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India is building up its city level solid waste management in an extensive manner. It has framed necessary rules and guidelines (MSW handling rules 2000). Within the state of Karnataka over 200 cities (urban local bodies) will attempt to set up necessary infrastructure for the collection, transport, processing and disposal sub-systems. The existing centralized collection and open landfill systems are gradually becoming expensive and will need to be closed for fermentable wastes (MSW handling rules 2000). Compliance to the new rules will enhance the current costs (Rs.700/t collection for Bangalore 2004, US$= Rs.45 and Euro=Rs.56) even further. Sustainable and economic alternatives are being developed within India to lower the cost burden and increase the marketable outputs from centralized and decentralized processing of MSW (Chanakya and Moletta 2005). In this scenario, alternatives that reduce the need for daily collection and transport will greatly bring down the overall costs. Most cities in Karnataka have determined characteristics of wastes (TIDE 2000, 2003) where fermentable components mainly fruit and vegetable wastes (FVW) dominate.

The generation of these wastes is localized in different parts of the city. Buenrostro et al. (2001) conceptualized on the solid waste generated within the territorial limits of a municipality independently of its source of generation. This aided in a hierarchical source classification of MSW based on the economic activity that generates a solid waste with distinct physical and chemical characteristics. This enabled the assessment of the volume of MSW generated and provided an overview of the types of residues expected to be generated in a municipality, region or state. By choosing proper processing options a significant component of the organic fractions in the wastes can be utilized (sometimes utilized many times over). Most countries are heading towards a zero landfill approach which then necessitates that wastes be characterized such that they be re-used or converted to reusable products.

It is possible to collect wastes zone, sector and time-wise such that different types of wastes can be collected separately and consigned to various types of processing and treatment (TIDE 2000; Aus-AID 2002) such that the end products accrue better value. The MSW collected in Bangalore, especially in residential and restaurant areas, consists of a large fermentable fraction (c.80% – mainly vegetable and fruit wastes, Rajabapaiah 1988; Sathishkumar et al. 2001; Aus-AID 2002; Ramachandra 2006). Such a large wet and fermentable component requires daily removal from places of generation because the high ambient temperatures are conducive to rapid initiation of fermentation and emanation of malodours. Models involving primary collection by handcarts and immediate composting /vermicomposting within the locality have been tried with mixed levels of success (CEE, TIDE personal communication). On the one side the processes have not sustained for long due to inadequate attention to economics and revenue collection. On the other side the composting techniques themselves have not been satisfactory and consistent quality end-products have not emerged. Some of the causes are examined.

Composition of MSW listed in Table 1 clearly shows the predominance of fermentable materials at all locations in the process of generation to its reaching the dump site. In residential areas, parks and vegetable markets, the presence of a large fraction of fruit and vegetable wastes (Fermentable fraction, 70–90%) increases the moisture content of MSW to about 70–80% (TIDE 2000). When composting of such high moisture feedstock is attempted by the standard windrow method there is excessive generation of leachates and its fermentation results in malodours (TIDE personal communication). High levels of such wastes arise even in business districts where there is a concentration of fresh fruit juice vending shops in the area. Citrus fruit skins, pineapple cores, sugarcane bagasse (from sugarcane juice), other fruit wastes, etc. are thus generated in large quantities in certain pockets of the city. These form nearly 80% of the waste collected in the area (Sathishkumar et al. 2001). It is therefore important that such wastes are treated rapidly in decentralized units. Two options available are aerobic composting and biomethanation (MSW handling rules 2000).

In many residential or quasi-residential areas of Bangalore a variety of slow to decompose biomass wastes such as paddy straw, sugarcane trash, photocopier paper, tree leaf litter, etc. also enter organic fraction of municipal solid waste (OFMSW) streams in the form of micro-point source discharge. Paddy straw is used as a packaging material and it is also found to occur in significant proportion in some parts of MSW – especially fruit and furniture packing. Today it has been increasingly found in and around fruit stalls. Paddy straw is a bulky material with a low packing density (Chanakya et al. 1997) has large particle size and has a medium level of lignocellulosics. Zhang and Zhang (1999) studied the anaerobic phased solids digester system for the conversion of rice straw to biogas. Ligno-cellulosic

rice straw is difficult to degrade biologically. Hence different pre-treatment methods such as physical, thermal and chemical treatment on the digestion of rice straw have been investigated. Results depict that the pre-treatment has some significant role on the digestibility of the straw. Lawn grass-major fraction of MSW was chosen and subjected to this digestion by Yu et al. (2002). The digester employed in this study was 8 m3 solid phase reactor (harbouring 155 kg of feedstock) coupled with methane phase reactor consisting of inert commercial packing media used to facilitate the bacterial attachment and growth. Maximum loading rate of this UAF digester was determined to be 2.7 kg of COD/m3 per day. Yu et al. (2002) also studied the effects of temperature on the biomethanation efficiency by using heated upflow anaerobic filter (UAF) in one of the reactor. Higher gas production reported in the heated UAF was due to the higher COD conversion. This COD conversion contributes 0.344 m3 and 0.339 m3 of CH4/kg of COD removed. Hence it suggests that 1 kg of grass gave a yield of 0.15 m3 of methane.

These components of OFMSW, when in excess of a threshold value, cause a different type of the problem for decentralized composting and vermicomposting facilities. All vegetable and fruit wastes tend to decompose within a span of 15–20 d. However, the slow to decompose components remain nearly intact. Therefore the resultant compost at this stage cannot be sieved and bagged for sale and subsequent use. This prolongs the composting process to nearly 75 d. It then requires that such types of wastes are processed singly and the composts are mixed later on to achieve a balanced product. Such problems of decentralized composting/vermicomposting may also be avoided if the primary treatment involves anaerobic digestion in simple biogas digesters. In this study we characterize how such problematic single feedstock dominant OFMSW decompose in a solid-state stratified bed (SSB) reactor. We also examined the digested feedstock for its suitability for subsequent use as a biofilm support in wastewater treatment (Chanakya et al. 1998) i.e. an additional use other than compost. We expect that in doing so, in addition to biogas generated in the process, the biofilm support will also provide a high value byproduct. We believe that the price paid to biogas as well as for digested biomass for use in biofilm support together will offset the rising prices of MSW collection and processing. (Yang et al. 2004)