Impact of Physical and Chemical Properties of Municipal Solid Waste on its Electrical Power Rating Potential

Waste-to-energy (WTE) management method, has been considered as the best option; because, it reduces the quantity of waste generated by about 71 %, and ensure energy recovery for efficient waste management. In this study, physical, chemical and the heating properties of the waste components, generated in Ilorin were determined. The heating value was modelled against the physicochemical properties of MSW components to ascertain their correlation. The electrical power rating potential of the MSW was determined using Dulong’s model. The regression model developed on the correlation analysis was used to predict the effect of the physicochemical properties on the heating value and the power generation potential. It was concluded that 1 % increase in fixed carbon and volatile matter, total carbon and Nitrogen content, increases electrical power rating by 8 %, 37 %, 21 % and 10.80 % respectively; while 1 % increase in moisture and hydrogen content, reduces the electrical power rating by 11 % and 69.3 % respectively.

. Factors like culture, education and socio-economic development also constitute major obstacles to efficient management of MSW.
Improper management and disposal of MSW would result to environmental challenges such as: pollution, infection transmission, flooding, surface water contamination, environmental degradation, emission of greenhouse gases and ozone depletion and. A typical case is the Ogunpa River flood of 1983 in Ibadan; which claimed many lives and properties. In Kano city, over 67 % of humanity are faced with the problem of inadequate and improper facilities for municipal solid waste management and disposal which led to the indiscriminate dumping of solid waste into streams, open dumps and public places [9]. In Nigeria, landfill is a major method of waste disposal because of its cost effectiveness; nevertheless, it has disadvantages which include: greenhouse gases emission, contamination of ground water through leaching and degradation of the land required for landfill construction [10]. Where incineration method is adopted, challenges like particulates, pollutants such as carbon dioxide (CO 2 ) and dioxins that contribute to climatic change, nervous system and heart diseases, as well as smog are encountered [2]. The MSW generated in the cities nowadays is too enormous for the traditional method of waste management. The global MSW data showed a generation rate of 0.68 billion tons per year in 2000 and 1.3 billion tons per year in 2010, while the projection for 2025 stands at 2.2 billion tons per year and 4.2 billion tons per year by 2055 [11]. MSW generation as reported by Kawai and Tasaki [12] shows 1.34 kg/capita/day (United Kingdom), 2.13 kg/capita/day (United States), 2.00 kg/capita/day (South Africa), 0.09 kg kg/capita/day (Ghana) and 0.58 kg/capita/day in (Nigeria).
Despite the rise in MSW generation rate in developing countries, the countries still face energy crisis wish poses their economic and social development to grave challenges. Adopting an integrated MSW management method that encompasses thermal degradation and energy recovery, recycling and others will ensure adequate and efficient waste management system [13]. In recent years, technologies were developed to generate power by utilizing renewable energy sources; despite the technological advancement on energy generation, only about 59 % of Nigeria population have access to electricity [14]. This indicates that about 74 million people in Nigeria are still without access to electricity. Since the quest and emergent need for sustainable renewable energy sources which include: wind, solar, hydro, photovoltaic and biomass; biomass energy source has been cited as the world"s largest renewable energy source and its resources are distributed around the world [15].According to Tan et al. [16], [17]; clean energy and green environment are very essential to the growth and living standard of every nation; this could be obtained from waste-to-energy (WTE) practices. This requires thermochemical and biological processes to extract useful energy from combustible biogenic fractions of the MSW to produce heat (steam) or power (electricity) or both (combined heat and power). Ayodele et al. [18] reported that average electrical energy and power rate in Nigeria is in the range of 107 kWh, 12 W per capita per annum. This is quite insufficient for social and economic demand. Energy supply in Ilorin and the entire Kwara State by the Power Holding Company of Nigeria (PHCN) is far below the power requirement for industrial and economic growth of the state and it is characterized with fluctuations, failures and outages. This accounts for widespread usage of fossil fuel generators in the metropolis. The unpredictable rise in the cost of fossil fuel products and the occasional/periodical scarcity makes the use of generators unreliable and uneconomical for most institutions and industries.
The municipal solid wastes generated in Ilorin Kwara State is huge, and the waste management system in place is insufficient and inefficient; hence the people indulge in illegal and indiscriminate disposal of wastes into open dumps and water ways. This consequentially causes pollution, unsightly scenes, direct blockage of waterways and biodegradation of organic fractions of the wastes that release greenhouse gas (GHG) such as methane which contributes to depletion of Ozone layer as well as climate change [19]. Therefore waste-to-energy method of MSW management will serve a dual purpose of converting the waste generated to clean energy as well as ensuring an adequate and efficient waste management practice. For WTE to be established in a metropolis, there is a need to first determine the power potential of the available waste fractions and validate the correlation between the power potential and the physicochemical properties.

Overview of municipal solid waste (MSW) management
Power can be considered as one of the principal input factors in the development of a nation. It plays a major role in the social and economic growth of a nation, thereby improving the quality of peoples" life. Nevertheless, the continuous utilization of natural resources, becomes dangerous to the ecosystem and the climate globally [20]. This necessitates the continuous search for clean and green energy sources that will serve as sustainable and reliable alternatives to natural resources particularly fossil. MSW is considered as reliable alternative because, waste to energy (WTE) system plays a dual purpose of efficient waste management and energy generation [21] The appropriate usage of MSW will improve on sanitation practices and as well ameliorate the emission of greenhouse gases (GHGs) in the landfill system of waste disposal [20], [22]. The WTE technology to be adopted in a locality, is determined by the quantity and quality of the waste streams, the composition, the heating value of the waste stream and the sustainability of the MSW flow [10] In WTE using incineration technology, it is necessary to determine the effect on the physical component on the power production potential, to ascertain whether it increases rate of power generation or otherwise.

MSW generation and composition
MSW generation refers to the quantity of material that enters the waste stream before recycling, reuse, recovery, composting, or combustion. Recovery refers to materials sorted from the waste stream for recycling or composting purposes [23]. MSW generation has increased globally because of an increase in family income, education level, and change in fashion, consumption pattern, and socioeconomic practices. In the developing nations of the globe, the organic components of wastes are more predominant [7], [24], reported that a lower quantity of MSW was associated with the nations, with lower GDP. The characteristics of municipal solid waste streams depend on their sources, seasons of generation, types of wastes, as well as the rate of generation and composition. MSW could be characterized into various types depending on the kind of exercises, materials and the environment concerned in the waste generation; they are: household wastes, garbage, ashes, rubbish, bulky wastes, Street wastes, dead creatures, construction and demolition wastes, industrial wastes, abattoir wastes, Medical or Hospital squanders, hazardous wastes and E-wastes [25]. Poorer households, with a lower level of income, generate more organic food waste. It has also been reported that waste components such as plastic, metals, and glasses, are predominant in high-income households due to high consumption of processed foods. According to Ajadi and Tunde [26], certain distinctions and likenesses exist in municipal solid waste generation and pattern of composition in Ilorin city, variation is shown inaccessibility of dumpsters (Roro-bins) according to neighbourhoods in Ilorin.
In the old residential areas, such as Magaji-Ngeri, food wastes, bones, polythene bags, rags, leathers, rubbers and aluminium form the largest solid waste components that are generated there. Food waste is about 28 % of the wastes generated, while other wastes mentioned takes about 21 %. Paper waste and nylon constitute about 27.3 %, leaves and human excrement constitutes 11.50 % while non-organic wastes like bottle and tins constitute about 11.5% of the aggregate wastes generated. In the new residential location, Oko-Erin war. Paper wastes have the largest proportion amounted to 27.8 % of the aggregate solid waste followed by food wastes with 25 % then leaves and nylon components amount to 26.1 %. In the Government Reservation Area (GRA), food wastes constitute 30.9 % of aggregate waste; followed by paper waste 23.0 %. The wastes classified as others constituting 16.0% while leaves and nylon 15 % and tins/bottles constitute 14.01 %. The data of the solid analyzed shows that food and paper wastes have formed a high percentage of the wastes generated. The food wastes from preparation processes left over after consumption, all contribute to a high rate of food wastes. Paper wastes, polythene sacks, metals, rubber among other wastes are The high food waste rate from the Government Reservation Area (GRA), can be associated with the socio-economic attributes and household factor in the area. About 75 % of the inhabitants in the GRA are high wage workers. This is high when comparing the old residential area to the new residential location; 27.1 % and 52.0 % of the general population falling into high pay. Both the Government Reservation Area (G.R.A). and Old Residential Area display comparative pattern in the family unit (household) estimate, as the rate of food waste is wide in the two zones. In the G.R.A, we have the largest constituents of tins/containers waste. This is in support of Awomuti [27], that rate of waste created in Residential and Commercial (market) land utilization is higher than the other land utilization regions. The municipal solid waste stream consists of a wide range of materials which depends on classes of people, socioeconomic development, population density and type of human activities as shown in Table 1. Municipal solid waste composition varies from one municipality to another [28], the variation is significant with time. In where there is a standard waste recycling system, the waste stream consists majorly the intractable wastes like packaging materials that are not recyclable and plastic film.

Energy Recovery from waste
Energy recovery from waste can be defined as the conversion of waste materials that are not recycled into fuel, heat and or electricity, that are of economic value through a variety of processes that includes combustion, gasification, pyrolization, anaerobic digestion, also landfill gas (LFG) recovery. Energy recovery from municipal solid waste can be obtained by utilizing different technological methods. The method to be adopted for a waste stream depends on the composition, its energy content, the desired form of the energy output, the thermochemical conditions in which the WTE plant is to operate, and the overall energy efficiency. WTE is an optimal method of solving waste management problems in a sustainable way while harnessing its hidden energy [33]. The most important parameters, which determine the potential of energy recovery from wastes (including MSW), are quantity and quality (physico-chemical characteristics) of waste. The important physical parameters of waste requiring consideration include density, moisture content and calorific value. The energy recovery process is part of the non-hazardous waste management hierarchy. The process of converting nonrecyclable waste materials into heat or electricity provides another source of renewable energy and this tends to ameliorate the emission of carbon because this is an alternative source of energy generation to fossil sources, thereby reducing the generation of methane from landfills.  Fig. 1.

3.2.2.Physical Characterization.
Several subsets of MSW components were collected from the dumpsite, mixed together on a polythene mat with the aid of shovel and heaped to a cone shape, and was divided into four (4) slices [39], [40]. A pair of diagonally opposite slices were discarded, and the other two parts were thoroughly mixed together to obtain a representative sample of a specific waste bin volume of 240 litres [41]. Sixtytwo samples (62) were taken to reduce error due to insufficient samples. Each sample was sifted and screened on a screening equipment, 1.5 m x 3 m with 10 mm x 10mm mesh surface designed for heterogeneous solid waste [42]. The waste sample was hand sorted into different fractions, kept in different receptacles and weighed to get the corresponding weight.

Preparation of Laboratory Samples
The samples were shredded into smaller pieces of about 25 mm and further grounded to less than 1 mm using grinding machine. This was done to increase the surface area of the samples to allow easy digestion and penetration of heat during laboratory analyses. The samples prepared for the laboratory tests are shown in Plates 4 to 12.  (2) where is the percentage volatile matter, A is the mass loss of the sample, and B is the mass of the sample taken. The residue left after determination of volatile matter was heated without the lid inside a furnace at 700 O C for 30 min. Ash content is the amount of residue obtained after ignition of solid waste which was obtained according to Kuleape et al. [20], [21] using equation 3: sh (%) = × 100 (3) where , is the mass of ash and is the mass of the sample considered for the test. The fixed amount of carbon left was calculated according to ASTM D3172-73 [47] by deducting the percentage amount of ash, moisture, and volatile matter from 100, using equation 4. Fixed carbon (%) = 100 -(Moisture + Volatile matter + Ash).

Ultimate analysis.
The percentage composition of the total carbon (C), hydrogen (H), nitrogen (N), Sulphur (S), and oxygen (O) after removal of volatile matters, the moisture and ash contents were determined. This analysis was performed based on ASTM C1111-10 by using Inductively Coupled Plasma -Optical Emission Spectrometer (ICP -OES Perkin Elmer 8000). About 1 ml of sample was digested in tubes inserted to Gerhardt -Kjeldatherm digestion machine, when maintained at about 180 0 C for 1hour. The digests became clear to light yellow, then temperature was raised to 240 0 Cand further heated to dryness. The tubes were then offloaded and to cool. The residue was dissolved in 1 ml of concentrated HCL and add 10 ml of 5 % 3 The aqueous solution formed was injected to ICP and was nebulized to form aerosol. The sample was dissociated into constituent atoms by argon plasma and excited to emitted light of characteristic wavelength that was measured as a quantity. The light was resolved into its component radiation (by means of a diffracting grating), and intensity of the light was measured with a photomultiplier tube at specific wavelength for each element line. The intensity of the electron signal was compared to previous measured intensities of known concentration of the element and the concentration was computed in the data analyzer of the system. The mineral constituents in each sample was analyzed by ICP -Spec. using"WINLAB 32" software. The spectrometer data collectionparameters were configured,viewed graphically and the results of the analysis was printed.Theexperiment was repeatedthree times on each sample of the waste components [10].

Heating value.
The HHV was determined using a bomb calorimeter (e2k combustion Calorimeter), based on standard ASTM D5468-02 [45]. 0.5 g of sample was burnt in a high-pressure oxygen environment in the bomb. About 0.5 g of test sample was inputted to the system through the computer input device. The output was displayed on the screen after completion. The test samples were replicated three times and the average value was considered as the "typical" value (MJ/kg).

Modelling of the heating value.
Multiple regression analysis was used for the modelling of the energy content of the municipal solid waste (MSW). The higher heating value of the MSW, was estimated based on proximate analysis, ultimate analysis, and physical composition of MSW. The regression analysis was performed using GRETL statistical software [21]. Diagnostic check was performed by using Jarque-Bera test to determine the error distribution. The correlation of the regressors were examined by using variance inflation factor (VIF) for a diagnostic check of a problem of multicollinearity. Three models were developed; in the models, the dependent variable was the heating value (HV).

Physical Characterization.
The characterization process was completed after the period of eight months. The characterization result reveals that the highest waste fraction is Food residue 10.37 %, followed by Plastic bottle 9.79 %, Packaging box (carton) 9.69 %, Textile (rag) 8.91 % and the least is Leather 0.07 %. The mean distribution range is from 39.80 ± 35.00 to 0.2 ± 0.36. Nine waste fractions which include: food residue, carton, rags, paper, poly-sac, wood, nylon, plastic-bottle, and grass were considered for laboratory tests out of nineteen waste components characterized as presented in Tables 2 and 3; because of their regular occurrence in the flow of the waste stream and combustibility.

Chemical Characterization.
Proximate analysis results given in Table 2. Show that the range of moisture content of the components analyzed is 6-13 % and the dispersion is 0.58-1.16 %; the highest is wood 13 %, followed by grass/trimmings 10 % and the least is packaging box (carton) 6 %. Volatile matter"s range is 2 -67 % and the dispersion is 0.58 -15.18 %; the highest is paper 68 %, wood 67 % and the least is plastic bottle 2 %. Ash content range is 1 -36 % with dispersion of 0.00 -4.04 %; the highest is grass 36 %, followed by Textile (rag) 23 % and the least is plastic 1.00 %. The ultimate analysis results in Table 2, shows that the carbon range of the components analyzed is 21-38 % with dispersion of 0.04-0.85 %; the highest is food residue 38.08 %, followed by wood 37.45 % and polythene 21.07 %. Hydrogen range is 0.09-0.17 % with standard deviation of 0.001 -0.031 %; the highest is food residue 0.17 %, Polythene-sac is 0.15 % and the least is Textile (rag) 0.09 %. Nitrogen range is 2.12 -5.10 % with dispersion of 0.01-0.71 %; the highest is paper 5.10 % followed by food residue 5.01 % and the least is Polythene-sac 2.12 %. Oxygen range is 0.065 -0.085 % with dispersion of 0.0006-0.001 %; the highest is nylon 0.085 %, followed by packaging box (carton) 0.083 % and grass/trimmings 0.065 %. Sulphur range is 0.05-3.13 %. With dispersion of 0.002-0.039 %; the highest is food residue 3.13 %, followed by wood 0.13 % and the least is nylon 0.52 %.

4.3.Heating Value
In Table 3, the net heating value of the waste components is determined to be about 20 MJ/kg. Nylon is the waste component that has the highest heating value of 20.4 %, Poly-sac 17.4 %, Plastic 16.5 % and the least is Textile (rag) 6.9 %.
Model developed on physical components of MSW: (9) where: HV is the heating value, FC is the fixed carbon, M is the moisture content, VM is the volatile matter, C is the carbon percentage content of the municipal solid waste, H is the hydrogen content percentage, N is the nitrogen percentage content and S is the Sulphur percentage content, G is the percentage garbage component, CE is the percentage cellulose component and P is the percentage polythene content.
Fixed carbon and volatile matter have positive effect on heating value while moisture has a negative effect. The model reveals that 1 % increase in fixed carbon will increase heating value by 8 %, and by calculation will increase electrical power generating potential by 8 %. From the model 1 % increase in volatile matter will increase heating value by 37 % and by calculation increases electrical power generating potential by 37 % meaning that the volatile matter present is a combustible one. While 1 % increase in moisture content will reduce the heating value and the electrical power generating potential by 11 % concurrently. The model presents that 1% increase in carbon will increase heating value by 79.08 % and by calculation increases electrical power potential of the MSW by 21%. Nitrogen will increase heating value by 10.83 % and the electrical power potential by 10.80 %; while 1 % increase in hydrogen reduces the heating value by 30.2 % and reduces electrical power potential by 69.3 %. It implies 1 % increase in Garbage, Cellulose and Polyethylene fractions, will cause the heating value to increase by 2 %, 17 % and 3 % respectively and will consequently increase the electrical power potential by 2 %, 17 % and 3 % respectively.

Conclusion
It is concluded that 1% increase in fixed carbon content of MSW characterized in Ilorin metropolis will increase electrical power generating potential by 8 % and 1 % increase in volatile matter will increase the electrical power generating potential by 37 %, which implies the volatile matter present is combustible; while 1 % increase in moisture content will reduce the electrical power generating potential by 11 % this could be as a result of heat lost during vapourization. 1% increase in carbon will increase electrical power potential of the MSW by 21 %. Nitrogen increases the heating value by 10.83 % indicating that the gas got combusted to generate heat and it increases the electrical power potential by 10.80% while 1% increase in hydrogen reduces the heating value by 30.2 % and reduces electrical power potential by 69.3%. It implies 1 % increase in Garbage, Cellulose and Polyethylene fractions, will cause the heating value to increase by 2 %, 17 % and 3 % respectively and will  11 consequently increase the electrical power potential by 2 %, 17 % and 3 % respectively. By conclusion every physico-chemical property (FC %, M %, VM %, Ash %, C %, H %, N %, S % and O %) of MSW that causes an increase in the heating value, also help to positively improve on the electrical rating potential of the MSW if used as fuel for power generation.