Wetlands as biomass producer

Wetlands constructed in the agricultural landscape have long been used as nutrient traps for nitrogen and phosphorous losses in run-off water from agricultural soils. The removal of these nutrients from surface water is an important measure to decrease effects of eutrophication in waterways and along coasts. However, nutrient-rich biomass from wetland plants is seldom utilized. In especially designed production wetlands the biomass can be harvested with ordinary agricultural machinery and then used, e.g. to produce biogas and a nutrient-rich digestate. Spreading the digestate as fertilizer on arable land can contribute to closing the nutrient cycle.

In this study, common reed (Phragmites australis) planted in experimental production wetlands was used as model plant to study the amount of nutrients removed from inflowing water. For this purpose, both water and biomass analyses were carried out to investigate the effect of nutrient removal from the water and the subsequent nutrient removal due to biomass harvest and recovery.

Results showed that harvest and removal of plant biomass containing plant nutrients substantially increased nitrogen and phosphorus removal rates for wetlands planted with common reed compared to non-vegetated wetlands. Common reed harvested in the middle of August had high biomass yields and the biomass showed low C/N ratios, which can be of advantage for anaerobic degradation. In conclusion, common reed grown in constructed wetlands can be a suitable feedstock for biogas production.

The project is funded by Partnerskap Alnarp and the municipality of Trelleborg

Duration of the project: 2015-2016

Project Leader: Thomas Prade
Other contributors: Linda Tufvesson

Publications:
Factsheet (in Swedish) - Skördad våtmarksvegetation renar vattnet bättre från närsalter!