EVALUATION OF GREENHOUSE GAS EMISSIONS FROM SOLID WASTE MANAGEMENT PRACTICES IN STATE CAPITALS OF NORTH EASTERN NIGERIA

Greenhouse gas (GHG) emissions due to solid waste management (SWM) techniques being practiced in the North eastern region of Nigeria are unaccounted for as such these emissions cannot be monitored or controlled. This research estimated GHG emissions into the atmosphere from the current SWM technique practiced in the region, GHG emissions from two different waste management techniques – open burning and incineration was also simulated. The research found that incineration with electricity recovery is the most suitable SWM process therefore suggested that the authorities and other stakeholders in the region should give it serious consideration.


INTRODUCTION
Generation of Municipal solid waste (MSW) is inextricably linked to daily human activities, this is more pronounced and prevalent in urban areas where most of the day-to-day items used by urban dwellers are bought in disposable bags and other packages which are later discarded. Food wastes are also more common in urban areas which are generally more affluent and can afford to have more than enough food [1,2].
Since the beginning of the industrial age around the middle of the 20 th century, there has been a wave of migration of rural dwellers into urban areas primarily seeking employment and a better life. For example, in China alone, about 340 million people migrated from rural to urban areas in the space of just about 30 years [3]. Increase in urban population means an increase in the quantity of MSW being generated and disposed of in these cities. Asides increase in urban population, other factors responsible for increase in MSW generation as found by researchers include: increase in Gross Domestic Product (GDP); increase in family or per capita disposable income; increase in consumption expenditure; levels of education; degree of industrialization; public habits; local climate; age of population; environmental laws/policies and improvement in the standard of living [4][5][6][7].
Large quantities of MSW generated in cities have their inherent disposal problems, chief among them is the greenhouse gas (GHG) emissions associated with their disposal. Whether MSW is landfilled, incinerated, openly burned, recycled, or just openly dumped, GHGs are emitted into the atmosphere in the process. Diverse solid waste management (SWM) techniques have been discovered to have varying degrees of impact on the environmentcarbon footprints [5,[8][9][10]. According to the IPCC's 2014 report, global GHG emissions from the waste sector have grown steadily and are expected to increase in the forthcoming decades especially in developing countries such as Nigeria because of the dramatic rise in their population and their growing economy [11]. It is estimated that globally, 20 % of emission of GHGs are from solid wastes, that amount is forecasted to reach up to 816 tonnes of carbon dioxide equivalent (tCO2eq) by the end of year 2020 [12].
North-eastern Nigeria which comprises of six states -Adamawa, Bauchi, Borno, Gombe, Taraba and Yobe have in recent years largely been faced with insurgency. The insurgents have perpetually been terrorizing the rural areas in this region thus forcing quite several residents of the rural areas to migrate into state capitals which are largely more secured [13,14]. It can be inferred that the increase in the number of residents of the capital cities of these north-eastern states i.e. Bauchi, Damaturu, Gombe, Jalingo, Maiduguri and Yola due to the insurgency induced rural-urban migration has resulted in a sharp rise in the MSW generation rate in these state capitals and thus a consequential increase in GHGs emissions from the waste sector in this region.
Evaluating GHG emissions from the current SWM techniques being practiced in the capital cities of north-eastern Nigeria is essential to the innovation of methods, policy formulation and implementation geared at reducing the GHGs emission from the solid waste sector in this region and the nation at large, hence the need for this research.

EXPERIMENTAL SETUP
Data for this study was sourced from a wide range of literature, research findings on MSW and SWM in each of the six state capitals were intensively studied so as to obtain the required data for this study. The key information fished out from literature in regard to each of the state capitals are MSW composition, annual MSW generation rate, average moisture content of MSW and SWM techniques being practiced. For uniformity, the MSW generation rate recorded in the year 2017 for each of the state capitals was used for this research.
Using the Institute for Global Environmental Strategies simulation tool for GHGs emission from solid waste management which is a tool based on IPCC's 2006 guidelines for quantification of GHGs from MSW [15], three common waste management scenarios were simulated for each of the state capitals and the corresponding GHGs emission for each scenario obtained. It was gathered from literature that all the six state capitals practice the same SWM techniqueopen dumping of collected MSW in unmanaged sanitary landfills [16][17][18][19], thus open dumping was used as the base scenario. Open burning and incineration with energy (electricity) recovery were used as the second and third simulated scenario respectively. A tailpipe emission analysis methodology was adopted, meaning emissions from other related activities such as collection and transportation of the MSW were not considered. For the incineration scenario, it was assumed that a continuous fluidised bed incinerator was used and that its efficiency is 22% [20].

Composition and quantities of MSW generated
It was found that the composition of MSW disposed of at the different sanitary landfills in the state capitals varied widely. Jalingo which experiences the highest average annual rainfall among the six state capitals [21] had the highest percentage of organic waste in the composition of its MSW. Meanwhile, Yola which is the more commerce-oriented state capital in the region unsurprisingly was found to have the highest percentage of plastics. The variation in the composition of the MSW can be said to largely depend on the type of commercial activities in the city and its climatic conditions as corroborated by Khan and Masebinu [22,23].
For the quantities of MSW disposed of at the sanitary landfills, Gombe which is less populated than Yola and Maiduguri surprisingly ranked first. This however does not mean that Gombe generates more MSW, it rather means the state capital has a better collection efficiency than its contemporaries, this, inference is supported by studies done by other researchers [24,25]. Damaturu was observed to have the least quantity of MSW disposed at its sanitary landfill, this is not surprising because the city has the least population in the region [26], and as it has been earlier stated, population is a key factor in determining MSW generation. The quantities and composition of MSW disposed of at the sanitary landfills in these cities as found in the literature used for this research are presented in Table 1 and Table 2 respectively [17,[27][28][29][30][31][32][33][34].

Greenhouse gas emissions from solid waste management practices
Open dumping as is being practiced in the region is responsible for emission of GHGs into the atmosphere due to the anaerobic digestion of the organic component of the waste, it was estimated that a total of 5880.95 tonnes of methane annually which translates to 123503.69 tonnes of carbon dioxide equivalent (tCO2eq) is emitted into the atmosphere due to this technique of SWM in the region. Gombe was noted to have the highest emission of GHGs into the atmosphere in the region from its current SWM technique: 50993.79 tCO2eq. Bauchi ranked second with 29419.76 tCO2eq, while Yola, Maiduguri and Damaturu ranked third, fourth and fifth with 17300.78 tCO2eq, 16442.70 tCO2eq, and 3852.15 tCO2eq respectively. When the GHGs emission from this waste management practice is considered through another perspectiveemission per tonne of MSW, the picture differs. On emission per tonne of MSW, Bauchi ranks first, Gombe second and Maiduguri least with about 268 kgCO2eq per tonne of MSW. Figure 1 shows the amount of GHG emitted into the atmosphere per tonne of MSW. It was found that if the cities being studied are to openly burn their MSWas is seldom done in some of the dumpsites in these cities [35], a total of 127812.63 tCO2eq will be emitted into the atmosphere. This means the emission of GHGs into the atmosphere if all the MSW in the region are openly burnt will be about 3.  Table 3 shows the amount of GHGs that will be emitted into the atmosphere if open burning of MSW is adopted as the preferred SWM technique in each of the state capitals in North-eastern Nigeria and the corresponding emission per tonne of MSW.  [36,37], it also reduces the characteristic bad odour associated with open dumping and open burning while equally avoiding the defacing of urban landscape with charred MSW. In addition, the recovery of energy from MSW incineration means reduction (offsetting) of GHGs from conventional fossil fuel, based means of generating electricity. Table 4 shows the gross emissions from incineration of MSW in the various state capitals, the corresponding avoided emission due to the production of electricity in the process and the subsequent net GHGs emission. The third simulation done showed that if incineration with energy recovery is used as the preferred SWM technique in the region, given the quantities and composition of MSW disposed of at sanitary landfills in the region in the year being reviewed, a total of 37042.84 tCO2eq will be emitted into the atmosphere. This is a reduction of approximately 42% from the existing SWM technique in practice. Clearly, this is the most environmentally friendly SWM technique and should be given serious consideration by the authorities and relevant stakeholders in the region. Incineration with electricity recovery not only reduces carbon emissions into the atmosphere, it can also serve as a source of income for the states when the CO2 offset from this process is traded in any of the certified emission trading schemes defined in the Kyoto protocol [38]. In addition, this SWM method also provides electricity which can complement what is being supplied to the states from the national grid which happens to be grossly inadequate.