solid waste management methods

Solid Waste Management

Neil Hutzler

Spring 2004

Sources of Solid Wastesin the United States

• Mining wastes (3 billion tons per year)

• Agricultural wastes (500 million tons/yr)

• Industrial wastes (400 million tons/yr)

• Municipal solid waste (210 million tons/yr)– About 4.5 lb/person/day

• Sewage sludge (40 million tons/yr)

Source: USEPA

Source of Solid Wastes

• Mining waste consist mainly of rock and soil overburden from mining operations – an earth moving project

• Agricultural wastes are typically organic residuals – biodegradable and recyclable

• Industrial wastes are widely varied – have the potential of being hazardous

• Municipal solid wastes (MSW) vary greatly in quantity and composition

• We will focus on the management of MSW

Composition of Solid Wastes

• Garbage (food rejects, organic wastes) Rubbish (nonputresible wastes)– Combustables (paper,plastic, wood, etc.) – Noncombustables (metal, glass, dirt, etc.)

• Yard wastes

• Other materials (almost anything can be found in MSW)

• Water (about 15 to 20% of MSW is water)

Composition of MSW

Source: USEPA

Other Solid Waste

• Discarded appliances, furniture, cars, etc.• Street sweepings and liter• Construction and demolition debris• Dead animals• Hazardous wastes from homes and industry• Sludge from water and wastewater treatment

plants.• Conclusion: the solid waste management

engineer must be prepared to deal with a wide variety of materials

Municipal Solid Waste Management System

• On-site Storage

• Collection

• Transport and transfer

• Processing

• Disposal

Storage

• Responsibility of the generator of solid waste

• Cans• Bags (sale can support cost of collection)

• Bins or dumpsters

• Compactors

• Waste separation of recyclables

MSW Collection

• Type of collection service– Self– Curbside pickup (most common)– Set out, set back– Backyard (most expensive)

• Frequency of collection– Daily (large generators)– Once per week (most common in northern states)– Twice per week (most common in southern states)– On demand (discards, special wastes)– Less frequent for recyclables

• Crew size (1 to 3 for curbside pick up, more for others)

Types of Collection Vehicles

• Packer trucks (to increase density of MSW and mass of collection, compacted density ~900 lb/yd3)– Rear loading– Side loading– Front loading– Manual loading– Mechanical loading– Chassis specified by volume (e.g., 20 yd3)

• Roll-off trucks (container left at site)• Truck for collection of recyclables

Source: USEPA

MSW Collection

• Collection Route Design– Macro routing– Districting– Micro routing

RefuseRecycling

(Every other)Green Waste

Street Sweeping(Once a month)

1Monday Monday Thursday

Friday

2Tuesday Tuesday Friday

Monday

3Wednesday Wednesday Monday

Tuesday

4Thursday Thursday Tuesday

Wednesday

5Friday Friday Wednesday

Thursday

DT

Special Schedules to be Provided

CC

Special Schedules to be Provided

Source: City of Sacramento, CA

Truck Routing

• Daily route method – A daily route is collected, workers work until entire

route is collecte

• Large route method– A weekly route is established, up to workers to

determine route

• Single load method– Collect until truck is full

• Definite working day method– Work 8 hour and then quit

Routing Hueristics -- examples

• Do not fragment routes, keep in same area• Collection time plus haul time should be about

equal for each route• Start collecting as close to the municipal garage

as possible to cut down travel time• Do not collect heavily traveled streets during

rush hours• Start routes at higher elevations• Make right turns as much as possible

Solid Waste- Truck Routing

Example - Routing

Start

Transfer

• In cases where the processing and disposal sites are near the collection area, the collection vehicle also hauls the full load to the site. Need to balance size to minimize number of hauls versus maneuverability needed for collection

• As distances increase the solid waste engineer should consider transferring the waste to a larger vehicle (e.g., semi trailer, rail car, barge)

Solid Waste Processing

• Objectives of Processing include– Volume reduction (baling, shredding,

incineration (also reduces mass)– Size reduction (shredding, grinding)– Component separation (hand sorting,

screening, magnetic separation, air classification)

– Resource recovery (composting, energy recovery, materials recovery)

Solid Waste Disposal

• No matter what processing is done, there will be some residue that needs to be disposed of safely

• Options for disposal– Modern, engineered landfill– Modern, engineered landfill– Modern, engineered landfill

Solid Waste - Sanitary Landfill

Is defined as a land disposal site employing an engineered method of disposing of solid wastes on land in a manner that minimizes environmental hazards by spreading the solid wastes to the smallest practical volume, and applying and compacting cover material at the end of each day.


Site Considerations:• Public Opinion• Proximity of major roadways• Speed Limits• Load limits on roadways• Bridge capacities• Underpass limitations• Traffic patterns and congestion• Haul distance (time)• Detours• Hydrology


Site Considerations:• Availability of cover material• Climate (e.g. floods, mud slides, snow)• Zoning requirements• Buffer areas around the site (e.g. high trees on

site perimeter)• Historic buildings, endangered species, wetlands,

and similar environmental factors.


Federal Regulations for Landfills:Subtitle D of the Resource Conservation and

Recovery Act (RCRA), EPA promulgated new federal regulations for landfills. Among these regulations are restrictions on distances from airports, flood plains, and fault areas, as well as limitations on construction in wetlands and others such as: 30 meters from stream, 160 m from drinking water wells, 65 m from houses, schools and parks, 3,000 m from air port runways, requires synthetic liner.


Methods of Operation:Area Method: solid waste is deposited on the

surface, compacted, then covered with a layer of compacted soil at the end of a working day.

This method is seldom restricted by topography: flat or rolling terrain, canyons, and other types of depressions are all acceptable.

Sanitary Landfill - Area Method


Methods of Operation:Trench Method: a trench is excavated and the

solid waste is placed in it and compacted; and the soil that was taken from the trench is then laid on the waste and compacted.

This method is used on level or gently sloping land where the water table is low. The advantage of this method is that the the soil taken from the trench can readily be used as cover.

Sanitary Landfill - Trench Method


Environmental Considerations:

A well designed and operated landfill will minimize vectors (carrier of disease), water and air pollution.

Burning is not permitted in a landfill. Keeping the waste covered will prevent the production of flies, control of rodents and fires.

Two other areas of pollution are landfill gases and leachate.


Landfill Gases:

Principal gaseous products emitted from a landfill (methane and carbon dioxide) are the results of microbial decomposition. During the early life of a land fill, the gas is primarily carbon dioxide. But as it matures, methane is produced in about equal quantities as carbon dioxide. Methane has an economic value.

There are also trace quantities of volatile organic chemicals deposited from industrial wastes that can be a concern.

Sanitary Landfill - Gas Composition

Component Percent (dry volume basis)

Methane 45-60Carbon dioxide 40-60

Nitrogen 2-5Oxygen 0.1-1.0

Sulfides, disulfides, mercaptans, etc. 0-1.0Ammonia 0.1-1.0Hydrogen 0-0.2

Carbon monoxide 0-0.2Trace constituents 0.01-0.06

Characteristics Value

Temperature, oC 35-50Specific gravity 1.02-1.05Moisture content Saturated

High heating value, kJ/m3 16,000-20,000

Gas Collection System

• Impermeable cap

• Granular material

• Collection pipes

• Gas treatment


Landfill Leachate:

Liquid that passes through the landfill and that has extracted dissolved and suspended matter from it is called leachate. Liquid enters the landfill from external sources such as rainfall, surface drainage, groundwater, and the liquid in and produced from the decomposition of the waste.

Solid Waste - Sanitary LandfillValue, mg/L

New landfill (less than 2 yrs)ConstituentRange Typical

Mature landfill(greater than 10 yrs)

BOD5 2,000-30,000 10,000 100-200TOC 1,500-20,000 6,000 80-160COD 3,000-60,000 18,000 100-500

Total suspended solids 200-2,000 500 100-400Organic nitrogen 10-800 200 80-120

Ammonia nitrogen 10-800 200 20-40Nitrate 5-40 25 5-10

Total Phosphorus 5-100 30 5-10Ortho Phosphorus 4-80 20 4-8

Alkalinity as CaCO3 1,000-10,000 3,000 200-1,000pH 4.5-7.5 6 6.6-7.5

Chloride 200-3,000 500 100-400Sulfate 50-1,000 300 20-50

Iron 50,1200 60 20-200

Leachate Collection System

• Impermeable liner

• Granular material

• Collection piping

• Leachate storage tank

• Leachate is trucked to a wastewater treatment facility

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