The 2nd 3R International Scientific Conference on Material Cycles and Waste Management
S1-01
Effect of Waste Lime on Bioavailability and Chemical Speciation of Heavy Metals in Rotary Drum Composting of Water Hyacinth Jiwan Singh1*, Ajay S. Kalamdhad2, Yoon-Young Chang1 1
Department of Environmental Engineering, Kwangwoon University, Seoul 139-701, Republic of Korea 2 Department of Civil Engineering, Indian Institute of Technology Guwahati (IITG), Guwahati-781039 Assam (India) *Corresponding author Tel: 82-2-940-5496, E-mail:
[email protected]
ABSTRACT The bioavailability and speciation of heavy metals (Cu, Pb, Cd and Cr) assist an important role in the toxicity of heavy metals in the compost applied for soil conditioning. The study was carried out on bioavailability and speciation of heavy metals in the composting of water hyacinth in rotary drum for 20 days. The exchangeable (F1), carbonate (F2), reducible (F3) and oxidizable (F4) fractions of Cu were decreased in the control and all calcium hydroxide addition compost. Reduction of F1 (88.6%), F2 (76.7%) and F3 (89.4%) fractions (percentage of total fraction) was observed in lime treatment 2. F1 and F2 fractions of Cd, Cr and Pb were reduced, and F5 fraction was increased in lime treatments as compared to the control. Present study concluded that, the optimum amount of waste lime was greatly effective of reduction of water solubility, plant availability, and most boilable fractions (exchangeable and carbonate fractions) of selected heavy metals. The effect of waste lime is highly recommended for immobilization of heavy metals for water hyacinth composting in rotary drum. Keywords: Composting, heavy metals, bioavailability, speciation, waste calcium hydroxide, rotary drum INTRODUCTION Composting of waste biomass in rotary drums is a highly promising technique for converting biomass into well stabilized organic matter. A high HM content in the final compost and vermicompost of water hyacinth is the major limitation in improving soil quality, and hence plant and human health (Singh and Kalamdhad, 2012). The application of such compost to agricultural fields is problematic due to the ease of transfer of HMs from compost to soil, to plant and then to humans. The bioavailability of HMs to plants depends on their different fractions or ways of binding, rather than on their total concentrations (Nair et al., 2008). Lime is a common amendment material for enhancing the composting process and reducing the bioavailability of HMs to plants (Wang et al., 2008). In India, about 0.75 million tonnes of lime sludge are generated per year during acetylene production (CPCB, 2006). The present study investigated the combined effects of waste lime in rotary drum composting in the immobilization of HMs. The study objectives were to reduce the bioavailability of HMs (Cu, Pb, Cd and Cr) in the rotary drum composting of water hyacinth with lime application, and to determine the mechanism for the immobilization of HMs.
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MATERIALS AND METHODS Water hyacinths were collected from the Amingoan industrial area near the Indian Institute of Technology Guwahati (IITG), India. Waste lime was collected from Assam Air Products, Guwahati, India. The collected lime dried in an oven at 105oC for 24 h, ground using an electrical grinder and sieved through 0.22 mm sieves. The initial characteristics of waste lime have already been reported elsewhere (Singh and Kalamdhad, 2013). Before starting the composting process, the particle size of the compost material was restricted to 1 cm, which is useful for good aeration and moisture control. A pilot-scale rotary drum composter with a capacity of 550 L was designed and operated in the batch-mode (Singh and Kalamdhad, 2012). Waste lime was added concentrations at 1 and 2% to the mixture of water hyacinth (90 kg), cattle manure (45 kg) and sawdust (15 kg). A flame atomic absorption spectrometer (FAAS) (Spectra 55B, Varian) was used to analyze the total concentration of Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr after digestion of 0.2 g sample with 10 mL of a mixture of H2SO4 (Purity 98 %, Loba Chemicals, North East Chemical Corporation, Guwahati, India) and HClO4 (5:1) (purity of HClO4 : 70 %, Merck Chemicals, A. B. Chemicals and Instruments Guwahati, India) digested in a block digestion system (Pelican Equipments, Chennai, India) for 2 h at 300 oC. Sequential extraction was carried out according to the procedure given by Tessier et al. (1979) to yield five fractions: exchangeable (EXCH), carbonate (CARB), reducible (RED), organic bound fraction (OMB), and residual (RESI). FAAS was used for analysis of different HM fractions. The sequential extraction has already been reported in detail (Singh and Kalamdhad, 2012). All the extractions/experiments were carried out in triplicate of all collected samples in different days.
RESULTS AND DISCUSSION These HMs were concentrated in the composting process due to weight loss in the course of aerobic degradation of organic matter during the process. The increment of total HM concentration in the compost is likely to increase the environmental HM risk. However, as discussed in the material and methods section, the bioavailability and eco-toxicity of HMs in the compost depend mainly on their specific chemical forms (Singh and Kalamdhad, 2013). Fractionation of HMs The greatest reduction of EXCH, CARB and RED fractions occurred in lime treatment 2 (Table 5). The smallest reduction of all mobile fractions occurred in lime treatment 3. One or more organic functional groups, mainly carboxylic, carbonyl, and phenolic groups, was present in the final compost, which allowed these groups to bind the EXCH and CARB fractions of Cu (Nomeda et al., 2008). The EXCH and CARB fractions of Pb were reduced in the range of 52.7-78.5% in lime treatments 1, and 2. The reductions of these fractions were greater in the lime treatments than in control. The RESI fraction of Pb was increased and was the dominant fraction in the range of 95.7-99.4 % in the final compost of control and all three lime treatments. The RED and OMB fractions of Pb were not detected at any stage of the composting process. The fractionation of Cd in control, and lime treatments 1 and 2 is presented in Tables 1 and 2.
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Table 1 Variations in the fractionation of HMs in lime treatment 1 during 20-day composting period (mean ± SD, n=3) Heavy metals
Days
Fractions (mg/kg) EXCH
CARB
RED
OMB
RESI
Cu
0 9.85±0.40 2.47±0.09 0.59±0.09 10.87±0.83 9.38±1.13 20 2.3±0.16 1.23±0.18 0.39±0.09 6.5±0.03 47.92±0.08 Pb 0 10.7±0.4 14.7±0.2 ND ND 640±4.6 20 1.65±0.2 3.9±0.3 ND ND 877±22 Cd 0 1.0±0.0 0.94±0.04 ND ND 44.7±2.2 20 0.13±0.03 0.3±0.03 ND ND 60.6±0.4 Cr 0 2.3±0.5 2.6±0.6 3.2±0.1 5.4±0.3 81±1.5 20 0.4±0.0 0.93±0.1 0.8±0.1 3.0±0.0 126±5.7 Mean values in columns are statistically different (ANOVA; p < 0.05); ND- not detected Table 2 Variation in the fractionation of HMs in lime treatment 2 during 20-day composting period (mean ± SD, n=3) Heavy metals
Days
Fractions (mg/kg) EXCH
CARB
RED
OMB
RESI
Cu
0 6.0±0.3 2.8±0.5 1.7±0.1 12.5±0.1 12.8±2.6 20 1.1±0.1 1.1±0.0 0.3±0.1 9.1±0.7 47.5±2.1 Pb 0 16.2±0.2 14.2±0.8 ND ND 683±52.4 20 2.43±0.07 3.07±0.27 ND ND 898±1.5 Cd 0 0.87±0.02 0.86±0.01 ND ND 37.5±5 20 0.33±0.03 0.53±0.17 ND ND 56.8±1.7 Cr 0 1.5±0.3 2.6±0.5 3.2±0.1 4.7±0.4 78.5±3.5 20 0.33±0.01 1.2±0.1 1.6±0.3 1.8±0.2 140.4±1.9 Mean values in columns are statistically different (ANOVA; p < 0.05); ND- not detected The reduction of EXCH and CARB fractions was in the range of 35.0-87.6% and 38.3-70.6% in control, and lime treatments 1 and 2. The greatest reductions of these fractions (EXCH and CARB) occurred in lime treatment1. The RESI fraction of Cd was in the range of 95.5-99.3% in the control and all three lime treatments. The highest reduction of EXCH and CARB fractions was detected at about 84.0 and 65.0 %, respectively, in lime treatment 1. Interestingly, the RED and OMB fractions of Cr were reduced more in control than in lime treatments 1 and 2. However, in lime treatments 1 and 2, EXCH and CARB fractions were reduced more than in control, which are the most bioavailable fractions. The greatest reduction in BAF for all selected metals in lime-treated compost can be attributed to the conversion of most bioavailable fractions (EXCH and CARB) into inert fraction (RESI fraction). In addition, the formation of metal ion complex with two or more functional groups, mainly carboxylic, carbonyl and phenolic, occurs in humic substances, leading to the immobilization of ions in a rigid inner-sphere complex (Qiao and Ho, 1997).
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CONCLUSION The combined effects of waste lime and rotary drum on the immobilization of HMs were highly efficient. The bioavailability of HMs was reduced greatly in the rotary drum composting of water hyacinth mixed with waste lime, cattle manure and sawdust. These study results have demonstrated the feasibility of applying waste lime to the immobilization of HMs under all favorable conditions for the composting process.
ACKNOWLEDGEMENT The authors gratefully acknowledge the financial support of the Department of Science and Technology (DST), Government of India. This research work was also partially supported by the ‘‘Research Grant-2015’’ from Kwangwoon University, Seoul.
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