Gaza Strip lies on the southwestern part of the Palestinian coastal plain.
Its total area is 378 km2 (UNEP, 2009) its
length is approximately 45 km. Bounded by the Negev desert to the Southeast
and the Sinai desert to the Southwest. Gaza is characterized by its desert nature.
The average daily mean temperature ranges from 25°C in the summer to 13°C
in the winter. Average daily maximum temperatures range from 29 to 17°C
and minimum temperatures from 21 to 9°C in the summer and in the winter,
respectively. The average annual rainfall varies from 450 mm year-1
in the north to 200 mm year-1 in the south (Daya,
2002). Regarding evaporation, maximum values of 140 mm month-1
have been quoted for the summer, while relatively low pan-evaporation values
of around 70 mm month-1 were measured during the months of December
and January. The daily relative humidity fluctuates between 65% in the daytime
and 85% at night in the summer and between 60 and 80%, respectively in the winter
Desalination provides a mean of upgrading brackish water (poor quality) to
produce fresh water. This method has been practiced regularly for over 50 years
and is a well-established means of water in many countries throughout the world
Gaza Strip suffering from depletion of available fresh water due to the over-pumping
of the groundwater the only resource of domestic purposes. This problem became
more severe by time as a result of sea water intrusion to the coastal aquifer,
in addition to the infiltration of partially treated wastewater to the aquifer
(Shomar, 2010; Qahman et al.,
2009; PWA, 2003). The water demand in Gaza Strip
is growing rapidly due the population growth and the willing of farmers to cultivate
the poor land as a strategy toward poverty alleviation (Al-Najar,
2007). The high salinity of the water and other contaminants, in addition
its bad health effect, undesirable tastes are motives to find new resource such
as the desalination and quality improvement technology in addition to other
means which are not included in the current research. The concentration of chemical
pollutants, including nitrate and chloride have exceeded the standards recommended
by WHO (MOH, 2009; Al-Najar and Adeloye,
2005; Daya, 2002) from most of the municipal wells.
Due to the pointed shortage of water and the bad quality of groundwater, desalination
plants were set up in the Gaza Strip. Reverse Osmosis (RO) systems reverse the
natural process of solvent transport across a semi-permeable membrane from a
region of lower solute concentration into one of higher solute concentration
to equalize the free energies. In RO external pressure is applied to the high
solute (concentrated) water to cause solvent (water) to migrate through the
membrane leaving the solute (salts and other non permeates) in a more concentrated
brine. Some membranes will reject up to 99% of all ionic solids and commonly
have molecular weight cut off in the range of 100 to 300 Daltons for organic
chemicals. RO processes can produce water in the range of 10 to 500 mg L-1
TDS (WHO, 2007).
Currently, there are six reverse osmosis desalination plants in the Gaza Strip
owned and operated by the Palestinian Water Authority (PWA) local municipalities.
In addition, there are many small desalination units owned and operated by private
investors for commercial purposes. Nowadays there is a plan for a regional seawater
desalination plant with a capacity up to 150,000 m3/y (CMWU,
2009; Baalousha, 2005). According to the Palestininan
Water Authority (PWA) and Coastal Municipal Water Utility (CMWU) plan, desalination
seems to be the only feasible alternative for potable water source for the residents
in the Gaza Strip. The desalinated water market has been developed by time;
about 95% of the people in Gaza Strip depend on the small-scale brackish water
desalination plants and home filter for drinking purposes (Abu-Amr
and Mayla, 2010). There are more than 50 Brackish Water Desalination Plants
(BWDPs) in Gaza Strip, more than 50% of these plants are unofficially registered
and therefore no quality monitoring program is applied. The current research
aims to evaluation the ground water quality in Gaza Strip in general and the
inlet and outlet water quality for small-scale brackish water BWDPs comparing
to the WHO standards. Various desalination techniques that are implemented in
the Gaza Strip and the main environmental impacts will be essential concern
in the current research.
MATERIALS AND METHODS
During the period from March 2009 to March 2010, samples of water from the
inlet and outlet of the desalination plants in the Gaza Strip were collected
for chemical water analysis such as pH, Total Dissolved Solids (TDS), Chloride,
Nitrate and Calcium to evaluate the desalinated water quality in Gaza Strip.
Ground water quality data of municipal wells were collected (ministry of health
monitoring program) for the same period 2009/2010 to evaluate the ground water
quality status during the research period. Chloride, Ca and HCO3¯
were measured by Titration while EC, TDS and pH were determined using electrode
and NO3¯ by spectrophotometer. Samples analysis were conducted
at the public health laboratory for foods and water at the Palestinian Ministry
of Health for the monitoring program implemented by Water control department
using the procedures described by the American Public Health
Association, 1992. Results of desalination plants water quality (inlet and
outlet) and the collected data were analyzed using software packages such as
Microsoft office (Excel) and Statistical Package for Social Sciences (SPSS).
RESULTS AND DISCUSSION
Groundwater quality beneath The Gaza Strip Governorates: Total Dissolved
Solids (TDS) and Cl used in the current research as an indicator of groundwater
salinity contamination in Gaza Strip while Nitrate is used as an indicator of
anthropogenic contamination of groundwater. High levels of chloride and TDS
in the groundwater cause high salinity in the water supply (Al-Jamal
and Al-Yaqubi, 2000). Table 1 summarize the average concentration
of TDS, Cl and NO3 for drinking water-wells in each Governorate of
Gaza Strip within one year. The Average TDS Concentration ranges from 720 mg
L-1 in the north to 2709 mg L-1 in Gaza Governorate. The
Average chloride concentration ranges from 181 mg L-1 in the North
to 772 mg L-1 in Gaza Governorate. Gaza city represent the main city
in the Gaza Strip, so nearly half of Gaza Strip population reside in Gaza city.
As a consequence water supply and demand are the highest, therefore more groundwater
abstracted from the aquifer beneath the Gaza city. This accelerates the rapid
sea intrusion which can be seen in the high concentration of TDS and chloride
compared to the north governorates. The average concentration of Nitrate ranges
from 97 mg L-1 in the north to 139 in Gaza Governorate. Similar investigation
also emphasis the fact of nitrate pollution due to the infiltration of partially
treated effluent and the excess use of nitrogen fertilizer to the groundwater
(Shomar et al., 2008) As shown in Table
1, the level of TDS, Cl and Nitrate were higher than WHO standards (1000,
250 and 50 mg L-1, respectively) for the entire Gaza strip Governorates
except the North Governorate which has a lower concentration of TDS than WHO
Table 2 presents the percentages of drinking water wells
that exceed WHO standards of TDS, Chloride and Nitrate. For TDS, about 49% of
drinking municipal water wells were exceed the WHO standards (1000 mg L-1).
The percentage ranges from 4% in the north Governorate to 81% in Middle Governorates.
Like TDS, the concentrations of Chloride in 58% of municipal water wells were
higher than WHO Standards (250 mg L-1) and its ranges from 8% in
the North to 94% in Middle Governorate.
||Average concentration of chemical parameters of the coastal
aquifer beneath the five geographical governorates in Gaza Strip at the
The major source of salinity in Gaza Strip aquifer is derived from the flow
of natural saline groundwater from the eastern part of the aquifer toward the
Gaza Strip. The long-term reduction of the water table because of overexploitation
has increased the water gradients and rate of lateral water flow toward Gaza
Seawater intrusion has also resulted in salinization of groundwater in the western
part of the aquifer (Qahman et al., 2005; Weinthal
et al., 2005). Seawater intrusion and uplift the deep brine water are
the direct consequences of over pumping and represent the greatest threats to
municipal and agricultural water supplies in Gaza Strip. The lateral inflow of
brackish water from the east is believed to be groundwater from the Eocene age
rocks that underlie the coastal aquifer in the east and is therefore of natural
origin (AL-Agha and EL-Nakhal, 2004). The relatively low
values of chloride in the north and demonstrates the shallow nature of wells that
are sampled. The increasing chloride trends in the Khan Younis municipal well
field are demonstrated by the deeper wells.
|| Chemical parameters (mg L-1) for inlet of small-scale
BWDPs in Gaza Strip (Brackish water wells)
In contrast to salinity, groundwater flowing from east has relatively low nitrate
levels (Nassar et al., 2009). As shown in Table
2, about 79% of municipal wells in the Gaza Strip have nitrate concentrations
that exceed WHO guidelines of 50 mg L-1. The level of nitrate contamination
has been rising so rapidly that most of Gazas drinking water wells are
no longer adequate for human consumption. Nevertheless, domestic wells continue
to supply groundwater of poor quality to local communities for domestic use
(Vengosh et al., 2002, 2005).
Chemical quality for inlet of small-scale BWDPs in Gaza Strip: About
43 desalination plants were distributing randomly in Gaza Strip Governorates.
The source of inlet water for these plants mainly from groundwater abstracted
by drilling boreholes in the site of this plants, which located in different
governorates as shown in Table 1. pH values in inlet for all
desalination plants arent exceed WHO standards (6.5-8.5), while, its less
than WHO limits for two plants in Gaza Governorate (6 and 6.2). For TDS concentration,
about 5 plants (45%) out of 11 in the North Governorate were exceed WHO Limits
(1000 mg L-1), while in Gaza City TDS level was higher than WHO standards
in 11 (73.3%) plants, the concentration of TDS was higher than WHO limits in
the inlet water for all desalination plants in Middle governorate; 5 plants
(100%), Khanyounis 4 (100%) and Rafah 8 (100%). The concentration of chloride
for inlet water of 6 (54%) plants in the North Governorate were more than WHO
standards (250 mg L-1). while, in Gaza Governorate, the concentration
level was exceeds WHO standards for inlet water of 12 (80%) desalination plants
as shown in Table 2. Like TDS, the concentration of Chloride
were higher than WHO standard for inlet water of all desalination plants in
Middle governorate, Khanyounis and Rafah; 5 (100%), 4(100%) and 8 (100%), respectively.
Its worth to mention that the percentages of desalination plants that higher
than WHO limits for concentration of TDS and Chloride were increasing from the
North to Rafah Governorate. The level of TDS, Cl and Nitrate were higher than
WHO standard for the Gaza Strip except in the North Governorate the concentration
of TDS were less than standards. Mayla and Amr 2010 declare
the similar results. For Nitrate Concentration, the inlet water for most desalination
plants in the North 11 (100%), Khanyounis 4 (100%) and Rafah 8 (100%) Governorates
were higher than WHO standards, while the level of Nitrate for inlet water of
plants in Gaza and Middle Governorates were higher than WHO standards in 10
(66.6%) and 3 (60%) of plants, respectively. Its reflects the contamination
of groundwater by Nitrate due to the infiltration of partially treated wastewater.
Generally, the Calcium concentration were not exceeds than WHO standards (200
mg L-1) for inlet water in the most desalination plants for all Gaza
Strip Governorates except one plants in the North.
Chemical quality for outlet of small-scale BWDPs in Gaza strip: To evaluate
the desalinated water quality, Table 3 presents the results
of chemical analysis for desalinated water from small-scale BWDPs in Gaza Strip.
Generally, pH values were less than 6.5 in the most desalination plants in Gaza
Strip except in some plants were fluctuates from 6.5 to 8.5. The Palestinian
Recommendation for the pH value of the drinking water is between 6.5-8.5 and
this value has healthy effects (PWA, 2000). The main
purpose in controlling pH is to produce water in which corrosion and incrustation
are minimized. These processes, which can cause considerable damage to the water
supply system, result from complex interactions between pH and other parameters
such as dissolved solids, dissolved gases, hardness, alkalinity and temperature.
By keeping the pH below 8.5, the rate of chlorine disinfection is increased
and the production of trihalomethanes is reduced. (WHO, 2003).
The level of both TDS and Chloride arent exceed the limits of WHO for
all desalination plants, while in some plants the level of TDS and Chloride
were less than 50 and 10 mg L-1, respectively. For Nitrate concentration,
3 desalination plants out of 43 in Gaza Strip resulting an increasing of Nitrate
level than WHO limits, while the other plants generally less than 38 mg L-1.
The level of calcium was not exceeds WHO standards moreover, the concentration
of calcium for all desalination plants were less than 25 mg L-1 except
in one plant in Gaza Governorate was 51 mg L-1. A certain Ca2+
concentration is required in drinking water not only because it induces CaCO3(s)
precipitation, but also because of health reasons. Calcium is vital for human
growth particularly for infants. Twenty percent of the recommended daily dosage
arrives from drinking water (Kozisek, 2003). Most guidelines
worldwide set the minimum Ca2+ concentration value at 20-25 mg Ca2+
Chemical parameters for inlet and outlet of small-scale BWDPs comparing with WHO standards: In order to achieve an obvious investigation and evaluate the efficiency of the small-scale BWDPs; chemical parameters of inlet and outlet of their plants have been compared with WHO standards .
As shown in Fig. 1, Generally, pH of inlet in most plants ranging within the acceptable WHO standards (6.5-8.5). While, pH of the outlet in most of their plants were less than WHO standards, as a result of lacking pH adjustment and clear control in desalination plants.
In Fig. 2 and 3, generally, there is a big gap between inlet and outlet concentrations of TDS and Chloride as a result to the high removal efficiency of desalination plants.
As shown in Fig. 4. Nitrate concentration for outlet of most plants is slightly lower than WHO standards, moreover, three plants produced a higher concentrations of nitrate than WHO standards. It is indicate that the efficiency of NO3 is lower the that in case of TDS and Chloride.
|| Chemical parameters (mg L-1) for outlet of small-scale
BWDPs in Gaza Strip
||pH concentration for inlet and outlet water of small scale
desalination plants comparing with WHO limit
||TDS concentration for inlet and outlet water of small scale
desalination plants comparing with WHO limit
||Chloride concentration for inlet and outlet water of small
scale desalination plants comparing with WHO limit
||Nitrate concentration for inlet and outlet water of small
scale desalination plants comparing with WHO limit
This fact is not appropriate in case of Gaza strip which has a higher concentration
of Nitrate in the groundwater aquifer, that motives to find other more efficient
technologies in removing of NO3 than the actual technology, particularly
in the regions that have a highest concentrations of NO3. In addition,
nitrate has more health impact than TDS and chloride specially if the blue babies
||Calcium concentration for inlet and outlet water of small
scale desalination plants comparing with WHO limit
As shown in Fig. 5, there is an excessive removing of calcium
element less than WHO standards (20-25 mg L-1). In many of small-scale
BWDPs in Gaza Strip it is clear that there is no any concerning of the concentration
level of the calcium and any of other vital elements needed to the human growth
particularly in case of infants. And there is no any official regulation or
clear monitoring body to control water quality parameters for drinking proposes.
The highest priority to offer good taste drinking water rather than healthy
Table 4 illustrates the Minimum, Maximum and Average concentration
of chemical parameters for desalinated water of small scale desalination plants
in Gaza Strip. Moreover, TDS concentration in desalinated water of small scale
plants ranges from 23 to 521 mg L-1. For chloride concentration,
the minimum value was 3.6 mg L-1 and the maximum value was 130 mg
L-1. The level of Nitrate in desalinated water for all plants ranges
from 2.6 to 84 mg L-1 and for Calcium concentration, the minimum
level was 0.7 and the maximum was 51 mg L-1. There is a big gab and
obvious variation between the minimum and maximum values for all chemical parameters
in desalinated water from desalinated plants due to the variations in inlet
water quality and the variety of desalination efficiency of elements removing
by using the small scale desalination plants. The concentration intervals for
chemical parameters of desalinated water also interpreted in Table
4 and Fig. 1-5.
Total Dissolved Solids (TDS) comprises inorganic salts and small amounts of
organic matter that are dissolved in water. The principal constituents are usually
the cations calcium, magnesium, sodium and potassium and the anions carbonate,
bicarbonate, chloride, sulphate and, particularly in groundwater, nitrate (WHO,
2003). Figure 6 shows that the intervals of TDS concentration
for desalinated water from small scale plants in Gaza Strip. The highest intervals
of TDS concentration showed from 61 to 90 and from 91 to 120 mg L-1,
respectively and the lowest interval was from 0 to 30 mg L-1. Recent
data on health effects associated with the ingestion of TDS in drinking water
have not been identified; however, associations between various health effects
and hardness, rather than TDS content, have been investigated in many studies.
Water with extremely low TDS concentrations may also be unacceptable because
of its flat, insipid taste. The WHO standard of chloride concentration in drinking
water is 250 mg L-1, The concentration intervals of chloride in desalinated
water showed in Fig. 7, chloride concentration in the most
desalination plants were ranges in the intervals from 0 to 30 and from 31 to
60 mg L-1, respectively. Chloride is the most abundant anion in the
human body and contributes significantly, along with its associated actions,
to the osmotic activity of the extra-cellular fluid; 88% of the chloride in
the body is extra-cellular.
|| Minimum, maximum, average and concentration intervals for
chemical parameters of small-scale BWDPs in Gaza Strip
|| TDS concentration intervals for desalinated water from small-scale
BWDPs in Gaza Strip
||Chloride concentration intervals for desalinated water from
small-scale BWDPs in Gaza Strip
|| Nitrate concentration intervals for desalinated water from
small-scale BWDPs in Gaza Strip
A normal 70 kg human body contains approximately 81.7 g of chloride and 45
L of water. The taste threshold for chloride in drinking water is dependent
on associated cation, but is usually within the range of 200-300 mg of chloride
per litter (WHO, 1996).
Nitrate (NO3) concentration intervals in desalinated water presents
in Fig. 8, the concentration of nitrate in the majority outlet
of desalination plants ranges in the interval from 0 to 30 mg L-1.
It has been well documented that, in some countries, water supplies containing
high levels of nitrate have been responsible for cases of infantile methaemoglobinaemia
||Calcium Concentration intervals for desalinated water from
small-scale BWDPs in Gaza Strip
The extent of the world wide problem has been reviewed in a WHO document. It
has been recommended that water supplies containing high levels of nitrate (more
than 100 mg L-1) should not be used for the preparation of infant
foods, alternative supplies having low nitrate content, even to the extent of
using bottled water, have been recommended (WHO, 1984).
Calcium is an essential part of the human diet. However, the nutritional value
from water is likely to be minimal compared to that from other food sources.
There is no health objection to high calcium content in water, the main limitations
being made on the grounds of excessive scale formation. Figure
9 showed the concentration interval for calcium in desalinated water from
small scale plants in Gaza Strip, the level of Calcium for all plants were ranging
in the interval from 0 to 30 mg L-1. WHO recommends a maximum level
of 200 mg L-1 as Ca, even if there is no health-base guideline value
recommended by WHO for water calcium. The taste threshold for the calcium ion
is in the range 100-300 mg L-1, depending on the associated anion.
Studies presented that the optimal Ca/Mg ratio should not exceed 2:1 (Kozisek,
According to the WHO standards, potable water may contain different minerals up to a certain limit. In the Gaza commercial desalination plants and in the absence of quality control, the desalinated water has negligible amounts of several minerals such as calcium. It is reported that the produced water of these plants has less than 30 mg L-1 Ca and similarly other elements, Therefore, the produced water contains no elements that are needed for human health.
The disadvantages and the environmental impacts of small-scale BWDPs:
Characteristics of effluent brine from desalination plants depend on the method
of desalination. However, all desalination plants use chlorine, which is hazardous
to the environment, to clean the pipes in the pretreatment process. In general,
salt concentration of brine effluent is almost double that of seawater (seawater
has about 35,000 ppm of salt concentration, while the brine has 46,000 to 80,000
ppm). Brine salinity measurements were at twice as high as these of the feed
water. Both the high bacterial counts and salinity values may cause risky environmental
changes in the Bay (coastal seawater) ecosystem especially on coral reefs, in
fish aquaria, as well as to effect swimmers, snorkeller and scuba divers, Despite
the high efficiency (100%) of the reverse osmosis membrane technology in removing
seawater and brackish water salts, the investigated desalination systems were
not satisfactory in producing bacteriologically- safe potable water, Furthermore,
There is a possibility of having a highly contaminated fresh water source with
bacteria other than the seawater, kitchen and/or swimming pool drains for example
and it may also indicate a bad fouled condition of the running reverse osmosis
membranes (Diab 2002). In such a case the reveres osmosis
membrane become a source of contamination (Durham, 1997;
Tua, 1996). In many cases reverse osmosis is the heart
of a high water purity system. The very high load of pathogenic bacteria in
the brine, such as Salmonella, Shigella, vibrio and Aeromonas are virulent against
both human and fish (Diab et al., 1995). It is
clear that the bad environmental impacts on the studied ecosystem is expected,
if not recognizable now it would be later (Diab, 2002).
RO membrane fouling is a complex phenomenon involving the deposition of materials
on the membrane surface rather than plugging of the system. Scaling of RO membrane
surfaces is caused by the precipitation of sparingly soluble salts from the
concentrated brine (especially CaCO3 and BaSO4). A number
of chemicals may be added to prevent membrane fouling. For example, sulfuric
or hydrochloric acid is employed to reduce pH and prevent CaCO3 precipitation.
Sulfuric acid, while safer and less expensive than HCl, will increase the content
of sulfate ions in the feed water and consequently the risk of CaSO4
precipitation. The addition of polyphosphates or, more recently, polycarboxylates
is employed for preventing CaSO4 scaling (Morales
and Barrufet, 2002).
In Gaza Strip small-scale BWDPs. Accordingly, effluent of these plants contains some chemicals like anti-scaling, surfactants, ferric chloride and acids, that may affect the environment if a proper dilution process not followed. The effluents of small-scale BWDPs which are also used in the Gaza Strip have characteristics totally different from that of groundwater. It has more calcium and magnesium besides other components. In the Gaza Strip, the effluents of these plants are not properly disposed. In all cases, the effluents are discharged in the nearby field and thus, it might lead to contamination of groundwater and leachate deposition may denigrate soil productivity. Besides commercial desalination plants, use of small RO units at home is very common in the Gaza Strip. The water produced by these units is generally not controlled or tested. In the absence of public awareness, people are using these RO units for a very long time without changing the membrane. As a result, the consumed water from the home units is rather unhealthy and might cause different diseases due to bacteria and virus accumulations.
Freshwater in the Gaza Strip coastal aquifer exists in the form of lenses which lie on more dense brackish water. These freshwater lenses are recharged by infiltration of rainfall and other minor sources (e.g., leakage from water system, sewer system). Over-pumping of freshwater causes upconing of brackish and saline water beneath. Although the desalination projects use brackish water beneath the fresh lenses as a feed, this has an adverse impact on the environment. Withdrawal of brackish groundwater might contribute to imbalance in the groundwater system, which is already very fragile. Continuous pumping of these dense layers of brackish groundwater might lead to lowering of water table above. The water table and transition zone between fresh and brackish/saline water will be changed. In coastal aquifers, like the case of the Gaza Strip aquifer, there is a saltwater boundary between the fresh groundwater and the seawater. The length of that boundary is highly dependent on the inflow and outflow of groundwater. In natural conditions, the length of the boundary is about tens to hundreds of meters. Extraction of groundwater causes an inland shift of this boundary, consequently affecting the freshwatersaline water balance. This balance is obviously disturbed in the Gaza Strip coastal aquifer. Given the high pumping rate, there is a strong evidence of seawater intrusion.
The groundwater beneath the Gaza Strip is unsuitable for drinking purposes; the low areas of chloride concentration has high nitrate concentration and vice versa. There are wide variations of water quality, therefore not all water in Gaza Strip need the same elements removal technology. The inlet water quality parameters in most plants are higher than WHO standards and Palestinian standards but the high desalination efficiency led to completely removal of essential elements that are essential to human health such as Calcium.
Using desalination as a source of water supply has many advantages. It seems that RO is the best choice in terms of quality of produced drinking water. However, the impact of these plants is not well investigated.
The environmental issue should be well discussed before implementing the small-scale or regional desalination plant. The relevant institutions should strictly control the private sector desalination units for commercial purposes to ensure that they consider environmental aspects. Currently, the brine of these inland units is disposed in the field, in the sewerage system or directly in the street. The quality of the produced water should be also monitored to ensure that it meets health requirements. Another important issue is the pumping of brackish water from the aquifer. It is true that this water is not potable, but it is located in layers beneath the underground freshwater. Depletion of these layers of brackish water could lead to lowering of the water table and intrusion of seawater affecting the unsaturated zone.
My deep grateful to the Al Azhar University, particularly the Institution of Water and Environment for giving me the real and appreciated opportunity to carry out the research and I wish to express my gratitude to Mr. Salem Abu Amr for his unlimited technical support and data analysis.