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Chemolytic and solid-state spectroscopic evaluation of organic matter transformation during vermicomposting of sugar industry wastes
Bioresource Technology 98 (2007) 1680–1683
Short Communication
Chemolytic and solid-state spectroscopic evaluation of organic matter transformation during vermicomposting of sugar industry wastes Biswarup Sen, T.S. Chandra
¤
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India Received 13 October 2005; received in revised form 6 June 2006; accepted 10 June 2006 Available online 6 December 2006
Abstract The molecular structure of humic acid (HA) extracted was investigated by FT-IR and 13C CP/MAS NMR spectroscopy during the vermicomposting of sugar industry wastes, viz. pressmud, trash and bagasse for 60 days. A rapid decrease in C/N and lignocellulosic (lignin, cellulose, hemicellulose) content was observed in vermicompost during early phase of the process. The FT-IR and 13C CP/MAS NMR spectra of HA indicated a high rate of change in structure with increase in the alkyl C/O-alkyl C ratio during the process. Aromatic structures and carboxyl groups showed an initial increase but decreased after »40 days indicating extensive mineralization during Wnal stages of vermicomposting. © 2006 Elsevier Ltd. All rights reserved. Keywords: Sugar industry wastes; Vermicompost; Lignocellulosic biofractionation; FT-IR; 13C CP/MAS NMR
1. Introduction Sugar industry belongs to the most important processing industries in India. According to the Indian Directorate of Economics and Statistics, India produces on average 270 million tones of sugar cane per year. During the production process considerable amounts of byproducts such as pressmud (p), bagasse (b), and trash (t) are produced. Pressmud generates intense heat (65 °C), foul odour and takes long time for natural decomposition. The crop residues bagasse and trash are very poor in N and need to be mixed with other, N-rich, organic wastes in order to provide nutrients and an inoculum of microorganisms (Elvira et al., 1996). Crop residues such as mustard residues and sugarcane trash can be converted into vermicompost when mixed with cattle dung (Bansal and Kapoor, 2000). * Corresponding author. Tel.: +91 44 22574103/6103; fax: +91 44 22574202. E-mail addresses: [email protected], [email protected] (T.S. Chandra).
0960-8524/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2006.06.007
The recycling of wastes through vermicomposting reduces problems of disposal of agricultural as well as industrial wastes. It provides two useful products; the earthworm biomass and the vermicompost. Vermicompost/ castings is an excellent product since it is homogenous, has desirable aesthetics, has reduced levels of contaminations and tend to hold more nutrients over a longer period, without adversely impacting the environment (Ndegwa and Thompson, 2000). However, Deportes et al. (1995) suggested that numerous harmful eVects to soil were caused by the application of non-matured composts i.e. those with an incomplete stabilization of their organic fraction. At the same time, excessive composting could lead to loss of nitrogen and polysaccharides; and immobilization of nutrients mainly N and P. Hence the maturity of compost is a very important parameter for both compost production process and its application (Meunchang et al., 2005). Despite the recognized importance of this aspect, no oYcial or generally accepted regulatory standards to evaluate organic amendment quality are currently available (Provenzano et al., 2001).
B. Sen, T.S. Chandra / Bioresource Technology 98 (2007) 1680–1683
Maturing process involves several changes in chemical content and transformation in the structure of compost, which can be predicted with the C/N, humiWcation indices and spectroscopic measurements including UV–Vis, FT-IR and NMR (Zbytniewski and Buszewski, 2005). Solid-state spectroscopy (FT-IR and 13C NMR) is the most powerful tool for examining the carbon composition of organic matter. Chen et al. (1989) showed that the carbohydrate content decreases during the composting process and that the content of aromatic and carboxyl groups increases. Baldock et al. (1997) found that decomposition of natural organic materials is usually associated with an increased content of alkyl C and a decreased content of O-alkyl C. The aim of this work was to analyze the transformation of organic matter and humiWcation process during vermicomposting of sugar industry wastes with cowdung under controlled conditions.
1681
(Walkley and Black, 1934). Total nitrogen was determined by Macrokjeldahl method (Jackson, 1958). 2.3. Fractional analysis of lignocellulosic substrate Oven-dried (100 °C) vermicompost samples were taken for the sequential analysis of soluble substances, lignin, hemicellulose and cellulose (Thronber and Northcote, 1961), which involves a series of steps. 2.4. Humic acid extraction
2. Methods
Humic acids were extracted with 0.5 M NaOH using vermicompost: solvent ratio of 1:15 (Stevenson, 1994). After centrifugation, the humic acids were separated from the supernatant by precipitation with 6 N HCl added to the extract until a pH of 2.0 was reached. The precipitated humic acids were separated by centrifugation and puriWed by successive repetition of the extraction procedure.
2.1. Vermicomposting of sugarcane industry biowastes
2.5. Fourier-transform infrared spectroscopy
Vermicomposting of pressmud, trash, bagasse and cow dung (ptbc) in the ratio of 7:1:1:1 w/w ratio was done in triplicate cement pots. After the thermophilic phase earthworms (Eudrilus eugeniae) were inoculated (15 g/kg) in the ptbc mixture. The moisture content was kept at »60%. The process was monitored for 60 days after thermophilic phase (see Fig. 1).
The Fourier-transform infrared (FT-IR) spectra of HA were obtained in a wavenumber of 4000–400 cm¡1 on a Perkin Elmer FTIR Spectrum one spectrometer equipped with spectrum software. HA were oven dried at 100 °C for 24 hr and Wnely ground prior to analysis. Samples were prepared for the analysis by mixing 1 mg HA with 100 mg KBr and then pressing the mixture into pellet.
2.2. Analysis of total carbon and total nitrogen
2.6. 13C CP/MAS NMR spectroscopy
Vermicompost samples were oven-dried at 100 °C, then ground in blender and sieved. Particles smaller than 2 mm in diameter were used for analysis. Total carbon was determined by wet oxidation with potassium dichromate
The 13C NMR spectra were obtained in solid state with CP/MAS using a Bruker Avance 400 MHz NMR spectrometer. The spectrometer was operated at a 1H frequency of 400 MHz and a 13C frequency of 100 MHz with contact time of 1 ms, recycle delay of 5 s, sweep depth of 31250 Hz, line broadening of 100 Hz and spinning speed of 8 kHz. The chemical shift was calibrated to tetramethylsilane ( D 0 ppm). For spectral interpretation the following ranges and preliminary assignations were considered: region I (0– 50 ppm) aliphatic C; region II (50–110 ppm) O-alkyl C; region III (110–160 ppm) unsaturated and aromatic C; region IV (160–190) carboxyl carbon.
350
mg/g dry weight vermicompost
300
TSS Hemicellulose Cellulose Lignin
250
200
3. Results and discussion 150
100
50
0 0
10
20
30 Days
40
50
60
Fig. 1. Lignocellulosic biofractionation of 7:1:1:1 mixture of pressmud, trash, bagasse and cow dung (ptbc).
The organic matter (OM) content of the ptbc mixture was very high (»66%), which decreased noticeably during vermicomposting, reaching a value of »48% towards 60 day, thus indicating the occurrence of extensive mineralization. Total Nitrogen content in ptbc was »1.75%, which increased to »2.74% in the 60th day compost (Table 1). The drift of C/N as a function of time was an important index used for the assessment of the eYciency of the vermicomposting process and compost maturity. The decline observed for the C/N ratio from an initial of 21.92 in the ptbc to a
1682
B. Sen, T.S. Chandra / Bioresource Technology 98 (2007) 1680–1683
Table 1 Time dependent variation in Total Carbon, Total Nitrogen and C/N of 7:1:1:1 mixture of pressmud, trash, bagasse and cow dung
% Total Carbon % Total Nitrogen C/N a
0 daya
10 day
20 day
30 day
40 day
50 day
60 day
37.77 § .34 1.8 § .06 20.98 § .54
38.17 § .50 2.49 § .04 15.32 § .68
34.75 § .23 2.68 § .02 12.96 § .34
32.13 § .13 2.71 § .03 11.85 § .21
32.84 § .38 2.74 § .01 11.98 § .43
30.81 § .35 2.7 § .01 11.41 § .53
27.97 § .36 2. 74 § .05 10.20 § .35
Zero day refers to start of vermicomposting after thermophilic phase.
Wnal value of 10.20 in the 60 day vermicompost indicated higher OM decomposition and the attainment of a suitable degree of OM stabilization. The major components of 7:1:1:1 pressmud, trash, bagasse and cowdung mixture were cellulose (33.8%), hemicellulose (8.6%) and lignin (26.4%). Cellulose, hemicellulose and lignin are the most important constituents of plant residues (trash, bagasse) and cow dung. In present study lignolysis was shown to be higher (»84%) as compared to cellulolysis (58%). Vinceslas-Akpa and Loquet (1997) reported increase in cellulose (weight and percentage) at the end of vermicomposting, hence, relative decrease in lignin compared to easily degradable cellulosics could be justiWed in this study. The FT-IR spectra of humic acid extracted from vermicompost showed a broad band at 3400–3300 cm¡1 due to the stretching of HAO bonds. This band was related to alcohol and phenol association. Two distinct peaks were present at 2930 and 2850 cm¡1, which corresponded to aliphatic CAH stretching. In the 2000–400 cm¡1 the following features were noted: A small shoulder around 1711 cm¡1 (not conjugated carboxylic CBO), a wide peak at 1650 cm¡1 (CBO conjugated and CBC aromatic structure). A peak evident at 1460 cm¡1 (CAH deformation of CH2 or CH3 groups) (spectra not shown). In HA sample, there was a peak at 1150 cm¡1 and shifts to 1170 cm¡1 (stretching of CAO in polysaccharides). As per Castaldi et al. (2005), FT-IR spectra of municipal solid waste shows a progressive transformation of the polysaccharides in other oxygenated compounds, particularly carboxylic and ester group, takes place. Present results showed similar pattern during vermicomposting. The changes in FT-IR spectra were also monitored by calculating the ratio between the intensities of major peaks. The ratio 1650/2930 (aromatic C/aliphatic C) increased rapidly during initial period of the process from 0.81 to 0.96. The increase could be caused by formation of humic polymer and/or by a reduction of aliphatic C. This was conWrmed by ratio 1650/2850 (aromatic C/aliphatic C) that increased from 0.64 to 0.91 with a similar behavior and by
the ratio 1650/1711 (aromatic C/carboxyl C) that progressively increased from 0.73 to 0.93 during the humiWcation process. After a period of 40 days, there was a decrease in peak intensity ratio of aromatic C/aliphatic C to 0.93, aromatic C/aliphatic C to 0.86, whereas aromatic C/carboxyl C decreased to 0.90, which suggested reduction of aromatic structures in the Wnal stages of vermicomposting process associated with extensive organic matter mineralization. The peaks in the 13C NMR were assigned to the diVerent carbon types. Alkyl groups were found around 21 ppm (terminal methyl) and 32 ppm (methylene in aliphatic rings and chains). The signal at 56 ppm could be assigned to methoxyl in lignin (phenolmethoxyl of coniferyl and sinapyl moieties) and in hemicellulose (glucoronic acid in xylan) (Veeken et al., 2001). The region between 60 to 110 ppm showed typical peaks of polysaccharides and proteins. Signals around 76 and 83 were due to C2, C3, C5 and non-crystalline component of C4 of cellulose. Signals derived from hemicellulose were contained within the cellulose peaks. Signals at 115 and 120 were due to H-aromatic C and peak around 140 was due to aromatic C. The peak at 170–173 ppm was assigned to carboxylic, amide and ester groups. Table 2 shows the distribution of diVerent carbon types that are typical for distinct type of organic carbon in the 13 C CP/MAS NMR spectra of HA’s extracted from vermicompost. Signals in the O-alkyl C region (50–110 ppm) dominated the spectrum of ptbc mixture after thermophilic phase (0 day). During the initial period of vermicomposting process the intensity of signals in the alkyl C and aromatic C region increased rapidly while the intensity of the O-alkyl C region decreased. At the end of 60 days, there was loss of aromatic C and carboxyl C whereas alkyl C and O-alkyl C increased. Earthworms are known to digest long chains of polysaccharides, enhancing microbial colonization simultaneously the structure of lignin also changes leading to new polysaccharides and humins. The increase observed for total aliphatic C and polysaccharides at the end of vermicomposting suggests neosynthesis or insolubilization in the vermicompost.
Table 2 Distribution of diVerent carbon types in the 13C NMR spectra of HA extracted from vermicompost at various stages of the process (% of total C) Chemical shift (ppm)
0–50 ppm (alkyl C)
50–110 ppm (O-alkyl C)
110–160 ppm (aryl C)
160–190 ppm (carboxyl C)
Alkyl C/ O-alkyl C
0 days 20 days 40 days 60 days
17.0 34.1 14.8 26.9
71.7 47.3 50.4 60.1
1.3 7.1 21.6 6.1
10.0 11.3 12.8 6.6
0.23 0.72 0.29 0.44
B. Sen, T.S. Chandra / Bioresource Technology 98 (2007) 1680–1683
4. Conclusions Vermicomposting of sugar industry wastes with cowdung signiWcantly reduced the C/N to »10 within 40 days. Lignocellulosic biofractionation results showed noticeable reduction in the lignin, cellulose and hemicellulose and high increase in total soluble substances (TSS). Vermicomposting led to homogeneous degradation of all types of C, with no selective accumulation of any preferentially stable forms. Acknowledgements We are grateful to Dr. Josef Zeyer of the Institute of Terrestrial Ecology, Zurich and Dr. L.S. Ranganathan, Department of Zoology, Annamalai University for initiating us in the study of pressmud vermicomposting during collaboration on the Indo-Swiss DBT project (ISCB project). We also thank Mr. S. Mohan (Department of Chemistry, IIT, Madras) for the analysis of 13CPMAS NMR spectroscopy. References Baldock, J.A., Oades, J.M., Nelson, P.N., Skene, T.M., Golchin, A., Clarke, P., 1997. Assessing the extent of decomposition of natural organic materials using solid-state 13C NMR spectroscopy. Aust. J. Soil. Res. 35, 1061–1083. Bansal, S., Kapoor, K.K., 2000. Vermicomposting of crop residues and cattle dung with Eisenia foetida. Bioresour. Technol. 73, 95–98. Castaldi, P., Alberti, G., Merella, R., Melis, P., 2005. Study of the organic matter evolution during municipal solid waste composting aimed at identifying suitable parameters for the evaluation of compost maturity. Waste Management 25, 209–213.
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Chen, Y., Inbar, Y., Hadar, Y., Malcolm, R.L., 1989. Chemical properties and solid-state CPMAS 13C NMR of composted organic matter. Sci. Total Environ. 81, 201–208. Deportes, I., Benoit, J.L., Zmirou, D., 1995. Hazard to man and the environment posed by the use of urban waste compost: a review. Sci. Total Environ. 172, 197–222. Elvira, C., Sampedro, L., Dominguez, J., Mato, S., 1996. Vermicomposting of wastewater sludge from paper pulp industry with nitrogen-rich material. Soil Biol. Biochem. 29, 759–762. Jackson, M.L.,1958. Soil Chemical Analysis, Wrst ed. Constable & Co Ltd., Prentice-Hall, INC. Meunchang, S., Panichsakpatana, S., Weaver, R.W., 2005. Co-composting of Wlter cake and bagasse; by-products from a sugar mill. Bioresour. Technol. 96, 432–437. Ndegwa, P.M., Thompson, S.A., 2000. EVects of C-to-N ratio on vermicomposting of biosolids. Bioresour. Technol. 75, 7–12. Provenzano, M.R., Oliveira, S.C., Silva, M.R.S., Senesi, N., 2001. Assessment of maturity degree of composts from domestic solid wastes by Xuorescence and fourier transform infrared spectroscopies. J. Agric. Food Chem. 49, 5874–5879. Stevenson, F.L., 1994. Humus Chemistry: Genesis, Composition, Reactions. Wiley, New York. Thronber, J.P., Northcote, D.H., 1961. Changes in the chemical composition of a cambial cell during its diVerentiation during its xylem and phyloem tissue in its trees. Biochem. J. 81, 445–449. Veeken, A.H.M., Adani, F., Nierop, K.G.J., Jager, P.A., Hamelers, H.V.M., 2001. Degradation of Biomacromolecules during high rate composting of wheat straw-amended feces. J. Environ. Qual. 30, 1675–1684. Vinceslas-Akpa, M., Loquet, M., 1997. Organic Matter transformation in lignocellulosic waste products composted or vermicomposted (Eisenia fetida anderei). Chemical Analysis and 13C CPMAS NMR Spectroscopy. Soil Biol. Biochem. 29 (3/4), 751–758. Walkley, A., Black, I.A., 1934. An examination of the DegtjareV method for determining soil organic matter and a proposed modiWcation of the chromic acid titration method. Soil Sci. 37, 29–38. Zbytniewski, R., Buszewski, B., 2005. Characterization of natural organic matter (NOM) derived from sewage sludge compost. Part 1: chemical and spectroscopic properties. Bioresour. Technol. 96, 471–478.
Short Communication
Chemolytic and solid-state spectroscopic evaluation of organic matter transformation during vermicomposting of sugar industry wastes Biswarup Sen, T.S. Chandra
¤
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India Received 13 October 2005; received in revised form 6 June 2006; accepted 10 June 2006 Available online 6 December 2006
Abstract The molecular structure of humic acid (HA) extracted was investigated by FT-IR and 13C CP/MAS NMR spectroscopy during the vermicomposting of sugar industry wastes, viz. pressmud, trash and bagasse for 60 days. A rapid decrease in C/N and lignocellulosic (lignin, cellulose, hemicellulose) content was observed in vermicompost during early phase of the process. The FT-IR and 13C CP/MAS NMR spectra of HA indicated a high rate of change in structure with increase in the alkyl C/O-alkyl C ratio during the process. Aromatic structures and carboxyl groups showed an initial increase but decreased after »40 days indicating extensive mineralization during Wnal stages of vermicomposting. © 2006 Elsevier Ltd. All rights reserved. Keywords: Sugar industry wastes; Vermicompost; Lignocellulosic biofractionation; FT-IR; 13C CP/MAS NMR
1. Introduction Sugar industry belongs to the most important processing industries in India. According to the Indian Directorate of Economics and Statistics, India produces on average 270 million tones of sugar cane per year. During the production process considerable amounts of byproducts such as pressmud (p), bagasse (b), and trash (t) are produced. Pressmud generates intense heat (65 °C), foul odour and takes long time for natural decomposition. The crop residues bagasse and trash are very poor in N and need to be mixed with other, N-rich, organic wastes in order to provide nutrients and an inoculum of microorganisms (Elvira et al., 1996). Crop residues such as mustard residues and sugarcane trash can be converted into vermicompost when mixed with cattle dung (Bansal and Kapoor, 2000). * Corresponding author. Tel.: +91 44 22574103/6103; fax: +91 44 22574202. E-mail addresses: [email protected], [email protected] (T.S. Chandra).
0960-8524/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2006.06.007
The recycling of wastes through vermicomposting reduces problems of disposal of agricultural as well as industrial wastes. It provides two useful products; the earthworm biomass and the vermicompost. Vermicompost/ castings is an excellent product since it is homogenous, has desirable aesthetics, has reduced levels of contaminations and tend to hold more nutrients over a longer period, without adversely impacting the environment (Ndegwa and Thompson, 2000). However, Deportes et al. (1995) suggested that numerous harmful eVects to soil were caused by the application of non-matured composts i.e. those with an incomplete stabilization of their organic fraction. At the same time, excessive composting could lead to loss of nitrogen and polysaccharides; and immobilization of nutrients mainly N and P. Hence the maturity of compost is a very important parameter for both compost production process and its application (Meunchang et al., 2005). Despite the recognized importance of this aspect, no oYcial or generally accepted regulatory standards to evaluate organic amendment quality are currently available (Provenzano et al., 2001).
B. Sen, T.S. Chandra / Bioresource Technology 98 (2007) 1680–1683
Maturing process involves several changes in chemical content and transformation in the structure of compost, which can be predicted with the C/N, humiWcation indices and spectroscopic measurements including UV–Vis, FT-IR and NMR (Zbytniewski and Buszewski, 2005). Solid-state spectroscopy (FT-IR and 13C NMR) is the most powerful tool for examining the carbon composition of organic matter. Chen et al. (1989) showed that the carbohydrate content decreases during the composting process and that the content of aromatic and carboxyl groups increases. Baldock et al. (1997) found that decomposition of natural organic materials is usually associated with an increased content of alkyl C and a decreased content of O-alkyl C. The aim of this work was to analyze the transformation of organic matter and humiWcation process during vermicomposting of sugar industry wastes with cowdung under controlled conditions.
1681
(Walkley and Black, 1934). Total nitrogen was determined by Macrokjeldahl method (Jackson, 1958). 2.3. Fractional analysis of lignocellulosic substrate Oven-dried (100 °C) vermicompost samples were taken for the sequential analysis of soluble substances, lignin, hemicellulose and cellulose (Thronber and Northcote, 1961), which involves a series of steps. 2.4. Humic acid extraction
2. Methods
Humic acids were extracted with 0.5 M NaOH using vermicompost: solvent ratio of 1:15 (Stevenson, 1994). After centrifugation, the humic acids were separated from the supernatant by precipitation with 6 N HCl added to the extract until a pH of 2.0 was reached. The precipitated humic acids were separated by centrifugation and puriWed by successive repetition of the extraction procedure.
2.1. Vermicomposting of sugarcane industry biowastes
2.5. Fourier-transform infrared spectroscopy
Vermicomposting of pressmud, trash, bagasse and cow dung (ptbc) in the ratio of 7:1:1:1 w/w ratio was done in triplicate cement pots. After the thermophilic phase earthworms (Eudrilus eugeniae) were inoculated (15 g/kg) in the ptbc mixture. The moisture content was kept at »60%. The process was monitored for 60 days after thermophilic phase (see Fig. 1).
The Fourier-transform infrared (FT-IR) spectra of HA were obtained in a wavenumber of 4000–400 cm¡1 on a Perkin Elmer FTIR Spectrum one spectrometer equipped with spectrum software. HA were oven dried at 100 °C for 24 hr and Wnely ground prior to analysis. Samples were prepared for the analysis by mixing 1 mg HA with 100 mg KBr and then pressing the mixture into pellet.
2.2. Analysis of total carbon and total nitrogen
2.6. 13C CP/MAS NMR spectroscopy
Vermicompost samples were oven-dried at 100 °C, then ground in blender and sieved. Particles smaller than 2 mm in diameter were used for analysis. Total carbon was determined by wet oxidation with potassium dichromate
The 13C NMR spectra were obtained in solid state with CP/MAS using a Bruker Avance 400 MHz NMR spectrometer. The spectrometer was operated at a 1H frequency of 400 MHz and a 13C frequency of 100 MHz with contact time of 1 ms, recycle delay of 5 s, sweep depth of 31250 Hz, line broadening of 100 Hz and spinning speed of 8 kHz. The chemical shift was calibrated to tetramethylsilane ( D 0 ppm). For spectral interpretation the following ranges and preliminary assignations were considered: region I (0– 50 ppm) aliphatic C; region II (50–110 ppm) O-alkyl C; region III (110–160 ppm) unsaturated and aromatic C; region IV (160–190) carboxyl carbon.
350
mg/g dry weight vermicompost
300
TSS Hemicellulose Cellulose Lignin
250
200
3. Results and discussion 150
100
50
0 0
10
20
30 Days
40
50
60
Fig. 1. Lignocellulosic biofractionation of 7:1:1:1 mixture of pressmud, trash, bagasse and cow dung (ptbc).
The organic matter (OM) content of the ptbc mixture was very high (»66%), which decreased noticeably during vermicomposting, reaching a value of »48% towards 60 day, thus indicating the occurrence of extensive mineralization. Total Nitrogen content in ptbc was »1.75%, which increased to »2.74% in the 60th day compost (Table 1). The drift of C/N as a function of time was an important index used for the assessment of the eYciency of the vermicomposting process and compost maturity. The decline observed for the C/N ratio from an initial of 21.92 in the ptbc to a
1682
B. Sen, T.S. Chandra / Bioresource Technology 98 (2007) 1680–1683
Table 1 Time dependent variation in Total Carbon, Total Nitrogen and C/N of 7:1:1:1 mixture of pressmud, trash, bagasse and cow dung
% Total Carbon % Total Nitrogen C/N a
0 daya
10 day
20 day
30 day
40 day
50 day
60 day
37.77 § .34 1.8 § .06 20.98 § .54
38.17 § .50 2.49 § .04 15.32 § .68
34.75 § .23 2.68 § .02 12.96 § .34
32.13 § .13 2.71 § .03 11.85 § .21
32.84 § .38 2.74 § .01 11.98 § .43
30.81 § .35 2.7 § .01 11.41 § .53
27.97 § .36 2. 74 § .05 10.20 § .35
Zero day refers to start of vermicomposting after thermophilic phase.
Wnal value of 10.20 in the 60 day vermicompost indicated higher OM decomposition and the attainment of a suitable degree of OM stabilization. The major components of 7:1:1:1 pressmud, trash, bagasse and cowdung mixture were cellulose (33.8%), hemicellulose (8.6%) and lignin (26.4%). Cellulose, hemicellulose and lignin are the most important constituents of plant residues (trash, bagasse) and cow dung. In present study lignolysis was shown to be higher (»84%) as compared to cellulolysis (58%). Vinceslas-Akpa and Loquet (1997) reported increase in cellulose (weight and percentage) at the end of vermicomposting, hence, relative decrease in lignin compared to easily degradable cellulosics could be justiWed in this study. The FT-IR spectra of humic acid extracted from vermicompost showed a broad band at 3400–3300 cm¡1 due to the stretching of HAO bonds. This band was related to alcohol and phenol association. Two distinct peaks were present at 2930 and 2850 cm¡1, which corresponded to aliphatic CAH stretching. In the 2000–400 cm¡1 the following features were noted: A small shoulder around 1711 cm¡1 (not conjugated carboxylic CBO), a wide peak at 1650 cm¡1 (CBO conjugated and CBC aromatic structure). A peak evident at 1460 cm¡1 (CAH deformation of CH2 or CH3 groups) (spectra not shown). In HA sample, there was a peak at 1150 cm¡1 and shifts to 1170 cm¡1 (stretching of CAO in polysaccharides). As per Castaldi et al. (2005), FT-IR spectra of municipal solid waste shows a progressive transformation of the polysaccharides in other oxygenated compounds, particularly carboxylic and ester group, takes place. Present results showed similar pattern during vermicomposting. The changes in FT-IR spectra were also monitored by calculating the ratio between the intensities of major peaks. The ratio 1650/2930 (aromatic C/aliphatic C) increased rapidly during initial period of the process from 0.81 to 0.96. The increase could be caused by formation of humic polymer and/or by a reduction of aliphatic C. This was conWrmed by ratio 1650/2850 (aromatic C/aliphatic C) that increased from 0.64 to 0.91 with a similar behavior and by
the ratio 1650/1711 (aromatic C/carboxyl C) that progressively increased from 0.73 to 0.93 during the humiWcation process. After a period of 40 days, there was a decrease in peak intensity ratio of aromatic C/aliphatic C to 0.93, aromatic C/aliphatic C to 0.86, whereas aromatic C/carboxyl C decreased to 0.90, which suggested reduction of aromatic structures in the Wnal stages of vermicomposting process associated with extensive organic matter mineralization. The peaks in the 13C NMR were assigned to the diVerent carbon types. Alkyl groups were found around 21 ppm (terminal methyl) and 32 ppm (methylene in aliphatic rings and chains). The signal at 56 ppm could be assigned to methoxyl in lignin (phenolmethoxyl of coniferyl and sinapyl moieties) and in hemicellulose (glucoronic acid in xylan) (Veeken et al., 2001). The region between 60 to 110 ppm showed typical peaks of polysaccharides and proteins. Signals around 76 and 83 were due to C2, C3, C5 and non-crystalline component of C4 of cellulose. Signals derived from hemicellulose were contained within the cellulose peaks. Signals at 115 and 120 were due to H-aromatic C and peak around 140 was due to aromatic C. The peak at 170–173 ppm was assigned to carboxylic, amide and ester groups. Table 2 shows the distribution of diVerent carbon types that are typical for distinct type of organic carbon in the 13 C CP/MAS NMR spectra of HA’s extracted from vermicompost. Signals in the O-alkyl C region (50–110 ppm) dominated the spectrum of ptbc mixture after thermophilic phase (0 day). During the initial period of vermicomposting process the intensity of signals in the alkyl C and aromatic C region increased rapidly while the intensity of the O-alkyl C region decreased. At the end of 60 days, there was loss of aromatic C and carboxyl C whereas alkyl C and O-alkyl C increased. Earthworms are known to digest long chains of polysaccharides, enhancing microbial colonization simultaneously the structure of lignin also changes leading to new polysaccharides and humins. The increase observed for total aliphatic C and polysaccharides at the end of vermicomposting suggests neosynthesis or insolubilization in the vermicompost.
Table 2 Distribution of diVerent carbon types in the 13C NMR spectra of HA extracted from vermicompost at various stages of the process (% of total C) Chemical shift (ppm)
0–50 ppm (alkyl C)
50–110 ppm (O-alkyl C)
110–160 ppm (aryl C)
160–190 ppm (carboxyl C)
Alkyl C/ O-alkyl C
0 days 20 days 40 days 60 days
17.0 34.1 14.8 26.9
71.7 47.3 50.4 60.1
1.3 7.1 21.6 6.1
10.0 11.3 12.8 6.6
0.23 0.72 0.29 0.44
B. Sen, T.S. Chandra / Bioresource Technology 98 (2007) 1680–1683
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