Performance evaluation of black liquor treatment by horizontal flow catalytic wet air oxidation reactor under batch mode

Abstract

The pulp and paper manufacturing industry is one of the oldest and a core industrial sector in India. It is a high capital, high energy, high water consuming and also highly polluting industry which needs substantial investment in pollution control equipment. Water consumption in a paper mill is 60 m3 and effluent generation is 50 m3 per tonne of paper production. The wastewater contains high organic load and is highly coloured. The treatment process falls in a wide spectrum ranging from oldest to the most modern. Based on the raw material utilization, the paper mills can be classified into three categories viz., wood-based, agro-based and waste- paper based. It falls under 17 categories of industries identified by CPCB as highly polluting and their compliance with environmental norms is inadequate.Black liquor is an intensely coloured effluent with very highorganic load i.e., COD which is generated from the pulping process. Lignin contributes to 40% of all pollutants by weight in the black liquor. Lignin and its aromatic intermediate compounds are highly toxic, carcinogenic and mutagenic, which may pose a potential health hazard to humans and other living organisms. In this research, an attempt was made to develop a clean wastewater treatment technology for the pulp and paper industry black liquor using CWAO at lab-scale and bench-scale. The black liquor samples viz., BL1-BL6 were used in lab-scale studies.The bench-scale studies were conducted in a pulp and paper industry located in Kagithapuram, Karur district and the samples viz., BL7 - BL12 for the field studies were obtained from the study unit. The catalysts viz., CuO, ZnO, MnO2, SeO2, TiO2 and CuSO4 were used in CWAO process. In the lab-scale studies, pH was varied from 4 13, catalyst dose from 1 6 g/L, temperature from 100 200oC, pressure from 0.7 1.7 MPa and contact time of 0-210 minutes, newline