SENSE AND NO-SENSE OF PRETREATMENT FOR INCREASING BIOGAS YIELDS

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1 SENSE AND NO-SENSE OF PRETREATMENT FOR INCREASING BIOGAS YIELDS HINRICH UELLENDAHL S E C T I ON F OR SUSTAINABLE B I OTECHNOLOGY AAL B O R G U N I V E R SITY COPENHAGEN A. C. M E Y E R S V Æ N G E 1 5, C O P E N H A G E N H B I O. A A U. D K, PH

2 Pretreatment for increasing biogas production Overview Lignocellulosic biomass resources for biogas production - where pretreatment may be relevant to increase biogas production Effects of biomass pretreatment Costs vs. benefits of pretreatment Different pretreatment methods Implementation of pretreatment - in combination with solid-liquid separation - before and after the biogas reactor Conclusions 2

3 Lignocellulosic biomass for biogas Waste Biomass BioGAS Energy crops Manure Manure fibers Agricultural residues Organic fraction of municipal solid waste Digestate Maize Miscanthus Catch crops 3

4 Biogas from straw focus in DK Seminar on straw for biogas 2 weeks ago: 4

5 Lignocellulosic biomass for biogas potential in DK 5

6 Pretreatment for increasing the biogas yield Effects: 1) Biomass is easier to handle -> smaller particle size, lower viscosity 2) Increasing the biodegradability by addition of cellulolytic activity -> Higher conversion rate 3) Increasing the release of cellulose and hemicellulose from lignin -> Higher final methane yield Lignocellulose Cellulose Hemicellulose Lignin

7 Pretreatment for increasing the biogas yield Effects: 1) Biomass is easier to handle -> smaller particle size, lower viscosity 2) Increasing the biodegradability by addition of cellulolytic activity -> Higher conversion rate 3) Increasing the release of cellulose and hemicellulose from lignin -> Higher final methane yield Lignocellulose Cellulose Hemicellulose Lignin

8 Pretreatment for increasing the biogas yield Effects: 1) Biomass is easier to handle -> smaller particle size, lower viscosity 2) Increasing the biodegradability by addition of cellulolytic activity -> Higher conversion rate 3) Increasing the release of cellulose and hemicellulose from lignin -> Higher final methane yield Lignocellulose Cellulose Hemicellulose Lignin

9 Pretreatment for increasing the biogas yield depending on biomass and desired product Manure Energy crops Agricultural residues Depending on the biomass Manure separation Fiber fraction Maize Catch crops Straw Anaerob digestion Pretreatment Enzymatic hydrolysis Fermentation Depending on the desired product(s) Biogas Downstream processing BioChemicals Bioethanol 9

10 Costs vs. benefit of pretreatment Limit of treatment costs depends on revenue from biogas production 300 Max. extra additional costs for costs pre-treatment for pretreatment 250 Treatment costs (kr/t) Surplus of biogas (m 3 /t)

11 Pretreatment methods for lignocellulosic biomass Physical/mechanical Thermal Chemical Grinding, milling, maceration, ultrasound etc. Steam explosion, Wet ºC, +/- O 2 Addition of acid, base etc. Biological Fungi, hydrolytic bacteria and their enzymes

12 Mechanical pretreatment/maceration for increasing the biogas potential of manure fibers % +25% -5% +24% +23% +5% +15% +2% Change of Biogas Potential Biogas Potential [lch 4 /kgvs] before mac. after mac. after 2nd mac. 0 Lab-Mac. Blåbjerg Sinding Snertinge Studsgård Thorsø Århus N Biogas Plant Hartmann et al. 2000

13 Change in biogas potential after maceration (%) Mechanical pretreatment/maceration for increasing the biogas potential of manure fibers Blåbjerg Snertinge Studsgård ÅrhusN %Ændringaf biogaspotentiale efter macerering Thorsø Sinding Biogaspotentialei influenten(l CH 4 /kgvs) Biogas potential of influent (L-CH 4 /kg-vs)

14 Mechanical pretreatment/maceration for increasing the biogas potential of manure fibers % Ind. affald m 3 Biogas/m 3 Gylle Day Dag % Ind. org. waste m 3 -biogas/m 3 -manure Macerator + Macerator Biogasudbyte Forventetbiogasudbyte %Industriafald

15 Mechanical pretreatment/maceration for increasing the biogas potential of manure fibers % Ind. Affald m 3 Biogas/m 3 Gylle Day Dag % Ind. org. waste m 3 -biogas/m 3 -manure ,0% + Macerator - 6,0% + Macerator Gennemsnit+/- Standardafvigelse Biogasudbyte Forventetbiogasudbyte %Industriafald

16 Dry matter concentration and pretreatment effect Biogas yield (m 3 biogas/t) Increase of biogas yield by pretreatment in combination with TS increase Wet explosion Pressure cooking Prolonged retention time Raw manure 0.29 m 3 CH 4 /kg-vs part 0.27 m 3 CH 4 /kg-vs part 0.20 m 3 CH 4 /kg-vs part 0 0% 5% 10% 15% 20% 25% 30% %TS in concentrated manure 0.23 m 3 CH 4 /kg-vs part 16

17 Pretreatment of raw manure and manure fibers Increasing the biogas yield by wet explosion Raw manure Separated Manure fibers cow pig pig after digestion Methane yield (L-CH 4 /kg-vs) before Wet explosion after % -26% -10% +42% 17

18 Most efficient concept Pretreatment of the digested fiber fraction Manure BioGAS 35 m 3 /ton feed Mixing tank Biogas plant Separation Liquid fertilizer Manure fibers + WEX treatment 51 m 3 /ton feed WEx treated digested fibers Digested fiber fraction Wet explosion (WEx) 43 m 3 /ton feed + recirculation 18

19 Methane yield (ml/g-vs) CH 4 Yield (ml/g-vs) Increasing the biogas production from manure Pretreatment of the digested fiber fraction Wet explosion ºC, +/- O 2 Reactor experiments: Batch tests: 300 R1 CH4 Yield R1 CH4 Yield Avg. R2 CH4 Yield R2 CH4 Yield Avg. R1 OLR R2 OLR R1+R2: Manure R1+R2: Man+DF R1: WF 33% 66% R1: 100% WEx treated fibers (WF) 250 DF WF1 WF2 WF3 WF4 WF Time (days) 0 0 Time (d) Increase by factor 2.36 Increase by factor 1.72

20 Further optimization of the concept The Re-injection loop (EU project BIOMAN) Digested manure fibers (DMF) Efficient low cost enzymatic treatment Low cost Wheat straw Pretreatment processes

21 Effect of enzyme addition on biogas yield BMP of digested manure fibers (DMF) and of wheat straw (WS) with addition of enzymes

22 Methane yield (L/kg-VS) ph Increasing the biogas production from manure Pretreatment of feedlot manure Wet explosion 170ºC, 4 bar O 2, 25 min. Methane yield ph Days

23 Conclusions (1) The choice of the most suitable pretreatment for a viable concept depends on several factors: The ADDITIONAL biogas yield (or other benefits) have to be higher than CAPEC and OPEC of the pretreatment -> The increase in biogas yield by the pretreatment should be significantly higher than the variation in biogas yield of the biomass. It has to be distinguished if the pretreatment should just increase the CONVERSION RATE or the FINAL YIELD of the biogas production -> In the 1 st case a larger reactor volume or a shift to thermophilic process operation may be just as effective 23

24 Conclusions (2) The choice of the most suitable pretreatment for a viable concept depends on several factors: The volume of the biomass to be pretreated should be reduced as much as possible -> For example by combination with solid-liquid separation The pretreatment should be specifically applied only to the biomass (fractions), which actually needs pretreatment -> Specific pretreatment of biomass (fractions) with a high lignin content; treatment of the fiber fraction after the first digestion in a biogas plant Economy of scale! Pretreatment will be in most cases only feasible for large biogas plants 24