Decolourisation of printing industry effluent Which treatment method is most commonly applied to remove color from dye-rich printing wastewaters in practice?

Introduction / Context:
Printing and dyeing effluents often contain chromophores that resist biodegradation and impart intense color. Removing color is crucial for meeting discharge standards and for downstream reuse or polishing.

Given Data / Assumptions:

• Wastewater contains soluble dyes and color bodies.
• Objective is practical, scalable decolourisation.
• Cost, robustness, and selectivity matter in plant operations.

Concept / Approach:
Adsorption, especially with activated carbon, is a widely used polishing step because it targets a broad spectrum of organic color-causing molecules, is modular, and integrates easily after biological treatment. Alternatives like reverse osmosis can remove color but at higher energy and with concentrate disposal issues, and ion exchange tends to be selective, less cost-effective for complex dye mixtures. Electrochemical methods may help but are less common at large scale for printing effluents.

Step-by-Step Solution:

Verification / Alternative check:
Plant case studies show activated carbon following secondary treatment consistently lowers color and COD; lab jar tests confirm rapid color uptake on carbon.

Why Other Options Are Wrong:

Common Pitfalls:
Relying solely on biological treatment; many dyes are recalcitrant and require a polishing step like adsorption.

Final Answer:
adsorption.