Development of Simulation Model for Leachate Migration near Vamanjoor Landfill and Treatment of Leachate by Nanoparticles

Abstract

The impact of leachate from landfill on groundwater has paid a lot of global attention because of its devastating environmental significance. The outputs from landfill induce heavy impacts or risks to the environment forcing the concerned authorities to impose more strict constraints and hence leachate is to be treated before it migrates to the neighboring environment. The Mangaluru City Corporation is collecting the waste on a daily basis and dumping it into a landfill at Vamanjoor located nearly 8.5 km from city centre. The landfill has got a bottom liner, but the drainage to collect leachate is not fully functional. Hence all the untreated leachate formed at the bottom, finds its trails into the neighbouring environment polluting the underlying aquifer. The water sample from observation wells were analysed and results shows that the wells located in 1 km around the landfill are contaminated with the landfill as point source from where contaminants are continuously injected. The leachate collected from landfill was analyzed in the laboratory for various physico-chemical parameters and were compared to the Standards of disposal for Indian standards for surface water IS 2296-1982. It showed that most of the parameters exceeded specified standard for the disposal of waste. Since the composition of the on-site leachate changes every day, in order to maintain repeatable composition, synthetic leachate was prepared in the laboratory. The nano iron was synthesized in the laboratory and characterized using Scanning Electron Microscope. The removal efficiency of chemical oxygen demand (COD) from synthetic leachate using nano iron was studied. For analyzing significant factors which favors the reaction such as pH, initial concentration, optimum concentration of adsorbent to be added, batch experiments were conducted using nano iron with and without starch coating. Batch experiments proved that pH of solution was an important parameter while kinetics coefficients were directly related to pH with correlation coefficients R2> 0.90. The nano iron dosage of 2 mg/l enhances removal efficiency of COD beyond that dosage the effluent will have traces of iron beyond the limit which is undesirable. Based on the removal efficiency which is around 60%, optimum conditions were adopted for continuous fixed-bed study. In a perspex column the nano iron coated with starch is sandwiched between ii untreated natural lateritic soil and the synthetic leachate was allowed to pass through it. The removal efficiency was obtained by comparing COD of influent and COD of effluent. A comparison of batch and column reactor has been done where continuous fixed-bed column was found to be more effective in removal of COD with removal efficiency of 68% in the remediation of leachate which may be due to the adsorption by laterite soil. Evaluation of Freundlich, Langmuir and D–R isotherm models were done. The kinetics of the experiments shows that it follows pseudo first order reaction kinetics. Because of its high removal efficiency, nano iron coated with starch has been taken as an effective remedial agent in treatment of leachate. As it showed better removal efficiency during continuous fixed-bed column studies, it can be used as adsorbent in permeable reactive barriers. Permanent reactive barriers are specially designed reactive zone which extends beneath water table which intercepts and degrade the contaminants in groundwater. The current study focuses on determination of extent of groundwater contamination on a typical tropical coastal aquifer due to a landfill located at Vamanjoor in Dakshina Kannada district, India. MODFLOW which is a standard and popular flow model was used to simulate groundwater flow and MT3DMS was used for simulating contaminant transport because of its ability to model various complexes such as advection, dispersion and chemical reaction involved in the solute transport. The aquifer considered is a shallow, unconfined one with laterite soil which gets good rains during monsoon and will be dry during rest of the year. The adsorption by laterite soil has been considered. The specific yield and transmissivity were estimated to be 7.85% and 213 m2/day respectively. After calibrating successfully with Nash–Sutcliffe efficiency 0.8, horizontal hydraulic conductivity was set as 7m/day. Validation of model was then done with the field data and is applied for forecasting the spread of contaminant for anticipated future scenarios. The results show that in spite of retardation offered by lateritic soil, contaminant trail is expanding with a velocity of 0.15 m/day in downstream direction. The solute transport model MT3DMS was successfully applied to simulate the contaminant transport of the study area. Since MT3DMS model involves the model structure involved in MODFLOW, the model domain was not altered. The model was iii calibrated and validated with reasonable precision (correlation coefficient R2> 0.7) which shows that the model performance is good. The simulated results show that the contaminant has spread for a distance of 1 km radius around the landfill which is in accordance with the actual value of the water quality analysis of observation wells. The model after calibration and validation is applied for the evaluation of general regional impact on the groundwater system for future scenarios. The study revealed that the contamination has spread for a distance of nearly 1 km from the landfill and plume is expanding at a rate of 0.15 m /day. By 15 years the plume will reach a distance of 1.8 km from the landfill. If permanent reactive barrier is installed the expansion of plume can prevented and the pollutant at the observation well located at 1 km from landfill can be reduced less than 400 mg /l. Hence installation of permeable reactive barrier with nano iron can be taken as a remedial alternative in order to control groundwater pollution due to landfill leachate.