Giant reed from wetlands as a potential resource for biomethane production

This study aimed to evaluate the potential and the use of the natural and treatment wetland biomass for local energy production. Specifically, it was addressed by determining the giant reed (Arundo donax L.) Biochemical Methane Potential at different harvest times, since plant characteristics vary noticeably along the growing season. In the last decades, this perennial rhizomatous grass has achieved great success in the renewable energy market to produce biogas through the anaerobic digestion process, because is a non-food crop with high biomass yield (about 35 Mg dry matter per hectare) and low input required for its growth. Several studies showed that the harvest time, in relation to the stage of the plant development, significantly affect the Biochemical Methane Potential. Moreover, it is well known that giant reed presents feature comparable in terms of biomass yield and physicochemical composition both in natural and treatment wetland systems. Anaerobic digestion laboratory tests were carried out to assess biomethane production from aerial biomass samples collected from July to November 2021. The average biogas production for the five different harvest times was of 312.77 Nm3/tVS (+/- 62.87), and the mean methane content was equal to 187.06 Nm3 CH4/tVS (+/- 38.32). The gas quality at the end of the Biochemical Methane Potential test displayed average contents of methane of 58.88% (+/- 5.06) and CO2 of 18.54% (+/- 7.91) and mean sulfides content of 112.10 ppm (+/- 103.61). The results highlighted that giant reed has a high energy returned on energy invested (EROEI) value. The research activity allowed to identify the harvest time associated with the highest Biochemical Methane Potential and biomethane production per hectare. Finally, the experimental results achieved in riverbank conditions could be applied to treatment wetland systems increasing their environmental sustainability and reducing their maintenance costs.