Study on Reduction of Mixed Water Salinity by Sound Wave —Toward Water Scarcity Issue-Solving in Isolated Islands in the World

There are so many Isolated Islands (inhabited islands) in the world, including Japan. However, at present islanders, there have been faced with the decline of industries, serious concerns of rapid aging and very low birthrate without children and water scarcity issues etc. It can be said that these situations are under the environment which shows a microcosm of Japanese and/or world survival society in the near future. In this paper, the experimental data on the reduction of the mixed water (seawater & rainwater) salinity by the sound wave when changing the volume ratio were first shown, taking into the cha-racteristics of the Isolated Islands. Next, the main analysis result on the water qualities of mixed water with which sound wave was irradiated was shown and the consideration mainly based on the WHO drinking water quality standards was carried out. Finally, through a simple water quality improvement apparatus using small hydroelectric power, a consideration regarding a possibility of the purification of the water (to be a drinking water) based on the solar circulation energy (regenerative type’s natural energy) such as small hydropower utilization, natural sunlight utilization, natural gravity utilization, natural oscillation utilization has been described in the paper.


Introduction
Authors have conducted the study on the sustainable water resource conservation and rainwater resource utilization so far [1] [2]. A possibility on the purifi-Journal of Water Resource and Protection cation regarding the environmental water and rainwater using both a simple water circulation equipment and a waterwheel rotation has been discussed in the papers. And especially, regarding the rainwater purification using a waterwheel, a problem that only 2 NO − removal has been difficult has been described. Therefore, a biological method (Heterotrophic denitrification) was adopted as a method of removing the 2 NO − from the water. That is, this one is to remove 2 NO − by the proliferated bacteria. At that time, an appropriate amount of apple water with the organic matter was added to the rainwater passed through the waterwheel [2]. The 2 NO − could have been kept within a drinking water standards by this method, and we could suggest a possibility of the rainwater as a drinking water as a whole. By the way, there is another way (Change/Mix of raw water or purified water) to decrease 2 NO − [3]. This would also be the least cost method for the purification, i.e., that is to decrease the 2 NO − by diluting a seawater with the rainwater properly. This method is also related not only to a decrease of the 2 NO − , but also to that of the salinity of the seawater itself.
In this study, we have tried the dilution of the salinity by changing the volume ratio of the mixed water (rainwater and seawater), and examined a possibility of the mixed water as a drinking water toward water scarcity issue-solving in Isolated Islands in the world in the 21 -23 centuries [4] and the recent background mentioned above. In the literature [4], the author foresights a civilization society until 21-23 centuries. The base of the post-modern civilization should be there renewable energy, and describes in detail about the structure of the world that has the basic structure i.e., "self-sustaining wide-area networking world" (i.e., Post modern civilization that could respond to the conditions such as aging, depopulation, low energy consumption) in which the humankind will create after the modern. In addition, we have based on the solar circulation energy as a most important energy source to secure a maximum sustainability, and a hydroelectric power has been put in the base. This intends to a self-managed water quality control.

Seawater Utilization and Rainwater Utilization
Japanese prominent medical Dr. M. Kimura (preventive medicine/environmental medicine) says that "21 st century will be an era of the water scarcity, and we need to put our focus on seawater utilization as a new resource". And she also mentions in the literature that "mineral concentration distribution and mineral balance in human body fluids have positive correlation as is said that the origin of species starts with the seawater. The sea as a mother of life has a very important meaning for human health (Intent)" [5]. In case of utilization of seawater as a water resource especially drinking water, we should note the presence of infection (Vibrio vulnificus [Vv.] as an invasive streptococcus, i.e., flesh-eating bacteria) etc., and that of Bisphenol A (a chemical substance well-known as an endocrine disrupting chemical which is floating with the plastics in the ocean appearing in the world news in recent years) etc. However, it is possible to remove the bacteria by the heat sterilization etc. regarding the bacteria in the former. And it is also A. Hiratsuka, A. Imamura Journal of Water Resource and Protection possible to remove the pollutions as endocrine disrupting chemicals by the point-of-use water treatment unit (water purifier) with appropriate filters, for example, RO filter which can remove that in the latter. However, this method is a little bit very expensive and has a high energy burden. Furthermore, the sustainability is left open to question. A possibility of the more sustainable, the more safe, the more secure and the more low-cost drinking water supply would be fundamentally expected by the water quality management based on the self-responsibility (self-help). Therefore, it is fundamentally thought that the flow such as 1) self-help → 2) mutual help → 3) public help in order will be good for achieving the sustainable drinking water supply goal in this system. Then, it is considered that the reduction of the salinity is the big point for the seawater as a drinking water. Regarding this, by doing properly the dilution and mixing of the raw water (i.e., diluting the seawater with the rainwater) the reduction of both the 2 NO − and the salinity of seawater itself will also be expected as mentioned above. Therefore, it is thought that a possibility toward a way in which we could drink the seawater as a drinking water (application of the WHO standards) will be increased.
In addition, the seawater desalination technology in Saudi Arabia etc. is one of the great techniques. However, as mentioned above, it has a high energy burden issue. Therefore, the unlimited spread of it to the Isolated Islands in the world will be difficult in the future. Therefore, it is thought that this way in which the self-managed water quality control system with a small hydroelectric power based on the solar circulation energy (i.e., a way of changing the lifestyle itself) will be wiser one in Isolated Islands in the world toward 21 -23 centuries. Small is exactly beautiful in the future.

The Choice of Sustainable Energy Source toward 21 -23 Centuries
We think that which energy source we should choose for humankind will be the most important keyword toward the 21 -23 centuries. [6] [7] [8] Here, we briefly want to overview the energy source mentioned so far based on the "stability" as a keyword.
First, there is a petroleum energy (1). This stabilizes at the present stage.
However, there still remains doubt about sustainability. And the areas where the petroleum is dug are politically volatile regions.
Second, there is a coal energy (2). This is also stable. However, the carbon dioxide (CO 2 ) emissions are large. And coal-fired power plant will have a high possibility of stranded assets in the future.
Third, there is a nuclear energy (3). Of course, although this can be the most stable supply, the risk brought about by an accident will have the maximum risk.
Three areas were pointed out as major accidents caused by the nuclear power plant. That is, Three Mile Island (USA, 1979), Chernobyl (former Soviet Union, Current Ukraine, 1986) and Fukushima (Japan, 2011). All the accidents were beyond what one expected and did severe damage to the areas. That is no match A. Hiratsuka, A. Imamura Journal of Water Resource and Protection for the thermal power. In foreign countries, the plutonium as a by-product of nuclear power plant is used as a material of an atom bomb. However, in Japan it is held in storage or left in a foreign country. Therefore, Japan has the first or second largest amount of plutonium in the world. And then, there is LNG (liquefied natural gas). As this is burned as a thermal power, CO 2 often comes out.
And the facilities are needed to liquefy the gas in Japan. Therefore, the cost is involved. Furthermore, although Japan has imported the LNG via the Middle East and Russia, the regions are also politically unstable.
Finally, there is a natural energy (regenerative type's natural energy) (4).
There exist solar power, wind power, water power (hydropower), wave power (tidal power), geothermal power, biomass power and so on as the types of energy. At first, a problem of the solar power is that this uses lots of petroleum and energy to make the solar panels including the gathering of the materials. Next, regarding the wind power, the wind blowing in Japan is not stable. In addition to this, Japan typhoons are common natural events in the late summer and autumn in Japan. Due to this, the windmills are often crushed. On the other hand, the wind power is suitable or acceptable for Europe because of a few weak typhoons unlike Japan. Third, the water power is suitable or acceptable more or less permanently for the areas in which there are so many rain and the mountains for storing the rain water. Fourth, the wave energy is utilizing the energy due to the rise and fall of the tide (tide level). However, it can be said that it is unstable as this is also affected by the weather. Fifth, although the geothermal energy is also stable. However, when the volcanic activity occurs briskly the one will have to run away to avoid that. At last, there is a biomass energy. The power generator can stably generate power if only there are biomass sources such as feces and urine of livestock, died trees and so on. However, the cost will be costly due to the fuel transportation to the power plant and the generation of wood chips etc.
in the case of woody biomass electric power generation. The almost all the energies ((1)~(4)) were overviewed as mentioned above. Of all energies it could be said that the energy having relatively high stability is the water power energy. In addition, it is considered that to make lots of small dams in valleys and on hill slopes is much safer in a practical application.
By the way, it can be said that it is necessary to make an effort to use all the energy technologies safely based on the cost in conclusion throughout all of the energies. For example, we use the drone (unmanned aircraft) as a weapon, on the other, as a liberation (reduction) apparatus from an agricultural workload etc. Then, it is important to improve the good point more, and correct the bad point further, respectively. Ultimately, it can be said that all the issues come down to a question of paradoxical one (trade-off/issue of choice).
Therefore, we have decided to choose the "water energy" in this paper with due consideration of all the energy features mentioned above. In addition, there is a problem, that is, "storage of electricity" as one of the unstable factors in the case of the water energy. However, there recently exists a super capacitor: Elec-A. Hiratsuka, A. Imamura Journal of Water Resource and Protection tric double-layer capacitor as one of the electricity storage technologies. This is a condenser (capacitor) which can store a large amount of energy utilizing a physical phenomenon of electric double layer. This is one of the storage batteries unlike usual ones. This has some capacity; then it has a substitution possibility as a part of battery if the performance has been improved further in the near future.
And as this does not need the maintenance of the battery (free discharge slightly exists), it can be nearly used for good. It is adequately considered that there is a possibility (flexibility) to use it during day time and night time.
And then, we adopt the super capacitor etc. for the storage of electricity by building lots of small dams to generate hydroelectric energy at every Isolated Islands. Then, it is desirable to utilize both the seawater and the rainwater as natural waters which have existed in abundance in the Islands when thinking about the water scarcity in the world. Therefore, we think that it is very important to examine the mixed water (seawater and rainwater) as a drinking water based on the electromotive force which has little impact on all living things. A. Hiratsuka, A. Imamura Journal of Water Resource and Protection of the mixed water in the apparatus is as follows. First, we store the rainwater brought about by the solar circulation energy. Second, we prepare the mixed water, that is, the mixture of the rainwater and the seawater by the volume ratio.

Small Waterwheel System
Third, we rotate the waterwheel by pouring the mixed water on that. The generator starts by the rotation of the waterwheel in battery-based energy. We have ever stored the electricity in the style of battery. But that style should be changed into the lithium-ion batteries. (It is said that batteries are an important technology in enabling the world to move away from fossil fuels. Incidentally, the 2019 Nobel Prize in chemistry has been awarded to a trio of scientists (Japanese, American, British) for the development of lithium batteries.) As the mixed water circulates with the apparatus, the storage of the electricity is continuously acted by the water power and the electric power of the solar panel. Therefore, the required energy for improving the water quality is sustainably and stably supplied.
Fourth, the mixed water quality passing through the waterwheel is more purified by both the Möbius effect and the Lenard's effect. Finally, we check whether we can drink the mixed water or not. If the standard we set up this time is recognized as being effective in the WHO standard after some refinements, it would be possible to drink this as a drinking water in the Islands in the world in the near future.
The outline of this apparatus is as follows. First, the rainwater which is continuously produced by the solar circulation energy is stored in the tank that was set up in a high location. Next, the waterwheel is rotated by the small hy-

Experimental Condition
The research stance on the rainwater we have carried out so far [1] [2] has been fundamentally followed in this study. The volume ratio of the mixed water was

Analytical Method of Water Quality
First of all, the water quality analysis was conducted after the filtration using the filter named HARIO dripper which is available on the market. Pocket Salt Meter (PAL-SIO) Cat. No. 4100 (ATAGO Co., Ltd.) was used to measure the salinity.
And, the measured salinity was converted to the Cl − as the salinity has an almost proportional relationship with the chloride ion concentration (Cl − ). The conversion formula is as follows.   Table 1 shows the reduction of the mixed water salinity by the sound wave.

Results and Discussions
From Table 1, the reduction of both the salinity (8900 → 160 mg/L) and the molar ratio of    Table 2 shows the result of water qualities obtained from the mixed water. We Inurin ( Regarding Table 2, the salinity (Cl − ) does not meet the WHO standards judging from the seawater vs. rainwater ratio 1. However, it is understood that the ratio meet the standards of both WHO (250 mg/L) & Japan (200 mg/L) viewed from the ratio 0.03. By the way, it is generally said that the major minerals per day for the human body are Na, Fe, Ca, Se, Cu, Zn, Mg, Cr, I etc. [14]. Some point out that it is rather important to take in the salinity properly as the natural salt obtained by seawater includes the minerals medically [15]. There is an aqueous solution of salt that is used for medical use, called Ringer's solution. It is said that this is made to conform to the blood components (salinity in human blood: about 0.9% [Cl − : 5000 mg/L]). Therefore, if the salinity concentration of 0.9% [that is equivalent to the sea water vs. rain water ratio 1] is allowed, it will be possible to serve about 800 ml/day of mixed water as a drinking one to the people. Incidentally, it is said that about 2400 ml (drinking water ≒ 1000 ml, Meal ≒ 1100 ml, metabolic water ≒ 300 ml) of water per day is necessary for human body. It is expected to consider the reviewing of the WHO standards on the salinity (Cl − ) in the future.TOC meets the criteria judging from WHO standards, but not Japanese ones [16]. In addition, the data by Prof. Inoue et al. was used as a reference value regarding the TOC (estimated) [17]. The previous data (2019) by the authors was used regarding Calcium, Magnesium, Then this data was here used as a reference value [11]. Besides, V.v is also possible to sterilize by the boiling (heating) [19].
This one does not include the WHO standards (i.e., non-standard item). Here we set this value to "ND". Bisphenol A (BPA) is one of the Parsistent Organic Pollutants (POPs). This POPs was used in the past. However, its hazardousness was observed, and then the production and the use of that have been prohibited since 2004 (UNEP). However, it has turned out by the recent studies that the organic pollutants remained in the seawater are stuck together and won't come apart to the plastics [20]. Therefore, BPA was here taken up as one of the typical ones [20] [21]. In the literature [21], a famous prof. H. Takada (Tokyo University of Agriculture and Technology, Environmental Chemistry) introduces a greatest 20th century physicist: Albert Einstein's word, that is, "A clever person solves a problem. A wise person avoids it", and the author says that the change of one's life style is wiser to solve the plastics pollution issue at the explanation of Japanese version in this book. The data published by the public institution was used as a reference value as mentioned before (Section 3.3) [13]. We used the es-A. Hiratsuka, A. Imamura Journal of Water Resource and Protection timated value ("0.007 μg/L") as the result of the treated one. Besides, the BPA in the POPs is at present a suspected substance as one of the endocrine disrupting chemicals as the PCB and Nonylphenol etc. In addition, this item is at present an additional one that is not included in the standards such as WHO, EU, US-EPA and Japan. We here set the standard value to "125 μg/L" referencing the data (an estimation of evaluation value by TDI approach) of Tyl et al. [22]. If one could evaluate the BPA by this value, the standard on this is met as a drinking water.
In addition, it is also said that the BPA can be decomposed by the chlorine (Cl) [23]. By the way, it is generally said, the seawater includes a mineral group (trace element) which is deeply involved in the human metabolism (basal metabolism, substitution   Figure 3 shows the relation between Chlorideion (Cl − ) and Nitrite ion ( 2 NO − ) in the mixed water. A general expression of the chemical reaction between Cl − and Nitrate ion ( 3 NO − ) is as follows [24].
Cl H O HClO HCl It is understood from Figure 3  It is thought that only proportional increase of 2 NO − in the rainwater increases fundamentally in the relation between the two. Then, the salinity reduction is accelerated with accumulating of 2 NO − by that amount. However, it is understood from Figure 3 that the reduction speed of Cl − is weakened at a point (i.e., 2 NO − (0.02 mg/L): changing point). There is an evaluation of the solid-liquid separation system of sewage sludge focused on the water quantity and water quality of the separated water. This is an evaluation technique using a consolidation point (changing point of sedimentation speed) [25].
Therefore, it is thought that this changing point of the salinity speed is one of the important points to examine the salinity reduction as this consolidation point in   (6)]. That is to say, we could obtain the salinity reduction phenomenon due to both of the absorbability of Cl − and the releasability of

Conclusions
In this paper, a reduction of mixed water salinity by the sound wave was confirmed toward water scarcity issue-solving in isolated islands in the world. That