Biol Fertil Soils (2009) 45:305–313 DOI 10.1007/s00374-008-0335-x
ORIGINAL PAPER
Physicochemical, including spectroscopic, and biological analyses during composting of green tea waste and rice bran Mohammad Ashik Iqbal Khan & Kihachi Ueno & Sakae Horimoto & Fuminori Komai & Kinji Tanaka & Yoshitaka Ono
Received: 13 May 2008 / Revised: 24 September 2008 / Accepted: 26 September 2008 / Published online: 15 October 2008 # Springer-Verlag 2008
Abstract The aims of this study were to monitor the changes in physicochemical, including spectroscopic, and biological characteristics during composting of green tea waste–rice bran compost (GRC) and to define parameters suitable for evaluating the stability of GRC. Compost pile temperature reflected the initiation and stabilization of the composting process. The pH, electrical conductivity, NO3−N content, and carbon-to-nitrogen ratio were measured as chemical properties of the compost. The color (CIELAB variables), humification index (the absorption ratio Q4/6 = A472 /A664 of 0.5 M NaOH extracts), absorption at 665 nm of acetone extracts, and Fourier-transform infrared (FT-IR) spectra were measured to evaluate the organic matter transformation; germination of komatsuna or tomato seeds was measured to assess the potential phytotoxicity of composting materials during composting. No single parameter was capable of giving substantial information on the composting process, the nutrient balance, phytotoxicity, and organic matter decomposition. The FT-IR spectra at 3,300, 2,930, 2,852, and 1,065 cm−1 provided information on the molecular transformation of GRC during composting and they decreased over the composting. Most of the assayed parameters showed no further change after about 90 days of composting suggesting that GRC can be used for agricultural purposes after this period. M. A. I. Khan : K. Ueno (*) : S. Horimoto : F. Komai : K. Tanaka : Y. Ono Faculty of Agriculture, Saga University, Kuboizumi, Saga 849-0903, Japan e-mail:
[email protected] M. A. I. Khan : K. Ueno : F. Komai : K. Tanaka : Y. Ono The United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima, Japan
Keywords Green tea waste . Rice bran . Composting . Stability indices
Introduction The disposal of large quantities of agro-based industrial waste causes energy, economic, and environmental problems. However, since these wastes have a high content of organic matter and mineral elements, they can potentially be used to restore soil fertility. Composting is useful for waste recycling and produces a chemically stable material that can be used as a source of nutrients and for improving soil structure (Castaldi et al. 2005). During composting, most of the biodegradable organic compounds are broken down and a portion of the remaining organic material is converted into humic-like substances, with production of a chemically stabilized composted materials. The agricultural application of partially decomposed or unstable compost causes nitrogen immobilization and decreases the oxygen concentration around root systems due to the rapid activation of microbes. In addition, chemically unstable compost is phytotoxic due to the production of ammonia, ethylene oxide, and organic acids (Mathur et al. 1993; Tam and Tiquia 1994). Therefore, evaluation of compost stability prior to its use is essential for the recycling of organic waste in agricultural soils. Tea is one of the world’s most popular beverages, with more than three million tons of tea leaves produced annually. Twenty percent of this production is green tea (ITC 2006). After extraction of the green tea from the processed tea leaves, the remainder of the leaves is discarded as waste, and most of the waste is burned or dumped into landfills. Burning and damping of these waste management practices have a serious negative impact on
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the economy and the environment (Kondo et al. 2004). Rice is the staple food of half of the world’s population and rice bran accounts for 5–8% of rough rice. Rice bran contains oil, protein, vitamins, and essential minerals and helps to maintain a high temperature in a compost pile when it is mixed with other materials for composting (Khan et al. 2007a). Moreover, rice bran compost is potentially useful as weed control in organic farming systems (Khan et al. 2007b). Although several indices and methods have been proposed for evaluating compost stability, to date, there is no single method that can be used for organic-residuederived compost. The discrepancy between methods is related to the measure of widely different chemical characteristics of organic waste (Benito et al. 2003; Mondini et al. 2003). Here, the dynamics of green tea waste and rice bran composting were analyzed by different physicochemical parameters such as temperature, pH, electrical conductivity (EC), nitrate nitrogen (NO3−-N) concentration, the carbon-to-nitrogen (C/N) ratio, spectroscopic characteristics (CIELAB color space, UV-Vis, and Fourier-transform infrared (FT-IR) spectroscopy), and a biological parameter (phytotoxicity). These parameters have been reported as good indicators of the stability of compost from different sources (Benito et al. 2003). Particularly, FT-IR spectroscopy was utilized to provide a modern molecular-based analysis of the composting process. The effect of green tea waste–rice bran compost (GRC) on soil fertility and productivity has been previously established (Khan et al. 2007a). However, little information is known about the physicochemical, spectroscopic, or biological characteristics of GRC during composting. The green tea waste–rice bran in a 30:70 ratio (v/v, on a dry basis) was found to produce the best compost quality among those tested, including the ability to enhance spinach growth and the potential for weed control (Khan et al. 2007a, c). Therefore, in this study, GRC with a 30:70 ratio was used to evaluate the composting process.
Materials and methods Composting of green tea waste and rice bran Green tea waste and rice bran were collected from JA Beverage, Saga Co. Ltd., Japan and Field Science Center, Saga University, Japan, respectively. The compost was prepared by mixing green tea waste and rice bran in a 30:70 ratio (v/v, on a dry basis) in a 45-L plastic bucket (height 49.5 cm and diameter 42.7 cm, Belc, Risu Corporation, Japan). Compost was prepared in triplicate (three buckets maintained separately) and allowed to decompose for 246 days (starting from April 2006) in a glasshouse of the Field Science Center, Saga University, Japan (Khan et al.
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2007a). The moisture content was adjusted to 65–70% at the start of composting and moisture was adjusted to around 50% in later stages of the composting when the temperature had stabilized. The composting buckets were turned upside down once a week. Every 2 weeks, ten subsamples were taken from each bucket covering the profile (from top to bottom) and pooled together to give a composite sample which was air-dried, ground to ≤850-μm particle size, and kept frozen (−30°C) until analyzed. Physicochemical analyses The temperature of the compost was measured hourly at a depth of 15 cm from the surface of the compost using a Thermo Recorder (RT-12, ESPEC MIC Crop, Japan). The pH and EC of the samples in distilled water (1:10 w/v on a dry weight basis) were measured by a pH meter (SARTORIUS, Professional meter PP-20) and an EC meter (EC Testr 11+, Oakton instruments), respectively. The concentration of NO3−-N, organic C, and total N were determined using the cadmium reduction method (Hach Company 1995a), the Tyurin (1931) method, and a Kjeldahl method (Hach Company 1995b), respectively. Spectroscopic analyses The organic matter transformation during composting was evaluated using CIELAB color space, Ultraviolet-Visible (UV-Vis) spectroscopy, and FT-IR spectroscopy. Changes in compost color over composting were measured directly from the bottom of a glass Petri dish filled with ground oven-dried sample using a Minolta Color Reader, CR-13 (0° viewing angle and CIELAB color space). The color reader was initially calibrated with a clean empty Petri dish placed on a white tile. We used the following parameters L*, a*, b*, and ΔE*ab to evaluate changes in color. The symbol L* is known as “lightness” and its value extends from 0 (black) to 100 (white). The symbols a* and b* are indicators of color ranging from red through green, yellow, and blue. A high a* value means that the sample is more red and less green in color, and a high b* value means that the sample is more yellow and less blue in color. The color change of the compost over time (ΔE*ab) was calculated by subtracting the color values of the initial material from the color values of the compost on a specific day of composting and inserting these values into the following formula: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ΔE ab ¼ ðΔLÞ2 þðΔaÞ2 þðΔbÞ2 (CIE 1986). To determine the humification index (HI), the material (1 g) was placed in a 250-mL polyethylene flask and it was
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The phytotoxicity of the composting materials was evaluated by the germination of komatsuna (Brassica rapa var. pervidis) and tomato (Lycopersicon esculentum) seeds. One hundred grams of dried compost sample (dried overnight with forced air at 60°C) and 1 L of distilled water were mixed and shaken for 12 h at high speed (250 rpm) at 4±1°C; then, the mixture was filtered through two layers of filter paper (Advantec No. 5A). Twenty-five seeds of either komatsuna or tomato were imbibed and incubated for 48 or 72 h, respectively, at 25°C under completely dark conditions on a double sheet of filter paper (Advantec No. 2). The paper was moistened with 5 mL of either compost water extract or distilled water (control) in a covered 9-cm glass Petri dish. The Petri dishes were sealed with parafilm (Parafilm “M” Laboratory Film American National Can TM). The results were expressed as the percentage of seed germination with compost water extract considering the number with distilled water equal to 100%. The experimental design was a completely randomized design and the treatment was repeated four times. Statistical analyses All the results reported in this paper were expressed as means of three replicates. The relationships among the selected parameters of GRC stability evaluation were
Results and discussion The compost pile temperature during composting The temperature of the composting material reached the thermophilic phase (>45°C) within 5 days of composting reflecting the initiation of the composting process (Fig. 1). From days 9 to 65, the daily average temperature was maintained, with some fluctuation, at the optimal values 50–60°C for effective composting (Wong et al. 2001). The highest hourly temperature (59.4°C) was attained within 40–50 days of composting. The temperature increased immediately after turning over the composting materials at the initial stage of composting. However, at the later stages of composting, the temperature did not increase any further even after addition of water and turning over the compost. The temperature of the composting materials reached a plateau on day 90, indicating that the compost had become stabilized. Temperature has been widely used as one of the most important parameters for evaluating compost stability since compost pile temperature is related to microbial activity and to the rate of decomposition during composting (Tiquia and Tam 2002). Moreover, a high temperature (50–60°C) is important for the destruction of weed seeds and for killing pathogens of the compost. The use of the compost pile temperature for evaluating the composting process is limited by its dependency on factors such as the type of material that is composted, the volume and moisture content of materials, the composting procedure, the season, and other variables (Ko et al. 2008). 60
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Biological analysis
analyzed by Pearson’s correlation coefficient using the SPSS statistical software (SPSS for Windows, version 12.0.1; SPSS Inc, Chicago, IL, USA).
Temperature ( C)
extracted with 50 mL 0.5 M NaOH by shaking for 2 h; then, the flask was left overnight. The next day, the suspension was centrifuged at 600×g for 25 min and the absorbance (A) of the supernatant was measured at 472 nm (A472) and at 664 nm (A664) so as to calculate the absorbance ratio Q4/6 =A472 /A664 often taken as the humification index (Zbytniewski and Buszewski 2005). As an index of decomposition, we measured the chlorophyll-type compounds (mainly chlorophyll a, chlorophyll b, pheophytin, chlorophyllide, and pheophorbide) of the composting materials over time (Hoyt 1966; Rajbanshi and Inubushi 1998) by extracting 100 mg of an oven-dried and finely ground compost sample with 20 mL 90% acetone for 24 h (
