Effects of Solid Waste on Urban Warming in Warri Metropolis, Nigeria ()
1. Introduction
The waste generation scenario in Nigeria has been of great concern globally and locally [1]. An average Nigerian in his household, institution and industry encounters some tones of solid waste yearly. Several Nigerians have considered it a cheap way of disposing off their solid waste by setting the mixed waste on fire in a little corner in their backyard or in a very open place resulting in the release of Greenhouse Gases (GHG) which is harmful to urban climate.
The rate of waste generation is highly influenced by the income of the populace [1]. In Nigeria, over 25 million tonnes of municipal solid waste are generated annually [2]. The role of methane in global atmospheric changes has received increasing attention recently. Methane from landfills contributes significantly to annual global emissions of (GHG) Greenhouse Gases.
Agbola and Jinadu [3] estimated that each person in Nigeria generates an average of 0.0005 tonnes of waste daily. The amount of solid waste generation rates ranges from less than 0.1 tonnes per capita per year in low income countries to less than 0.8 tonnes per capital per year in high income industrialized countries [4].
In Warri metropolis, some of the dump sites are deliberately set on fire by dump site managers, scavengers and individuals in order to reduce the volume of the waste, to allow more waste to be disposed there. The fire from the waste dump in turn pollutes the atmosphere, thereby increasing the concentration of carbon dioxide (CO2), methane (CH4) etc. in the area. The decomposition of organic materials produces methane, which can cause fire and explosions, and contributes to global warming.
Fire is periodically set on by dump site manager in open dumps, generating smoke and contributing to air pollution. For example, in one of the waste dump sites at the Effurun-PTI express way, fire burned for over 3 days at the local open dump. This could lead to increased urban temperatures in Warri. Furthermore, the waste dump sites in Warri destroy the beauty of the area, thus reducing the aesthetic beauty. It is against this background that there is a need to study the ever increasing contribution of solid waste to urban warming. This paper examines the effects of solid waste generation on urban warming in Warri and environs, so as to provide necessary answers to the questions raised.
2. Study Area
Warri metropolis is located between latitude 5˚30'N and 5˚35'N and Longitude 5˚29'E and 5˚48'E. The areal expansion of Warri during the past two decades has been remarkable. Warri has grown to cover the surrounding towns of Effurun, Ekpan, Enerhen, Edjeba, Ogunu, Jakpa, Ovwian-Aladja, Udu Road, etc. with an areal expansion of over 100 sqr.km [5]. This areal expansion has led to increase in temperature and precipitation in the area [6].
The area is characterized by hydromorphic soils, which is a mixture of coarse alluvial and colluvial deposits. The indiscriminate dumping of waste on the soil enhances anaerobic processes more, leading to the release of (CH4) methane to the atmosphere resulting to urban warming.
The area is characterized by tropical equatorial climate with mean annual temperature of 32.8˚C and annual rainfall amount of 2673.8 mm. Rainfall period ranges from January-December, with the minimum value of 8.2 mm in January and over 536.6 mm in September. There are high temperatures of 36˚C and 37˚C in the heavily built up and traffic congested areas of Enerhen junction, Enerhen road area, Estate, Okere road areas, Jakpa junction, Jakpa roads areas, Hausa quarters and Igbudu market areas respectively [7]. The temperature has led to an increase in urban micro heat island.
Warri metropolis is one of the rapidly growing cities in Nigeria, with a population rising rapidly from 19,526 in 1933, 55,256 in 1963, 280,000 in 1980, 500,000 in 1991 to 536,023 in 2006 [5]. The population growth will lead to an increase in the amount of solid waste generated which will potentially escalate Methane emission from solid waste and further leads to urban warming
3. Conceptual Issues
The links between urbanization, waste and global climate change are complex [8]. The irregular dumping of waste will tend to increase temperatures in the city thus causing urban warming. One of the most well-known anthropogenic climate modifications is the phenomenon of urban heat Island (see Figure 1).
The best-known urban effect of such development is urban warming; globally cities are almost always warmer than the surrounding rural area [9]. The magnitude of urban warming is highly variable over both time and space. According to Fuchs [10] the main cause of urban heat island is the modification of the land surface by urban development, waste heat generated. The form and intensity of the UHI varies temporally and spatially depending on local/regional meteorological, geographical, and urban development characteristics [11] and is a complex function of many interacting variables [12].
Methane is the most significant greenhouse gas produced in the disposal and treatment of municipal and industrial solid waste is methane [13]. Methane (CH4) is generated as a result of degradation of organic material under anaerobic conditions. Part of the CH4 generated is oxidised in the cover of the solid waste disposal sites, or can be recovered for energy or flaring. The CH4 actually emitted from the solid waste disposal sites will hence be smaller than the amount generated.
The major factors affecting methane (CH4) emissions from municipal solid wastes are mainly, the amount of waste generated, the composition of the waste, the conditions under which the waste is disposed, and the climate of the region under study [14]. Moreso, all the factors, except the last, are dependent one way or the other on the socio-economic characteristics of the region.
4. Methods and Materials
The procedure adopted for the collection of data was full range of concurrent temperatures, GHG emissions and waste measurements. The temperature measurement was carried out at an intermediate standard observation hour of 900, 1200, 1500 and 1800 GMT. These hours selected for measurement is in line with the World Meteorological Organisation standards [15]. The temperature reading was taken at 1.5 m above waste dumps at the four major waste dump sites for a period of two months (January and February) on a weekly basis in 2011.
The greenhouse gases were measured during early hours of morning (7 am) and evenings (7 pm). This time duration were selected as a result of the volatile nature of the gases. For the Hydrocarbons/volatile organic compounds (CxHy/VOC), Nitrogen Oxides (NOx), Sulphur Oxides (SOx) and Carbon Monoxide (CO) measurements, a Testo 350 flue gas analyser was used. It performs automatic analysis of ambient air through the use of physical properties, giving cyclic or continuous output signal. Air is continuously extracted from the atmosphere and the sample is sent to the analyser for the determination of the pollutant gas of interest.
Moreso, measurement of waste volumes was carried out at the five major waste dump sites in 25 neighbourhoods on weekly basis for two (2) months. The five (5)
wastes dump sites are as follows; Igbudu market, Orhuwhorun, Iyara, Army barracks and Okuokoko. To ensure adequate measurement the quadrat technique was adopted where a quadrat of 1 m × 1 m is thrown on the waste at each sample sites, thus making a total of 1458 quadrats in all (see Table 1).
Before this was done, the area of waste occupancy was measured using a measuring tape. After which, the waste in the selected quadrat area was scooped and further placed into a trash bin whose weight has been measured already. This was done so as to anticipate the actual volume of the waste scooped. In doing so the trash bin was suspended on a spring balance instrument, so as to get the volume of the waste. Thereafter, the volume of the trash bin was subtracted, so as to get the net volume of the waste. Furthermore, the net volume was multiplied by the number of quadrat squares in the area occupied by waste. Thereafter, the sample was used to multiply the number of quadrat squares in the study site to get the total volume of waste generated.
The waste scooped into the waste bin was further segregated to identify the various waste categories using alphabetical notation such as follows: A = Leaves, B = Paper, C = Metals, D = Glass, E = Rags, F = Plastics, G = Dust, H = Wood, I = Moisture (Organic waste). These alphabetical notations were used based on convenience and as the typical nature of solid waste in Nigerian cities [16]. After the segregation and separation of the waste, it was further measured so as to get the volume of the various waste categories. To ensure an adequate study on the distribution of waste in Warri metropolis, waste bins were placed in a household in each of the twenty-five (25) neighbourhoods. These waste bins were measured on a weekly basis for two months and the net volume of the waste were measured and recorded.
Data on temperature and volume of waste were analysed using the bivariate correlation analysis. While the data on temperature and greenhouse gases emitted were analysed using the multiple regression analysis. These data was entered in Statistical Package for Social Sciences (SPSS) version 19 and double checked before analysis.
5. Results and Discussion
Table 2 shows the household waste generated in Warri metropolis.