Package Sewage Treatment Equipment for Plastic Washing Wastewater

Package Sewage Treatment Equipment for Plastic Washing Wastewater

Effectively Treating the Complex Effluent from Plastic Recycling Operations

The plastic washing process, essential in recycling operations, generates challenging wastewater containing a high load of suspended solids (dirt, labels, adhesives), organic contaminants (food residues, oils), detergents or cleaning agents, dissolved polymers, and critically, microplastics. Discharging this effluent without thorough treatment poses significant environmental risks, including microplastic pollution and contamination of water bodies. Specialized Package Sewage Treatment Equipment (PSTE) is vital for plastic recyclers to operate sustainably and comply with environmental regulations.

Targeting the Specific Contaminants in Plastic Wash Water

Effective treatment requires a multi-stage approach designed to handle high solids, oils, chemicals, and microplastics:

1. Primary Treatment - Coarse Solids & Large Particle Removal:

• Screening: Robust bar screens or drum screens remove large debris, plastic fragments, and gross solids right at the source.

• Grit Removal: Grit chambers or cyclones separate heavy inorganic particles like sand and glass that could abrade downstream equipment.

2. Secondary Treatment - Fine Solids, Oils & Microplastics Removal:

• Dissolved Air Flotation (DAF): This is often the cornerstone of plastic wash water treatment. By introducing fine air bubbles under pressure, DAF effectively separates suspended solids, colloidal particles, oils, grease, and crucially, microplastics. The bubbles attach to these particles, floating them to the surface where a skimmer removes them as sludge (float). Chemical coagulants (e.g., ferric chloride, PAC) and flocculants (polymers) are typically dosed ahead of the DAF to aggregate fine particles and microplastics, dramatically enhancing their removal efficiency.

• Sedimentation/Clarification: In some flows, or as a follow-up to DAF, settling tanks allow remaining heavier flocs to settle. Lamella clarifiers increase settling surface area in a compact footprint.

3. Tertiary Treatment - Dissolved Organics & Residual Contaminants:

• Biological Treatment (If Needed): If significant dissolved organic matter (BOD/COD from food residues, surfactants) remains after primary/DAF treatment, biological processes like Sequencing Batch Reactors (SBRs) or Moving Bed Biofilm Reactors (MBBRs) may be employed. These use microorganisms to break down soluble organics.

• Advanced Oxidation Processes (AOPs) (Optional): For persistent organic pollutants or trace chemicals, AOPs (e.g., ozone/H2O2, UV/H2O2) can break them down into harmless substances. This is less common unless specific contaminants are a concern.

• Filtration: Sand filters, activated carbon filters, or more advanced membrane filtration (Ultrafiltration - UF) can remove residual fine suspended solids, trace microplastics, dissolved organics, and color. UF provides a very high barrier to microplastics and colloids.

4. pH Adjustment: The washing process often uses caustic or acidic cleaners. Neutralization (using acid or alkali dosing) is essential before biological treatment or discharge to meet pH requirements.

5. Sludge Management: Sludge from DAF float, sedimentation, and biological processes is thickened (gravity thickeners) and dewatered (filter presses, centrifuges, screw presses) to reduce volume. The resulting cake requires responsible disposal (landfill, incineration) or, if contaminant-free, potential utilization. Microplastic content in sludge is a key disposal consideration.

6. Water Reuse/Recycling: Treated water, especially after UF, can often be recycled back into the washing process, significantly reducing freshwater consumption and wastewater discharge volume. This requires careful monitoring of water quality parameters like salinity build-up.

Critical Role of Package Equipment in Plastic Recycling

• Microplastic Capture: DAF with chemical conditioning is highly effective at removing microplastics, a primary environmental concern.

• High Solids Handling: Designed to cope with the heavy solids load characteristic of wash water.

• Oil & Grease Removal: DAF efficiently separates emulsified and free oils/grease from detergents and plastic residues.

• Detergent/Surfactant Reduction: Biological treatment or AOPs address the BOD/COD from cleaning agents.

• Regulatory Compliance: Ensures effluent meets standards for TSS, FOG, BOD/COD, pH, and increasingly, microplastics (indirectly via TSS limits).

• Water Conservation: Enables high rates of water recycling within the washing line.

• Compact & Integrated Design: Pre-engineered modules save space and simplify installation in industrial settings.

• Operational Consistency: Automated systems provide reliable treatment performance despite fluctuations in wash water composition.

Implementing dedicated Package Sewage Treatment Equipment is fundamental for plastic washing facilities to mitigate their environmental footprint, adhere to regulations, realize significant water savings through reuse, and contribute to truly sustainable recycling practices.