Stochastic modelling of landfill processes incorporating waste heterogeneity and data uncertainty

A landfill is a very complex heterogeneous environment and as such it presents many modelling challenges. Attempts to develop models that reproduce these complexities generally involve the use of large numbers of spatially dependent parameters that cannot be properly characterised in the face of data uncertainty. An alternative method is presented, which couples a simplified microbial degradation model with a stochastic hydrological and contaminant transport model. This provides a framework for incorporating the complex effects of spatial heterogeneity within the landfill in a simplified manner, along with other key variables. A methodology for handling data uncertainty is also integrated into the model structure. Illustrative examples of the model's output are presented to demonstrate effects of data uncertainty on leachate composition and gas volume prediction.     

A multi-component two-phase flow algorithm for use in landfill processes modelling

This paper describes the finite difference algorithm that has been developed for the flow sub-model of the University of Southampton landfill degradation and transport model LDAT. The liquid and gas phase flow components are first decoupled from the solid phase of the full multi-phase, multi-component landfill process constitutive equations and are then rearranged into a format that can be applied as a calculation procedure within the framework of a three dimensional array of finite difference rectangular elements.The algorithm contains a source term which accommodates the non-flow landfill processes of degradation, gas solubility, and leachate chemical equilibrium, sub-models that have been described in White and Beaven (2013).The paper includes an illustration of the application of the flow sub-model in the context of the leachate recirculation tests carried out at the Beddington landfill project. This illustration demonstrates the ability of the sub-model to track movement in the gas phase as well as the liquid phase, and to simulate multi-directional flow patterns that are different in each of the phases.     

Evaluating effects of wind-induced pressure fluctuations on soil-atmosphere gas exchange at a landfill using stochastic modelling.

The impact of wind turbulence-induced pressure fluctuations at the soil surface on landfill gas transport and emissions to the atmosphere at an old Danish landfill site was investigated using stochastic modelling combined with soil property and gas transport data measured at the site. The impacts of soil physical properties (including air permeability and volumetric water content) and wind-induced pressure fluctuation properties (amplitude and temporal correlation) on landfill gas emissions to the atmosphere were evaluated. Soil-air permeability and pressure fluctuation amplitude were found to be the most important parameters. Wind-induced gas emissions were further compared with gas emissions caused by diffusion and by long-term pressure variations (due to passing weather systems). Here diffusion and wind-induced gas transport were found to be equally important with wind-induced gas transport becoming the most important at lower soil-air contents.     

Compartment model of aerobic and anaerobic biodegradation in a municipal solid waste landfill

The mathematical formulations in a one-dimensional compartment model of the biodegradation of organic landfill components are described. The model is designed to switch between anaerobic and aerobic conditions, depending on the local oxygen concentration. The model also includes the effect of environmental factors, such as moisture content, pH, and temperature, on reaction rates. The model includes not only biodegradation processes for carbon compounds (acetate, CO2, CH4), but also for nitrogen compounds involved in nitrification and denitrification due to their significance in landfills. Two example runs to simulate anaerobic and aerobic waste were conducted for a single landfill unit cell by changing the organic content and diffusion coefficient.     

Estimation of biogas produced by the landfill of Palermo, applying a Gaussian model

In this work, a procedure is suggested to assess the rate of biogas emitted by the Bellolampo landfill (Palermo, Italy), starting from the data acquired by two of the stations for monitoring meteorological parameters and polluting gases. The data used refer to the period November 2005-July 2006. The methane concentration, measured in the CEP suburb of Palermo, has been analysed together with the meteorological data collected by the station situated inside the landfill area. In the present study, the methane has been chosen as a tracer of the atmospheric pollutants produced by the dump. The data used for assessing the biogas emission refer to night time periods characterized by weak wind blowing from the hill toward the city. The methane rate emitted by the Bellolampo dump has been evaluated using a Gaussian model and considering the landfill both as a single point source and as a multiple point one. The comparison of the results shows that for a first approximation it is sufficient to consider the landfill of Palermo as a single point source. Starting from the monthly percentage composition of the biogas, estimated for the study period, the rate of biogas produced by the dump was evaluated. The total biogas produced by the landfill, obtained as the sum of the emitted component and the recovered one, ranged from 7519.97 to 10,153.7m3/h. For the study period the average monthly estimations of biogas emissions into the atmosphere amount to about 60% of the total biogas produced by the landfill, a little higher than the one estimated by the company responsible for the biogas recovery plant at the landfill.     

Leachate recirculation in a landfill: some insights obtained from the development of a simple 1-D model

The re-introduction of leachate back into the waste can play an important part in landfill management. It can encourage biodegradation by raising the water content and transporting bacteria, nutrients and waste products. It also enables leachate to be stored within the body of the landfill, for example to help minimise temporal variations in the load on a leachate treatment plant. It is helpful for a landfill operator to be able to estimate the rate at which the landfill can accept leachate (the maximum infiltration or injection rate), the storage capacity of the landfill and the leachate retention time. This paper discusses some of the insights obtained from the development and application of a simple conceptual model of leachate recirculation that can be used to estimate key parameter values on the basis of the hydraulic properties of the waste. The model is described, partly validated against a more rigorous numerical analysis, and then used to interpret data obtained from field tests on a real site. The shortcomings of the model in its current form are discussed, and suggestions are made as to how these might be addressed in the context of developing the model as a design tool.     

Assessment of performance of solid waste management contractors: a simple techno-social model and its application

Despite being in operation for more than 7 years now, privatised solid waste management (SWM) service in Tanzania has not been formally assessed. This is the premise for the techno-social performance assessment model for SWM contractors, which is presented in this paper. This paper outlines the background of SWM privatisation in Dar es Salaam City in addition to describing and demonstrating the application of the assessment model. The model has three components: service beneficiaries' assessment sub-model, service area technical assessment sub-model, and contractors' attributes sub-model. The model can be used to assess the performance of SWM contractors and in so doing provide data for assessing SWM privatisation as a whole. In the application of the model presented in this paper scores for 5 assessed contractors are in the range 24-65%. The contractor who scored highest is also the most experienced and also the best equipped. Nevertheless, all contractors scored poorly with the respect to their ability and attributes in SWM mainly because most of them are new to the solid waste management field.     

Quantification of landfill emissions to air: a case study of the Ano Liosia landfill site in the greater Athens area.

Fugitive pollutant emissions from municipal solid waste landfills have the potential to cause annoyance and health impacts in the surrounding residential areas. The overall objective of this research was to perform an assessment of fugitive pollutant emissions and a dispersion analysis downwind of a specific landfill site. The study was performed at the closed Ano Liosia landfill site which is located in the greater Athens area. The human exposure from priority to health-risk pollutants emitted from landfill, such as vinyl chloride and benzene, was estimated by the landfill gas emission LandGEM 2.01 software combined with the atmospheric long-term dispersion model ISC3-LT. The emission and meteorological conditions under which the models were applied referred to the worst-case scenario. This scenario was used for the evaluation of the maximum human exposure assessed beyond the Ano Liosia landfill towards the residential areas. The above scenario provides the minimum downwind distance of the health-risk zone which is calculated to be equal to 1.5 km from the landfill. Within this distance the assessed air pollutant concentration for several air pollutants was significantly above the World Health Organization reference lifetime exposure health criteria. Finally, the applied methodology was used in the Ano Liosia landfill, where atmospheric concentrations of pollutants measured in the field were compared with model predictions.     

Assessing the use of poplar tree systems as a landfill evapotranspiration barrier with the SHAW model.

The use of poplar tree systems (PTS) as evapotranspiration barriers on decommissioned landfills is gaining attention as an option for leachate management. This study involved field-testing the Simultaneous Heat and Water (SHAW) model for its ability to reliably estimate poplar transpiration, volumetric soil water content, and soil temperature at a landfill located in southern Ontario, Canada. The model was then used to estimate deep drainage and to ascertain the influence of a young PTS on the soil water balance of the landfill cover. The SHAW model tended to underestimate poplar transpiration [mean difference (MD) ranged from 0.33 to 3.55 mm on a daily total basis] and overestimate volumetric soil water content by up to 0.10 m3 m(-3). The model estimated soil temperature very well, particularly in the upper 1 m of the landfill cover (MD ranged from -0.1 to 1.6 x degrees C in this layer). The SHAW model simulations showed that deep drainage decreased appreciably with the presence of a young PTS largely through increased interception of rainfall, and that PTS have a good potential to act as effective evapotranspiration barriers in northern temperate climate zones.     

An attempt to perform water balance in a Brazilian municipal solid waste landfill

This paper presents an attempt to model the water balance in the metropolitan center landfill (MCL) in Salvador, Brazil. Aspects such as the municipal solid waste (MSW) initial water content, mass loss due to decomposition, MSW liquid expelling due to compression and those related to weather conditions, such as the amount of rainfall and evaporation are considered. Superficial flow and infiltration were modeled considering the waste and the hydraulic characteristics (permeability and soil-water retention curves) of the cover layer and simplified uni-dimensional empirical models. In order to validate the modeling procedure, data from one cell at the landfill were used. Monthly waste entry, volume of collected leachate and leachate level inside the cell were monitored. Water balance equations and the compressibility of the MSW were used to calculate the amount of leachate stored in the cell and the corresponding leachate level. Measured and calculated values of the leachate level inside the cell were similar and the model was able to capture the main trends of the water balance behavior during the cell operational period.     

Investigations on enhanced in situ bioxidation of methane from landfill gas (LFG) in a lab-scale model

The performance of an exogenous bacterium, Methylobacterium extorquens, in inducing bioxidation of methane from landfill gas (LFG) was assessed in a laboratory scale bioreactor. The study show that enhanced oxidation of methane is attained when the bacteria are introduced into the landfill soil. The maximum percentage reduction of methane fraction from LFG when the bioreactor was inoculated with the methanotrophic bacteria was 94.24 % in aerobic treatment process and 99.97 % in anaerobic process. In the experiments with only the indigenous microorganisms present in the landfill soil, the maximum percentage reduction of methane for the same flow rate of LFG was 59.67 % in aerobic treatment and 45 % in anaerobic treatment. The methane oxidation efficiency of this exogenous methanotrophic bacterium can be considered to be the optimum in anaerobic condition and at a flow rate of 0.6 L/m²/min when the removal percentage is 99.95 %. The results substantiate the use of exogenous microorganisms as potential remediation agents of methane in LFG.     

Formulation of a landfill pollution potential index to compare pollution potential of uncontrolled landfills

Generally speaking, landfilling is one of the prominent methods of waste disposal around the globe, but some under-developed and developing countries still continue to practice uncontrolled open dumping of waste. These uncontrolled landfills pose a relatively high threat to the various elements of the environment in comparison with the conventional engineered landfills that are used in many developed countries. However, some closed, un-engineered landfills do exist in developing countries. This paper presents a novel approach to compare the pollution potential of uncontrolled landfills using an index. The landfill pollution potential index (LPPI) has been developed using the Delphi technique and is an aggregation of six pollution indices that have already been developed for the quantification of different environmental elements. The LPPI is an increasing scale index, in which a higher index value indicates a higher pollution threat. The LPPI of a landfill in Delhi was calculated and the high LPPI value indicates that the respective landfill poses a significant threat to the environment. The LPPI can be used as an aid to diagnose a landfill's pollution potential relative to other landfills and therefore also to rank remediation investments.     

湿法烟气脱硫过程中石灰石离解模型及应用

石灰石—石膏法烟气脱硫工艺已在我国得到了广泛的应用,其中石灰石的活性是湿法脱硫工艺中的一个重要指标.为了深入认识石灰石湿法脱硫体系中石灰石的溶解特性,以单个石灰石颗粒为研究对象,根据双膜理论提出了石灰石离解模型.此外,分析了石灰石的掩蔽效应产生原因和发生机理,建立了掩蔽效应存在下的石灰石离解速率模型,进而找到更好的防止石灰石掩蔽的控制措施.     

Application of response surface methodology to the treatment landfill leachate in a three-dimensional electrochemical reactor

The influence of different variables on the removal of ammonia nitrogen and COD from landfill leachate was investigated in a three-dimensional electrochemical reactor. Box–Behnken statistical experiment design and the response surface methodology were used to investigate operating condition effects, such as current density, activated carbon to water ratio and the reaction time, on ammonia nitrogen removal efficiency and COD removal efficiency. The positive and negative effects of variables and the interaction between variables on ammonia nitrogen removal and COD removal were determined. The response surface methodology models were derived based on the results and the response surface plots were developed accordingly.     

Assimilation of radar measured surface current fields into a numerical model for oil spill modelling

In summer 1996, surface current fields were measured in the central Strait of Georgia using the SeaSonde, a portable shore-based HF radar system. The objective of the study was to assess the feasibility of blending SeaSonde currents with numerical model fields to fill gaps in the measured fields and reduce noise. Our eventual goal is to assimilate the blended SeaSonde fields into a three-dimensional numerical model to improve short-range current forecasts.The first part of the study involved using the blended current fields as input to a set of auto-regressive moving-average (ARMA) statistical models. The blended fields were found to give forecasts comparable in terms of RMS error with forecasts using raw SeaSonde measurements. Moreover, the blended fields were smoother and more spatially complete than the raw data. The second part of the study examined the suitability of using the SeaSonde current fields to update the surface layer of Seaconsult's C3 hydrodynamic model. A simple nudging method is presented as an economical way to drive the model surface layer using operationally gathered SeaSonde information.     

Use of a biologically active cover to reduce landfill methane emissions and enhance methane oxidation

Biologically-active landfill cover soils (biocovers) that serve to minimize CH4 emissions by optimizing CH4 oxidation were investigated at a landfill in Florida, USA. The biocover consisted of 50 cm pre-composted yard or garden waste placed over a 10-15 cm gas distribution layer (crushed glass) over a 40-100 cm interim cover. The biocover cells reduced CH4 emissions by a factor of 10 and doubled the percentage of CH4 oxidation relative to control cells. The thickness and moisture-holding capacity of the biocover resulted in increased retention times for transported CH4. This increased retention of CH4 in the biocover resulted in a higher fraction oxidized. Overall rates between the two covers were similar, about 2g CH4 m(-2)d(-1), but because CH4 entered the biocover from below at a slower rate relative to the soil cover, a higher percentage was oxidized. In part, methane oxidation controlled the net flux of CH4 to the atmosphere. The biocover cells became more effective than the control sites in oxidizing CH4 3 months after their initial placement: the mean percent oxidation for the biocover cells was 41% compared to 14% for the control cells (p<0.001). Following the initial 3 months, we also observed 29 (27%) negative CH4 fluxes and 27 (25%) zero fluxes in the biocover cells but only 6 (6%) negative fluxes and 22 (21%) zero fluxes for the control cells. Negative fluxes indicate uptake of atmospheric CH4. If the zero and negative fluxes are assumed to represent 100% oxidation, then the mean percent oxidation for the biocover and control cells, respectively, for the same period would increase to 64% and 30%.     

Contribution of 3-D time-lapse ERT to the study of leachate recirculation in a landfill

Leachate recirculation is a key process in the operation of municipal waste landfills as bioreactors. It aims at increasing the moisture content to optimise the biodegradation. Because waste is a very heterogeneous and anisotropic porous media, the geometry of the leachate plume recirculation is difficult to delineate from the surface at the scale of the bioreactor site. In this study, 3-D time-lapse electrical resistivity tomography (ERT) was used to obtain useful information for understanding leachate recirculation hydrodynamics. The ERT inversion methodology and the electrode arrays were optimised using numerical modelling simulating a 3-D leachate injection scenario. Time-lapse ERT was subsequently applied at the field scale during an experimental injection. We compared ERT images with injected volumes to evaluate the sensitivity of time-lapse ERT to delineate the plume migration. The results show that time-lapse ERT can accomplish the following: (i) accurately locate the injection plume, delineating its depth and lateral extension; (ii) be used to estimate some hydraulic properties of waste.     

Development of a basic procedure to design sorption processes

The intention of this work is to offer, within the shortest time, an appropriate sorption separation process for almost any odour problem. The development is based on the preparation and characterisation of new adsorbents, the strategy for the selection of the best adsorbent, the process engineering and the choice of a suitable regeneration procedure. In this context a new method for the characterisation of the adsorbents - the adsorption profile analysis - was developed. The classification of the adsorbents was carried out by means of a cluster analysis, which simplifies the selection of the most suitable adsorbent for a particular problem. The physical and chemical behaviour of silica-adsorbents could be tailored by silanisation of the surfaces. Methods for the determination of process engineering parameters were developed, established and used. Adsorption kinetics and isotherms were determined with a magnetic adsorption balance. In a laboratory-scale fixed bed adsorber, breakthrough curves of different support materials were investigated and compared. For the investigations of different regeneration procedures, four innovative methods were employed: microwave desorption, ultrasonic desorption, ultrasonic-water desorption and extraction with water. Of the four desorption methods examined, microwave desorption and ultrasonic-water desorption demonstrated the best results.     

National and subnational outcomes of waste management policies for 1718 municipalities in Japan: development of a bottom-up waste flow model and its application to a declining population through 2030

Journal of Material Cycles and Waste Management - Japan has been promoting 3R (reduce, reuse, and recycle) policies for several decades, but the recycling rate of the whole country has leveled off,...     

Mechanically-biologically treated municipal solid waste as a support medium for microbial methane oxidation to mitigate landfill greenhouse emissions

The residual fraction of mechanically-biologically treated municipal solid waste (MBT residual) was studied in the laboratory to evaluate its suitability and environmental compatibility as a support medium in methane (CH(4)) oxidative biocovers for the mitigation of greenhouse gas emissions from landfills. Two MBT residuals with 5 and 12 months total (aerobic) biological stabilisation times were used in the study. MBT residual appeared to be a favourable medium for CH(4) oxidation as indicated by its area-based CH(4) oxidation rates (12.2-82.3 g CH(4) m(-2) d(-1) at 2-25 degrees C; determined in CH(4)-sparged columns). The CH(4) oxidation potential (determined in batch assays) of the MBT residuals increased during the 124 d column experiment, from <1.6 to a maximum of 104 microg CH(4) g(dw)(-1) h(-1) (dw=dry weight) at 5 degrees C and 578 microg CH(4) g(dw)(-1) h(-1) at 23 degrees C. Nitrous oxide (N(2)O) production in MBT residual (<15 microg N(2)O kg(dw)(-1) d(-1) in the CH(4) oxidative columns) was at the lower end of the range of N(2)O emissions reported for landfills and non-landfill soils, and insignificant as a greenhouse gas source. Also, anaerobic gas production (25.6 l kg(dw)(-1) during 217 d) in batch assays was low, indicating biological stability of the MBT residual. The electrical conductivities (140-250 mS m(-1)), as well as the concentrations of zinc (3.0 mg l(-1)), copper (0.5 mg l(-1)), arsenic (0.3 mg l(-1)), nickel (0.1 mg l(-1)) and lead (0.1 mg l(-1)) in MBT residual eluates from a leaching test (EN-12457-4) with a liquid/solid (L/S) ratio of 10:1, suggest a potential for leachate pollutant emissions which should be considered in plans to utilise MBT residual. In conclusion, the laboratory experiments suggest that MBT residual can be utilised as a support medium for CH(4) oxidation, even at low temperatures, to mitigate greenhouse gas emissions from landfills.