Improvement of Biogas and Ethanol Production from Safflower Straw Using Sodium Hydroxide Pretreatment

Safflower straw is one of the agricultural residues that currently have no specific use. So, it can be used as a cheap source for biofuel production.
Alkaline pretreatment with NaOH was used to improve enzymatic hydrolysis, ethanol, and biogas production from safflower straw. The pretreatment was performed with 8% (w/v) NaOH solution at two different temperatures (0 and 100 °C) for 10-60 min. The liquid fraction of the pretreatment was subjected to anaerobic digestion for methane production. Solid fraction obtained from the pretreatments was used for bioethanol and biogas production in a parallel process. Therefore, two routes were followed for energy production from safflower straw: (1) ethanol production from solid fraction (2) biogas production from liquid fraction. In order to optimize the production of biofuels and compare different pretreatment conditions, the gasoline equivalents were calculated based on one tone of safflower straw after all pretreatment conditions. Statistical validation of the results was carried out using Minitab 16 software.
The highest glucose and ethanol production yields were obtained after the pretreatment at 100°C for 60 min. The glucose yield from untreated straw was only 20.6% and improved to 84.5%, whereas the corresponding ethanol yield was improved from 10.8% to 83.2%. The best improvement in methane production from solid fraction was achieved by pretreatment at 0 °C for 60 min, and resulted in 191.4 ml/g VS which was 99.6% higher than methane yield obtained from untreated straw. The highest gasoline equivalent was 124.9 L obtained after pretreatment at 0 oC for 60 min.
Discussion and Enzymatic hydrolysis and ethanol yields from the safflower straw were improved more by the pretreatment at high temperature. However, low temperature is desirable for methane production.