Textile bioreactor for ethanol production

Problem statement: To achieve optimal production, optimal process conditions needs to be used. However, this increases the cost of fermentation. How can a bioreactor be developed to produce at optimal levels under suboptimal conditions with a substantial reduction of the fermentation cost. Purpose: Designing and developing the bioreactor features like temperature control, mixing, aeration, charging in and transfer out, and appropriate biomass contacting pattern within the textile bioreactor, with the overall goal of optimal productivity with substantial savings in the fermentation cost. Methods: A 30 L prototype of the textile bioreactor, with a working volume of 25 L was worked on. Temperature was controlled by a PVC tubing and a thermostatic circulator. Mixing and aeration control was achieved by using silicone tubing. Fermentation experiments with yeast as biomass were performed using temperature (30 °C to room temperature of 22 °C), mixing (with and without mixing), and flowrates (1.5 L/min – 0.04 L/min) as process variables. Results: No bacteria contamination was observed in all experiments performed. Optimum fermentation time of 15 h and ethanol yield of 0.48 ± 0.01 g/g sucrose was gotten from experiments performed at 30 °C with mixing and a flowrate of 0.92 L/min. Experiments done without mixing and at room temperature had the longest fermentation time of 42 h and an ethanol yield of 0.49 ± 0.02 g/g sucrose. Temperature was found to be the process variable with the highest impact on the fermentation rate. The specific productivity reduced from 1.34 ± 0.02 g L −1 h −1 under optimal temperature and mixing conditions to 0.53 ± 0.02 g L −1 h −1 at room temperature without mixing. The same optimal ethanol production rate can be gotten under sub optimal production conditions. At room temperature and without mixing, using a bioreactor volume 2.53 times the volume of that used with optimal temperature and mixing would give the same optimal productivity. This can reduce the fermentation investment cost of a 100,000 m3/y ethanol production facility by 26 %. While using a 1300 m3 textile bioreactor in place of a stainless steel reactor in this plant can reduce the fermentation cost by 19 %. Conclusion: 26 % investment cost reduction, and optimal ethanol production can be achieved under sub optimal conditions by using appropriate volume of the textile bioreactor.