Energy
Optimised biogas production from the co-digestion of sugar beet with pig slurry: integrating energy, GHG and economic accounting
Supporting information
Alessio Boldrin1,*, Khagendra Raj Baral2, Temesgen Fitamo1, Ali Heidarzadeh Vazifehkhoran3, Ida Græsted Jensen4, Ida Kjærgaard5, Kari-Anne Lyng6, Quan Van Nguyen7, Lise Skovsgaard Nielsen4, and Jin Mi Triolo3
1Department of Environmental Engineering, Technical University of Denmark, Miljoevej, 2800 Kgs. Lyngby, Denmark; (Alessio Boldrin); tefi@ env.dtu.dk (Temesgen Fitamo)
2Department of Agroecology - Soil Fertility, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark;
3Biotechnology and Environmental Engineering, Institute of Chemical Engineering, Biotechnology and Environmental Technology, Faculty of Engineering, University of Southern Denmark (SDU), Odense M5230, Denmark; (Ali Heidarzadeh Vazifehkhoran); (Jin Mi Triolo)
4Department of Management Engineering, Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde, Denmark; (Ida Græsted Jensen); (Lise Skovsgaard Nielsen)
5Knowledge Centre for Agriculture, Agro Food Park 15, 8200 Aarhus, Denmark;
6 Ostfold Research, Stadion 4, 1671 Kråkerøy, Norway;
7Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg, Denmark;
*Author to whom correspondence should be addressed; E-Mail: (Alessio Boldrin);
Tel.: +45-45251585; Fax: +45- 45932850.
Table of Contents
List of Tables...... 3
List of figures...... 5
1.Mass and substance balance of the biogas chain...... 7
1.1.Harvest and storage...... 7
1.2.Laboratory experimental work...... 7
1.3.BioChemical methane potentials (BMP) and anaerobic digestion in CSTR test...... 8
2.GHG balance of the biogas chain...... 10
2.1.Emission factors for energy inputs...... 10
2.2.Estimation of N2O emissions after field application...... 10
2.2.1.Estimation of VSD and VSND in digestate...... 10
2.2.2.Nitrous oxide emissions...... 13
3.The economic analysis...... 15
3.1.Feedstock and scale...... 15
3.2.Direct use vs. upgrade...... 16
3.3.Total net income (TNI)...... 16
3.4.Total Income (TI)...... 17
3.4.1.Yield...... 17
3.4.2.Prices...... 18
3.5.Total costs (TC)...... 19
3.5.1.Transportation costs (Ctrans)...... 19
3.5.2.Operational expenditures (Copex)...... 24
3.5.3.Investment costs (Ccapex)...... 26
3.6.Gas quality and upgrading...... 29
3.7.Results...... 30
3.7.1.Total Income (TI)...... 30
3.7.2.Total Costs (TC)...... 30
3.7.3.Total Net Income (TNI)...... 32
3.8.Nomenclature...... 33
4.Results for Mass, Substance and Energy Flow Analysis...... 35
4.1.PSSB-0: 100 % pig slurry...... 35
4.2.PSSB-12.5: 87.5 % ww pig slurry, 12.5 % ww sugar beet...... 37
4.3.PSSB-25: 75 % ww pig slurry, 25 % ww sugar beet...... 40
5.References...... 44
List of Tables
Table S1 - Determination of fraction of beet root and top according to wet weight, dry matter (DM) and harvest per hectare (ha) (Schelde et al., 2011). 7
Table S2 - Total solids (TS) and Volatile solids (VS) loss during the storages...... 7
Table S3 - Composition of pig slurry (PS) and beet silage (BS) used for this study...... 8
Table S4 - Biogas production for the different feeding scenarios...... 8
Table S5 – Content of total solids (TS) and votatile solids (VS) before and after digestion...... 8
Table S6 - Emissions factors for energy inputs to the biogas chain...... 10
Table S7 – Overview of materials used for VSD determination...... 10
Table S8 - Characteristics of material and soil used for the incubation tests...... 11
Table S9 - Emissions of N2O from application of different digestates on land (NH3 loss 10%, soil water potential -0.015 MPa). 14
Table S10 – Estimation of N2O from application of different digestates on land...... 14
Table S11 – Yearly biomass supply (Mg/y) to biogas plants according to plant size...... 15
Table S12 - Yearly biogas production (m3/y) according to plant size...... 15
Table S13 – Distribution of Total Income (TI) per Mg of input to the biogas plant...... 17
Table S14 - Biogas Yield according to input material and size of the plant...... 17
Table S15 – Average transportation distance (∆d, in km) for biomass supply to the biogas plant..20
Table S16 – Annual costs (€) for transportation of biomass to and from the biogas plant...... 21
Table S17 – Estimation of the number of loads (N.) needed for the fulfilling the biogas plant capacity. 21
Table S18 - Annual costs (€) for loading/unloading of the biomass needed for the fulfilling the biogas plant capacity. 22
Table S19 – Average collection cost (Ctrans,in) per Mg of input ot the biogas plant...... 22
Table S20 – Average transportation distance (∆d, in km) for excess digestate...... 24
Table S21 – Estimation of the number of loads (N.) needed for excess digestate...... 24
Table S22 - Annual costs (€) for loading/unloading of the excess digestate...... 24
Table S23 – Annual costs (€) for transportation of excess digestate...... 24
Table S24 – Average cost (Ctrans,in) per Mg of excess digestate...... 24
Table S25 – Costs (€/MgSB) induced by increasing utilization of sugar beet in the input mix.....26
Table S26 – Operation costs for biogas upgrading (Copex,UP) according to type and size of system (€/m3biogas/h/year). 26
Table S27 – Overview of basis investment costs (Ccapex,basis) for the biogas production (in €/Mg/y). 27
Table S28 – Investment costs (Ccapex,stor,gas) for temporary storage (€/Mg)...... 28
Table S29 – Investment costs (Ccapex,pipe,gas) for pipeline connection (in €/Mg)...... 28
Table S30 – Investment costs for biogas upgrading (Ccapex,UP) according to type and size of system (€/m3biogas/h/year). 28
Table S31 - Investment costs (Ccapex,clean,gas) for biogas upgrading (in €/Mg)...... 28
Table S32 – Yields (m3/Mginput) of CH4, and normalized biogas and BNG...... 30
Table S33 – Total Income (TI) for the biogas chain (€/Mginput)...... 30
Table S34 – Contributions to Total Income (TI) from gas and digestate (€)...... 30
Table S35 – Annual Total Cost (TC) for the biogas chain (€/Mginput)...... 30
Table S36 - Total investment costs (€/Mginput) per year for the biogas chain...... 31
Table S37 – Operation costs (€/Mginput) per year for the biogas chain...... 31
Table S38 - Annual costs (€/Mg) for transportation of biomass to and from the biogas plant....31
Table S39 - Investment costs associated with outputs (biogas plant excluded)...... 31
Table S40 - Overview of Total Net Income (TNI) [€/Mg] for the biogas chain, according to the plant size and the input mixture. 32
Table S41 - Nomenclature for the economy model...... 33
List of figures
Figure S1 – Experimental setup for the incubation test. On the right, detail of an incubation box.11
Figure S2 – Cumulative CO2 production during incubation tests...... 11
Figure S3 – Total CO2 production as a function of the added C...... 12
Figure S4 – Effect of VS application (left) and C:N ratio (right) on CO2 production over time.....12
Figure S5 - Division of the land for calculating average transportation distance...... 19
Figure S6 - Gas quality - Biogas before upgrading related to upgraded biogas (BNG) and natural gas, Source: Presentation from Energinet.dk at a theme day on biogas in Skive: 28
Figure S7 - Trade off between rising operational costs (including transport) and reduced capital costs 31
Figure S8 – Mass balance (kg, wet weight) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-0, i.e. 100 % pig slurry. 34
Figure S9 – TS balance (kg) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-0, i.e. 100 % pig slurry. 34
Figure S10 – VS balance (kg) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-0, i.e. 100 % pig slurry. 35
Figure S11 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-0, i.e. 100 % pig slurry, the size of the plant is 110’000 Mg/y. 35
Figure S12 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-0, i.e. 100 % pig slurry, the size of the plant is 320’000 Mg/y. 36
Figure S13 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-0, i.e. 100 % pig slurry, the size of the plant is 500’000 Mg/y. 36
Figure S14 – Mass balance (kg, wet weight) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-12.5, i.e. a mix of pig slurry (87.5 % ww) and sugar beet (12.5 % ww). 37
Figure S15 – TS balance (kg) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-12.5, i.e. a mix of pig slurry (87.5 % ww) and sugar beet (12.5 % ww). 37
Figure S16 – VS balance (kg) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-12.5, i.e. a mix of pig slurry (87.5 % ww) and sugar beet (12.5 % ww). 37
Figure S17 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-12.5, i.e. a mix of pig slurry (87.5 % ww) and sugar beet (12.5 % ww), the size of the plant is 110’000 Mg/y. 38
Figure S18 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-12.5, i.e. a mix of pig slurry (87.5 % ww) and sugar beet (12.5 % ww), the size of the plant is 320’000 Mg/y. 38
Figure S19 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-12.5, i.e. a mix of pig slurry (87.5 % ww) and sugar beet (12.5 % ww), the size of the plant is 500’000 Mg/y. 39
Figure S20 – Mass balance (kg, wet weight) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-25, i.e. a mix of pig slurry (75 % ww) and sugar beet (25 % ww). 39
Figure S21 – TS balance (kg) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-25, i.e. a mix of pig slurry (75 % ww) and sugar beet (25 % ww). 40
Figure S22 – VS balance (kg) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-25, i.e. a mix of pig slurry (75 % ww) and sugar beet (25 % ww). 40
Figure S23 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-25, i.e. a mix of pig slurry (75 % ww) and sugar beet (25 % ww), the size of the plant is 110’000 Mg/y. 41
Figure S24 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-25, i.e. a mix of pig slurry (75 % ww) and sugar beet (25 % ww), the size of the plant is 320’000 Mg/y. 41
Figure S25 – Energy balance (MJ of primary energy) of the biogas chain relative to 1 Mgww of input to the anaerobic digestor. The input is PSSB-25, i.e. a mix of pig slurry (75 % ww) and sugar beet (25 % ww), the size of the plant is 500’000 Mg/y. 42
1.Mass and substance balance of the biogas chain
1.1.Harvest and storage
Data are based on experimental work on eight different sugar beet cultivars, 4 from the company DLF-Trifolium and 4 from the company KWS. Whole sugar beets were topped and harvested in November 2012, and the roots stored on the farm in a clamp. The whole sugar beets were stored from November to February in a clamp covered with straw. The roots were chopped finely using a Tim Envipro SD-1600 (AB Skovservice, Denmark) on 12 February 2013. The finely chopped beet rootswere transported and loaded into 3.3 m tall outdoor silos with a diameter of 1.0 m. On 4 September 2013 the ensiling was terminated and beet root silage samples were taken.Determination of fraction of beet root and top according to wet weight, dry matter (DM) and harvest per hectare was followed by Schelde et al.(2011), where the average value was taken for the mass balance model.Results are shown in Table S1 andTable S2.
Table S1 - Determination of fraction of beet root and top according to wet weight, dry matter (DM) and harvest per hectare (ha)(Schelde et al., 2011).
Beet cultivar / Root / Top / Root / TopUnit / Mg ha-1 / Mg ha-1 / Mg DM ha-1 / Mg DMha-1
Angus / 92.0 / 34.7 / 22.3 / 5.1
Colosse / 109.2 / 35.1 / 21.1 / 4.3
Hamilton / 94.2 / 35.6 / 22.4 / 4.8
EB0604 / 97.1 / 36.5 / 23.0 / 4.8
Average / 98.1 / 35.5 / 22.2 / 4.8
Table S2 - Total solids (TS) and Volatile solids (VS) loss during the storages.
Harvest / After stored pulp in a clamp / After ensilingTime / November / Sep. – Feb. / Feb.- Sep.
TS g kg-1 / 226a (221b) / 196 / 179
VS g kg-1 / 208a (213b) / 153 / 129
a Thalbitzer (2011) used for modelling; b Experimental results for comparison.
1.2.Laboratory experimental work
The samples were stored in a freezer at -18 °C until laboratory analysis. Dry matter (DM), Volatile Solids (VS), Total Kjeldahl nitrogen (TKN) and total ammoniacal nitrogen (TAN) were determined according to standard procedures (APHA, 2005). During DM measurement, easily volatile compounds, i.e. alcohols and volatile fatty acids, evaporate. Therefore measured DM was corrected according to(Weissbach and Strubelt, 2008). Ethanol was measured using high-performance liquid chromatography (HPLC, Agilent 1100, Germany). Volatile fatty acid (VFA) concentrations from C2-C5 were measured using a gas chromatograph (Hewlett Packard 6890, Italy) with a flame ionisation detector and 30m x 0.25mm x 0.25μm column (HP-INNOWax, USA). Determination of hemicellulose, cellulose and lignin can be found inTriolo et al.(2011).Results are shown in Table S3.
Table S3 - Composition of pig slurry (PS) and beet silage (BS) used for this study.
Unit / Pig slurry / Beet silageTotal Solid (TS) / g kg-1 / 39.6 / 179
Volatile Solid (VS) / g kg-1 / 30.4 / 129
Volatile Fatty Acid (VFA) / % of VS / 24.1 / 5.8
Protein / % of VS / 21.3 / 8.1
Hemicellulose / % of VS / 4.6 / 3.2
Cellulose / % of VS / 17.8 / 10.0
Lignin / % of VS / 17.1 / 4.1
Carbohydrate / % of VS / 15.2 / 68.8
Ammonia / g kg-1 / 2.11 / 0.00
TKN / g kg-1 / 3.14 / 1.65
1.3.BioChemical methane potentials (BMP) and anaerobic digestion in CSTR test
The German standard method(VDI 4630, 2006) was applied to determine BMP. Inoculum was collected from an industrial biogas plant Fangel, located on Funen Island in Denmark, processing 75 % of animal manure and 25 % of industrial food processing waste on mass basis atmesophilic temperatures. The inoculum-to-substrate ratio (I/S ratio) was set to 3 based on DM (De Paoli et al., 2011; Kryvoruchko et al., 2009; Triolo et al., 2012). Methane concentration in biogas was measured using the gas chromatograph (7890A, Agilent technology, USA) equipped with a thermal conductivity detector and a 30 m × 0.320 mm column (J&W 113-4332, Agilent technology, USA). The biomethane concentration in dried biogas was determined by means of gas chromatography analysis, and the determined biomethane corrected to standard condition (273 K and 101.325kPa) according to (VDI 4630, 2006). Detailed procedure can be found in Triolo et al.(2012), results are shown in Table S4 and Table S5.
Table S4 - Biogas production for the different feeding scenarios.
Parameter / Unit / PSSB-0 / PSSB-12.5 / PSSB-25CH4 yield / CH4 L/L / 9.10 / 12.3 / 18.0
CH4 yield / CH4 L/VS / 296 / 343 / 369
CH4 / % in biogas / 57.2 / 57.1 / 57.2
Table S5 – Content of total solids (TS) and votatile solids (VS) before and after digestion.
Feedstock / Unit / SB / PS / Before digestion / After digestionPSSB-0 / g/kg / TS / 184.0 / 39.5 / 39.5 / 25.9
g/kg / VS / 127.3 / 31.8 / 31.8 / 17.2
PSSB-12.5 / g/kg / TS / 184.0 / 39.5 / 57.1 / 29.7
g/kg / VS / 127.3 / 31.8 / 43.8 / 19.4
PSSB-25 / g/kg / TS / 184.0 / 39.5 / 75.6 / 34.1
g/kg / VS / 127.3 / 31.8 / 55.7 / 22.9
For the anaerobic digestion in contentious mode, anaerobic IMT bioreactors (Andtec, Ski, Norway), made from 316 AISI steel and casting acrylic tubes were used. Each CSTR was made of acrylic cylinder (diameter 360 mm and height 360 mm) fitted with stainless steel plates on the top and bottom. Each CSTR had a total volume of 20 L. The agitation was kept at 90 rpm and the operating temperature was 37 °C. Total ammoniacal nitrogen (TAN = NH3+ NH4+) and VFA concentrations in the digestate and CH4 and CO2 content in the biogas were regularly monitored. After an acclimatization period of 2 weeks, the reactors were operated for two months. Organic loading rate was 1.24 g VS L-1 d-1 when only pig manure was digested and 1.73 g VS L-1 d-1 for 87.5% of pig slurry and 12.5% of beet silage, and 2.22 g VS L-1 d-1 for 75% of pig slurry and 15% of beet silage by mass base. The biogas production was determined when they reached a steady state.
2.GHG balance of the biogas chain
2.1.Emission factors for energy inputs
Emission factors employed in the GHG analysis are shown in Table S6.
Table S6 - Emissions factors for energy inputs to the biogas chain.
Process / Unit / Amount / Note, referenceDiesel combustion / kg CO2-eq/liter / 3.1 / Provision + combustion (Fruergaard et al., 2009)
Electricity production / kg CO2-eq /kWh / 0.95 / Hard coal, NORDEL (Fruergaard et al., 2009)
Heat production / kg CO2-eq/GJ / 72 / District heating, natural gas (Fruergaard et al., 2009)
2.2.Estimation of N2O emissions after field application
Short-term N2O emissions were predicted using the N2O sub-model developed by Sommer et al.(2004), which considers N2O emissionto be a function of volatile solids (VS) in slurry or digestate, reactive slurry nitrogen (N), and soil water potential (). In this model, two pools of VS are defined, i.e., easily degradable VS (VSD) and slowly degradable (“non-degradable”) VS (VSND). When it is applied to freely-draining soil, slurry/digestate will redistribute in response to water potential gradients in the soil, but part of the liquid is retained by particulate VS (Petersen et al., 2003). The model calculates the fractions of slurry liquid,VSDand reactive N that is retainedand transformed in slurry/digestate “hotspots” on the basis ofsoil water potential and slurry/digestate composition by an iterative procedure (see Sommer et al. (2004) for details). The pools VSD and VSND are assumed to have similar N concentrations, and VSDto represent a pool of reactive N. According to the model, N in VSDand total ammoniacal N (corrected for NH3 loss) will be nitrified within the period considered for short-term N2O emissions.
2.2.1.Estimation of VSDand VSND in digestate
Sommer et al. (2004) estimated VSDin pig and cattle slurry from literature values, but the present study included a range of experimentally produced materials, and therefore a different approach was used, in which VSD was estimated from the short-term evolution of CO2-C after incubation of slurry/digestate in soil under aerobic conditions.Based on preliminary tests, the soil water content was selected so that it could be assumed that VSD in applied materials were degraded under aerobic conditions. It was further assumed that VSD was fully degraded when CO2 evolution rates corrected for background became constant. An overview of the materials for which VSDwas determined is presented in Table S7, including in total 6 treatments: 3 digestates, 2 undigested samples of sugar beet pulp silage (SB) and pig slurry (PS), and a control sample made of soil.
Table S7 – Overview of materials used for VSDdetermination.
Material / Treatment name / Sugarbeet pulp silage (%) / Pig slurry (%)Digestates / PSSB-0 / 0 / 100
PSSB-12.5 / 12.5 / 87.5
PSSB-25 / 25 / 75
Untreated materials / SB / 100 / 0
PS / 0 / 100
Control / Ctrl / 0 / 0
Soils and digestates
The three digestates presented in Table S7were produced in laboratory scale reactors (20 L) operated at 37 °C with an HRT of 20 days at Southern Denmark University. Soil sample was collected from 0 to 25 cm depth at Foulumgård experimental field, Foulum Research Centre, Denmark. The fresh soil was passed through a 4-mm sieve to remove any stones, roots and vegetations; mixed homogeneously, and stored in a closed plastic container at storage room 10oC after the collection. The soil was taken out from cold room and left at room temperature (22oC) two hours prior to the experiment. Samples of soil and digestates were analyzed for total carbon (TC) and total nitrogen (TN) using a Europa 20-20 continous flow- isotope ratio mass spectrometer (CF-IRMS; Sercon Ltd., Cheshire, UK). Inorganic nitrogen concentration (NH4+-N, NO3--N) of amended soil were analyzed by Flow Injection Analyzer (QuickChem FIA-series 8000) after extraction with 1M KCl (dilution ratio 1:4). The characteristics of these materials are presented in Table S8.
Table S8 - Characteristics of material and soil used for the incubation tests.
Material / Dry matter (DM) / Total VS / Total C / Total N / C:N%ww / g kg-1 DM / SE / % DM / SE / % DM / SE
PSSB-0 / 2.47 / 593 / 20.6 / 33.3 / 0.10 / 9.17 / 0.17 / 4
PSSB-12.5 / 2.94 / 584 / 63.2 / 35.4 / 0.38 / 7.34 / 0.11 / 5
PSSB-25 / 3.67 / 640 / 12.9 / 36.0 / 0.05 / 5.37 / 0.12 / 7
BS / 15.38 / 668 / 8.6 / 31.0 / 0.66 / 2.29 / 0.10 / 14
PS / 2.81 / 643 / 64.6 / 37.4 / 0.55 / 7.55 / 0.15 / 5
Soil / 86.77 / 2.03 / 0.03 / 0.27 / 0.01 / 8
Experimental design and incubation
Incubation conditions (soil moisture, duration) were selected on the basis of a pilot experiment where PSSB-12.5 or water were mixed with soil and packed to a bulk density of 1.2 g cm-3 and final water-filled pore space (WFPS) of 40, 50, 60 or 70%. Development of anoxic conditions were evaluated by measuring N2O evolution rates on separate samples after 1 and 4 d of incubation. Based on these results a 14-d incubation at 40% WFPS was selected for the determination of VSD.