1. Co-digestion of manure with straw and perennial grasses Henrik Bjarne Møller, Department of Engineering, Aarhus University, Denmark

2. Straw and perennial grass for biogas Why use straw and perennial grass?  Biogas plants miss high value substrates for biogas production as co-substrates for livestock manure - crops should be phased out.  Straw is the agricultural by-product with the highest energy potential.  Recycle nutrients from uncultivated meadows to organic arable land.  Harvest of meadows has a number of positive side effects What conditions must be met?  There must be a positive economy and in the short term the economy must be in line with corn.  Biogas technology should be optimized to handled and convert the biomass

3. Biogas research plant Fullscale plant 1,200 m3 digester, 22,000 tonnes manure) 4,100 tonnes straw, Grass and maize Research plant 2 x 30m 3 CSTR pilot digesters 2 x 10m 3 CSTR pilot digesters Gas upgrading Fullscale pre-treatment Extruder Briquetting >1.7 mill. m3 biogas 3,223 MWh el 6,200 MWh heat Solid feeding

4. Handling and pre-treatment of grass/straw at Foulum Storage Pre-treatment Digestion Feeding Dry-line (>80% DM) Wet-line (20-80% DM)

5. Transition from maize to fiber rich material In warm periods dosing of solid material is reduced due to lack of gas sale

6. Biomass – Foulum biogas plant

7. cellulose Lignin hemicellulose Pre-treatment of ligno-cellulose - why? Improvement  Lowering of viscosity and mixing ability  Higher methane yield Drawbacks  Higher energy demand  Investment and running costs

8. Types of pre-treatment of ligno- cellulose - why? Untreated Macerated Extrudation Briquetting

9. Gas potentials of straw/grass – effect of briqueting/extrudation 9

10. Gas potentials – effect of briqueting and chemicals 10

11. Pre-treatment – Energy demand 11 Energy consumption Mixing/dosingExtrudation Bale openerHammermillBriquetting

12. Energy balances by pre-treatment 12

13. Economy

15. Experiments with co-digestion of straw Volume: 15 L Temperature: 49±1 o C Stirring: 100 rpm HRT: 20 days 30 m 3 Temperature : 50 o C HRT: 25 days Briqueting of straw

16. Thermophilic co-digestion of straw influence of sulfur in gas Addition of 8,3% wheat straw reduce sulphur to 25% of original

17. Co-digestion of straw influence of hydraulic retention time + 30% ThermophilicThermophilic/mesophilic If retention time should be prolonged mesophilic conditions is sufficient + 30%

18. Foulum biogas plant – primary and post digestion Thermophilic 53 o C HRT=13 days Mesophilic 25- 30 o C HRT=40 days Psycrophilic 10-20 o C HRT=40 days Psycrophilic 0-20 o C HRT=100 days 0,5-5 m3/ton + 37% Thermophilic Thermophilic/mesophilic

19. Conclusion Straw can succesfully be used for co-digestion of straw and manure, pre-treatment can enhance the yield. The increased yield depends on technology and retention time in the biogasplant. With short retention time, post digestion is recomended Mechanical and chemical pre-treatment can be combined with briquetting technology Foulum biogas plant has been through a succesfull transition from high value energy crops to straw Straw reduces sulphur in the gas significantly

20. 20 Thanks for your attention