Lecture 7: Sustainable Waste Management

Overview

Quiz Reflections: Generally found to be manageable, indicating that students performed relatively well.
Course Focus: Shift to study material that will be showcased in quiz during week 11, emphasizing the importance of preparing for both multiple-choice and open-ended questions.
Group Work Reminder: Urgency for students to report any challenges with group projects for presentations and reports before deadlines.

Sustainable Waste Management

Definition of Waste Management:
- Management of resources at the end of their life cycle.
- Anything that is disposed of, considered trash, classified as waste.
- Waste management is a collective responsibility as everyone generates waste that is eventually processed or treated.
Unawareness of Treatment Processes:
- Many lack knowledge of what happens post-collection.
Environmental and Health Impacts of Waste:
- Uncollected or poorly managed waste leads to unhygienic conditions in communities and can severely impact people’s health.
- Managing waste is also important for the environment as it is a significant contributor to greenhouse gas emissions and can cause soil and water pollution.

Sustainable Solutions in Waste Management

Waste Management Systems in Singapore:
- Waste is collected and sent to treatment facilities such as incinerators.
- Heat from waste incineration is utilized for energy recovery:
- Heat converts water into steam, subsequently into electricity via steam turbines.
- Incinerators function as both treatment and energy recovery facilities.
- Residual Waste Management: Ash produced by incineration is managed in Semco landfill, which is designed to prevent contamination leaching into the environment.
Landfill Types and Environmental Impact:
- Differing landfill systems exist globally; understanding their classification (e.g., sanitary, protected) is crucial.
- Decomposition processes can produce methane, a potent greenhouse gas, and efforts are made in some regions to capture and utilize it.

Waste as Resources

Concept of Waste:
- "There are no waste; only misplaced resources."
- Recognizing value in waste can lead to resource recovery and business opportunities.
Environmental Concerns:
- The relationship between a country’s GDP and waste generated; wealthier nations tend to produce more waste.
Forecasting Waste Generation:
- Waste generation trends are increasing due to urbanization and growing populations.
- Global annual waste generation is expected to jump to $3.9$ billion tonnes over the next $30$ years, up from $2.2$ billion tonnes in $2020$ , a total increase of $73\%$ .
- This necessitates new technologies and practices for waste recovery and materials reuse.
- Different regions exhibit varying projected waste generation rates, emphasizing the need for sustainable practices.

Techniques for Sustainable Waste Management

Reutilizing Ash:
- Examples from the Netherlands or Denmark utilizing ash from incineration for construction (e.g., concrete applications).
- Ash recovery reduces the demand for virgin materials (e.g., sand in concrete).
Circular Economy Concept:
- Transition from linear economy ("take-make-dispose") to circular economy:
- The traditional linear economy follows a step-by-step plan where raw materials are collected, transformed into products, used, and then discarded as waste.
- The circular economy is a model of production and consumption, which involves sharing, leasing, reusing, repairing, refurbishing, and recycling existing materials and products as long as possible, thereby extending the life cycle of products.
- Focus on recycling, reusing resources, and maintaining product value.
- Cycle of Manufacturing: Includes design, distribution, consumption, repair, reuse, and recycling.
- Role of Consumers: Consumers directly influence production and recycling efforts through buying choices and waste management practices.

Biological and Technical Cycles in Circular Economy

Living Systems:
- Reflects a natural model without waste where all materials cycle through usage (waste to food and nutrients).
- Contrast with human linear approaches that lead to resource depletion and pollution.
Rethinking Product Lifecycle: Transition to a model where products are designed for return and regeneration, rather than disposal.
- Resource recovery is a critical part of the circular economy, wherein the extraction of natural resources and generation of wastes are minimized.
- Materials and products are designed more sustainably for durability, reuse, repairability, remanufacturing, and recycling.
- Resources are kept in use for as long as possible through a closed-loop system.
Company Initiatives: Collaboration among companies encourages resource flow and sustainability.

Summary of Circular Economy Principles

Principles:
1. Eliminate Waste and Pollution: Recycling diminishes waste and pollution while maximizing products’ material value.
2. Circulate products and materials at their highest value.
3. Regenerate nature.
Benefits:
- To protect the environment.
- Utilize less virgin resources, limit dependence on raw materials, and create jobs.
- Save consumers money.
Upcycling vs. Downcycling:
- Upcycling: Improving product value.
- Downcycling: Reducing product quality.

Circular Economy Initiatives Example

Composting Practices:
- Historically done but can now be unified and systematized.
- Singapore lacks specific separation for food waste.
Waste Collection Systems: Need improvement; for better reuse, each waste type should ideally have designated bins rather than commingled collection.

Waste Generation in Singapore

High Food Waste Proportion:
- Food constitutes significant waste due to cultural eating habits and food choice diversity, leading to incomplete consumption (up to $30\%$ food waste).
- In $2021$ alone, Singapore generated $6.91$ million tons of solid waste and only recycled about $13\%$ .

Waste Management Strategies

Waste to Energy (WtE):
- Iconic to Singapore's waste management strategy.
- WtE is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source.
- Approximately $3\%$ of Singapore's energy needs are met through incineration.
- Various treatment methods exist to generate energy while reducing waste volume.
- Unlike traditional waste disposal, WtE converts inherent energy in waste into a valuable resource, addressing the dual challenge of waste management and energy demand.
- It positions itself as a critical component in maximizing resource recovery by tapping into the energy potential of waste, offering an alternative to conventional fossil fuel-based energy sources.
- WtE unlocks the resource potential of non-recyclable residual waste streams to achieve a more circular economy.
Potential Feedstocks for WtE Systems:
- Classified according to its origin: Agricultural, Industrial, Residential.

Thermal and Biological Waste Treatment Options

Thermal Processes:
- Incineration: Full combustion with heat recovery.
  - Waste is subjected to a high temperature of between $850$ and $1100^{\circ}\text{C}$ in the presence of oxygen, reducing its weight and volume significantly by $70\%$ and $90\%$ respectively, while utilizing the generated heat and energy.
  - Advantages: Energy Generation, Waste volume Reduction, Simple operation, Lower land requirement.
  - Disadvantages: Air pollutants, Greenhouse emission, Health risks, Ash residues.
- Gasification: Partial combustion generating syngas (hydrogen and carbon monoxide).
  - Achieved by reacting carbonaceous materials at high temperatures (typically >700^{\circ}\text{C}) with a controlled amount of oxygen or steam. The resultant syngas can be used for electricity generation or converted into other fuels and chemicals.
  - Four processes take place in a gasifier:
    1. Drying: Moisture $\rightarrow$ water vapor.
    2. Pyrolysis: Decomposition with heat.
    3. Combustion: Oxidation/burning occurs.
    4. Reduction: $\text{CO}2$ and $\text{H}2\text{O} \rightarrow \text{CO}$ and $\text{H}_2$ .
  - Advantages: Syngas production, Reduced emission, Wide waste feedstock, High efficiency.
  - Disadvantages: Technique complexity, Feedstock quality, Tar formation, High capital cost.
- Pyrolysis: A no-oxygen heat treatment producing gas, oil, and solid residuals.
  - Consists of thermally degrading waste in an oxygen-free atmosphere at temperatures between $300^{\circ}\text{C}$ and $800^{\circ}\text{C}$ . By-products include syngas, bio-oil, and char.
  - Advantages: Reduced emission, Wide waste feedstock, Biochar production, Bio-oil production.
  - Disadvantages: High temperature, Technique complexity, Feedstock quality, Scale issues.
Biological Processes:
- Composting: Utilizing aerobic decomposition for producing soil enrichment.
  - When solid organic waste is composted, enzymes produced by microorganisms and other microscopic animals break it down into carbon dioxide and water, creating compost for agriculture. Heat is constantly released during this process.
  - Advantages: Organic Waste Processing, Soil enrichment, Low energy input, Cost-effective.
  - Disadvantages: Time-consuming, Limited waste types, Emission issues, Insignificant volume reduction.
- Anaerobic Digestion: Decomposition in absence of oxygen yielding biogas and digestate.
  - Microorganisms degrade biodegradable materials without oxygen to produce biogas. Multiple organic materials can be combined in one digester (co-digestion).
  - Biogas energy can be used like natural gas to provide heat, generate electricity, and power cooling systems.
  - Biogas major components: Methane ( $\text{CH}4$ ) $48-65\%$ , $\text{CO}2$ $36-41\%$ .
  - Advantages: Biogas production, Organic Waste Processing, Nutrient-rich digestate, Captured $\text{CH}_4$ emission.
  - Disadvantages: Time-consuming, Temperature sensitive, Limited waste types, Land requirement.
Landfilling:
- The landfill consists of a natural or artificial trench subjected to preparation processes, including compaction, waterproofing, and leveling. It also has equipment for the drainage system, leachate pumping, monitoring, capture, and biogas extraction.
- A properly constructed, well-managed, and operated landfill can significantly reduce waste in volume and weight and generate biogas.
- Landfill Gas (LFG) Benefits: Reduces odors and other hazards, prevents methane migration, generates revenue, creates jobs.
- Biogas major components: Methane ( $\text{CH}4$ ) $48-65\%$ , $\text{CO}2$ $36-41\%$ .
- Advantages: Convenient, Low initial cost, Methane capture, Reduced emission.
- Disadvantages: Limited resource recovery, Soil and water contamination, High land requirement, Fire / explosion hazard.

Global Waste-to-Energy Initiatives

Context of CE Adoption: In the early $1990$ s, industrialized countries began to regard Circular Economy adoption as a tool to achieve long-term development strategies. Governments worldwide have adopted top-down (legislation, policies) and bottom-up (manufacturing industries, society, individual company effort) measures to speed the arrival of the circular economy.
Singapore - Waste-to-Energy Research Facility (WTERF) at Tuas South:
- Based on high-temperature slagging gasification technology, the first of its kind to employ biomass charcoal as an auxiliary fuel.
- Treats waste at much higher temperatures than typical mass burn incinerators, reducing the amount of produced ash.
- Functions as an open platform for research, translation, demonstration, and testbedding for new WtE technologies.
- Compatible with diverse feedstocks: sludge, biomass, contaminated soil, solid recovered fuel, hazardous waste.
Japan - Kishiwada Biogas Plant:
- Processes $17$ tons of food waste, producing $853 \text{ m}^3$ of biogas used for combined heat and power, which is then fed into the public electricity network.
Austria - The Spittelau Waste Incineration Plant (Vienna):
- Built between $1969$ and $1971$ , rebuilt after a fire in $1987$ at the same site.
- Processes $250,000$ tons of household waste annually.
- Produces $60 \text{ GWh}$ of electricity (powering $60,000$ households) and $500 \text{ GWh}$ of green heat (supplying $50,000$ households) every year.
India - Mechanical & Biological Waste Treatment (MBT) Plant in Saligao, North Goa:
- Commissioned in $2016$ with a capacity to treat $100$ tons/day of municipal solid waste and generate $0.8\text{–}1.0 \text{ MWh}$ of energy.
- Designed to recover recyclable materials, segregate them into dry and wet fractions by organic extrusion, followed by bio-methanation of the wet part to generate electricity and compost.
- Expanded to handle $250\text{–}300$ metric tons per day by December $2021$ . From an economic point of view, this generates an estimated $\$995$ per day/$148$ tons of waste processed (6.72$/ton).
Sweden - Biofuel Combined Heat and Power (CHP) Plant in Stockholm:
- Produces heat and electricity through the combustion of solid biomass, mainly residuals from the forest product industry.
- Annual Output Capacity: 1,700 \text{ GWh} $of heat (equivalent to$ 190,000 $average-sized apartments) and$ 750 \text{ GWh} $of electricity (charging$ 150,000 $electric cars).</li><li>Benefits: Offsets$ 126,000 $tons of$ \text{CO}_2 $emissions.</li></ul></li><li>United States - Landfill Gas (LFG) Energy Projects:<ul><li>As of July$ 2023 $, there are$ 532 $operational LFG energy projects in the U.S., with$ 463 $additional landfills identified as good candidates.</li><li>LFG is the third-largest source of human-related methane emissions in the U.S.</li><li>Greater Lebanon Refuse Authority Landfill Gas Collection and Combustion Project (GLRA):<ul><li>Since$ 2007 $, it generates an average of$ 3,200 $kilowatts of electricity per hour, enough to supply approximately$ 2,400 $homes daily.</li><li>This project generates an annual$ 15,000 \text{ MWh} $of renewable energy.</li><li>Serves the$ 26,000$$-person community of Lebanon and improves local health by destroying the majority of hazardous air pollutants on site.
- Home to the Renewable Energy Education Center, hosting students, teachers, and community groups to demonstrate the cost-effectiveness of clean energy resources.

Challenges and Regulatory Factors

Waste-to-Energy Benefits:
- WtE is an indispensable link of the circular economy, creating value for society by diverting waste from landfills, recovering metals and minerals, and producing renewable energy.
- Other benefits include providing hygienic service, material recovery, energy recovery, and carbon capture.
Challenges to Optimizing WtE Operations:
- Technological Barriers: Certain WtE technologies may have limitations in handling specific types of waste (e.g., hazardous or medical waste). Researchers and engineers constantly seek innovative approaches to maximize energy recovery.
- Public Acceptance: Often resistance due to concerns about air pollution, odors, and health risks, which can lead to delays in project approvals and implementation.
- Regulatory Framework: Meeting stringent environmental regulations and standards can be challenging, as compliance with emission limits and other requirements adds complexity to project development and operation.
- Infrastructure Development: Securing suitable land for WtE facilities and navigating zoning regulations can be a challenge. Proximity to residential areas, environmental sensitivity, and land availability require careful consideration.

Waste-to-Energy Roadmap

Key Strategies:
- Research and Development: Focusing on innovative solutions and collaborative efforts.
- Public Engagement: Raising public awareness and communication about WtE benefits and processes.
- Collaboration between Government and Industry: Fostering partnerships for effective implementation.
- Infrastructure Investments: Securing and allocating funds for necessary WtE infrastructure.
- International Cooperation: Working with global partners to advance WtE technologies and policies.

Conclusion

Waste-to-energy plays a crucial role in leveraging environmental benefits while steering society towards sustainable waste management practices, rooted in a circular economy framework that encourages material recovery and resource amplification.
The most common WtE technologies include thermal conversion, biological treatment, and landfilling.
To establish a successful WtE framework, existing challenges need to be addressed through innovation, communication, and collaboration.
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