Effect of SO2 Removal on the Biodegradability of Arbiso Spent Sulphite Liquor

Abstract

The spent sulphite liquor derived from Abitibi Paper Company, Iroquois Falls Mills Arbiso process contained about 11.3% dissolved solid, 0.52% (W/V) residual SO2 and had a low pH of 4.3. The COD of the liquor was about 109,000 ppm and BOD5 26,000 ppm. The objective of the study was to investigate the technical feasibility of utilizing biodegradation to reduce the BOD5 of the spent liquor to acceptable levels. Upon first analysis, it appeared that the liquor would be amenable to biological degradation because of the presence of wood sugars. However, biological oxidation was retarded due to the presence of SO2. The maximum SO2 concentration tolerated by the microbes was about 0.32% (W/V). Boiling and lime treatment were found to be effective in reducing the SO2. Other major factors affecting biological activity were initial pH adjustment and nutrient addition. Nutrients required and optimal operating conditions are discussed. Under optimal conditions, a batch biological system was capable of removing 60% BOD5, in 11 days and 80% BOD5 in 16 days.