Determination the Concentrations of Heavy Metals in Seawater Intake of Desalination Plant

The desalination plants are considered to have a major role in developing human life. Recently this technology has become widely distributed along the coastal area. Many countries are adopting these technologies for securing the fresh water supply for consumer consumption all over the world. Therefore, it's necessary to evaluate the Environmental Impact Assessment (EIA) of these technologies on the coastal line . This study has been monitoring sea water quality used for feeding desalination plant to determine the heavy metals of iron ( Fe ), cupper ( Cu ), manganese ( Mn ) and zinc ( Zn ) by using chemical monitoring system to know their effects on the desalination units and other components. This study was conducted in the year 2010 from March to October, samples were collected from feed water intake of Tripoli’s West Desalination Plant (Janzour), the plant was chosen because of its importance in supplying fresh water for potable water and industrial uses . The results of this study showed monthly differences in most tested parameters. These differences lead to the scale and corrosion by precipitation on the components of the desalination unites. On the other hand the concentration of Fe , Cu , Mn and Zn were very high compared to the standard rates of the sea water. The mean concentration in ppm at site 1 and 2 of Fe , Cu , Mn and Zn were (0.044 & 0.043), (2.30 & 2.85), (0.0585 & 0.0593) and (0.0712 & 0.0713) respectively.


Introduction
Provision of potable water by seawater desalination is generally considered a benefit despite high construction and operating costs of plants.This is especially true when conventional sources of freshwater are absent or cannot be exploited without severe environmental damage.However, is familiar with the situation in arid countries knows that desalination plants are often large industrial facilities, which consume space and emit substantial amounts of combustion gases.It is also known that potable water production means emitting a concentrate into the sea, into the ground or into evaporation ponds (Desalination & Water Reuse, 1997).Though, a generally less noted fact is that this concentrate contains not only the contents of the seawater taken in, but also additives (or their conversion products) necessary for the desalting process and corrosion by-products (Dural et al., 2007).The response of the impacted marine ecosystem depends on its sensitivity and the magnitude of the impact, which in turn depends on factors such as distance, transport direction and dilution.Small enclosed or semienclosed seas may be understood as entire ecosystems, although sub-ecosystems may be defined and examined separately (Bradl, 2005).For example, one half of the world's seawater desalination capacity is located in the Arabian Gulf, and overall impacts on this enclosed sea may be considered in addition to local effects on certain biotopes.In contrast, the accumulation of desalination plants (Hassan & Elaber, 2003) on the Canary Islands (GECOL, 2003) will not produce measurable effects on the Atlantic Ocean as a whole, but distinct coastal ecosystems may be affected by the discharge.
Libya is water dependency consists of 90% ground water and 10% on other resources combined.The desalination plants and co-generation power plants in Libya were established between .The Tripoli's West Desalination Plant has started the production of water in 1999.The plant consists of two units using two types of fuel which are HFO+Gas.It's also a cogeneration of steam turbine, and it has been operating with MSF process and possess 2 units with design capacity (20000 m 3 /day) and (4120 MW, Unit Design Output 480 MW/hr).
On other hand, the EIA is a very important process to know the positive and the negative environmental impact for any new or existing industrial projects to encourage the positive factors and eliminate negative factors in order to lead a sustainable development concept.

Determination The Concentrations of Heavy Metals in Seawater Intake…………
Faculty of Marine Resources, Alasmarya Islamic University, Libya.

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The aim of this study to measure some pollutants such as heavy metals (Fe, Cu, Mn and Zn) and their effects on desalination components.

Methodology
Samples are collected from many pointes and sites of Tripoli's West Desalination Plant.The samples were collected from the two intakes channels and around that area for 8 months (March-October, 2010).The conductivity, pH and Temperature were measured immediately.The samples were filtered through 11 µm pore size Whatman No. 1 membrane filter paper.The proper filter is very important for the preservation of samples, when they are kept for a long period of time before the analysis.On the other hand, the samples were added (2 ml Nitric Acid Conc.) as according to the Standard Methods, preservation for determination of metal (APHA et al., 1975) and all the samples were kept in polyethylene bottles, then transferred to the laboratory of The Libyan Petroleum Researches Center.The collected samples have been testing for chemical analysis to know the level of maximum concentration and its impact, the following elements was analyzed (Fe, Cu, Mn and Zn) by using of the photometric measurements (Ultra-Violet Dr 2010-spectro-photometer), all the analysis are done according to Standard Methods.

Results & Discussion
This study was conducted in the year 2010 from March to October, samples were collected from two sites of Tripoli's West Desalination Plant (Janzour).The samples were collected weekly from both sites.According to the data obtained which is showing in this paper, indicates that the difference in concentrations of pollutants (Fe, Cu, Mn, and Zn) between the two sites, were very obvious for all testing parameters.

Iron Concentration
The mean concentrations of Iron from March to October are presented in Table (1).The standard concentration average of Iron in the sea water (0.004 ppm).The results show that the mean concentration of Iron in all months were very high comparing with the standard concentration in the clean sea water.
The mean maximum concentrations of iron in sites 1 and 2 were recorded in August (0.087 ppm, and 0.091 ppm), while the mean minimum concentrations were in October (0.016 ppm, and 0.011 ppm) respectively.On the other hand, the average concentration of all months in site 1 and 2 were 0.044 and 0.043 ppm respectively, which is 10 times higher than the standard concentration of the sea water.May be the iron is dissolved in the seawater and precipitate into the bottom and forming the red ferrous hydroxide, it means may came with chemical waste water which is rejected to the sea side without treatment.

Copper Concentration
According to the data obtained which is showing in Table (2), the mean maximum concentration of cupper in sites 1 and 2 were recorded in October (4.02 ppm, and 5.03 ppm), and the mean minimum concentration in June (1.04ppm, and 1.06 ppm) respectively.However, the average copper concentration of 8 months in site 1 and 2 were (2.30 ppm, and 2.85 ppm) respectively.The standard copper concentration in the clean sea water is about (0.023 ppm).The average results which obtained in the study were very high comparing with standard concentration of copper in the clean sea water, which means that this pollution maybe due to the pretreatment of the plant and the industrial sources located near the plant location.

Manganese Concentration
As presented in Table (3), the minimum mean concentration of manganese in sites 1 and 2 were recorded in may (0.039 ppm, and 0.041 ppm), whereas the maximum concentration in September (0.084 ppm, and 0.086 ppm) respectively.All the results of the manganese concentrations are higher than the standard concentration of the sea water, perhaps due to the high salinity of brine solution after desalted and reject of all the wastewater disposal from power plant station.Moreover, some of industrial pollutant which near-by the study area may found its way to sea water.

Determination The Concentrations of Heavy Metals in Seawater Intake…………
Faculty of Marine Resources, Alasmarya Islamic University, Libya.

Zinc concentration
The results presented in Table (4), show that the zinc concentration at both sites ranged from 0.031 ppm to 0.12 ppm with an average of 0.071 ppm.On the other hand, the maximum mean value of zinc concentration in sites 1 and 2 were in October, while the minimum Faculty of Marine Resources, Alasmarya Islamic University, Libya.

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ISSN: 2413-5267 concentration was recorded in March.The corrosion of the pipes due to high salinity of the brine may cause high concentration of the zinc.Finally the main reason of these pollutants (Fe, Cu, Mn, and Zn) is the geographic environmental location and predominant condition, such as the motion of water current which helps to transport the pollutants into the sea side (study area) from all the different pollutant sources such as a high salinity of brine solution after desalted which are rejected to the seaside without treatment and nearby the location of the industrial activities also wastewater disposal into the sea without any control.Also these metals are normally associated with corrosion.

Table 2 .
The mean copper concentrations in sites 1 and 2

Table 3 .
The mean manganese concentrations in sites 1 and 2

Table 4 .
The mean zinc concentrations in sites 1 and 2