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The effect of organosolv pretreatment on the structure of rice straw was analyzed under different treatment severities and solvent concentrations. At higher severities, on account of a greater fragmentation of less crystalline parts, including amorphous cellulose, hemicellulose, and lignin, the severer the pretreatment was, the higher the crystallinity index became; however, changes in the index was less tangible with a severity factor lower than 3.3. At the low to mild pretreatment temperatures (120 °C and 150 °C), higher ethanol concentrations led to the lower crystallinity index. Despite an increasing trend of crystallinity index at harsh conditions, SEM images indicated the formation of spherical droplets and pores on the treated rice straw, which is symptomatic of improved hydrolysis yields. A more detailed scrutiny of the flux patterns for the anaerobic metabolism of E. aerogenes revealed that the increase in both simple (glucose from 3 to 60 g l−1) and more complex (rice straw from 3.33 to 33.33 g l−1) substrate concentrations resulted in a lower hydrogen yield (54% and 77% reductions). Nonetheless, techno-economic assessments should be conducted to determine the optimum concentration. A preliminary economic evaluation of a simulated biorefinery showed due to the larger vessels and equipment, when the rice straw concentration in hydrolysis step decreased from 50 to 3.33 g l−1, the fixed capital investment sharply ascended by approximately 980% and, in contrast, the unit production cost decreased by 78%.

This study aims to construct a quantitative framework to assess biological production of hydrogen from agricultural residues in a country or region. The presented model is able to determine proper crops for biohydrogen production, its possible applications and use as well as environmental aspects. A multiplicative decomposition method was designed to forecast future production and Monte Carlo simulation was employed in the model to evaluate the risk of estimations. From 2013 to 2050, the hydrogen production capacity could increase from 53.59 to 164.41 kilotonnes (kt) in Iran. The highest contribution to biohydrogen production (52.1% in 2013 and 73.3% in 2050) belongs to cereal crops including wheat, barley, rice and corn and the share of horticultural products including apples, grapes and dates is the lowest (2.7% in 2013 and 2.2% in 2050). For possible variations in the quantity of collectable residue and biohydrogen yield, the production may change in the range of 40.16% and 209.48% of the base value in 2013 and 41.64% and 233.18% of that in 2050. Ammonia production as nitrogen fertilizer and the area could be cultivated by that for each crop were calculated. The amount of natural gas saving and reduction in greenhouse gas (GHG) emissions using biohydrogen were discussed. Development of hydrogen fuel cell vehicles and their impacts on the environment and consequent social costs as well as the quantity of gasoline would be saved were estimated by 2050.