cive230 lec15 - solid waste management and treatment methods

hazardous waste properties

toxic, infectious, radioactive, flammable

hazardous waste defined based on

concentration, toxicity to humans, toxicity to ecosystems

1989 basel convention

164 countries agreed to minimize the generation of hazardous waste

• to assure sound management of hazardous wastes

• to control transboundary movement of hazardous wastes

• to improve institutional and technical capabilities especially for developing countries and countries with economies in transition

solid waste management system objectives

• To minimize the production of solid waste.

• To prevent the production or enhance the treatment of hazardous waste

  products.

• To minimize negative impacts of solid waste on the environment in terms of water quality, air quality, land consumption, and natural habitats .

• To minimize the negative externalities associated with solid waste treatment, including odour, natural environment degradation, and land value impacts.

• To minimize energy consumption associated with the production and treatment of waste.

• To minimize the cost of treatment.

lansinks ladder

One of the first waste hierarchies proposed by the Dutch politician Ad Lansink in 1979

• prevent

• reuse

• recycle

• energy

• incinerate

• landfill

landfill

Process of disposing solid waste in a specified location. Typically involves compressing the waste and allowing natural breakdown of materials

landfill impacts on water quality

Leachate: Leachate is a mixture of water, other liquids, and solids entering natural waterways from the landfill area. It contains chemicals such as zinc, mercury and other metals as well as hydrocarbons such as benzene and xylene

leachate characteristics depend on

• Composition of the landfill

• Temperature and moisture content

• Age of landfill

leachtate treatment

• amount of leachate produced is reduced by covering (capping) to reduce precipitation entering landfill

• Liner (typically clay or geosynthetics; clay less expensive but more permeable in long term). In Canada 46% of landfills are lined; these landfills treat about 75% of all MSW.

• Liner (typically clay or geosynthetics; clay less expensive but more permeable in long term). In Canada 46% of landfills are lined; these landfills treat about 75% of all MSW.

landfill impacts on air quality

landfill gases (CO2, CH4, NHx) - O2 is produced as waste is aerobically digested while methane is produced as organics are broken down in an anaerobic environment by microorganisms. The amount of these gases produced is influenced by the percentage of organics in the waste stream, by the temperature, by the moisture content and the pH.

treating LFG

• Landfill gases maybe collected (actively or passively) and burned to

  produce electricity (Approximately 41 Canadian landfills are producing electricity from LFG.)

• LFG can be collected and burned or flared. Methane can be flared

  to produce CO2 The goal is to reduce the amount of methane entering the atmosphere because methane is a much stronger GHG than carbon dioxide.

GWP for methane

approx 23

landfill impacts on land use

• Reuse of landfill sites is limited to recreational activities.

• Closing existing landfills requires that additional capacity be added to the system in other locations.

• 50% of Canada’s landfills have < 10 years capacity remaining which presents a challenge.

incineration

• Incineration is the process by which solid waste is burned, typically to

  produce energy, which significantly reduces the volume of solid waste to be treated by other means.

• In Canada in 2000, 21 incinerators burned ~ 5% of all solid waste

• Mass Burn System, Starved Air System, Fluidized Bed System, Refuse Derived System, Plasma System

mass burns systems

• the least sophisticated system in terms of pre- sorting; lowest cost and most frequent operation.

starved air systems

two-stage combustion method in which the first chamber is stoichiometrically (pressure, oxygen content, etc.) controlled to slowly convert solid waste to non-combustible materials collected and treated in the first chamber and highly combustible, cleaner materials (syn gas) which are combusted at higher speeds in the second chamber.

starved air systems benefits

The benefits of this system are that difficult to treat emissions are produced with low flow rates in the first chamber and are therefore easier to treat.

fluidized bed systems

combustion occurs in a chamber beneath a thin bed of sand-like materials; the flue gas produced passes through and raises the bed material causing it to act like a fluid. The bed material acts as a filter to control emissions and as a method to control the rate of combustion in the main chamber.

refuse derived fuel

solid waste is converted to a fuel which is then used as a power source in other industry/manufacturing applications for which very clean fuel is not a necessity.

plasma systems

solid waste is exposed to very high temperatures (1,500°C - 15,000°C) achieved by creating huge potential differences. At these temperatures, the waste is converted to a gaseous state comprised of their base compounds. Difficult to treat byproducts are collected as ash. These systems have a long history in metallurgy but have not yet been implemented in solid waste.

inceneration impacts on water quality

Incineration plants often use water-based technologies (scrubbers) to reduce air pollutant entering the atmosphere. The runoff from this activity must also be treated in incineration plants.

incineration impacts on air quality

Incineration contributes to air pollutant, therefore impacting air quality. But the percentage is very low and therefore the negative impacts are minimal. However, the incineration of solid waste is associated with the formation of two highly dangerous (carcinogenic and toxic in relatively low concentrations) substances known as dioxins and furans.

incineration - solid waste

Ash (inorganic compounds that do not combust even at high temperatures) is produced. Ash maybe reused in concrete, or roads, or landfilled

incineration impacts - potential for energy

Energy derived is a function of heat value (HV in kJ/kg) of the chemical and its carbon content.

• Some component in the waste stream have high HV – for example HV of plastics is 33,000 kJ/kg which is higher than coal.

• Economical comparison (life cycle analysis) between recycling and incinerating material should be conducted

recycling

Process by which goods/materials are removed from the disposal waste stream and reprocessed into a usable form

recycled material - energy savings

• impacts of recycling include net changes in energy throughout the

  waste treatment cycle.

• Recycling stores much of the embodied energy of a product.

What steps in a product lifecycle become a source for energy savings in a recycling process?

The energy associated with the extraction and transportation of raw materials is completely eliminated by recycling. The energy from processing raw materials to goods or packaging is reduced. The energy consumption from treatment and disposal of waste is also completely eliminated.

What steps in a product lifecycle consumes energy in a recycling process?

sorting discarded materials increases energy consumption and a loss of potential energy that could’ve come from incineration/gases

composting

Breaking down the organic materials from the waste stream by aerobic or anaerobic microorganisms. It is usually done in two steps: a stabilization period of 1-2 weeks, and a final curing period of 6-12 weeks.

composting impact

• There is potential for generating energy from gases resulting from the composting process

• Composting can achieve 96% reduction in weight of organics sent to landfills and ~ 57% of all MSW

composting efficiency factors

• Temperature of the composting material: 30°C is desirable.

• Oxygen content: 15% is desirable.

• Ratio of carbon to nitrogen: 30:1 is desirable. Typically waste streams have much higher ratios, so nitrogen rich materials are added.

• Moisture content: above 50%.

composting negative impacts

• CO2 production

• Odour (if anaerobic)

• Greater energy consumption than landfills

• Attracts pests