The Issue Of Water Security Biology Essay

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Due to the importance of the water strategy, it was considered the issue of water security and the importance of preserve water resources are a big case in human life, has also became an urgent need to support a global stability at all levels of scientific and environmental and economic and social development. It has been estimated the world's water demand will exceed supply by 56% in 2025 (WWO, 2007).

Desalination is one of human race earliest forms of water treatment, and it is still a popular treatment solution throughout the world today. Most desalination plants currently are used the regular energy resource such as oil and natural gas which are costly and exhaustible, It has been estimated that the production of 1000 m3 per day of freshwater requires 10,000 tons of oil per year (Kalogirou, 2005), therefore the scientists began to develop the researches of other sources of renewable energy like solar energy in the last three decades. Some countries actually began to use this technology to produce electricity at remote areas. After that they concerned about water desalination with solar energy, they reconsider about solar still which first appeared on modern era extends back to the early 1950s when simple solar stills were studied for remote desert and coastal communities. However, due to the water pumps are not costly and the energy price was low in the 20th century, solar stills were not a good solution for the water desalination to the society.

Solar still is composed of basin which is painted in dark color to absorb more solar energy. The saline water is placed on the basin and the top of the basin is opened and covered by glass or translucent plastic which is placed in the diagonal position about 10o ¿½ 50o .The bottom has holes to enter the saline water and exit the salts residuum. Its function is similar to rainfall, the basin is heated with solar radiation, and then the saline water that contacts with the basin is evaporated up to the glass cover and then is condensed, due to the low temperature of the cover. Due to the glass cover is titled in specific angle, the desalinated water flows down to be collected by the vessel.

Fig.1. Solar still process

The solar desalination system divided into two groups which are passive distillation and active solar still. The passive solar still depends its energy only on sun, in other hand the active solar still, extra thermal energy is given to the passive solar still for faster evaporation. The types of solar still can be summarized in the following table1:

Table 1 Types of solar still

However, the rate of production of the solar stills is low comparing to other methods of desalination process, because of this the scientists worked on several studies toincrease the rate of production of the solar still. One of these studies is using photocatalysts for solar stills.

Semiconductors have been utilizes as photo catalysts for example TiO2, ZnO, Fe2O3,CuO, etc. The basic process of photocatalytsis is the photo catalysts cupric oxide will create a pair of electrons and holes, when it absorbs UV radiation from the sun. The electron of the valence band of the cupric oxide will become excited when exposed to sun light. The negative electron ( e- ) and the positive hole ( h+ ) will be created, when the excess energy of the excited electron promoted the electron to the conduction band of the cupric oxide.

CuO + hv ? e- + h+

Then the water molecules will be broken by the positive hole of the cupric oxide to form H+ and hydroxyl radical ( .OH ).

H2O + h+ ? H+ +¿½OH

Then the following reactions occur:

O2 + e- ? O2-

O2- + H+ ? ¿½HO2

¿½HO2 + e- ? H2O2

H2O2 + 2 H+ + e- ? HO2

Fig.2. Mechanism of photocatalyst

Chapter 2

2. Literature review

There are a lot of studies have been worked on solar still to improve its performance such as its designs and its parameters ( wind velocity, ambient temperature, cover slope, angle, feed water temperature, solar intensity and other effect). The studies can be summarized with the following fact:

1- Inclination and the direction of the cover that used to collect the condensate water then to be collected in the vessel, if the inclination is low, then the condensate water may falls down to the basin or if the inclination is high, the solar radiation intensity maybe low (Singw et al.,1995). The inclination and the direction of the cover depend on the location and latitude, so various researchers studied about the inclination of a cover plate and the latitude. This can be summarized in the table 1.

Table 2. Studies of the optimum angle at different location

Researcher Tested angles Optimum angle Location and latitude



Achilov(1970) 30o and 40o 30o Bukhara-Uzbekistan,


Garg and

Mann (1976) 10o, 20o and 30o 10o Madras 13.06oN, Jodhpur




Khalifa (1982) 5o, 15o, 20o and 25o 25o Baghdad-Iraq, 33.3oN

Akash et al. (2000) 15¿½55o step 10o 35o Amman-Jordan, 31.57oN

Al-Hinai et al. (2002) 5¿½40o step 5o 23o Muscat-Oman, 23.36oN

Abd Elkader (1998) 30o, 35o and 40o 30¿½35o Port Said-Egypt, 31.17oN

Kumar et al. (2000) 5¿½30o step 5o 15o New Delhi-India, 28.36oN


et al. (2004) 13¿½17.5o step 1.5o 16o Cameron, 5oN

Omri et al. (2005) 25o and 35o 35o Tunisia, 34.0oN

Bahadori and

Edlin (1973) 1.5o, 3o, 6o and 10o 1.5o Arizona-USA, 34.0oN

Khalifa and

Hammod (2009) 5¿½45o step 10o 35o Baghdad-Iraq, 33.3oN

Dev and

Tiwari (2009) 15o, 30o and 45o 45o

New Delhi-India, 28.36oN

Aybar and

Assefi (2009) 5¿½85o step 10o 35o North Cyprus-35oN

2- Glass is the preferred material for cover, because it has higher solar transmittance for different angle and it has long life. The surface wets with condensed water and allow film condensation at the bottom surface which results in less loss in transmittance. The other cheap transparent plastic materials do not reach the above required qualities (Malik et al., 1982).

3- The solar conductivity depends on the thickness of the cover plate, so Ghoneyem (1997) noticed that the glass cover of the solar still with 3 mm can produce water 17% more than the glass cover with 6 mm.

4- When the cover temperature is decreasing, the productivity is increasing, because the temperature difference between the cover and the basin increases, due to the heat transfer of evaporation and convection increase between basin and the glass. The velocity of wind is affecting the cover temperature. At higher wind velocity the convective heat transfer from the cover to atmosphere increases, due to increase in convective heat transfer coefficient between cover and atmosphere. This effect increases the condensing and evaporation rate and productivity of the still (El-Sebaii, 2000).

5- Cooper (1969) observed that when the depth of water is low the productivity increases, because it will decreases amount of basin heat capacity, then it will increase the water temperature.

6- Around 12% of radiation received by the still basin is reflected back without using it, this loss can be minimized, if the absorption coefficient of the still basin and water is increased (Malik et al., 1982). Rajvanshi (1981) reported that when the black dye is added to the water, the rat of evaporation increases, then the productivity increases, due to the basin radiation absorption increases.

7- Some black materials can store more amount of heat energy and increase the heat capacity of the basin in addition to increasing the basin absorption (Nafey et al., 2001). Abdel-Rehima and Lasheen (2002) tested the black rubber and gravel for storing the heat energy, they found that the black rubber can increase the productivity about 20% and the gravel about 19%.

8- Nafey et al. (2000) reported that solar still with black aluminum painted plate increases the productivity about 17% for 4 cm of water layer and about 39% for 6.5 cm water layer. However, El-sebaii et al. (2000) found that mica plate as suspended absorbers can increases the productivity about 43%.

Regarding to photocatalyst, (Cermanati,1997) proposed about mechanism of photocatalyst in water purification by use quinoline, photofenton generate OH radicals and superoxide dismutase. Guillard et al. (2003) conducted an experiment to investigate about using titanium dioxide as photocatalyst for chlorophenol, days and pesticides. Dillert et al. (1999) used photocatalyst for wastewater treatment. Herrmann et al. (1998) noticed that titanium dioxide as photocatalyst can remove toxic material from water. Suresh et al. (2005) conducted an experiment about solar still by using different photocatalysts (Mno2, and PbO2). They found that the production rate of the desalinated water by using different photocatalyts increased the total amount of desalinated water almost double comparing total amount of desalinated water without photocatlayts and also found the water quality can be improved.

Chapter 3

3.1 Materials


CuO Fe2O3 ZnO

-Glass cover 3mm thickness.

Two aluminum trays (421*282*70)



Waterproof hardboard 18 mm.

Car reflector

PVA binder

Chapter 4

4.1 Fabrication of solar still (see figures 3, 4 & 5)

1- Glass cover (760*600) mm and 3 mm thickness was used to allow the sun ray to come inside the solar still. The inclination of the glass cover is 23¿½ which is optimum inclination fixed to the vertical wall of the solar still. The direction of the glass cover is south to get maximum radiation.

2- The body of the solar still is 18 mm thickness of waterproof hardboard to reduce the heat loss from the bottom as well as from the side of the still. The vertical wall is 710 mm.

3- The white paint was used to paint the vertical walls and the side walls for reflecting the incident radiation.

4- The supply which is used to collect the condensed water inside the solar still was fixed at the lower end of the glass cover. The pipe 1 meter length was fixed on the supply and pass through the hole then to the vessel.

5- The aluminum tray entrance (600*200) mm was made.

6- The adhesive was used to cover the gaps to save maximum heat inside the solar still.

Fig.3. Design of solar still

Fig.4. Solar still in front side

Fig.5. Solar still in back side

4.2 Calculation of desalinated water (without photocatalyst)

1- Amount of sea water was placed on the two aluminum trays (without photo catalyst). One day for 3 liters (1.5 liters each tray, 11 mm) and the next day for 6 liters (3.0 liters each tray, 23 mm) for 10 days.

2- Amount of desalinated water and temperature were noted hourly from 8 a.m. to 8 p.m.

3- The First experiment started on 30/3 and continued to 10 days the maximum temperature was 39, the maximum desalinated water for 3000ml was 499 ml and 421ml for 6000 ml as shown in following graphs and tables:

A) Table 3. Input 3000 ml of sea water

B) Table 4. Input 6000ml of sea water

Graph 1. Production rate of desalinated water at different depths

4.3 calculation of desalinated water using different reflector

The car reflector was added instead of white color for reflection to test if the amount of desalinated water could be increased, the result was the total desalinated water increased about 20% as shown in the tables and graphs.

Fig. 6. Solar still with car reflector

A) Table 5. Input 3000 ml of sea water

B) Table 6. Input 6000 ml of sea water

Time A.Temp

( C¿½) Desalinted water (ml) Production rate


8 34 0 0

9 36 2 2

10 39 12 10

11 40 37 25

12 41 109 72

13 40 203 94

14 39 317 114

15 39 424 107

16 38 489 65

17 36 529 40

18 34 574 18

19 30 552 5

20 28 552 0

Graph. 2.

Graph. 3. Production rate of desalinated water with different reflctors

4.4 Calculation of desalinated water (with photocatalyst)

Each two G.I plates (421*282) were coated with one photocatalyts (ZnO,CuO,Fe2O3) by using PVA binder and they were palced on the aluminum trays as shown in the (figures 7, 8 & 9).

Amount of sea water was placed on the two aluminum trays (with photo catalyst). The experiments were as following:

Two days for G.I plates (on the aluminum trays) which were coated with ZnO 2.6 liter (1300 ml each tray. 11 mm depth)

Two days for G.I plates coated with CuO 2.6 liter (1300 ml each tray. 11 mm depth)

Two days for G.I plates coated with Fe2O3 2.6 liter (1300 ml each tray. 11 mm depth)

One day for trays which do not contain G.I plates that coated with photocatalyst 3 liters ( 1500 ml each tray ,11 mm depth).

The experiments took 8 days in sequence to compare if the photo catalysts could increase the total amount of desalinated water

The result was Fe2O3 and CuO increased amount desalinated water, however ZnO instead of increasing the total amount of desalinated, it decreased it comparing with total amount of desalinated water without photocatalyst as shown graph 4 and tables(7, 8, 9 & 10).

Fig. 7. Fe2O3 Fig. 8. CuO

Fig. 9. ZnO

Table 7. Input 3000 ml (11mm depth) of sea water without photocatalyst

Time A.Temp( C¿½) Desalinted water (ml) Production rate (ml/hr)

8 33 0 0

9 34 5 5

10 35 26 21

11 38 60 34

12 39 153 93

13 40 258 105

14 39 385 127

15 39 497 112

16 38 568 71

17 37 617 49

18 34 639 22

19 31 644 5

20 29 644 0

Table 8. Input 2600 ml (11mm depth) of sea water with photocatalyst(ZnO)

Time A.Temp( C¿½) Desalinted water (ml) Production rate (ml/hr)

8 33 0 0

9 35 4 4

10 37 16 12

11 38 47 31

12 39 90 43

13 40 158 68

14 39 237 79

15 38 308 71

16 36 361 53

17 33 399 38

18 31 420 21

19 30 427 7

20 29 427 0

Table 9. Input 2600 ml (11mm depth) of sea water with photocatalyst(CuO)

Time A.Temp( C¿½) Desalinted water (ml) Production rate (ml/hr)

8 34 0 0

9 35 7 7

10 37 28 21

11 38 71 43

12 39 195 124

13 40 336 141

14 39 495 159

15 38 634 139

16 35 701 67

17 32 742 41

18 31 762 20

19 30 770 8

20 29 770 0

Table 10. Input 2600 ml (11mm depth) of sea water with photocatalyst(Fe2O3)

Time A.Temp( C¿½) Desalinted water (ml) Production rate (ml/hr)

8 33 0 0

9 35 7 7

10 37 30 23

11 38 82 52

12 39 225 143

13 40 391 166

14 39 572 181

15 38 726 154

16 36 795 69

17 33 834 39

18 31 855 21

19 30 862 7

20 29 862 0

Graph. 4. Production rate of desalinated water (with & without photocatralyst)

4.5 comparing the quality of desalinated water with and without photocatalyst

Parameters Unit Raw material Desalinated water without photocatalyst Desalinated water with using photocatalyst

CuO Fe2O3 ZnO

pH 8 5.63 6.3 6.8 5.7

Conductivity us/cm 58300 326 160 123 321

TDS Us/cm 39253 163 107 82.2 215

Total Alkalinity ppm 162 34 18 21 27

Total Hardness ppm 6780 28 12 10 32

Calcium Hardness ppm 1210 8 4 3 10

Chloride ppm 21276 78 64 60 60

Magnesium ppm 1336.8 4.8 3.2 3.3 3.2


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