Introduction

Rapid industrialization and population explosion in India has led to the migration of people  from villages  to cities, which generate thousands of tons of MSW daily. The MSW amount  is expected to increase  significantly in the  near future  as  the country strives  to attain an industrialized nation status  by the year 2020 Sharma  and Shah (2005) CPCB (2004) Shekdar et al., , (1992).  Poor collection and inadequate transportation are responsible for the accumulation of MSW at every nook and corner.The management of MSW is going through a critical phase, due to the unavailability of suitable facilities to treat and dispose of the larger amount of MSW generated daily in metropolitan cities. Unscientific disposal causes an adverse  impact on all components of the environment and human health Rathi, (2006) Sharholy et al., , (2005) Ray et al., ,(2005) Jha et al., , (2003) Kansal (2002) Kansal et al., , (1998) Singh and Singh (1998) Gupta et al., , (1998). The waste  generated is  consequently released into the nearby environment.  Consequently, the management  of the MSW needs  to be  revamped to accommodate the  changes  in the quantity and quality to ensure  the  longevity of the environment.  Due  to several legislative, environmental,  economic  and social constraints, the identification of most sustainable disposal route for MSW management remains an important issue in almost all industrialized countries Adani et al., , (2000). 

Generally, MSW is disposed of in low­lying areas without  taking any precautions or operational controls. Therefore, MSWM  is one of the major environmental problems of Indian megacities.  It  involves activities associated with generation,  storage, collection,  transfer and transport, processing and disposal of solid wastes. But, in most cities,  the  MSWM  system comprises  only four activities,  i.e., waste generation, collection, transportation,  and disposal.The  management  of MSW requires  proper infrastructure, maintenance  and upgrade for all activities.  This becomes  increasingly expensive and complex due to the continuous and unplanned growth of urban centers. The difficulties in providing the desired level of public service in the urban centers are often attributed to the  poor financial status  of the managing municipal corporations Mor et al., , (2006) Siddiqui et al., , (2006) Raje et al.,  , (2001) MoEF (2000) Ahsan (1999). Agricultural application of MSW, as  nutrient  source  for plants  and as  soil conditioner, is the most cost­effective MSW disposal option because of its advantages over traditional means such as landfilling or incineration. According to Canellas et al., , (2001), the use of MSW in agricultural lands can be justified by the need of finding an appropriate destination for waste recycling. However, agricultural application of MSW may present a potential threat to the environment due to the presence of pathogens and several pollutants (i.e., heavy metals or organic pollutants). An attractive alternative to recycling such wastes  is  composting. Composting is a  stabilization process through aerobic decomposition of waste, which has  been widely used for different types  of wastes  Cai et  al., , (2007). During composting,  through microbial  action organic nutrients present  in the wastes are  converted into plants available  forms Ndegwa and Thompson (2001). The process can effectively reduce the mixture volume by 40–50%  and by means  of the metabolic heat  generated in the thermophilic  phase  destroy the pathogens  Epstein (1997). Composting cannot  be considered a  new  technology,  but among the MSW management  strategies  it is gaining interest as  suitable  option for chemical fertilizers with environmental profit, since  this process eliminates or reduces the toxicity of MSW  Araujo et  al., (2001) Kaushik and Garg (2003) Arau´jo and Monteiro (2005) and leads to a final  product which can  be  used in improving and maintaining soil quality Larney and Hao (2007).  Application of MSW  compost in agricultural soils can directly improves  soil physico­chemical properties such as: soil structure,  water retention capacity, buffering capacity and nutrient  status  Reeves (1997). In relation to soil biological properties,  numerous researchers  have reported different effects of MSW compost on soil microbial biomass and activityMoreno et al., (1999) Selivanovskaya et  al., (2001) Saviozzi et al., (2002) Arau´jo and Monteiro (2006) Pedra et al., (2007) Barral et al., (2009) Roca­Perez et al., (2009).

Composting of MSW

Composting is a spontaneous biological decomposition process of organic materials in a  predominantly aerobic  environment. During the  process bacteria, fungi and other microorganisms,  including micro arthropods, break down organic materials  to stable, usable organic substances called compost Bernal et al., (2008).  It  is also known as a biological reduction of organic  wastes to humus  or humus­like  substances. The extension or efficiency of the composting process is dependent  on various  factors Bernal et al., (2008) such as  on the formulation of the  composting mix,  nutrient balance, pH, particle size, porosity andmoisture, and also on the process management, such as O2 concentration,  temperature and water content. Nutrient balance  is basically defined by C quality and C/N  ratio. Thus,  the presence of readily degradable carbon (C),  like carbohydrate  in waste, accelerates  the process of decomposition. Thereafter, decomposition slows  on account  of the greater resistance to decomposition of remaining C compounds (lignin and cellulose). Generally,  the  higher the  lignin and polyphenolic content  of organic materials, the  slower their decomposition Palm and Sanchez  (1991). The process of composting occurs  into two stages Pereira Neto and Stentiford (1992).  The  initial stage  is  known as  the thermophilic  stage in which an increase in temperature occurs  (about 65o C).  In this stage,  there is the decomposition of readily degradable compounds  like sugars,  fats and proteins. During this stage, the organic  compounds are degraded to CO2 and NH3, with the consumption of O2. The pH typically decreases  since  organic  acids  are produced (Chen and Inbar 1993). Additionally,  pathogenic microbes  and helminthes  eggs  are eliminated as  a result  of heat  generated during this  process.  Thus, the  organic  compost is  safer for use by farmers.  The second and final stage  is known as stabilization stage, where  there is decrease  in temperature which remains  about  25–30oC.  In this  step the process of humification of organic compost occurs. At the end of this stage, the organic compost is cured and there are  increases in humic matter content and cation exchange capacity (CEC) of the  compost. Thus,  compost can be defined as  the  stabilized and sanitized end product of composting,  which has undergone an initial rapid stage  of decomposition. The compost has certain humic characteristics and is beneficial to plant growth thus making the  composting of MSW  a  key issue for sustainable agriculture and resource management Bernal et  al., (2008) Arau´jo et  al., (2008) Arau´jo and Monteiro (2006) Zucconi and Bertoldi (1987).