Wetland biomass - suitable for biogas production?

Abstract

Wetlands have long been used as natural waste water treatment systems to remove excess nutrients from agriculture or other waste waters. Common reed (Phragmites australis) is the most prominent feature of wetlands in Sweden. This wetland vegetation needs to be harvested and can be used as substrate for biofuel production. In this study, common reed and submerged vegetation from two wetlands outside Halmstad have been harvested in August and October and have been used as substrate for anaerobic digestion in a laboratory experiment. August harvested common reed produced on average 147 ml CH4/g VS, October harvested common reed produced 150 ml CH4/g VS while August harvested free floating vegetation produced 130 ml CH4/g VS. Similar methane production was seen from reed harvested in August and reed harvested in October, but the dry weight of October harvested reed is much higher indicating that harvesting in October can be beneficial not only because of more biogas production but also because a late harvest reduces the amount of biomass to be harvested and transported. Apart from that harvesting in October will not affect the migratory birds which use wetlands as resting place during autumn migration.