The assessment of environmental parameter along the desalination plants in the Kingdom of Saudi Arabia

: The Kingdom of Saudi Arabia obtains the most desalination water from the Red Sea. In Saudi Arabia, 14 desalination plants receive water from the Red Sea, and three are located in the country ’ s east and rely on the Arabian Gulf. The study has observed 16 desalination plants out of 17 desalination plants in the kingdom. Most of the desalination plants in Saudi Arabia currently use the advanced technologies to produce potable water with less impact on the surrounding environment. The current study examined the variation of hydrographic parameters along all available desalination plants in Saudi Arabia. This is the ﬁ rst inter - annual database of hydrographic parameters in the last 4 years. The peak salinity was measured at the Duba desalination plant in 2020, and it was 67.2 ppt. During 2018, the Azizia desa - lination plant reported the lowest value of 36.8 ppt. The maximum temperature recorded at the Qunfudah desalination plant in 2019 was 34.6°C. In 2017, the minimum temperature was 19.1°C at the Jubail desalina - tion plant. The level of dissolved oxygen and pH were likewise not signi ﬁ cantly changed along the brine out - ﬂ ow and in the outfall, in contrast to temperature and salinity. On the basis of 4 years ’ of data from observed desalination facilities, the current study sheds light on the less environmental impact with regard to hydro - graphic factors.


Introduction
Over the past 30 years desalination has grown into excellent solution for water supply with respect to the potable water crisis.We would cease to exist if there was no enough supply of drinking water.Water is regarded as the foundation of life.Each cell needs water to complete the chemical activities that define each stage of the cell's life cycle [1].Fresh water resources are scarce in many nations around the world, particularly in developing and Middle Eastern nations.Groundwater and surface water sources provide the majority of the readily accessible drinkable water [2].The overuse of potable water has resulted in a decrease in surface water and groundwater availability [3,4].The major desalination dependent countries are located in the Gulf area [5].Specifically, 70% in the Kingdom of Saudi Arabia, the United Arab Emirates, Kuwait, Algeria, and Libya [6].Many nations around the world are quite concerned about the availability of freshwater, which will become even more precious in the near future.The Kingdom of Saudi Arabia obtains the most water from the Red Sea for desalination.There are 14 desalination plants in Saudi Arabia that receive water from the Red Sea, and three desalination plants in the east of the country that rely on the Arabian Gulf.
In fact, seawater desalination has a variety of human health, socioeconomic, and supply of high-quality drinking water benefits, as well as help to maintain agricultural production [4,7], despite the fact that equally negative effects have been documented [4].Desalination plants employing cutting-edge technology nonetheless run the risk of causing environmental concerns, as was seen in other studies as well [7].Desalination plants are widely documented to have a detrimental effect on the marine environment [8,9].In order to avoid unsustainable development of marine environment desalination activities should be looked at carefully into environmental management, which regulates the use of water resources and need to estimate the adverse impacts and limit it as far as possible [7].There are various studies highlighting the environmental impact studies with respect to the desalination plants and the rejection of brine [10].The characteristics of rejected brine depend on the type of feed water and type of desalination process [3,[11][12][13].The major concern of this study is near the outfall locations due to the discharge of hypersaline water and its consequences for marine organism and environment.However, there is also concern about the use and release of other toxic chemicals [14], as well as the temperature elevation due to the thermal processes inside the plants [10,15,16].There are reports on the negative influence of desalination plants on the activities of marine organisms [7,17,18].The present study assessed the variation of hydrographic parameters along with the all available desalination plants in Saudi Arabia.This is the first inter-annual database of hydrographic parameters in the last 4 years.

Materials and methods
The present study assessed 16 desalination plants (Ras Al Khair, Jubail, Al Khobar, Haql, Duba, Alwajh, Umluj, Jeddah, Farasan, Yanbu, Shaqiq, Qunfudah, AL Lith, Shoiba, Azizia, and Rabigh) located in Saudi Arabia.Each desalination plants in this study assumed as 1-16 numbering system, respectively, for easier annotations in the graphs.The different hydrographic parameters were collected using yellow springs instruments (YSI) multiparameter and the details are shown below.

Temperature
The sondes utilize a thermistor of sintered metallic oxide that changes predictably in resistance with temperature variation.The algorithm for conversion of resistance to temperature is built into the sonde software, and accurate temperature readings in degrees Celsius, Kelvin, or Fahrenheit are provided automatically.The accuracy was in the range of 0.2°C.No calibration or maintenance of the temperature sensor is required.

Salinity
Salinity is determined automatically from the sonde conductivity and temperature readings.The use of the Practical Salinity Scale results in values that are unitless, since the measurements are carried out in reference to the conductivity of standard seawater at 15°C.The unitless salinity estimates, however, are quite close to those obtained using the earlier technique, which stated the amount of dissolved salts in a given mass of water (parts per thousand).Hence, the designation "ppt" is reported by the instrument to provide a more conventional output.The accuracy was in the range of 0.1 ppt.

Dissolved oxygen
In general, optical dissolved oxygen sensors from a variety of manufacturers are based on the well-established notion that dissolved oxygen reduces the luminescence associated with precisely chosen chemical dyes' intensity and longevity.The 6150 sensor operates by shining a blue light of the proper wavelength on this luminescent dye which is immobilized in a matrix and formed into a disk about 0.5 in in diameter.This dye-containing disk will be evident on inspection of the sensor face.To increase the accuracy and stability of the technique, the dye is also irradiated with red light during part of the measurement cycle to act as a reference in the determination of the luminescence lifetime.For most lifetime based optical dissolved oxygen (DO) sensors (including the YSI 6150), this Stern-Volmer relationship (((T zero /T)-1)) versus O 2 pressure) is not strictly linear (particularly at higher oxygen pressures) and the data must be processed using analysis by polynomial non-linear regression rather than the simple linear regression used for most polarographic oxygen sensors.The accuracy was in the range of 0.2 mg/L.

pH
The sondes employ a field replaceable pH electrode for the determination of hydrogen ion concentration.The probe is a combination electrode made up of an Ag/AgCl reference electrode using gelled electrolyte and a proton selective glass reservoir filled with buffer at a pH of about 7. The accuracy was in the range of 0.1 unit.

Results and discussions
The most sophisticated technologies were used in the desalination technologies.However, the system faces many drawbacks with respect to the environmental concern [7].While focusing on the importance of the portable water, it is always given a secondary priority to the environmental issues with respect to the desalination plants [19].Saudi Arabia, the United Arab Emirates, Kuwait, and Qatar produce 55% of the world's brine.It is crucial to take into account the value of proper brine management by reducing environmental hazard concerns.Moreover, the suggested management should be economically and environmentally viable.Hence, the development of advanced facilities for the production of portable water is a significant priority on the long-term aspects.

Inter-annual variations of hydrographic parameters
The study discussed the inter-annual variation of hydrographic parameters from 2017 to 2020.The result can be used as a baseline datasets.

Salinity
Most of the studies focused on the saline water expansion from the discharge plume to the open sea.Both the Red Sea and the Arabian Gulf have extremely high evaporation rates, ranging from 1.2 to 2 m per year, and extremely low annual precipitation rates, ranging from 90 to 150 mm.If increasing amounts of desalinated water are removed from water bodies, the salinity in the recipients may rise in the long run [20,21].According to published research, desalination plants have varying effects on the salinity of receiving waters.The majority of observation reflects the fading of elevated salinity within few meters [10,22,23] to hundreds of meters [24][25][26].The variation depends on different factors like plants' varying capacity, diffuser designs, and environmental hydrology [25].In general concept, S Intake and Q Intake are the salinity and volume of seawater intake, S Brine and Q Brine are the salinity and volume of brine discharge, and S F and Q F are the salinity and volume of fresh water produced by desalination plants.Moreover, S Brine = S Intake /(1 − r) and Q Brine = (1 − r)Q Intake , where r is the recovery ratio, generally between 35 and 45% of the intake [27].According to this relation if the intake salinity is 42 and the recovery is assumed to be 44%, the salinity of brine will be 75 ppt.For all systems, the recovery ratio rises as the quality of the feed water does (salinity decreases).The inter-annual distribution pattern of average salinity at the discharge along the different desalination plants is shown in Figure 1.The maximum salinity was observed at Duba desalination plant during 2020 and the value was 67.2 ppt.The lowest value was reported at Azizia desalination plant during 2018 and the value was 36.8 ppt.
In most cases the discharge brine without the proper treatment will be dumped into the surface of coastal water (such as oceans and seas) [28].Almost 50% is formed within a kilometer of the coastline and approximately 75-80% within the 10 km range.In all the desalination plants the discharge plume salinity was not going to an exacerbated level.Moreover, the recent studies from the desalination plants of Saudi Arabia [29][30][31][32] show the dilution effect of the brine discharge within 10-20 m of the outfall from the discharge.These data indicate that the background value will dilute the elevated amount of hypersaline water.As a result, the detrimental effects of brine discharge will be minimized.However, with respect to the long-term consideration more sustainable brine management system will be recommended.In order to accomplish this more precise dispersing modeling has to be performed.

Temperature
By far the most prevalent desalination technology, reverse osmosis (RO) accounts for 85% of all operating desalination facilities and generates 70% (65 million m 3 /day) of all desalinated water produced globally.With market shares of 18 and 7%, respectively, the two primary thermal technologies, multi-stage flash (MSF) and multiple-effect distillation, still produce the majority of the remaining desalinated water.Plants using nano-filtration (3%), electro dialysis (2%), and electrodeionization (1%) produce a lesser amount of desalinated water than those using these three technologies, which together account for 94% of all desalinated water production [33].Currently majority of the desalination plants in Saudi Arabia using the RO technologies and the corresponding lowering of environmental pollution at the desalination plants with respect to high brine discharge.The primary flaw of MSF technology was the high temperature discharge, despite the fact that the temperature in the discharge plume would rise as a result of the distillation process.In relation to the input water, the elevation values typically reach 15°C [7,29].The discharge area's water temperature swings are fewer than the seasonal variance that occurs naturally in the winter and summer.As opposed to the upper water column, the temperature at the discharge location is often lower and may not be high enough to have a substantial impact on the macrobenthos [34].
It was discovered that increased warmth from nuclear power plant discharge increased the phytoplankton density [35].Globally, membrane technologies currently outsell thermal technologies in the market.The distribution pattern of the temperature from 2017 to 2019 from all the desalination plants observed in this study is shown in Figure 2. The maximum temperature was observed at Qunfudah desalination plant in 2019 and the value was 34.6°C.The minimum was observed at Jubail desalination plant in 2017 and the value was 19.1°C.In Saudi Arabia the variation of temperature for the surface samples of the water during winter and summer will alter significantly.However, the elevation from the desalination plant is not affecting in a profound manner.The majority of the desalination facilities will experience a minor temperature increase in 2019 and 2020.This might be brought on by an increase in atmospheric temperature, and as a result, it might be connected to surface water.The current pattern of dispersion is consistent with the scattering of high temperatures within a few meters of the outfall [29].

Dissolved oxygen and pH
There has been some reported observation of oxygen depletion near the outfall [27,[36][37][38].The elevated level of temperature and salinity have a significant effect on the effluent DO level [39].A chemical that consumes oxygen will often be added to the desalination plants to reduce the DO, particularly sodium bisulfate.However, mixing with nearby well-oxygenated water will help to maintain a normal oxygen environment.The inter-annual distribution pattern of dissolved oxygen along the observed locations is shown in Figure 3.The maximum value was observed at Jubail desalination plant in 2017 and the value was 7.07 mL/L.The minimum was observed at Qunfudah desalination plant in 2018 and the value was 3.1 mL/L.Acidification could be caused by acids released into the marine environment as a result of chemical cleaning used in RO desalination processes.Redox interactions between the numerous chemical contaminants present in plant brine and those already present in sea water may take place under these circumstances.Because oxygen was a necessary component of these oxidation-reduction reactions, the amount of this element in the environment decreased.Additionally, distillation factories have purposefully decreased their oxygen levels through physical de-aeration as well as the insertion of oxygen chemical sensors such sodium bisulfite (NaHSO), which is used to stop corrosion.This chemical additive was also commonly used as a chlorine neutralizer [7,[40][41][42].However, none of the desalination plants found in this study's research significantly reduced the amount of dissolved oxygen, and the results are consistent with that of the Red Sea and the Arabian Gulf.The inter-annual variation of pH along the observed desalination plants from the period of 2017-2020 is shown in Figure 4.The maximum pH was observed at Ras Al Khair in 2019 and the value was 8.31.The minimum value was observed at Haql desalination plant in 2019 and the value was 7.12.All the observed desalination plants was not showing much alteration with respect to the background value except in some locations.Normally, the addition of sulfuric acid favors the reduction of scaling and the reduction of pH to remove a part of the dissolved carbonate, followed by an increase in pH to the background value [8].The effluent will typically decline with a lower pH solution.It has the potential to lead to significant issues.The currently available pH dataset does not demonstrate a rapid decrease or more significant pH variations along the studied areas.The analysis of the literature reveals that with proper mixing, the pH of the discharged water will not differ much from the pH of the feed water [43].

A comparative study of hydrographic distribution pattern of desalination plants through worldwide
As it is clear that the majority of freshwater production in Saudi Arabia is through desalination plants, it is highly significant to compare the discharge outfall from different desalination plants in the world.A comparative study of salinity at the discharge brine along the different parts of the world is shown in Table 1.As mentioned earlier, the salinity of brine discharge purely depends on the intake water salinity and the recovery ratio of intake and freshwater produced.Apart from this the technology will also play a role.However, the majority of desalination plants in the Middle East follows the RO.The influence of tide will greatly affect the elevation of salinity based on the model study [44].The ocean circulation model clearly suggests the elevation of salinity with tidal cycle and this will light on the optimization of the outfall design.According to models, the strong currents carry the brine discharge closer to the shoreline than offshore [10,29,45].Thus, brine exposures in recipient systems are probably going to vary in intensity over time and space at scales between 10 and 100 m.Previous studies have revealed that the surrounding water bodies quickly dilute the high salinity, bringing the concentrations back to normal with only a slight adjustment.Majority of the time, plumes that covered hundreds of meters were between 0.5 and 1 ppt higher than the prior level [10].In balance with the surrounding environment, the salinity around the outlet discharge ranges from about 80 ppt to the actual seawater salinity of 35-36 ppt.According to some studies, the excess salinity level of discharge brine seawater is a direct function of the distance from the desalination charge site.While the salinity of saltwater may not dramatically change in the sea's profile from the surface to the bottom, it can change significantly between the surface and 10 m of depth in the vicinity of the discharge brine outfall, for instance [24].

Conclusion
The study investigated the inter-annual variation of hydrographic parameters from 2017 to 2020.The results show that the elevated level of hypersaline water is diluted by the background value.Hence, the detrimental effects of brine discharge will be lessened.Globally, membrane technologies presently outsell thermal technologies in market share.Between winter and summer, temperature differences for surface water samples in Saudi Arabia will differ greatly.On the other side, the desalination plant's elevation has a negligible effect.The levels of dissolved oxygen are consistent with those found at the surface of the Red Sea and the Arabian Gulf, and they were not considerably lowered in any of the desalination plants that were investigated.The current pH dataset shows no abrupt drops or large variations in pH along the observed locations.The comparison data of the present study with the worldwide data reflect the favorable condition for the surrounding environment of desalination plants in Saudi Arabia.

Figure 1 :Figure 2 :
Figure 1: The inter-annual distribution pattern of average salinity at the discharge brine along the observed desalination plants.

Figure 3 :Figure 4 :
Figure 3: The inter-annual distribution pattern of average dissolved oxygen at the discharge brine along the observed desalination plants.

Table 1 :
A comparative study of salinity at discharge brine along the different parts of the world