Energy potential for combustion and anaerobic digestion of biomass from Low-Input High-Diversity systems in conservation areas

In this study, we assessed the potential for bioenergy production of Low-Input High-Diversity (LIHD) systems in temperate West-European conservation areas. A wide range of semi-natural ecosystems (wet and dry grasslands, marshes, tall-herb vegetation and heathlands) was sampled. Because LIHD biomass is often scattered and discontinuously available, we only considered the potential for anaerobic digestion and combustion. Both technologies are suitable for decentralized biomass utilization. The gross energy yield showed a promising range between 46-277 GJ per hectare per mowing cycle (MC). The energy efficiency of the anaerobic digestion process was rather low (10-30%) with a methane energy yield of 5.5-35.5 GJ ha−1 MC−1, experimentally determined by batch digestion tests. The water content, functional group composition and biochemical composition (hemicellulose, cellulose, lignin and Kjeldahl-nitrogen) of the biomass were analyzed to assess the suitability of different valorization pathways. Based on the results, we were able to propose recommendations regarding the appropriate conversion techniques. Biomass from plant communities with ‘late’ harvest dates (August-October) or a high fraction of woody species like heathland and dune slacks, is best valorized through combustion, while herbaceous biomass of ‘early’ harvested grasslands (June-July) and tall-herb vegetation can better be digested. The main advantages of the production of bioenergy from LIHD biomass originating from conservation management are the minimization of the competition with food production and its potential to reconcile renewable energy policies and biodiversity goals.status: publishe