This study is mainly focused on the phytotoxicity improvement within five to six weeks of thermophilic composting of biowastes. Two sets of experiments were conducted involving both sawdust and rice husk as bulking agents, which were composted in self-heating reactors with potato-peel industrial waste and grass clippings as organic materials. The main variables observed over time were temperature, oxygen uptake rate (OUR), biodegradability, and germination index (GI). The effects of compost water extracts on seed germination and primary root growth of garden cress (Lepidium sativum) were measured to calculate the germination index (GI). The biodegradability was well assessed by measuring lignin content, using the Klason method. The experimental results showed that initial compositions strongly determined the profiles of phytotoxicity and the period of maturation. The phytotoxicity assessment in the experiments with sawdust revealed that after 39 days of composting, the GI attained the maximum value of 30%, but using rice husk, it was possible to reach 70% in the same period of time. Our findings showed that, at a certain point, higher cumulative OUR led to lower germination index, and proportional relationship between the cumulative OUR and GI was observed, after thermophilic phase. 1. Introduction Nowadays, the natural resources are consumed at unsustainable rates, and consequently a huge amount of waste is produced, which can cause environmental damage if it is not well managed. In particular, the European Union policy states that the diversion of biowastes from landfill to anaerobic digestion or to composting should be improved for reducing pollution and recovering energy or soil conditioner materials. Composting can be defined as the aerobic microbial decomposition of organic matter, under controlled conditions that allow the development of thermophilic temperatures as a result of the heat released in the biochemical reactions, leading to a stabilized and sanitized final product (free of pathogens and seeds), commonly known as compost [1]. Indeed, although composting is not a recent technology, it can be considered as one of the most flexible methods for handling biodegradable wastes, from small scales such as household bins to large industrial plants [2]. To successfully accomplish composting, favorable physical and chemical conditions to the growth and activity of microorganisms should be promoted, accounting for some essential nutrients, namely, carbon and nitrogen as well as oxygen for metabolic activity. In this context, it is important to
References
[1]
R. T. Haug, The Practical Handbook of Compost Engineering, CRC-Press, Boca Raton, Fla, USA, 1993.
[2]
S. Gajalakshmi and S. A. Abbasi, “Solid waste management by composting: state of the art,” Critical Reviews in Environmental Science and Technology, vol. 38, no. 5, pp. 311–400, 2008.
[3]
N. Trautmann and M. Krasny, Composting in the Classroom, Cornell University Press, 1997.
[4]
M. of A. & Food, Resource Management Branch, Ministry of Agriculture, Food and Fisheries, Abbotsford, Canada, 1996.
[5]
M. Tosin, F. Degli-Innocenti, and C. Bastioli, “Effect of the composting substrate on biodegradation of solid materials under controlled composting conditions,” Journal of Enviornmental Polymer Degradation, vol. 4, no. 1, pp. 55–63, 1996.
[6]
A. de Guardia, C. Petiot, and D. Rogeau, “Influence of aeration rate and biodegradability fractionation on composting kinetics,” Waste Management, vol. 28, no. 1, pp. 73–84, 2008.
[7]
A. de Guardia, P. Mallard, C. Teglia et al., “Comparison of five organic wastes regarding their behaviour during composting—part 2: nitrogen dynamic,” Waste Management, vol. 30, no. 3, pp. 415–425, 2010.
[8]
S. Ponsá, T. Gea, and A. Sánchez, “Different indices to express biodegradability in organic solid wastes,” Journal of Environmental Quality, vol. 39, no. 2, pp. 706–712, 2010.
[9]
R. Barrena, T. Gea, S. Ponsá et al., “Categorizing raw organic material biodegradability via respiration activity measurement: a review,” Compost Science & Utilization, vol. 19, no. 2, pp. 105–113, 2011.
[10]
L. Berthe, C. Druilhe, C. Massiani, A. Tremier, and A. de Guardia, “Coupling a respirometer and a pycnometer, to study the biodegradability of solid organic wastes during composting,” Biosystems Engineering, vol. 97, no. 1, pp. 75–88, 2007.
[11]
M. López, O. Huerta-Pujol, F. X. Martínez, and M. Soliva, “Approaching compost stability from Klason lignin modified method: chemical stability degree for OM and N quality assessment,” Resources, Conservation and Recycling, vol. 55, no. 2, pp. 171–181, 2010.
[12]
R. Barrena, J. Turet, A. Busquets, M. Farrés, X. Font, and A. Sánchez, “Respirometric screening of several types of manure and mixtures intended for composting,” Bioresource Technology, vol. 102, no. 2, pp. 1367–1377, 2011.
[13]
M. Tuomela, M. Vikman, A. Hatakka, and M. It？vaara, “Biodegradation of lignin in a compost environment: a review,” Bioresource Technology, vol. 72, no. 2, pp. 169–183, 2000.
[14]
D. P. Komilis and R. K. Ham, “The effect of lignin and sugars to the aerobic decomposition of solid wastes,” Waste Management, vol. 23, no. 5, pp. 419–423, 2003.
[15]
S. M. Tiquia, “Reduction of compost phytotoxicity during the process of decomposition,” Chemosphere, vol. 79, no. 5, pp. 506–512, 2010.
[16]
M. Gao, F. Liang, A. Yu, B. Li, and L. Yang, “Evaluation of stability and maturity during forced-aeration composting of chicken manure and sawdust at different C/N ratios,” Chemosphere, vol. 78, no. 5, pp. 614–619, 2010.
[17]
D. Caba？as-Vargas, M. Sánchez-Monedero, S. Urpilainen, A. Kamilaki, and E. Stentiford, “Assessing the stability and maturity of compost at large-scale plants,” Ingeniería, vol. 9, pp. 25–30, 2005.
[18]
P. Helfrich, B. Chefetz, Y. Hadar, Y. Chen, and H. Schnabl, “A novel method for determining phytotoxicity in composts,” Compost Science and Utilization, vol. 6, no. 3, pp. 6–13, 1998.
[19]
T. Nolan, S. M. Troy, M. G. Healy, W. Kwapinski, J. J. Leahy, and P. G. Lawlor, “Characterization of compost produced from separated pig manure and a variety of bulking agents at low initial C/N ratios,” Bioresource Technology, vol. 102, no. 14, pp. 7131–7138, 2011.
[20]
G. H. Yu, M. J. Wu, Y. H. Luo, X. M. Yang, W. Ran, and Q. R. Shen, “Fluorescence excitation-emission spectroscopy with regional integration analysis for assessment of compost maturity,” Waste Management, vol. 31, no. 8, pp. 1729–1736, 2011.
[21]
D. P. Komilis and I. S. Tziouvaras, “A statistical analysis to assess the maturity and stability of six composts,” Waste Management, vol. 29, no. 5, pp. 1504–1513, 2009.
[22]
T. Gea, R. Barrena, A. Artola, and A. Sánchez, “Monitoring the biological activity of the composting process: oxygen uptake rate (OUR), respirometric index (RI), and respiratory quotient (RQ),” Biotechnology and Bioengineering, vol. 88, no. 4, pp. 520–527, 2004.
[23]
S. M. Tiquia, N. F. Y. Tam, and I. J. Hodgkiss, “Effects of composting on phytotoxicity of spent pig-manure sawdust litter,” Environmental Pollution, vol. 93, no. 3, pp. 249–256, 1996.
[24]
N. Zhu, “Composting of high moisture content swine manure with corncob in a pilot-scale aerated static bin system,” Bioresource Technology, vol. 97, no. 15, pp. 1870–1875, 2006.
[25]
C. J. An, G. H. Huang, Y. Yao, W. Sun, and K. An, “Performance of in-vessel composting of food waste in the presence of coal ash and uric acid,” Journal of Hazardous Materials, vol. 203-204, pp. 38–45, 2012.
[26]
B. Scaglia, F. Tambone, P. L. Genevini, and F. Adani, “Respiration index determination: dynamic and static approaches,” Compost Science and Utilization, vol. 8, no. 2, pp. 90–98, 2000.
[27]
M. Delgado, “Phytotoxicity of uncomposted and composted poultry manure,” African Journal of Plant Science, vol. 4, pp. 154–162, 2010.
[28]
M. Gómez-Brandón, C. Lazcano, and J. Domínguez, “The evaluation of stability and maturity during the composting of cattle manure,” Chemosphere, vol. 70, no. 3, pp. 436–444, 2008.
[29]
M. Gao, B. Li, A. Yu, F. Liang, L. Yang, and Y. Sun, “The effect of aeration rate on forced-aeration composting of chicken manure and sawdust,” Bioresource Technology, vol. 101, no. 6, pp. 1899–1903, 2010.
[30]
Y. Xiao, G. M. Zeng, Z. H. Yang et al., “Continuous thermophilic composting (CTC) for rapid biodegradation and maturation of organic municipal solid waste,” Bioresource Technology, vol. 100, no. 20, pp. 4807–4813, 2009.
