Technical Bulletin No. 0105: Activated Sludge Treatment of Neutral Sulfite Semi-chemical Waste
Following the research experience on the production of a super protein feed supplement from spent sulfite liquor, it was felt that the high oxidation rates obtained in this process might be translatable to spent neutral sulfite semi-chemical pulping liquor if a similar technique was employed. In accordance with this idea, the Council's Virginia Polytechnic Institute Project, under the direction of Mr. Millard H. Robbins, Jr., undertook the studies reported in the Technical Bulletin attached. Operating with a bench-scale aerobic oxidation pilot plant, it was found that BOD reductions from 73 to 99 percent could be obtained at loading rates as high as 325 pounds per thousand cubic feet of aerator capacity when treating a liquor having an initial 5-day BOD value of 9,600 ppm. Seed sludge concentrations as high as 12,000 ppm were carried in the system, producing a BOD to dry sludge solids ratio as high as 4.6 to 1.0. A high rate of return sludge recirculation was employed (1 cycle in 3 hours), which practice maintained a seed sludge of excellent settling and compacting qualities. From the standpoint of practical application of the process, higher loadings would be most desirable. Since oxygen exchange appeared to be the limiting factor, attempts to improve efficiencies through improved methods of carrying oxygen to the liquid phase will be explored.