من انا

صورتي
الرياض, Saudi Arabia
مسلم، وأناأحوج ما أكون إلى معرفة نفسي

الاثنين، 30 يناير، 2012

Water Pollution and Treatment


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).



Initial analysis of water pollution management issues
  • Impact issues
  • User management issues


Assessment of management functions and objectives for all administrative levels
  • Required management interventions
  • Long term objectives
  • Potentials and constraints
  • Short term strategy


Management tools and instruments
  • Regulation
  • Standards
  • Economic instruments
  • Monitoring system
  • Water quality modelling tools
  • Environmental impact assessment and cross-sectoral co-ordination


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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