Waste by yaoyufang

VIEWS: 7 PAGES: 18

									Waste Management

  It Stinks in the City
                    Waste
• Virtually every human activity generates
  waste. Even eating!
• Eating => digesting => fecal matter => sewage
• Sewage is one of the most challenging waste
  problems of modern society.

• If you’re out camping in the bush, what are
  you supposed to do with your... Sewage?
                   Waste
• Solid waste: waste material that cannot be
  easily passed through a pipe
• Liquid waste: can be passed through a pipe,
  ex. sewage or watery mud

• Solid waste can be soluble and dissolve in
  water; liquid waste can be concentrated to a
  more solid form.
             Sources of Waste
• Solid waste sources:
  – Agriculture (farms, orchards, ranches, animal
    feedlots), waste is almost entirely organic
  – Mining (discarded piles of waste rock, tailings,
    slags and sludges left over from smelting of ores)
  – Industry (paper, cardboard, scrap metal, wood,
    plastics, glass, tires, rags)
  – Many of these wastes are recyclable: extraction of
    raw materials from waste products
• Tipping fees: fees charged for the disposal of
  solid wastes at dumpsites.
  – Industrial recycling improves when tipping fees
    increase – why?
• Source reduction: cutting back on wastes
  through production efficiencies, increasing the
  useful lifetimes of products, and reducing
  packaging
• Waste exchange: a central agency endeavours
  to find a market for industrial waste products;
  using leftovers from one industrial process as
  raw materials for another
          Municipal Solid Waste
• MSW: the smallest but fastest-growing source
  of solid waste; anything routinely collected by
  city trucks on garbage day.
   – Composition of MSW in US: Paper – 38%, Yard
     Waste – 18%, Misc. (including HHW) – 14%, Plastic
     – 8%, Metal, Food, Glass – 7% each.
• Hazardous wastes: waste materials that are
  toxic, caustic, acidic, explosive, infectious, or
  radioactive.
       The 4 R’s (There are 4!?!)
• Refuse: simply consume less and buy less
• Reduce: ex. avoid products with excessive
  packaging
• Reuse: don’t throw away anything that might still
  be usable
• Recycle: blue box for glass, metal, paper, and
  plastics
• Composting: providing a contained environment
  in which organics can biodegrade quickly
                Waste Disposal
• Open dumps: in the past, most towns used a
  hole in the ground where garbage was
  allowed to accumulate.
  – Problems?


• Incineration: the burning of refuse in a
  specially designed facility.
  – Toxic by-products: toxic metals, dioxins, furans
                  Landfills
• Waste disposal sites engineered and
  monitored to contain wastes within a site
• Most common approach to waste
  management
• Sanitary landfill: designed to confine waste
  and prevent it from causing environmental
  and health problems in nearby areas; layers of
  compacted waste covered in layers of soil
  and/or clay
                       Landfills
• Leachate: rainwater percolates through a pile of
  solid waste and picks up soluble (easily dissolved)
  materials
   – Significant environmental problem
   – Can be highly toxic or contain infectious agents
• Must select an appropriate site that will prevent
  leachate from forming, or once formed, prevent it
  from migrating very far.
• Considerations: level of water table, porosity of
  surrounding rock or sediment, amount of
  precipitation, groundwater flow system
                   Landfills
• Dry is better than wet
• Clay layers below are beneficial
  – Porous, store fluids, impermeable, bond with
    metals and other contaminants
• Arctic landfill? (too cold for natural
  biodegradation)
• Where is the municipal landfill nearest us?
  When is it expected to be full?
            NIMBY Syndrome
• “not in my backyard”
• Economic incentives are used to overcome
  social objections... What town really wants to
  host a landfill?
• Leachate control: liners, impermeable caps,
  drainage pipes and leachate collection
  systems, monitoring wells around the site
• Also, collecting gas generated by the decay of
  materials within the refuse pile.
                Landfill Gas
• Mostly methane (CH4) (smells bad, can be
  explosive)
• May also contain carbon monoxide (CO) and
  other gases
• Some landfills collect and sell methane as fuel
                    Landfills
• Secure landfills: specifically designed to contain
  hazardous materials; onsite facility for the
  treatment of hazardous wastes (chemical
  stabilization, neutralization, or incineration)
• Deep-well injection: toxic liquids are injected
  deep underground into an appropriate reservoir
  rock.

• What is the difference between a sanitary landfill
  and a secure landfill?
                    Answer
• A sanitary landfill is intended to accept mainly
  municipal waste. A secure landfill is
  specifically engineered to accept hazardous
  wastes.
• Many controls are the same, but secure
  landfills are engineered and monitored more
  carefully.
                      Sewage
• Toilets and drains
• On average, 550 litres/person EACH DAY

• Septic tank system: holding tank designed to receive
  domestic sewage from a single household (used in
  rural areas)
• Holds waste long enough to allow organic material to
  partially biodegrade and the solids to settle
• Clear liquid component released slowly into
  surrounding sediment (leach field) and undergoes
  natural filtration and purification
                        Sewage
• Some communities, even in North America, release
  sewage directly into lakes, rivers, bays and open ocean
  without any prior treatment!
• Problems?
• Primary treatment: mechanical removal of solids (ex. trash
  and fine sediment)
• Secondary treatment: bacteria used to assist in
  biodegradation of dissolved organic material. Sewage
  sometimes chlorinated at this stage to disinfect it
• Tertiary treatment: chemical process for removing
  remaining contaminants like heavy metals and inorganic
  dissolved solids. Few municipalities can afford this.
                     Sewage
• Gray water: treated sewage
  – Can be used for watering boulevards or city
    landscaping (reuse water resources)
• Sludge: solid material removed from sewage
  – Usually landfilled, incinerated or placed in a large
    body of water
  – Can be used as fertilizer for non-agricultural
    purposes (ex. parks or golf courses)
  – However, can contain high levels of toxic
    chemicals or heavy metals

								
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