2.3. Energy efficiency analysis
To evaluate the life CD 2314 energy efficiency of bioethanol produced from sweet sorghum stem on saline–alkali land, net energy ratio (NER) and net energy gain (NEG) as two key indicators were calculated in accordance with the method described by Papong and Malakul (2010):equation(1)NER=EO/PEINER=EO/PEIequation(2)NEG=EO–PEINEG=EO–PEIwhere EO is the lower heating value of 1 L of bioethanol, and PEI is the total amount of primary energy inputs required to produce 1 L of bioethanol. PEI was calculated as the sum of the primary energy input per FU in each unit. PEI included not only the direct energy consumed, such as coal, natural gas, diesel and electricity, but also the indirect energy consumed during the production of fertilizers, pesticides, H2SO4, NaOH, enzymes, and yeast.
2.4. Life cycle impact assessment (LCIA)
LCIA was performed in this study to further interpret the LCI data through characterization and normalization.