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Solid waste management
Introduction to solid waste management
Solid waste is the unwanted or useless solid materials generated from combined
residential, industrial and commercial activities in a given area
...
Management of solid waste reduces or eliminates adverse impacts on the environment
and human health and supports economic development and improved quality of life
...
These include monitoring, collection, transport, processing, recycling and disposal
...
There are many environmental benefits that can be derived from the
use of these methods
...
Therefore it is advisable that these methods be
adopted and incorporated as part of the waste management plan
...
They
eliminate the production of waste at the source of usual generation and reduce the
demands for large scale treatment and disposal facilities
...
All of the methods of waste prevention mentioned require public participation
...
Also the government may need to
regulate the types and amount of packaging used by manufacturers and make the reuse of
shopping bags mandatory
...
Thus from this definition recycling occurs
in three phases: first the waste is sorted and recyclables collected, the recyclables are
used to create raw materials
...
The sorting of recyclables may be done at
the source (i
...
within the household or
office) for selective collection by the
municipality or to be dropped off by the
waste producer at a recycling centres
...
Also a system of selective
collection by the government can be
costly
...
Colour coded recycling bins for
neighbourhood or the importation of more waste separation at the source of production
vehicles to facilitate the collection
...
unpluggedliving
...
The sorting by the municipality has the advantage of
eliminating the dependence on the public and ensuring that the recycling does occur
...
Waste Collection
Waste from our homes is generally collected by our local authorities through regular
waste collection, or by special collections for recycling
...
Other factors to consider
when deciding on frequency of collection are the odours caused by decomposition and
the accumulated quantities
...
Table 1 Descriptions of the main collection systems
...
mit
...
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System
Description
Advantages
Disadvantages
SHARED: Residents can bring out waste at any time
Dumping at
designated
location
Residents and other
generators are
required to dump their
waste at a specified
location or in a
masonry enclosure
...
Waste is scattered around
the collection point
...
Shared
container
Residents and other
generators put their
waste inside a
container which is
emptied or removed
...
Adjacent residents complain about the
smell and appearance
...
Block collection
Collector sounds horn
or rings bell and waits
at specified locations
for residents to bring
waste to the collection
vehicle
...
Less waste
on streets
...
If all family members are out when
collector comes, waste must be left
outside for collection
...
Curbside
collection
Waste is left outside
property in a container
and picked up by
passing vehicle, or
swept up and collected
by sweeper
...
No
permanent
public
storage
...
If collection service is delayed, waste
may not be collected or some time,
causing considerable nuisance
...
Convenient
for resident
...
Residents must be available to hand
waste over
...
Yard collection
Collection laborer
enters property to
remove waste
...
No
waste in
street
...
Cultural beliefs,
security considerations or architectural
styles may prevent laborers from
entering properties
...
Treatment methods are selected based on the composition, quantity,
and form of the waste material
...
It should be noted that treatment and
disposal options are chosen as a last resort to the previously mentioned management
strategies reducing, reusing and recycling of waste (figure 1)
...
sustainabilityed
...
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Thermal treatment
This refers to processes that involve the use of heat to treat waste
...
Incineration
Incineration is the most common thermal treatment process
...
After incineration, the wastes are converted to carbon
dioxide, water vapour and ash
...
In addition to supplying energy
incineration technologies have the advantage of reducing the volume of the waste,
rendering it harmless, reducing transportation costs and reducing the production of the
green house gas methane
Pyrolysis and Gasification
Pyrolysis and gasification are similar processes they both decompose organic waste by
exposing it to high temperatures and low amounts of oxygen
...
These techniques use heat and an
oxygen starved environment to convert biomass into other forms
...
All of these products have a high heat value and can be utilised
...
Open burning
Open burning is the burning of unwanted materials in a manner that causes smoke and
other emissions to be released directly into the air without passing through a chimney or
stack
...
Openburning has been practiced by a number of urban centres because it reduces the volume
of refuse received at the dump and therefore extends the life of their dumpsite
...
In countries where house holders are required to pay for
garbage disposal, burning of waste in the backyard allows the householder to avoid
paying the costs associated with collecting, hauling and dumping the waste
...
This
uncontrolled burning of garbage releases many pollutants into the atmosphere
...
All of these chemicals pose
serious risks to human health
...
The polycyclic aromatic compounds and the
hexachlorobenzene are considered to be carcinogenic
...
The harmful effects of open burning are also felt by the environment
...
Nitrogen oxides contribute to acid rain, ozone depletion, smog and global
warming
...
The particulate matter creates smoke and haze
which contribute to air pollution
...
They are usually placed in areas
where land features act as natural buffers between the landfill and the environment
...
In addition to the strategic placement of the landfill other protective measures are
incorporated into its design
...
The
leachate is collected and pumped to the surface for treatment
...
A landfill is divided into a series of individual cells and only a few cells of the site are
filled with trash at any one time
...
The daily
waste is spread and compacted to reduce the volume, a cover is then applied to reduce
odours and keep out pests
...
Some sanitary landfills are used to recover energy
...
Methane can be used as an energy source to produce
heat or electricity
...
The process of generating gas is
very slow, for the energy recovery system to be successful there needs to be large
volumes of wastes
...
Figure 3 Main features of a modern landfill (source
http://www
...
doe
...
h
tml)
Controlled dumps
Controlled dumps are disposal sites which comply with most of the requirements for a
sanitary landfill but usually have one deficiency
...
These dumps have a reduced risk of environmental contamination,
the initial costs are low and the operational costs are moderate
...
Bioreactor Landfills
Recent technological advances have lead to the introduction of the Bioreactor Landfill
...
The main controlling factor is the constant addition of liquid to
maintain optimum moisture for microbial digestion
...
In cases where leachate in not enough, water or other
liquid waste such as sewage sludge can be used
...
These enhanced
microbial processes have the advantage of rapidly reducing the volume of the waste
creating more space for additional waste, they also maximise the production and capture
of methane for energy recovery systems and they reduce the costs associated with
leachate management
...
Biological waste treatment
Composting
Composting is the controlled aerobic decomposition of organic matter by the action of
micro organisms and small invertebrates
...
These include: in vessel composting, windrow composting,
vermicomposting and static pile composting
...
The rate of
compost formation is controlled by the composition and constituents of the materials i
...
their Carbon/Nitrogen (C/N) ratio, the temperature, the moisture content and the amount
of air
...
The micro organisms
require carbon as an energy source and nitrogen for the synthesis of some proteins
...
A high C/N ratio
can be corrected by dehydrated mud and a low ratio corrected by adding cellulose
...
The microbes need the
moisture to perform their metabolic functions
...
If however there is too much moisture then it is possible that
it may displace the air in the compost heap depriving the organisms of oxygen and
drowning them
...
However, if
temperatures are too high, above 75oC then the organisms necessary to complete the
composting process are destroyed
...
Aeration is a very important and the quantity of air needs to be properly controlled when
composting
...
The anaerobes are undesirable since they will slow the process,
produce odours and also produce the highly flammable methane gas
...
Anaerobic Digestion
Anaerobic digestion like composting uses biological processes to decompose organic
waste
...
Aerobic respiration, typical of composting, results in the formation of Carbon
dioxide and water
...
In addition to generating the humus which is used as a soil
enhancer, Anaerobic Digestion is also used as a method of producing biogas which can
be used to generate electricity
...
Integrated Solid Waste Management
Integrated Solid Waste Management (ISWM) takes an overall approach to creating
sustainable systems that are economically affordable, socially acceptable and
environmentally effective
...
It is important to note that no one single
treatment method can manage all the waste materials in an environmentally effective
way
...
Effective management schemes therefore need to operate in ways which best
meet current social, economic, and environmental conditions of the municipality
...
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...
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Useful Websites
•
United Nations Environment Programme International Source Book on
Environmentally Sound Technologies (ESTs) for Municipal Solid Waste
Management (MSWM)
or
...
asp
•
Sewerage and Solid Waste Project Unit
...
The solid waste management
programme
...
gov
...
asp >
http://www
...
org
...
htm
http://www
...
doe
...
ht
ml
http://web
...
edu/urbanupgrading/upgrading/issues-tools/issues/wastecollection
...
sustainability-ed
...
htm
http://www
...
org/downloads/projectfiles/1826-00237
...
cecs
...
edu/Lesson8-Incineration
...
csiro
...
html
http://viso
...
jrc