Treatment of Pulp Mill D-Stage Bleaching Effluent Using a Pilot-Scale Electrocoagulation System

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Pulp and Paper Industry

Background:

• Pulp and paper mills generate significant effluent, often containing challenging pollutants.
• Chlorine dioxide bleaching stages produce effluent requiring effective treatment for water reuse and environmental compliance.

Purpose of the Study:

• To evaluate the performance of electrocoagulation technology for treating chlorine dioxide bleaching-stage effluent.
• To determine the optimal operating parameters for electrocoagulation in this specific application.

Main Methods:

• A pilot-scale study was performed using electrocoagulation.
• Investigated operating variables included current density (0–133.3 A/m²) and hydraulic retention time (HRT, 6.5–16.25 minutes).
• Analyzed water quality parameters: conductivity, suspended solids (SS), chemical oxygen demand (COD), true color, and hardness.

Main Results:

• Electrocoagulation demonstrated effectiveness in treating D-stage bleaching effluent.
• Increased current density and HRT consistently improved the removal of conductivity and COD.
• Highest removals achieved with aluminum electrodes at 133.3 A/m² and 16.25 min HRT: conductivity (44.2%), SS (98.5%), COD (75.0%), true color (85.9%), and hardness (36.9%).
• Iron electrodes were unsuitable due to undesirable complex formation.

Conclusions:

• Electrocoagulation is a viable technology for treating pulp mill D-stage bleaching effluent.
• Optimized electrocoagulation parameters enable significant pollutant reduction for water reuse.
• Aluminum electrodes are recommended over iron electrodes for this specific effluent treatment.