Waste Engineering Introduction

Waste Engineering Introduction

• Waste management steps: Generation, collection, transport, and treatment
• Generation/production refers to the source and quantification of waste before management.
• Waste treatment can be done in transport stations with mechanical methods like compacting or shredding.
• Desired waste treatment reductions are odor, volume, and impurities.
• Thermal treatments for waste include incineration and gasification/pyrolysis.
• Biological treatments include composting and biogasification (anaerobic digestion).
• Waste utilization options include land application, construction materials, and fuel.
• Materials Recovery Facility (MRF) sorts, processes, and recovers recyclable materials from mixed waste streams.

Waste Management in Denmark

• Denmark has 12 million tons of waste.
• Construction and demolition (40%) and households (29%) are the largest waste contributors.
• Residential waste categories include household, garden, bulky, and hazardous household waste.

Solid Waste Issues

• Solid waste main issues: Space, collection/separation, health issues, toxicity, different systems, cost, complex materials, and odor.

Waste Characterization Methods

• Waste characterization challenges include spatial, temporal, and uncertainty due to mixtures.
• Waste sample analysis methods include physical, chemical, and performance tests.
• Disc screens are used for organic waste characterization.

Organic Household Waste Sub-sampling

• Waste sub-sampling process steps are documented in figures.
• Step-by-step procedure details from field to laboratory stages, including mass, screening and shredding, mixing in pile, barrel, dry/wet blending, high-speed blending, drying, hammer milling and final dry sample are documented.

Waste Definitions

• Waste categories are broad classes with common characteristics. Categories include residential, commercial/institutional, industrial and construction/demolition waste.
• Waste types are subclasses within categories with common characteristics in source and composition, potentially resulting in separate collection and handling. Examples for residential waste are household, garden, bulky and hazardous waste. Industrial waste types vary according to the industry.

Waste Quantification

• Waste quantities are usually reported as wet weight.
• Unit generation rate (kg/year/person, kg/week/household, etc.) is a key parameter for estimating waste quantities.

Waste Minimization and Prevention

• Waste minimization and recycling prevention is a key area.
• A typical analysis considers factors such as material fractions, substances, wet weight, etc.

Mechanical Treatment at MRFs

• Purpose is to separate recyclables and residual streams, and to improve handling and transport.
• Technologies used are separation, reduction in size, and compacting.

Composting Technological Factors

• Key parameters are oxygen content, particle size, aeration, pH, biodegradation, temperature, moisture content, and nutrients.

Composting Plant Design

• Critical components are source, weighting/storage, pre-processing, composting, refining/screening, and market production.
• Emissions include liquid (leachate, etc.) and air emissions (NH3, N2O, CH4, dust, bioaerosols).

Composting Process Steps

• Degradation, stabilization, and curing.

Nitrogen Transformation During Composting

• Nitrogen transformation through microbial activity is an important process.

Anaerobic Digestion

• Hydrolysis is the first step, involving extracellular enzymes on carbohydrates, proteins, and lipids to break down organic waste. This results in dissolved organic matter, relevant in digestion and landfill processes.

Biogas Formation

• Biogas formation steps include hydrolysis, fermentation, acetogenesis, and methanogenesis.

Oxidation and Methane Potential

• Oxidation state and degradability are key factors in methane potential.
• Anaerobic digestion process steps include receiving, pretreatment, digestion, and gas collection, utilization and digestate management.

Incineration

• Incineration energy contribution percentage to heating is 6% (energy), and 24% (heating).
• LHV (lower heating value) and HHV (higher heating value) are used to determine energy content.
• Pyrolysis is thermal degradation in the absence of oxidising agents.
• Gasification is partial oxidation of carbon with oxidizing agents.
• Combustion is full oxidation of carbon.
• APC (air pollution control) systems are used for dust/fly ash removal.

CCS (Carbon Capture and Storage)

• CCS benefits: Energy, material and heat recovery, CO2 storage.
• CCS burdens: Electricity, air emissions, residues, and extra materials
• Difference in kg Co2-eq is -820; reduction of ~90%.

Air Pollution Control

• Dust control methods: Electrostatic precipitators, fabric filters, wet scrubbers, dry/semi-dry systems, and dust filters.
• Acid gas control methods: Wet scrubbers, dry/semi-dry systems.
• Heavy metal control methods: Activated carbon, SNCR, SCR.
• Dioxin control methods: Activated carbon.
• CO2 control methods: Carbon capture and amine.

Incineration Residues

• Bottom ash (mixture of metals and solids), fly ash (fine ash), and other residues (sludge, etc.).
• Ash treatment methods: Extraction, separation, thermal treatment, chemical stabilization, and solidification.

Landfill Emission

• Landfill emissions include global warming, ozone depletion, toxic gases, odours, noise, litter/dust, fire risk, vegetation damage, soil, and surface water pollution, and ground water pollution.

Landfill CH4 Contribution

• Landfill methane (CH4) contribution is in the 6–13% range.

Landfill Risks

• Landfill risks: Odour, vectors, explosions, groundwater pollution, surface water, soil, vegetation damage, noise, litter, dust, global warming, and ozone depletion.

Landfill Water Balance

• Water balance in landfill involves leachate generation, change in moisture storage in top covers, precipitation, evapotranspiration, surface runoff, change in moisture content, surface water inflow, managed water input, water vapour, and water consumption.
• Water input is often used in landfill procedures to control dust production and improve degradation processes.
• Key factors for landfilling include total waste managed in Denmark (3–4%), combustible waste disposal, tax on landfilling, enhanced waste sorting, and post-sorting at landfills.
• Temperature (T) below 72°C is beneficial for CH4 release in landfills.

Landfill Gas Generation

• Landfill gas generation (LFG) is influenced by anaerobic digestion of organic waste (CH4 and CO2).
• Key factors are waste composition, waste age, temperature, and moisture content.
• Peak CH4 emissions typically occur around 7 years into landfill lifespan.

LFG Utilization Issues

• LFG utilization issues include potential aeration, vertical/horizontal pipes, corrosion, blockage by water, and discontinuity.

Landfill Collection Efficiency

• Landfill gas collection efficiency in Denmark is about 50%.

Leachate Generation and Factors

• Factors influencing leachate generation in landfills include water (diffusion, advection, concentration), chemical factors (solubility, availability, pH – metals), and environmental factors.

Landfill Liners

• Liner functions include gas control, leachate drainage and collection, impermeability, and separation.

Leachate Treatment

• Leachate treatment options include biological treatment (tertiary/advanced/polishing), reverse osmosis, and physicochemical processes.
• Sequencing batch reactor (SBR) is one system for leachate treatment, involving reactor monitoring along with it.

General Questions (A1-A16)

• Various questions are included, addressing waste hierarchy, waste generation rates, and waste characteristics.
• These include factors like waste composition, different types of waste, waste management, treatment methods, and environmental effects.