Views: 888 Author: Yosun Publish Time: 2025-10-21 Origin: Site
Plastic recycling plays a vital role in reducing environmental pollution and promoting the circular economy. However, one of the major challenges in the recycling process is the generation of large volumes of plastic cleaning wastewater. During the washing and separation stages, plastics are rinsed to remove labels, adhesives, organic matter, and dirt. This cleaning process consumes thousands of gallons of wastewater daily, which contains suspended solids, oils, detergents, and microplastics.
To achieve sustainable recycling and meet environmental regulations, the wastewater treatment process must include technologies that can efficiently remove contaminants and allow the recycling of treated wastewater. One of the most effective methods used in modern recycling facilities is the Dissolved Air Flotation (DAF) system, which provides superior separation performance and helps reduce operating costs.
Water used in plastic washing lines carries a wide range of pollutants, depending on the type of plastic and washing method. The major contaminants include:
Suspended solids: Plastic fragments, sand, and soil residues.
Oils and grease: From plastic additives and lubricants used during processing.
Detergents and surfactants: Used to improve cleaning efficiency.
Organic matter: Labels, food residues, and adhesives.
Microplastics: Extremely fine particles that are difficult to remove by filtration.
If this wastewater is discharged directly without proper treatment, it causes serious environmental hazards, including soil contamination and water body pollution. Therefore, it is essential to adopt an efficient wastewater treatment system that focuses on separation, clarification, and water recovery.
The Dissolved Air Flotation (DAF) system is a physical separation technology that removes suspended solids, oils, and grease using microbubbles. In this process, air is dissolved in water under pressure and then released at atmospheric pressure. The released air forms microbubbles that attach to contaminants, reducing their density and causing them to float to the surface. The floated layer is then removed by a skimming device, while clarified water flows out from the bottom.
High separation efficiency: Removes up to 90% of suspended solids and floating oils.
Compact design: Requires less space compared to traditional clarifiers.
Low maintenance: Few moving parts ensure stable, long-term operation.
Improved water quality: Produces clear effluent suitable for reuse.
Energy-efficient process: Lower energy consumption compared to filtration systems.
Because of these features, DAF is widely used in plastic cleaning wastewater recycling as both a primary and secondary treatment step.
A typical plastic cleaning wastewater treatment plant includes multiple stages to achieve effective pollutant removal and water recycling:
Screening and grit removal: Removes large debris and coarse particles.
Chemical coagulation and flocculation: Adds coagulants to aggregate fine particles into larger flocs.
Dissolved Air Flotation (DAF): Separates floating solids and oils through air flotation.
Secondary treatment: Biological or membrane filtration removes remaining organic pollutants.
Water reuse system: Treated water is recycled back into the washing process, reducing overall consumption.
In many recycling facilities, the DAF unit serves as the core primary treatment device, as it handles high loads of suspended solids and oil contaminants efficiently.
The DAF dissolved air flotation system operates by generating air-saturated water using a pressurization system. When the pressurized water is released into the flotation tank, microbubbles form and adhere to particles. The bubbles and solids float to the surface, creating a sludge layer. A skimming device continuously removes this layer into a collection hopper, while clarified water exits from below.
| Parameter | Typical Range |
|---|---|
| Removal Efficiency (SS/FOG) | 80–95% |
| Hydraulic Retention Time | 10–25 minutes |
| Air-to-Solids Ratio | 0.02–0.06 |
| Operating Pressure | 4–6 bar |
| Effluent Turbidity | < 10 NTU |
This performance data demonstrates that DAF systems can handle high contaminant loads while maintaining stable effluent quality, making them ideal for plastic cleaning wastewater recycling.
Although DAF provides excellent removal of oils and suspended solids, it is often integrated with additional wastewater treatment technologies for complete recycling.
Biological treatment removes soluble organic matter.
Sand or carbon filtration improves water clarity and odor control.
Membrane filtration (UF/RO) enables high-quality water reuse for washing applications.
By combining these technologies, facilities can create a closed-loop recycling system that minimizes freshwater demand and discharge volume.
Implementing a Dissolved Air Flotation system in plastic cleaning operations provides both environmental and economic advantages:
Reduced water consumption: Treated water can be reused multiple times in washing lines.
Lower chemical usage: Efficient separation minimizes coagulant and flocculant demand.
Stable operation: Handles fluctuating wastewater characteristics from different plastics.
Improved product quality: Cleaner recycled plastics free of contamination.
Regulatory compliance: Ensures treated effluent meets environmental discharge limits.
These benefits help recycling plants operate more sustainably while reducing overall operating costs.
While DAF systems are efficient, their performance depends on several operational factors:
Chemical dosage control: Correct coagulant and pH adjustment are essential for floc formation.
Bubble size management: Smaller bubbles improve contact with fine particles.
Sludge handling: Regular removal prevents floating sludge from recontaminating effluent.
Flow rate regulation: Maintaining consistent flow ensures uniform air distribution.
Continuous monitoring and optimization of these parameters are crucial to achieve reliable long-term operation in plastic cleaning wastewater treatment plants.
The future of plastic cleaning wastewater recycling lies in the combination of mechanical separation, chemical optimization, and digital automation. New DAF systems are being designed with:
Energy-efficient air saturation systems
Automated sludge control and discharge monitoring
Compact modular design for flexible plant installation
Integration with smart sensors for real-time data tracking
With increasing global emphasis on circular economy and resource efficiency, Dissolved Air Flotation will continue to be a key component of sustainable wastewater treatment in the recycling sector.
