Technical Bulletin No. 0082: Aerobic Fermentation of Spent Liquor for the Production of Protein Concentrate Animal Feed Supplement

Laboratory and bench scale pilot plant experiments have been completed by Dr. Herman R. Amberg, former leader of the Council's Oregon State College Project, toward the development of a process for removing the oxygen demand from spent sulfite liquor and producing a material of extremely high protein and amino acids content suitable for use as an animal feed supplement. An aerobic fermentation process employing a specialized mixed microbial cell culture was found capable, in a small-scale operation, of removing 80 to 90% of the BOD of spent sulfite liquor and producing a cell residue approaching 70% in protein content. The production rate was about 200 dry pounds from the quantity of liquor obtained in the production of one ton of sulfite pulp. This compares with the 50 to 55% protein content of other supplemental animal feeding materials. The necessary amino acids and vitamins present in this material were found, in most instances, to be as high as or higher than similar products now on the market. From data presented in the attached report, it appears that this process may prove less costly to operate than competitive processes and there is a possibility that de-sugared lignin can be obtained as a by-product. Preliminary animal feeding tests were successful, but need to be extended for final evaluation of the product.