Bioconversion of Solid Organic Wastes and Molecular Characterization of Bacterial Population During the Decomposition Process
Mohd Arshad Siddiqqui, R. Hiranmai Yadav, and B. Vijayakumari
Soil forms the resource of agriculture with its organic and inorganic content reflecting the fertility of soil and thereby productivity of crops (Nagarathinam 2004). Soil aggregates play a significant role in water retention and movement, a gas diffusion that helps in root growth that in turn increases nutrient-holding capacity (Sultan 2001). The adverse effects of fertilizers are usually manifested when the high analysis fertilizers are added continuously to soil without monitoring the soil fertility health. Various reports indicate that soil health continues to be deteriorated, particularly its physical, chemical, and biological properties by the continuous, indiscriminate use of inorganic fertilizers. The use of inorganic fertilizers, though essential for increasing crop production, can also prove to be hazardous to the environment (Kumar and Sharma 1998). Higher levels of fertilizer application might result in certain antagonistic interactions between and among the plant nutrients within the soil which adversely affect the mobility of nutrients in the soil solution and as far as the roots (Saikia and Pathak 1997).
The biodegradation of organic substances by vermicomposting results in a stable eco-friendly soil conditioner that facilitates plant growth. The application of ver- micompost helps to reduce pollution and minimizes the use of chemical fertilizers, as it contains organic carbon and matter, macro and micronutrients in addition to microbes, enzymes, and growth regulators (Gupta 2003).
There are numerous microorganisms that are involved in different stages of composting. They play a significant role in the degradation of waste, the stabilization of decomposed material, and the quality of the final product. Identification of these organisms is crucial for utilizing them effectively in waste management. From the conventional morphological and biochemical methods of identification, now technological advances help to identify them by molecular methods, which are more accurate.
Role of Organic Wastes in Soil Fertility
The addition of organic waste has increased soil porosity and modified the pore size pattern (Pagligai et al. 1981). Organic matter perhaps associated with relatively high sugar content is known to be attractive to earthworms (Lee 1985). It is also known that application of town refuse compost increases soil pH and electrical conductivity. The sustainable agricultural practices help to avoid soil degradation and declining crop yields and compensate rising fertilizer costs. The use of chemical fertilizers to increase crop production is coupled with the adverse effects on the environment. Vermicomposting converts solid organic wastes to manure and is used to improve soil fertility and crop yields (Chaudhary et al. 2004). Hemalatha (2012) observed an increased nutrient content and reduced C/N ratio in vermicompost prepared from partially decomposed fruit waste, paper, and tannery sludge.
Soil moisture retention facilitates root penetration and crop growth. This could be achieved by the amendment of organic matter that improves the water holding capacity of soil (Son 1995). The application of locally available organic waste materials after vermicomposting could replenish soil physio-chemical properties. Nitrogen, phosphorus, potassium, and micronutrients like iron, zinc, magnesium, and calcium are found to be high in vermicompost (Mary and Sivagami 2014). Angelova et al. (2013) have reported that composts and vermicompost application have a positive influence on soil quality and reduce metal toxicity. The conversion of organic waste materials by vermicomposting and applying them to soil could be an effective method for soil waste management (Bajsa et al. 2003). Vermicomposting is a feasible process that reduces waste and adds the organic matter to the soil to maintain soil fertility (Garg et al. 2006; Van Gestel et al. 1992; Edwards 1998; Kaur et al. 2010; Suriyanarayanam et al. 2010; Sinha et al. 2008). Soil quality was improved by vermicompost application that promises a beneficial effect (Ansari 2008) in sustainable agriculture. Integrated organic and inorganic manure application is found to be suitable to improve per capita income (Sharma and Singh 2012).
This is a biotechnological process to produce nutrient-rich material from organic waste that is converted by earthworm activity. This quality product with available forms of macro and micronutrients has a positive effect on growth and yield of plant, fertility of soil, and microbial population (Tharmaraj et al. 2011). Moradi et al. (2014) have reported that vermicomposting of organic piles results in a manure with rich humus, microbial population, and high content of nutrients and plant growth hormones. The bioconversion process of organic waste is where earthworms feed on the materials to produce more earthworms, vermicomposts, and vermiwash as products. The process ranges with varying temperature, pH, and moisture content to produce a manure with total nitrogen, available phosphorus, and exchangeable potassium that can be applied to plants as biofertilizers (Manyuchi and Phiri 2013).
Earthworms have traditionally been used in domestic compost heaps for breaking down organic waste to produce better quality compost. Compost produced by earthworm activity will have a higher level of plant nutrients than the normal organic manures (Lee 1985). It is generally known that the epigeic species Eudrilus eugeniae has greater potentiality for degrading organic waste (Dash and Senapati 1986). Epigeic species like Eisenia foetida and others are also identified as potential organic waste decomposers (Kale and Bano 1986). Eudrilus eugeniae serves as the most suitable species for the degradation of organic waste and production of vermicompost (Bano and Kale 1988). Earthworm, Eudrilus eugeniae, was found to grow in abundance in farmyard manure (FYM) and the compost recovered was 60-70%.
Eudrilus eugeniae species converted organic matter at a rate of 4.5 kg per 100 g of worms, when cultured in a combination of feed consisting of cattle dung, coir waste and vegetable waste in 10:1:1 ratio with a worm biomass increase of more than 75% (Bano 1997). Thakur et al. (2000) reported that composted domestic organic waste materials with Eisenia foetida increased potassium and carbon content significantly. Earthworms play a crucial role in the various soil processes, particularly in the improvement of soil structure, fertility, and mineralization (Divya 2001) (Figure 6.1).
The bio-oxidative process of waste conversion by the combined activity of earthworms, microorganisms, and fauna of a decomposer community modifies the substrate properties. The substrate fragmentation increases the surface area for activity
FIGURE 6.1 Schematic representation of various stages of vermicomposting.
by microbes and turnover and aeration. This leads to further degradation through enzymes released by microorganisms and the enrichment of organic and inorganic materials (Edwards et al. 1998; Aira et al. 2002; Loh et al. 2005; Molina et al. 2013). Vermicomposting using a suitable species has a significant influence on the degradation process. Vermicomposting is equally beneficial in the recycling of animal waste, crop residues, and industrial waste (Bansal and Kapoor 2000; Kaushik and Garg 2003; Yadav and Garg 2010; Garg et al. 2012).