Assessment of Recovery Techniques for Solids Produced from Biological Conversion of Corn Syrup to Single Cell Protei

Corn syrup, a liquid waste stream of corn ethanol industry containing high soluble organic matter, can be used as a substrate for growth and production of protein-rich single cell protein (SCP) that can be applied for animal or aquaculture feed. In the production process, harvesting of the biomass from the fermentation broth is a crucial step. However, there has not been optimized harvesting methodology proposed in the literature for the SCP biomass. In this study, water-solid separation experiments including sedimentation and centrifuge were performed to understand the efficacy of SCP solid harvesting. In addition, commercial separation technologies and particles size analysis were also investigated to provide recommendations for the separation.;Primary solids were harvested from diluted corn syrup before fermentation and secondary solids were recovered after fermentation. Sedimentation and centrifugation processes recovered 95% and 75% primary solids in laboratory experiments and in pilot plant production, respectively. The primary solids are of larger particles that can be easily recovered by the two conventional separation methods examined. For secondary solids, these separation methods recovered only 44% and 21% in laboratory experiments and in pilot plant production due to the smaller size and lower densities of bacterial biomass and presence of filamentous bacteria hindering the settling process. The pilot scale centrifuge recovered smaller amounts of solids due to its shorter retention period. The protein content of recovered secondary biomass was 72% (dry basis), comparable to that of soy protein concentrate commonly used protein source for aquaculture. The protein content of primary biomass was 58%, higher than that of corn syrup (28%) and dried distiller grain solubles (DDGS).;Investigation of commercial separation technologies to improve secondary solids recovery was performed based on data of particle size distribution of suspensions and supernatants of the settled suspended solids. Based on the effective size range of evaluated technologies and the particle size regimes of suspensions, disk stack centrifuge was recommended for harvesting the secondary biosolid suspensions. Disk stack centrifuge produced a cake of 9-12% solid content with a recovery of 72%. Results of qualitative evaluation of other separation technologies were also performed for future quantitative assessment upon availability of the separation apparatus.