, reducing overall resource consumption.
Additionally, the process eliminates chemical usage and sludge disposal, minimizing indirect CO₂ emissions and generating both environmental and corporate social responsibility value.
YIME believes that with the localization of special membrane materials and advances in multiphase membrane reactor systems, waste emulsion treatment will achieve low energy consumption, high recovery, and near-zero discharge, unlocking new growth potential for both metal processing and hazardous waste management industries.
