20-06-2014, 01:00 PM
Solid waste management
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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. It may be categorised
according to its origin (domestic, industrial, commercial, construction or institutional);
according to its contents (organic material, glass, metal, plastic paper etc); or according to
hazard potential (toxic, non-toxin, flammable, radioactive, infectious etc).
Management of solid waste reduces or eliminates adverse impacts on the environment
and human health and supports economic development and improved quality of life. A
number of processes are involved in effectively managing waste for a municipality.
These include monitoring, collection, transport, processing, recycling and disposal
Reduce, Reuse, Recycle
Methods of waste reduction, waste reuse and recycling are the preferred options when
managing waste. There are many environmental benefits that can be derived from the
use of these methods. They reduce or prevent green house gas emissions, reduce the
release of pollutants, conserve resources, save energy and reduce the demand for waste
treatment technology and landfill space. Therefore it is advisable that these methods be
adopted and incorporated as part of the waste management plan
Recycling
Recycling refers to the removal of items from the waste stream to be used as raw
materials in the manufacture of new products. 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. These raw materials are then used in the production of new
products.
The sorting of recyclables may be done at
the source (i.e. within the household or
office) for selective collection by the
municipality or to be dropped off by the
waste producer at a recycling centres. The
pre-sorting at the source requires public
participation which may not be
forthcoming if there are no benefits to be
derived. Also a system of selective
collection by the government can be
costly. It would require more frequent
circulation of trucks within a
neighbourhood or the importation of more
vehicles to facilitate the collection.
Another option is to mix the recyclables with the general waste stream for collection and
then sorting and recovery of the recyclable materials can be
Waste Collection
Waste from our homes is generally collected by our local authorities through regular
waste collection, or by special collections for recycling. Within hot climates such as that
of the Caribbean the waste should be collected at least twice a week to control fly
breeding, and the harbouring of other pests in the community. Other factors to consider
when deciding on frequency of collection are the odours caused by decomposition and
the accumulated quantities. Descriptions of the main types of collection systems are
given in the table below.
Treatment & Disposal
Waste treatment techniques seek to transform the waste into a form that is more
manageable, reduce the volume or reduce the toxicity of the waste thus making the waste
easier to dispose of. Treatment methods are selected based on the composition, quantity,
and form of the waste material. Some waste treatment methods being used today include
subjecting the waste to extremely high temperatures, dumping on land or land filling and
use of biological processes to treat the waste. It should be noted that treatment and
disposal options are chosen as a last resort to the previously mentioned
Anaerobic Digestion
Anaerobic digestion like composting uses biological processes to decompose organic
waste. However, where composting can use a variety of microbes and must have air,
anaerobic digestion uses bacteria and an oxygen free environment to decompose the
waste. Aerobic respiration, typical of composting, results in the formation of Carbon
dioxide and water. While the anaerobic respiration results in the formation of Carbon
Dioxide and methane. 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.
Optimal conditions for the process require nutrients such as nitrogen, phosphorous and
potassium, it requires that the pH be maintained around 7 and the alkalinity be
appropriate to buffer pH changes, temperature should also be controlled
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. An integrated solid waste management system involves the
use of a range of different treatment methods, and key to the functioning of such a system
is the collection and sorting of the waste. It is important to note that no one single
treatment method can manage all the waste materials in an environmentally effective
way. Thus all of the available treatment and disposal options must be evaluated equally
and the best combination of the available options suited to the particular community
chosen. Effective management schemes therefore need to operate in ways which best
meet current social, economic, and environmental conditions of the municipality.
Figure 4