solid waste
Solid Wastes
Contents of entire course
Disposal
Methods
Historical
Patterns in Waste Disposal
Sanitary
Landfills Site Selection
Pollution
from Sanitary Landfills
Incineration
Source
Reduction
adapted to HTML from lecture
notes of Prof. Stephen A. Nelson Tulane University
Up until the last 5 to 10 years or so,
the major form of solid waste disposal in many places was burying in
landfills.
Today, we can only use landfills to deposit ash from incineration or
debris
from construction or demolition processes.
Waste Energy Sites - Incineration sites
that use the burning process to produce electricity.
Disposal
Methods
Source Reduction - Reducing the amount
of solid waste that is initially produced. This is the ideal solution,
but so far, has been unsuccessful.
Reducing Waste Volume
Pigs -- A major source of reducing food
wastes until the 1960's. This practice was stopped because diseases
were
spread in this manner.
In-sink garbage disposals -- This method
doesn't really reduce the volume of waste; rather, it transfers the
waste
into the sewer system (or into the septic tanks).
Composting -- Really a method of recycling,
it works very well to reduce the volume of organic wastes. The waste
can
the be used in gardens, fields etc.
Recycling -- Australia recycled much
of its garbage until WWII, when it became unpopular to recycle.
-- Brings up the question: Who should
do the sorting, the source or the facility?
Open dumps and sanitary landfills -- Open
dumps are often sited in wetlands, which, along with the fact that they
are unlined, make them very unsafe, in terms of water contamination.
Sanitary
landfills are also covered up daily, to reduce vermin and smell.
Incineration-- Beginning to play a much
larger part in solid waste disposal. Incinerated waste has a much
smaller
volum as ash, which is a lot easier (and safer) to dispose of.
Ocean dumping This practice is no longer
allowed, although at one time it was fairly popular.
Illegal Dumping-- A prolific disposal method,
whether individually (tossing trash out of a window while driving down
the highway) or on a large scale by industries.
Historical
Patterns in Waste Disposal
in many developed countries, we produce
a ton of garbage per person per year. This breaks down to a
couple
of kilograms per person per day.
Recently, near major cities, the
policy of Integrated Waste Management has become more popular, which
involves
the following:
Recycle -- First, all of the waste that
can be recycled is.
Incinerate -- The remainder of the waste
is incinerated, to reduce its volume (by 90%) and transform it all into
ash. Also, the excess heat generated from the incineration process is
used
to spin a turbine, generating electricity.
Landfill -- The ash, along with waste from
construction and demolition practices, is then dumped into a landfill.
Typical
Pattern of Trash Disposal
| Number
of |
1986 |
1991 |
1994 |
| Landfills |
12 |
9 |
6 |
| Incinerators |
2 |
5 |
5 |
Recycling
Programs |
2 - Pilot |
15 |
15 |
| Composting |
- |
? |
7 |
| Shipping |
- |
7 |
? |
| |
|
|
|
|
Percent
of Trash
disposed
of by |
1987 |
1991 |
1994 |
1997 |
| Landfills |
80% |
25% |
3% |
0% |
| Incinerators |
6% |
39% |
47% |
46% |
| Recycling |
1% |
19% |
25% |
25% |
| Shipping |
13% |
18% |
25% |
29% |
in many places llaw now forbids
placing raw garbage into landfills, due to the dangers of groundwater
contamination
from landfill leeching.
Sanitary
Landfills Site Selection
Should be above the water
table, to minimize interaction with groundwater.
Preferably located in clay
or silt.
Do not want to place in a
rock quarry, as water can leech through the cracks inherent in rocks
into
a water fracture system.
Do no want to locate in sand
or gravel pits, as these have high leeching. Unfortunately, most of
Long
Island is sand or gravel, and many lanfills are located in gravel pits,
after they were no longer being used.
Do not want to locate in
a flood plain. Most garbage tends to be less dense than water, so if
the
area of the landfill floods, the garbage will float to the top and wash
away downstream.
Pollution
from Sanitary Landfills
Volatiles (from Anaerobic
processes) include:
Methane (CH4)
Ammonia (NH3)
Hydrogen Sulfide
Leachates include:
Heavy Metals (Pb, Cr,
Cd)
Soluble Salts (Chloride,
Nitrate, Sulfate)
Organic Compounds
Modern Landfill with plastic, clay liner and collection pipes to
prevent
leachate from entering the groundwater. Vadose Wells are situated in
the
unsaturated zone to monitor gas emissions. Things do not
biodegrade
in a landfill. Anaerobic processes are the only ones that take place
after
the landfill is sealed, and this makes organic decay very slow, as
there
is no oxygen or moisture tosupport the decomposition process.
Incineration
Reduces the volume of solid
waste - only the ash (approximately 90% reduced in volume) needs
landfilling.
Metals may be recovered from
the incineration process, and are usually recycled by the incineration
plant.
Converts waste to energy,
by using the heat given off by the incinerating waste to fuel a
turbine,
which is used to generate electricity.
May result in air pollution
(although recent regulations severely restrict the amount of pollution
from incineration).
Ash may be a hazardous waste
(this is not true in most cases, although there are exceptions).
Burns at 1800° F.
Source Reduction
The following are
all methods of initiating source reduction:
Do not purchase as much,
or reduce use.
Purchase products with reduced
toxics.
Purchase environmentally
preferred products.
Purchase products with less
packaging.
Purchase concentrated products.
Purchase products in bulk
or larger sizes.
Buy multiple use products.
Do not replace for style.
Purchase more durable products.
Maintain properly and repair
instead of replace.
Purchase reusable products,
and then reuse or donate to charity.
Purchase more efficient products,
or use products more efficiently.
Purchase manufactured product.
Borrow, share, or
rent product.
