Sustainable coastal halophyte farming for biofuel in arid regions: site and feedwater screening using geochemical modeling

Halophyte agriculture in marginal soils using saline water offers a sustainable solution for generating biomass feedstock for carbon-neutral aviation biofuels. A full-scale sustainable energy and agriculture system (SEAS) demonstration is planned for the Abu Dhabi coast, where evaporitic gypsiferous soils pose a challenge to long-term operation because of the potential for land degradation. In this study, geochemical modeling on the Geochemist’s Work Bench (GWB^®) platform was employed to (1) evaluate the feasibility of using coastal groundwater versus seawater as irrigation feedwater, (2) determine the change in agricultural return water salinity through site-specific soils upon different seawater irrigation rates, and (3) assess mineral deposition effects in the soil column as a function of site-specific soil characteristics at candidate sites over a 1-year period of continuous seawater irrigation. Evaporation modeling was used to evaluate potential feedwater sources while varying feedwater composition and electrolyte activity coefficient models. 1-D saturated–flow advection–precipitation/dissolution modeling was utilized to assess return water quality and mineral deposition as a function of both the electrolyte activity coefficient model and the mineral composition of site-specific soils. Results pointed to seawater as the more viable feedwater option compared to coastal groundwater because of slower onset of precipitation. This effort demonstrated that soil type did not influence agricultural return water salinity (except for strongly gypsic soils) but influenced mineral precipitation under surficial evaporation conditions. Porosity loss correlated with layers of mineral deposition. The study points to the need for careful screening of land and saline water resources for the sustainable farming of halophytes.