لخّصلي

The science and engineering of wastewater treatment has evolved signifi- cantly over the last century.With industrialization and scientific advances, chemical and toxic compounds have been detected in municipal wastewater treatment plant influents.Sustainable wastewater engi- neering involves application of the principles of science and engineering for the treatment of wastewater to remove pollutants or reduce them to an acceptable level prior to discharge to a water body or other environment, without compromising the self-purification capacity of that environment.Toward the beginning of the twentieth century, sewage treatment plants mainly used settling tanks (primary treatment) to remove suspended par- ticles from the wastewater before discharge to streams and rivers.An increasing body of scientific knowledge relating waterborne microorgan- isms and constituents to the health of the population and the environment has spurred the development of new engineered technologies for treatment of wastewater and potential reuse.In sev- enteenth century Colonial America, household wastewater management consisted of a privy (toilet) with an outlet constructed at ground level that discharged outside to a cesspool or a sewer.Wastewater may contain high con- centrations of organic and inorganic pollutants, pathogenic microorgan- isms, as well as toxic chemicals.The term wastewater includes liquid wastes and wastes transported in water from households, commercial establishments, and industries, as well as stormwater and other surface runoff.The earlier objectives were mainly to reduce the total suspended solids (TSS), biochemical oxygen demand (BOD), and pathogens.Nuisance caused by odors, outbreak of diseases, e.g. cholera, and other public health concerns prompted the design of a comprehensive sewer system in Chicago in the 1850s.In the early 1900s, the first trickling filter was constructed in Madison, Wisconsin, to provide biological (secondary) treat- ment to wastewater.If we look back in time, wastewater engineering has progressed from collection and open dumping, to collection and disposal without treatment, to collection and treatment before disposal, all the way to collection and treatment prior to reuse.In addition, he showed statistically that cholera victims had drawn their drinking water from a sewage-contaminated part of the river Thames, while those who remained healthy drew water from an uncontaminated part of the river.These find- ings, together with the discoveries by Pasteur and Koch, prompted the British Parliament to pass an act in 1855 to improve London's waste management system.From the mid-1900s to the present time, we have seen development of various types of biologi- cal and biochemical processes for the removal of pollutants from waste- water.Primary and secondary biological treatment was considered sufficient for produc- tion of treated wastewater of acceptable standards.If the wastewater is discharged without treatment to a stream or river, it will result in severe pollution of the aquatic environment.In 1843, the first sewer system, in Hamburg, Germany, was officially designed by a British engineer, Lindley (Anon, 2011).With low population densities, privies and cesspools constructed in this way did not cause many problems (Duffy, 1968).But as the population increased, the need for an engineered system for wastewater management in large cities became more evident.At that time, the sewer system was used to transport the untreated wastewater outside of the residential com- munity to a stream or river.Dilution of the wastewater with the stream water was the primary means of pollutant reduction.A chol- era epidemic struck London in 1848 and again in 1854, causing more than 25,000 deaths (Burian et al., 2000).The first activated sludge process was constructed in San Marcos, Texas, in 1916 (Burian et al., 2000).The decline in water quality will render the stream water unusable for future drinking water purposes.This has shifted our focus toward pollution reduction and control.

The science and engineering of wastewater treatment has evolved signifi-
cantly over the last century. As the population of the world has increased,
our sources of clean water have decreased. This has shifted our focus
toward pollution reduction and control. Disposal of wastes and wastewater
without treatment in lands and water bodies is no longer an option. An
increasing body of scientific knowledge relating waterborne microorgan-
isms and constituents to the health of the population and the environment
has spurred the development of new engineered technologies for treatment
of wastewater and potential reuse.
The term wastewater includes liquid wastes and wastes transported in
water from households, commercial establishments, and industries, as well
as stormwater and other surface runoff. Wastewater may contain high con-
centrations of organic and inorganic pollutants, pathogenic microorgan-
isms, as well as toxic chemicals. If the wastewater is discharged without
treatment to a stream or river, it will result in severe pollution of the aquatic
environment. The decline in water quality will render the stream water
unusable for future drinking water purposes. Sustainable wastewater engi-
neering involves application of the principles of science and engineering
for the treatment of wastewater to remove pollutants or reduce them to an
acceptable level prior to discharge to a water body or other environment,
without compromising the self-purification capacity of that environment.
The treatment and disposal of the generated solids and other by-products is
an integral part of the total process.
If we look back in time, wastewater engineering has progressed from
collection and open dumping, to collection and disposal without treatment,
to collection and treatment before disposal, all the way to collection and
treatment prior to reuse. Evidence of waste collection in the streets and then
use of water to wash the waste through open sewers has been found in the
ancient Roman empire. In the early 1800s, the construction of sewers was
started in London. In 1843, the first sewer system, in Hamburg, Germany, was officially designed by a British engineer, Lindley (Anon, 2011). In sev-
enteenth century Colonial America, household wastewater management
consisted of a privy (toilet) with an outlet constructed at ground level that
discharged outside to a cesspool or a sewer. With low population densities,
privies and cesspools constructed in this way did not cause many problems
(Duffy, 1968). But as the population increased, the need for an engineered
system for wastewater management in large cities became more evident.
Scientists and public health officials started to understand the relation-
ship between disease outbreaks and contamination of drinking water from
wastewater. Nuisance caused by odors, outbreak of diseases, e.g. cholera,
and other public health concerns prompted the design of a comprehensive
sewer system in Chicago in the 1850s. At that time, the sewer system was
used to transport the untreated wastewater outside of the residential com-
munity to a stream or river. Dilution of the wastewater with the stream
water was the primary means of pollutant reduction. These were called
water-carriage sewer systems.
Public health concern in the 1850s also resulted in the planning and devel-
opment of a water-carriage sewer system for the city of London. A chol-
era epidemic struck London in 1848 and again in 1854, causing more than
25,000 deaths (Burian et al., 2000). Dr. John Snow was the first doctor
at that time to establish a connection between the cholera outbreak and a
contaminated water supply at the Broad Street public well. In addition, he
showed statistically that cholera victims had drawn their drinking water from
a sewage-contaminated part of the river Thames, while those who remained
healthy drew water from an uncontaminated part of the river. These find-
ings, together with the discoveries by Pasteur and Koch, prompted the British
Parliament to pass an act in 1855 to improve London’s waste management
system. This led to the development of a comprehensive water-carriage sewer
system for London, designed by Joseph Bazalgette (Hey and Waggy, 1979).
Toward the beginning of the twentieth century, sewage treatment plants
mainly used settling tanks (primary treatment) to remove suspended par-
ticles from the wastewater before discharge to streams and rivers. In the
early 1900s, about one million people in the United States were served by
60 such treatment plants. In the early 1900s, the first trickling filter was
constructed in Madison, Wisconsin, to provide biological (secondary) treat-
ment to wastewater. The Imhoff tank was developed by German engineer
Karl Imhoff in 1906 for solids separation and further treatment. The first
activated sludge process was constructed in San Marcos, Texas, in 1916
(Burian et al., 2000). Advances in sludge digestion and gas production were
also being accomplished by researchers and utilities. From the mid-1900s
to the present time, we have seen development of various types of biologi-
cal and biochemical processes for the removal of pollutants from waste-
water. The earlier objectives were mainly to reduce the total suspended
solids (TSS), biochemical oxygen demand (BOD), and pathogens. Primary and secondary biological treatment was considered sufficient for produc-
tion of treated wastewater of acceptable standards. With industrialization
and scientific advances, chemical and toxic compounds have been detected
in municipal wastewater treatment plant influents. This has resulted in the
need for additional treatment beyond the secondary, giving rise to tertiary
treatment. Tertiary or advanced treatment can be physical, chemical, or
biological, or a combination of these processes.