Microbial Upgrading of Cellulose-Based Materials

Abstract

The main objective of the research was to develop and design a process for the microbial upgrading of cellulosic waste materials by solid substrate fermentation to produce a protein rich animal feed-stuff, A large number of fungi wer2 tested for their cellulolytic activity and their ability to produce protein when grown on the selected raw material: barley-straw. Both mono and mixed cultures were used either in single-or multi-stage fermentation systems. As a result of this work a single-stage, mixed culture (cellulolytic and non cellulolytic) system operating in the thermophilic range wa3 selected for more detailed work. The optimum carbon to nitrogen ratio for growth and protein production was established, The effect of different raw material treatments (Ball milling) on fungal growth was also examined but no improvements were achieved. Preliminary feeding trials indicated that the end-product was acceptable and non-toxic to mice. The detailed design of a plant to treat 1,000 tons of straw per year was carried out. This design work highlighted a number of biological and process engineering problems, including:- 1. maintenance of sterile conditions 2. maintenance of uniform aeration, 3. temperature control, 4, recirculation and usage of nutrient salt solution, 5. removal and transport of fungal material by the salt solutions, and 6. process start up. An attempt was made to develop preliminary models for microbial growth on solid substrates under therraophilic, isothermal conditions. Finally an economic feasibility study was carried out. This involved estimation of capital costs, operating costs, cost of end-product, and a cost comparison with existing; competing products,