Introduction
1.1 Definition of waste
Waste is defined as eliminated or discarded unwanted or unusable material, substances, or by products (Al-khatib et al., 2014). According to the Basel Convention of the United Nations environment program “Wastes are substances or objects, which are disposed of or are intended to be disposed of or are required to be disposed of by the provisions of national law (Zemena, 2014). Glossary of Environment Statistics (Strategies, 2012) defines waste in another way as following: “Wastes are materials that are not prime products (that is products produced for the market) for which the initial user has no further use in terms of his/her own purposes of production, transformation or consumption, and of which he/she wants to dispose”. As a result waste is a complex mixture of different substances, only some of which are intrinsically hazardous to health (Rushton, 2018).
Human activities have always generated waste (Giusti, 2019). Increasing population levels, booming economy, rapid urbanization and the rise in community living standards have greatly accelerated the municipal solid waste generation rate in developing countries (Abarca et al., 2013). It became a serious problem with urbanization and the growth of largepopulation.
Environmental Conservation (2014) also defined solid wastes in simple words as any discarded (abandoned or considered waste-like) materials. There are different types of waste: municipal waste (including household and commercial waste), industrial waste (including manufacturing), hazardous waste, construction and demolition waste, mining waste, waste from electrical and electronic equipments, biodegradable municipal waste, packaging waste, and agricultural waste.
Waste is anything discarded by an individual, household or organization. As a result waste is a complex mixture of different substances, only some of which are intrinsically hazardous to health (Rushton, 2018). Municipal solid waste (MSW) is defined to include refuse households, non- hazardous solid waste from industrial, commercial and institutional establishments including hospitals, market waste, yard waste, and street swiping (Ch, 2019).
Domestic wastes are wide variety produced from household activities such as food preparation and consumption, sweeping, burning, and garden wastes, and used items like clothing, furnishings, and abandoned equipment. Domestic waste includes both solid and liquid and sometimes hazardous wastes generated from residential areas and sometimes referred to as household wastes (Mohammed, et.al, 2017).
1.2 Types of Waste
Wastes are generally categorized into solid and liquid waste, which are materials discharge in household dustbins, flush-down toilets and chemical processing. Household waste includes bottles, vegetables, trimmings, cans, plastics and the waste from the toilets (sludge and sewage). Furthermore, other waste may come from chemicals and industrial processes. These include the chemical by-product from brewing, pharmaceuticals and electroplating. Solid wastes are the products of urban metabolism.
Agunwamba (2018), regard cities as the most efficient agents of production and consumption and observed that as the city grows in population and size so does the complexity in its land uses and its ability to generate variety of solid wastes. In the rural areas where the only significant land uses are residential and agricultural, mostly domestic and agricultural wastes are generated. The mixture of commercial, industrial, institutional and other land uses, each of which generates its own peculiar type of solid waste, compounds the situation in the city. Urban society generates solid material regularly due to rapid increase in production and consumption habits.
There are various types of waste which includes: municipal waste, industrial waste, agricultural waste, hazardous waste, construction and demolition waste, mining waste, waste from electrical and electronic equipment (WEEE), packaging waste,end-of-lifeVehicles (ELVs) and tyres. Though the study is focused on municipal waste, the other types of waste will be discussed briefly (www.eea.europa.eu).
1.2.1 Industrial Waste
Manufacturing industry waste comprises many different waste streams arising from a wide range of industrial processes. Some of the largest waste generating industrial sectors in Western and Central Europe include the production of basic metals, food, beverage and tobacco products, wood and wood products and paper and paper products. It has been estimated that over 33 million tonnes of industrial waste was generated in Europe in 2018. Waste from the manufacturing sector continues to rise, despite national and international declarations to reduce waste from manufacturing industry, to introduce cleaner technologies and other waste minimisation initiatives and to work towards manufacturing practices that are sustainable in the long term. The manufacturing industry has a central role to play in the prevention and reduction of waste as the products that they manufacture today become the wastes of tomorrow. (www.eea.europa.eu)
1.2.2 Agricultural Waste
Agricultural waste is composed of organic wastes (animal excreta in the form of slurries and farmyard manures, spent mushroom compost, soiled water and silage effluent) and waste such as plastic, scrap machinery, fencing, pesticides, waste oils and veterinary medicines. No overall estimates are available on the quantity of agricultural waste produced in the EU. Ireland has estimated that in 2018 over 80% of national waste arising were from agriculturalsources.Thereareanumberofmethodsusedtotreatagriculturalwaste.Theseinclude spreading the waste on land under strict conditions, anaerobic digestion and composting. There are a number of potential environmental impacts associated with agricultural waste if it is not properly managed not least of which is the run-off of nutrients to surface waters which can cause over enrichment of the water body. (www.eea.europa.eu)
1.2.3 Hazardous Waste
Hazardous waste arises from a wide range of different sources including households, commercial activities and industry. Waste are classified as being hazardous depending on whether they exhibit particular characteristics.The main disposal route for hazardous waste is landfill, incineration and physical or chemical treatment. On the recovery side, a significant proportion of hazardous waste is recycled or burned as a fuel.
1.2.4 Construction and Demolition Waste
Construction and demolition waste is made up of two individual components: construction waste and demolition waste. It arises from activities such as the construction of buildings and civil infrastructure, total or partial demolition of buildings and civil infrastructure, road planning and maintenance. In some countries even materials from land levelling are regarded as construction and demolition waste.
Construction and demolition waste makes up approximately 25% of all waste generated in the EU with a large proportion arising from the demolition and renovation of old buildings. It is made up of numerous materials including concrete, bricks, wood, glass, metals, plastic, solvents, asbestos and excavated soil, many of which can be recycled in one way or another. (www.eea.europa.eu)
1.2.5 Waste electrical and electronic equipment
Waste electrical and electronic equipment (commonly referred to as WEEE) consists of end of life products and comprises of a range of electrical and electronic items such as: Refrigerators, IT and telecommunication equipment, Freezers, Electrical and electronic tools, Washing machines, Medical equipment Toasters, Monitoring and control instruments, Hair driers, Automatic dispensers, Televisions, etc. Thus, sources are all users of electrical and electronic equipment from householders to all kinds of commercial and industrial activities. (www.eea.europa.eu)
1.2.6 Mining Waste
Mining waste is generated in three primary wastes. First, in the most mining operations, large amount of rock and soil need to be removed to get to the valuable ore. This waste material is generally left on the surface at the mine site. Second, mining operations use various technologies to extract the valuable materials from the sites. The techniques vary from relatively simple grinding and sorting to sophisticated chemical separation processes. Regardless, of the technology involved once the valuable material is recovered, the remaining waste materials, commonly known as tailing must bedisposedof solid. Materials are typically dumped on the land near the mining site, and liquid wastes are typically stored in ponds. It is difficultto get vegetation to grow on these piles of waste rock and tailings, so they are unsightly and remain exposed to rain and wind (Enger and Smith,2018).
1.2.7 Municipal Waste
Municipal waste is generated by households, commercial activities and other sources whose activities are similar to those of households and commercial enterprises. It does not include other waste arising e.g., from mining, industrial or construction and demolition processes. Municipal waste is made up to residual waste, bulky waste, secondary materials from separate collection (e.g., paper and glass), household hazardous waste, street sweepings and litter collections. It is made up of materials such as paper, cardboard, metals, textiles, organics (food and garden waste) and wood. Municipal Solid Waste (MSW) consists of all the materials that people in a region no longer want because they are broken, spoiled, or have no further use, it includes waste from households, commercial establishments, institutions, and some industrial sources. (www.eea.europa.eu)
1.3 Characterization of wastes
Solid waste are characterize on the basis of following parameters
- Their sources
- By the types of wastes produced
- By generation rates and composition.
1.4 Waste Generation
Waste generation is an integral part of human activity influenced by social dynamics and economic development. Although nature has the capacity to dilute, disperse, degrade, absorb and reduce the impact of unwanted residues in the environment. Ecological imbalances have occurred where the natural assimilative capacity has been exceeded (Tchobanoglouset al.,2016b). Improper waste handling and management pose great threats to the environment and public health. In Nigeria, The commonly practised waste management option in Nigeria, basically involves the collection of mixed waste materials and subsequent dumping at designated dumpsites. It is not a practice to separate waste materials at source or any point during its management (Adekunleet al., 2011).
Solid waste is generated from households, offices, shops, markets, restaurants, public institutions, industrial installations, water works and sewage facilities, construction and demolition sites, and agricultural activities (emissions from manure management as well as on-site burning of agricultural residues are treated in the Agriculture, Forestry and otherland use. It is good practice to account for all types of solid waste when estimating waste- related emissions in the greenhouse gas inventory (Riittaet al., 2006). Despite these difficulties, there is general agreement that residents of industrialized countries dispose of much more waste than residents of developing countries.
A World Bank study (Cointreau, 1982) found that urban areas in industrialized countries generate 2 to 3 times more waste per capita than low income nations. In developing countries, waste is a luxury available to only the wealthy minority. Most wastes are recycled or reused by residents who scavenge through the waste stream for valuable materials (Medina,1997).In 2006, the total amount of municipal solid waste generated in Africa was estimated to be2.02 billion tones being about 7% annual increase since 2013 (UNEP, 2015). It is was also estimated that between 2014 and 2011, generation of municipal waste must have raised to 37.3%, equivalent to roughly 8% increase per year most especially those wastes categorized as hazardous. UNEP (2015) estimated the total health-care waste per person per year in most low income countries range from 0.5 kg to 3 kg while the European Union estimated that its 25 member states produces 700 million tons of agricultural wastes annually.
Although there has been no estimate about global industrial wastes generation, American industrial facilities generated and disposed some 7.6 billion tons of non-hazardous industrial solid waste each year. If the solid wastes could be diverted for material and resource recovery then a substantial reduction in final volumes of waste could be achieved and could be utilized to generate revenue to fund waste management. This formed the premise for Integrated Solid Waste Management system based on reduce, re-use and recycle principle. (Seadon, 2006).
1.5 Waste Composition
There is no consistent definition of what constitutes municipal solid waste. For example, some countries consider construction and demolition debris as part of the municipal waste stream, while others do not. Wastes from low and middle income countries contain fewer paper products and non-food items than waste from industrialized countries. The composition of solid waste is a key determinant in decisions concerning types of vehicles needed for collection and transfer, requirements for final disposal, and resource recovery alternatives. In both developing and industrialized countries, human and hazardous wastes may contaminate the waste stream.
Municipal solid waste of Lagos state is a composition of heterogeneous and mixed; non- degradable materials and degradable components. The waste bulk is mainly made up of plastics, paper, glass, metal and other recyclable components. The degradable portions of the waste consist of food waste and garden or yard waste (Ayuba, Manaf, Sabina and NurAzmin, 2013).
