Development of solid-liquid separation technologies in bioprocessing

An innovative bioprocess utilizing thin stillage from dry-grind corn ethanol plants was used to produce a valuable filamentous fungus (R. microsporus var. oligosporus). A 1,500-L bioreactor was built to optimize operating parameters, produce fungal biomass for animal feed trials and develop equipment and processes for industrialization. Dewatering equipment was tested to determine proper solid-liquid separation equipment for the industrial process. Studies indicate that a two-step dewatering process is most effective utilizing a gravity fed, concave screen followed by a centrifuging filter. Solids content greater than 30 percent is not possible, as this value approaches theoretical limits due to intracellular water. This new fungal co-product has some superior feed properties in comparison to distillers grains. Selection of proper processing equipment minimizes capital and operating costs, making this process economically feasible for ethanol producers or other investors. Methods to concentrate and remove phosphorus from a waste bioprocessing stream utilized as a fertilizer was investigated to produce two more desirable products, liquid fertilizer with a larger nitrogen to phosphorus (N:P) ratio and a solid phase with a lower N:P. A large percentage of phosphorus in this liquid slurry, left over from an industrial fermentation process, is tied up in the suspended solids. The study focuses on the use of coagulants and polymers to aid separation of suspended solids from the bulk liquid, ultimately producing a liquid fertilizer with a higher nitrogen to phosphorus ratio over the initial liquid slurry