Anaerobic digestion of wetland biomass from conservation management for biogas production

Abstract

In this study, we examined the biogas and methane production of wetland plants species harvested in the Narew River Valley protected as national park, NE Poland. In the experiment, we used the aboveground biomass of five species: reed canary grass (Phalaris arundinacea), common reed (Phragmites australis), reed sweet-grass (Glyceria maxima), tufted sedge (Carex elata) and woollyfruit sedge (Carex lasiocarpa). The plants were harvested in three seasons of the year 2015: mid-summer, late summer, and early fall.The chemical composition of wetland plants was not beneficial for the anaerobic digestion, because of the sub-optimal C:N ratio. Consequently, the wetland species exhibited rather average methane production (102–221 NL kg−1 VS). These values were similar to that observed for grasses collected in extensive grasslands and wetlands by other researchers. They were, however, much lower than those obtained for species harvested in cultivated grasslands. Methane and gross energy yield differed significantly (p < 0.05) depending on the season of the biomass cut. The optimal period for the harvest of wetland biomass for biogas generation was the middle of summer, July–August.Phragmites australis appeared to be the most promising energy species. Despite the low methane yield per kg VS, common reed, due to its high aboveground biomass, achieved quite high methane production per area (1,16·106 NL CH4 ha−1). Our findings suggest that biomass of reed rushes can provide a substantial source of renewable energy used for biogas generation, which will make possible economic exploitation of wetlands combined with the conservation of their natural functions and services.