Factors Affecting Methane Production from Energy Crops and Crop Residues

Transcription

1 VIII Latin American Workshop and Symposium on Anaerobic Digestion Punta del Este, Uruguay, October 2005 Factors Affecting Methane Production from Energy Crops and Crop Residues Annimari Lehtomäki, Outi Ronkainen, Jukka Rintala Dept.. of Biological and Environmental Science Taina Viinikainen, Raimo Alen Dept. Of Chemistry University of Jyväskyl skylä Finland

2 Energy crops Abundant producers of biomass with modest production inputs Consume atmospheric CO 2 during growth => no net CO 2 release Increasing interest in the European Union as set aside land becomes available for cultivation

3 Methane from Energy Crops Selection of Crop Crop Cultivation Harvest Time Methane Heat Electricity Vehicle Fuel Harvesting Size Reduction Pre- Treatment (1) Storage - Silage - Dry Storage Pre- Treatment (2) Biogas Production Storage of Digestate, Post-Gasification Post- Treatment Digestate

4 Selection of crops for methane production Main criteria for selection of boreal energy crops: High energy yields with low cultivation inputs Rapid growth, high biomass yields Easy to cultivate, harvest and store As modest and tolerant as possible Good over-wintering ability Convertibility to methane

5 Screening potential boreal energy crops and crop residues for methane production Methane production potentials of potential boreal energy crops and crop residues 400 inoculum straw of oats grass hay sugar beet tops Cum.mlCH4/gVS Time (d)

6 Examples of methane production potentials Substrate Methane production potential Rhubarb Reed canary grass Nettle Jerusalem artichoke Timothy-clover grass Lupine Tops of sugar beet Straw of oats Red clover m 3 CH 4 / kg VS m 3 CH 4 / t ww

7 Methane and Gross Energy Yields per Hectare Substrate Jerusalem artichoke Yield (t TS /ha) 9-16 Methane yield (m 3 CH 4 /ha) Energy (MWh/ha) Passenger car transport (km/ha) Reed canary grass Timothy-clover grass Straw of oats

8 How to improve methane yield from a specific crop? Timing of harvest - age and maturity of plant at harvest Storage Pre-treatment

9 Timing of harvest Substrate Harvest Methane production potential m 3 CH 4 / kg VS m 3 CH 4 / t ww Reed canary grass Timothy-clover grass Jerusalem artichoke

10 Storage Traditional methods: drying, ensiling Ensiling: soluble carbohydrates contained in plant matter undergo lactic acid fermentation ph drop Inhibition of growth of detrimental microorganisms The process can be controlled by Preventing the growth of all micro-organisms (e.g. acids) Stimulating the growth of lactic acid bacteria (e.g. bacterial inoculum or enzymes)

11 Storage trials Objective: to determine the optimal method for ensiling grass for methane production Storage as silage with and without additives formic acid, enzymes, lactic acid bacteria, mixed culture taken from a farm biogas reactor Storage for 3 and 6 months in laboratory silos Substrate: timothy-clover grass

12 Results Storage without additives led to losses of % in methane potential. Ensiling with additives was shown to have potential in improving the methane yield of grass. Most efficient being storage with formic acid After storage with formic acid, the methane potential of grass was % higher compared with fresh grass and up to 86 % higher compared with grass stored without additives.

13 Pre-treatment of energy crops Increasing available surface area Breaking polymeric chains to more easily accessible soluble compounds Promoting subsequent biodegradation Physical Chemical Biological

14 Pre-treatment trials Physical autoclaving, pre-incubation in water Biological enzymes, composting, white-rot fungi Chemical alkalis (NaOH,, Ca(OH) 2 +Na 2 CO 3 ), peracetic acid Substrate: timothy-clover grass

15 Results Alkali treatments (NaOH, Ca(OH) 2 +Na 2 CO 3 ) 15 % increase in CH 4 yields Physical, biological, peracetic acid treatment High losses of organic matter No increase in methane yield

16 Theoretical Methane Potentials Crop Biomass yield Methane potential t TS /ha Fresh crop m 3 / t ww m 3 /ha After pre- treatment m 3 / t ww m 3 /ha After storage and pre-treatment m 3 / t ww m 3 /ha Timothy- clover grass Reed canary grass Jerusalem artichoke

17 Thank You for Your Attention!