The importance of green technologies is steadily growing. Salt-tolerant plants have been proposed as energy crops for cultivation on saline lands. Halophytes such as Salicornia europaea, Tripolium pannonicum, Crithmum maritimum and Chenopodium quinoa, among many other species, can be cultivated in saline lands, in coastal areas or for treating saline wastewater, and the biomass might be used for biogas production as an integrated process of biorefining. However, halophytes have different salt tolerance mechanisms, including compartmentalization of salt in the vacuole, leading to an increase of sodium in the plant tissues. The sodium content of halophytes may have an adverse effect on the anaerobic digestion process, which needs adjustments to achieve stable and efficient conversion of the halophytes into biogas. This review gives an overview of the specificities of halophytes that needs to be accounted for using their biomass as feedstocks for biogas plants in order to expand renewable energy production. First, the different physiological mechanisms of halophytes to grow under saline conditions are described, which lead to the characteristic composition of the halophyte biomass, which may influence the biogas production. Next, possible mechanisms to avoid negative effects on the anaerobic digestion process are described, with an overview of full-scale applications. Taking all these aspects into account, halophyte plants have a great potential for biogas and methane production with yields similar to those produced by other energy crops and the simultaneous benefit of utilization of saline soils.

The halophyte plant species Salicornia europaea and Salicornia ramosissima were investigated for their potential to serve as a substrate for biogas production. Salicornia europaea was cultivated in hydroponic systems under varying salt concentrations (0, 10, 20, and 30 g/L NaCl), while S. ramosissima was grown in greenhouse farming with aquaculture effluent irrigation. The biomethane potential of the two halophyte feedstocks was determined through batch experiments, and correlations to the plant biochemical composition were investigated. Ash and mineral content of S. europaea was correlated to the increasing salt concentration used for plant cultivation in hydroponic systems. No indication of inhibition of the anaerobic digestion process was detected for sodium concentrations of up to 2400 mg/L in the anaerobic batch-test assays. The highest biomethane yield of S. europaea of 250 mL CH4/gVS was obtained when grown under 20 g/L NaCl and up to 300 mL CH4/gVS for S. ramosissima. By concentrating the dry matter content, the biomethane yield per ton of feedstock could be increased from 24 m3 CH4/t of the fresh halophyte plant to 74 m3 CH4/t by fractionation into a pulp fraction and to 149 m3 CH4/t by drying of the plant at room temperature for 1 week.

Readily available lignocellulosic biomass as substrate for biogas plants is gaining popularity amongst biogas plant operators. Results of low‐temperature pretreatment (light cooking) of wheat straw to remove waxes and prepare the biomass for microbial action are described. Benefits of light cooking are low thermal energy demand and low investment cost compared to conventional techniques such as steam explosion. The novelty lies in utilizing the low temperature range 25–100 °C for pre‐soaking the biomass. Two different types of wheat straws were pretreated at varying temperatures and sizes. The results were compared with Buswell's equation for theoretical maximum biomethane yield. Compared to untreated straw, pre‐soaking leads to a significantly higher methane yield. Size reduction combined with light‐cooking does not affect the methane yield in the same manner as pre‐soaking of the biomass.