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 Garbage The Varying Components of Garbage 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 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 Garbage Burying 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 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 3 Stages 1. Aerobic Stage: O 2 oxidizes organic materials to CO 2 and H 2 O, releases heat CO 2 produced makes leachate acidic, leaches metals from wastes OM oxidized to aldehydes, ketones and alcohols 2. Anaerobic acid phase: acidic fermentation occurs, produces NH 3, H 2, and CO 2. 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 CH 4 and CO 2. CH 4 continues for 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 Typical components: –Volatile organic acids such as acetic acid and longer chain fatty acids –Bacteria –Heavy metals –Salts of common inorganic ions (e.g. Ca 2+ )

Domestic and Commercial Garbage Leachate 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 clay seal in trash Methane storage and compressor building Leachate storage tank Leachate monitoring well Groundwater monitoring well Electricity generator building Leachate treatment system Methane gas recovery well Compacted solid waste Leachate pipes Leachate pumped up to storage tank for safe disposal Groundwater Clay and plastic lining to prevent leaks; pipes collect leachate from bottom of landfill Topsoil Sand Clay Subsoil Probes to detect methane leaks Garbage Synthetic liner Sand Clay Pipes collect explosive methane as used as fuel to generate electricity

Domestic and Commercial Garbage Incineration 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

Domestic and Commercial Garbage Incineration 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 ~ % 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

Domestic and Commercial Garbage Incineration

Recycling of Household and Commercial Waste A

Recycling of Household + Commercial Waste General Features of Recycling A

Recycling of Household + Commercial Waste Recycling Metals and Glass A

Recycling of Household + Commercial Waste Recycling Paper A

Recycling of Household + Commercial Waste Recycling Tires A

Recycling of Household + Commercial Waste Recycling Plastics A

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Soils and Sediments A

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Soils and Sediments Sediments A

Soils and Sediments Binding of Heavy Metals A

Soils and Sediments Mine Tailings A

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Soils and Sediments Remediation A

Soils and Sediments A

Soils and Sediments Analysis and Remediation A

Soils and Sediments A

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