What is wastewater treatment?
Wastewater is water that has been used and must be treated before it is released into another body of water,
so that it does not cause further pollution of water sources. Wastewater comes from a variety of sources.
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In the industrialised countries the first wastewater treatment
techniques involved processes of a purely
physical and mechanical nature to reduce the solid
content. The limitations of both the results and the
applicability of these processes later led to the use of
treatments of a chemical nature. At the beginning of
the 20th century water hygiene problems were overcome
by adding chlorine. At the same time other
types of treatment were introduced, with specific
objectives, such as rendering the water softer or reducing
the iron content.
There has been a gradual progression fiom the haphazard
treatment of wastewater treatment by dilution in large
tanks to the use of spreading areas andt o creation of
centralised systems. Originally the initial stage in
these systems aimed at reducing substances in suspension
by using chemo-physical methods. As a result
of findings in England during the last twenty
years of the 19th century, which led to the activated
sludge process, a second stage in the process was introduced
by which organic matter was stabilised by
As a consequence, the technological evolution of
these processes has led to widespread mechanisation
of the systems, especially in the initial treatment
stage. So far as the secondary treatment stage
is concerned, trickling filters, rotating biological
disks, different versions of activated sludge processes
and rapid filtration systems have been introduced
The quality of water supplies has gradually declined,
largely because of high and often excessive
consumption of natural water and the abuse of the
ground soil as a recipient of wastewater treatment.Pollution
has also contributed to this effect. The situation is
so bad that it is now necessary to process water for
certain uses for whicihn the past no processing was
ever considered necessary. Therefore, highly advanced
processes have been introduced to reclaimur -
ban effluent for agricultural and industrial purposes.
Fundamental studies in the fields of chemistry and
microbiology and findings fiom research into process
techniques provide the foundations on which
new methodologies for planning and laying out
wastewater treatment systems are currently built.
Today these technologies con€orm with environmental
politics which ftohre near fiture foresees the
integration of systems and devices for reducing the
impact of anthropic processeosn the environment.
Waters that are used for drinking, manufacturing, farming, and other purposes by residences (toilets, baths, showers, kitchens, sinks), institutions, hospitals, commercial and industrial establishments are degraded in quality as a result of the introduction of contaminating constituents. Organic wastes, suspended solids, bacteria, nitrates, and phosphates are pollutants that commonly must be removed.
To make wastewater acceptable for reuse or for returning to the environment, the concentration of contaminants must be reduced to a non-harmful level, usually a standard prescribed by the Environmental Protection Agency.
Sewage can be treated close to where it is created (in septic tanks, bio-filters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant.
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. The task of designing and constructing facilities for treating wastewaters falls to environmental engineers. They employ a variety of engineered and natural systems to get the job done, using physical, chemical, biological, and sludge treatment methods. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with many toxic organic and inorganic compounds.
The features of wastewater treatment systems are determined by (1) the nature of the municipal and industrial wastes that are conveyed to them by sewers, and (2) the amount of treatment required to preserve and/or improve the quality of the receiving bodies of water. Discharges from treatment plants usually are disposed by dilution in rivers, lakes, or estuaries. They also may be used for certain types of irrigation (such as golf courses), transported to lagoons where they are evaporated, or discharged through submarine (underwater) outfalls into the ocean. However, outflows from treatment works must meet effluent standards set by the Environmental Protection Agency to avoid polluting the bodies of water that receive them.
Sewage Treatment Plant is basically characterized as below system based on usage of Oxygen / Air in Secondary Treatment Stage (Biological Decomposition of organic matter).
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