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Effects of composing on sorption capacity of bagasse-based chars
Waste Management 30 (2010) 995–999
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Effects of composing on sorption capacity of bagasse-based chars Lo Tsui *, Ming-An Juang MingChi University of Technology, Safety, Health and Environmental Engineering, 84 Gungjuan Rd., Taishan, Taipei, Taiwan
a r t i c l e
i n f o
Article history: Accepted 10 February 2010 Available online 4 March 2010
a b s t r a c t A fresh bagasse sample (0-month) and two composted bagasse and pig manure mixed samples (1-month and 6-month) were used to produce carbon chars. Sample pyrolysis showed greater carbon char yields were obtained from the compost samples than from the bagasse sample. Fourier transform infrared spectra suggested that the chemical structures of the bagasse sample and the two compost samples were quite different, but that the three carbon chars obtained from those precursors were similar. Among the three pyrolyzed chars, the 0-month bagasse char displayed the largest sorption capacity of 3333 mg kg 1 for the hydrophilic pollutant phenol, presumably resulting from its greater carbon content and O/C ratio. However, the sorption capacities for the hydrophobic pollutant naphthalene of the tow compost chars (3-month, 2001 mg kg 1; 6-month, 1667 mg kg 1) were greater than that of the 0-month bagasse char (1428 mg kg 1). The results indicate that the compost chars had a greater preferential affinity for naphthalene than that in the bagasse char, suggesting that the compost chars possessed greater hydrophobicity. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Activated carbons (AC) are often used as an adsorbent for controlling environmental pollutants. Traditionally, the main precursor in the production of commercial AC is coal, but, due to the high cost of coal, some researchers have focused on finding lower cost materials to produce AC (Sharma et al., 2004; Carrott and Carrott, 2007; Dias et al., 2007; Ioannidou and Zabaniotou, 2007). Although several studies have demonstrated that high surface area AC can be produced from some agricultural wastes, not all wastes are suitable as precursors for AC, mainly due to their high content of volatile substances and their low thermal stability. However, most organic wastes can be composted, and composted materials have shown greater thermal stability than their corresponding precursors (Dell’Abate et al., 1998; Pietro and Paola, 2004; Lopez-Capel et al., 2005), suggesting that it may be possible to produce AC from composted material. Thermal analysis is a rapid method to assess the thermal stability of organic materials (Dell’Abate et al., 1998; Pietro and Paola, 2004; Lopez-Capel et al., 2005). In general, such analysis reveals that more labile carbon sources are decomposed at lower temperatures than more recalcitrant components. For example, when using thermal analysis to study organic matter evolution during the composting of municipal solid waste, Pietro and Paola (2004) found that weight loss in less-mature composted samples happened at lower temperatures (210–320 °C) than in matured compost (400–520 °C). Those results were consistent with their * Corresponding author. Tel.: +886 2 29089899x4652; fax: +886 2 29041914. E-mail address: [email protected] (L. Tsui). 0956-053X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2010.02.014
additional observations that less-mature compost was characterized by greater amount of aliphatic components, and that moremature compost was characterized by aromatic moieties. If mature compost shows greater thermal stability than the initial organic waste, a greater yield of carbon char might be obtained from a more-mature compost sample. In our previous study, we demonstrated that carbon char produced from a yard-waste compost sample produced a sorption capacity for the hydrophobic pollutant atrazine that was comparable to that from AC produced from corn stillage waste, even though compost char had much less surface area than that of the corn stillage AC (Tsui and Roy, 2008). In that study, however, the mechanism contributing to the high hydrophilic sorption capacity of compost char was not determined, because the precursor materials for producing the carbon char and the AC were different. In this study, therefore, we selected bagasse compost samples with different maturities as the precursors for producing carbon chars in order to study the effects of compost maturity on the quality of carbon chars. In addition, the sorption capacities of the produced carbon chars for both hydrophobic and hydrophilic pollutants were evaluated.
2. Materials and methods 2.1. Materials One fresh sugarcane bagasse sample (0-month) and two bagasse and pig manure compost samples (1-month and 6-month) were collected from one composting facility in Taiwan. The three
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samples were selected to represent initial agricultural residue, less-mature compost, and fully mature compost, respectively. At the composting facility, the bagasse/manure composting pile was prepared by mixing bagasse with pig manure at an approximately ratio of 20:1 weight/weight (w/w) on a dried weight basis. Subsequently, the moisture content of the composting mass was kept at 45–60% (w/w). The pile was turned mechanically every 2 weeks during the initial bio-oxidative phase (the first 2 months), and once a month thereafter. The collected samples were gently ground in an agate mortar, and screened through a 1.0-mm sieve. The sieved samples were heated at 105 °C overnight prior to chemical characterization or carbonization treatment.
2.2. Samples characterizations Thermogravimetric (TG) analysis coupled with differential thermogravimetric (DTG) analysis of the bagasse and the two bagasse/ manure compost samples were carried out carried out using a Perkin–Elmer DTA/TGA 7 analyzer (Perkin–Elmer, Shelton, CT, USA). Briefly, 3 mg of a dried sample was placed in an alumina crucible, which was then introduced into the thermobalance. The temperature was increased from 20 to 800 °C at a rate of 20 °C min 1 under a nitrogen flow of 20 mL min 1. TG analysis showed that all tested samples reached relatively thermal stability at 400 °C; thus, that temperature was selected as the pyrolyzed temperature. During pyrolysis, 50 g of dried sample was put in a 5 cm diameter horizontal quartz tube in a Lindberg 59344 furnace (Lindberg/MPH, Riverside, MI, USA). The tube was then heated at a rate of 20 °C min 1 to a carbonization temperature of 400 °C in flowing ultra-high purity N2. The sample was maintained at the final temperature for 1 h, then allowed to cool to ambient temperature under continuous flowing N2. The sample remainder was weighed, and the carbon char yield defined as the ratio of the weight of the pyrolyzed char to that of the original sample. The ash content of each pyrolyzed carbon char and the respective precursors were determined by combustion at 800 °C in air. Measurements of C, H, N, and S were obtained using a LECO CHNS-932 microanalysis apparatus (Leco Corp., St. Joseph, MI, USA). The ultimate analyses of C, H, N, and S content were calculated on an ash-free basis, with O content determined by the difference. Fourier transform infrared (FTIR) spectra were obtained on a Nicolet 550 Magna-IR spectrometer (Nicolet Instrument Corp., Madison, WI, USA). The samples were prepared for analyses by mixing 200 mg of KBr with 2.0 mg of sample material. That mixture was then pressed into pellets. Thirty-two scans per sample were performed in the 4000–400 cm 1 wavelength range, in transmission mode, and the collected spectra were averaged and corrected against ambient air as the background level. The surface areas and pore volume of each sample were assessed by Brunauer–Emmett–Teller (BET) nitrogen adsorption measurement in a static volumetric apparatus (ASAP 2010, Micrometrics, Norcross, GA, USA). Before N2 adsorption, each sample was outgassed (30:70, N2:He) under vacuum at 300 °C overnight. The subsequent nitrogen adsorption measurement was conducted at 77 K to estimate total pore volume (Vpore). Surface area (Spore) was calculated from the linearized BET equation, and micropore volume (Vmicro) and mesopore surface area were obtained by using the t-plot method (Nagano et al., 2000). The micropore surface area (Smicro) was obtained by deducting the mesopore surface area from Spore. In addition to obtaining the N2-BET measurement, the iodine indexes of the three carbon char samples were determined according to the procedure described by Aziz et al. (2009). Briefly, a carbon char sample (0.1 g) was placed in a dry Erlenmeyer flask and wetted with 10 cm3 of diluted HCl (5% by weight). A volume (100 cm3) of 0.1 mol L 1 was added to the flask and the mixture
vigorously shaken for 30 s. The liquid was filtrated and 50 cm3 removed and titrated with 0.01 mol L 1 sodium thiosulfate. 2.3. Adsorption studies Phenol and naphthalene were chosen as test pollutants in this study to evaluate the sorption capacities of the resultant chars. The water solubility of phenol and naphthalene is 83 g L 1 and 30 mg L 1, respectively. For adsorption equilibration 0.1 g of each carbon char were placed in separate flasks. Solutions of phenol or naphthalene (100 mL) with different initial concentrations (25– 300 mg L 1) were then added to the flasks. The flasks were then hermetically closed, and placed on an isothermal shaker and shaken at 25 ± 2 °C for 24 h. Solution pH was not adjusted. After equilibration, the carbon char suspensions were filtered, and the concentrations of the residual phenol or naphthalene measured using a Varian Cary 50 Bio UV–Vis spectrophotometer (Varian Australia Pty Ltd., Malgrave, Victoria, Australia). The wavelengths corresponding to phenol and naphthalene were 270 and 275.5 nm, respectively (Ania et al., 2007; Hameed and Rahman, 2008). To compare the maximum sorption capacities of the chars, the obtained equilibrium adsorption data were fitted to the Langmuir adsorption model. 3. Results and discussion 3.1. Thermal stability of bagasse samples The carbon char yields obtained from TG and pyrolysis analyses are shown in Table 1. The TG analysis was performed at a maximum temperature of 800 °C while pyrolysis was performed at 400 °C; regardless, the char yields from pyrolysis were smaller than the TG measured yields. The pyrolysis yield data, however, were still consistent with the TG results, with both showing that the samples with greater thermal stability produce larger char yields. The lower char yields from pyrolysis could be related to atmospheric oxygen entering the heating tube through an imperfect seal, thus causing burn-off of a portion of the carbon char; however, we have no data to support that conjecture. The lower char yield could also result from the longer time required for pyrolysis than for the TG procedure (total time for TG was 40 min while that for pyrolysis was 1 h). Among the three tested samples, the 0-month bagasse demonstrated the lowest thermal stability with a char yield of 16%, while the two compost samples had char yields greater than 50% (Table 1). The TG data also showed that the weight loss in the bagasse sample occurred at a lower temperature than in the two compost samples (Fig. 1), indicating that the 0-month sample was less thermally stable. There were two distinct DTG peaks (205 and 285 °C) in the 0-month sample. The two peaks may correspond to devolatilization of volatile matter and hemicellulose component (Lapuerta et al., 2004; Yang et al., 2007). All three samples exhib-
Table 1 The thermal stability and char yield of different compost samples. Samples
Thermal stability from TGa (%)
Char yield from pyrolysisb (%)
0-month bagasse sample 1-month bagasse/manure compost 6-month bagasse/manure compost
19 57
16 51
79
68
a The thermal stability was measured by heating the samples in TGA analyzer at maximum temperature of 800 °C. b The char yield was obtained by heating the samples in furnace at 400 °C for 1 h.
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Fig. 1. The thermal analysis of three bagasse samples with different maturity (a) TG curve (b) DTG curve.
ited a DTG peak at about 345 °C, which may be associated with the decomposition of the cellulose component (Yang et al., 2007). 3.2. Characteristics of collected samples and corresponding pyrolyzed chars The 6-month compost sample possessed the greatest thermal stability among the three tested samples, and its high thermal stability may be mainly related to its relatively high ash content (Table 2). In both compost samples, the relatively high ash content could result from the addition of 5% pig manure, which was mixed with the bagasse at the beginning of composting process. In addition, some soil clay particles could have been incorporated into the compost pile during mechanical turning, which would contribute to the total ash content in the compost samples. Although inorganic elements in the compost would reduce the carbon content, they could serve as catalysts to enhance the thermal decomposition of compost during pyrolysis (Muller et al., 1995), which could further promote the breakdown of the C–O bonds in compost char. This may help to explain why the two compost chars had smaller O/C ratios when compared with the 0-month bagasse char, even though the two raw materials (bagasse and pig manure) had similar initial O/C ratios (0.52 and 0.55, respectively; Table 2). Among the three carbon chars, the 1-month compost sample contained the largest fulvic acid content, while the 6-month sample had the largest humic acid content (data not shown). Based on
Fig. 2. The FTIR spectra of three bagasse samples with different (a) before pyrolysis (b) after pyrolysis.
a van Krevelan diagram depicting the atomic ratio of hydrogen to carbon on the y-axis versus the atomic ratio of oxygen to carbon on the x-axis, Schnitzer and Hoffman (1964) suggested that cellulose or wood materials are first converted to humic or fulvic acid before forming coal. Hence, if only the organic portion of the precursors is considered, it may be easier to produce carbon from the compost samples than from the fresh bagasse sample. Our results, which show that the two compost chars had greater carbon content than the bagasse char (Table 2), support that hypothesis. The results also imply that a better quality of carbon char can be
Table 2 Chemical characteristics of selected bagasse samples. Asha (%)
Samples
0-month bagasse sample 0-month bagasse char 1-month bagasse/manure sample 1-month bagasse/manure char 6-month bagasse/manure char 6-month bagasse/manure char a b c d
Ultimate analysisa,b
Chemical element measurementa C (%)
N (%)
H (%)
S (%)
C (%)
N (%)
H (%)
S (%)
Oc (%)
H/C (atomic ratio)
O/C (atomic ratio)
O/H (atomic ratio)
compost
1.89 6.05 29.09
51.41 74.96 32.84
0.69 0.12 1.72
8.84 1.09 3.42
1.31 0.21 0.47
52.40 79.79 46.31
0.70 0.13 2.43
9.01 1.16 4.82
1.34 0.22 0.66
36.55 18.70 45.78
2.06 0.17 1.25
0.52 0.17 0.74
0.25 1.01 0.59
compost
51.85
44.80
1.23
0.62
0.22
93.04
2.55
1.29
0.46
2.66
0.16
0.02
0.12
compost
46.23
28.96
1.56
4.16
0.93
53.86
2.90
7.74
1.73
33.77
1.72
0.47
0.27
compost
61.83
36.78
0.83
0.34
0.20
96.36
2.17
0.89
0.52
0.06
0.11
0.01d
0.01
Dry base. Ash-free base. Calculated by difference. The actual O/C ratio of 6-month bagasse compost char was 0.0005.
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Table 3 The surface area and iodine index of three carbon chars.
a b c d
Char samples
Sporea (m2 g
0-month bagasse char 1-month bagasse/manure compost char 6-month bagasse/manure compost char
2.57 5.22 7.81
1
)
Vporeb (cm3 g
1
)
0.0035 0.0126 0.0201
Smicroc/Spore
Vmicrod/Vpore
Iodine index (mg g
0.369 0.015 0.047
0.1065 0.0008 0.0049
12 16 38
1
)
Spore: Surface area obtained by N2-BET method. VPore: Total pore volume of carbon chars. Smicro: Micropore surface area. Vmicro: Micropore pore volume.
Fig. 3. Sorption isotherms for (a) phenol and (b) naphthalene onto various bagasse chars with different maturity.
produced from compost than that from fresh bagasse. Among the three samples, the 0-month bagasse had the lowest O/C ratio, implying it had the lowest level of oxygen-containing functional groups. After pyrolysis, however, the two compost chars had smaller O/C ratios than those of bagasse char sample, suggesting that the compost chars would have greater hydrophobicity. The 0-month bagasse sample produced a different FTIR spectrum than the spectra of the two compost samples (Fig. 2a), and that difference may be related to the addition of 5% pig manure to the compost samples. The compost samples showed two distinct peaks at 2920 and 2850 cm 1, and a smaller, sharp peak at 1515 cm 1. The two higher peaks correspond to aliphatic C–H, and a smaller peak related to aromatic skeletal (Huang et al., 2006; Perez-Sanz et al., 2006; Smidt et al., 2008). In contrast, the bagasse samples had a broad band at 3379 cm 1 (strongly hydrogen-bonded OH including OH of carboxylic acids), a peak at 1740 cm 1 (typical of C@O of undissociated COOH), a sharp peak of unsaturated C@C at 1640 cm 1 (C@O, C@C stretch), and a peak at 1250 cm 1 (C–O stretch of polysaccharide). All three samples created a peak at 1430 cm 1 (COO stretch), and a broad peak at 1080–1040 cm 1 (C–O stretch, Si–O stretch). After the samples were pyrolyzed, the FTIR spectra of the three carbon chars were similar (Fig. 2b), except that the 0-month bagasse char still showed a C@O stretch peak at 1720 cm 1. After pyrolysis of the 0-month sample, the peaks at 3379 cm 1 (H bonds) and 1250 cm 1 (polysaccharide) disappeared, and the peaks at 2920 and 2850 cm 1 (aliphatic C–H) significantly increased. The N2-BET surface areas and the iodine indexes of the three chars are compared in Table 3. After pyrolysis at 400 °C in nitrogen, the surface area of the three samples was generally low, with a maximum value of 7.81 m2 g 1 in the 6-month sample. The microporosities (Smicro/Spore) of the two compost chars were markedly smaller than that in the bagasse sample. These observations were consistent with other studies that have shown that natural organic matter surface areas are small when based on N2-BET measurement (De Jonge and Mittelmeijer-Hazeleger, 1996; Kaiser and Guggenberger, 2003; Makris et al., 2006). Those studies, however, also acknowledged that the N2-BET method generally underestimates the microporosity of organic matter, because N2 adsorption at 196 °C could be kinetically restricted. Among the three carbon
Table 4 The sorption parameters for phenol and naphthalene by different bagasse chars. Samples
Phenol Qmaxa (mg g
0-month 0-month 1-month 1-month 6-month 6-month a b
bagasse char bagasse char based on per gram of measured carbon base bagasse/manure compost char bagasse/manure compost char based on per gram of carbon base bagasse/manure compost char bagasse/manure compost char based on per gram of carbon base
Qmax: The maximum sorption capacity calculated from Langmuir isotherms. KL: The Langmiur affinity constant.
3333 4446 2512 5607 2000 5437
Naphthalene 1
)
r2
Qmax (mg g
21
0.97
15
0.98
11
0.96
1428 1905 2001 4466 1667 4532
KLb (mL g
1
)
1
)
KL (mL g
1
)
r2
125
0.96
178
0.95
143
0.95
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chars, the largest surface area and the highest iodine index were associated with the 6-month char; however, it should be noted that the measured surface area and iodine index could have be related, in part, to its high ash content (Table 2).
authors would like to thank William R Roy from ISGS for critically reading this manuscript.
3.3. The sorption behaviors of carbon chars
Ania, C.O., Cabal, B., Pevida, C., Arenillas, A., Parra, J.B., Rubiera, F., Pis, J.J., 2007. Effects of activated carbon properties on the adsorption of naphthalene from aqueous solution. Appl. Surf. Sci. 253, 5741–5746. Aziz, A., Quali, M.S., Elandaloussi, E.H., De Menorval, L.C., Lindheimer, M., 2009. Chemically modified olive stone: a low-cost sorbent for heavy metals and basic dye removal from aqueous solutions. J. Hazard. Mater. 163, 441–447. Carrott, S.P.J.M., Carrott, M.M.L.R., 2007. Lignin-from natural adsorbent to activated carbon: a review. Bioresour. Technol. 98, 2301–2312. De Jonge, H., Mittelmeijer-Hazeleger, M.C., 1996. Adsorption of CO2 and N2 on soil organic matter: nature of porosity, surface area, and diffusion mechanisms. Environ. Sci. Technol. 30, 4008–4013. Dell’Abate, M.T., Canali, S., Trinchera, A., Benedetti, A., Sequi, P., 1998. Thermal analysis in the evaluation of compost stability: a comparison with humification parameters. Nutr. Cycling Agroeco. 51, 217–224. Dias, J.M., Alvim-Ferraz, M.C.M., Almeida, M.F., Rivera-Utrilla, J., Sánchez-Polo, M., 2007. Waste materials for activated carbon preparation and its use in aqueousphase treatment: a review. J. Environ. Manage. 85, 833–846. Hameed, B.H., Rahman, A.A., 2008. Removal of phenol from aqueous solutions by adsorption onto activated carbon prepared from biomass material. J. Hazard. Mater. 160, 576–581. Huang, G.F., Wu, Q.T., Wong, J.W.C., Nagar, B.B., 2006. Transformation of organic matter during co-composting of pig manure with sawdust. Bioresour. Technol. 97, 1831–1842. Ioannidou, O., Zabaniotou, A., 2007. Agricultural residues as precursors for activated carbon production—a review. Renew. Sustain. Energy Rev. 11, 1966–2005. Kaiser, R., Guggenberger, G., 2003. Mineral surfaces and soil organic matter. Eur. J. Soil Sci. 54, 219–236. Lapuerta, M., Hernandez, J.J., Rodriguez, J., 2004. Kinetics of devolatilisation of forestry wastes from thermogravimetric analysis. Biomass Bioenergy 27, 385– 391. Lopez-Capel, E., Sohi, S.P., Gaunt, J.L., Manning, D.A.C., 2005. Use of thermogravimetry-differential scanning calorimetry to characterize modelable soil organic matter fractions. Soil Sci. Soc. Am. J. 69, 136–140. Makris, K.C., Sarkar, D., Datta, R., Ravikovitch, P.I., Neimark, A.V., 2006. Using nitrogen and carbon dioxide molecules to probe arsenic(V) bioaccessibility in soils. Environ. Sci. Technol. 40, 7732–7738. Muller, M.W., Hoffmann, W.R., Huttinger, K.J., 1995. Organic iron compounds as catalyst precursors in pitch pyrolysis. Fuel 74, 953–959. Nagano, S., Tamon, H., Adzumi, T., Nakagawa, K., Suzuki, T., 2000. Activated carbon from municipal waste. Carbon 38, 915–920. Perez-Sanz, A., Lucena, J.J., Graham, M.C., 2006. Characterization of Fe–humic complexes in an Fe-enriched biosolid by-product of water treatment. Chemosphere 65, 2045–2053. Pietro, M., Paola, C., 2004. Thermal analysis for the evaluation of the organic matter evolution during municipal solid waste aerobic composting process. Thermochim. Acta 413, 209–214. Schnitzer, M., Hoffman, I., 1964. Pyrolysis of soil organic matter. Soil Sci. Soc. Am. Proc. 28, 520–525. Sharma, R.K., Wooten, J.B., Baliga, V.L., Lin, X., Chan, W.G., Hajaligol, M.R., 2004. Characterization of chars from pyrolysis of lignin. Fuel 83, 1469–1482. Smidt, E., Meissl, K., Schwanninger, M., Lechner, P., 2008. Classification of waste materials using Fourier transform infrared spectroscopy and soft independent modelling of class analogy. Waste Manage. 28, 1699–1710. Tsui, L., Roy, W.R., 2008. The potential applications of using compost chars for removing the hydrophobic herbicide atrazine from solution. Bioresour. Technol. 99, 5673–5678. Yang, H.P., Yan, R., Chen, H.P., Lee, D.H., Zheng, C., 2007. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel 86, 1781–1788.
The sorption capacities for phenol and naphthalene of the three carbon chars are shown in Fig. 3 and Table 4. The 0-month bagasse char had the largest sorption capacity of 3333 mg kg 1 for phenol among the three carbon chars (Table 4). This result may be related to the high carbon content (75.0%) in the bagasse char, along with its high level of oxygen-containing functional groups (high O/C content) (Table 2). In contrast, the 1-month compost char had the greatest sorption capacity for naphthalene, despite it only having a 44.8% carbon content. The 6-month compost char also sorbed more naphthalene than did the 0-month bagasse char. The high sorption capacities of two compost chars for naphthalene may be related to their high hydrophobicity (low O/C content), as naphthalene has a low water solubility (30 mg L 1). When calculating the sorption capacity per gram of the carbon base, both of the compost chars sorbed more phenol than did the 0-month bagasse char. The results suggest that more-adsorptive pyrolyzed chars could be produced from composted material than from fresh material, as long as the ash content can be removed from the composted chars. 4. Conclusions Surface area is generally a useful index to evaluate the sorption capacity of AC. In our previous study, however, compost char had an equivalent sorption capacity for a hydrophobic pollutant when compared with AC derived directly from an agricultural residue, even though the compost char had a much smaller surface area than the AC (Tsui and Roy, 2008). The current study illustrates that the high sorption capacity of compost char mainly results from its high hydrophobicity. The results also show that compost chars can have greater sorption capacities for both phenol and naphthalene than fresh material chars, on a per gram of carbon basis (Table 4). Based on the greater yield of carbon char from the compost samples relative to the fresh bagasse sample, it may be economically feasible to produce adsorbent materials from compost rather than from fresh agricultural wastes, despite the energy and time needed to produce the composted material. However, because of the relatively high ash content of compost chars, research into concentrating carbon from the compost char is needed in order to increase the efficiency of producing and using compost char to remove hydrophobic pollutants from the environment. Acknowledgements This work was financially supported by the National Science Council (Taiwan) under Project No. NSC 95-2221-E-131-019. The
References
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Effects of composing on sorption capacity of bagasse-based chars Lo Tsui *, Ming-An Juang MingChi University of Technology, Safety, Health and Environmental Engineering, 84 Gungjuan Rd., Taishan, Taipei, Taiwan
a r t i c l e
i n f o
Article history: Accepted 10 February 2010 Available online 4 March 2010
a b s t r a c t A fresh bagasse sample (0-month) and two composted bagasse and pig manure mixed samples (1-month and 6-month) were used to produce carbon chars. Sample pyrolysis showed greater carbon char yields were obtained from the compost samples than from the bagasse sample. Fourier transform infrared spectra suggested that the chemical structures of the bagasse sample and the two compost samples were quite different, but that the three carbon chars obtained from those precursors were similar. Among the three pyrolyzed chars, the 0-month bagasse char displayed the largest sorption capacity of 3333 mg kg 1 for the hydrophilic pollutant phenol, presumably resulting from its greater carbon content and O/C ratio. However, the sorption capacities for the hydrophobic pollutant naphthalene of the tow compost chars (3-month, 2001 mg kg 1; 6-month, 1667 mg kg 1) were greater than that of the 0-month bagasse char (1428 mg kg 1). The results indicate that the compost chars had a greater preferential affinity for naphthalene than that in the bagasse char, suggesting that the compost chars possessed greater hydrophobicity. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Activated carbons (AC) are often used as an adsorbent for controlling environmental pollutants. Traditionally, the main precursor in the production of commercial AC is coal, but, due to the high cost of coal, some researchers have focused on finding lower cost materials to produce AC (Sharma et al., 2004; Carrott and Carrott, 2007; Dias et al., 2007; Ioannidou and Zabaniotou, 2007). Although several studies have demonstrated that high surface area AC can be produced from some agricultural wastes, not all wastes are suitable as precursors for AC, mainly due to their high content of volatile substances and their low thermal stability. However, most organic wastes can be composted, and composted materials have shown greater thermal stability than their corresponding precursors (Dell’Abate et al., 1998; Pietro and Paola, 2004; Lopez-Capel et al., 2005), suggesting that it may be possible to produce AC from composted material. Thermal analysis is a rapid method to assess the thermal stability of organic materials (Dell’Abate et al., 1998; Pietro and Paola, 2004; Lopez-Capel et al., 2005). In general, such analysis reveals that more labile carbon sources are decomposed at lower temperatures than more recalcitrant components. For example, when using thermal analysis to study organic matter evolution during the composting of municipal solid waste, Pietro and Paola (2004) found that weight loss in less-mature composted samples happened at lower temperatures (210–320 °C) than in matured compost (400–520 °C). Those results were consistent with their * Corresponding author. Tel.: +886 2 29089899x4652; fax: +886 2 29041914. E-mail address: [email protected] (L. Tsui). 0956-053X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2010.02.014
additional observations that less-mature compost was characterized by greater amount of aliphatic components, and that moremature compost was characterized by aromatic moieties. If mature compost shows greater thermal stability than the initial organic waste, a greater yield of carbon char might be obtained from a more-mature compost sample. In our previous study, we demonstrated that carbon char produced from a yard-waste compost sample produced a sorption capacity for the hydrophobic pollutant atrazine that was comparable to that from AC produced from corn stillage waste, even though compost char had much less surface area than that of the corn stillage AC (Tsui and Roy, 2008). In that study, however, the mechanism contributing to the high hydrophilic sorption capacity of compost char was not determined, because the precursor materials for producing the carbon char and the AC were different. In this study, therefore, we selected bagasse compost samples with different maturities as the precursors for producing carbon chars in order to study the effects of compost maturity on the quality of carbon chars. In addition, the sorption capacities of the produced carbon chars for both hydrophobic and hydrophilic pollutants were evaluated.
2. Materials and methods 2.1. Materials One fresh sugarcane bagasse sample (0-month) and two bagasse and pig manure compost samples (1-month and 6-month) were collected from one composting facility in Taiwan. The three
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samples were selected to represent initial agricultural residue, less-mature compost, and fully mature compost, respectively. At the composting facility, the bagasse/manure composting pile was prepared by mixing bagasse with pig manure at an approximately ratio of 20:1 weight/weight (w/w) on a dried weight basis. Subsequently, the moisture content of the composting mass was kept at 45–60% (w/w). The pile was turned mechanically every 2 weeks during the initial bio-oxidative phase (the first 2 months), and once a month thereafter. The collected samples were gently ground in an agate mortar, and screened through a 1.0-mm sieve. The sieved samples were heated at 105 °C overnight prior to chemical characterization or carbonization treatment.
2.2. Samples characterizations Thermogravimetric (TG) analysis coupled with differential thermogravimetric (DTG) analysis of the bagasse and the two bagasse/ manure compost samples were carried out carried out using a Perkin–Elmer DTA/TGA 7 analyzer (Perkin–Elmer, Shelton, CT, USA). Briefly, 3 mg of a dried sample was placed in an alumina crucible, which was then introduced into the thermobalance. The temperature was increased from 20 to 800 °C at a rate of 20 °C min 1 under a nitrogen flow of 20 mL min 1. TG analysis showed that all tested samples reached relatively thermal stability at 400 °C; thus, that temperature was selected as the pyrolyzed temperature. During pyrolysis, 50 g of dried sample was put in a 5 cm diameter horizontal quartz tube in a Lindberg 59344 furnace (Lindberg/MPH, Riverside, MI, USA). The tube was then heated at a rate of 20 °C min 1 to a carbonization temperature of 400 °C in flowing ultra-high purity N2. The sample was maintained at the final temperature for 1 h, then allowed to cool to ambient temperature under continuous flowing N2. The sample remainder was weighed, and the carbon char yield defined as the ratio of the weight of the pyrolyzed char to that of the original sample. The ash content of each pyrolyzed carbon char and the respective precursors were determined by combustion at 800 °C in air. Measurements of C, H, N, and S were obtained using a LECO CHNS-932 microanalysis apparatus (Leco Corp., St. Joseph, MI, USA). The ultimate analyses of C, H, N, and S content were calculated on an ash-free basis, with O content determined by the difference. Fourier transform infrared (FTIR) spectra were obtained on a Nicolet 550 Magna-IR spectrometer (Nicolet Instrument Corp., Madison, WI, USA). The samples were prepared for analyses by mixing 200 mg of KBr with 2.0 mg of sample material. That mixture was then pressed into pellets. Thirty-two scans per sample were performed in the 4000–400 cm 1 wavelength range, in transmission mode, and the collected spectra were averaged and corrected against ambient air as the background level. The surface areas and pore volume of each sample were assessed by Brunauer–Emmett–Teller (BET) nitrogen adsorption measurement in a static volumetric apparatus (ASAP 2010, Micrometrics, Norcross, GA, USA). Before N2 adsorption, each sample was outgassed (30:70, N2:He) under vacuum at 300 °C overnight. The subsequent nitrogen adsorption measurement was conducted at 77 K to estimate total pore volume (Vpore). Surface area (Spore) was calculated from the linearized BET equation, and micropore volume (Vmicro) and mesopore surface area were obtained by using the t-plot method (Nagano et al., 2000). The micropore surface area (Smicro) was obtained by deducting the mesopore surface area from Spore. In addition to obtaining the N2-BET measurement, the iodine indexes of the three carbon char samples were determined according to the procedure described by Aziz et al. (2009). Briefly, a carbon char sample (0.1 g) was placed in a dry Erlenmeyer flask and wetted with 10 cm3 of diluted HCl (5% by weight). A volume (100 cm3) of 0.1 mol L 1 was added to the flask and the mixture
vigorously shaken for 30 s. The liquid was filtrated and 50 cm3 removed and titrated with 0.01 mol L 1 sodium thiosulfate. 2.3. Adsorption studies Phenol and naphthalene were chosen as test pollutants in this study to evaluate the sorption capacities of the resultant chars. The water solubility of phenol and naphthalene is 83 g L 1 and 30 mg L 1, respectively. For adsorption equilibration 0.1 g of each carbon char were placed in separate flasks. Solutions of phenol or naphthalene (100 mL) with different initial concentrations (25– 300 mg L 1) were then added to the flasks. The flasks were then hermetically closed, and placed on an isothermal shaker and shaken at 25 ± 2 °C for 24 h. Solution pH was not adjusted. After equilibration, the carbon char suspensions were filtered, and the concentrations of the residual phenol or naphthalene measured using a Varian Cary 50 Bio UV–Vis spectrophotometer (Varian Australia Pty Ltd., Malgrave, Victoria, Australia). The wavelengths corresponding to phenol and naphthalene were 270 and 275.5 nm, respectively (Ania et al., 2007; Hameed and Rahman, 2008). To compare the maximum sorption capacities of the chars, the obtained equilibrium adsorption data were fitted to the Langmuir adsorption model. 3. Results and discussion 3.1. Thermal stability of bagasse samples The carbon char yields obtained from TG and pyrolysis analyses are shown in Table 1. The TG analysis was performed at a maximum temperature of 800 °C while pyrolysis was performed at 400 °C; regardless, the char yields from pyrolysis were smaller than the TG measured yields. The pyrolysis yield data, however, were still consistent with the TG results, with both showing that the samples with greater thermal stability produce larger char yields. The lower char yields from pyrolysis could be related to atmospheric oxygen entering the heating tube through an imperfect seal, thus causing burn-off of a portion of the carbon char; however, we have no data to support that conjecture. The lower char yield could also result from the longer time required for pyrolysis than for the TG procedure (total time for TG was 40 min while that for pyrolysis was 1 h). Among the three tested samples, the 0-month bagasse demonstrated the lowest thermal stability with a char yield of 16%, while the two compost samples had char yields greater than 50% (Table 1). The TG data also showed that the weight loss in the bagasse sample occurred at a lower temperature than in the two compost samples (Fig. 1), indicating that the 0-month sample was less thermally stable. There were two distinct DTG peaks (205 and 285 °C) in the 0-month sample. The two peaks may correspond to devolatilization of volatile matter and hemicellulose component (Lapuerta et al., 2004; Yang et al., 2007). All three samples exhib-
Table 1 The thermal stability and char yield of different compost samples. Samples
Thermal stability from TGa (%)
Char yield from pyrolysisb (%)
0-month bagasse sample 1-month bagasse/manure compost 6-month bagasse/manure compost
19 57
16 51
79
68
a The thermal stability was measured by heating the samples in TGA analyzer at maximum temperature of 800 °C. b The char yield was obtained by heating the samples in furnace at 400 °C for 1 h.
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Fig. 1. The thermal analysis of three bagasse samples with different maturity (a) TG curve (b) DTG curve.
ited a DTG peak at about 345 °C, which may be associated with the decomposition of the cellulose component (Yang et al., 2007). 3.2. Characteristics of collected samples and corresponding pyrolyzed chars The 6-month compost sample possessed the greatest thermal stability among the three tested samples, and its high thermal stability may be mainly related to its relatively high ash content (Table 2). In both compost samples, the relatively high ash content could result from the addition of 5% pig manure, which was mixed with the bagasse at the beginning of composting process. In addition, some soil clay particles could have been incorporated into the compost pile during mechanical turning, which would contribute to the total ash content in the compost samples. Although inorganic elements in the compost would reduce the carbon content, they could serve as catalysts to enhance the thermal decomposition of compost during pyrolysis (Muller et al., 1995), which could further promote the breakdown of the C–O bonds in compost char. This may help to explain why the two compost chars had smaller O/C ratios when compared with the 0-month bagasse char, even though the two raw materials (bagasse and pig manure) had similar initial O/C ratios (0.52 and 0.55, respectively; Table 2). Among the three carbon chars, the 1-month compost sample contained the largest fulvic acid content, while the 6-month sample had the largest humic acid content (data not shown). Based on
Fig. 2. The FTIR spectra of three bagasse samples with different (a) before pyrolysis (b) after pyrolysis.
a van Krevelan diagram depicting the atomic ratio of hydrogen to carbon on the y-axis versus the atomic ratio of oxygen to carbon on the x-axis, Schnitzer and Hoffman (1964) suggested that cellulose or wood materials are first converted to humic or fulvic acid before forming coal. Hence, if only the organic portion of the precursors is considered, it may be easier to produce carbon from the compost samples than from the fresh bagasse sample. Our results, which show that the two compost chars had greater carbon content than the bagasse char (Table 2), support that hypothesis. The results also imply that a better quality of carbon char can be
Table 2 Chemical characteristics of selected bagasse samples. Asha (%)
Samples
0-month bagasse sample 0-month bagasse char 1-month bagasse/manure sample 1-month bagasse/manure char 6-month bagasse/manure char 6-month bagasse/manure char a b c d
Ultimate analysisa,b
Chemical element measurementa C (%)
N (%)
H (%)
S (%)
C (%)
N (%)
H (%)
S (%)
Oc (%)
H/C (atomic ratio)
O/C (atomic ratio)
O/H (atomic ratio)
compost
1.89 6.05 29.09
51.41 74.96 32.84
0.69 0.12 1.72
8.84 1.09 3.42
1.31 0.21 0.47
52.40 79.79 46.31
0.70 0.13 2.43
9.01 1.16 4.82
1.34 0.22 0.66
36.55 18.70 45.78
2.06 0.17 1.25
0.52 0.17 0.74
0.25 1.01 0.59
compost
51.85
44.80
1.23
0.62
0.22
93.04
2.55
1.29
0.46
2.66
0.16
0.02
0.12
compost
46.23
28.96
1.56
4.16
0.93
53.86
2.90
7.74
1.73
33.77
1.72
0.47
0.27
compost
61.83
36.78
0.83
0.34
0.20
96.36
2.17
0.89
0.52
0.06
0.11
0.01d
0.01
Dry base. Ash-free base. Calculated by difference. The actual O/C ratio of 6-month bagasse compost char was 0.0005.
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Table 3 The surface area and iodine index of three carbon chars.
a b c d
Char samples
Sporea (m2 g
0-month bagasse char 1-month bagasse/manure compost char 6-month bagasse/manure compost char
2.57 5.22 7.81
1
)
Vporeb (cm3 g
1
)
0.0035 0.0126 0.0201
Smicroc/Spore
Vmicrod/Vpore
Iodine index (mg g
0.369 0.015 0.047
0.1065 0.0008 0.0049
12 16 38
1
)
Spore: Surface area obtained by N2-BET method. VPore: Total pore volume of carbon chars. Smicro: Micropore surface area. Vmicro: Micropore pore volume.
Fig. 3. Sorption isotherms for (a) phenol and (b) naphthalene onto various bagasse chars with different maturity.
produced from compost than that from fresh bagasse. Among the three samples, the 0-month bagasse had the lowest O/C ratio, implying it had the lowest level of oxygen-containing functional groups. After pyrolysis, however, the two compost chars had smaller O/C ratios than those of bagasse char sample, suggesting that the compost chars would have greater hydrophobicity. The 0-month bagasse sample produced a different FTIR spectrum than the spectra of the two compost samples (Fig. 2a), and that difference may be related to the addition of 5% pig manure to the compost samples. The compost samples showed two distinct peaks at 2920 and 2850 cm 1, and a smaller, sharp peak at 1515 cm 1. The two higher peaks correspond to aliphatic C–H, and a smaller peak related to aromatic skeletal (Huang et al., 2006; Perez-Sanz et al., 2006; Smidt et al., 2008). In contrast, the bagasse samples had a broad band at 3379 cm 1 (strongly hydrogen-bonded OH including OH of carboxylic acids), a peak at 1740 cm 1 (typical of C@O of undissociated COOH), a sharp peak of unsaturated C@C at 1640 cm 1 (C@O, C@C stretch), and a peak at 1250 cm 1 (C–O stretch of polysaccharide). All three samples created a peak at 1430 cm 1 (COO stretch), and a broad peak at 1080–1040 cm 1 (C–O stretch, Si–O stretch). After the samples were pyrolyzed, the FTIR spectra of the three carbon chars were similar (Fig. 2b), except that the 0-month bagasse char still showed a C@O stretch peak at 1720 cm 1. After pyrolysis of the 0-month sample, the peaks at 3379 cm 1 (H bonds) and 1250 cm 1 (polysaccharide) disappeared, and the peaks at 2920 and 2850 cm 1 (aliphatic C–H) significantly increased. The N2-BET surface areas and the iodine indexes of the three chars are compared in Table 3. After pyrolysis at 400 °C in nitrogen, the surface area of the three samples was generally low, with a maximum value of 7.81 m2 g 1 in the 6-month sample. The microporosities (Smicro/Spore) of the two compost chars were markedly smaller than that in the bagasse sample. These observations were consistent with other studies that have shown that natural organic matter surface areas are small when based on N2-BET measurement (De Jonge and Mittelmeijer-Hazeleger, 1996; Kaiser and Guggenberger, 2003; Makris et al., 2006). Those studies, however, also acknowledged that the N2-BET method generally underestimates the microporosity of organic matter, because N2 adsorption at 196 °C could be kinetically restricted. Among the three carbon
Table 4 The sorption parameters for phenol and naphthalene by different bagasse chars. Samples
Phenol Qmaxa (mg g
0-month 0-month 1-month 1-month 6-month 6-month a b
bagasse char bagasse char based on per gram of measured carbon base bagasse/manure compost char bagasse/manure compost char based on per gram of carbon base bagasse/manure compost char bagasse/manure compost char based on per gram of carbon base
Qmax: The maximum sorption capacity calculated from Langmuir isotherms. KL: The Langmiur affinity constant.
3333 4446 2512 5607 2000 5437
Naphthalene 1
)
r2
Qmax (mg g
21
0.97
15
0.98
11
0.96
1428 1905 2001 4466 1667 4532
KLb (mL g
1
)
1
)
KL (mL g
1
)
r2
125
0.96
178
0.95
143
0.95
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chars, the largest surface area and the highest iodine index were associated with the 6-month char; however, it should be noted that the measured surface area and iodine index could have be related, in part, to its high ash content (Table 2).
authors would like to thank William R Roy from ISGS for critically reading this manuscript.
3.3. The sorption behaviors of carbon chars
Ania, C.O., Cabal, B., Pevida, C., Arenillas, A., Parra, J.B., Rubiera, F., Pis, J.J., 2007. Effects of activated carbon properties on the adsorption of naphthalene from aqueous solution. Appl. Surf. Sci. 253, 5741–5746. Aziz, A., Quali, M.S., Elandaloussi, E.H., De Menorval, L.C., Lindheimer, M., 2009. Chemically modified olive stone: a low-cost sorbent for heavy metals and basic dye removal from aqueous solutions. J. Hazard. Mater. 163, 441–447. Carrott, S.P.J.M., Carrott, M.M.L.R., 2007. Lignin-from natural adsorbent to activated carbon: a review. Bioresour. Technol. 98, 2301–2312. De Jonge, H., Mittelmeijer-Hazeleger, M.C., 1996. Adsorption of CO2 and N2 on soil organic matter: nature of porosity, surface area, and diffusion mechanisms. Environ. Sci. Technol. 30, 4008–4013. Dell’Abate, M.T., Canali, S., Trinchera, A., Benedetti, A., Sequi, P., 1998. Thermal analysis in the evaluation of compost stability: a comparison with humification parameters. Nutr. Cycling Agroeco. 51, 217–224. Dias, J.M., Alvim-Ferraz, M.C.M., Almeida, M.F., Rivera-Utrilla, J., Sánchez-Polo, M., 2007. Waste materials for activated carbon preparation and its use in aqueousphase treatment: a review. J. Environ. Manage. 85, 833–846. Hameed, B.H., Rahman, A.A., 2008. Removal of phenol from aqueous solutions by adsorption onto activated carbon prepared from biomass material. J. Hazard. Mater. 160, 576–581. Huang, G.F., Wu, Q.T., Wong, J.W.C., Nagar, B.B., 2006. Transformation of organic matter during co-composting of pig manure with sawdust. Bioresour. Technol. 97, 1831–1842. Ioannidou, O., Zabaniotou, A., 2007. Agricultural residues as precursors for activated carbon production—a review. Renew. Sustain. Energy Rev. 11, 1966–2005. Kaiser, R., Guggenberger, G., 2003. Mineral surfaces and soil organic matter. Eur. J. Soil Sci. 54, 219–236. Lapuerta, M., Hernandez, J.J., Rodriguez, J., 2004. Kinetics of devolatilisation of forestry wastes from thermogravimetric analysis. Biomass Bioenergy 27, 385– 391. Lopez-Capel, E., Sohi, S.P., Gaunt, J.L., Manning, D.A.C., 2005. Use of thermogravimetry-differential scanning calorimetry to characterize modelable soil organic matter fractions. Soil Sci. Soc. Am. J. 69, 136–140. Makris, K.C., Sarkar, D., Datta, R., Ravikovitch, P.I., Neimark, A.V., 2006. Using nitrogen and carbon dioxide molecules to probe arsenic(V) bioaccessibility in soils. Environ. Sci. Technol. 40, 7732–7738. Muller, M.W., Hoffmann, W.R., Huttinger, K.J., 1995. Organic iron compounds as catalyst precursors in pitch pyrolysis. Fuel 74, 953–959. Nagano, S., Tamon, H., Adzumi, T., Nakagawa, K., Suzuki, T., 2000. Activated carbon from municipal waste. Carbon 38, 915–920. Perez-Sanz, A., Lucena, J.J., Graham, M.C., 2006. Characterization of Fe–humic complexes in an Fe-enriched biosolid by-product of water treatment. Chemosphere 65, 2045–2053. Pietro, M., Paola, C., 2004. Thermal analysis for the evaluation of the organic matter evolution during municipal solid waste aerobic composting process. Thermochim. Acta 413, 209–214. Schnitzer, M., Hoffman, I., 1964. Pyrolysis of soil organic matter. Soil Sci. Soc. Am. Proc. 28, 520–525. Sharma, R.K., Wooten, J.B., Baliga, V.L., Lin, X., Chan, W.G., Hajaligol, M.R., 2004. Characterization of chars from pyrolysis of lignin. Fuel 83, 1469–1482. Smidt, E., Meissl, K., Schwanninger, M., Lechner, P., 2008. Classification of waste materials using Fourier transform infrared spectroscopy and soft independent modelling of class analogy. Waste Manage. 28, 1699–1710. Tsui, L., Roy, W.R., 2008. The potential applications of using compost chars for removing the hydrophobic herbicide atrazine from solution. Bioresour. Technol. 99, 5673–5678. Yang, H.P., Yan, R., Chen, H.P., Lee, D.H., Zheng, C., 2007. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel 86, 1781–1788.
The sorption capacities for phenol and naphthalene of the three carbon chars are shown in Fig. 3 and Table 4. The 0-month bagasse char had the largest sorption capacity of 3333 mg kg 1 for phenol among the three carbon chars (Table 4). This result may be related to the high carbon content (75.0%) in the bagasse char, along with its high level of oxygen-containing functional groups (high O/C content) (Table 2). In contrast, the 1-month compost char had the greatest sorption capacity for naphthalene, despite it only having a 44.8% carbon content. The 6-month compost char also sorbed more naphthalene than did the 0-month bagasse char. The high sorption capacities of two compost chars for naphthalene may be related to their high hydrophobicity (low O/C content), as naphthalene has a low water solubility (30 mg L 1). When calculating the sorption capacity per gram of the carbon base, both of the compost chars sorbed more phenol than did the 0-month bagasse char. The results suggest that more-adsorptive pyrolyzed chars could be produced from composted material than from fresh material, as long as the ash content can be removed from the composted chars. 4. Conclusions Surface area is generally a useful index to evaluate the sorption capacity of AC. In our previous study, however, compost char had an equivalent sorption capacity for a hydrophobic pollutant when compared with AC derived directly from an agricultural residue, even though the compost char had a much smaller surface area than the AC (Tsui and Roy, 2008). The current study illustrates that the high sorption capacity of compost char mainly results from its high hydrophobicity. The results also show that compost chars can have greater sorption capacities for both phenol and naphthalene than fresh material chars, on a per gram of carbon basis (Table 4). Based on the greater yield of carbon char from the compost samples relative to the fresh bagasse sample, it may be economically feasible to produce adsorbent materials from compost rather than from fresh agricultural wastes, despite the energy and time needed to produce the composted material. However, because of the relatively high ash content of compost chars, research into concentrating carbon from the compost char is needed in order to increase the efficiency of producing and using compost char to remove hydrophobic pollutants from the environment. Acknowledgements This work was financially supported by the National Science Council (Taiwan) under Project No. NSC 95-2221-E-131-019. The
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