Anaerobic digestion of waste Tunisian date (Phoenix dactylifera L.): effect of biochemical composition of pulp and seeds from six varieties.

Large amounts of secondary date waste (pulp and seeds) are produced and discarded in Tunisia without proper valorisation methods. To study the possibility of valorising different varieties of Tunisian date waste (pulp and seeds) via anaerobic digestion, batch biochemical methane potential (BMP) tests were carried out under mesophilic temperature. The bio-methane production curves were fitted to the model of modified Gompertz in search of the kinetic parameters. The bio-chemical characterisation of the substrates from different varieties (total and volatile solids, COD and contents in carbohydrates, proteins, lipids, polyphenols) was realised. Principal component analysis (PCA) was used to investigate the correlations between the model parameters and biochemical variables. Results show that the biochemical compositions of date pulp and seeds strongly depend on the varieties. The BMP are in the range of 0.295-0.345 and 0.267-0.327 Nm3 CH4·kg COD-1 for pulp and seeds respectively, resulting from the significant biochemical variance among the varieties. The BMP of date seeds was significantly correlated with their VS/TS ratio, carbohydrate and protein contents (p < 0.05). For the pulp, significant correlation was found between BMP, carbohydrate and lipid contents. PCA shows that certain varieties (like pulp and seeds of Deglet Nour and seeds of Bejou) are most suitable for being valorised by anaerobic digestion. The most suitable date varieties for this innovative approach were revealed. This research provided useful knowledge for bioconversion of waste date pulp and seeds to biomass energy.

The validity of carbon isotope discrimination as a screening criterion for grain yield in two barley landraces under deficit irrigation with saline water in southern Tunisia.

Arid and semiarid regions with rain shortage and scarce good quality water must make use of low-quality water for irrigation. Consequently, improved plant cultivars for use in these areas should show adaptation capacities to confer drought and salt resistance and allow the cultivation under limited water availabiltiy. The present study was conducted to determine the effect of deficit irrigation with saline water on two local barley landraces, "Karkeni" and "Bengardeni". Plants were saline-irrigated with three watering regimes during tillering, heading, and grain filling stages. Biochemical traits, carbon isotope discrimination (Δ13C), mineral composition, grain yield (GY) and water use efficiency based on grain yield (WUEgy) were evaluated as performance indicators. Almost all of the studied traits (e.g. soluble carbohydrates, proline, ∆13C, Na concentration, and GY) were significantly affected by deficient saline-irrigation regimes at different growth stages. The hierarchical clustering analysis clearly showed that Δ13C placed very close to GY averaging two barley landraces, which was in accordance with the scatter plot result. Multiple linear regression performed between GY as the dependent variable and other traits studied as the independent variables indicated that WUEgy, Δ13C, and soluble carbohydrates significantly explained the variability in GY (R 2=95.64%). A significant positive correlation that observed between ∆13C and GY at three growth stages, indicated that ∆13C may be an important proxy component for indirect selection of yield potential in barley under deficient irrigation regimes with saline water. According to our result, "Karkeni" seems to be more efficient in terms of higher GY, WUEgy, proline and carbohydrate contents, K, Mg and Zn concentrations, as well as lower Δ13C and lipid peroxidation as compared with "Bengardeni", under low osmotic potential imposed by deficient irrigation treatments with saline water, "Karkeni" can thus be selected and used as a parent in order to obtain more tolerant plants against such stresses in future breeding programs.