Ethanol production from xerophilic and salt-resistant Tamarix jordanis biomass

• Tamarix spp. biomass production in desert areas ranged from 18 to 36 Mg ha−1.
• T. jordanis exhibited the highest cellulose mass fraction (45%).
• Ethanol production yield in repeated batches was close to the theoretical value.
• Biomass pretreatments and fermentation led to circa 114 kg ethanol Mg−1.

Three different Tamarix species, namely Tamarix aphylla, T. aphylla “Erect”-type and Tamarix jordanis, were grown in an experimental field under extreme desert conditions and irrigated with either reclaimed sewage or brackish water. Depending on both species and source of irrigation, the above-ground biomass production ranged from 18 to 36 Mg ha−1 in the first year. Among the three chemically characterized Tamarix species, T. jordanis was selected due to its higher cellulose content, and lower hemicellulose and phenol contents so as to outline a preliminary process flow sheet for ethanol production. This included steam-injection heating under acidic conditions (200 °C; 90 s; 0.5% H2SO4; 160 g L−1 solid loading) using a novel lab-scale Direct Steam Injection Apparatus, enzymatic saccharification (50 °C; pH 5.0; 200 g L−1 solid loading; 20 FPU g−1 cellulose) and subsequent ethanolic fermentation (30 °C; Saccharomyces cerevisiae F-15 as the inoculum). Lab-scale fermentation runs were carried out in a 3-L stirred bioreactor in repeated-batch mode and showed an almost quantitative conversion of glucose into ethanol (0.507 ± 0.006 g g−1), thus leading to a satisfactory overall process ethanol yield of about 145 L Mg−1Tamarix biomass.