Characterization of Refractory Organic Matter in Pulp and Paper Mill Effluents

Abstract

The quality of wastewater from Japanese pulp and paper mills has been recently improved, due to regulation of effluent standards which has been stricter since the Water Pollution Control Law was enforced in 1972. However, it has not attained yet in some mills that the level of COD (Chemical Oxygen Demand) of the wastewater becomes below the environmental standard. Accumulation of refractory organic matter has been pointed out as a new problem especially for a part of the closed water area in spite of regulation of total emission. Japan Pulp and Paper Research Institute is researching this problem.As the first step of this theme, the characterization of the refractory organic matter was studied. Dissolved organic matter in wastewater was fractionated into five fractions ; hydrophobic acid, hydrophobic neutral, base, hydrophilic acid, hydrophilic neutral. Based on measurements of the degradation rates of the fractionated compo-nents, it was confirmed that the most refractory matter was fractionated into the hydrophobic acid.Furthermore, we compared softwood and hardwood kraft pulp (KP) bleaching drainages. Softwood KP bleaching drainage was more resistant to decomposition than hardwood KP bleaching drainage, and contained the hydrophobic acid in a higher ratio. In addition, the hydrophobic acid in softwood in hardwood KP bleaching drainage.In order to investigate the source of the hydrophobic acid, the each process drainage was fractionated as well. As a result, the maximum source of the hydrophobic acid was KP bleaching process. Pyrolysis GC-MS analysis of the hydrophobic acid of bleaching drainage indicated that lignin was a major composition of the refractory organic matter.