environmental chemistry chapter 16: wastes, soils, and sediments copyright © 2012 by dbs

Environmental Chemistry

Chapter 16:Wastes, Soils, and Sediments

Copyright © 2012 by DBS

Contents

• Waste

• Recycling

• Soils and Sediments

Introduction

• Solid State:– Waste– Soils– Sediments

Question

‘The Throw-Away Society’

One country with 5 % of the world’s population produces 33% of the world’s solid waste…

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• Garbage or refuse

• Municipal Solid Waste (MSW)

• Greatest source is construction and demolition debris

• Followed by commercial and industrial

• Typical N. American produces ~ 2 kg a day more than any other country

• Waste from petroleum, agriculture, fly ash from power plants is not included in this section

Domestic and Commercial GarbageThe Varying Components of Garbage

• Fraction of vegetable waste declines as level of development increases

• Food waste is major component of all

Domestic and Commercial GarbageBurying Garbage in Landfills

• Municipal Solid Waste (MSW) mainly buried

• Costs are lower than any other method

• In the past landfills were simple ‘holes in the ground’

• Modern landfills are better designed, accept no hazardous materials and are site selected to have minimal impact on the environment

Domestic and Commercial GarbageBurying Garbage in Landfills

• 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

– Resulting cells are capped with clay to resist rainfall entry

– Leachate: precipitation, water from the waste and groundwaterContains dissolved, suspended and MO contaminants

Domestic and Commercial Garbage Burying Garbage in Landfills

Domestic and Commercial GarbageStages in the Decomposition of Garbage

• 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 GarbageStages 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 GarbageLeachate

• 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 GarbageLeachate

• Micropollutants present in MSW leachate include common VOCs such as toluene and dichloromethane

• 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

Sand

When landfill is full,layers of soil and clayseal in trash

Methane storageand compressorbuilding

Leachatestoragetank

Leachatemonitoringwell

Groundwatermonitoringwell

Electricitygeneratorbuilding Leachate

treatment system

Methane gasrecovery well

Compactedsolid waste

Leachatepipes

Leachate pumpedup to storage tankfor safe disposal

GroundwaterClay and plastic liningto prevent leaks; pipescollect leachate frombottom of landfill

Topsoil

SandClaySubsoil

Probes todetectmethaneleaks

Garbage

Garbage

Syntheticliner

Sand

Clay

Pipes collect explosive methane as used as fuel to generate electricity

Domestic and Commercial GarbageIncineration

• Oxidizing by controlled burning

• Substantially reduces volume ( ~ 1/8 original volume)

• Eliminates toxic threat of hazardous wastes (e.g. hospital wastes)

• Japan and Denmark burn > 50 % of their waste

• Incinerators may be one-stage or more modern two-stage type

• Heat from combustion process may be captured and used to produce steam, hot water or electricity

Incineration

‘Waste to energy’ incinerator


• Bottom ash – noncombustible airborne material that collects at the bottom of the incinerator

• Fly ash – trapped by environmental pollution controls in the stack (see chp 3)

• Fly ash ~ 10-25 % of total ash mass, much more toxic since heavy metals, dioxins etc. condense onto its small particles

• Taken to hazardous waste landfill. Techniques such as addition of adhesive, or melting and vitrification produce leachate resistant material

• Some countries recycle ash into asphalt

Recycling of Household and Commercial Waste

• A

Recycling of Household + Commercial WasteGeneral Features of Recycling

• A

Recycling of Household + Commercial WasteRecycling Metals and Glass

• A

Recycling of Household + Commercial WasteRecycling Paper

• A

Recycling of Household + Commercial WasteRecycling Tires

• A

Recycling of Household + Commercial WasteRecycling Plastics

• A

Soils and Sediments

• A

Soils and SedimentsSediments

• A

Soils and SedimentsBinding of Heavy Metals

• A

Soils and SedimentsMine Tailings

• A

Soils and SedimentsRemediation

• A

Soils and Sediments

• A

Soils and SedimentsAnalysis and Remediation

• A

Soils and Sediments

• A

environmental chemistry chapter 16: wastes, soils, and sediments copyright © 2012 by dbs

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