Solid Waste Management: Key Concepts and Practices

Posted on Feb 19, 2025 in Business Administration and Innovation Management

Q1 What is the purpose of a solid waste management plan for a county? Name the elements that should be considered in a SWM plan.

Solid Waste Management: Combination of best engineering, scientific, environmental, public health, resource conservation, and economic principles associated with control of solid wastes from point of generation to disposal to protect and minimize any adverse effects on human health and the environment and conserves resources.

Elements:

1. Waste generation
2. Waste handling and separation, storage, and processing at the source
3. Collection
4. Separation, processing, and transformation (at the Materials Recovery Facility – MRF)
5. Transfer and transport (at the Transfer Station)
6. Disposal

Q2 Define the integrated solid waste management plan. What is the hierarchy of ISWM

Integrated Solid Waste Management (ISWM) refers to the selection and application of a combination of suitable techniques, technologies, and management programs to achieve specific waste management objectives and goals. It emphasizes a comprehensive approach to managing municipal solid waste (MSW), using various methods to reduce or manage waste effectively based on a community’s specific needs.

Hierarchy of ISWM:

1. Source Reduction (Waste Prevention): This is the most preferred method, aiming to reduce the amount and toxicity of waste before it is generated. Practices include altering product design, manufacturing processes, or usage to minimize waste generation. Examples: Grass-cycling, backyard composting, two-sided paper printing, and reducing transport packaging.
2. Recycling and Composting:

• Recycling involves collecting, separating, and processing materials for reuse, remanufacturing, or reprocessing. It reduces demand for virgin materials and lessens the need for disposal.
• Composting decomposes organic waste (e.g., food scraps, yard trimmings) with microorganisms, creating a nutrient-rich soil additive.

Both recycling and composting divert waste from landfills and incinerators and provide significant environmental benefits like saving energy, reducing greenhouse gas emissions, and conserving natural resources.

Combustion with Energy Recovery: Waste-to-energy (WTE) facilities combust MSW at high temperatures, converting waste into energy while reducing the waste’s volume and weight. These facilities recover energy in the form of electricity or heat, but this method is less preferred than recycling because of the pollutants generated, and the energy required. Disposal (Landfilling and Incineration without Energy Recovery):

• Landfilling is the least preferred option in the hierarchy, used only when other methods are not feasible. MSW landfills are engineered to manage waste safely by using liners and monitoring systems to protect the environment.
• Incineration without energy recovery is a method of simply burning waste without generating usable energy.

Q4 What is the difference between proximate analysis and the ultimate analysis of MSW?

Proximate analysis focuses on physical properties (moisture, volatile matter, fixed carbon, ash) and is simpler. Proximate analysis focuses on determining the physical characteristics and basic components of MSW through relatively simple measurements. The primary components analyzed are:

1. Moisture Content: The percentage of water present in the waste.
2. Volatile Matter: The fraction of the waste that will vaporize or burn off when heated, excluding moisture.
3. Fixed Carbon: The portion of the waste that remains after volatile matter has been removed, which can undergo further combustion.
4. Ash Content: The non-combustible residue left after burning, including minerals and inorganic materials.

Ultimate analysis provides a detailed chemical composition (carbon, hydrogen, oxygen, nitrogen, sulfur) and is more complex. Ultimate analysis provides a more detailed breakdown of the chemical composition of MSW. It measures the elemental composition, including:

1. Carbon (C)
2. Hydrogen (H)
3. Oxygen (O)
4. Nitrogen (N)
5. Sulfur (S)
6. Chlorine (Cl) (sometimes included)

Q5 List 5 reasons to justify the prohibition on the disposal of discarded tires and or truck of yard waste in landfills. (same to the HW)

1. Space Conservation: Tires and yard waste take up significant landfill space.
2. Reduce Environmental Impact: Tires release methane and can damage landfill structures, while yard waste generates greenhouse gases.
3. Resource Recovery: Tires can be recycled, and yard waste can be composted.
4. Fire Hazard: Tires are highly flammable and difficult to extinguish if ignited.
5. Prevent Leachate Contamination: Decomposing yard waste can create harmful leachate, which may pollute groundwater.

Q6 Regarding remedial actions at inactive waste disposal sites, what are the following terms (short answers)

Preliminary Assessment (PA): An initial investigation of a waste site to determine if hazardous substances are present and whether further investigation or cleanup is needed.

Q7 What is the difference between compaction and consolidation of MSW?

Compaction vs. Consolidation

Compaction: The process of densification, i.e., reducing the volume by filling in the void spaces short-time duration process that requires an external energy input

Consolidation: long term, slow process in which the volume change is caused by the expulsion of pore water at the bottom of landfills

Compaction: It is the process of reducing the volume of waste by applying external force or energy to densify the material, primarily by filling void spaces. Compaction is a short-term process that requires immediate external energy input, such as heavy machinery compressing waste layers during landfill operations.

Consolidation: It is a long-term, slow process where the volume change in waste occurs due to the gradual expulsion of pore water, especially at the bottom layers of a landfill. Consolidation happens naturally over time as the weight of the waste increases due to overlying layers, causing water to be squeezed out and leading to a gradual decrease in volume.

Q8 Name and describe 2 of important legislation which have had significant direct impacts on SWM Name three federal and 4 state/local agencies with their impacts on SWM.

1. Resource Conservation and Recovery Act (RCRA) – 1976: This law regulates the management of both hazardous and non-hazardous solid waste. It established the “cradle-to-grave” system, ensuring hazardous waste is tracked from its generation to its ultimate disposal. It also set standards for the operation of landfills and treatment facilities and promoted waste reduction through recycling and resource recovery.
2. Clean Water Act (CWA) – 1977: The CWA has a significant impact on SWM, particularly through its regulations on discharges to water bodies. It set standards for wastewater management, including pre-treatment requirements for waste that might be discharged into the water system, thereby influencing how solid waste facilities manage their liquid waste and leachate.

Three Federal Agencies and their impacts on SWM:

1. U.S. Environmental Protection Agency (EPA): Develops regulations, standards, and guidelines for solid and hazardous waste management. Oversees compliance with federal SWM regulations, such as RCRA, and enforces environmental laws to ensure public health and environmental protection.
2. U.S. Department of Transportation (DOT): Regulates the transportation of hazardous waste, including packaging, labeling, and handling, to ensure safe transit and reduce risks associated with waste spills or accidents.
3. U.S. Geological Survey (USGS): Provides crucial information on landfill siting by assessing geological conditions, such as fault areas and seismic impacts, to minimize environmental risks associated with waste disposal.

4 state/local agencies:

1. State Department of the Environment (e.g., Maryland Department of the Environment): Implements state-specific regulations on solid and hazardous waste management. Issues permits for landfills and waste treatment facilities, ensuring they meet environmental and public health standards.
2. State Geological Survey: Provides data on the geological characteristics of potential landfill sites, helping ensure that landfills are located in areas that minimize environmental risk.
3. Local Health Agencies: Monitor waste management activities to ensure public health is protected. They may enforce local ordinances related to waste collection, recycling, and disposal.
4. Local Zoning and Land-use Commissions: Regulate the siting of solid waste facilities through local land-use planning. These agencies ensure that proposed facilities are compatible with the community’s zoning regulations and land-use goals.

Q9 A new municipal solid waste landfill has just been opened in a county near your county. The tipping fee at this new landfill is 40% lower than elsewhere, including those landfills currently in your county. The landfills in your county only have less than 5 yrs of active life before closure and final capping begins. The county executive asks for your recommendations on managing the municipal solid waste generated in your county considering the situation, summarize your recommendations.

Short-term Strategy:

1. Utilize the New Landfill
   • Cost savings: Take advantage of the lower tipping fees at the newly opened landfill. This will provide immediate financial relief and reduce the operational burden on the county’s existing landfills.
   • Extend lifespan: Diverting waste to the new landfill will help extend the operational life of the county’s landfills, delaying the costly closure and post-closure processes.
2. Long-term Planning: Closure and Post-closure Strategy
   • Develop a comprehensive closure plan: Ensure that a detailed closure plan is in place for existing landfills, covering final cover design, gas and leachate management, and long-term monitoring as required by federal and state regulations.
   • Plan for final use: Consider potential post-closure uses for the existing landfills, such as converting them into public parks or renewable energy sites (e.g., solar fields).
3. Waste Reduction and Diversion Initiatives
4. Encourage waste reduction programs: Promote waste minimization, recycling, and composting initiatives to reduce the volume of waste sent to landfills, thereby extending the life of existing and new facilities.
5. Explore waste-to-energy options: Consider investing in waste-to-energy technologies to further reduce landfill dependence and recover energy from the waste stream.
6. Contractual and Regulatory Considerations
   • Renegotiate contracts: If applicable, renegotiate contracts with waste haulers to adjust for the lower tipping fees and ensure that waste is diverted to the most cost-effective disposal option.
   • Regulatory compliance: Ensure that all landfill operations, including closure and post-closure care, comply with federal, state, and local environmental regulations.

Q10 The following pollutants are generated by modern MSW combustion facilities, indicate the post combustion control tech/process for each

• Dioxins: dry and wet scrubbers.
• Mercury: Removed effectively by dry scrubbers.
• SO2: Neutralized and removed using Wet Scrubbers: Pulverized limestone (CaCO3) is mixed with water to create a slurry, sprayed into flue gases
• NOx:
  1. Selective Catalytic Reduction (SCR): This involves injecting ammonia into the flue gas, which then passes over a catalyst bed (made of copper, iron, nickel, or cobalt). This process occurs at a lower temperature than the combustion chamber.
  2. Selective Non-Catalytic Reduction (SNCR): Ammonia gas is injected directly into the furnace to reduce NOx emissions.

Q11 Indicate the EPA monitoring requirements (CEMS or annual stack test, no numbers) for each and What does CEMS stand for:

• CO emissions limit:
  1. Continuous monitoring
  2. 100 ppmv, one-hour rolling average, corrected to 7% O2 in the flue gas (on a dry basis)
  3. Total hydrocarbons (THC) limit of 20 ppmv may be used instead, particularly in batch-fed rotary kiln incinerators
• PM Emission Limits:
  1. Annual stack test
  2. 180 mg/dscm (mg/dry standard cubic meter)
  3. “Corrected for the amount of oxygen in the stack gas to 7% oxygen (volume, dry basis)”
  4. STP = 1 atm, 60°F (gas industry)
• HCl Emission Standard:
  1. Solid Waste Inc: 25 ppmv or 95% removal
  2. Hazardous Waste Inc: 4 lb/h or 99% removal
  3. Annual stack test.

Continuous Emissions Monitoring System: Instruments that analyze flue gases in the stack continuously for the above critical parameters as well as SO2, NOx, and opacity

Q12 Describe a fluidized bed incinerator and its advantages.

Fluidized Bed Incinerator (FBI): A fluidized bed incinerator utilizes a moving bed of inert particles, such as sand, in the bottom section of the combustor to improve heat transfer to the waste streams and water tubes via conduction. The bed is kept in motion by a stream of air, which also serves as the combustion air. It operates at a lower temperature than other types of incinerators and is more energy-efficient. It handles gases, liquids, sludges, and granulated solids but cannot handle containerized wastes directly, making it less versatile than other types like rotary kiln incinerators.

Advantages:

• Energy Efficiency: Operates at a lower temperature, requiring less energy for combustion.
• Improved Heat Transfer: The moving bed of inert particles enhances heat transfer, improving combustion efficiency.
• Versatile Waste Types: Can handle a variety of wastes, including gases, liquids, sludges, and granulated solids.
• Better Temperature Control: Uniform airflow distribution and bed temperature help maintain stable combustion conditions.

Q13 Describe and compare the advantages and disadvantages of the 2 major categories of MSW combustion systems (mass burn and RDF)

Mass Burn Incinerators:

Advantages:

• Simplicity: Handles unprocessed MSW, which requires minimal pre-combustion preparation.
• Versatility: Can incinerate large, bulky items and even potentially hazardous materials like containerized gas.
• Lower preprocessing costs: No need for extensive waste sorting or shredding before combustion, reducing handling costs.

Disadvantages:

• Lower efficiency: Due to the variability in waste composition, the combustion process can be less efficient, leading to inconsistent heating values and higher emissions.
• Higher ash generation: Produces more ash due to the combustion of non-combustible materials within unprocessed MSW.
• Larger space requirement: Typically requires more space due to handling bulkier items and the need for ash management.

Refuse-Derived Fuel (RDF) Incinerators:

Advantages:

• Higher efficiency: Produces a more uniform and predictable fuel (RDF) with consistent heating values, leading to better combustion control.
• Lower emissions: Improved performance of air pollution control systems (APCS) and the ability to remove non-combustible materials before combustion minimizes air emissions.
• Smaller system size: RDF systems are physically smaller due to the use of processed fuel and more controlled combustion conditions.
• Minimizes ash generation: Since non-combustible materials are removed before incineration, RDF generates less ash compared to mass burn systems.

Disadvantages:

• Higher preprocessing costs: Requires extensive preprocessing, including shredding, sorting, and separation of materials, which adds to the overall system cost.
• Less versatility: Cannot handle bulky or containerized wastes directly, limiting the types of MSW it can process.
• Reliance on consistent waste streams: RDF systems depend on a steady, homogeneous waste supply for optimal operation, which may not always be feasible in some areas.

Comparison Summary:

Mass burn is simpler and more versatile but less efficient with higher emissions and ash generation. RDF is more efficient, produces fewer emissions and less ash, but requires more preprocessing and a steady waste stream, making it more costly upfront.

Q14 Describe the difference between the following thermal processes of MSW:

• Stoichiometric Combustion: Exact amount of oxygen for complete combustion, producing CO₂, H₂O, and no free oxygen. Perfect combustion is not achievable in practice.
• Pyrolysis: Thermal decomposition of waste in the absence of oxygen. Produces gas, liquid (tar/oil), and char (solid carbon).
• Gasification: Partial combustion of waste with less oxygen than stoichiometric conditions, producing a combustible gas rich in CO, H₂, and CH₄.
• Excess Air Combustion: Uses more oxygen than required. Improves mixing and temperature control but increases fuel consumption and emissions.

Q15 List and describe the purpose of 3 types of processing methods commonly used in Material Recovery Facilities.

• Trommel Screens: Trommel screens are used to separate oversized objects, including metal cans, textiles, and plastic containers, from the waste stream. The goal is to remove materials that are not suitable for further processing or combustion.
• Granulators: Granulators are used to reduce the size of the material after initial screening. By cutting down the size of materials, they help prepare the waste for further separation and classification.
• Air Classifiers: Air classifiers are used to separate the lighter fraction of materials, like flock RDF (fRDF), from heavier, non-combustible residues. This process is essential to ensure that the combustible fraction is isolated for further processing.

Q16 List 4 of the engineering considerations involved in the development and implementation of material recovery facilities.

1. Screening and Classification: Machinery such as trommel screens and air classifiers are used to separate oversized and non-combustible materials from the waste stream, which is a key step in ensuring efficient sorting and recovery.
2. Moisture Reduction: The implementation of driers, such as rotary cascade driers, helps reduce the moisture content of materials like Refuse Derived Fuel (RDF). Lower moisture content improves the efficiency of further processing
3. Densification: pelletizers are employed to increase the bulk density of materials, making them easier to handle, store, and transport.
4. Cooling and Storage: After densification, coolers (e.g., perforated belt coolers) are used to harden materials, which allows for easier storage and transportation without compromising material integrity
5. Material Flow and Layout Design: Purpose: To ensure efficient movement of materials through the facility. Engineers must design the layout of conveyors, sorting lines, and storage areas to maximize space and optimize material handling, reducing bottlenecks and ensuring smooth processing.
6. Equipment Selection: Purpose: Choosing the appropriate machinery (e.g., screens, magnetic separators, air classifiers) for the specific types of materials being processed. The selection is based on the types of waste streams, the desired recovery rates, and the facility’s operational goals.
7. Environmental Control: Purpose: To minimize environmental impact, engineers must design systems to manage dust, noise, odors, and emissions. This includes installing air filtration systems, noise dampening equipment, and dust suppression technologies.
8. Safety: Purpose: Ensuring the facility is safe for workers and complies with health and safety regulations. This includes designing for proper lighting, ventilation, and worker access to machinery, as well as implementing ergonomic workstations to reduce strain on manual laborers.

Q3 Draw a simple diagram showing the interrelationship between the functional elements in the solid waste management system.