Sea Water Characterization at Ujung Kulon Coastal Depth as Raw Water Source for Desalination and Potential Energy

Fresh water is basic need for life while the source is limited. Therefore, sea water is used as fresh water through desalination process. Sea water has different physical and chemical properties ranging from the surface to the seabed. The energy potential that can be obtained from the hydrostatic pressure also changes according to the depth. As part of the research of the utilization of sea water into fresh water, the aim of this study is to know the characteristics of sea water in the depth that can be utilized as source of fresh water. The sea water samples were taken at 11km from Ujung Kulon beach with depth of 0m, 20m, 40m, 60m, 80m, and 100m under the surface. The results showed that the physical properties at every depth were below the maximum allowable drinking water except for the amount of dissolved solids. Chemical characteristics at any depth above allowable level were fluoride, hardness (CaCo3), chloride, sodium, sulphate, and (KMnO4). In addition to the properties, pressure is one of the considerations in this study to determine the depth of sea water as sources for desalination. Pressure increased by 36.11% as the depth of the sea increased.


Introduction
Fresh water is a necessity for every creature on earth to stay alive.Population growth in Indonesia has a direct impact on the use of freshwater in the soil.This situation is completed with the reducing of water absorption area in various places due to the increase of buildings and factories.This resulted in the availability of clean water become threatened.UNICEF reports that 1 in 4 children will live in rare areas of water [1].The condition is compounded by the decline in the soil surface due to the increasing amount of clean water taken from the soil [2].Globally, water usage has tripled in the last 50 years [3], while the amount of fresh water on the surface of the earth is only 2.8% and the rest of 97.2% is sea water [4].Therefore, the utilization of sea water as clean water becomes very potential.The problem is that seawater contains a greater amount of dissolved salt than fresh water, especially NaCl.Table 1 shows the dissolved salt content in different oceans and oceans in different parts of the world.Therefore, efforts to convert sea water into fresh water and efforts to eliminate salt content from seawater are widely practiced.
Various desalination technologies and their combination with renewable energy are shown in Figure 1.The utilization of solar energy for the desalination process is the least costly way, especially in tropical regions such as Indonesia.Direct heating method with solar heat is the most suitable way to produce fresh water up to 200 m 3 /day [5].For larger scales, the use of solar energy coupled with other energy sources such as heat collectors, waves, and geothermal is sufficient [6].Seas and Oceans [4]   Sea or Ocean TDS (ppm) Renewable energies are energy sources that continually replenished by nature and derived directly from the sun (such as thermal, photo-chemical, and photo-electric), indirectly from the sun (such as wind, hydropower, and photosynthetic energy stored in biomass), or from other natural movements and mechanisms of the environment (such as geothermal and tidal energy) [7].The solar energy collector is one of the tools that developing in renewable energy.The various types of collectors such as flat-plate, compound parabolic, evacuated tube, parabolic trough, fresnel lens, parabolic dish, and Heliostat field collector (HFC) widely used as a tool for collecting solar energy [8].Wind, solar, and other renewable technologies that can be used for desalination are rapidly emerging with the promise of economic and environmental viability on a large scale [9].Renewable energy provides solutions to lower energy costs.One of the energy that can be utilized for the desalination process is hydrostatics pressure10.Hydrostatic pressure reduces the electricity consumption for the reverse osmosis process from 10 kwh/m 3 to 2.98 kwh/m 3 [11].Efficiency of hydrostatic usage as energy source is 80% in desalination process with RO [12] .
At the depth of the ocean, the available pressure and power generated by the turbine can be estimated using the following equations [13] : At the depth of the ocean, the available pressure and power generated by the turbine can be estimated using the following equations [13] : (1) (2) Where is the pressure due to the height difference ( ), is the power generated turbine (watt), Q is Flow Rate , is the density , is gravity 9,81 , and H is head difference (m).
Utilization of hydro energy storage, where the water is taken from the depth of the ocean, the water will be different from the water on the surface, such as temperature.Since ocean's temperature decreases steadily with depth, although the ocean's surface temperature varies from 40°C to -2°C, the average temperature in ocean's depth is almost constant and around 3 -4°C [14].In addition, sea water content will also change where salinity increased 4.52%, pH decreased an average of 1.46% and the conductivity increase an average 0.03% in line with the addition of depth [15] .
In this study, the sample of sea water content was taken from depth 0m, 20m, 40m, 60m, 80m, and 100m.Tests were performed using drinking water standards.In addition, the potential power at each depth to be obtained will also be calculated

Method
The sea water used in this study was taken from offshore of Ujung Kulon, West Java, Indonesia.The depth of sampling is 0m, 20m, 40m, 60m, 80m, and 100m.Samples at each depth were taken as many as 40 liters and stored in jerrycan.Sampling is done by using 2 inch hose that closed at the end by using valve.The sample test was conducted at the Mechanical Engineering Laboratory, Prof. Dr. HAMKA University and at the Regional Health Laboratory (LABKESDA) of DKI Jakarta, in Rawasari.The comparative standard used is the drinking water standard applicable in the Republic of Indonesia, Permenkes 492 Tahun 2010 [16].

Result and Discussion
In this study, the testing of sea water content taken from a depth of 0 m, 20 m, 40 m, 60 m, 80 m, and 100 m.The test is performed using the Drinking Water Standard as shown in Table 2.

Kedalaman Kadar Maksimum yang Diperbolehkan untuk Air Minum
Table 2 is the result of testing of seawater physical properties that follow to the standard on drinking water testing.The test results showed that TDS (Total Dissolved Solid) was in the range of 30,000 mg/l, while the standard allowed for drinking water was 500 mg/l.In addition, turbidity at a depth of 80m differs from other Fig. 2. Deep sea reverse Osmosis scheme [19] At a depth of 0m, 20m, 40m, 60m, and 100m average turbidity is 0.628 below the drinking water standard, 5. Turbidity at a depth of 80m is different because at that depth there is undersea water flow.This is evidenced by the carrying of a hose by the water current at the depth.Furthermore, the chemical properties of seawater are shown in Table 3.
In Table 3, it appears that parameters that exceed the maximum permissible levels of drinking water are Flouride, Hardness, Chloride, Sodium, Sulfate, and Organic.This is consistent with that stated by Vassilis Belesiotis, et.Al [4].Furthermore, data that is above the maximum level shown in Figure 3.In Figure 3, TDS that is above the maximum level increases with increasing depth.An average TDS increase of 10% for every 20m depth increase.Turbidity at depths of 0m, 20m, 40m, 60m, and 100m below permissible levels except at a depth of 80m.In Figure 4, it appears that organic increases by 30% in line with increasing ocean depth.Mean while, on the average of flouride is no increase with the depth of the sea.This is in line with that proposed by Bewers [17] that there is no increase in levels of fluoride along with the addition of the depth of the ocean.The increase also does not occur in Chloride and Sulphate, as can be seen in Figure 5.In contrast to other elements, sodium has decreased by 20% with increasing sea depth, while Hardness is up 23% along with increasing depth of sea depth.In addition to sea water testing, the potential power obtained by the pressure due to the depth of the sea is calculated, assuming the water requirement is 200 liters/person/day with the population on one island is 100 people, then the required debit is 20,000 liters/day or 0.8 m 3 /hour.The gravity of sea water is 1.025 kg/m 3 and gravity is 9.81 m/s 2 , the increase in hydrostatic pressure is 36.11%with increasing sea depth.

Conclusions
Based on the results of the test, it can be concluded that TDS, hardness, sodium, and organic have changed sequentially by 10%, 23%, -20%, and 30%.Flouride, chloride, and sulphate do not change with increasing sea depth.Potential pressure increased by 36.11% with increasing sea depth.

Table 1 .
Mean Value of Total Dissolved Salts in Various