Halophyte Biomass - a Promising Source of Renewable Energy
Halophytes are suggested as energy crops in arid saline lands. Anaerobic digestion of 7 halophytes collected in the Kyzylkum desert (Uzbekistan) were studied in batch-mode tests in mesophilic (35°C) and thermophilic (55°C) conditions with stirring and F/M=0.2. Obtained results showed that halophytic biomass should be considered as a valuable renewable source of biogas. Though high mineral content was detected in the biomass (i.e., Na+, K+, Cl- and SO4 2-), total biogas yields in results of anaerobic degradation were about 200-400 mL (at 35°C) and 300-500 mL (at 55°C) from 1 gDM (with 60% of methane-gas). Total organic matter and organic carbon (OC) concentrations were determined to investigate plant biomass. Organic matter concentrations were between 736-900 mg VS/gDM. The highest organic carbon content found in biomass of Suaeda paradoxa, Atriplex nitens, Karelinia caspia and conventional grass Cynodon dactylon were 243.9, 337.6, 394 and 396 mg OC/gDM, respectively. Low OC content (about 200 mgOC/gDM) was measured in biomasses of Salicornia, Halostachys and Climacoptera. Results indicated that 40-60% of total organic matter in halophyte biomass can be decomposed into biogas. The highest yield of approximately 300-500 m3 of biogas from 1 t DM could be produced from Atriplex nitens, Karelinia caspia, Suaeda paradoxa and Cynodon dactylon. After considering annual biomass yield of the studied plants, their current use, and biogas generation measured in the laboratory, Karelinia caspia (wild associations or cultivated plantations) is recommended as one of the most promising renewable sources for biogas production in desert salt-affected areas of Central Asia.