1. Anaerobic digestion of crop residues at low temperatures Irene Bohn LUND UNIVERSITY Department of Biotechnology

2. Lund University, Department of Biotechnology Background Digestion of manure on the farm Degradation of low strength wastewaters + high strength wastewaters Post digestion or storage Low temperature digestion: Is low-temperature digestion of crop residues feasible?

3. Lund University, Department of Biotechnology Motivation ? Nordberg et al. 1998. Biogaspotential och framtida anläggningar i Sverige. Kretslopp och avfall No 17, JTI, VBB Viak, Uppsala. The Swedish Biogas Association, 2001. Swedish Biogas production 2001.

4. Lund University, Department of Biotechnology Reactor types Commercially available reactor High Low Modified manure tank Low High Cost Capacity vs. volume Heat loss

5. Lund University, Department of Biotechnology Inoculum: Digested cow manure from unheated anaerobic digestion tank Total volume:2.2 m 3 Active volume: 1.8m 3 Digester set-up Kg Substrate: Ensiled sugar beet tops and straw 4.5 % volatile solids in ready substrate

6. Lund University, Department of Biotechnology Effect of temperature on yield Loading rate: 0.5 kg VS m -3 d -1 and hydraulic retention time: 90 days Methane yield decreased with decreasing temperature but no VFAs accumulated at the high hydraulic retention time Hydrolysis was limiting the methane yield

7. Lund University, Department of Biotechnology Yield and rate Methane production rate Methane yield

8. Lund University, Department of Biotechnology Stirrer Heating-substrate Heating-reactor Substrate Gas Energy-balance 15  C 30  C

9. Lund University, Department of Biotechnology Stirrer Heating-substrate Heating-reactor Substrate Gas Energy-balance 15  C 30  C

10. Lund University, Department of Biotechnology Yield obtained in batch-experiments The effect of temperature on yield was lower for the sludge adapted to 15  C 28 21 23 The yield in the batch-experiment was higher than in the reactor

11. Lund University, Department of Biotechnology Accumulation of acetate and propionate Acetic acid Propionic acid Butyric acid Valeric acid OLR in kg VS m -3 day Results from continuously stirred pilot scale reactors fed with beet top slurry 30  C15  C

12. Lund University, Department of Biotechnology Packed-bed methane-filters Inoculum: Sludge from pilot-scale reactors or lake sediment Substrate: Leachate from ley-crop silage

13. Lund University, Department of Biotechnology Results from methane-filters Acetic acid Propionic acid OLR in kgCOD m -3 day 10  C 15  C During start-up: After 1 year:

14. Lund University, Department of Biotechnology Acetate Propionate other VFAs Unidentified CH4 produced Lake sediment Reactor sludge 15  C 10  C Results from methane-filters

15. Lund University, Department of Biotechnology Results from methane-filters

16. Lund University, Department of Biotechnology Yield from solid substrate decreases with temperature Feasibility of low temperature digestion depends on insulation of the reactor utilization of the capacity High yield is obtained for soluble substrate at 10°C Conclusions

17. Lund University, Department of Biotechnology Acknowledgements Financiation: The Energy Supply Comittee of Southern Sweden (DESS) The Swedish Research Council (VR) The Swedish Energy Agency (STEM) Co-authors: Bo Mattiasson Lovisa Björnsson Andreas Bengtsson Melvice Bessem Ayuk