Effect of Pretreatment of Resin Acids on Anaerobic Digestibility of Pulp and Paper Mill's Primary Sludge
Abstract
Pulp and paper (P&P) mills’ wastewater contain high concentrations of resin acids (10–10,000 mg/L) which are toxic to aquatic organisms. In mill’s primary and waste activated sludge treatments reduced concentrations of resin acids in effluent; however, most of the resin acids are ultimately ended up in sludge after primary and secondary clarification due to their extreme hydrophobic nature (log Kow 6.0). Nevertheless, adsorbed resin acids on the surfaces of anaerobes and substrates affect anaerobic digestion (AD) process negatively. The objective of the present work was to determine the effect of pretreatment of thermomechanical pulping mill’s primary sludge (TMP-PS) on AD. The performance of ozone and ferrate pretreatment of TMP-PS on AD was evaluated at their optimum pH around 11.0 and 7.0, respectively. Pretreatment of TMP-PS using 0.150 mg dosages /mg tCOD of ferrate and ozone increased sCOD by around 28.35% and 22.88%, respectively besides reduction of 23.63%, and 37.07% resin acids, respectively. AD showed negligible biodegradation of resin acids by anaerobic consortia. Pretreatment with ferrate and ozone increased the methane yield by maximum of 60.15% and 49.62%, respectively. Compared to ozonation, 11–13% more methane was generated in ferrate pretreated digesters. However, according to cost analysis, ozonation of TMP-PS is economically more feasible than ferrate pretreatment.