jr Department of Water Resources Engineering Lund Institute of Technology, Lund University, Sweden GENERATION OF LEACHATE AND THE FLOW REGIME IN LANDFILLS by David Bendz Report No 1023 APR report 191 Lund, Sweden, 1998 DISCLAIMER Portions of this document may be illegible electronic image products. Images are produced from the best available original document. Organization Document name LUND UNIVERSITY DOCTORAL DISSERTATION Department of Water Resources Engineering Date of issue 9g.05.15 Box 118 221 00 Lund, SWEDEN CODEN: LUTVDG/TWR-1023 Authors) Sponsoring organization David BENDZ Swedish Waste Research Council (APR) Tide and subtitle GENERATION OF LEACHATE AND THE FLOW REGIME IN LANDFILLS Abstract The environmental impacts of landfills are associated mainly with the emission of leachate and biogas. Sanitary landfilling aims to stabilize the landfill in a efficient and controlled way, so that the environmental impacts are minimized. When a sanitary landfill has attained its final storage quality, it can be integrated into the environment. Both the presence and the flux of water play key roles in the stabilization process. Water redistributes chemicals, microorganisms and nutrients within the landfill. It is also needed for the first step in the anaerobic degradation process, that is, hydrolysis. In this thesis the generation of leachate and the presence and movement of water in landfilled municipal solid waste (MSW) is investigated. The precipitation-leachate discharge relationship for landfills was found to be dominated by evaporation, accumulation in the soil cover, accumulation in the solid waste and fast gravitational flow in a network of channels. The flow regime is governed by the heterogeneity of the internal geometry of the landfill, which is characterized by a discrete structure, significant horizontal stratification (resulting from the disposal procedure), structural voids, impermeable surfaces, and low capillarity. Also the boundary conditions, that is the water input pattern, has shown to be important for the flow process. Based on this, landfilled waste can be conceptualized as a dual domain medium, consisting of a channel domain and a matrix domain. The matrix flow is slow and diffusive, whereas the channel flow is assumed to be driven solely by gravity and to take place as a thin viscous film on solid surfaces. A kinematic wave model for unsaturated infiltration and internal drainage in the channel domain is presented. The model employs a two-parameter power expression as macroscopic flux law. Solutions were derived for the cases when water enters the channel domain laterally and when water enters from the upper end. The model parameters were determined and interpreted in terms of the internal geometry of the waste medium by fitting the model to one set of infiltration and drainage data derived from a 21 large scale laboratory experiment under transient conditions. The model was validated using another set of data from a sequence of 41 water input events and was shown to perform accurately. 61 A solute transport model was developed by coupling a simple piston flux expression and a mobile-immobile SIS conceptualization of the transport domains with the water flow model. Breakthrough curves derived from steady and transient tracer experiments where interpreted with the model. The transport process was found to be dependent on the boundary conditions. DOKUMBNTDATABLAD enl Keywords Landfill, MSW, hydrology, leachate, water, flow, transport, model Classification system and/or index terms (if any) Supplementary bibliographical information LaCgUa8e English ISSN and key title 1101-9824 ISBN Recipient's notes Number of pages 159 Price Security classification Distribution by (name and address) Department of Water Resources Engineering Box 118,221 00 Lund, SWEDEN I, die undersigned, being die copyright owner of the abstract of the above-mentioned dissertation, hereby grant to aD reference sources permission to publish and disseminate the abstract of the above-mentioned dissertation. — CvLA^yL Date GENERATION OF LEACHATE AND THE FLOW REGIME IN LANDFILLS av David Bendz AKADEMISK AVHANDLING som for avlaggande av teknisk doktorsexamen vid tekniska fakulteten vid Lunds Universitet kommer att offentligen forsvaras vid Sektionen for vag och vattenbyggnad, John Ericssons vag 1, horsal V:C, fredagen den 15 maj, kl. 10.15. DEPARTMENT OF WATER RECOURCES ENGINEERING LUND INSTITUTE OF TECHNOLOGY, LUND UNIVERSITY CODEN: LUTVDG/(T VRR-1023)/(1998) GENERATION OF LEACHATE AND THE FLOW REGIME IN LANDFILLS by David Bendz ABSTRACT The environmental impacts of landfills are associated mainly with the emission of leachate and biogas. Sanitary landfilling aims to stabilize the landfill in a efficient and controlled way, so that the environmental impacts are minimized. When a sanitary landfill has attained its final storage quality, it can be integrated into the environment. Both the presence and the flux of water play key roles in the stabilization process. Water redistributes chemicals, microorganisms and nutrients within the landfill. It is also needed for the first step in the anaerobic degradation process, that is, hydrolysis. In this thesis the generation of leachate and the presence and movement of water in landfilled municipal solid waste (MSW) is investigated. The precipitation-leachate discharge relationship for landfills was found to be dominated by evaporation, accumulation in the soil cover, accumulation in the solid waste and fast gravitational flow in a network of channels. The flow regime is governed by the heterogeneity of the internal geometry of the landfill, which is characterized by a discrete structure, significant horizontal stratification (resulting from the disposal procedure), structural voids, impermeable surfaces, and low capillarity. Also the boundary conditions, that is the water input pattern, has shown to be important for the flow process. Based on this, landfilled waste can be conceptualized as a dual domain medium, consisting of a channel domain and a matrix domain. The matrix flow is slow and diffusive, whereas the channel flow is assumed to be driven solely by gravity and to take place as a thin viscous film on solid surfaces. A kinematic wave model for unsaturated infiltration and internal drainage in the channel domain is presented. The model employs a two- parameter power expression as macroscopic flux law. Solutions were derived for the cases when water enters the channel domain laterally and when water enters from the upper end. The model parameters were determined and interpreted in terms of the internal geometry of the waste medium by fitting the model to one set of infiltration and drainage data derived from a large scale laboratory experiment under transient conditions. The model was validated using another set of data from a sequence of water input events and was shown to perform accurately. A solute transport model was developed by coupling a simple piston flux expression and a mobile-immobile conceptualization of the transport domains with the water flow model. Breakthrough curves derived from steady and transient tracer experiments where interpreted with the model. The transport process was found to be dependent on the boundary conditions. CONTENTS Introduction 6 Management of municipal solid waste 6 Environmental Concern 9 Scope and Aims 12 The Landfill as a Hydrological System 13 Water Input 14 Storage and Leachate Flux 15 Flow and Transport Processes 17 Process Assumptions 17 Governing Equations 19 Applicability of the Kinematic Wave Model 21 Conclusions 22 Acknowledgments 23 References 24 This thesis is based on the following papers, which are referred to in the text by their Roman Numerals: I Bengtsson, L., Bendz, D., Hogland, W., Rosqvist, H., Akesson, M (1994) Water balance for landfills of different age, J. Hydrol., 158:203-217. II Bendz, D., Bengtsson, L. (1996) Evaporation from an active uncovered landfill, J. Hydro!., 182:143-155. III Bendz, D., Singh, V.P., Akesson, M. (1997) The accumulation of water and the generation of leachate in a young landfill., J. Hydrol., 203:1-10. IV Bendz, D., Singh, V.P., Bengtsson, L. (1997) Hydrological characteristics of landfills - implications for modeling, (Submitted) V Bendz, D., Singh, V.P., Rosqvist, H., Bengtsson, L. (1997) Kinematic wave model for water movement in municipal solid waste, Water Resour. Res. (In Press) VI Bendz, D., Singh, V.P. (1997) Solute Transport under Steady and Transient Conditions in Municipal Solid Waste. (Submitted) INTRODUCTION Management of municipal solid waste With industrialization and as the worlds population have become increasingly urbanized the production of municipal solid waste (MSW) has increased. The production of municipal solid waste in the industrialized countries varies from under 1 kg per person per year, e.g. Germany, to 2 kg per person per year in the USA according to figures given by the US Environmental Protection Agency [EPA, 1997]. MSW may be landfilled, incinerated, composted or recycled. Incineration and landfilling are the dominating waste management methods. Today the proportions of MSW which are landfilled and incinerated vary greatly between industrialized countries [Carra and Cossu, 1990]. Switzerland, where 80% of the MSW is incinerated and 20% is landfilled, represents one extreme. Canada and Finland represent the other extreme, where 95% of the MSW is landfilled. The UK and the USA can also be found at this end of the scale, where 88% and 83% of the MSW is landfilled, respectively.