39 CHAPTER III
RESEARCH METHODOLOGY
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Figure 3.1: Flow chart of this study.
In the selected disposal site, MSW is dumping with neither planning nor proper operation.
MSW spreads all over the site, and even to the surrounding water bodies. Figure 3.2 shows the present scenarios of the selected open dumping site at Rajbandh, practice of vegetation and fishing near to the site. The hand pumps/tube-wells are located nearby to the waste disposal site (about 300 m) and people use the groundwater for drinking, bathing and washing purposes.
Detail literature review related to this topic
Collection of soil samples from different selected locations of waste disposal site at Rajbandh, Khulna, Bangladesh
Investigation of metal element concentrations in soil in the laboratory through the standard test methods
Evaluation of soil quality comparing with the allowable limit of metal elements in soil from different countries
Evaluation of the level of contamination of soil using various indices and their limits available in the literature
Analysis of correlations and temporal variation of metal elements in soil using descriptive statistical analysis and Pearson's correlation
Distribution of metal elements and various indices spatially using ArcGIS
Assessment of overall ecological risk associated with heavy metal in soil of waste disposal site based on the level of contamination
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Figure 3.2: (a) Waste disposal site at Rajbandh, (b) vegetation on a layer of waste in the site and (c) fishing in a pond near to the site.
3.2.1 Geological Setting of Study Area
Khulna is a district among total sixty four districts in Bangladesh. Besides, the Khulna city is in the northern part of the district, acknowledged as third largest among ten metropolitan cities of Bangladesh. Geographically, Khulna lies between 22°47'16" to 22°52'0" north latitude and 89°31'36" to 89°34'35" east longitude. This city situated on the Rupsha and Bhairab river-banks shown in Figure 3.3. The MSW of Khulna city is dumped at Rajbandh disposal site. However, in this study only the old Rajabndh waste disposal site was chosen as a case study to assess the quality, level of contamination and ecological risk of soil of this disposal site.
(a) (b)
(c)
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Figure 3.3: Location map of Rajbandh at Khulna city of Bangladesh.
3.3.2 Soil and MSW Condition of Waste Disposal Site
The waste disposal site is located at Rajbandh, Khulna, 7 km far from the city center i.e.
Royal & Castle Salam Square of Khulna city and situated along the North-side of Khulna- Satkhira highway. It is important to know the physical and mechanical properties of underlying soils as thoroughly as possible before assessing their physico-chemical or hydro- mechanical behavior. Based on these concepts, in laboratory through standard methods, some relevant physical and mechanical properties of soil from this selected disposal site were determined by Rafizul (2014). Soil moisture content, plastic limit, liquid limit, plasticity index and shrinkage limit of soil were found 22, 22, 43, 21 and 16 %, respectively. In addition, the percentages of soil constituents were found as sand, silt and clay of 10, 56.6 and 33.4%, respectively. Then the value of soil pH, optimum moisture content, maximum dry density and coefficient of permeability were found 6.7, 18 %, 16 kN/m3 and 1.90x10-7 cm/sec, respectively.
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In Bangladesh, MSW mainly consist of food and vegetables waste (Rafizul, 2014). Other items are presents in negligible percentages. For a basic understanding of the nature of MSW that are generally encountered, the type distribution of particle sizes must be known. The degradation of the organic fraction from MSW in disposal site produces a number of gases which degrades environmental condition. In contrary, the MSW of the study site mainly consists of pH, volatile solids (VS), and ash residue and bulk density of 7.79, 58 %, 46 % and 1000-1066 kg /m3, respectively. In addition, the percent finer of MSW was 100 % in 300 and 200 mm sieve openings, whereas the values were found as 76.25, 63.72, 45.22 and 24.34 % for the opening of 100, 76.2, 38.2 and 19.1 mm, respectively. Moreover, the chemical characteristics in terms of carbon (C), nitrate (N) potassium (K), phosphorous (P) and C/N ration was found as 25.63, 1.84, 1.37, 0.41% and 13.92, respectively.
Figure 3.4: Soil sampling location in waste disposal site at Rajbandh.
44 3.3 Soil Sampling
In this study, sixty soil samples were collected from different selected locations of waste disposal site shown in Figure 3.5. Soil samples were collected at a depth of 0-30 cm from the existing ground surface of waste disposal site. The latitude and departure of all the soil sampling locations was recorded using GPS device. In total sixty soil samples, forty samples were collected in dry season (March to May, 2016) then rest twenty samples were collected in rainy season (June to August, 2016). In dry season, the sampling points were selected maintaining gradual addition of about 10 m distance from the 1st borehole (BH-1) by the subsequent boreholes. The first sampling point, BH-1 is located at the centre of the waste disposal site. The first borehole of rainy season (BH-41) is about 30 m apart from BH-1 which is the centre of disposal site and maintains a gradual addition of about 15 m in selecting of following boreholes. Proper care was taken to remove any loose material, debris etc. from the bottom of the excavated pit. The soil samples were collected from the bottom of the borehole by excavating the ground manually by using hand shovels. The soil samples were taken in large polythene bags and eventually transported to the laboratory.