Municipal Solid Waste

Living in the Material World

• For the most part, the Earth is a closed system with respect to materials

– Whatever “stuff” we’re going to have is already here

• The concept of “consumption” is really a misnomer

– We don’t really consume matter - we convert it

• Matter must therefore cycle throughout the Earth’s ecosystem

– At the atomic level

– At the molecular level

An example we’ve seen: Carbon

• Carbon in the atmosphere (in the form of CO2) is removed by plants through photosynthesis and converted to their tissue

• We make paper from some plants and use it as packaging

• When we dispose of the paper, we might compost it, causing it to be eaten by scavenging organisms

• The respiration of these organisms releases the carbon to the atmosphere in the form of CO2 or CH4 (depending on the nature of the decomposition)

“Use it up, wear it out, make do, or do without!”

• During World War II material conservation became a public focus as part of the war effort

– Rationing of materials

– “Victory Gardens”

– “Armstrong” starters

• This led to the “reduce, reuse, recycle” slogan of the 1970s

Part I: Definitions and Trends

Definition

• Solid waste from residential, commercial, institutional, and industrial sources, not including such things as construction waste, automobile bodies, municipal sludge, combustion ash, and industrial process waste even though those wastes might also be disposed of in municipal waste landfills or incinerators.

• See http://www.epa.gov/epaoswer/osw/index.htm for current information on trends and technologies.

MSW Terms

1990 2006

Food 17 12

Yard/Wood 13 18

Plastic 8 12

Glass 12 5

Metal 10 8

US EPA

US EPA

MSW Generation

MSW Disposition

Recycling

US EPA

US EPA

Part II: Life Cycle Assessment

Life Cycle Assessment

• Consideration of the energy and material flows at every stage in the life cycle of a product so that new insights can be gained into the product’s contributions to overall environmental quality.

Product Lifecycle

Example of Paper v.

Polyfoam ==>

Source Reduction

• Reducing garbage at the source with Green Product Design strategies.

• Examples include product system life extension, material life extension, material selection, reduced material intensiveness, process management, efficient distribution, and various policy options.

Part III: Methods for Reducing, Handling, and Disposing of MSW

Methods Labeling—inform consumers through the use of labels on

products about Green Products.

Recycling—collecting pre-used materials to be used as raw materials for a new product. Often, creating a new product with recycled material reduces the energy requirements for making the same product with virgin material.

Composting—containment and aerobic degradation of organic materials, yielding marketable soil amendment or mulch.

Methods (con’d)

Waste-to-Energy Combustion—the process of incinerating waste to generate useable energy, usually in the form of steam. Energy content of waste is a function of the type of waste.

Landfills—burying waste in sanitary landfills that contain the waste and allow for safe accumulation and/or decomposition.

Consideration of an Integrated Strategy

Part IV: Issues to Consider for Each Approach

Recycling

Recycling

What prevents us

from recycling

more?

Materials Recovery Facility

Handling Commingled Waste

Synthetic Polymers

• Many of the structures in nature are constructed of polymers

• Polymers are chains of monomers - molecular structures which can be joined by covalent bonds

• In the 20th century chemists developed the ability to imitate natural polymers, using petroleum hydrocarbons as a starting point

• Today many of the tools and toys on which we depend are derived from petroleum in this way

– More recently non-petroleum starters have been used

The “Big Six”

• LDPE: Low Density Polyethylene (#4)

– E.g. Plastic bags, bubble wrap

• HDPE: High Density Polyethylene (#2)

– E.g. Milk jugs

• PVC: Polyvinyl chloride (#3)

– E.g. Plumbing pipes

• PS: Polystyrene (#6)

– Styrofoam insulation, drinking glasses

• PP: Polypropylene (#5)

– Bottle caps, automobile trim

• PET: Polyethylene Terephthalate (#1)

– Pop bottles, video tape

How do you separate aluminum cans from a co-mingled waste stream?Stay tuned for recitation!

Pay-per-container: The Chester, NJ Model

• Recognized that cost was a driving factor• Also saw the importance of convenience• Adopted a system which permitted co-mingled recyclable

pickup once per week as part of base fee, and garbage pickup at $2 per 30-pound container (based on tipping fee)

• Results were astounding:– Recycled fraction: 9% → 42%– Participation: < 10% → 90%+

– In one month!• See NY Times article (July 14, 1992)

Waste to Energy

Energy Content of Waste

• High Heating Value = gross energy content, including energy contained in the vaporized water that is produced

• Low Heating Value = net energy content, not including energy in water vapor

Calculation of LHV• Most of the time, we lose the latent heat in the water vapor and the

heat possible from hydrogen (since when it burns it generates water vapor), thus we need to calculate LHV from HHV values

• The latent heat and heat lost from hydrogen is:

QL = 2440 kJ/kg (W kg+ 9H kg)

(Why do we multiply “H” by 9? Hint: consider molecular masses)

• To get LHV, take HHV and subtract QL

Environmental Impacts of Incineration

• Solids - bottom ash and fly ash

• Gases:

– dioxins and furans

– polychlorinated biphenyls (PCB)

– heavy metals

– polycyclic aromatic hydrocarbons (PAH)

Landfilling

RCRA Landfill Design