Environmental feasibiltiy of coarser fraction of MSW legacy waste and cost analysis of its biomining and biocapping at landfill

Abstract

Urban India accounts for 62 million metric ton (MT) of MSW generally annually. Increased growing rate of waste generation has acquired huge land area by converting virtual mountains of old legacy waste. These old landfills are possessing real threat to the environment in terms of contaminating air, water and land. Emission of methane, carbon dioxide, ammonia, hydrogen sulphide, and volatile organic carbon (VOCs) causing from the landfill degradations, persistence of heavy metals, to vegetations, groundwater and surface water due to leaching of toxic leachate, emission of carcinogenic compounds, Hydrocarbons (HC), dioxins and furans from landfill fires are all such aspects not only deteriorating environmental standards but also inculcating human and ecological risk. In India, around 10,000 hectares of urban land is locked in these open dumpsites. Open dumping is the major problem associated with most of the Asian cities. Thus, it is needed to reclaim the existing open dumping grounds in many Asian cities and nowadays biomining remediation methods will be the most viable solution for the reclaimation. Biomining is advantageous than biocapping of closed dumping site in terms of reducing the greenhouse gas emissions, reducing the footprint area of landfill, avoiding the surface water and groundwater contamination, improving reuse and recycling concepts and reducing the post-closure operation and maintenance costs which raise the requirement of biomining concepts. Biomining involves the processes like excavation, waste stabilization, screening and separation of materials from landfills into various components including recyclable materials, combustibles, inert materials and soil-like materials (both finer & coarser fraction) with a sustainable approach to prolong the landfill life and to remediate the contamination from unlined open dumpsites. A precise study was carried out on the environmental feasibility of the coarser fraction of the legacy waste excavated from the age-old dumpsites. A correlation matrix and ANOVA helps in assessing the relationships and differences among variables in coarser fraction of soil-like materials. The study investigates the depthwise and seasonal variations of the coarser fraction of soil-like materials obtained from legacy waste at Dhapa. The coarser fraction comprising particles greater than 4.75mm was analyzed for physical and chemical properties at different depths (0 - 20)m and seasons (winter, summer and monsoon). Results show significant depthwise variations in particle-size distribution, density and moisture content. The top (0-8) m layer exhibited lower moisture content (water holding capacity – 34%) and higher coarser particles (Gravel – 21%) while the lower layers of depth between 17m and 20m showed increased density (1.47 gm/m³) and finer particles (Sand - 78.38%). Seasonal variation revealed higher moisture content during monsoon (43.2%) and lower value in summer (38%). Physicochemical analysis indicated minimum seasonal changes for significant depthwise variations in pH, EC, and organic content. Principle component analysis identified depth and season as key factors influencing the coarser fractions characteristics’. These findings have implication for resource recovery, waste management and environmental monitoring, highlighting the importance of considering depthwise and seasonal variation in soil-like material characterization. These statistical techniques are essential for unlocking the full potential of soil-like material from legacy waste, ensuring its safe and sustainable management. Assessments of the total heavy metals and leachate characteristics have been done in order to trace out the variation of the concentration of the above mentioned parameters with respect to the soil depths. The concentrations (mg/kg) of the heavy metals like lead (49±21.5), nickel (20.74±7.64), cadmium (0.701±0.62), copper (44.28±7.30), and zinc (257.77±72.11) are very much below the suitable range. For Leachate characteristics of the soil-like materials, it can be said that concentration (mg/l) of the lead (1.04±0.58), nickel (0.60±0.45), copper (0.45±0.28), total chromium (0.75±0.42), mercury (0.00±0.00), arsenic (0.01±0.00), cadmium (0.02±0.02), zinc (5.58±3.06), iron (10.13±4.82), manganese (10.13±4.82) are within the range. Exception is the mercury concentration (0.00±0.00) which is almost negligible. Biomining and Biocapping are the two options of bioremediation techniques. By conducting a cost comparison, stakeholders can make informed decisions, optimize resources and ensure this sustainability of legacy waste management project. Cost comparison is required (i) to determine the cost effective approach for legacy waste management, ensuring optimal use of resources, (ii) to establish a realistic budget for the project considering the cost of different approaches, (iii) to inform decision makers about the financial implications of different options, enabling him to make informed choices, (iv) to prioritise projects or activities based on their cost effectiveness and potential impact, (v) to evaluate the financial performance of different approaches and identify areas for improvement, (vi) to compare costs with industry standards, benchmarks, or other similar projects (vii) to identify opportunities for cost reduction or optimization without compromising environmental or social benefits, (viii) to communicate costs and benefits to stakeholders, ensuring transparency and accountability, (ix) to identify and mitigate potential costs related risks associated with different approaches, (x) to ensure that the chosen approach is sustainable in the long term considering both environmental and financial aspects. The comparative cost analysis of biomining and biocapping for legacy waste management reveals (i) biomining is more cost effective approach with a total cost of Rs. 260 crores compared to biocapping which costs Rs. 115 Crores including the 5 years operation and maintenance cost (ii) Biomining offers significant saving of Rs. 1800 Crores due to the recovery of valuable resources and reduced landfill costs, along with the cost of land recovered after biomining (iii) biocapping, while more expensive, provides a higher level of environmental protection & safety.