The compost products of <i>Camellia oleifera</i> shell/meal mixed at different mass ratios were characterized by Fourier-transform infrared spectroscopy (FTIR) at different composting stages to monitor the structural changes of their components. The results showed that the amount of <i>Camellia oleifera </i> meal significantly affected the composting rate of the shell, but did not change the degradation order and decomposition of the related compounds. During the composting process, microorganisms used the highly decomposable carbon source materials, such as proteins and sugars, first to grow and multiply, and then decomposed hemicellulose, cellulose and lignin by oxidative cleavage after these nutrients were consumed to a certain extent. The decomposition products were then condensed into more stable humic acids. The degradation rates of the compounds were directly proportional to the amount of <i>Camellia oleifera</i> meal. The compounds in <i>Camellia oleifera</i> shell were composted faster with higher amounts of <i>Camellia oleifera</i> meals, resulting in less lignocellulose in the final products.
Camellia oleifera is the largest woody oil crop in China [
Composting has been demonstrated an efficient approach to utilizing Camellia oleifera shell and meal. During composting, the unstable Camellia oleifera shell and meal are converted into stable humus substances by aerobic fermentation under artificially controlled conditions including water, C/N ratio and air, resulting in good soil improvers and organic fertilizers [
Fourier-transform infrared spectroscopy (FTIR) provides the infrared spectrum of absorption or emission of a compound based on the constant vibrations and rotations of its atomic groups, which gives the composition information of atomic groups, and thus facilitates the understanding of structure of a compound. FTIR analysis has exhibited great advantages including low sample loss, easy operation, fast detection and good stability [
In the present work, the composted Camellia oleifera shell/meal was characterized by FTIR to investigate the effects of the ratio of shell to meal of on the degradations of various compounds during composting, aiming to establish the scientific foundation for the utilization of Camellia oleifera shell and meal and the corresponding compost maturity indicators.
Camellia oleifera shells with the sizes < 3.5 cm were collected from Dongfanghong Forest Farm, Jinhua City, Zhejiang Province, China and Camellia Oleiferaseed meal provided by Zhejiang Tiantai Kangneng Tea Oil Co., Ltd.. White Urea granular was purchased from Henan Jinkai Chemical Holdings Group Co., Ltd. The microorganisms (EM, 1.05 × 1012 CFU/ml) was purchased from Henan Nanhua Qianmu Biotechnology Co., Ltd. Other bacterial strains included aspergillus awamori for the degradation of tannin and Bacillus amyloliquefaciens and Meyerozyma guilliermondii for the degradation of saponins. The additive amount of bacterial strains (submerged culture) was 1.5% of the weight of Camellia oleifera shells used in composting. The basic properties of raw materials are shown in
The composting was conducted in an insulated and highly ventilated ecological composter (73 cm × 115 cm × 80 cm, 220 L, BIOLAN). Four experimental groups with different shell/meal ratios were designed, and ech experiment was conducted in 3 replicates (
Raw material | Cellulose | Hemicellulose | Lignin | C | N | C/N | Tannins | Saponins |
---|---|---|---|---|---|---|---|---|
Camellia oleifera shell | 18.62 | 49.34 | 29.71 | 48.6 | 0.42 | 116.00 | 2.26 | 4.80 |
Camellia oleifera meal | 21.01 | 24.76 | 21.59 | 47.8 | 1.22 | 39.18 | 1.03 | 16.35 |
Compost group | Raw materials |
---|---|
1/3 Camellia oleifera meal | Camellia oleifera shell + 1/2 dry wt. Camellia oleifera meal |
1/4 Camellia oleifera meal | Camellia oleifera shell + 1/3 dry wt. Camellia oleifera meal |
1/5 Camellia oleifera meal | Camellia oleifera shell + 1/4 dry wt. Camellia oleifera meal |
1/10 Camellia oleifera meal | Camellia oleifera shell + 1/9 dry wt. Camellia oleifera meal |
The samples collected from composters were analyzed with a Fourier-transform infrared spectrometer (Nicolet iS50, Thermo Fisher Scientific, USA) using KBr pellets. Briefly, 0.001 g sample was dried at 105˚C for 1 h, mixed with 0.1 g KBr powder, and pressed into a thin and transparent disk by the pressed-disk technique for FTIR measurement. For each measurement, a 32-scan absorption interferogram was collected with the resolution of 4 cm−1 in the range of 400 - 4000 cm−1 at ambient temperature. Each measurement was repeated three times, and the peak positions and heights were measured in the software Origin 8.0.
The spectra were plotted in EXCEL and Origin 2017 to determine peak position and height.
As shown in
68˚C and 29 days high temperature stage. The 1/10 group that contained 1/9 dry wt. meal reached the high temperature of 50˚C last with the shortest high temperature stage of 11 days, and its highest temperature was only 66˚C. The temperatures of all groups exhibited similar changing trends, but with different values and different lengths of each stage. It is clear that the high temperature stage was reached sooner, and was longer with more Camellia oleifera meals added. The compost stack temperature change was caused by the microbial activities that were also affected by the temperature. Therefore, the compost stack temperature can be used to evaluate the composting progress as an indicator of compost maturity. However, the temperature cannot directly reflect the changes in the composition of the stack [
The Camellia oleifera shell sample exhibited three strong absorption peaks at 3415.69 cm−1, 1617.33 cm−1 and 1049.51 cm−1, respectively (
Wavenumber/cm−1 | Assignment | Representative compounds |
---|---|---|
3415.69 | -OH vibration and N-H stretching vibration | Carbohydrates including cellulose, hemicellulose, and lignin and water |
2926 | Symmetric or asymmetric stretching vibrations of C-H in -CH3 and -CH2 | Polysaccharides, lignin, fatty acids and saturated hydrocarbons |
1737 | Stretching vibration of C=O in non-conjugated ketones, carbonyl groups and esters | Polysaccharides, lignin, and hemicellulose |
1654 | Stretching vibration of C=O in p-substituted conjugated aromatic groups | Lignin |
1617 | Stretching vibration of C=O and skeletal vibration of aromatic groups | Lignin |
1516 and 1513 | Deformation of N-H and stretching vibration of C=N | Aminos and lignocellulose |
1445 | Bending vibration of C-H and skeletal vibration of benzene ring | Lignin and polysaccharides Lignin |
1236 and 1261 | Stretching vibration of CO-OR and Ph-O | Acetoxy group in hemicellulose and lignin |
1049 | Asymmetric stretching vibration of Si-O-Si and stretching vibration of C-O | Silicic compounds cellulose, polysaccharides, lignin, and hemicellulose |
These characteristic IR peaks suggest that the Camellia oleifera shell and meal mainly contain carbohydrates, such as cellulose, hemicellulose, lignin, polysaccharides, and so on, proteins, amides, silicates etc. The peaks of Camellia oleracea meal at 2926 cm−1, 1737 cm−1, 1513 cm−1, 1445 cm−1 and 1049 cm−1 are stronger than those in the shell sample, suggesting that the meal sample contains more polysaccharides, fatty acids and amides than the shell sample. No multiple complex bands of -NH4+ at 2400 - 2200 cm−1 were found in the shell sample, indicating that it contained high amounts of lignocellulose and low amounts of proteins [
The IR peak positions of the compost give the structural information of its compounds, and the peak intensities can be used to evaluate the degradation progress of these compounds [
including proteins and polysaccharides were degraded, consistent with the high temperatures during this period. The microorganisms used these proteins and polysaccharides to multiply and grow [
The peak intensity at 2920 cm−1 exhibited an increasing trend from day 0 to 30, decreased thereafter and remained constant from day 40 to day 60, indicating that the decomposition of large amounts of macromolecules increased the numbers of methylene and carboxyl groups in the first 30 days, and then those degradation products were further consumed to afford humic acids. The intensities of the characteristic peaks of cellulose, hemicellulose and lignin at 1420 cm−1,
1640 cm−1, 1320 cm−1 and 1030 cm−1 were dramatically decreased from day 0 to 12 because of the degradation of large amounts of hemicellulose, slightly increased right before day 30, decreased again from day 30 to 40 and increased slightly thereafter. The second decrease and increase fluctuation might be due to the burst growth of microorganisms for the degradation of cellulose and lignin at appropriate temperatures and accumulated nutrition during the cooling stage. The increased absorptions at 1420 cm−1 and 1640 cm−1 indicated that some of the degradation products were converted into humus in the composter [
The relative intensity changes of peaks at 1640 cm−1 for aromatic carbon, 1030 cm−1 for polysaccharide carbon, 1420 cm−1 for carboxyl carbon and 3400 cm−1 for aliphatic carbon can be used to evaluate the degrees of decomposition of different compounds, as well as their degrees of aromatization, during the composting [
Time/ day | 1/3 | 1/4 | 1/5 | 1/10 | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
3400/1640 | 1030/1640 | 1420/1640 | 3400/1640 | 1030/1640 | 1420/1640 | 3400/1640 | 1030/1640 | 1420/1640 | 3400/1640 | 1030/1640 | 1420/1640 | |
0 | 1.99 | 1.27 | 0.728 | 1.99 | 1.27 | 0.728 | 1.99 | 1.27 | 0.728 | 1.99 | 1.27 | 0.728 |
9 | 1.940 | 0.738 | 0.531 | 1.677 | 0.885 | 0.616 | 1.847 | 0.747 | 0.578 | 1.861 | 0.767 | 0.584 |
12 | 1.668 | 0.895 | 0.640 | 1.864 | 1.00 | 0.584 | 1.557 | 0.845 | 0.637 | 2.104 | 0.600 | 0.477 |
30 | 1.936 | 0.692 | 0.560 | 1.411 | 0.833 | 0.620 | 1.563 | 0.734 | 0.601 | 1.811 | 0.631 | 0.567 |
40 | 0.998 | 0.677 | 0.536 | 1.354 | 0.663 | 0.606 | 1.583 | 0.473 | 0.444 | 1.549 | 0.810 | 0.655 |
60 | 1.431 | 0.672 | 0.617 | 1.601 | 0.642 | 0.536 | 1.473 | 0.670 | 0.612 | 1.521 | 0.683 | 0.587 |
contents of carboxyl groups in each group decreased, and those of aromatic carbons increased, yet with different reduction degrees at different times. In addition, the absorption peaks at 1030 cm−1 and 1420 cm−1 were significantly weakened at the heating stage, indicating that the polysaccharides were degraded rapidly at the high temperatures. All groups exhibited similar change trends and final values of 1030/1640. Those results, along with the temperature change trend of each group during the composting indicate that the protein degradation is more vigorous, and the composting is faster with the higher amounts of Camellia oleifera meal. The 1/3 group exhibited the highest 1420/1640 and that of the 1/10 group was the lowest, suggesting that Camellia oleifera meal could increase the degradation degrees of cellulose, hemicellulose and lignin.
In summary, Camellia oleifera meal can significantly affect the decomposition degrees of the compounds in Camellia oleifera shell during composting but does not change their degradation order. The amount of Camellia oleifera meal affects the degradation rate and the quality of the final composting product of the shell.
The variation trend of absorption peaks in IR spectra of compost samples with different amounts of Camellia oleifera meal was basically consistent, but the temperature during composting increased more rapidly at the heating stage and the high temperature stage lasted longer as more meal added, reflected as increasing rate of change of height of the infrared characteristic peaks. Compared with temperature, IR spectra are less affected by the environment, and the height of the characteristic peak is directly related to the content of substances in composting. Therefore, IR spectra can be used as one of the indicators for judging compost maturity.
According to the infrared characteristic peaks, the amount of Camellia oleifera meal affected the progress of composting, but did not change the degradation order of the components in the shell. The microorganisms used the easily decomposable carbon source materials including proteins and sugars to grow and multiply first, and, after these nutrients were consumed to a certain extent, oxidatively cleaved the compounds, mainly hemicellulose, cellulose and lignin, and decomposed them. The decomposition products were then condensed into more stable humic acids. The degradation rate of Camellia oleifera shell is proportional to the amount of Camellia oleifera meal. The compounds in the shell were degraded more rapidly as higher amounts of meal added, resulting in less lignocellulose in the final compost. Therefore, Camellia oleifera meal can be used to promote the composting of Camellia oleifera shell, and improve the quality of composting products.
The authors are grateful for the financial support from Provincial Department of Science and Technology of Zhejiang, China, Grant No. 2017C02022.
The authors declare no conflicts of interest regarding the publication of this paper.
Zhang, J.P., Ying, Y., Li, X.B. and Yao, X.H. (2018) Infrared-Spectral Characteristics of Camellia oleifera Shell/Meal during Composting. Agricultural Sciences, 9, 1286-1298. https://doi.org/10.4236/as.2018.910090