Geoenviromental Assessment of Ultimate Disposal Sites of Municipal Solid Waste in Some Major Cities of Bangladesh

Abstract

The disposal site, ternied as landfill can pose a long term threat to the human health and environment if not designed properly. This study aims to describe the present status and site potentiality of four ultimate disposal sites (UDS) receiving municipal solid waste (MSW) from the four major cities of Bangladesh, namely, Dhaka, Khulna, Rajshahi and Barisal through field survey, impact analysis, laboratory tests. Physical, Environmental and geotechnical parameters are considered for the assessment of these UDS. The study reveals that there is no controlled/engineered/sanitary landfill in the Dhaka, Khulna, Rajshahi and Barisal city of Bangladesh, the disposal sites are simply uncontrolled open dump. However, recently, Dhaka city has taken some practical initiatives to convert Matuail open dumping site into controlled landfill. The physical and technical facilities are almost absent in all sites. The leachate samples were collected from the studied sites and the laboratory analyses reveal wide variation of magnitudes as pH (6.2 to 8.2), Chloride (7.5 to 3000 mg/1), Iron (0.4 to 55 mg/1), TDS (260 to 8652 mg/1), BOD5 (40 to 2550 mg/1), COD (110 to 5550 mg/l), Pb (0 to 0.425), Ni (0.001 to 0.46) and Cd (0 to 0.105). The ratio of BOD/COD ranges from 0.01 to 0.46 which shows biodegradability of leachate is very low. Leachate Risk Factors (LRF) was derived for identifying sites that may pose significant risk to the environment. It is depicted that the leachate poses significant risk to the environment and it requires treatment to ensure safety before discharge to the receiving environment. This study also presents an estimation of methane (CH4) emissions from the four actively functioning UDS by using the methodology developed by the Intergovernmental Panel on Climate Change (IPCC) which provides the baseline information of the contribution of MSW Sector to global worming potential and waste-to-energy facilities. The total CH4emissions from the four studied sites were estimated as 31.18 Gg in the year of 2006. The ratio of CH4 emitted to the amount of waste generated in four cities of Bangladesh varies from 0.008 to 0.015 which is analogous to the other developing countries of the world. The sub-soil investigation was carried out at the close vicinity of landfill sites to identify the soil strata, physical and engineering properties and mineralogical compositions. Boring to a depth of 60 ft revealed that the fine sediment forms to a depth of about 5 ft followed by clay more than 30 ft thick having clay content ranges from 30 to 50% and hydraulic conductivity varies from 1.05x -9 to 11 .50x-9m/s. Clay minerals account for more than two-thirds of the overall mineralogical composition in which non-swelling clay minerals, quartz varies from 20 to 60% and illite/muscovite ranges from 20 to 45%, while small amounts of kaolinite and feldspar also exist. Swelling clay minerals present in varying amounts of 10 to 25% of the composition and the CEC ranges from 13 to 25 meq/100g as estimated. Especially, the sub-soil formation of Dhaka. Khulna and Rajshahi appears to have suitable composition required for the construction of geologic clay liner (GCL). However, the soil samples from Barisal site exhibit low CEC values due to the existence of low amount of swelling clay minerals. The characterization of clay of selected shallow layer from the studied sites is suitable as compacted clay liner (CCL) for the construction of sanitary landfill.