Municipal Solid Waste/Composting/Landfill/Air Pollution Flashcards
What are the objectives of the Solid Waste Management System?
- Protect public health
- Protect the environment and biodiversity
- Address social concerns, eg, equity, environmental justice, aesthetics and public preferences
- Minimise cost
What waste is considered to be hazardous waste?
Wastes are considered hazardous waste when they pose a direct threat to human health or the environment.
How do we limit risk from toxic hazards?
Risk = Quantity stored
- Emission factor
- Transport to receptor factor
- Time of exposure
- Effectiveness of toxic uptake
- Toxicity
Which wastes should be collected from the generator, and which should the generator transport to a processing facility? Residential waste and commercial/industrial waste.
Residential waste is collected by the council.
Commercial/Industrial waste is collected by the generator (source).
Waste generator responsible for taking other waste (e.g. hazardous) to transfer stations and recycling centres.
To what extent should the generator be asked to separate collected waste into different fractions?
By separating collected waste at source, we can increase the chances of actually recycling.
If all together, it is more costly and is more difficult to separate them at the transfer station.
For eg, residential waste collected via green, yellow and red bins (separated).
Should waste be transported directly to a treatment/disposal facility, or should collection vehicles transfer wastes into a more efficient vehicle first?
Depends on:
- Proximity of landfill
- Volumes of waste generated
- Behaviour of waste generator
- Preferences of the public
- Costs
What are the objectives of composting?
- Reduce mass (carbon, water)
- Reduce pollution potential
- Destroy pathogens
- Produce product with a value
- Minimise cost
What are the environmental factors of composting?
Environmental and nutritional factors determine the rate and extent of composting.
• Temperature - It changes during
the process, from mesophilic to
thermophilic and back to
mesophilic. It must not be >65 o C.
• pH - Organic acids produced at the beginning cause pH to drop but when they are consumed, the pH rises up to 8-9. Buffering is usually unnecessary except in the case of sugar-rich wastes (e.g., fruit scraps)• Temperature - It changes during the process, from mesophilic to thermophilic and back to mesophilic. It must not be >65 o C.
• Moisture content - It should be in the
range of 50 to 60%. Low moisture
levels reduce microbial activity but too high free moisture reduce available
volume for oxygen-rich air. A balance
must be struck between moisture content and available oxygen, this is a ‘permissible moisture content’.
• Aeration - Composting is largely an
aerobic process, thus aeration is an air, water and interstices in composting important process parameter. The rate of aeration needed to maintain aerobic conditions depends upon the nature
and structure of the waste and the size and activity of the microbial population.
- Temperature rise and fall - Temperature should rise sharply after 3 to 5 days. There should be enough waste mass (insulation) for heat to accumulate. Compost is ready after temperature has dropped to about 40 degrees celsius
- Changes in physical characteristics - The waste gradually darkens during composting and the finished product usually has a dark grey or brownish colour. The original odour of the substrate changes to an earthy aroma at the curing and maturing stages. Particle size of the substrate material becomes smaller and amorphous material becomes somewhat granular.
• Destruction of volatile solids - Some substrate volatile solids (i.e., organic matter) are destroyed and complex
molecular structures are converted to simpler forms.
What are landfills?
Landfills are engineered facilities designed and operated for the long term confinement of solid wastes.
What are the two main outputs and potential concerns of landfills?
- Leachate – water in contact with waste
- Gas – methane-rich gas biologically produced from organic wastes.
In landfills, wastes are (1) placed and compacted into solid
forms, and (2) covered to limit exposure to water and air.
Locations to avoids for landfill siting
- Floodplains
- Active geological faults
- Land prone to slips and erosion
- Wetlands and intertidal zones
- Areas with significant ecosystems and important biodiversity
- Areas of cultural and archaeological significance
- Drinking-water catchments
Other items to consider for landfill siting
• Minimise costs for transport of wastes
• Minimise costs required for construction of transportation infraestructure (e.g., roads) to access the site
• Identify sites less prone to extremes of rain or wind
• Identify sites with soils that can be used during construction
• Match the potential site to a final use of the landfill
• Eliminate issues of environmental justice and other social
objections
• Location of users that can make beneficial use of waste materials or derived energy
What are some negative factors on Landfill gas?
- Can be explosive
- A health concern
- Create odours
What are the concerns of young and old leachates?
- Young leachates are a concern because of BOD and pH
- Old leachates are a concern because of N and toxins
Leachate is the liquid formed when waste breaks down in the landfill and water filters through that waste. This liquid is highly toxic and can pollute the land, ground water and water ways
Describe environmental concerns associated with landfills
Landfill leachate contains a wide range of toxic substances arising from the decomposition of waste, and causes contamination of domestic groundwater sources and eutrophication (deterioration of water ecosystems through oxygen depletion) of watercourses.
Along with methane, landfills also produce carbon dioxide and water vapor, and trace amounts of oxygen, nitrogen, hydrogen, and non methane organic compounds. These gases can also contribute to climate change and create smog if left uncontrolled.
