Extensive studies on the treatment of pulp mill wastewater using aerobic granular sludge (AGS) technology

Aerobic granular sludge (AGS) offers the potential to degrade tannin/lignin found in pulp and paper wastewater (PPW). In this study, aerobic granules were cultivated in a sequencing batch reactor (SBR) with tannin/lignin present in the range of 50-200 mg/L. The mature granules were transferred to a real PPW wastewater system containing tannin/lignin concentration up to 500 mg/L. Biodegradation and biosorption were observed to be the two pathways for the removal tannin/lignin. Biosorption was a primary form of removal at lower concentrations, achieving 74% removal at 50 mg/L. The biosorption ability reduced to 58% removal at 200 mg/L. This reveals that biodegradation prevails at these higher concentrations. The Haldane kinetic parameters were: V-max=0.93 (g tannin/lignin/g VSS.day), K-s=1910 mg/L, and K-i=27 mg/L. Various adsorption kinetic models and isotherms were fitted to the system. The Langmuir isotherm coefficients were: (x/m)(max)=21.5 (mg tannin/lignin/g SS), b=0.00386 L/mg. The Freundlich isotherm had coefficients of n=1.172, K=0.1174. The study also delves into applying the technology towards real wastewater, achieving a COD removal of 79% and a tannin/lignin removal of 56%. Furthermore, experimental runs in warmer and more humid temperature conditions revealed higher removal efficiencies, achieving about 80% tannin/lignin degradation at a concentration of 130 mg/L. Results from this study will help ascertain an appropriate design protocol for full-scale industrial applications.