Water Pollution and Treatment
Introduction
Water pollution is broad
term that includes contamination of different water bodies such as lakes,
rivers, oceans, and groundwater. Water pollution is caused by pollutants,
mostly in form of different chemicals that are discharged either directly or
indirectly into the water bodies without the adequate treatment to remove their
harmful effects. Water pollution is not only huge ecological problem but also
huge health problem. It is believed that water pollution is the leading
worldwide cause of deaths and diseases responsible for around 15,000 deaths
each day (Tawfiq and Olsen 1993).
The two main causes of
water pollution are waste water and sewage waste. Each year the world generates
around 400 billion tons of industrial waste, and lot of this waste gets
discharged into different water bodies causing serious water pollution problem.
Diarrhoea, caused by water pollution, is worldwide responsible for 1,5 million
deaths of children each year (AI-Abdali et al. 1996).
Arabian Gulf Pollution
The Arabian Gulf is a
shallow marginal sea of the Indian Ocean. It is a semi-closed basin which
extends for nearly 1000 km from Shatt A1-Arab, the nexus of the Tigris,
Euphrates, and Karun Rivers in the northwest, to the Strait of Hormuz in the
southeast, and covers a surface area of about 239000 km 2 (Fig. 1).
Fig. 1.
Bathymetric map of the Arabian Gulf
Oil
and natural gas represent the main source of pollution in the Arabian Gulf
Region. A region, which represents the biggest oil producing area in the
world, began to suffer from the problem especially after the industrial
development and the growth of urban settlements. Therefore, pollution caused by
sea-bed drilling and exploitation, oil spill from vessels and tankers, urban
sewage are the main sources of present and future pollution in the region (Reynolds 1993).
The
discharge of untreated industrial waste (liquid and gases) from oil refineries
and industry particularly Petrochemicals and fertilizer plants are rapidly
increasing along the Gulf. The development of urban centers in the Gulf are
forms another source of pollution owning to the discharge of great quantities
of untreated sewage into the Gulf. Consequently the Arabian Gulf region became
polluted. It is expected that the problem will be very serious if steps
for pollution control have not been taken.
Massoud
et al., (1996) reported that: A case for pollution problems is found in
Kuwait where Shuiba village has suffered severely from air pollution.
These facts and information about housing planning was obliged to migrate the
people to a new location far from the Shuiba industrial complex. So plans for
pollution control are very urgent to save the region and to create clean and
healthy environment. Some ideas to realize this aim can be
performed.
Firstly,
the regional co-operation is very important for abating pollution. All
Gulf States should co-operate in taking the necessary measures for dealing with
the pollution problem in the region. Establishment of a regional Oil
Center for pollution research is very urgent. This center will help all
the states to co-operate in the fields of scientific research, to exchange data
as well as other scientific information.
Secondly,
owing to the danger of large oil spill, the Gulf states ensure adequate
equipments and qualified personnel to deal with this problem.
Thirdly,
the industrial authorities in the Gulf States must take all necessary measures
to prevent and combat pollution through sound plans. Factories must use
the new equipments, which reduce or prevent the dangerous pollution.
Finally,
dumping the sewage into the Gulf without treatment must bee forbidden by law
and all states must establish stations to treat sewage water and plants to
convert urban solid wastes into fertilizers. This has been, partly,
achieved in Kuwait.
Red Sea Pollution
The major threats to the marine environment of the Red Sea
and Gulf of Aden are related to land-based activities. These include
urbanization and coastal development (for example, dredge and fill operations),
industries including power and desalination plants and refineries, recreation
and tourism, waste water treatment facilities, power plants, coastal mining and
quarrying activities, oil bunkering and habitat modification such as the
filling and conversion of wetlands (Horowitz 1991).
AI-Ghadban et
al., (1996) reported that: Physical
alteration and destruction of habitats, by such activities as urbanization,
coastal development (for example, dredge and fill operations and coastal mining
and quarrying, are considered the major environmental threat in several
countries of the region - Jordan, Saudi Arabia, Egypt - and are among the most
important in Sudan and Yemen.
Saudi Arabia is a considerable number of large scale
coastal construction projects - including recreational facilities, hotels and
restaurants - have been developed in the last few years that have caused
significant destruction of marine habitats and marine environment. Saudi Arabia is most of the treatment plants in Jeddah are
overloaded and, hence, the effectiveness of treatment is very low, hence, the
low quality of treated effluent from the plants. In Saudi Arabia's Red Sea
coastal cities of Jeddah and Yanbu, domestic waste water treatment is
considered quite adequate. The advanced Yanbu treatment plant produces waste
water suitable for irrigation, and only a limited amount is discharged to the
sea (Massoud et al. 1996).
Saudi Arabia. In Jeddah an industrial area comprising
approximately 300 small and medium-sized industries is situated in the southern
part of the city. In Yanbu, a large industrial facility is located in Madenat
Yanbu Al-Sinayah, comprising two oil refineries, petrochemical plants, a power
plant, food industry and other small industries. These industries are connected
to industrial waste water treatment plants (Massoud et al. 1996).
Much of the rapid expansion of Saudi Arabia's urban centers
has been achieved through the extensive use of desalinated water to meet
demands of the population and industry. As of 1992, there were 18 desalination
plants operating along Saudi Arabia's Red Sea coast with a total combined
capacity of 726,343 cu m/ day. The resulting impact
on the marine ecosystems due to thermal pollution and the elevated levels of
salt and chlorine in the return waters vary with the volumes of water and the
location of the discharge. Discharges into the marine environment from the
Jeddah plants include chlorine and anti-sealant chemicals as well as brine
which exceeds by 1.3 times the ambient salinity of the Red Sea, at a
temperature of 41°C (approximately 9°C above the average ambient Red Sea
temperature) (Massoud et al. 1996).
A power and desalination complex at Yanbu provides potable
water for the community within the city and for the industrial facilities, as
well as process water and industrial cooling seawater for various industries.
The total quantity of cooling water used by various industries is about 190,000
cu m/day.
Jeddah has eight desalination plants which discharge
cooling seawater (at about 39°C) and concentrated brine (with a concentration
of 50,000 ppm) into the sea, using an outfall channel. There are four oil refineries located along the eastern
side of the Red Sea. Although treatment facilities are provided for all the
refineries and data on the quality of the treated effluent is generally
acceptable, the refineries poses a threat to the marine environment in the
absence of adequately enforced regulations related to effluent discharges into
the coastal and marine environment. In Yanbu,
off-loaded ballast water is discharged into the Red Sea after removal of
residual oil, although 8.8 tones/year of oil and grease are discharged into the
sea (Massoud et al. 1996).
Saudi Arabia. Large recreational cities and centers have
been developed along the Jeddah coastline without any adequate evaluation of
potential environmental impacts. The construction of these large projects has
required significant dredge and fill operations, which adversely impact the
coastal environment. In addition to the direct destruction of marine life and
key habitats, the suspended fine materials resulting from these activities can
result in widespread damage to marine life. Such sedimentation results in the
suffocation of the benthic communities and has an adverse effect on the
surrounding ecosystems (mangroves, seagrass beds and coral reefs) and, as a
consequence, a decline in the productivity of the sea as measured by shrimping
grounds and other demersal fisheries. The practice of extending plots onto the
coast and into the sea can change the current pattern, morphology and
substrate, thus affect the marine life, and usually provide new sources of
continuous degradation (Massoud et al. 1996).
Methodology
of water pollution treatment
Preliminary Wastewater Treatment
Preliminary wastewater treatment is the
removal of such wastewater constituents that may cause maintenance or
operational problems in the treatment operations, processes, and ancillary systems.
It consists solely of separating the floating materials (like dead animals,
tree branches, papers, pieces of rags, wood etc.) and the heavy settleable
inorganic solids. It also helps in removing the oils and greases, etc. from the
sewage. This treatment reduces the BOD of the wastewater, by about 15 to 30%. Examples
of preliminary operations are:
• Screening and communition for the removal of debris
and rags.
• Grit removal for
the elimination of coarse suspended matter that may cause wear or clogging of
equipment.
• Floatation / skimming for the removal of oil and
grease.
Primary wastewater treatment
In primary treatment, a portion of the
suspended solids and organic matter is removed from the wastewater. This
removal is usually accomplished by physical operations such as sedimentation in
Settling Basins. The liquid effluent from primary treatment, often contains a
large amount of suspended organic materials, and has a high BOD (about 60% of
original). Sometimes, the preliminary as well as primary treatments are
classified together, under primary treatment. The organic solids, which are
separated out in the sedimentation tanks (in primary treatment), are often
stabilized by anaerobic decomposition in a digestion tank or are incinerated.
The residue is used for landfills or as a soil conditioner. The principal
function of primary treatment is to act as a precursor to secondary treatment.
Secondary Wastewater Treatment
Secondary treatment involves further
treatment of the effluent, coming from the primary sedimentation tank and is
directed principally towards the removal of biodegradable organics and suspended
solids through biological decomposition of organic matter, either under aerobic
or anaerobic conditions. In these biological units, bacteria will decompose the
fine organic matter, to produce a clearer effluent. The treatment reactors, in
which the organic matter is decomposed (oxidized) by aerobic bacteria are known
as Aerobic biological units; and may consist of:
• Filters (intermittent sand filters as well as
trickling filters),
• Aeration tanks, with the feed of recycled
activated sludge (i.e. the sludge, which is settled in secondary sedimentation
tank, receiving effluents from the aeration tank).
• Oxidation ponds and aerated lagoons. Since all
these aerobic units, generally make use of primary settled sewage; they are
easily classified as secondary units. The treatment reactors, in which the
organic matter is destroyed and stabilized by anaerobic bacteria, are known as Anaerobic
biological units and may consists of:
• Anaerobic lagoons,
• Septic tanks,
• Imhoff tanks, etc.
Out of these units, only anaerobic
lagoons make use of primary settled sewage, and hence, only they can be
classified under secondary biological units. Septic tanks and Imhoff tanks,
which use raw sewage, are not classified as secondary units. The effluent from
the secondary biological treatment will usually contain a little BOD (5 to 10%
of the original), and may even contain several mg/l of DO. The organic solids/
sludge separated out in the primary as well as in the secondary settling tanks
is disposed off by stabilizing under anaerobic conditions in a Sludge digestion
tank.
Tertiary/ Advanced Wastewater Treatment and
Wastewater Reclamation
Advanced
wastewater treatment, also called tertiary treatment is defined as the level of
treatment required beyond conventional secondary treatment to remove
constituents of concern including nutrients, toxic compounds, and increased
amounts of organic material and suspended solids and particularly to kill the
pathogenic bacteria. In addition to the nutrient removal processes, unit
operations or processes frequently employed in advanced wastewater treatment
are chemical coagulation, flocculation, and sedimentation followed by
filtration and chlorination. Less used processes include ion exchange and
reverse osmosis for specific ion removal or for the reduction in dissolved
solids. Tertiary treatment is generally not carried out for disposal of sewage
in water, but it is carried out, while using the river stream for collecting
water for re-use or for water supplies for purposes like industrial cooling and
groundwater recharge. Disinfection,
typically with chlorine, can be the final step before discharge of the effluent.
However, some environmental authorities are concerned that chlorine residuals
in the effluent can be a problem in their own right, and have moved away from
this process. Disinfection is frequently built into treatment plant design, but
not effectively practiced, because of the high cost of chlorine, or the reduced
effectiveness of ultraviolet radiation where the water is not sufficiently
clear or free of particles.
Water
Pollution Control
The suggested approach for water
pollution control may be applied at various levels; from the catchment or river
basin level to the level of international co-operation (Fig. 2).
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Initial analysis
of water pollution management issues
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Assessment of
management functions and objectives for all administrative levels
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Management tools
and instruments
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Action
plan for water pollution control
Figure
2. Elements and processes of an action plan for water pollution control
References:
AI-Abdali, F.;
Massoud, M.S.; A1-Ghadban, A.N. Bottom sediments of the Arabian Gulf: III.Trace
metal contents as indicators of pollution and implications for the effect and
fate of Kuwait oil slick. Environ. Pollut. 93: 285-301; 1996.
A1-Ghadban, A.N.;
Massoud, M.S.; AI-Abdali, F. Bottom sediments of the Arabian Gulf: I.
Sedimentological characteristics. J. Univ. Kuwait (Sci.) 23: 71-88; 1996.
Horowitz, A.G. A
primer on sediment trace element chemistry. Second edition. Chelsea, MI: Lewis
Publishers Inc.; 1991.
Massoud, M.S.;
AI-Abdali, F.; AI-Ghadban, A.N.; AI-Sarawi, M. Bottom sediments of the Arabian
Gulf: II. TPH and TOC contents as indicators ofoil pollution and implications
for the effect and fate of Kuwait oil slick. Environ. Pollut. 93: 271-284;
1996.
Reynolds, R.N.
Physical oceanography of the Gulf, Strait of Hormuz, and the Gulf of Oman:
Results of the Mt. Mitchell expedition. Mar, Pollut. Bull. 27: 35-59; 1993.
Tawfiq, N.; Olsen,
D.A. Saudi Arabia's response to the 1991 Gulf oil spill. Mar. Pollut. Bull. 27:
333-345; 1993.
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