Study on solid waste and leachate characteristics at Matuail dumping site

Abstract

Dhaka City produces tons of solid wastes everyday. Due to crude, unsanitary dumping procedure these wastes in a disposal site have significant impacts on the soil, surface water and ground water. In this study an attempt has been taken to analyze the composition and leaching characteristics of solid waste at Matuail dumping site and to assess the contamination of soil and surface water from this waste. Five types of samples were collected to assess the contamination. These are (i) solid waste (ii) converted soil (iii) natural soil (iv) leachate and (v) surface water. Solid waste samples collected randomly from five different locations within the dumping site were analyzed for parameters such as unit weight, moisture content, organic content, ash content and heavy metals including Fe, Mn, Cd, Ni, Cu, Zn and Pb. Unit weight of solid waste varies within the range of 667 kg!m3 to 750 kg!m3 and organic content varies from 26.98% to 44.36 %. The average moisture content and ash content of the solid waste samples are in close agreement with the results reported in the BCSIR, 1998. Among all the heavy metals tested, the concentration of iron is the highest (9600 mg! kg), whereas cadmium concentration is the lowest (0.804 mg! kg). The concentration of other heavy metal varies as follows: iron > zinc > copper > lead > manganese > nickel > cadmium. Twelve converted soil samples collected from four locations at the dumping site from different depths (Le., at 0 ft, 1.5 ft, 3.0 ft) were analyzed for heavy metal concentration such as Fe, Pb, Cu, Zn, Mn, Cd, and Ni. Three natural soil samples were collected from only one location at different depths (i.e., 0 ft, 1.5 ft, 3.0 ft) to analyze the heavy metal concentration and a comparison was made with the heavy metal concentration that found in converted soil sample. It has been observed from the data that except for Fe, concentration of all heavy metals in converted soil is significantly higher than that in natural soils irrespective of depth. This finding shows that the converted soil, which is formed due to dumping of wastes over the years, is highly contaminated with toxic metals. Leachate collected from four points and the samples were analyzed to determine the concentration of pH, color, TS, TSS, TDS, Fe, Pb, Cu, Zn, Mn, Cd and Ni. Leachate from the dumping site flows into the surface water bodies around the dumping site and then the surface water becomes polluted. Five surface water samples were collected from the water bodies surrounding the dumping site and were analyzed for a wide range of parameters such as pH, color, TS, TSS, IDS, DO, BOD5, COD, TC, FC, Fe, Pb, Cu, Zn, Mn, Cd and Ni. Analyzed test results show surface water to be polluted from leachates flowing into them. The concentrations of Color, DO, BOD5, COD, TC and FC found in surface water show that this water is not suitable for any domestic purpose. TCLP tests were carried out on five solid waste samples to study the leaching behavior of solid wastes. The average concentration of heavy metals that leached during the TCLP tests ranges from 6.74 mgIJ(134.86 mglkg) for zinc to O.oI mg!1(0.2018 mglkg) for cadmium. According to TCLP results, maximum leaching was observed for manganese (about 33%) and minimum for iron (about 1%). The high concentration of heavy metals in TCLP extract only indicates that there is a great possibility of soil and ground water contamination due to leaching of heavy metals from solid wastes. Matuail dumping site is not properly designed to protect the environment from adverse impact of landfill gas and leachate. Moreover, due to the unsanitary and crude dumping system, soil pollution, surface water pollution etc. pose great threat to the public health. It may be cause of fire explosions, vegetation damage, unpleasant odour and air pollution.