Waste Management Flashcards
Waste Produced by Industry
o Raw material extraction, material processing, product manufacture
Solid Waste Management System
See notes for diagram
Definitions of Waste
o Household waste
• Municipal solid waste (MSW) – goes to landfill
• Recyclables, organic, garden waste etc.
• Non-hazardous waste
o Industrial & commercial
• All sources that are not collected at kerbside e.g. shops, offices etc.
• Some is MSW e.g. restaurant food waste
• Largest component is wastewater sludge
o Construction waste
• Not MSW, does not go to landfill
• Building & demolition sites
• Inerts (solids, cement), biodegradables (vegetation from land clearing), hazardous waste (paints, solvents, glue)
o Regulated waste
• Institutional waste, MSW
• Hazardous waste: medical waste, organic solvents, acidic chemicals, explosives
o Agricultural waste
• Plant and animal residues
Waste Management Hierarchy
o Reduce: lowering amount of waste produced (most favoured)
o Reuse: using materials repeatedly
o Recycle: using materials to make new products
o Recovery: recovering energy from waste
o Landfill: safe disposal of waste to landfill (least favoured)
Waste as a Resource
o Paper, glass, plastic, ferrous metals, building materials,
o Energy: conversion to methane, direct incineration
Waste Collection and Disposal
o MSW collection systems
• Kerbside collection: route planning, optimisation ($)
• Transfer station: sorting, compaction, bulk transfer
• Landfill: final disposal
o Landfill
• Most common form of waste management
• Is not a dump – planned & engineered
• Main issues: void space, leachate, biogas (GHG)
Biological Processes in Landfills
o Stages in decomposition
• Aerobic vs. anaerobic
• Anaerobic gives GHG and acidity
• Microbially driven and affected by temperature, pH, waste composition and availably oxygen
Landfill Design Considerations
o Site: appropriate size, safety, transport form waste source, availability of materials
o Waste type: inert, hazardous, non-hazardous
o Waste containment: protecting surface, groundwater & air
o Asset of landfill: charge until it is full
o Waste is sorted to decrease amount going into void
o Waste is compacted to increase bulk density
Calculating Required Landfill area/volume
o Population (people) x waste generation (kg/capita/year) / weight ratio (kg/m3) / average depth x landfill life (years)
Environmental Issues
o Leachate: liquid percolate through waste (made up of dissolved or suspended compounds)
o Liquid from within waste (vegetation, actual liquid waste) and from external water entering the cells (rainfall, groundwater)
o Decomposition creates liquids
o Low pH and high COD
Covers and Liners
o Required to protect groundwater & soil, and contain gases within landfill
o Type of cover/liner depends on type of waste (hazardous, non-hazardous, inert)
• Natural clay
• Engineered clays
• Geo-synthetic clay
• Flexible membrane liners, geo-membranes
• New combinations of natural & man-made materials
• Sand & gravel for drainage layers, or geo-nets
• Geotextiles used to keep sand & gravel etc. from mixing
o Protective layer: typically 0.5m
o Geo-fabric to separate cover material from drainage layer
o Drainage layer (gravel 0.3m or geo-net)
o Barrier layer: geo-membrane
o Barrier layer: compacted clay, 0.5-1 metres thick
Cover and Capping
o Contains & protects waste, prevents excess water entering, controls release of gases and infiltration of air
o Daily cover:
• Prevents wind-blown litter, contains odours & gas, prevents animals, improves visual impact
• Usually comprised of soil
o Final capping layer
• Installed upon completion
• Contains gas, excludes surface water, allows reshaping of land, provides medium for planting
Biogas System
o Anaerobic digestion
• No O2, so organic matter is converted to CO2 and CH4 (biogas)
• Both of these are greenhouse gases
• CH4 is also a fuel
o Collection of biogas using vertical wells
- Gas will move by pressure gradient: uncontrolled migration can lead to collection in sewers, sumps and basements
- Passive gas venting: use natural convective forces within waste bed to direct gas to atmosphere without treatment, higher risk of fugitive emissions, loss of fuel and release of odours, toxic gases and greenhouse gases
- Active gas control: linked extraction wells with gas extracted under vacuum created by central blower
- Increases capture efficiency and decreases fugitive emissions
Waste Reduction
o Recycling
• Advantages: reduced raw materials use, energy use, emissions, landfill volumes
• Considerations:
• Secure & stable supply of waste materials
• Suitable collection & transportation system
• Reliable separation & clean up
• Secure & stable market for waste products
• Energy and transportation needed
o Recycling MSW
• High recycling potential
• Source separation increases this potential
• Sorting & transportation are energy & labour intensive
o Recycling construction & industrial waste
• Commonly recycled
• High financial incentive to producer
• Relatively ‘clean’ waste streams if source separated
o Aluminium recycling
• Massive energy savings: requires only 5% of power to re-melt
• Stable local supply: cans
• Consistent quality and uniform composition: does not degrade during recycling
o Recycling paper
• Every tonne recycled saves 3 m3 of landfill
• Decreases chemical waste – decreased pulp production
• Can only be recycled average of 7 times as fibres degrade
Pre-Treatment of Waste
o Accelerate decomposition
o Incineration
• Burned at approx. 800 degrees Celsius
• 5MW / hour used onsite, 60MW / hour district heating
• 18 tonnes waste / hour
• ‘Clean’ incineration is complex and expensive
• Potential air pollutants if not burnt properly
• SOx, NOx, particulates, dioxins, CO2
• Waste water from flue gas treatment
• No MSW incineration used in Australia, only for hazardous chemicals and agricultural waste
o Biological treatment of waste
Advantages Disadvantages
Composting (aerobic) Volume reduction, faster than anaerobic, simple operation, decrease GHG Net energy consumption
Anaerobic digestion Net energy production, volume reduction, decrease GHG Complex operation
o Composting:
• Biodegradable waste only
• Relatively fast (4-6 weeks)
• Small scale (household) vs. large scale (commercial)
• Organic matter + O2 + nutrients = biomass + compost + CO2 + H2O + NO3 + SO4 + … + heat
o Anaerobic digestion
• Formation of methane and CO2 from biological breakdown of organic waste, can take decades to occur in landfills, weeks to occur in digesters
• Process occurs in landfills, harnessed in digester system to allow easy capture and increase rates
• Organic matter + H2O + nutrients = biomass + solid residue + CO2 + CH4 + NH3 + H2S + heat
