Chemical and biological changes during composting of different organic wastes and assessment of compost maturity Sneh Goyal * , S.K. Dhull, K.K. Kapoor Department of Microbiology, CCS Haryana Agricultural University, Hisar 125 004, India Received 31 August 2004; received in revised form 25 October 2004; accepted 20 December 2004 Available online 29 March 2005 Abstract Changes in organic C, total N, C:N ratio, activities of cellulase, xylanase and protease, and microbial population were deter- mined during composting of different organic wastes such as mixture of sugarcane trash and cattle dung, press mud, poultry waste and water hyacinth biomass. There were losses of N in poultry waste and water hyacinth with the effect an initial increase in C:N ratio was observed which decreased later on due to decomposition. The activities of cellulase, xylanase and protease were maximum between 30 and 60 days of composting in various wastes. Similar trend was observed with respect to mesophilic bacterial and fungal population. Various quality parameters like C:N ratio, water soluble C (WSC), CO 2 evolution and level of humic substances were compared after 90 day composting. There was statistically significant correlation between C:N ratio and CO 2 evolution, WSC and humic substances. Significant correlation between CO 2 evolved and level of humic substances was also observed. The study shows that no single parameter can be taken as an index of compost maturity. However, C:N ratio and CO 2 evolved from finished compost can be taken as the most reliable indices of compost maturity. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Composting; Organic wastes; Enzyme activities; C:N ratio; Water soluble carbon; Humic substances 1. Introduction The use of organic manures as amendments to im- prove soil organic matter level and long term soil fertil- ity and productivity is gaining importance. The benefits of composted organic wastes to soil structure, fertility as well as plant growth have been increasingly emphasized (Chen et al., 1992; Murwira et al., 1995; Esse et al., 2001). Composting is a widely used method for disposal of organic wastes. Application of undecomposed wastes or non-stabilized compost to land may lead to immobi- lization of plant nutrients and cause phytotoxicity (Butler et al., 2001; Fuchs, 2002; Cambardella et al., 2003). Mesophilic and thermophilic microorganisms are involved in the composting and their succession is important in the effective management of composting process (Beffa et al., 1996; Ishii et al., 2000). The heat generated during composting helps in destruction of pathogens (Golueke, 1977). Different hydrolytic enzymes are released by microorganisms, which are involved in the depolymerization of different constituents of organic wastes (Kandeler et al., 1999; Marx et al., 2001). Impor- tant enzymes involved in the composting process include cellulases, hemicellulases, proteases, lipases, phospha- tases and arlylsulphatases. High levels of protease, lipase and cellulase activities have been detected throughout the active phase of composting (Herrman and Shann, 1993; Cunha Queda et al., 2002; Mondini et al., 2004). The composts prepared from different organic wastes differ in their quality and stability, which further de- pends upon the composition of raw material used for the compost production (Poincelot, 1974; Gaur and 0960-8524/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2004.12.012 * Corresponding author. Tel.: +91 1662 243065; fax: +91 1662 234952. E-mail address: snehgoyal@hau.ernet.in (S. Goyal). Bioresource Technology 96 (2005) 1584–1591