Environmental sustainability evaluation of solid waste management of Dhaka city through life cycle assessment

Abstract

The management of municipal solid waste in an environmentally safe and sustainable way is becoming a major challenge for today’s urban areas. Dhaka, the capital of Bangladesh generates an average of 7,476 tons of solid waste daily of which most of its wastes is disposed of in landfills in an unsanitary way. The current Municipal Solid Waste Management (MSWM) practice is posing a serious threat to the environment and public health. Moreover, absence of source separation, recycling, composting, and recovery makes the system unsustainable and heavily dependent on land disposal in a land scarce city like Dhaka. The present study has been undertaken with an objective to evaluate the MSWM system of Dhaka using Life Cycle Analysis (LCA) and to find out suitable strategies to make the system sustainable. In this analysis, four alternative LCA scenarios (A1, A2, A3 and A4) are formed by combining composting, recycling, and incineration along with the existing baseline scenario B0 (only landfilling). A1 and A2 scenarios are organic waste composting-based alternatives. In alternative A2, other combustibles are considered for incineration. In alternatives A3 and A4, half and full quantity of organic wastes are considered for composting and incineration respectively. The analysis result shows that the combination of organic wastes composting and incineration of remaining combustible wastes in scenario A2 is the most environmental friendly option in major midpoint and endpoint impact categories. As a second choice, alternative scenario A1 which is formed by composting of organic waste and landfilling of the remaining wastes is found suitable. Incineration of organic waste is found to be less environmentally sound and less energy efficient due to low calorific value and high moisture content of wastes. In marine eutrophication midpoint impact category, the scenario A2 has the highest environmental savings with negative value of 8.77E+06 kg N equivalent. In this category, baseline B0 has the highest emission with an adverse environmental impact of 9.78E+06 kg N equivalent. Remaining scenarios named A1, A3 and A4 scenarios, values for eutrophication are -5.56E+06, -4.12E+06 and 5.30E+05 kg N equivalent respectively. Similarly, in endpoint marine eutrophication, the values of lost in species per year for B0, A1, A2, A3 and A4 scenarios are 1.85E-3, -1.52E-2, -1.55E-2, -7.71E-3 and 1.12E-4 species per year respectively. In tropospheric ozone formation and stratospheric ozone depletion categories, baseline practice (scenario B0) is found to be the most suitable. Global warming is least occurred by alternative scenario A4 where most of the waste is considered for incineration. But incineration is also found to be the most polluting option in ozone formation, carcinogenic toxicity and terrestrial ecotoxicity categories. It has been found that in the incineration process, the land requirement for one year is 7918 m2 and for a ten-year period it would be 32238 m2 unless the incineration ash will not be recycled. On the other hand, land requirement for composting of organic wastes would be the same (7918 m2) for one year. And this requirement will remain unchanged after ten years as this land will be reusable. The endpoint burdens (impact over human life and change in species on ecosystems) in all the scenarios follow the patterns of midpoint categories. A comparison is also conducted between two city corporations of Dhaka (North and South) and the analysis result indicates that South City Corporation’s waste management is more environment friendly although various factors like waste quantity, number of vehicles and secondary transfer stations (STSs), landfill type etc. influence the performance.