Removal of organic pollutants in tannery wastewater from wet-blue fur processing by integrated Anoxic/Oxic (A/O) and Fenton: Process optimization

• A new type of tannery wastewater was treated by combined processes of A/O and Fenton.
• COD composition based on particle size and biodegradability was obtained.
• The appropriate OLR (organic load rate) for A/O process was determined.
• Fenton performance was optimized by response surface methodology.

Treatment of tannery wastewater has been a challenge in remediation of aquatic environment in developing countries. Removal of organic pollutants in tannery wastewater from wet-blue fur processing was studied using integrated processes of Anoxic/Oxic and Fenton. Analysis of COD composition based on particle size found about 10% of the total COD was in the particulate and colloidal range, the remaining 90% was soluble with 72% biodegradable. Biodegradation of real tannery wastewater as well as typical tanning agents were performed in batch experiments, aerobic degradation presented much better performance than anaerobic degradation. Effect of hydraulic retention time on A/O performance in terms of COD removal efficiency was evaluated, excess HRT like 60 h would reduce the effluent quality, and the appropriate organic load rate was at least up to 0.8 kg COD m−3 d−1 with corresponding COD removal of about 80%. In the subsequent Fenton oxidation, effects of initial pH and H2O2 dose on COD removal were investigated, and response surface methodology was adopted to obtain the optimal conditions as initial pH of 4.0, H2O2 dose of 14.0 mM, H2O2:Fe2+ molar ratio of 10.6, and reaction time of 3 h to achieve the highest COD removal of 55.87%. GC–MS analysis was carried out to observe the change of organic composition during Fenton oxidation, and most of the residual organic pollutants resistant to Fenton treatment belonged to organosilanes and saturated alkanes. This study will provide useful information for treatment of a special type of tannery wastewater from wet-blue fur processing with low organic load.