Introduction

India generates > 0.2 Teragram (Tg) of municipal solid wastes (MSW) everyday and in many cities facilitiess exist to treat Organic Fraction of Municipal Solid Waste (OFMSW) through either aerobic or anaerobic methods (Asnani and Zurbrugg 2008; Census of India 2011; CPHEEO 2016). About 10–20% of the collected waste is often disposed of unscientifically in the vacant land around these cities and subjected to open degradation in uncontrolled conditions without any recovery of resources. Open decomposition is evident in many emerging towns and cities and these sites are generally difficult to locate (Chanakya et al. 2015). Such open dump sites can pose a threat to the immediate environ- ment and result in air, soil, and water contamination.
Most Indian cities have solid wastes where > 80% is OFMSW, especially when MSW is collected and sam- pled from households (Chanakya and Sharatchandra 2005; Chanakya and Swamy 2011). This is largely comprised of biodegradable organic fractions such as leftover food, veg- etables, and fruit peels. Many of these open dumps within cities also act as ephemeral storage sites lasting 2–7 days (Chanakya et al. 2009). In these temporary open dumps, the major fraction of MSW is organic and easily fermentable and therefore has the propensity to undergo rapid microbial degradation (Biddlestone and Gray 1988; Bot and Benites 2005; Ferronato and Torretta 2019). OFMSW components. such as fruits, vegetables, and food wastes tend to degrade rapidly, whereas the mature leafy components (e.g. leaf lit- ter, garden wastes, etc.) of organic waste decompose slowly (Biddlestone and Gray 1988; Chanakya et al. 2009). This degradation process involves the biochemical transforma- tion of complex organic materials into simple organic and inorganic compounds.
The degradation of organic waste residues cycles the nutrients contributing to biological growth and the nutrient recycling processes (Chanakya and Sharatchandra 2005). The degradation rate of organic matter also depends on the physical and chemical nature of organic matter, the ambi- ent environment, and also the activity of soil organisms. In dispersed piles of MSW, the soil ecosystem functions both as a source of microbial and faunal inoculum as well as a sink for the decomposition intermediates and end-products. Under such conditions, these systems resemble decay of the fallen fruits and leaf litter of typical semi-deciduous ecosystems where contributions to the degradative process come from various modes of faunal and soil micro-flora assisted degradation. The soil microorganisms assist in the breakdown of carbon and its mineralization, fauna help in the mechanical breakdown of organic wastes, a part of which is subsequently ingested and broken down through their metabolism to be finally excreted back to soil (Brus- saard 1997; Paris et al. 2008; Gougoulias et al. 2014). The degradation of organic matter added on to soil surface as similar to aerobic windrow composting has generally been represented as Y₀e−kt; an exponential decay model where k modifies the degradation rates to suit temperate and tropi- cal environments (Jenkinson and Ayanaba 1977; Jenkinson 1981; Middleton 2020). Anaerobic decomposition of vari- ous components of MSW held in pile can also be described as a two-component model wherein the first-rate describes the loss of easy to decompose constituents and the second slope describes the degradation of the slow to decompose recalcitrant components of the feedstock (Chanakya et al. 1999, 2009; Ravikumar 2014).
Earlier studies were collated to model and represent OFMSW in large and deep dumpsites and arrive at nor- mative indices (IPCC 2000). However, there is inadequate information about the degradation pattern of OFMSW in open dump sites, especially when there is a mix of biomass with a large fraction of easy to degrade waste components and the degradative conditions fluctuate between partially aerobic to partially anaerobic. This necessitates identifica- tion and understanding of the relative contribution of different actors to the overall process, degradation pattern, and the role of agents of degradation. The objective of this study was to identify different actors involved in the open degradation pattern of dumped OFMSW and to understand the degradation pattern of MSW with the kinetics. This study is important to various developing countries where MSW with a large OFMSW content gets disposed in several forms of open dump sites. The importance and extent of various routes thus need to be elucidated to forecast possible environmental, ecological, sustainability, and human health issues