Katheem Kiyasudeen S

An Introduction to Anaerobic Digestion of Organic Wastes

The problem of waste disposal from a myriad of industries, is becoming increasingly acute, the world over. The burning of such wastes in open dumps or in poorly designed incinerators could be a major source of air pollution (Ndegwa and Thompson. Bioresour Technol 76:107–112, 2001). On the other hand, open dumps and poorly designed sanitary landfills can pollute surface and ground waters causing public health hazards. Meanwhile, the unavailability and rising cost of land near urban areas have made dumps and landfills increasingly expensive and impractical. The production of both livestock and grain on the other hand has increasingly relied on enormous chemical and energy inputs, leaving soils depleted of indigenous nutrients and organic matter, and resulting in wide-scale surface and groundwater contamination. As discussed earlier, recycling and utilization of organic wastes and by products through development of an economically viable, socially accepted and eco-friendly technologies are required. Over the years an array of innovative ideas for the utilization of these wastes have been put forward (Callaghan et al. Bioresour Technol 67:117–122, 1999) to increase productivity and to meet the heavy demand for food of the growing population (Jeyabal and Kuppuswamy. Eur J Agron 15:153–170, 2001). But these wastes could not be fully exploited without a viable technology for their economic recycling. It is well demonstrated that both fresh and composted amendments over these waste materials are potent to stimulate soil biological activities. Fresh wastes produces an initial burst of biochemical activity by the releasing easily degradable organic compounds whereas compost induces lower biochemical activities but more resistance to soils (Masciandaro et al. Soil Biol Biochem 32:1015–1024, 2000). Biological treatments plays a pivotal role in treating organic wastes these days. Among them, anaerobic digestion is frequently the most cost effective method because of the high energy recovery and its limited environmental impacts. Biogas production throughout Europe, could reach over 15 million m3/day of methane reported during 1998 (Tilche and Malaspina. Biogas production in Europe. Paper presented at the 10th European conference biomass for energy and industry, Wurzburg, 8–11 June, 1998). Presently, biogas production is considered to be an inevitable way of energy production.

Prospects of Organic Waste Management and the Significance of Earthworms

Each year, approximately 38 billion metric tons of organic wastes are produced all over the world. Human behaviour, consumption rate, and population explosion are the generally proposed factors responsible for this dramatic increase. As wastes materials are always considered to be either unusable or disposable, burning and deposition has always been the result. Burning and deposition in turn results in numerous environmental problems. Burning pollutes atmosphere whereas land disposal of organic waste materials may directly or indirectly alter the heavy metal status of the soil by affecting metal solubility or dissociation kinetics (Del Castilho et al. J Environ Qual 22:689–697, 1993). In order to deal with this challenging area, various treatment methods and practices have been formulated and applied by countries all over the world. Hence, much attention has been paid to convert such nutrientrich organic waste materials into useful outcome for sustainable agricultural practices (Suthar Biorem. J 13(1):21–28, 2009). The utilization of the organic materials of animal and plant origin is a viable means of improving soil fertility and a reliable way of disposing wastes (Adegunloye et al. Pak J Nutr 6(5):506–510, 2007). Solid organic waste is understood as organic-biodegradable waste with a moisture content below 85–90 % and these organic materials are recycled by a variety of decomposer microorganisms such as bacteria, fungi and detritus-feeding invertebrates.

Composting: A Traditional Practice of Waste Treatment

The intensity and concentrated activity of the livestock industry and other sources generate vast amounts of biodegradable wastes, which must be managed under appropriate disposal practices to avoid a negative impact on the environment (odour and gaseous emissions, soil and water pollution, etc.) (Burton and Turner. Manure management, 2nd edn. Treatment Strategies for Sustainable Agriculture Silsoe Research Institute, Lister and Durling Printers, Flitwick, 2003). Micro-organisms are largely responsible for the cycles of the elements within a soil and are involved in decomposing of organic substances at the ecosystem level (Bastida et al. Appl Soil Ecol 40:318–329, 2008). Composting process can substantially reduce the environmental problems associated with the treatment of wastes by transforming them into stabilized and safer materials in order to apply on soil by employing microbial activities (Carr et al. Commercial and on-farm production and marketing of animal waste compost products. In: Steele K (ed) Animal waste and the land–water interface. Lewis Publishers, Boca Raton, pp 485–492, 1995). Schematic representation of evolution of organic substances during composting process is shown in Fig. 3.1. Composting cannot be considered a new technology since it has been used by our ancestors as a traditional practice for agriculture based wastes (Chauhan and Singh. World J Zool 7(1):23–29, 2012), but amongst the waste management strategies it is gaining interest as a suitable option for manures with economic and environmental profits. Composting eliminates or reduces the risk of spreading of pathogens, parasites and weed seeds associated with direct land application of manure and leads to a final stabilized product which can be used to improve and maintain soil quality and fertility (Larney and Hao. Bioresour Technol 98:3221–3227, 2007). Composting provides a means of recycling solid wastes and has the potential to manage most of the organic material in the waste, animal manure, paper products, sewage sludge and domestic wastes (Adegunloye et al. Pak J Nutr 6:506–510, 2007). However, depending on the production of good quality compost, specifically, compost that is mature and sufficiently low in metals and salt content (Hargreaves et al. Agric Ecosyst Environ 123:1–14, 2008), the compost will be suitable for plants.

Microbial Ecology Associated with Earthworm and Its Gut

Soil bears infinite life that promotes diverse microflora. Soil bacteria viz., Bacillus, Pseudomonas and Streptomyces etc., are prolific producers of secondary metabolites which act against numerous co-existing phytopathogeic fungi and human pathogenic bacteria (Pathma and Sakthivel. SpringerPlus 1:1–26, 2012). Microbial communities also support a large number of soil invertebrates, which in turn have an important regulatory effect on the microbial populations (Edwards. Earthworm ecology, 2nd edn. CRC Press, Boca Raton, 2004). Decomposition of organic material is assumed to be mainly mediated by microorganisms. The rate and extent of the decomposition depends on the chemical composition of the material, environmental factors, and on the microbial community. The activity of the decomposing microorganisms is accelerated by the activity of the soil fauna (Schonholzer et al. FEMS Microbiol Ecol 28:235–48, 1999). According to Lavelle and Spain (Soil ecology. Kluwer Academic Publishers, Dordrecht, 2001), microorganisms show a high degree of specialization and display a large number of enzymes for the breakdown of organic matter. It is certainly proven that the growth of earthworms is dependent on microbial associations. In fact, microorganisms are largely responsible for the decomposition of the materials ingested by earthworms and in turn earthworm regulates modifications in microbial communities thus sharing a mutualistic relationship.

Vermicomposting: An Earthworm Mediated Waste Treatment Technique

Biodegradable organic wastes such as crop residues, municipal, hospital and industrial wastes pose major problems in disposal and treatment. Release of unprocessed animal manures into agricultural fields contaminates ground water causing public health risk (Gandhi et al. Environ Ecol 15:432–434, 1997). Vermicomposting and composting are the most efficient way for converting sludge into useful products. These two well-established processes have been adopted for solid organic waste reclamation – and the final products, composts and vermicomposts, can be used as sources of organic matter for soil amendment, as sources of nutrients for soil fertilization or as growing media constituents for soilless cultivation (Gonzalez et al. Bioresour Technol 101:8897–8901, 2010). Lorimor et al. (Manure management strategies/technologies. White paper on animal agriculture and the environment for national center for manure and animal waste management. Midwest Plan Service, Ames, 2001) concluded that, compared to conventional composting system, the vermicomposting often results in mass reduction, shorter time for processing, and high levels of humus with reduced phytotoxicity in ready material. Vermiculture is a cost-effective tool for environmentally sound waste management (Banu et al. J Environ Biol 22:181–185, 2001; Asha et al. J Hum Ecol 24:59–64, 2008). This low cost technology uses earthworms as bio-agents to treat waste materials (Alidadi et al. Iran J Environ Health Sci Eng 2(4):251–254, 2005). Reduction of particle size and increased nutrient availability in the vermicomposted outputs are reported by many researchers (Ndegwa and Thompson. Bioresource Technol 76:107–112, 2001).

Vermicompost, Its Applications and Derivatives

Vermicomposts are products derived from the accelerated biological degradation of organic wastes by interactions between earthworms and microorganisms as we have discussed in previous chapters. Earthworms consume and fragment the organic wastes into finer particles by passing them through a grinding gizzard, and they derive their nourishment from the microorganisms that grow on the organic matter. The process accelerates the rates of microbiological decomposition of the organic matter, increases microbial populations, and alters the physical and chemical properties of the material, leading to accelerated humification, during which the unstable organic matter is fully oxidized and stabilized (Albanell et al. Biol Fertil Soils 6:266–269, 1988). Vermicomposts are finely divided peat-like materials with high porosity, aeration, and drainage and good water-holding capacities (Edwards and Burrows. The potential of earthworm composts as plant growth media. In: Edwards CA, Neuhauser E (eds) Earthworms in waste and environmental management. SPB Academic Press, The Hague, pp 21–32, 1988; Edwards and Arancon. BioCycle 45:51–53, 2004). High-quality vermicompost has a good physical texture and color, no odors, and few contaminants or pollutants (Edwards. Breakdown of animal, vegetable and industrial organic wastes by earthworms. In: Edwards CA, Neuhauser EF (eds) Earthworms in waste and environmental management. SPB, The Hague, pp 21–31, 1988; Edwards and Arancon. BioCycle 45:51–53, 2004). Vermicomposts are suitable both as plant growth media and as soil amendments. Graphical representation of percentage recovery of vermicasts from earthworms is shown in Fig. 9.1.

Important Digestive Enzymes of Earthworm

The living cell is the site of tremendous biochemical activity called metabolism. This is the process of chemical and physical change which goes on continually in the living organism. The greatest majority of these biochemical reactions do not take place spontaneously (Bennett and Frieden. Modern topics in biochemistry. Macmillan, London, pp 43–45, 1969). The phenomenon of catalysis makes possible biochemical reactions necessary for all life processes. The catalysts of biochemical reactions are enzymes and are responsible for bringing about almost all of the chemical reactions in living organisms (Holum. Elements of general and biological chemistry, 2nd edn. Wiley, New York, p 377, 1968). Without enzymes, these reactions take place at a rate far too slow for the pace of metabolism (Martinek. J Am Med Tech 31:162, 1969). All known enzymes are proteins. They are high molecular weight compounds made up principally of chains of amino acids linked together by peptide bonds (Pfeiffer. Enzymes, the physics and chemistry of life. Simon and Schuster, New York, pp 171–173, 1954). A protein molecule consists of one or more polypeptide chains which continue without interruption throughout the molecule folded into a uniquely defined configuration held together by hydrogen bonds between the peptide nitrogen and oxygen atoms also between the charged sidechains (Blow. Structure 8(4):R77–R81, 2000). It has long been assumed that most invertebrates do not possess the enzymatic complement to digest polysaccharides, but now the opposite is often shown for different groups of soil fauna, enabling us redefine species diets and therefore their ecological function. Enzymatic activities have been widely used as an index of soil fertility or ecosystem status because they are involved in biological transformation of native and foreign compounds in soils (Tate. Soil microbiology, 2nd edn. Wiley, New York, 2000). The digestive enzymes of the litter feeding animals, particularly oligochaetes, are responsible for decomposition and humification processes (Parthasarathi and Ranganathan. Trop Ecol 41(2):251–254, 2000). The interpretation of data arising from enzyme assay is complicated since enzyme activity depends on several factors and different locations of enzymes in the studied system (Nannipieri et al. Enzyme activities and microbiological and biochemical processes in soil. In: Burns RG, Dick R (eds) Enzymes in the environment. Marcel Dekker, New York, pp 1–33, 2002). So far only a few enzymatic studies on earthworm casts have been published, and they are limited to observations on soil only (Parthasarathi and Ranganathan. Trop Ecol 41(2):251–254, 2000). Some authors have described a direct role of earthworms in the decomposition of plant debris, and presume the existence of their own digestive enzymatic activities. Worms being hermaphrodites with simultaneous functioning gonads may require more energy and increased enzyme activities during this active phase of reproduction. Enzyme activity is influenced also by type of food. The differential enzyme-activity is perhaps related to the type of food and rate of eating of each species (Table 5.1). Earthworm which feed and depend on microbes, litter, and grit present in soil should contain battery of enzymes. Earthworm castings are known to be a rich source of plant growth promoting substances viz., growth hormones, enzymes and vitamins (Karthikeyan et al. AgroIndia 7:34–353, 2004). Earthworm castings also contains a number of beneficial microorganisms, nitrogen fixing, phosphorous solubilizing and cellulose decomposing organisms, which help in improving soil productivity. Earthworms have an in-house supply of enzymes like Nitrate reductase, acid phosphatase and alkaline phosphatase, which are involved in the metabolism of nitrogen and phosphate materials present in the compost. The earthworms speed up the composting process and transform wastes into nutrient rich castings with the help of the enzymes (Prabha et al. South Asian J Socio-Polit Stud 2:129–130–156, 2005).

Earthworm Based Products, Scope and Future Perspectives

Scientists suggest that earthworms contained sufficient protein to be considered as animal food or sources of feed protein (Lawrence and Millar. Nature Lond 3939:517, 1945). The first successful animal-feeding trials were organized on chicken and suckling pigs (Sabine. The nutritive value of earthworm meal. In: Hartenstein R (ed) Proceedings of conference on utilization of soil organisms in sludge management, Syracuse, Kalamazoo, pp 122–130, 1978). There have been numerous analyses of the constituents of the tissues of different species of earthworms. The mean amounts of essential amino acids recorded are very adequate for a good animal or fish feed as recommended by Food and Agriculture organization of United Nations (FAO) and World Health Organization (WHO), particularly in terms of lysine and the combinations of methionine and cysteine, phenylalanine and tyrosine, all of which are important components of animal feeds. Earthworm tissues contain a preponderance of long-chain fatty acids, many of which non-ruminant animals cannot synthesize, and an adequate mineral content. The production of earthworm protein for feeding fish, crustaceans, chickens, and pigs is marginally uneconomical in developing countries because of the high cost of labor involved in separating earthworms from vermicomposts. In countries such as India and the Philippines the economics of earthworm feed protein are much more favorable due to lower labor costs, and many more commercial projects are underway.

Optimal Conditions and Environmental Factors Involved in Breeding Earthworms for Vermicomposting

Like any other living organism, earthworm requires certain favourable conditions to feed, grow and survive (Table 7.1). As a potentially important bio-agent in waste management practises, earthworms are cultured in large scale depending on the species required. To achieve better growth, certain environmental conditions are usually provided in laboratory or industrial level. Such optimal conditions and the effect of various environmental factors are discussed in this chapter.

Organic Waste Management Practices and Their Impact on Human Health

Human activities have always generated waste. This was not a major issue when the human population was relatively small and nomadic, but became a serious problem with urbanization and the growth of large conurbations. Poor management of waste led to contamination of water, soil and atmosphere and to a major impact on public health. In medieval times, epidemics associated with water contaminated with pathogens decimated the population of Europe and even more recently (nineteenth century), cholera was a common occurrence (Guisti. Waste Manag 29:2227–2239, 2009). Some of the direct health impacts of the mismanagement of waste are well known and can be observed especially in developing countries. As science and technology developed, the management of an ever increasing volume of waste became a very organized, specialized and complex activity. The characteristics of waste material evolved in line with changes in lifestyle, and the number of new chemical substances present in the various waste streams increased dramatically. The long-term health effects of exposure to substances present in the waste, or produced at waste disposal facilities are more difficult to measure, especially when their concentrations are very small and when there are other exposure pathways (e.g. food, soil). Nonetheless, lack of evidence can cause public concern. Well-publicized industrial accidents, often unrelated to waste management activities, have produced a NIMBY (not in my backyard) syndrome that causes fierce opposition to the construction of landfills, incinerators, or other waste disposal facilities. Government and health authorities are under increasing pressure from the public to provide epidemiological evidence of potential adverse health effects produced by these activities. Thousands of manuscripts have been published on the impact of emissions in proximity of waste disposal sites.