Environmental impact of bio-mining of legacy waste using life cycle assessment methodology

Abstract

Urban India accounts for 62 million MT of MSW generation 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 CH4, CO2, NH3, H2S and VOCs causing from landfill degradations, persistence of heavy metals to vegetations, groundwater and surface water due to leaching of toxic leachate, emission of carcinogenic compounds, 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. From 2014 onwards, the Swachh Bharat Mission has giving importance on reclamation of landfill sites and minimization of adverse environmental impact adhering to the Solid Waste Management (SWM) Rules, 2016. Recently, Hon National Green Tribunal (NGT) mandated for implementing bio-mining and bioremediation of legacy waste throughout the Indian landfills. Bio-mining involves the excavation, waste stabilization, screening and separation of materials from landfills into various components including soil i.e., good earth or bio earth, recyclable materials, combustibles and residuals with a sustainable approach to prolong the landfill life and to remediate contamination from unlined open dumps. A precise study on the potential environmental impact of bio-mining is of utmost importance in the Indian scenario. The Bio-mining project has already started in the major dumpsite of Kolkata city i.e., Dhapa landfill. This landfill site follows open dumping for more than 30 years. The condition of Dhapa has been exhausted with a huge pollution impact. The research methodology will rely on this case study. The impact analysis study is of utmost importance because of the following reasons i.e., conservation of landfill space, reduction in landfill area, elimination of a potential contamination source, mitigation of an existing contamination source, energy recovery from excavated legacy waste, reuse and recycling of recovered materials, reduction in waste management costs, GHG emission reduction and site re-development. This study is done in two parts. In the first part, legacy waste characterization followed by its landfill degradation nature, material balancing of different bio-mining components, landfill gas and leachate generation have been studied. And in the second part, the quantitative environmental impact of bio-mining has been calculated using life cycle assessment tool.Firstly, from onsitemonthly data analysis of legacy waste, it is found that legacy waste consists of decomposable components such as Waste Soil (55.12%), Wood (0.42%), Coconut (1.01%), Animal Bone (0.66%), Textile Fabric (0.51%) and non-decomposable components such as Plastic (21.16%), Glass (1.21%), Thermocol (0.45%), Ceramic (1.55%), Gravels (9.22%), Kankar (6.61%), Mix (2.08%).During compositional analysis, the degradable matter such as food waste, wood, coconut shell, animal bone and textile fabric is assumed that the degradation pattern follows the IPCC model i.e., first-order kinetic decay rate model. Using these assumptions, the percentage transformed or degradation a portion of above-mentioned waste i.e., food waste, wood, coconut shell, animal bone and textile fabric from landfill comes 93±2%, 39±2%, 88±1%, 88±1%and 59±2% respectively consideringdecay rate constant according to the mean annual temperature (MAT) and mean annual precipitation (MAP) of the study area.The percentage transformed or average degradation of non-decomposable waste is done based on literature and from field data analysis.After taking all consideration, average physical material compositions have redistributed into six components i.e., Recyclable, Construction and Demolition waste (C & D waste), Refused-Derived-Fuel (RDF), Bio-Earth or Good Earth, Coarser Fraction and Process Rejects and material balance diagram have formed which can be used for quantity estimation of actual amount of legacy waste processing. The percentage of bio-earth obtained is around 22.484%, recyclable fraction as 3.32%, C&D waste as 18.14%, RDF as 19.747%, Coarser fraction as 19.947% and process reject is found to be 2.477%. The generated landfill gases can be reduced by around 41% in 25 years potential after implementation of bio-mining treatment. Total land area 23.5 ha can be reclaimed after bio-mining for which an estimated reduction of leachate by 68% is achievable over the bio-mining period. In the present work, the estimation of PEI of bio-mining process is done based on LCIA approach considering three impact categories i.e., global, regional and local. Weightage of different categories and sub-categories are calculated based on analytical hierarchy process (AHP). After normalizing different sub-categories respective PEI have been calculated for different bio-mining scenario. During bio-mining condition, ATP is the highest PEI contributor (38.14%) among all sub-category due to its high weightage value and relatively higher equivalency factor. PEI contribution of HTPI and TTPL are 34.65% and 12.59%. Higher value of HTPI and TTPL are due to local impact of liquid pollutants is much more than gaseous pollutant. Percentage of PEI contribution of HTPE and TTPG are 8.53% and 2.07% respectively. In sub- category acidification potential (AP), PEI is very less due to emission of PEI contributing pollutants in this sub-category is substantially lower in quantity. But, POCP has a significant impact potential (3.18%) majorly due to toluene. The impact sub-category ODP did not contribute any PEI value as no pollutant is generated to breakdown the ozone layer in this system. The PEI value of GWP is less (0.81%) in local perspective as the relative weightage value is less compared to other impact sub- category but it is very significant in global perspective. The resource is recovered in the form of land though the PEI value of RDP is not much but it has a significant positive impact in local perspective. The overall potential impact obtained from during bio-mining scenario is 0.3167 whereas PEI obtained before bio-mining as 0.39. So, the percentage reduction of impact is around 19% after one year of implementation of bio-mining operation. Though all the potential environmental impact will be minimized after completion of bio-mining operation.