Transcript Environmental Chemistry - Robert Morris University

Environmental Chemistry
Chapter 16:
Wastes, Soils, and Sediments
Copyright © 2012 by DBS
Contents
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Waste
Recycling
Soils and Sediments
Introduction
• Solid State:
– Waste
– Soils
– Sediments
Question
One country with 5 % of the world’s population
produces 33% of the world’s solid waste…
‘The Throw-Away Society’
Solid Waste
• solid waste: any unwanted or discarded material that is not a
liquid or gas;
• U.S. 5% of world population, generates 33% of solid waste, 10
billion metric tons/year
• 99% is industrial
+ hazardous
waste
Domestic and Commercial Garbage
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Garbage or refuse
•
Municipal Solid Waste (MSW)
•
Greatest source is construction and demolition debris
•
Followed by commercial and industrial
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Typical N. American produces ~ 2 kg a day more than any other country
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Waste from petroleum, agriculture, fly ash from power plants is not included in
this section
Domestic and Commercial Garbage
The Varying Components of Garbage
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Fraction of vegetable waste declines as level of development increases
•
Food waste is major component of all
Domestic and Commercial Garbage
Burying Garbage in Landfills
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Municipal Solid Waste (MSW) mainly buried
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Costs are lower than any other method
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In the past landfills were simple ‘holes in the ground’
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Modern landfills are better designed, accept no hazardous materials and are
site selected to have minimal impact on the environment
Domestic and Commercial Garbage
Burying Garbage in Landfills
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Sanitary landfill:
–
Site is lined with a plastic liner
–
MSW is compacted into layers (reduces volume), covered with 8 in of soil at the end
of the day
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Resulting cells are capped with clay to resist rainfall entry
–
Leachate: precipitation, water from the waste and groundwater
Contains dissolved, suspended and MO contaminants
Domestic and Commercial Garbage
Burying Garbage in Landfills
Domestic and Commercial Garbage
Stages in the Decomposition of Garbage
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3 Stages
1. Aerobic Stage: O2 oxidizes organic materials to CO2 and H2O,
releases heat
CO2 produced makes leachate acidic, leaches metals from wastes
OM oxidized to aldehydes, ketones and alcohols
2. Anaerobic acid phase: acidic fermentation occurs, produces NH3,
H2, and CO2. Large quantities of partially degraded OM (organic acids
and esters)
Leachate has high BOD/COD, high heavy metal conc.
Domestic and Commercial Garbage
Stages in the Decomposition of Garbage
•
3 Stages
3. Anaerobic – methanogenic – stage: starts about 6 months to 1 year
after covering. Anaerobic bacteria slowly decompose the organic
acids and hydrogen produced in stage 2.
pH rises to 7 or 8, main products are CH4 and CO2.
CH4 continues for 10-20 years, leachate has lower BOD and lower
heavy metal conc.
CH4 often vented and combusted, may be used to generate energy
Domestic and Commercial Garbage
Leachate
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Typical components:
– Volatile organic acids such as acetic acid and longer chain fatty
acids
– Bacteria
– Heavy metals
– Salts of common inorganic ions (e.g. Ca2+)
Domestic and Commercial Garbage
Leachate
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Micropollutants present in MSW leachate include common VOCs
such as toluene and dichloromethane
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Control of leachate:
– Collection and removal system, followed by treatment
– Liner – plastic high density polyethylene or clay. Since 1991 all
new landfills have 6 layers of protection including bentonite clay
which is very effective at binding heavy metals
– Return to top of landfill, OM degraded during percolation
Topsoil
Sand
Clay
Garbage
Probes to
detect
methane
leaks
When landfill is full,
layers of soil and clay
seal in trash
Electricity
Methane storage
and compressor
building
Methane gas
recovery well
Synthetic
liner
Sand
Clay
Subsoil
Leachate
treatment system
Pipes collect explosive
methane as used as fuel
to generate electricity
Leachate
storage
tank
Compacted
solid waste
Garbage
Sand
generator
building
Leachate
pipes
Leachate pumped
up to storage tank
for safe disposal
Clay and plastic lining
to prevent leaks; pipes
collect leachate from
bottom of landfill
Groundwater
Groundwater
monitoring
well
Leachate
monitoring
well
Domestic and Commercial Garbage
Incineration
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Oxidizing by controlled burning
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Substantially reduces volume ( ~ 1/8 original volume)
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Eliminates toxic threat of hazardous wastes (e.g. hospital wastes)
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Japan and Denmark burn > 50 % of their waste
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Incinerators may be one-stage or more modern two-stage type
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Heat from combustion process may be captured and used to produce
steam, hot water or electricity
Incineration
‘Waste to energy’ incinerator
Domestic and Commercial Garbage
Incineration
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Bottom ash – noncombustible airborne material that collects at the
bottom of the incinerator
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Fly ash – trapped by environmental pollution controls in the stack (see
chp 3)
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Fly ash ~ 10-25 % of total ash mass, much more toxic since heavy
metals, dioxins etc. condense onto its small particles
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Taken to hazardous waste landfill. Techniques such as addition of
adhesive, or melting and vitrification produce leachate resistant
material
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Some countries recycle ash into asphalt
Domestic and Commercial Garbage
Incineration
Recycling of Household and Commercial
Waste
•
A
Recycling of Household + Commercial Waste
General Features of Recycling
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A
Recycling of Household + Commercial Waste
Recycling Metals and Glass
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A
Recycling of Household + Commercial Waste
Recycling Paper
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A
Recycling of Household + Commercial Waste
Recycling Tires
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A
Recycling of Household + Commercial Waste
Recycling Plastics
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A
Recycling of Household + Commercial Waste
Recycling Plastics
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A
Soils and Sediments
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A
Soils and Sediments
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A
Soils and Sediments
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A
Soils and Sediments
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A
Soils and Sediments
Sediments
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A
Soils and Sediments
Binding of Heavy Metals
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A
Soils and Sediments
Mine Tailings
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A
Soils and Sediments
Mine Tailings
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A
Soils and Sediments
Remediation
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A
Soils and Sediments
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A
Soils and Sediments
Analysis and Remediation
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A
Soils and Sediments
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Soils and Sediments
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Soils and Sediments
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Soils and Sediments
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Soils and Sediments
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Soils and Sediments
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A