Effects of residence time on life cycle assessment of bioenergy production from dairy manure

This study simulated the effect of time on bioenergy production from dairy manure and associated variation in energy demand and GHG emission in Ohio and Hawaii. Increasing the residence-time (RT) decreases the bioenergy-production in a nonlinear-fashion, for both the states (Ohio and Hawaii). Using the main scenario in Hawaii, the highest bioenergy production for 30 days RT was 11.2 × 104 GJ. Life-cycle-assessment of produced bioenergy showed that energy requirement and GHG emission of the produced-bioenergy (GJ) varied from 0.65 to 0.67 and 28-35 kg CO2/GJ bioenergy respectively. Year-round bioenergy production through main scenario was more advantageous with respect to bioenergy production and GHG emission. Decreasing nitrogen concentration for algal biomass production increased the bioenergy production significantly with a reduced energy demand and marginally increased GHG emission. Hence, the LCA model predicted that running a biorefinery for short residence time, and using diluted waste, could provide bioenergy with reduced energy requirement and GHG-emission.