Giuseppe Di Girolamo Dept. Agricultural Sciences Alma Mater Studiorum - University of Bologna

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1 Pre-treatments B I O M ASS YIELD, M ETHANE POTENTIAL AND BIOMASS PRE- T REAT M ENTS OF L I G NO- CELLULOSIC DEDICAT ED ENERGY CROPS Giuseppe Di Girolamo Dept. Agricultural Sciences Alma Mater Studiorum - University of Bologna Summer School Lignocellulosic Crops as Feedstock for Future Biorefineries Lisbon, July 2014

2 OUTLINE Introduction Bioenergy from Agriculture Biogas and Anaerobic Digestion (AD) Aims and scope AD of multi-annual and annual species Experimental process Results Conclusions What are pre-treatments? Experimental process Results Conclusions

3 INTRODUCTION 20% energy from RES EU Directive 2009/28/EC by 2020 Reduction GHG emission by 20% Increase energy efficiency by 20% Edenhofer et al., 2012

4 BIOENERGY: ADVANTAGES AND DRAWBACKS BIOENERGY from AGRICULTURE Advantages Mitigate GHG emission (IEA, 2010); Alternative to traditional fossil fuels (IEA, 2010); Alternative economic sources in rural areas (Zegada-Lizarazu et al., 2010); Promotion in the use of marginal lands (Zegada-Lizarazu et al., 2010). Drawbacks Competition for land: fuels vs. food (Land Use Change) (Murphy et al., 2013); High volatility of food price resulting from the use of good agricultural lands for energy crops (FAO, 2008). To overcome these drawbacks the research is developing second generation biofuels from ligno-cellulosic crops and crop residues

5 Multi-Annuals Annuals FIBRA summer school, Lisbon, July 2014 INTRODUCTION BIOENERGY from AGRICULTURE Ligno-cellulosic crops Bioenergy chains Sorghum (biomass, forage, etc.) Thermal conversion Giant reed Switchgrass Miscanthus Others (multi-annual sorghum) Biomass energy Biodiesel Bioethanol Biogas

6 BIOGAS ANAEROBIC DIGESTION PROCESS Complex organic matter Carbohydrates, Proteins, Lipids Hydrolysis Soluble organic matter Sugars, Amino Acids, Fatty Acids Acidogenesis Intermediary products VFA, Alcohols Different substrates can be used during AD (e.g. energy crops, agricultural residues, urban solid waste, manure, agro-industrial waste); Biogas can be used for heat and power (combustion) or as bio-methane for automotive (upgrade); Digestate, substrate remaining after AD, can be used for crop production and play a remarkable role in promoting sustainable biomass production systems (Krishania et al., 2013). Acetogenesis Acetate CO 2, H 2 acetoclastic Methanogenesis hydrogenotrophic CH 4 + CO 2 adapted from Angelidaki et al., 2002; Demirel and Scherer, 2008 Methanosarcina mazei (Archea)

7 AIMS The aims of this work are: 1. to assess biomass yield in field plots and methane output from dedicated crops; 2. to investigate the effects mild NaOH pre-treatments on chemical composition and methane yield of dedicated crops and agricultural residues;

8 MATERIALS AND METHODS 1 ST AIM CROPS EXPERIMENTAL FARM UNIVERSITY OF BOLOGNA Experimental farm University of Bologna; Deep alluvial soils with clayey-loamy texture (sand 340 g kg -1 ; silt 360; clay 300). Warm-temperate climate: precipitation 700 mm; minimum and maximum temperature 8.3 and 18.3 C. All crops were grown with 4 replicates

9 MATERIALS AND METHODS 1 ST AIM CROPS Multi-annuals species Giant reed (Arundo donax L.) Switchgrass (Panicum virgatum L.) Sorghum Silk ((S. halepense x S. roxburghii) x S. arundinaceum)

10 Annuals species MATERIALS AND METHODS 1 ST AIM CROPS Biomass 133 (Fibre sorghum) Sucros 506 (Sweet sorghum) Trudan Headless (Forage sorghum) Maize (Hybrid Klip 700)

11 MATERIALS AND METHODS 1 ST AIM BIOMASS YIELD AND CHARACTERIZATION Fresh Biomass Yield (FBY; Mg ha -1 ) Dry Biomass Yield (DBY; Mg ha -1 ); Total Solid (TS; mg g -1 TS); Volatile Solids (VS; mg g -1 TS); Total Organic Carbon (TOC) by Springer-Klee method; Total Kjeldahl Nitrogen (TKN) by Kjeldahl method; C/N Proteins: TKN * 6,25; Lipids by Soxhlet method; Soluble sugars; Starch by the amyloglucosidase-α-amylase method; Cellulose, Hemicellulose and Lignin (AIL) by NREL* method. NREL: New Renewable Energy Laboratory

12 MATERIALS AND METHODS 1 ST AIM ANAEROBIC DIGESTION ASSAY Inoculum was collected from a commercial plant and pre-incubated at 35 C (about 1 week) in order to deplete the residual biodegradable organic matter present in it. TS: 36 mg g -1 ; VS: 22.6 mg g -1 fresh weight; C/N: 3.2; ph 8.3; total alkalinity 28.2 g CaCO 3 l -1. The incubation was conducted in 100 ml serum bottles with: working volume 60 ml; organic load 4 g VS l -1 ; 80% V/V of inoculum; no buffer and nutrients added. Procedure: headspace was flushed with N 2 for 3-5 min to ensure anaerobic conditions; 35 C of temperature incubation (mesophilic condition); Control: inoculum alone (blank) and positive control (Glucose, 4 g VS l -1 ); 4 replicates

13 MATERIALS AND METHODS 1 ST AIM ANAEROBIC DIGESTION ASSAY Periodical biogas release and analysis (12 times in 58 d): Biogas volume by water displacement (Mariotte bottle); Biogas characterization by MicroGC 3000A (Agilent): H 2 O 2 CH 4 CO 2 CH 4 expressed in Standard Temperature Pressure (273 K; 100 kpa); CH 4 production cumulated at the net of blank; Cumulated CH 4 expressed in ml CH 4 g -1 VS and fitted by the Gompertz equation (sigmoid family)

14 RESULTS 1 ST AIM CROP YIELD AND CHEMICAL CHARACTERISTICS Crop FBY DBY TS VS C/N Mg ha -1 mg g -1 mg g -1 TS Giant reed 62 c 27 ab 438 a 926 c 57 b Switchgrass 53 cd 22 abc 431 a 957 a 119 a S. Silk 46 d 18 c 397 a 943 b 108 a Trudan H. 75 b 21 bc 275 b 929 c 49 b B a 29 a 325 b 949 ab 54 b S a 27 ab 284 b 940 b 54 b Maize 96 a 28 a 290 b 961 a 39 b FBY, fresh biomass yield; DBY, dry biomass yield; TS, total solids; VS, volatile solids. ANOVA always significant at P In each trait, different letters indicate statistically different means (SNK test; P 0.05). Dry biomass yield varied between 18 (S. Silk) and 29.5 Mg ha -1 (B 133 and Maize); VS values range from 926 mg g -1 TS (Giant reed) to 961 mg g -1 TS (Maize); C/N showed two crop groups: Switchgrass and S. Silk (average, 113) and the other crops (average, 50).

15 RESULTS 1 ST AIM CROP YIELD AND CHEMICAL CHARACTERISTICS Crop Proteins Lipids Soluble sugars Starch Cellulose Hemicellulose AIL mg g -1 VS Giant reed 51 a 9 d 24 e 39 b 315 a 237 a 193 a Switchgrass 24 b 10 d 40 d 54 b 283 a 235 a 177 b S. Silk 27 b 9 d 42 d 48 b 306 a 227 a 161 c Trudan H. 60 a 18 b 76 b 39 b 238 b 190 b 154 c B a 16 c 130 a 53 b 232 b 181 b 149 c S a 16 c 134 a 48 b 229 b 179 b 148 c Maize 65 a 34 a 64 c 319 a 130 c 123 c 77 d AIL, acid insoluble lignin. ANOVA always significant at P In each trait, different letters indicate statistically different means (SNK test; P 0.05). Soluble sugars exhibited notable differences among crops: B 133 and S 506 prevailed on Trudan H. followed by Maize; three multi-annual species exhibited the lowest values; Starch was very low in sorghum hybrids and multi-annual species, while was very much higher in Maize; Cellulose and hemicellulose outlined three different group: Maize showed the lowest level; three sorghum hybrids staged intermediate values; three multi-annual species attained top levels; Lignin described a similar pattern as cellulose and hemicellulose

16 RESULTS 1 ST AIM SPECIFIC METHANE YIELD CH 4 (ml g -1 VS) Cumulative CH 4 during AD and fitted functions Days of incubation Giant reed Switchgrass Silk Trudan H. B 133 S 506 Maize Slow kinetics Intermediate kinetics Fast kinetics Gompertz equation (sigmoid family) CH 4 CH t t e ( 4;0 * e b CH 4 : methane yield at the time (t); CH 4;0 : potential methane yield; b: substrate degradation rate (d); t 0: point of inflection (d). Crop CH 4; 0 b t 0 R 2 adj. ml g -1 VS d d Giant reed 217 (5.3) 9.5 (0.9) 9.2 (0.5) 0.99** Switchgrass 216 (5.5) 11.4 (0.9) 11.0 (0.6) 0.99** S. Silk 271 (5.9) 8.5 (0.7) 9.2 (0.4) 0.99** Trudan H. 251 (5.6) 8.4 (0.7) 9.4 (0.5) 0.99** B (5.5) 8.7 (0.7) 9.4 (0.4) 0.99** S (6.0) 8.2 (0.8) 8.7 (0.5) 0.99** Maize 316 (3.7) 5.6 (0.3) 5.9 (0.2) 0.99** CH 4; 0, potential CH 4 yield; b, substrate degradation rate; x 0, point of inflection. **, significant at P )

17 CONCLUSION 1 ST AIM Seven crops featured remarkable differences in field biomass production, methane yield and methane output per hectare; Characteristics of substrates may influence methane yield. Giant reed and Switchgrass, having a low amount of easily degradable compounds (proteins, soluble sugars, lipids), associated with a high content of structural carbohydrates and lignin, have a slow methane kinetic and low methane yield, compared sorghum groups and Maize; Despite low CH 4 output, multi-annual species retain a special interest in view of the limited need of external inputs (energy, fertilizers, water, etc.) for their cultivation, reflecting in a lower environmental impact; Therefore, biomass pre-treatments should be tried to reduce the gap separating multi-annual species from maize. Can biomass pre-treatments increase biodegradability?

18 INTRODUCTION 2 ND AIM PRE-TREATMENTS GOALS Bacteria Bacteria? Before Pre-treatments After to avoid the formation of inhibitors to increase surface area for enzymatic attack; to change lignin structure; to dissolve hemicellulose; to reduce cellulose crystallinity; to avoid the loss of carbohydrates; Lignin Cellulose Hemicellulose Kumar et al., 2009, modificato Lignin Cellulose Hemicellulose

19 INTRODUCTION 2 ND AIM PRE-TREATMENTS CATEGORIES Ligno-cellulosic materials Physical Physicochemical Chemical Biological Mechanical size reduction Hydrothermal with chemical agents Acid Alkali Oxidizing agents Enzymes Increase in specific surface area and size pores Decrease in crystallinity Increase in specific surface area and size pores Partial degradation hemicellulose and lignin transformation 2 nd aim Increase in porosity Hemicellulose Arundo B 133 degradation sorghum Lignin removal Barley straw Increase in specific surface area and size pores Degradation of hemicellulose and lignin

20 MATERIALS AND METHODS 2 ND AIM ALKALINE PRE-TREATMENTS Substrates: Giant reed B 133 (biomass sorghum) Barley straw Alkaline pre-treatments: Three different NaOH concentration - 0 (untreated) N N N T = 25 C Time = 24 h Determinations after pre-treatments Chemical analysis: Cellulose, Hemicellulose and Lignin by NREL methods before and after pretreatments. Physical analyses: FTIR spectrometry (Fourier transform infrared); SEM (scanning electron microscopy). Anaerobic digestion and methane determination: Incubation at 35 C; organic load 4 g VS l -1 ; for 58 days. Assay was conducted in triplicates; CH 4 production cumulated at the net of blank; Cumulated CH 4 expressed in ml CH 4 g -1 VS and fitted by 1 st order kinetics; T 80 (technical digestion time) = time needed to produce 80% of potential methane yield (Palmowski and Müller, 2000)

21 RESULTS 2 ND AIM ALKALINE PRE-TREATMENTS Cumulative CH 4 during AD Giant reed 300 Substrate treatment interaction on CH 4 yield at the end of AD a +23% a % b b ab CH 4 (ml g -1 VS) B 133 Untreated NaOH 0.05 N NaOH 0.10 N NaOH 0.15 N CH 4 (ml g -1 VS) c d f c e +14% d +21% +10% c +30% Giant reed B 133 Barley straw 50 0,00 0,05 0,10 0, B. straw NaOH (N) Giant reed: CH 4 yield augmented in parallel with the increase NaOH concentration +14, 21 and 30% over untreated; B 133: moderate CH 4 increase was obtained at two highest NaOH levels (10% over untreated); Days of incubation Barley straw: CH 4 increase by 15% at NaOH 0.05 N and by 23% at NaOH 0.10 and 0.15 N.

22 RESULTS 2 ND AIM ALKALINE PRE-TREATMENTS Kinetics T 80 0,12 0,10 Giant reed B 133 Barlery straw d -1 0,08 Days 25 0, ,04 0,00 0,05 0,10 0,15 NaOH (N) 0,00 0,05 0,10 0,15 NaOH (N)

23 CONCLUSION 2 ND AIM Pre-treatments are seen as a valuable tool in a portfolio of strategies supporting bio-energy growth; In literature, different type of pre-treatments were tested, but the high variability of pre-treatments conditions and substrate composition influence their results, in term of methane yield increase; When improvements of final methane production are obtained, it is necessary to evaluate their viability in full scale biogas plants; Future progress may be envisaged, amid other strategies, in bland pretreatments (e.g., lower temperatures and weaker catalysts) as a potential means to improve net energy gain and methane production efficiency.

24 CONCLUSION 2 ND AIM Mild alkaline pre-treatments at low temperature permitted to enhance the methane yield of Giant reed, B 133 sorghum and Barley straw (+21, +20 and +7% as average of all pre-treatments, respectively); Moreover, pre-treatment benefits were also shown in terms of process kinetics and technical digestion time; In conclusion, a standardization of operational parameters associated with energy, economic and environmental evaluation are fundamental before pre-treatment implementation in full scale biogas plants.

25 THANKS FOR YOUR ATTENTION