development of nutrient-embedded biochar pellets as a slow ... · in terms of bioenergy crop...
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Development of nutrient-embedded biochar pellets as a slow-release fertilizer for maximizing bioenergy crop production
A Final Report Submitted to
The Southeastern Sun Grant Center
Submitted by
Dr. Nicole Labbé Dr. Amy Johnson
Dr. Pyoungchung Kim
Center for Renewable Carbon
And
Department of Biosystem Engineering and Soil Science University of Tennessee
Knoxville, TN 37996
Project Period, July 1, 2011 – June 30, 2013
November 10, 2013
This project was funded by a grant from the Southeastern Sun Grant Center with funds provided by the United States Department of Transportation, Research and Innovative Technology
Administration.
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ABSTRACT
Biochar pellets produced by blending switchgrass biochar, lignin and fertilizer P and K together and followed by pelletization were characterized. In addition, their release of nutrients was investigated for a period of 18 days. Pellets processed at 180 oC with lignin content increasing from 10 to 30 wt% had higher thermal stability, surface functionality, and durability than pellets dried at 105 oC. In addition, pellets dried at 180 oC had a slower nutrient release than pellets dried at 105 oC, with a high release rate within the first 24h followed by a more gradual release for the next 432h. An increase in lignin content in the biochar pellets also reduced nutrient release over time. Therefore, both, lignin content and drying temperature of the pellets, control the release rate of nutrients present in biochar pellets.
Acknowledgment “Support for this research was provided in part by a grant from the Southeastern Sun Grant Center with funds provided by the U.S. Department of Transportation Research and Innovative Technology Administration (DTOS59-‐07-‐G-‐00050).”
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Table of Contents ABSTRACT ................................................................................................................................................ 2
Acknowledgment ......................................................................................................................................... 2
Executive Summary ................................................................................................................................... 4
Problem ...................................................................................................................................................... 4
Approach and Methodology ........................................................................................................................ 5
Findings ....................................................................................................................................................... 7
Conclusions ............................................................................................................................................... 21
Final (actual) budget ............................................................................................................................... 24
Publication and Presentations ............................................................................................................ 25
Contracts Related to this Project since Project Inception .............................................................. 25
Fig. 1. TGA of biochar and biochar pellets produced with 10, 20, 30% lignin and dried at 105 and 180 oC. (a) TG (b) DTG of biochar and biochar pellet 10-105 and 10-180. (c) TG (d) DTG of biochar pellet 20-105 and 20-180 (e) TG and (d) DTG of biochar pellet 30-105 and 30-180. ................................ 9
Fig. 2. PCA of FTIR spectra collected from raw biochar and biochar pellets produced at different lignin content and drying temperature (105 and 180 oC). (a) Scores plot and (b) loadings plot of all biochar and pellets. (c) Scores plot and (d) loadings plot of biochar pellets 10-105 and 10-180. (e) Scores plot and (f) loadings plot of biochar pellets 20-105 and 20-180. (g) Scores plot and (h) loadings plot of biochar pellets 30-105 and 30-180. ....................................................................... 11
Fig. 3. Water uptake of biochar pellets. Lines presented triplicate runs of each sample. (a) 10-105, (b) 10-180, (c) 20-105, (d)20-180, (e) 30-105, and (f) 30-180 represent biochar pellets produced with 10, 20 and 30% lignin and dried at 105 and 180 oC respectively. ......................................................... 14
Fig. 4. Nutrient release (K and P) from biochar pellets with lignin content 10, 20 and 30% and dried at 105 and 180 oC. ............................................................................................................................... 17
Fig. 5. Nutrient release (Ca and Mg) from biochar pellets with lignin content 10, 20 and 30% and dried at 105 and 180 oC. ............................................................................................................................... 18
Fig. 6. Nutrient release (K and P) from biochar pellets embedded with K and P fertilizer, lignin content 10, 20 and 30 %, and dried at 105 and 180 oC. ..................................................................................... 19
Fig. 7. Nutrient release (Na and S) from biochar pellets with lignin content 10, 20 and 30% and dried at 105 and 180 oC. ............................................................................................................................... 21
Table 1 Proximate analysis and inorganic elements presented in biochar and biochar pelletsa. .................. 7 Table 2 Mechanical properties of biochar pellets produced with different lignin contents and at different drying temperature. .................................................................................................................................... 12
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Executive Summary For the last five years, the application of as-produced biochar for amending soil quality and increasing crop production has been documented in the literature (Lehmann et al., 2011). Although biochar is incorporated into soil as an amendment, organic or inorganic fertilizer is still required to maximize crop production. However, conventional fertilizers are inefficient, in particular, in soils with low cation exchange capacity and in humid climate conditions. Low nutrient retention capacity in soil causes low crop production and contaminates the ground water leading to financial loss for farmers. Therefore, it is essential to design slow-release fertilizers with low solubility that can supply nutrients to soil and plants over long period of time. Biochar embedded with fertilizer is one potential way to slowly release nutrients to soil throughout plant growing season and to provide most of the nutrients to bioenergy crops without leaching losses. In addition, nutrients already contained in the biochar, such as P and K, are recycled into soil. These benefits will increase energy crop yields and reduce costs for fertilizer. Therefore, utilization of biochar pellets embedded with fertilizer could enhance soil productivity and quality in terms of bioenergy crop production and carbon sequestration. In this work, we developed a soil fertilizer product “biochar pellets embedded with fertilizer” which could maximize bioenergy crop production and reduce CO2 emissions in soil and therefore be an environmentally benign slow-release fertilizer.
Problem
Biochar is a carbon-rich product that is produced from biomass through thermochemical process, pyrolysis and gasification, under limited or absent oxygen (Lehmann et al., 2011). Biochar contains recalcitrant carbonaceous structures and minerals depending on biomass types and operation parameters of process. Biochar produced from lignocellulosic feedstock has high carbon content, whereas biochar generated from nutrient-rich feedstock such as poultry litter has characteristics similar to a fertilizer (Cantrell et al., 2012). Biochar pH ranges from 5 to 13, ash content from 1.4% to 73%, carbon content from 66.5 to 91.6%, and surface areas range from 1 to 400 m2 g-1. Cation exchange capacity (CEC) of biochar ranges from 10 to 69 cmol kg-1 (Kim et al., 2013). When applied to soil, biochar provides plant nutrients, increases CEC and water holding capacity, and improves the soil as a microbial habitat (Lehmann et al., 2011).
When lignocellulosic biomass-derived biochar produced by fast pyrolysis is incorporated into soil application, organic or inorganic fertilizers are still needed to improve crop yield. Many studies that have investigated value-added biochars as a soil amendment suggested the blending of lignocellulosic biochars with nutrient-rich manures, compost or poultry litter before soil application (Hua et al., 2009; Ro et al., 2010). The incorporation of biochar with sludge composite into land application was found to significantly reduce nitrogen loss (Hua et al., 2009). However, storage, transportation and soil application of biochar are challenging because biochar is brittle, and has wide particle size distribution and low density. Blue Leaf Inc. reported a loss as high as 30% by wind-blown during handing, transport to the field and soil application of biochar. In particular, 25% of the biochar applied was lost during spreading to the field (Husk & Major, 2008). 20 - 53% of biochar incorporated into soil was also lost by surface runoff during intense rain events (Major et al., 2010).
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Therefore, it is essential to design value-added biochar materials that can supply nutrients to soil over long period of time with minimum loss of biochars and nutrients. Pelletization of biochar is one potential way to reduce transportation and handling costs and significantly decrease loss of biochar during soil application (Reza et al., 2012). Biochar pellet has been used as an alternative to biomass pellet mostly for heating material (Abdullah & Wu, 2009). For soil application, lignocellulosic and poultry litter feedstocks were blended, pelletized and slowly pyrolyzed to produce biochar pellets (Cantrell & Martin II, 2012). However, there is little information available on biochar pellets that can control nutrient release rate from the pellets as a slow release fertilizer. Slow release fertilizer is required to gradually release nutrients to soil throughout the growing season and to provide most of the nutrients to plant without leaching losses (Fernández-Escobar et al., 2004), which can, furthermore, reduce loss in farmer profit and minimize potential damage to the environment (Mortain et al., 2004). Therefore, the objective of this study was to develop biochar pellets embedded with plant fertilizer as an environmentally benign slow-release fertilizer. Biochar generated in the process of bio-oil production by fast pyrolysis was blended with commercial fertilizer and different ratio of lignin, and subsequently pelletized. The produced biochar pellets were mechanically and chemically characterized and their capacity to release nutrients was assessed.
Approach and Methodology 1. Production of biochar
Air-dried switchgrass (Panicum virgatum L.) was obtained from a local producer in eastern Tennessee. The switchgrass containing 7 - 8% moisture was milled to less than 4 mm particle sizes and then pyrolyzed at 525 oC with a residence time of 40s and feeding rate of 10kg h-1 in the presence of N2 using a continuous auger pyrolysis process. A detailed description of the process is provided elsewhere (Kim et al., 2011). 2. Pelletization of nutrient-embedded biochar
The biochar produced by the auger pyrolysis process was blended with different percentages of lignin (10, 20 and 30 wt%) as a binder using a mixer (Black lynx mixer, Monarch In.). Lignin (Indulin AT, kraft pine lignin) was obtained from MeadWestvast Inc. Indulin AT lignin was a purified kraft lignin, where sodium and hemicellulose were removed by an acid hydrolysis process (Beis et al., 2010). During mixing biochar and lignin, liquid fertilizer (12: 4: 8 = N: P2O5 : K2O, Scotts Miracle-Gro) was added to water at 1.0 wt% of total biochar and lignin mixture and then the water mixture (40 - 50 wt% of total biochar and lignin) was sprayed into the mixture of biochar and lignin. The moisturized biochar mixtures were pelletized using a pellet mill (model PP220, Pellet Pros) that consisted of a die with cylindrical press channels (6mm diameter) and rollers that force the biochar to be squeezed through the channels. Pressures in the die can reach up to 172 MPa and the pelletized biochars came out of the mill with a temperature around 65 - 85 oC (Manufacturer’s information). Pellets with dimensions of 6 - 10 mm in length and 5.9 – 6.0 mm in diameter were produced. The pelletized biochars were then heated at 105 or 180 oC for 24 h to dry. The heated biochars were cooled down and then stored in glass bottles. The biochar pellets produced with different lignin wt% and drying temperature are referred as 10-105, 10-180, 20-105, 20-180, 30-105 and 30-180, where the first number refers to % of lignin and the second the temperature used to dry the pellets
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3. Characterization of biochar pellets Raw biochar and the corresponding biochar pellets produced using different lignin ratios
(10, 20 and 30 wt%) and drying temperatures (105 and 180 oC) were mechanically and chemically characterized. Proximate analysis, including moisture content, volatile matter and ash content, was measured by following ASTM D1762-84. Ultimate analysis, including carbon, hydrogen and nitrogen, was measured by CHN analyzer (PerkinElmer). Inorganic elements in biochars were analyzed by inductively coupled plasma-optical emission spectroscopy with an optima 7300 DV spectrometer (ICP-OES, PerkinElmer) after microwave digestion (Kim et al., 2011). Surface functionality was measured by Fourier Transform Infrared (FTIR) spectroscopy with an attenuated total reflectance mode (PerkinElmer Spectrum One spectrometer). FTIR spectra were analyzed using principal component analysis (PCA) to classify the samples by their spectral features (Kim et al., 2011). Thermal decomposition of biochar pellets under air atmosphere was analyzed using a thermogravimetric analyzer (Pyris 1 TGA, PerkinElmer) (Kim et al., 2011).
Density of biochar pellets was calculated by measuring diameter, length and mass of 10 cylindrical biochar pellets. Compressive mechanical strength of the biochar pellets was obtained by compression testing and determined as the force at break (Instron). Compression tests were performed using a disc shaped metal probe that was attached to a 100 kN load cell. The test was run at a compression rate of 1.0 mm min-1 and stopped after the pellet fell apart. The average force at break and standard deviation were calculated based on 10 replications per test. Durability of biochar pellets was tested by abrasion index using the MICUM test (Reza et al., 2012). The rotating drum featured an inner diameter of 100 mm and a depth of 95 mm with three baffles of 25×50. Sixty pellets were loaded into a rotating drum and rotated with 50 rotations per minute. After rotation, the pellets were screened using a 2 mm sieve. Particles that fall through screen were weighed. Water adsorption behavior of biochar pellets was measured by the capillary rise method (Zhang et al., 2011). Cylindrical pellet (3 - 4g) hung to the microbalance (Dynamic contact analyzer, DCA-32, Thermo Cahn Ins.) was immersed into distilled water and held below the water surface (1.0 mm) for a total of 8h run. The amount of adsorbed water as a function of time was recorded every 3 sec. This test was performed at room temperature and in triplicates.
4. Nutrient release from biochar pellets Nutrient release from biochar pellets was assessed by batch extraction experiment using a vacuum extractor (Sampletek) equipped with 24 cylinders. The vacuum extraction was performed by drawing the extractant into receiving syringes through mechanical force controlled by a programmable micro-processor. Filter pulp (1g) was put into the bottom of the cylinder (60 mL) and thereafter biochar pellets (approximately 5g) were added (60 mL). Successive batch extraction was performed with removal and replacement of water (50 mL) for desired time until 432h (18 days). The collected water was filtered using 0.45 mm filter and stored in a refrigerator until analysis by ICP-OES.
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Findings 1. Characterization of biochar pellets 1.1. Chemical composition The chemical characteristics of the biochar pellets are presented in Table 1. Switchgrass biochar contained 5.6% of ash, 40.6% of volatile matter and high amounts of inorganic compounds such as K (3622 mg kg-1), Ca (4055 mg kg-1), Mg (2504 mg kg-1) and other compounds. Lignin, used in this study as a binder, contained 2.4 wt% of ash and high amount of Na (6397 mg kg-1) and S (10381 mg kg-1), which derived from the Kraft process, although Indulin AT lignin was purified by acid hydrolysis. As lignin was blended with biochar with increasing ratio from 10 to 30 wt%, volatile matter increased from 42.2 to 46% in biochar pellets dried at 105 oC and from 41.6 to 44.7% in biochar pellets dried at 180 oC. With increasing lignin ratios, the amount of major inorganic compounds K, Ca, Mg and P in biochar pellets decreased, whereas the amount of Na, and S increased. The pellets embedded with fertilizer contained 8366 – 8500 mg kg-1 of K and 2050 – 2324 mg kg-1 of P. Table 1 Proximate analysis and inorganic elements presented in biochar and biochar pelletsa.
Sample Proximate analysis (%) Inorganic elements (mg/kg)
Water content
Volatile Matter
Ash content
Fixed carbon K Ca Mg Na P S
Biochar 1.4 (0.3)
40.6 (1.9)
5.6 (0.9)
52.4 (1.6)
3622 (118)
4055 (105)
2504 (10)
87 (1)
815 (28)
498 (29)
Lignin - - 2.4 - 605 (14)
137 (9)
164 (2)
6397 (193)
14 (1)
10381 (209)
Biochar Pellet
10% lignin
0.9 (0.6)
42.2 (2.1)
5.6 (0.3)
52.1 (2.4)
4368 (153)
4308 (36)
2713 (32)
1202 (17)
836 (15)
1630 (23)
20% lignin
0.3 (0.3)
43.2 (0.9)
5.0 (0.2)
51.8 (1.0)
3266 (74)
3996 (220)
2457 (71)
1950 (106)
801 (47)
2595 (134)
30% lignin
1.1 (0.1)
46.0 (2.1)
4.8 (0.3)
49.2 (1.8)
2852 (97)
3432 (210)
2179 (74)
2816 (94)
722 (24)
3745 (115)
Biochar Pellet with fertilizer
10% lignin
0.9 (0.6)
42.2 (2.1)
5.6 (0.3)
52.1 (2.4)
8366 (195)
4308 (36)
2713 (32)
1202 (17)
2324 (176)
1630 (23)
20% lignin
0.3 (0.3)
43.2 (0.9)
5.0 (0.2)
51.8 (1.0)
8500 (222)
3996 (220)
2457 (71)
1950 (106)
2250 (96)
2595 (134)
30% lignin
1.1 (0.1)
46.0 (2.1)
4.8 (0.3)
49.2 (1.8)
8428 (15)
3432 (210)
2179 (74)
2816 (94)
2050 (53)
3745 (115)
a All samples were average values calculated from N = 3 replicate measurements, with standard deviation values in parentheses
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1.2. Thermal properties Thermogravimetric (TG) and derivative TG (DTG) combustion curves (Fig. 1) under air condition were analyzed for thermal decomposition of biochar pellets. Raw biochar and biochar pellets produced with 10 wt% lignin and dried at 105 and 180 oC possessed similar TG and DTG thermograms (Fig. 1a and 1b). The DTG curves in Fig. 1b showed that the maximum mass loss rate (DTG peak) occurred at 327 - 330 oC and was associated with thermal decomposition of cellulose, hemicellulose and lignin that volatilized and followed by producing the corresponding biochars. The DTG peaks at 412 – 445 oC were assigned to thermal degradation of the biochars derived from cellulose, hemicellulose and lignin (Kim et al., 2011). As lignin content increased from 10 to 20 and 30 wt% in biochar, a shift toward higher combustion temperature (Fig. 1c) was observed in the pellets dried at 180 oC (Fig. 1d). The peaks at 327-330 oC did not shift in biochar pellets dried at 105 oC. However, the DTG peaks at 450-480 oC were broader at higher temperature in biochar pellets dried at 180 oC with increasing lignin content to 30 wt%. The observed shift of DTG shoulder peak was attributed to condensed and cross-linked lignin that was produced at high temperature (180 oC).
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Fig. 1. TGA of biochar and biochar pellets produced with 10, 20, 30% lignin and dried at 105 and 180 oC. (a) TG (b) DTG of biochar and biochar pellet 10-105 and 10-180. (c) TG (d) DTG of biochar pellet 20-105 and 20-180 (e) TG and (d) DTG of biochar pellet 30-105 and 30-180.
Temp (oC)200 400 600 800
DTG
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t)
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TG (c) DTG (d)
TG (e) DTG (f)
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1.3. Surface functionality The surface functionality of biochar pellets was assessed by FTIR-ATR (in the 4,000 -
600 cm-1 range). As expected, the addition of lignin as a binder (from 0 to 30 wt%) led to a significant increase in the peak intensity at 1266 cm-1 (C-O stretching in lignin) and at 1511 cm-1 (C=C stretching vibration of lignin). In order to clearly delineate the differences in the FTIR spectra collected on the biochar pellets with different binder ratios and drying temperatures, principal component analysis (PCA) was performed on the 1,800 – 600 cm-1 region (Fig. 2). The scores plot (Fig. 2a) of the PCA for biochar and the corresponding pellets containing 10 to 30 wt% of lignin and drying temperature at 105 and 180 oC showed a noticeable separation with increasing amount of lignin by the first principal component (PC1, accounting for 64% of the total spectral variance). As expected from the PC1 loadings (Fig. 2b), the variables responsible for this separation were bands related to lignin (C-H bonds in guaiacyl ring (1140 cm-1), C-O stretching (1200 and 1266 cm-1) and C=C stretching (1511cm-1)).
PCA was also conducted on biochar pellets containing the same amount of lignin but processed at two temperatures (Fig. 2c, 2e and 2f). A separation between the two sample sets demonstrated that temperature significantly impacted the chemistry of the pellets. The corresponding loadings plots (Fig. 2d, 2f and 2h) showed that biochar pellets dried at 180 oC contained higher amount of aromatic rings (1430 – 1630 cm-1) and C-O-C stretching (1385 cm-1), which evidenced the formation of ether groups through condensation. These results indicate that lignin dried at higher temperature (180 oC) than its glass transition temperature (150 - 160 oC) softens and flows, resulting in bonding biochar particles and followed by aromatic condensation and cross-linking (Stelte et al., 2012).
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Fig. 2. PCA of FTIR spectra collected from raw biochar and biochar pellets produced at different lignin content and drying temperature (105 and 180 oC). (a) Scores plot and (b) loadings plot of all biochar and pellets. (c) Scores plot and (d) loadings plot of biochar pellets 10-105 and 10-180. (e) Scores plot and (f) loadings plot of biochar pellets 20-105 and 20-180. (g) Scores plot and (h) loadings plot of biochar pellets 30-105 and 30-180.
PC1 (64%)-3 -2 -1 0 1 2
PC2
(18%
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-2
-1
0
1
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Wavenumber (cm-1)60080010001200140016001800
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Wavenumber (cm-1)60080010001200140016001800
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PC1 (59%)-2.0-1.5-1.0-0.50.00.51.01.5
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PC1 (55%)-2.0-1.5-1.0-0.50.00.51.01.5
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(28%
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0.0
0.5
1.0
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Wavenumber (cm-1)60080010001200140016001800
Load
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0.00
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PC1 (55%)
1.0 0.5 -1.5 -1.0 -0.5 1.5 2.0
1.0 0.5 -1.5 -1.0 -0.5 1.5 2.0
0.10
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0.10
0.05
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(a) (b)
(c) (d)
(e) (f)
(g) (h)
Raw biochar
10-105 10-180
20-105
20-180
30-105
30-180
10-105
10-180
20-105
20-180
30-105 30-180
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1.4. Mechanical properties Density calculated by measuring weight and dimension of the pellets showed that biochar
pellets dried at 105 oC with different lignin content of 10, 20 and 30% had similar density, ranging from 861 to 878 kg/m3, whereas biochar pellets dried at 180 oC had a lower density from 875 to 776 kg/m3 with increasing lignin ratios. This was attributed to the removal of volatile matters present in lignin (Table 1) without any change in the shape of the pellet during drying (180 oC). Maximum compressive strength, measured by applying the maximum load that a biochar pellet can sustain without any crack or breakage, decreased from 3.54 to 2.33 MPa for pellets dried at 105 oC. The same pattern was observed for biochar pellets dried at 180 oC (4.68 to 2.51 MPa). These results indicate that biochar pellets containing higher lignin amount became harder and more brittle due to the excessive glass transition temperature of lignin during drying temperature (180 oC) (Reza et al., 2012). When compared to torrefied biochar pellet produced using hydraulic press (7.5 Megaton, estimated 2,000 MPa) with a controlled temperature (140 oC) (Reza et al., 2012), our biochar pellets produced using a pellet mill (172 MPa) under temperature of 65 - 85 oC had approximately 21 - 85 times lower compressive strength. Biochar pellets produced with increasing lignin content from 10 to 30 % showed a decrease in abrasion index from 15.3 to 5.6 % when dried at 105 oC and from 14.1 to 3.9 % when dried at 180 oC. Decreasing abrasion index with increasing lignin content indicates the increase of durability of biochar pellets.
Table 2 Mechanical properties of biochar pellets produced with different lignin contents and at different drying temperature.
a Density was calculated by measuring diameter, length and mass of 10 cylindrical biochar pellets. b Durability was calculated by difference (durability % =100 – abrasion index %).
Sample aDensity (kg/m3)
Abrasion index
(wt %)
bDurability (%)
Maximum compressive
strength (MPa)
Drying temp.
Added binder
Biochar pellet
105 oC
10% 878(45) 15.3 (0.6) 84.7 3.54 (1.38)
20% 861(57) 11.8 (0.0) 88.2 2.48(0.84)
30% 863(36) 5.6 (0.1) 94.4 2.33 (0.76)
180 oC
10% 875(22) 14. 1 (0.5) 85.9 4.68 (0.99)
20% 812(48) 11.1 (1.5) 88.9 3.26 (0.89)
30% 776(35) 3.9 (1.5) 96.1 2.51 (0.35)
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1.5. Water uptake of biochar pellets Capillary rise (wicking), a process by which liquid penetrates spontaneously into porous material by capillary force (Siebold et al., 1997), was applied to measure water uptake of biochar pellets (Fig. 3). The water uptake curves of biochar pellets produced with 10, 20 and 30% lignin and dried at 105 oC (Fig. 3a, 3c and 3e) showed two stages of water uptake; a sharp increase in the first 10 - 20 min followed by a gradual increase overtime. During the first stage of the rapid water uptake, biochar pellets with 10% lignin and dried at 105 oC, adsorbed up to 35 - 41 wt% of water, while pellets with 20 % lignin adsorbed 51 – 53 wt% and pellets with 30% lignin adsorbed 64 – 69 wt% of water. This difference in adsorption could be attributed to the presence of hydrophilic surface functionalities (C=O, O-H and C-O-C) in the biochar pellets and lignin (Fig. 2). Biochar pellets dried at 180 oC had a water uptake of 57 – 63 wt% within the first 23 min followed by a gradual uptake overtime, a trend similar to that of biochar pellets dried at 105 oC. However, biochar pellets dried at 180 oC demonstrated a higher water adsorption capacity (accumulated 72 – 76 wt%) than biochar pellets dried at 105 oC (accumulated 52 – 56 wt%) after 8h, which may be attributed to increasing functional groups by lignin condensation at 180 oC (Fig. 2). Biochar pellets produced with higher amount of lignin (20 and 30 %) and dried at 180 oC possessed a different water uptake behavior than the other biochar pellets. Within the first 15 min, a sharp water uptake (19 – 22 wt%) was observed, however compared to biochar pellets dried at 105 oC, the amount adsorbed is lower. In the second stage of water uptake, a sharper water uptake was observed for the pellets with 20 % lignin at 180 oC. Biochar pellets with 30% lignin at 180 oC had sharper water uptake slop than other biochar pellets within the first 4h and thereafter gradual uptake (90 – 92 wt%). The sharp water uptake in the second stage in biochar pellets with 20 and 30% lignin and dried at 180 oC may result from production of high porosity among the biochar particles and lignin, which is produced by removing volatile matter from lignin (Table 1), decreasing density (Table2) and increasing lignin condensation and cross-linking (Fig. 2) at 180 oC.
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Fig. 3. Water uptake of biochar pellets. Lines presented triplicate runs of each sample. (a) 10-105, (b) 10-180, (c) 20-105, (d)20-180, (e) 30-105, and (f) 30-180 represent biochar pellets produced with 10, 20 and 30% lignin and dried at 105 and 180 oC respectively.
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80
100
Time (hr)0 2 4 6 8
Ads
orbe
d H
2O/p
elle
t (w
/w%
)
0
20
40
60
80
100
(a) 10-105 (b) 10-180
(c) 20-105 (d) 20-180
(e) 30-105 (f) 30-180
15
2. Nutrient release 2.1. Nutrient release from biochar pellets
The cumulative nutrients (sum of all nutrients released at a particular time) naturally present in raw biochar and biochar pellets were rapidly released within the first 24 h followed by a more gradual release rate within 432 h (Fig.4). Raw biochar released 49.8 % of total K (3622 mg kg-1) within 24 h and 82 % by 432 h. Biochar pellets blended with 10, 20 and 30% lignin and dried at 105 oC released 79, 82 and 76% within 24 h, respectively. All biochar pellets released more than 97% of total K within 432 h. Biochar pellets dried at 105 oC demonstrated higher K release rates than raw biochar. This difference in K release may be attributed to smaller particle sizes generated by the pellet mill during the pelletization step. This could imply that nutrients present in smaller particle sizes of biochars are released faster than in larger particle sizes. However, biochar pellets dried at 180 oC showed a significant decrease of release rate of K with increasing lignin amount. Biochar pellets with 10% lignin released 74.1% of total K (4368 mg kg-1) while biochar pellets with 30% lignin released only 39.5% of total K (2852 mg kg-1) within 24h, and then released 97 and 75% within 432h, respectively. Therefore, by controlling the amount of binder, one can control the amount of K that is being released in biochar pellets.
The cumulative release percentage of P from raw biochar was 46.3% within 24 h and 56.4% within 432 h. Biochar pellets with 10% lignin and dried at 105 and 180 oC possessed similar release pattern with 65% within 24 h and 95% within 432 h. This result could also be attributed to smaller particle sizes of biochar in the pellets with low lignin content. P release % in biochar pellets with 20 and 30% lignin and dried at 105 oC was lower than P release in the biochar pellets with 10% lignin and higher in raw biochar. However, when biochar pellets were dried at 180 oC, P release % was 41.5% in biochar pellets with 20% lignin and 39.1% in biochar pellets with 30% lignin within 24 h, and then 57 and 48.4% in 432 h, respectively.
The cumulative release percentage of Ca and Mg from raw biochar and biochar pellets by time showed similar trend than K and P. Total release % was 31% of total Ca and 45.3% in raw biochar within 432 h. Biochar pellets with increasing lignin % released lower amount of Ca (3 - 6%) and Mg (12.9 - 20%) within 432 h. These findings could be explained by the fact that Ca and Mg have lower solubility than K and these elements may be bonded with surface negative functional groups present in biochar and lignin.
16
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
5000
6000
K_Biochar
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
P_Biochar
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
5000
6000
K_10-100K_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
P_10-100P_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
5000
6000
K_20-100K_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
P_20-100P_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
5000
6000
K_30-100K_30-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
P_30-100P_30-180
K 3622 mg kg-1 P 815 mg kg-1
K 4368 mg kg-1 P 836 mg kg-1
K 3266 mg kg-1 P 801 mg kg-1
K 2852 mg kg-1 P 722 mg kg-1
(a) (b)
(c) (d)
(e) (f)
(g) (h)
105 105
105 105
105 105
17
Fig. 4. Nutrient release (K and P) from biochar pellets with lignin content 10, 20 and 30% and dried at 105 and 180 oC.
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
Ca_Biochar
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
3000
Mg_Biochar
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
Ca_10-105Ca_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
3000
Mg_10-105Mg_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
Ca_20-105Ca_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0200400600800
100012001400
Ca_30-105Ca_30-180 Time (hr)
0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
3000
Mg_20-105Mg_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
3000
Mg_30-105Mg_30-180
Mg (2504 mg/kg)
Mg (2713 mg/kg)
Mg (2457 mg/kg)
Mg (2174 mg/kg)
Ca (4055 mg/kg)
Ca (4308 mg/kg)
Ca (3996 mg/kg)
Ca (3432 mg/kg)
(a) (b)
(c) (d)
(e) (f)
(g) (h)
18
Fig. 5. Nutrient release (Ca and Mg) from biochar pellets with lignin content 10, 20 and 30% and dried at 105 and 180 oC.
2.2. Nutrient release from biochar pellets embedded with K and P fertilizer Biochar pellets embedded with K fertilizer (8366 – 8499 mg kg-1) dried at 105 oC
released 74 - 77% of K with 10, 20 and 30% lignin. Subsequently, all biochar pellets released 87, 85, and 77%, respectively. Biochar pellets dried at 180 oC and containing 10, 20 and 30% lignin, released 62, 59 and 53% of K, respectively within 24 h. After 432 h, K released was 87, 85 and 78% for pellets with 10, 20 and 30% lignin, respectively. Biochar pellets with P fertilizer dried at 105 oC released 77 – 85 % of total P (2049 – 2323.5 mg kg-1) within 24 h and 89 - 95% within 432 h. However, biochar pellets dried at 180 oC released only 49 – 62 % within 24 h and 73 – 78% within 432 h. These findings demonstrate that the release of fertilizers embedded in biochar pellets can also be regulated by controlling the amount of binder.
As Indulin AT lignin, containing high amounts of Na (6397 mg kg-1) and S (10381 mg kg-1), was added to biochar pellets (Table 1), amount of Na in biochar pellets increased from 1202 to 2816 mg kg-1 with increasing lignin content from 10 to 30 wt%. All biochar pellets dried at 105 oC released abruptly 68 – 75% of Na within the first 24h. However, biochar pellets dried at 180 oC released 59 and 50% in biochar pellet with 10 and 30% within 24 h and thereafter released 78 and 71% of Na with 10 and 30% of lignin within 432 h. The release pattern of S was also similar with that of Na, but release % of S in 432 h was significantly lower than that of Na, which is attributed to the covalently bound S with lignin derived from the kraft process (Beis et al., 2010). These findings demonstrate that nutrient-release rates can be controlled by binder amount and by drying temperature.
19
Fig. 6. Nutrient release (K and P) from biochar pellets embedded with K and P fertilizer, lignin content 10, 20 and 30 %, and dried at 105 and 180 oC.
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
2000
4000
6000
8000
10000
K_20-105K_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
P_10-105P_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
2000
4000
6000
8000
10000
K_10-105K_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
P_20-100P_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
2000
4000
6000
8000
10000
K_30-105K_30-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
500
1000
1500
2000
2500
P_30-105P_30-180
K 8428.1 mg kg-1 P 2049.6 mg kg-1
K 8499.6 mg kg-1 P 2250 mg kg-1
K 8366.1 mg kg-1 P 2323.5 mg kg-1
105
20
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
50
100
150
200
Na_Biochar
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
Na_10-105Na_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
Na_20-105Na_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
Na_30-105Na_30-180
Na (87 mg/kg)
Na (1202 mg/kg)
Na (1980 mg/kg)
Na (2816 mg/kg)
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
100
200
300
400
500
600
S_Biochar
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000S_10-105S_10-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000S_20-100S_20-180
Time (hr)0 100 200 300 400
Cum
ulat
ive
rele
ase
(mg/
kg)
0
1000
2000
3000
4000
S_30-105S_30-180
S (498 mg/kg)
S (1630 mg/kg)
S (2595 mg/kg)
S (3745 mg/kg) (h)
(a) (b)
(c) (d)
(e) (f)
(g)
105
21
Fig. 7. Nutrient release (Na and S) from biochar pellets with lignin content 10, 20 and 30% and dried at 105 and 180 oC.
Conclusions This study concludes that when switchgrass-derived biochars produced by fast pyrolysis are blended with fertilizer and lignin followed by pelletization and then a drying process at temperature higher than lignin’s glass transition temperature, the resulting biochar pellets are more durable and have higher porosity and surface functionality. These properties in biochar pellets contribute in holding nutrients for a longer time in the biochar pellets and participate in their slow release. Therefore, nutrient-rich biochar pellets may be a potential candidate for a cost-effective slow-release fertilizer in soil.
22
Reference
Abdullah, H., Wu, H. 2009. Biochar as a Fuel: 1. Properties and Grindability of Biochars Produced from the Pyrolysis of Mallee Wood under Slow-Heating Conditions. Energy & Fuels, 23(8), 4174-4181.
Beis, S.H., Mukkamala, S., Hill, N., Joseph, J., Baker, C., Jensen, B., Stemmler, E.A., Wheeler, M.C., Frederick, B.G., van Heiningen, A., Berg, A.G., DeSisto, W.J. 2010. FAST PYROLYSIS OF LIGNINS. Bioresources, 5(3), 1408-1424.
Cantrell, K.B., Hunt, P.G., Uchimiya, M., Novak, J.M., Ro, K.S. 2012. Impact of pyrolysis temperature and manure source on physicochemical characteristics of biochar. Bioresource Technology, 107(0), 419-428.
Cantrell, K.B., Martin II, J.H. 2012. Poultry litter and switchgrass blending and pelletizing characteristics for biochar production. 2012 ASABE Annual International Meeting, 2012, Dallas, Texas. American Society of Agricultural and Biological Engineers. pp. 12-1337605.
Fernández-Escobar, R., Benlloch, M., Herrera, E., Garcı́a-Novelo, J.M. 2004. Effect of traditional and slow-release N fertilizers on growth of olive nursery plants and N losses by leaching. Scientia Horticulturae, 101(1–2), 39-49.
Hua, L., Wu, W.X., Liu, Y.X., McBride, M., Chen, Y.X. 2009. Reduction of nitrogen loss and Cu and Zn mobility during sludge composting with bamboo charcoal amendment. Environmental Science and Pollution Research, 16(1), 1-9.
Husk, B., Major, J. 2008. Commercial scale agricultural biochar field trial in Quebec, Canada, over two years: Effects of biochar on soil fertility, biology, crop productivity and quality. Blue Leaf.
Kim, P., Johnson, A., Edmunds, C.W., Radosevich, M., Vogt, F., Rials, T.G., Labbe, N. 2011. Surface Functionality and Carbon Structures in Lignocellulosic-Derived Biochars Produced by Fast Pyrolysis. Energy & Fuels, 25(10), 4693-4703.
Kim, P., Johnson, A.M., Essington, M.E., Radosevich, M., Kwon, W.T., Lee, S.H., Rials, T.G., Labbe, N. 2013. Effect of pH on surface characteristics of switchgrass-derived biochars produced by fast pyrolysis. Chemosphere, 90(10), 2623-2630.
Lehmann, J., Rillig, M.C., Thies, J., Masiello, C.A., Hockaday, W.C., Crowley, D. 2011. Biochar effects on soil biota – A review. Soil Biology and Biochemistry, 43(9), 1812-1836.
Major, J., Lehmann, J., Rondon, M., Goodale, C. 2010. Fate of soil-applied black carbon: downward migration, leaching and soil respiration. Global Change Biology, 16(4), 1366-1379.
Mortain, L., Dez, I., Madec, P.J. 2004. Development of new composites materials, carriers of active agents, from biodegradable polymers and wood. Comptes Rendus Chimie, 7(6-7), 635-640.
Reza, M.T., Lynam, J.G., Vasquez, V.R., Coronella, C.J. 2012. Pelletization of Biochar from Hydrothermally Carbonized Wood. Environmental Progress & Sustainable Energy, 31(2), 225-234.
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Ro, K.S., Cantrell, K.B., Hunt, P.G. 2010. High-Temperature Pyrolysis of Blended Animal Manures for Producing Renewable Energy and Value-Added Biochar. Industrial & Engineering Chemistry Research, 49(20), 10125-10131.
Siebold, A., Walliser, A., Nardin, M., Oppliger, M., Schultz, J. 1997. Capillary rise for thermodynamic characterization of solid particle surface. Journal of Colloid and Interface Science, 186(1), 60-70.
Stelte, W., Sanadi, A.R., Shang, L., Holm, J.K., Ahrenfeldt, J., Henriksen, U.B. 2012. RECENT DEVELOPMENTS IN BIOMASS PELLETIZATION - A REVIEW. Bioresources, 7(3), 4451-4490.
Zhang, Y., Hosseinaei, O., Wang, S.Q., Zhou, Z.B. 2011. INFLUENCE OF HEMICELLULOSE EXTRACTION ON WATER UPTAKE BEHAVIOR OF WOOD STRANDS. Wood and Fiber Science, 43(3), 244-250.
24
Final (actual) budget 1. Actual Dollars Spent:
BUDGET ITEM SUN GRANT $ COST SHARE $
a. Total Salaries & Wages $35,000
b. Fringe Benefits $16,884
c. Supplies $10,000
d. Equipment
e. Travel $5,000
f. Publications $2,000
g. Other (Subcontractors, Consultants) $3,000 $20,000
Total DIRECT COSTS (Sum of A-G) $74,884
Total INDIRECT (i.e. F&A) COSTS
(IDC Usually = Total Direct Costs*.25)
$18,721
h. Graduate Student Tuition
i. Permanent Equipment ($5,000 or More)
j. Other Costs Not Requiring Indirect
Total DOLLARS SPENT
(Total Direct + Total Indirect + H + I + J)
2. Describe all Cost Share: a) Sources b) Proton Power supported the project by making in-kind contribution in the optimization of
the pyrolysis system, the production of the biochars, and the pellets.
25
Publication and Presentations Kim, P. et al. (2012), Poster presentation, “Characterization of nutrient-embedded biochar pellets as a slow release fertilizer material”, 2012 National conference, Science for biomass feedstock production and utilization, October 2-5, 2012, New Orleans, LA. USA.
Labbé, N. and Kim, P. (2013), Poster presentation, “Nutrient release of biochar pellets embedded with fertilizers”, 2013 BIO Pacific Rim Summit on Industrial Biotechnology and Bioenergy, Dec. 8-11, 2013, San Diego, CA, USA.
Kim, P. and Labbé, N. (2013) “Nutrient release from switchgrass-derived biochar pellets embedded with fertilizers”, in preparation.
Contracts Related to this Project since Project Inception Nicole Labbé, “Screening of biomass and processes to upgrade bio-fuels”, supported by Proton Power Inc. 10/2012 - 04/2013 ($174,000). Nicole Labbé and Pyoungchung Kim, “Characterization and upgrade of bio-oils and development of activated carbons from biochars, supported by Proton Power Inc. 05/2013-05/2015 ($285,879).