초록
Economic evaluation of a membrane-integrated bioreactor system for lactic acid production from sugarcane juice was performed. The production process consisted of sterilization, fermentation, microfiltration, nanofiltration and final concentration by vacuum evaporation. Membrane recycle fermentor operating at a cell concentration of 22g/L resulted in a productivity of 53g/Lh with a lactic acid concentration of 106g/L and a yield of 0.96. The membrane units (cross-flow microfiltration and nanofiltration) and pump contribute about 2% to the total fixed capital cost whereas fermentation unit along with holding tank contribute about 36% to the total fixed capital cost. The two largest cost components were raw material and yeast extract costs contributing about 6% and 87% respectively to the total operating cost. Total product cost stood at 3.15 US $/kg of 80% (w/w) concentrated and 95% pure lactic acid. The study reveals that operating cost could be reduced further by using a cheaper nitrogen source like silk worm larvae or yeast autolysate and installing the lactic acid plant in the sugarcane-growing areas or by optimizing the recycle of nanofiltration retentate to the fermentor.