Single‐cell protein production from spent sulfite liquor utilizing cell‐recycle and computer monitoring

Abstract

AbstractSpent sulfite liquor (SSL), a waste product of the paper pulping industry, is produced at a rate of 1 ton (dry basis) per ton of pulp. The sugar content of SSL is about 30 g/L. To reduce the biological oxygen demand (BOD) of SSL before disposal, torula yeast (Candida utilis) is produced by a continuous culture process, the productivity of which is limited by sugar concentration and cell growth rate. To increase productivity, a recycle system has been designed and tested. Cells were sedimented continuously with a flocculating agent (bentonite) before being recycled to the fermentor. A bentonite concentration of 0.02 g/g cell was required. A computer monitoring system based on material balancing techniques was developed to monitor and control the recycle system. With this computer system, productivity was raised to 6.1 g/L h, with cell concentration up to 65 g/L in the recycle stream and 24 g/L in the fermentor. This represents a productivity increase of 150% over continuous culture with no recycle.