Journal of Environmental Protection, 2010, 1, 216-225
doi:10.4236/jep.2010.13026 Published Online September 2010 (
Copyright © 2010 SciRes. JEP
Evaluation of Treated Municipal Wastewater
Quality for Irrigation
Abdul Hameed M. Jawad Alobaidy, Mukheled A. Al-Sameraiy, Abass J. Kadhem, Athmar Abdul
Environmental Research Center, University of Technology, Baghdad, Iraq.
Received May 27th, 2010; revised June 24th, 2010; accepted June 27th, 2010.
Wastewater reuse is a useful tool in minimizing the amount of wastewater in the environment. Therefore, evaluation of
the suitability of Al-Rus tamiyah WWTP municipal treated wastewater for irrigation was mad e according to its compo -
sition and the internation al irrigation water quality standards. In additio n, to classify water quality and to evaluate its
suitability for irrigation purposes, Sodium Adsorption Ratio (SAR), Soluble Sodium Percentage (SSP) and Residual
Sodium Carbonate (RSC) were calculated following standard equations and found experimentally as (2.11), (35.67)
and (–12.75) respectively. Plottin g the values of conductivity (EC) and sodium absorption ratio (SAR) on the US salin -
ity diagram illustrated that most of the samples fall in the field of C3-S1, indicating high salinity and low sodium water
which can be used for irrigation on almost all types of soil without danger of exchangeable sodium. Furthermore, the
data indicate slight to moderate degree of restriction on the use of this treated wastewater in irrigation due to chloride
hazard. RSC value is negative at all sampling sites, indicating that there is no complete precipitation of calcium and
magnesium. Overall, the treated wastewater can be classified with few excep tions as suitable for irrigation use.
Keywords: Wastewater Reuse, Irrigation, Sodium Adsorption Ratio (SAR), Residual Sodium Carbonate (RSC), Soluble
Sodium Perc entage (SSP)
1. Introduction
In many arid and semi-arid countries water is becoming
an increasingly scarce resource and planners are forced
to consider any sources of water which might be used
economically and effectively to promote further devel-
opment. Thus, the availability of good-quality water for
irrigation is threatened in many places [1] and irrigated
agriculture faces the challenge of using less water, in
many cases of poorer quality, to irrigate lands that pro-
vide food for an expanding population.
The irrigation water needs can be met by using the
available water more efficiently, but in many cases it will
prove necessary to make increased use of municipal
wastewaters [2]. The use of wastewater in agriculture has
potential for both positive and negative environmental
impacts [3]; with careful planning and management the
use of wastewater in agriculture can be beneficial to the
environment. However, the direct and indirect use of
untreated wastewater in irrigated agriculture is increasing
as a result of increasing global water scarcity, inadequate
and inappropriate wastewater treatment and disposal,
increased food insecurity and escalating fertilizer costs
[4-6]. Consequently, the reuse of wastewater for agricul-
ture is highly encouraged [7,8] and it is a common prac-
tice for many reasons, not least of which is nutrient value
and environmental protection [1,9]. Irrigation with treated
municipal wastewater is considered an environmentally
sound wastewater disposal practice compared to its direct
disposal to the surface or ground water bodies [3,8].
Wastewater is a valuable source of plant nutrients and
organic matter [10]. Nevertheless, it may contain unde-
sirable chemical constituents and pathogens that pose
negative environmental and health impacts [11]. At the
same time, a number of risk factors have been identified
in wastewater reuse, some of them are short term (e.g.,
microbial pathogens) whereas others have longer-term
impacts that increase with the continued use of recycled
water (e.g., salinity effects on soil). So, many guidelines
have been developed to give a quality criteria and guid-
ance on how treated wastewater (effluents) should be
reused for irrigation purposes [12,13].
Evaluation of Treated Municipal Wastewater Quality for Irrigation
Copyright © 2010 SciRes. JEP
The amount of collected and treated wastewater is
likely to increase significantly with population growth,
rapid urbanization, and improvement of sanitation ser-
vice coverage [14-16]. Hence, the use of treated waste-
water in agriculture is one of the strategies adopted for
increasing water supply in arid and semi arid countries
[17,18]. Wastewater also has been used in agriculture for
decades in many countries like India [15], Nepal [19],
China [20], Spain [21] and Italy [22]. Under the condi-
tions of increased freshwater scarcity at Arabian coun-
tries like Saudi-Arabia [17], Kuwait [23,24] and Jordan
[25,26], the reuse of wastewater in agriculture is receiv-
ing great attention and increased recognition as a poten-
tial water source.
It is generally accepted that wastewater use in agricul-
ture is justified on agronomic and economic grounds but
care must be taken to minimize adverse health and envi-
ronmental impacts. However, in Iraq such usage of
treated or untreated wastewater has not been widely in-
vestigated and evaluated. In view of these facts, the pre-
sent study was undertaken to characterize the secondary
treated wastewater produced from Al-Rustamiyah WWTP
and to evaluate its suitability for irrigation purposes as
non-conventional water resources.
2. Materials and Methods
2.1. The Study Area
The Iraqi capital, Baghdad, has the highest level of sani-
tation provision with about 80% of the population con-
nected to sewer conveying sewage to treatment facilities.
It is located in the Mesopotamian alluvial plain between
latitudes 33°14’-33°25’ N and longitudes 44°31’-44°17’ E.
The general altitude ranges between 30.5 and 34.85 m
a.s.l. Tigris River divides the city into a right (Karkh) and
left (Risafa) sections (Figure 1). The area is character-
ized by arid to semi arid climate with dry hot summers
and cold winters; the mean annual rainfall is about 151.8
mm [27].
The sewerage network that was established between
1960 and 1980 worked on the basis of the separate sys-
tem, but a combined system has been adopted since 1980.
In general, the wastewater quantities generated within the
urban and rural areas of the mayoralty of Baghdad are
estimated at 1,426,013 and 2,354 cubic meters per day
respectively. However, the capacity of all wastewater
treatment plants in the mayoralty of Baghdad was esti-
mated at 789, 200 cubic meters per day, in which it rep-
resents as 55% of the total capacity of wastewater. The
secondary treated wastewater effluent for Iraqi (WWTP)
was designed to produce an average of final effluent qual-
ity of biological oxygen demand (BOD) and total sus-
pended solids (TSS) as 20 and 30 mg/L, respectively to
Figure 1. Base map of Baghdad city.
meet the Iraqi National Standards set by the Regulation
25 of 1967. It reported that each day 500,000 cubic me-
ters of raw sewage are discharged into Iraqi waterways
In the Iraqi wastewater treatment plants, the existing
pumping stations are also inefficient because of the lack
of proper operation and maintenance and unavailability
of spare parts. Despite this, most of the treated wastewa-
ter in the area under study (Baghdad City) was mixed
with freshwater from the Diyala River and used down-
stream for unrestricted irrigation. Thus around 50% of
the total treated wastewater generated could be reused
2.2. Sampling and Analysis
Treated wastewater samples from Al-Rustamiyah WWTP
were bimonthly collected during January 2009 to De-
cember 2009 in stopper fitted polyethylene bottles that
prewashed with dilute hydrochloric acid and then rinsed
several times with the effluent sample before filling them
to the required capacity. These samples were stored at a
temperature below 4 prior to analysis in the laboratory.
Procedures followed for analysis have been in accor-
dance with the Standard methods for examination of wa-
ter and wastewater [28]. The calibration for different
chemical constituents was done by preparing low-level
standard solutions using AR-grade chemicals and was
periodically repeated to check the accuracy. Calcium
(Ca2+) and Magnesium (Mg2+) were determined titrimet-
rically using standard EDTA, while Chloride (Cl) was
determined by standard AgNO3 titration. Carbonate
2-) and Bicarbonate (HCO3
-) were determined by
titration with HCl. Sodium (Na+) and Potassium (K+)
were measured by flame photometry and Sulphate (SO4
by spectrophotometer turbidimetry. Total Suspended
Solid (TSS) and Total Dissolved Solid (TDS) were de-
Evaluation of Treated Municipal Wastewater Quality for Irrigation
Copyright © 2010 SciRes. JEP
termined by gravimetric method (dried at 103). Bio-
logical Oxygen Demand (BOD) was determined by the 5
Day BOD test while Chemical Oxygen Demand (COD)
was determined in the laboratory by the standard Open
Reflux Method. Other tests such as Conductivity (EC)
and pH were directly measured in situ using portable
measuring devices (HANNA instruments, HI 9811, port-
able pH-EC-TDS METER, Italy). Note that before each
measurement, the pH meter was calibrated with reference
buffer solution. Each analysis was carried out in triplicate
and then the mean value was taken.
2.3. Indicators of Water Quality for Irrigation
Important irrigation water quality parameters include a
number of specific properties of water relevant in rela-
tion to the yield and quality of crops, maintenance of soil
productivity and protection of the environment. These
parameters mainly consist of certain physical and che-
mical characteristics of water that are used in the evalua-
tion of agricultural water quality. Numerous water qual-
ity guidelines have been developed by many researchers
for using water in irrigation under different condition
[29-32]. However, the classification of US Salinity
Laboratory (USSL) is used most commonly. Parameters
such as EC, pH, Sodium Adsorption Ratio (SAR), ad-
justed SAR (adj SAR) and the Exchangeable Sodium
Percentage (ESP), Soluble Sodium Percentage (SSP) and
Residual Sodium Carbonate (RSC) were used to assess
the suitability of water for irrigation purposes. The crite-
ria used to evaluate quality of wastewater for use in ag-
riculture are listed in Table 1.
3. Results and Discussion
Descriptive statistics for all characteristics are presented
in Table 2. An explanation of the observed characteris-
tics follows in the following sections.
3.1. Hydrogen Ion Activity (pH)
The values of pH varied from 6.87 to 8.40 with an aver-
age value of 7.70, which indicates that the treated mu-
nicipal wastewater is slightly alkaline in nature. The
normal pH range for irrigation water is from 6.5 to 8.4.
Irrigation water with a pH outside the normal range may
cause a nutritional imbalance or may contain a toxic ion
3.2. Salinity Hazard
Electrical conductivity (EC) is the most important pa-
rameter in determining the suitability of water for irriga-
tion use and it is a good measurement of salinity hazard
to crop as it reflects the TDS in wastewater. The most
important negative effect on the environment caused by
agricultural wastewater is the increases in soil salinity,
which if not controlled, can decrease productivity in long
term [3]. EC values of experimental samples varied from
1910 to 2120 μS/cm (mean value = 1949.78 μS/cm)
while TDS values varied from 1164 to 1350 mg/L (mean
value = 1234.6 mg/L) indicating slight to moderate de-
gree of restriction on the use of this wastewater in irriga-
tion due to salt build-up in soils and its adverse effects on
plant growth [32]. Furthermore, the results indicted also
that this type of water can be used on the soils with re-
stricted drainage. Special salinity control management
with selection of good salt tolerant plants is required.
However, irrigation water with conductivity in the range
of 750-2250 μS/cm is permissible for irrigation and
widely used. Satisfactory crop growth is obtained under
good management and favorable drainage conditions but
saline conditions will develop if leaching and drainage
are inadequate [30]. It is clear that irrigation using saline
water can add salt concentration to the soils and a prob-
lem may be occurred due to the increase in concentration
that is harmful to the crop or landscape. Therefore, it is
necessary to combine the use of wastewater with prac-
tices to control salinization, such as soil washing and
appropriate soil drainage [3]. The primary effect of high
EC reduces the osmotic activity of plants and thus inter-
feres with the absorption of water and nutrients from the
soil [34].
3.3. Sodium Hazard
Sodium content is the most troublesome of the major
constituents and an important factor in irrigation water
quality evaluation. Excessive sodium leads to develop-
ment of an alkaline soil that can cause soil physical pro-
blems and reducing soil permeability [35]. Furthermore,
irrigation water containing large amounts of sodium is of
special concern due to absorbed sodium by plant roots
which is transported to leaves where it can accumulate
and cause injury [36]. However, there is a restriction in
use of overhead sprinklers method with water contained
a high level of sodium salts because these salts can be
absorbed directly by plant leaves and will produce
harmful effects.
The water can be used for irrigation when the concen-
tration of sodium is about 8.0 meq/L (184.0 mg/L) [37].
Sodium concentrations in the samples varied from 123.60
to 221.0 mg/L (mean value = 171.11), indicating slight to
moderate to high degree of restriction for sensitive crops
on the use of this wastewater in irrigation [32]. Sensitive
crops include deciduous fruits, nuts, citrus, avocados and
beans, but there are many others. In the case of tree crops,
sodium in the leaf tissue in excess of 0.25-0.50 percent
(dry weight) is often associated with sodium toxicity
Evaluation of Treated Municipal Wastewater Quality for Irrigation
Copyright © 2010 SciRes. JEP
Table 1. Water quality classes for agricultural irrigation.
Reference [30] Reference [32]
Salinity Hazard
Irrigation water classification Degree of restriction on use
Excellent Good PermissibleUnsuitable None Slight to Moderate Severe
EC (dS/m) < 0.25 0.25-0.75 0.75-2.25 2.25-5.0 < 0.7 0.7-3.0 > 3.0
TDS (mg/L) < 200 200-500 500-1500 1500-3000 < 450 450-2000 > 2000
Soil Water Infiltration (Evaluate using EC and SAR together)
EC (dS/m) SAR Degree of
restriction Remarks Degree of restriction on use
< 0.25 < 10 Low Satisfactory for all crops EC (dS/m)
& SAR None Slight to
Moderate Severe
0.25-0.75 10-18 Medium Satisfactory, some salt sensitive crops will
be affected
If SAR 0-3
& EC > 0.7 0.7-0.2 < 0.2
If SAR 3-6
& EC > 0.2 0.2-0.3 < 0.3
6-12 &EC> 1.9 1.9-0.5 < 0.5
0.75-2.25 18-26 High
Satisfactory for most crops, salinity condi-
tion will be develop unless leaching and
drainage are adequate If SAR
> 2.9 2.9-1.3 < 1.3
2.25-5.0 > 26 Very high Suitable for most salt tolerant plants, leach-
ing and drainage are imperative
20-40 &
> 5.0 5.0-2.9 < 2.9
Specific Ion Toxicity
Degree of restriction on use Degree of restriction on use
Low Medium High Very high None Slight to
Moderate Severe
Na+ (mg/L) - - - - < 100 > 100 > 100
Na+ (SAR) < 10.0 10-18 18-26 > 26.0 < 3.0 3-9 > 9.0
Na+ (SSP) < 20.0 20-40 40-80 > 80 - - -
Irrigation Water Classification Irrigation Water Classification
Safe Sensitive plants
Moderately to
tolerant plants
Unsuitable or
tolerant plants
problem Sever problem
Cl- (meq/L) < 2 2-4 4-10 > 10 < 4 4-10 > 10
Miscellaneous Effects
Irrigation water classification Degree of restriction on use
Safe Permissible Unsuitable None
Slight to
Moderate Severe
pH (pH unit) - - - Normal range = 6.5-8.4
RSC (meq/L) < 1.25 1.25-2.5 > 2.5 - - -
HCO3 (meq/L) - - - < 1.5 1.5-8.5 > 8.5
Sodium hazard is usually expressed in terms of So-
dium Adsorption Ratio (SAR) and it can be calculated
from the ratio of sodium to calcium and magnesium.
SAR is an important parameter for the determination of
the suitability of irrigation water because it is responsible
for the sodium hazard [38], since it is more closely re-
lated to exchangeable sodium percentages in the soil than
the simpler sodium percentage [39]. Sodium replacing
adsorbed calcium and magnesium is a hazard as it causes
damage to the soil structure. It becomes compact and im-
Evaluation of Treated Municipal Wastewater Quality for Irrigation
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Table 2. Summary statistics of the analytical data.
Characteristics Min. Max. Mean
pH (standard units) 6.87 8.40 7.70 ± 0.39
EC (μS/cm) 1910.0 2120.0 1949.78 ± 48.75
TDS (mg/L) 1164.0 1350.0 1234.60 ± 63.09
TSS (mgL) 10.00 112.00 49.30 ± 27.67
Ca2+ (mg/L) 99.70 290.18 157.54 ± 40.34
Mg2+ (mg/L) 33.00 149.20 69.02 ± 29.60
K+ (mg/L) 9.00 26.90 16.38 ± 5.19
Na+ (mg/L) 123.60 221.00 171.11 ± 22.28
HCO3- (mg/L) 24.88 73.80 45.16 ± 11.07
CO32- (mg/L) 0.00 12.30 9.80 ± 3.44
Cl- (mg/L) 171.44 254.92 205.25 ± 21.67
SO42- (mg/L) 199.00 358.00 245.09 ± 43.76
BOD (mg/L) 12.00 66.00 26.36 ± 10.85
COD (mg/L) 36.00 80.00 53.10 ± 13.90
pervious. It has been calculated as follows:
Ca Mg
where: Na+, Ca2+ and Mg2+ are in meq/L.
For waters containing significant amounts of bicar-
bonate, Bower and Maasland [40] proposed a modifica-
tion in the old SAR procedure to include changes in soil
water composition that are expected to result due to dis-
solution/precipitation of lime in the soil upon irrigation.
Therefore, the adjusted sodium adsorption ratio (adj SAR)
is sometimes used [32], and it is an SAR value corrected
to account for the removal of Ca2+ and Mg2+ by their pre-
cipitation with CO3
2- and HCO3
- ions in the water added
[37]. It can be calculated as in reference [41] by using the
following formula:
adj SAR = SAR 1 + 8.4 pHc
where 8.4 is the approximate of a nonsodic saline soil in
equilibrium with CaCO3 and is substituted for the pH of
water. This substitution reflects the high buffering capac-
ity of calcareous soils. pHc is defined by:
2+ 2+
Hc = pK + pK + p Ca + Mg + pAlk (3)
where p refers to the negative logarithm, K2 is the second
dissociation equilibrium constant of carbonic acid, Kc is
solubility equilibrium constant for calcite. Concentra-
tions of Ca2+, Mg2+, CO3
2- and HCO3
- in meq/L.
The pHc can be calculated using the standard table
given by reference [41] which related to the concentra-
tion values from water analysis. This concept has been
found very useful for predicting the effect of sodium
hazard of irrigation water on soil properties. Values of
pHc above 8.4 indicate tendency to dissolve lime from
soil through which the water moves; values below 8.4
indicate tendency to precipitate lime from waters applied
A new adj SAR method [42] is derived which adjusts
the calcium concentration of the irrigation water to the
expected equilibrium value and includes the effects of
carbon dioxide CO2, carbonate (HCO3
-) and of salinity
(EC) upon the calcium originally present in the applied
water but now a part of the soil water. The new adjusted
SAR is termed widely as adj RNa, and the equation is as
adj RNa =
Ca Mg
where Cax
2+, a modified calcium concentration value in
meq/L expected to remain in near surface soil water fol-
lowing irrigation with water of given HCO3
-/Ca2+ ratio
and EC available from the standard Tables [32].
The SAR value of the treated wastewater ranges from
1.43 to 3.19 (mean = 2.11), while adj SAR and adj RNa
values range from 2.35 to 4.40 (mean = 3.12) and from
1.52 to 3.03 (mean = 2.03) respectively (Table 3). The
comparison between SAR, adj SAR and adj RNa values
and their standard values reflects water is suitable for
Total salt concentration of irrigation waters should not
be used as single criteria to prevent it in irrigation use.
Table 3. Calculated irrigation quality charact eristics.
Characteristics Min. Max. Mean
SAR 1.43 3.19 2.11 ± 0.43
adj SAR 2.35 4.40 3.12 ± 0.58
adj RNa 1.52 3.03 2.03 ± 0.36
SSP 21.38 50.82 35.67 ± 6.75
ESP (SAR) 0.84 3.34 1.82 ± 0.61
ESP (adj SAR) 2.16 4.97 3.25 ± 0.80
ESP (SAR RNa) 1.00 3.12 1.70 ± 0.51
pHc 7.63 8.14 7.90 ± 0.3
RSC –25.91–7.07 –12.75 ± 4.002
Mg2+ Hazards 7.97 56.53 39.86 ± 10.44
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Even water with high salt concentration can still be used
for irrigation without endangering soil productivity. High
sodium content common to recycle water can cause de-
flocculating (breakdown) of soil clay particles, severely
reducing soil aeration and water infiltration and percola-
tion. In other words, soil permeability is reduced by irri-
gation with water high in sodium [35,43]. It is therefore,
the best measure of a water likely effect on soil perme-
ability is the waters SAR considered together with its EC.
In this respect, the US salinity diagram (Figure 2) which
is based on the integrated effect of EC (salinity hazard)
and SAR (alkalinity hazard), has been used to assess the
water suitability for irrigation [30]. When the analytical
data of EC and SAR plotted on the US salinity diagram,
it is illustrated that most of the treated wastewater sam-
ples fall in the class of C3-S1 indicating high salinity
with low sodium water, which can be used for irrigation
on almost all types of soil, with only a minimum risk of
exchangeable sodium. This type of water can be suitable
for plants having good salt tolerance but restricts its
suitability for irrigation, especially in soils with restricted
drainage [30,44]. Figure 3 shows the positive correlation
between EC and SAR with a correlation coefficient (R2)
= 0.193. The lower values of R2 show that there is a
higher variation in the EC values.
3.4. Soluble Sodium Percentage (SSP)
It is also used to evaluate sodium hazard. The Soluble
Sodium Percentage (SSP) was calculated as in reference
[29] by the following equation:
Na 100
SSP = CaMgNa K
where all the ions are expressed in meq/L.
Water with SSP greater than 60 percent may result in
sodium accumulations that will cause a breakdown of the
soil’s physical properties [45]. The calculated values of
SSP varied from 21.38% to 50.82% (mean value =
35.67%) indicating moderate degree of restriction on the
use of this wastewater in irrigation. When the concentra-
tion of sodium ion is high in irrigation water, Na+ ion
tends to be absorbed by clay particles, displacing Mg2+
and Ca2+ ions. This exchange process in soil reduces the
permeability and eventually results in soil with poor in-
ternal drainage [32]. Figure 4 shows the positive correla-
tion between SSP and SAR with a coefficient of 0.786.
Irrigation with waters that have high concentrations of
Na+ ion relative to divalent cations may cause an accu-
mulation of exchangeable Na+ on soil colloids. Contin-
ued uses of alkaline waters for irrigation in a closed sys-
tem may have adverse effects on soil physical properties
[46,47], deteriorate the soil and water resources of the
region and affect the sustainability of crop production in
the long run.
It is reported that salinity and sodicity are the principal
water quality concerns in irrigated areas receiving such
water [48]. Saline-sodic irrigation water, coupled with
limited rainfall and high evaporation, may increase soil
sodicity significantly. In general, when sodium is an im-
portant component of the salts, there can be a significant
amount of adsorbed sodium making the soil sodic [31].
Figure 2. Rating of water samples in relation to salinity and sodium hazard.
Evaluation of Treated Municipal Wastewater Quality for Irrigation
Copyright © 2010 SciRes. JEP
= -0.193
Sodium Adsorption Ratio
Conductivity (µS/cm)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Figure 3. Correlation betwe en sodium adsorption ratio and c onductivity.
= 0.786
Sodium Absorption Ratio
Soluble Sodium Percentage
Figure 4. Correlation between sodium adsorption ratio and percentage sodium.
The ratio of the exchangeable Na+ to total exchange-
able cations (Exchangeable Sodium Percentage, ESP) is a
good indicator for soil structure deterioration. Although,
the ESP of 10-15% is generally accepted as a critical
level, an ESP of 25% may have little effect on soil struc-
ture in a sandy soil, whereas an ESP of 5% is considered
high particularly in soils containing 2:1 clay minerals
like montmorillonite [49]. The ESP of soils can be pre-
dicted quite well from the following the empirical rela-
tionship [30]:
1000.0126 0.01475SAR
ESP = 10.0126 0.01475SAR
  (6)
The expected ESP for the experimental data would be
Evaluation of Treated Municipal Wastewater Quality for Irrigation
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in range of 0.84-3.34 SAR, 2.16-4.97 adj SAR and
1.0-3.12 SAR RNa as shown in Table 3. The ESP pre-
dicted from adj SAR of treated wastewater was higher
than those predicted from SAR and SAR RNa.
3.5. Chloride Hazard
The most common toxicity is from chloride (Cl-) in the
irrigation water. Cl- is not adsorbed or held back by soils,
therefore it moves readily with the soil-water, is taken up
by the crop, moves in the transpiration stream, and ac-
cumulates in the leaves. If the Cl- concentration in the
leaves exceeds the tolerance of the crop, injury symptoms
develop such as leaf burn or drying of leaf tissue. Nor-
mally, plant injury occurs first at the leaf tips (which is
common for chloride toxicity), and progresses from the
tip back along the edges as severity increases. Excessive
necrosis (dead tissue) is often accompanied by early leaf
drop or defoliation [33]. The obtained Cl- ion concentra-
tion of the samples varied from 171.44 to 254.92 mg/L
(mean value = 205.25) representing slight to moderate
degree of restriction on the use of this wastewater in irri-
gation [32]. While, according to USSL classification of
irrigation water, the effluent samples can be used for
moderately tolerant plants [30]. Chemical analysis of
plant tissue is commonly used to confirm chloride toxicity.
The part of the plant generally used for analysis varies
with the crop, depending upon which of the available
interpretative values is being followed. However, for ir-
rigated areas, the chloride uptake depends not only on the
water quality but also on the soil chloride, controlled by
the amount of leaching that has taken place and the ability
of the crop to exclude chloride. Crop tolerances to chloride
are not nearly so well documented as crop tolerances to
salinity [32]. On the other hand, significant correlation
was found between Na+ and Cl- of wastewater (R2 = 0.60),
suggesting that the common source of these ions is salt
dissolution. The possible sources of these ions were an-
thropogenic and natural.
3.6. Magnesium Hazard
Generally, Ca2+ and Mg2+ maintain a state of equilibrium
in most waters. Both Ca2+ and Mg2+ ions are associated
soil aggregation and friability, but they are also essential
plant nutrients. High concentration of Ca2+ and Mg2+ ions
in irrigation water can increase soil pH, resulting in re-
ducing of the availability of phosphorous [23]. Water con-
taining Ca2+ and Mg2+ higher than 10 meq/L (200 mg/L)
cannot be used in agriculture [50]. The observed results
show that 60% of the samples have exceeded 200 mg/L.
High correlation was found between Ca2+ and Mg2+ of
wastewater (R2 = 0.68), suggesting that the common
source of these ions is carbonate dissolution.
Another indicator that can be used to specify the mag-
nesium hazard (MH) is proposed by reference [51] for
irrigation water as in the following formula:
MH = 100
Ca Mg
where, Ca2+ and Mg2+ ions are expressed in meq/L.
If the value of MH is less than 50, then the water is safe
and suitable for irrigation [50]. From the calculated value
(Table 3), the MH values range between 7.97-56.53%,
(mean = 39.86) and the treated wastewater can be classi-
fied with few exception as suitable for irrigation use.
3.7. Residual Sodium Carbonate (RSC)
The excess sum of CO3
2- and HCO3
- in wastewater over
the sum of Ca2+ and Mg2+ influences the unsuitability of
wastewater for irrigation. In water having high concen-
tration of CO3
2- and HCO3
-, there is tendency for Ca2+
and Mg2+ to precipitate as carbonates. To qualify this
effect, an experimental parameter termed as RSC [29]
was used. It can be calculated as follows:
 
  (8)
All ion concentrations are reported in meq/l.
The water with high RSC has high pH and land irri-
gated by such waters becomes infertile owing to deposi-
tion of sodium carbonate as known from the black colour
of the soil [29]. According to the USSL [30], RSC value
less than 1.25 meq/L is safe for irrigation, a value be-
tween 1.25 and 2.5 meq/L is of permissible quality and a
value more than 2.5 meq/L is unsuitable for irrigation.
The calculated RSC value (–12.75) show that all samples
have RSC less than zero and are good suitable for irriga-
tion purposes.
3.8. Other Related Characteristics
The oxygen demand arises from the biochemical degra-
dation of organic materials, the oxidation of inorganic
material such as sulphides and ferrous and possibly the
oxidation of reduced from of nitrogen [28]. The BOD,
COD and TSS values in the present study varied from12
to 66 mg/L, 36 to 80 mg/L and 10 to 112 mg/L, respec-
tively. With few exceptions, the treated wastewater in
this study area displayed higher values of BOD, COD
and TSS. Calculated results highlight that the final efflu-
ent produced from Al-Rustamiyah WWTP did not meet
the Iraqi National Standards set by Regulation 25 of 1967.
Ultimately, reconsideration of the WWTPs system and
completed environmental impact assessment are needed.
4. Conclusions
Interpretation of physical and chemical analysis revealed
Evaluation of Treated Municipal Wastewater Quality for Irrigation
Copyright © 2010 SciRes. JEP
that the treated wastewater of Baghdad City is slightly
alkaline in nature. The US salinity diagram illustrates that
most of the treated wastewater samples fall in the field of
C3S1, indicating high salinity and low sodium water,
which can be used for irrigation on almost all types of
soil without danger of exchangeable sodium. Therefore,
the sustainable use of treated wastewater in agriculture
can be beneficial to the environment in such a way that
minimizes the side effects on the quality of downstream
water resources, but it requires the control of soil salinity
at the field level.
Based on these results that proper management of
wastewater irrigation and periodic monitoring of quality
parameters are required to ensure successful, safe and
long term reuse of wastewater for irrigation. It is recom-
mended as a matter of high priority that treated wastewa-
ter is considered and made a reliable alternative source in
water resources management. Agricultural wastewater
reuse can effectively contribute to fill the increasing gap
between water demand and water availability particularly
in semi-arid areas. In future, further work is needed to
examine organic and toxic constituents in wastewater and
more intensive sampling and studies to measure any
change of chemical elements in wastewater, irrigated soil
and plant.
5. Acknowledgements
Many thanks to Ministry of Higher Education and Scien-
tific Research, Research and Development Office, with-
out their financial support the work would have not been
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