Exploration of algal biorefinery frameworks: Optimization, quantification of environmental impacts and economics

Abstract

The integrated algal biorefinery (IABR) was considered as a feasible alternative to fossil fuels. After the processes of algae cultivation and pretreatment, the algae biomass with different carbohydrate/lipid contents is split into the carbohydrate process for producing fuel/chemicals and the oil process for producing fuel/energy. Four frameworks of IABR are presented: (i) Scenario 1 (SC1) is designed to produce lactic acid/biodiesel, (ii) Scenario 2 (SC2) is an extension of SC1 by increasing the production of biooil, (iii) Scenario 3 (SC3) is an extension of SC2 by adding the combined heat and power (CHP) process, and (iv) Scenario 4 (SC4) is an extension of SC3 by increasing the production of acetone, butanol, and ethanol (ABE). Through sensitivity analysis of environmental impacts and economics to assess the influences of parameters of four scenarios, it shows that (i) SC1 ensures the lower total eCO2 emission than other scenarios, (ii) SC3 with the low carbohydrate content and the low percentage of carbohydrate process could suppress eCO2 emission, (iii) SC3 with the high lipid content and the low percentage of carbohydrate process has the higher total profit than SC2 due to the extra green electricity from CHP for sale. To address an IABR with high economic potential and low environmental impact, the process optimization of SC4 under prescribed algae carbohydrate/lipid contents shows that (i) the total profit of SC4 is higher than SC3 by 81.8 % and (ii) the eCO2 emission of SC4 is lower than SC3 by 51.9 %.