Enviormintal hw
Noaf18
masters_9b.pptxMasters 9B
Solid Waste Management and
Resource Recovery
Management of MSW in the U.S.
In 2005 (246 million tons generated),
54.3% Discarded
32.1% Recovery
13.6% Combustion with Energy Recovery
In 2011 (250 million tons generated),
53.8% Discarded
34.5% Recovery
11.7% Combustion with Energy Recovery
In 2012 (251 million tons generated),
53.6% Discarded
34.7% Recovery
11.7% Combustion with Energy Recovery
Recycling
After source reduction, the recovery of materials for recycling and composting are generally thought to be the next most important component of integrated solid waste management programs.
Resource recovery means that materials have been removed from the waste stream and purchased by an end user:
Yard trimmings composted at home are considered to be source reduction, not recycling
Yard trimmings that are delivered to an offsite compositing facility and then sold are considered to be recovered or recycled materials.
Recycling
Recycling is where materials are collected and used as raw materials for new products.
The recycling process:
Collecting recyclables
Separating them by type
Processing them into new forms that are sold to manufacturers
Purchasing and using goods made with reprocessed materials
Preconsumer recyclable materials consist of scrap that is recycled by manufacturers back into the original manufacturing process without ever been turned into a useful product.
Postconsumer recyclables are products that have been used by consumers for their originally intended purposes before being recycled.
Paper and Paperboard Recycling
Paper and paperboard products account for the largest single category of waste generation.
In 2005, 84 million tons of paper products were generated and 50% of that was recovered.
Corrugated cardboard boxes and newspapers account for half of the paper products generated and three-fourths of paper products recovered.
Roughly half of U.S. recycled paper products are used to make paperboard (cereal boxes, tablet backs, shoe boxes, etc.) and containerboard (corrugated cardboard).
Recycled wastepaper commonly used for construction projects like cellulose insulation, fiberboard, and flooring material.
Other uses include animal bedding, nursery pots, garden mulch, and trays.
Glass Container Recycling
The amount of glass seen in the municipal wastestream has declined.
About 100 pounds of glass is generated per person per year, and the recovery rate is about 22%
85% of glass is used for bottles and jars, the remaining 15% being used for durable goods such as window glass, fiberglass, mirrors, ceramic dishes, porcelain, glassware, ovenware, and light bulbs.
Recycling rate for durable goods is zero, they are considered contaminants in container glass recycling.
Glass Container Recycling
Recovered glass that will be remade into new container glass needs to separated by color: clear (flint), green (emerald), or brown (amber).
Colored polymer coatings can applied to the outside of glass containers, allowing all glass containers to be made clear and can provide extra strength.
Recovered and separated glass gets crushed into smaller pieces called cullet, which are remade into new glass bottles and jars (saving a lot of energy).
Other uses for cullet include: glasphalt (road paving material), fiberglass, abrasives, reflective paint for road signs, lightweight aggregate for concrete, glass polymer composites, and glass wool insulation.
Aluminum Recycling
One of the most valuable collectables in a municipal recycling program is aluminum cans.
A ton of aluminum is typically work 10 times as much as a ton of PET or HDPE (plastics), and it generates an on the order of 20 times as much revenue per ton as glass, steel cans, or newspapers.
This is because recycled aluminum uses only 2-3% of the energy required to make new aluminum from bauxite ore.
It’s estimated that 95% of recovered aluminum goes back into the production of the next generation of cans.
The next biggest source of aluminum comes from durable and nondurable goods such as home appliances and furniture.
Other Metals
Metals are of two categories: ferrous and nonferrous.
Nonferrous metals (aluminum, copper, lead, and zinc) have little or no iron in them, while ferrous metals do.
Discarded refrigerators, stoves, and water heaters are sources for metals in the municipal wastestream.
In 2005, 18.7 million tons of metals entered the municipal solid waste system (37% of metals were recovered):
74% ferrous metals
17% aluminum
9% other nonferrous metals
This has lead to appliance recycling, which is now close to 90% recovery.
Construction and Demolition Debris
Construction and demolition debris is generated when new structures are built and when existing structures are renovated or demolished:
Wood
Metals
Gypsum wallboard
Roofing
Concrete
Asphalt
Trees
Stumps
Earth
Rock
Construction and Demolition Debris
Most of building construction waste is relatively clean, unmixed, nonhazardous material that is easily disposed of without harm to the soil or groundwater.
As much as 95% of it can be recycled, but only about on-fourth actually gets reused or reprocessed into new material.
This is beginning to change due to the green building industry and the U.S. Green Buildings Council’s Leadership for Energy and Environmental Design (LEER) rating system which recognizes buildings that have outstanding environmental attributes.
Materials Recovery Facilities
Recyclable materials need to be sorted to separate the glass, plastics, newspapers, cans, and so forth.
Sorting is done by consumers, recycling pickup workers, and at a materials recovery facility (MRF).
The primary function of a materials recovery facility is to separate bottles by color, plastics by resin, cans by their metal content, newspapers, old corrugated containers, and compostable organics.
The second function is to densify those separated materials so they can be easily shipped to end users:
Crushing bottles
Flattening metal cans
Granulating and baling plastics
Baling waste paper
Waste Processing Facility
Waste that enters waste processing facilities could be landfilled as collected, but often contain valuable resources that should be recovered.
Not only can recyclables be removed, but combustible products can be prepared for waste-to-energy incineration, and materials to be landfilled can be densified to take up less space.
To facilitate recovery, the waste must be broken down into smaller pieces and is done so through a combination of machines that screen and shred the waste:
Screening (separation of particles through holes in a large drum)
Shredder (pounding, crushing, pulverizing, and shredding of waste)
Magnetic separation (magnets to remove ferrous metals)
Air classifier (separation of heavy and lighter particles)
Composting
Yard trimmings and food waste account for one-fourth of the mass of all municipal solid waste generated in the U.S.
Composting is the aerobic degradation of organic materials under controlled conditions, yielding a marketable soil amendment or mulch.
Composting is a natural process that can be carried out with modest human intervention, or can be carefully controlled to shorten composting time, space required, and minimize offensive odors.
The stabilized product of composting is rich in organic matter, which makes it a fine soil conditioner (though it lacks concentrations of key nutrients to compete with commercial fertilizers).
Discarded Materials
Discarded materials are materials that don’t get recovered from the wastestream, recycled, or composted.
Discarded materials are either burned or buried.
See table 9.21 on page 658.
Waste-to-Energy Combustion
Incineration is a preferred method of dealing with discarded materials because of:
Volume reduction
Immediate disposal
Possibility of recovering useful energy
Concerns about incineration include:
Questions about whether to burn for energy or recover for recyclable materials
Toxic substances released through burning
Reluctance to accept incinerator technology
Competition between recycling and incineration
The need for a constant flow of waste to burn to pay off the facility
Landfills
The number of landfills has been rapidly decreasing:
In 1988, 8,000 landfill sites
In 1995, 3,200 landfill sites
In 2005, 1,650 landfill sites
New landfill facilities are larger than before, offering larger overall capacity.
New RCRA rules, additional maintenance requirements, and tight capacity constraints have improved the operation of landfills and waste disposal.
