Treating Light-Colored Water-Based Paint Wastewater: 3 Field-Tested Dosing Schemes
Introduction
Light-colored water-based paint wastewater — pink, reddish-brown, gray — is generated wherever waterborne paints are produced or applied. Although lighter in color than ink-type streams, it is still a stable emulsion carrying pigments, resins and surfactants, and it cannot be cleared by simple settling.
Field trials show that a short four-step chemical train delivers clear, compliant effluent in these cases:
Decolorization → pH adjustment to 7–8 → anionic PAM flocculation → solid-liquid separation
The three case studies below are jar-test validated schemes using commercially available Treatment Chemicals. Dosages are expressed per ton (m³) of wastewater and must be re-validated on site, since water quality varies by paint formulation.
Case Study 1: Pink Water-Based Paint Wastewater
| Step | Operation | Chemical / Parameter | Purpose |
|---|---|---|---|
| 1 | Decolorization | decolorizer, 6.7 kg per ton of water | Remove the pink color from the water body |
| 2 | pH adjustment | Caustic soda (NaOH flakes), 500 g per ton, adjust to pH 7–8 | Create suitable conditions for subsequent flocculation |
| 3 | Flocculation | Anionic PAM, 15 ppm | Aggregate suspended particles into large flocs for easy separation |
| 4 | Solid-liquid separation | Sedimentation or filtration | Obtain a clear supernatant; treatment complete |
Case Study 2: Reddish-Brown Water-Based Paint Wastewater
| Step | Operation | Chemical / Parameter | Purpose |
|---|---|---|---|
| 1 | Decolorization | decolorizer, 1% by weight (≈ 10 kg per ton) | Remove the reddish-brown color |
| 2 | pH adjustment | Caustic soda, 650 ppm (≈ 650 g per ton), adjust to pH 7–8 | Create suitable conditions for flocculation |
| 3 | Flocculation | Anionic PAM grade, 35 g per ton | Aggregate particles into large flocs |
| 4 | Solid-liquid separation | Sedimentation or filtration | Obtain a clear supernatant |
Case Study 3: Gray Water-Based Paint Wastewater
| Step | Operation | Chemical / Parameter | Purpose |
|---|---|---|---|
| 1 | Decolorization | decolorizer, 1 kg per ton | Remove the gray color |
| 2 | pH adjustment | Caustic soda, 650 g per ton, adjust to pH 7–8 | Create suitable conditions for flocculation |
| 3 | Flocculation | Anionic PAM, 35 g per ton | Aggregate particles into large flocs |
| 4 | Solid-liquid separation | Sedimentation or filtration | Obtain a clear supernatant |
Key Takeaways
Same four-step logic, adjusted doses.
All three streams follow the same train: decolorizer first, caustic soda to pH 7–8 second, anionic PAM third, separation last. Only the doses change.
pH 7–8 is the working window.
Caustic soda dosing is modest because these streams are already near-neutral; the adjustment mainly secures the flocculation window.
Decolorizer dose does not simply scale with perceived color depth
— pink needs 6.7 kg/t while gray needs 1 kg/t. The required dose depends on the specific pigment system, which is exactly why jar testing on the actual wastewater is non-negotiable.
PAM dose and grade matter.
Anionic PAM at 15–35 g/t, with the appropriate grade (e.g., 1825), produces dense, fast-settling flocs.
Conclusion
Light-colored water-based paint wastewater is treatable with a short, proven chemical train: decolorization, pH control to 7–8 and anionic PAM flocculation, followed by solid-liquid separation. The three cases above give concrete starting doses for pink, reddish-brown and gray streams — always confirm with jar tests on site before scaling up to the full treatment system.