Energy Recovery (Incineration)
Municipal Solid Waste (MSW) contains organic components which are combustible. Thus, energy could be gained from incineration of waste or landfill gas combustion, which may be used to generate electric power (from steam under high thermal conditions) or produce heat for buildings (through boilers) (Williams, 2005). As such, the process of converting solid waste of organic nature into other useful forms such as gas, heat, steam and ash residues via combustion is referred to as incineration and such process is carried out in places often referred to as Waste- to-Energy (WtE) plants (Magutu & Onsongo, 2011).
In the reduction of solid waste volume by 70 to 80% lies also a main advantage of this method of waste disposal, as this minimizes the quantity of waste that is eventually sent to the land fill. Consequently, for nations where land space challenges exist for example, Japan and Singapore, incineration is a popular waste disposal option (Magutu et al, 2011). Further, following the introduction of bans and taxation on landfills with regard to biodegradables, countries such as Sweden and Denmark in the European Union (EU) have been reported to be the most active in the use of incineration for disposal of MSW (EEA, 2007).
According to Williams (2005), simultaneous production of heat and power (combined heat and powers) from landfill gas and incineration makes optimum energy recovery from (organic) waste achievable. However, in comparison with their initial forms, new products that arise from incineration of waste (liquid and air discharge inclusive) pose more difficult management and environmental challenges- a development which has increasingly seen many countries banning this option for waste management (Narayana, 2009).
Land filling is the deposition of waste either in a specific land area with the goal of preventing such waste from impacting negatively on the environment (Narayana, 2009). The landfill directive has its roots in the hierarchical prioritization of waste management options- giving maximum preference to prevention of waste, with reuse, recycling, recovery options following and land filling having the least priority. Realizing how land filling could be impactful on the environment through greenhouse gas (GHG) emissions and other forms of pollution (through soil, surface and ground water) and how inadequate space could be a challenge, the landfill directive discourages heavy reliance on this option by setting goals which gradually reduce the quantity of municipal waste that is relegated to the landfill until the year 2016 (EEA, 2009).
Despite being widely considered as the least desirable option, the most prevalent approach to the disposal of waste globally has been the utilization of landfills. This remains an important aspect of the Solid Waste Management (SWM) plan of most countries and varies in structure; ranging from sanitary landfills, to semi-controlled landfills and uncontrolled (or open) dumpsites (Remigios, 2010).
Sanitary landfills are designed according to specifications which help to ensure minimal impact of the disposed waste on the environment. As such, they are structured for leachate containment and treatment, as well as management of greenhouse gases (carbon dioxide and methane) which are produced in the event of waste decomposition. Such well-structured landfills exist in nations with developed economies. Generally in North America and other countries such as,
Australia and New Zealand, the most utilized option for waste disposal on a large scale remains land filling. However, such is highly controlled and goes with adherence to corresponding legislative land filling and air quality requirements.
For highly industrialized Asian countries such as Singapore where space for perpetual land filling is a challenge, this option is only utilized when other means for waste disposal are not feasible (Zhang, Keat, & Gersberg, 2009). In the global South, partly operated waste disposal sites, referred to as semi-controlled landfills and uncontrolled dumps exist. For the former, compaction of waste and subsequent covering with topsoil is carried out. However, structures for leachate and greenhouse gas containment as well as restriction on the type of waste being deposited are absent. Uncontrolled dumping is the main and favored means of solid waste disposal in a majority of nations on the African continent. This involves disposal of waste on open, non-structured area of land without considerations for environmental impact (Remigios, 2010).
In conclusion, the most favoured option being waste reduction (waste prevention and minimization and the least favoured option is sending wastes to landfills. Solid wastes segregation technique which enables individuals to segregate wastes at the source of generation is also an important technique that should be developed in individuals in other to attain effective management of wastes in Nigeria.
Solid waste disposal methods which are mostly preferred and considered as environmentally friendly in waste management business are: incineration, composting, dumping in approved dumpsites and land filling. However, littering, open burning and open dumping of solid wastes which are practiced by many individuals are not environmentally friendly because they aid in the spreading of diseases and the pollution of the environment.
The primary objectives of effective solid waste management as highlighted by Oreyomi (1998) are:
- To eliminate health hazards in the community by removing all the physical, biological and chemical agents like bottles, vectors or diseases and toxic substances that are harmful to man in his environment.
- To protect the natural environment being polluted or damaged. This is achieved by discouragement of wastes being dumped indiscriminately on either land or river.
- To provide gainful employment for many young men who would have been
- To enhance regular supply of raw materials to industries through salvaging and recycling of materials of economic value from wastes.
Effective solid waste management by adult citizens will entail reduction of wastes, segregation of wastes into degradable and non- degradable materials, reuse, composting and recycling of wastes. The dumping of wastes in the designated collection centers is equally needed in order to main clean and healthy environment (Oreyomi, 1998).
Elements of Solid Waste Management System
The main elements of solid waste management system comprises of: waste generation, waste composition, waste collection and transportation, waste treatment and disposal (Asase, Yanful, Mensah, Stanford, & Amponsah, 2009).
Waste generation encompasses activities in which materials are identified as no longer being of value (in their present form) and are either thrown away or gathered together for disposal. Waste generation is, at present, an activity that is not very controllable (Vergara &Tchobanoglous, 2012). In the future, however, more control is likely to be exercised over the generation of wastes. Reduction of waste at source, although not controlled by solid waste managers, is now included in system evaluations as a method of limiting the quantity of waste generated (Vergara et al, 2012).
Municipal Solid Waste (MSW) generation rates are influenced by economic development, the degree of industrialization, public habits, and local climate. Generally, the higher the economic development and rate of urbanization, the greater the amount of solid waste produced. Income level and urbanization are highly correlated. Waste generation varies as a function of affluence, however, regional and country variations can be significant, as can generation rates within the same city. Waste generation in sub-Saharan Africa is approximately 62 million tonnes per year (Stanford, 2000).
Waste Handling, Sorting, Storage, and Processing at Source
The second of the six functional elements in the solid waste management system is waste handling, sorting, storage, and processing at the source. Waste handling and sorting involves the activities associated with management of wastes until they are placed in storage containers for collection (Stanford, 2000). Handling also encompasses the movement of loaded containers to the point of collection. Sorting of waste components is an important step in the handling and storage of solid waste at the source. For example, the best place to separate waste materials for reuse and recycling is at the source of generation. Households are becoming more aware of the importance of separating newspaper and cardboard, bottles/glass, kitchen wastes and ferrous and non-ferrous materials (Steblin & Stanford, 2008). Labspace, (2013) agreed that onsite means solid waste at the place where the waste is generated and residential waste means waste at home within the household. ‘Handling’ means the separation of wastes into their different types so they can be dealt with in the most appropriate way. The benefits of appropriate onsite handling include reducing the volume of waste for final disposal and recovering usable materials (Labspace, 2013).
Onsite storage means the temporary collection of waste at the household level. It is important that waste is stored in proper containers. These could be baskets, preferably made from locally available materials, plastic buckets or metal containers. Larger containers or dustbins, especially those used for food waste, should be leak proof, have tight lids and be long-lasting, having onsite storage facilities with greater capacity (Labspace, 2013).The cost of providing storage for solid wastes at the source is normally borne by the household in the case of individuals, or by the management of commercial and industrial properties.
Processing at the source involves activities such as backyard waste composting (McDougall, White, Franke, & Hindle, 2001).
The functional element of collection includes not only the gathering of solid wastes and recyclable materials, but also the transport of these materials, after collection, to the location where the collection vehicle is emptied. This location may be a material processing facility, a transfer station, or a landfill disposal site (McDougall & Hruska, 2000). Labspace (2013), indicated that in urban centres,
collection is a function that has its own process and services. Waste is collected and held at central transfer stations where waste is stored before it is transported to a final disposal site.
Transfer and Transport
The functional element of transfer and transport involves two steps:
- The transfer of wastes from the smaller collection vehicle to the larger transport equipment.
- The subsequent transport of the wastes, usually over long distances, to a processing or disposal The transfer usually takes place at a transfer station (Vergara et al, 2012).
The final functional element in the solid waste management system is disposal. Today the disposal of wastes by land filling or uncontrolled dumping is the ultimate fate of all solid wastes, whether they are residential wastes collected and transported directly to a landfill site, residual materials from Materials Recovery Facilities (MRFs) residue from the combustion of solid waste, rejects of composting, or other substances from various solid waste-processing facilities (McDougall et.al, 2001). A municipal solid waste landfill plant is an engineered facility used for disposing of solid wastes on land or within the earth’s mantle without creating nuisance or hazard to public health or safety, such as breeding of rodents and insects and contamination of groundwater (Vergara et al, 2012).
Municipal solid waste can be used to generate energy. Several technologies have been developed that make the processing of MSW for energy generation cleaner and more economical than ever before, including landfill gas capture, combustion, pyrolysis, gasification, and plasma arc gasification (Vergara et al, 2012). While older waste incineration plants emitted high levels of pollutants, recent regulatory changes and new technologies have significantly reduced this concern. United States Environmental Protection Agency (EPA) regulations in 1995 and 2000 under the Clean Air Act have succeeded in reducing emissions of dioxins from waste-to-energy facilities by more than 99 percent below 1990 levels, while mercury emissions have been by over 90 percent. The EPA noted these improvements in 2003, citing waste-to-energy as a power source “with less environmental impact than almost any other source of electricity” (Wikipedia, 2013).
Constraints / Challenges of Solid Waste Management
Researchers have identified several factors that militate against solid waste management efforts in poor countries. These are:
Lack of finance
Lack of training/human resource
Lack of political support
Lack of legislation
Policy conflict among levels of government /overlapping responsibilities
Rapid increase in waste generation and limited data
Lack of awareness among the populace
Limited land areas and land tenure issues.
These have posed serious constraints to the waste sector and dampened efforts towards waste management in the city. Many other writers have elaborated on how the factors cited above (plus others) interact to aggravate the solid waste problem in poor country cities. What follows from here is a detailed examination of the factors responsible for the abysmal waste situation in poor country cities (Babayemi & Dauda, 2009).
Problems of Waste Disposal
The deterioration of the Nigerian urban environment in terms of irresponsible dumping and accumulated solid waste is most apparent in our growing cities today. The dehumanizing effects of these circumstances in our urban lives and blighted environment have often been cited and noted as contributing causes of the Nigerian urban decay, (Asuquo, 1979).
As population increases, as more people move to this few primate cities in search of better life, the generation and disposal of waste becomes a major public issue effecting both health and the aesthetic value of urban centre. Oldnira (1995), argued that one of the major environmental health problems facing Nigerian especially in the major cities is poor waste management. Edu (2003), stated that waste is the greatest physical problem that persistently poses a grave challenge to man on earth. The indiscriminate dumping of waste along streets, market places, residential axis in Port-Harcourt constitutes nuisance which causes serious health hazard, as dumping leads to percolation to pollute ground water supplies, breeding ground for such annoying and disease bearing organisms, such as rats, cockroaches, flies, etc.
Uchegbu (1998), in his words said man’s unguided development and ineffective solid waste management in urban centers of Nigeria has resulted to urban degradation and outbreak of diseases like cholera, malaria, typhoid, bronchial disorders. Udo (2003), has observed that decomposed waste emits carbondioxide (CO2) methane gas (CH4), which enhances global warming. White nitrite and nitrate emission causes health hazard such as carcinogenic and mutagenic nitrosamines.
Effects of Solid Waste
It is the fact that, if solid wastes are not managed properly there are many negative impacts on aesthetic, human health and ecology (water and air pollution). Therefore, in order to control the management activity in a good manner and have a proactive measure for such negative impact, one must have a good understanding about the effects and risks that may arise from improperly managed solid wastes. According to Melaku (2008), the following are some of the most important effects because of uncontrolled solid waste disposal systems.
Uncollected wastes cause blockage of drains, which result in flooding and unsanitary conditions.
Flies and Mosquitoes breed in some constituents of solid wastes, and flies
are very effective vectors that spread disease.
Waste dumps are good shelter for rats. Rats consume and spoil food, spread disease, damage electrical cables and other materials.
Uncollected wastes degrade the urban environment, discouraging efforts to
keep the streets and open places in a clean and attractive conditions.
Dangerous items (such as broken glass, razor blades, needles and other healthcare wastes, aerosol cans and potentially explosive containers) may pose risks of injury or poisoning, particularly to children and people, who sort through waste.
Waste items that are recycled without being cleaned effectively or sterilized can transmit infection to later users.
Polluted water (leachate) flowing from waste dumps and disposal sites can cause serious pollution of water supplies.
Waste that is treated or disposed of in unsatisfactory ways can cause a severe aesthetic nuisance in terms of smell and appearance.
Fires on disposal sites can cause major air pollution, causing illness and reducing visibility, making disposal sites dangerously unstable, causing explosions of cans, and possibly spreading to adjacent property