Bioconversion of rice straw and certain agro-industrial wastes to amendments for organic farming systems: 1. Composting, quality, stability and maturity indices Ferial M. Rashad * , Walid D. Saleh, Mohamed A. Moselhy Dept. of Microbiology, Faculty of Agriculture, Cairo Univ., Giza 12613, Egypt article info Article history: Received 21 October 2009 Received in revised form 24 February 2010 Accepted 26 February 2010 Available online 23 March 2010 Keywords: Composting Rice straw Rock phosphate Microbial population Maturity indices abstract The microbiological and physicochemical parameters were monitored for 12 weeks during composting of five piles (1.5  1.0  0.80 m 3 ) containing mainly rice straw, soybean residue and enriched with rock phosphate. Two treatments were inoculated with buffalo’s manure or composite inoculum, two were supplemented with vinasse and inoculated with either the composite inoculum or with both, the last one was served as a control. Four typical phases of composting were observed during the bioprocess: short initial mesophilic phase followed by, thermophilic, cooling and maturation phases. Physicochemical changes confirmed the succession of microbial populations depending on the temperature of each phase in all treatments. Intense microbial activities led to organic matter mineralization and simultaneously narrow C/N ratios. Inoculation of composting mixtures enhanced the biodegradation of recalcitrant sub- stances. The duration of exposure to a temperature above 55 °C for at least 16 consecutive days was quite enough to sanitize the produced composts. After 84 days, all composts reached maturity as indicated by various parameters. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Organic wastes from animal production, agricultural and by- products of agricultural and food processing industries have be- come major sources of environmental and social problems throughout the world in both developed and developing countries. In Egypt, rice straw is considered one of the main agricultural wastes which represent about 4 million tons annually produced every autumn. It is traditionally disposed of, by burning in situ, causing real harmful environmental implications through produc- ing huge black clouds of smoke that affect all the adjacent munic- ipalities. The problems are varied and even affect human health. Furthermore, the production of CO 2 during burning has been linked to global warming as green house gases. Vinasse, as another main by-product waste in Egypt, is the dark brown aqueous generated from the distillation of ethanol follow- ing fermentation of carbohydrates in volume more than 2000 m 3 day 1 from Sugar and Integrated Industries Company in Hawamdia. It creates serious environmental problems when throw out into either water bodies and/or land (Diaz et al., 2002). Okara, or soy pulp, a rich protein by-product, is another pollu- tion problem added during the manufacturing of soymilk and tofu (Wang and Cavins, 1989). Manures also represent a serious pollution problem resulting from the huge accumulation of such material. These animal wastes are known to be heavily contaminated with pathogenic bacteria and parasites causing a direct health risk (Hanajima et al., 2006). The increase in the production of wastes in a society can be diminished or even ceased to be a problem if an added value was attributed to them. Composting is one of the natural bioprocesses capable of treating organic wastes through the microbial activity. However, rice straw among certain organic materials are resistant to microbial attack because of the wide C/N ratio and the high con- tent of ligno-cellulose (Zhu, 2007). Therefore, co-composting of rice straw with the aforementioned wastes is likely to provide bet- ter results than rice straw alone. Composting can destroy patho- gens; converts nitrogen from unstable ammonia to stable inorganic forms, reduces the volume of waste, and satisfies the needs of fertilizer for agricultural use seasonally (USEPA, 1993; Zhu, 2007). Because of phosphorous is the second limiting nutrient after nitrogen in majority of soils for crop production, many attempts had been made by some workers to produce compost from rice straw enriched with RP to increase the availability of P. The direct application of rock phosphate (RP) is not reasonably suitable for direct use in neutral to alkaline soils such as in Egyptian ones (Zayed and Abdel-Motaal, 2005; Biswas and Narayanasamy, 2006). The most important factors affecting the composting include temperature, moisture content, C/N ratio, degree of aeration, pH level, and the physical structure of the waste material. 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.02.103 * Corresponding author. Tel.: +20 105525039; fax: +20 235717355. E-mail address: ferialrashad@yahoo.com (F.M. Rashad). Bioresource Technology 101 (2010) 5952–5960 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech