Waste is defined as any unwanted or discarded material that has served its intended purpose or is a byproduct of a process. Effective management is necessary to protect public health and the environment. Based on their source, composition, and regulatory requirements, these materials are categorized into four primary types.
Municipal Solid Waste
Municipal Solid Waste (MSW) is the non-hazardous waste stream generated by the public, primarily originating from households, commercial businesses, and institutions like schools and offices. This category is often referred to simply as trash or garbage. The composition of MSW is highly heterogeneous, meaning it is a mix of many different materials.
Major components include paper, plastic packaging, food waste, yard trimmings, glass, and metals. Local governments are generally responsible for the collection and disposal of this material.
Management often involves strategies to divert MSW from landfills. These strategies include mechanical sorting at recycling facilities, composting of organic matter, and incineration for energy recovery.
Industrial Waste
Industrial waste is defined as the non-hazardous materials resulting from manufacturing, processing, and production operations across various sectors. This includes byproducts of activities such as electric power generation, textile production, and food processing. The key distinction is that this waste type does not possess the harmful characteristics that would classify it as hazardous material.
This stream commonly includes process residues, non-contaminated sludges, scrap metals, excess packaging, and spent non-hazardous liquids. Because industrial waste streams are often homogenous, they are frequently managed privately.
Many facilities implement internal recycling or reuse programs to recover valuable resources or reduce disposal costs. Scrap metal and paper byproducts are commonly separated at the source and sent directly to specialized processors, allowing for more efficient resource recovery.
Hazardous Waste
Hazardous waste is the most strictly regulated category of discarded material because it poses a substantial threat to human health or the environment when improperly managed. This classification is based on specific properties, defined by four characteristics: ignitability, corrosivity, reactivity, or toxicity.
Ignitable waste can readily catch fire and sustain combustion, such as liquids with a flash point below \(140^{\circ}\text{F}\) (\(60^{\circ}\text{C}\)), like certain used solvents. Corrosive materials are highly acidic (\(\text{pH} \le 2\)) or highly basic (\(\text{pH} \ge 12.5\)), including spent battery acid.
Reactivity describes materials that are unstable, prone to violent change, or can create an explosion or release toxic gases when mixed with water. Toxicity means the waste contains harmful chemicals that can leach into groundwater at dangerous concentrations. This potential for leaching is determined through the Toxicity Characteristic Leaching Procedure (TCLP), which often identifies wastes containing heavy metals such as lead or mercury.
Construction and Demolition Waste
Construction and Demolition (C\&D) waste consists of debris generated during the construction, renovation, repair, and demolition of structures like buildings, roads, and bridges. This waste stream is notable for its substantial volume and the bulky, heavy nature of its components.
The main components of C\&D debris include concrete, asphalt, wood, gypsum wallboard, masonry, and metals. Demolition activities typically generate the vast majority of this waste, often accounting for over 90% of the total volume.
C\&D waste has a high potential for recycling and reuse, which helps conserve natural resources and landfill space. Concrete and asphalt are routinely crushed for use as aggregate in road bases or fill material. Wood scraps are often chipped for mulch or used as a fuel source.