CE 326 - Principles of Environmental Engineering Solid Waste Management What is Solid Waste? - all wastes arising from human and animal activities that are normally solid or semisolid and that are discarded as useless or unwanted (includes both municipal (nonhazardous) and hazardous waste) What is Solid Waste Management? - defined as the discipline associated with the control of generation, storage and transport, processing, and disposal of solid wastes - in a manner that is in accord with the best principles of public health, economics, engineering, conservation, aesthetics and other environmental considerations. The Municipal Solid Waste Problem • Estimated Total Solid Waste Disposed in 1990 • Average solid waste generated per person • In perspective, Waste generated per day = ___ million tons ≈ ____ lbs/day ≈ ____ million tons Density = ___ lbs/yd3 If placed 3 feet layer (1 yard), it will cover an area of _______ yd 2 ≈ ________ m2 ≈ _____ acres US EPA preferred hierarchy of Waste Management _____________ _______ __________ - reduction in both the quantities of waste generated and the toxic constituents in the products __________ -- use or reuse of a waste as an effective substitute for a commercial product or as an ingredient or feedstock in an industrial process ___________ - process which changes the physical, chemical and biological character of any waste so as to recover energy or material resources _________ - discharge, deposit, dumping and placing of waste on any land or water ____________ Characteristics of Municipal Solid Wastes Classified in several ways • _________________ • _________________ • _________________ Point of Origin or Sources • __________ • __________ • __________ • __________ • _____________ • _____________ • _____________ • _____________ Nature of Materials • Organic • Combustible • Inorganic • Non combustible Kind of Material Domestic • Garbage • Rubbish • White Goods • Ashes - waste from domestic processing of food, originates from kitchens and restaurants, decomposes rapidly - both combustible and noncombustible wastes, does not include garbage, eg., paper, wood, rags - large and bulky appliances. eg., refrigerators, washing machine - residue from fires used for cooking and heating Average Composition of Municpal Solid Waste (Residential) 1970 • Paper 37.4 • Food Waste 20.0 • Yard Waste 13.9 • Glass 9.0 • Metal 8.4 • Wood 3.1 • Leather 1.2 • Textiles 2.2 1990 43.4 14.0 12.3 9.5 8.6 2.0 1.2 2.7 • Plastics • Miscellaneous Composition is dependent on: • Season • location • economic conditions 1.4 3.4 3.9 2.4 Simplified Diagram of Various Components in Solid Waste Management Waste Generation Waste handling, separation, storage and processing at the source • shredding, baling, etc. • separation for recycling Collection Separation, Processing and Transformation of Solid Waste • recycling • resource recovery plants • incinerators • composting Transfer and Transport Disposal • landfills Disposal and Processing Methods - landfills – disposal of municipal waste on land engineered to contain the waste - incinerators – controlled high-temperature destruction of primarily organic compounds to carbon dioxide and water, applicable for waste with a heat content greater than 2,500 BTU/lb - less than this heat content, auxiliary fuel is needed - recycling – return of useful materials through individual or centralized efforts - Resource recovery plants – recovery of useful materials using centralized and mechanized equipment - Composting – conversion of organic waste such as food and garden wastes into a stabilized product that can be used as fill materials or as a fertilizer Federal Regulations for Municipal Landfills • principal federal requirements are contained in Resource Conservation and Recovery Act (RCRA) Subtitle D and 40 Code of Federal Regulations (CFR) 258 - Criteria for Classification of Solid Waste Disposal Facilities and Practices. Definitions of different parts of a Municipal landfill • Landfill Liners - manufactured and natural materials that lined the bottom and below grade sides of a landfill to prevent migration of landfill leachate and gases. • Leachate - liquid that collects at the bottom of a landfill - result from percolation or precipitation, water initially contained in the waste and infiltrating groundwater • Leachate collection and removal system (LCRS) - drainage system to allow easy movement and removal of landfill leachate • Cell - volume of material placed in a landfill during one operating period usually one day • Daily cover - 6 to 12 ins of native soil or alternative materials such as compost that are applied to the working faces of the landfill at the end of each operating period • Lift - a complete layer of cells over the active area of the landfill • Final Lift - last layer of cells plus the landfill final cover • Final cover - multiple layers of soil and/or geomembrane materials designed to enhance drainage, minimize percolation through the landfill and support surface vegetation. • Postclosure - refers to activities associated with the long-term monitoring and maintenance of completed landfill - typically 30 years. US EPA Minimum Requirements for Municipal Landfill Bottom Liner should consists of a composite liner and a leachate collection system (LCRS) • leachate collection system must be designed to maintain < 30-cm depth of leachate over the liner • Composite - consists of two components - upper component - a minimum of 30 mil (0.076 cm) flexible membrane liner - lower component - at least a two- foot layer of compacted soil with an hydraulic conductivity of 1 x 10 -7 cm/sec Final Cover must have a permeability less than or equal to the permeability of any bottom liner system or natural subsoils or a coefficient of permeability (hydraulic conductivity) no greater than 1 x 10-5 cm/sec which ever is less a minimum of 18 inches of earthen material and a minimum of 6 inches of earthen material that is capable of sustaining plant growth and minimizing erosion Top Layer Drainage Layer Final Cover Vent Layer Waste Daily Cover Waste LCRS FM L Soil Liner Subsurface Soil What is hydraulic conductivity? Flow rate (Q) Q v Area (A) pressure gradient (∆ H/L) = K A dH/dL = K dH/dL Types of Soil Gravel Fine sand silt clay Example (similar to example 9-5) Darcy's Law (see page 88 -equation 2-11) where K is the hydraulic conductivity (m/s) Hydraulic conductivity (cm/s) 3.0 to 3 x 10-2 2 x 10-2 to 2 x 10-5 2 x 10-3 to 1 x 10-7 2 x 10-7 to 1 x 10-9 How long will it take the leachate to migrate through a 2 ft. clay liner with a hydraulic conductivity of 1 x 10 -7 cm/sec if the depth of the leachate is 30 cm above the soil liner?