Saudi Arabia is an arid country facing the acute problem of an irrigation water shortage due to high evaporative conditions and non-renewable groundwater resources. The agriculture sector is the main consumer of groundwater in the kingdom. Groundwater, specifically the deep aquifer, in Saudi Arabia is considered to be a non-renewable resource (fossil water). The cost of pumping water from the deep aquifer is increasing every year and in some areas, the aquifer is dried out or its quality has significantly deteriorated. Farmers facing this dilemma are forced to search for an alternate solution to irrigate their farms. Wastewater reuse is considered to be an important source of water to the agricultural sector in arid countries all over the world.
The production of wastewater is increasing manifold due to urban and rural expansion, resulting from the increased population of the country. The use of treated wastewater and in some areas, untreated wastewater is a known practice in Saudi Arabia. Wastewater contains not only a high salt content, it is polluted with different types of organic, inorganic and biological pollutants.
The sources of these pollutants are mainly from household and industrial uses and other waste effluents, such as hospitals and laundries which use different reagents types for cleaning and healthcare management.
According to a report, the standards for effluent reuse are not addressed properly due to the unnecessary limitations imposed on the disposal and reuse of wastewater (Abu-Rizaiza, 1999). In Bahrain, drainage water has high salinity and sodium and chloride contents with ranges of 4.0-46.0 ppt, 645-1480 and 1400-2669 mg L-1, respectively. Elevated concentrations of bicarbonate, sulfate and calcium were also measured and ranged from 140-352, 1316-3617 and 512-990 mg L-1, respectively. Additionally, the quality of drainage water reflected the quality of groundwater due to exclusive use of groundwater for irrigation purposes (Raveendran and Madany, 1991a, b; Madany and Akhter, 1990). However, El-Din et al. (1993) reported that seepage of sewage from septic tanks and cesspools was responsible for the deterioration of both the chemical and biological quality of well water in Saudi Arabia (Hejazi, 1989). Many investigators have evaluated the water quality in different regions of Saudi Arabia, such as Al-Hassa Oasis spring and drainage water (Hussain and Sadiq, 1991; Al-Hawas, 2002), Wadi Al-Yamaniyah (Bazuhair and Alkaff, 1989); the Al-Qassim Region (Faruq et al., 1996); Saudi ground water chemistry (Mee, 1983) and the chemical composition of the ground waters of Saudi Arabia (WRD., 1985; El-Din et al., 1993). Jun et al. (2005) applied a hydrogeological characterization and isotope investigation to identify the source location and to trace a plume of groundwater contamination by nitrate. Natural and fertilized soils were identified as non-point sources of nitrate contamination in the study area, while septic and animal wastes were identified as small point sources.
On a long-term basis, sewage water irrigation has been reported to be a potential source of carbon accumulation and the major and micronutrients in the soil (Yadav et al., 2002). Previously, the concentration of nitrate (NO3) in the groundwater varied from 50-130 mg L-1 in the croplands that were irrigated with wastewater. However, in well water irrigated croplands, the NO3 concentrations were less than 35 mg L-1 (Tang et al., 2004; Bae and Lee, 2008). Similarly, research has highlighted the potential contamination of groundwater from on-site domestic wastewater systems in the Wadi Fatimah basin, Western Saudi Arabia (Alyamani, 2007) at the Loess Plateau in Dongzhi, China (Wang et al., 2007) and on the groundwater aquifer in arid regions of Southern Tunisia (Chamtouri et al., 2008).
Kalavrouziotis et al. (2008) compared the effect of Treated Municipal Wastewater (TMWW) with ordinary irrigation water to determine the reuse of waste effluent for vegetable irrigation. They reported the careful use of treated effluent for vegetable irrigation to avoid biological contamination for human consumption. In another study, Ghafari et al. (2008) reviewed many studies on the biological denitrification of nitrate-containing water resources, aquaculture wastewaters and industrial wastewater for the remediation of different concentrations of nitrate. However, Ayers and Westcot (1985) classified irrigation water into three groups based on the salinity, sodicity, toxicity and miscellaneous hazards. They also reported phytotoxic threshold levels of toxic trace elements in the water used for crop irrigation.
Alaboud (2009) investigated a pilot scale MBR plant located in AlKhomra, Jeddah, Saudi Arabia, on the wastewater from a residential area and adjoining workshops. Irrespective of the applied Mixed Liquor Suspended Solids (MLSS) concentrations (10, 15 and 20 g L-1), the MBR units had an excellent potential for the removal of organics, nutrients and pathogens. Selim (2008) highlighted the economic aspects of re-using secondarily treated wastewater in irrigation for the efficient utilization of the existing resources. Similarly, Massoudinejad et al. (2007) showed that water quality indicators of treated effluent from a Zamyard factory wastewater, such as the sodium adsorption ratio, sodium percentage, chloride content and electrical conductivity, were higher compared to the Food and Agriculture Organization (FAO) and Department of the Environment of Iran standards. Bouwer (2000) reported the increased use of sewage effluent for urban and agricultural irrigation. Tang et al. (2004) stated that in arid and semi-arid regions, wastewater as well as other low quality water resources, is an important source of water due to the shortage of irrigation water. Mahmood and Maqbool (2006) concluded that the application of untreated wastewater increased the levels of EC, TDS, SAR and RSC compared to the National Environmental Quality Standards (NEQS). Carr et al. (2004) stated that the use of wastewater in agriculture is occurring more frequently because of the water scarcity and population growth.
An extensive review of the literature indicated that there is an acute shortage of freshwater irrigation in Saudi Arabia due to the low annual mean rainfall, high arid climatic conditions and limited and non-renewable groundwater resource. Therefore, it is pertinent to explore alternative water sources to supplement the existing irrigation water resources for sustainable irrigated agriculture and to increase crop production for food self-sufficiency. The main objective of this study was to evaluate the drainage water quality that some farmers use for irrigation in Al-Ahsa, Eastern Province of Saudi Arabia and determine its reuse potential for irrigated agriculture expansion.
MATERIALS AND METHODS
The study was performed in Al-Ahsa Oasis, where high levels of free flowing wastewater are disposed through drainage canals (D-1 and D-2) in natural open lakes in the Al-Oyun and Al-Asfar areas, respectively.
Collection of water samples
Drainage water: A total of 25 drainage water samples were collected from the D-1 and D-2 main drainage canals. One liter drainage water samples were collected in sterile plastic bottles from selected sampling stations on the drainage channels. The water samples were stored in an icebox and then transported to an analytical laboratory for chemical analysis.
Microbiological analysis: Water samples were collected from both the D-1 and D-2 drainage canals for microbiological analysis to determine the contamination levels of fecal coliform and E. coli in the drainage water as well as their impact on the groundwater contamination from the seepage loss of drainage water collected from the canal beds or from the intrusion of wastewater from the main drainage canals that run across the Oasis to evaporation lakes.
Analytical study: All of the water samples were analyzed for different cations, anions, trace elements and heavy metals by following the standard procedures as described in APHA., AWWA. and WEF (1998). These include cations (Na, Ca, Mg and K), anions (CO3, HCO3, Cl, SO4, NO3 and PO4), trace elements (Sr, Al, Be, Co, F, Mn, Mo, Fe, Se and B) and heavy metals (As, Cd, Cr, Cu, Pb, Hg and Zn) that can create possible health hazards when consumed by plants.
The physical parameters, such as the pH, EC, temperature, Dissolved Oxygen (DO), Total Suspended Solids (TSS) and turbidity, were measured immediately at the time of sample collection.
|Table 1:|| Instruments used for water analysis
Additionally, 100 mL of each water sample was separately collected in a 100 mL capacity plastic bottle, acidified by adding approximately 1 mL of nitric acid and stored in an icebox for trace elements and heavy metal analysis.
In addition to the above water quality criteria, the SAR, adj.SAR and adj.RNa were determined according to USDA (1954), Ayers and Westcot (1985) and Suarez (1981), respectively; we also determined the predicted Exchangeable Sodium Percentage (ESP) of the soil from different SARs and the ion-interrelationship to evaluate the thermodynamic equilibrium occurring in soil solutions after irrigation. The drainage waters were classified according to the guidelines of Ayers and Westcot (1985) for agriculture use.
Data analysis: The data were statistically analyzed according to procedures of Snedecor and Cochran (1973) and SAS (2010).
Analytical procedures/methods: The drainage water samples were analyzed by following the standard analytical procedures for microbiological, physical and chemical analysis. The following instruments were used for the different analyses (Table 1).
RESULTS AND DISCUSSION
Main drain D-1:
The mean ranges of the different water quality parameters were 7.78-8.19 (pH), 6.88-8.85 (EC, dS m-1
), 1011-1358 (Na), 372-444 (Ca), 121-174 (Mg), 72-125 (K), 1618-2227 (Cl), 972-1321 (SO4
), 65-1321 (NO3
), 414-454 (HCO3
), 11.52-14.75 (SAR), 15.62-18.19 (adj.RNa
), 34.05-44.14 (adj.SAR) and 13.57-16.75 (ESP) at different locations in the D-1 main drain (Table 2
). The drainage water from the D-1 drainage canal has high to very high salinity. The values of the Exchangeable Sodium Percentage (ESP) indicate that approximately 5% of the samples of drainage waters fall into the Na hazardous category and could create soil physical and chemical deterioration by replacing the Ca from the soil exchange complex with a high concentration of Na in water. However, according to the USDA (1954)
, the drainage water belongs to the C4S4 category of very high salinity and very high sodium water.
The mean ranges of micro-elements (expressed as micrograms per liter) were 3.03-6.54 (Co), 1.41-1.59 (F), 21.73-49.44 (Mn), 117.59-215.04 (Fe), 635.19-702.6 (B), 1.33-2.85 (As), 8.81-25.31 (Cu), 195.55-807.83 (Zn), 4.60-27.75 (Pb), 0.13-5.61 (Cd) and 13.65-20.82 (Cr) at different locations along the main drain (Table 3).
Main drain D-2: The mean ranges of the different water quality parameters were 7.75-8.10 (pH), 2.25-6.92 (EC, dS m-1), 397-905 (Na), 162-352 (Ca), 64-153 (Mg), 29-88 (K), 606-1571 (Cl), 390-927 (SO4), 30-99 (NO3), 330-401 (HCO3), 6.76-10.54 (SAR), 8.61-13.41 (adj.RNa), 17.31-29.76 (adj.SAR) and 7.94-12.44 (ESP) at different locations in the D-2 main drain (Table 4).
|Table 2:|| Chemical analysis of the D-1 drain samples
|Table 3:|| Micro-element analysis of the D-1 drain samples
Based on the USDA irrigation water classification scheme, the drainage water falls in the category of C4S3 to C3S2 category with a very high salinity and high sodium water to high salinity and medium sodium water.
|Table 4:|| Chemical analysis of the D-2 drain samples
|Table 5:|| Micro-elements analysis of the D-2 drain samples
The mean ranges of micro-elements (expressed as micrograms per liter) were 3.32-6.46 (Co), 1.22-1.51 (F), 20.07-59.80 (Mn), 115.99-132.85 (Fe), 552-701 (B), 0.72-2.87 (As), 9.23-10.64 (Cu), 199-414 (Zn), 2.00-5.79 (Pb), 0.71-1.16 (Cd) and 11.55-13.46 (Cr) at different locations along the main drain D-2 (Table 5).
Cl vs. Na, Ca, Mg and K: The data in Fig. 1 illustrate the relationship between Cl and the major cations. The relationship between Cl and Na is very strong as shown by the high value of the coefficient of determination (R2 = 0.951) followed by a weak relationship between Cl vs. Ca (R2 = 0.423), Cl vs. Mg (R2 = 0.200) and Cl vs. K (R2 = 0.144) in the drainage water. This indicates that the order of major salts in the drainage water is NaCl>CaCl2>MgCl2>KCl due to the salt solubility constants. The solubility constants of Na salt are very high compared to all other cations.
SO4 vs. Na, Ca, Mg and K ions: A regression analysis was performed to determine the relationship between SO4 and other major cations (Na, Ca, Mg and K) in the drainage waters of the D-1 main drain (Fig. 2). The SO4 ion has a strong relationship with Ca (R2 = 0.513) and Mg (R2 = 0.608) compared to the Na (R2 = 0.230) and K (R2 = 0.006) ions. This indicates that the SO4 radical is strongly associated with Ca and Mg ions, making CaSO4 and MgSO4 salt ion pairs comparable to Na2SO4 and K2SO4 salts. In other words, D-1 drain drainage water is dominated by Ca and Mg salts, followed by Na and K sulfate salts. This may be due to the difference in the solubility constants of different salts in association with different major cations.
SO4 vs. Na, Ca, Mg and K ions: A regression analysis was performed to determine the relationship between SO4 and other major cations (Na, Ca, Mg and K) in the drainage waters of the D-1 main drain (Fig. 2).
|Fig. 1:|| Relationship between CI and major cations of drainage water
|Fig. 2:|| Relationship between SO4 and major cations of drainage water
The SO4 ion has a strong relationship with Ca (R2 = 0.513) and Mg (R2 = 0.608) compared to the Na (R2 = 0.230) and K (R2 = 0.006) ions. This indicates that the SO4 radical is strongly associated with Ca and Mg ions, making CaSO4 and MgSO4 salt ion pairs comparable to Na2SO4 and K2SO4 salts. In other words, D-1 drain drainage water is dominated by Ca and Mg salts, followed by Na and K sulfate salts. This may be due to the difference in the solubility constants of different salts in association with different major cations.
EC vs. Cl and SO4 ions: The data in Fig. 3 indicated a linear increase in the Cl content (R2 = 0.832) compared to the SO4 content (0.167) and there was an increase in the total salinity of the drainage water in the D-1 drain. This variation may be due to the addition of the Na dominant salt (NaCl) in the drainage waters as the seepage water is collected from adjacent, high salt affected lands with high NaCl salts compared to SO4 salts under the reclamation process. The data also indicate that most of the drainage water salinity is dominated by the Cl ion compared to the sulfate ion because of the difference in the solubility constant between the two anions (higher for the Cl ion than the SO4 radical).
|Fig. 3:|| Relationship between EC vs. CI and SO4 of drainage water
|Fig. 4:|| Relationship between EC and NO3 of drainage water
EC vs. NO3 contents: The regression analysis showed a very poor relationship between the total water salinity and NO3 content (R2 = 0.164) of drainage water (Fig. 4). Although the NO3 content of drainage water ranged between 60 and 110 mg L-1 which is considered to be high, the poor relationship indicated there was an insignificant relationship between the water salinity and NO3 content. The high NO3 concentration in the drainage water may be due to the seepage of nitrogen compounds from the adjacent fields that receive excessive nitrogen fertilizer to promote increased crop production.
HCO3 vs. Na, Ca, Mg and K ions: The data in Fig. 5 shows a fairly strong relationship between Ca and HCO3 (R2 = 0.648) but the relationship was very poor between HCO3 and Na (R2 = 0.351), HCO3 and Mg (R2 = 0.274) and HCO3 and K (R2 = 0.009) at different sampling stations in the D-1 drain. The study results showed that the HCO3 anion is strongly associated with Mg cation compared to Na, Ca and K cations.
|Fig. 5:|| Relationship between HCO3 vs. major cations of D-1 drainage water
|Fig. 6:|| Relationship between predicted ESP vs. different SARs of drainage water
Exchangeable Sodium Percentage (ESP) vs. SARs: The relationship between the predicted ESP and different sodium adsorption ratios of drainage water is very strong as indicated by the high value of R2 values which were 0.983 for ESP vs. SAR, 0.954 for ESP vs. adj.RNa and 0.998 for ESP vs. adj, SAR (Fig. 6). The data indicate that the values of the predicted ESP of the soil increased linearly with increasing SAR values of the drainage water. Overall, the ESP values were within acceptable limits, indicating that irrigation with these drainage waters will not pose any soil physical or chemical deterioration after irrigation.
EC vs. different SARs of drainage water: There is a good relationship between the EC and SARs of drainage water (Fig. 7). It is known that the SAR of water increases with the square root of the increasing total water salinity. The R2 value was 0.750 for EC vs. SAR, 0.605 for EC vs. adj.R Na and 0.727 for EC vs. adj.SAR in different locations.
Cl vs. Na, Ca, Mg and K in the D-2 drain: The Cl content of drainage water had a strong relationship with Na (R2 = 0.567), Ca (R2 = 0.993) and K (R2 = 0.619) ions but had a poor relationship with Mg (R2 = 0.282) ions (Fig. 8).
|Fig. 7:|| Relationship between EC vs. different SARs of drainage water
|Fig. 8:|| Relationship between Cl vs. major cations D-2 drain
This indicated that the drainage water in the D-2 drain was dominated by Na, Ca and K salts compared to Mg salt.
SO4 vs. Na, Ca, Mg and K ions: The regression analysis showed a strong SO4 anion with all of the major cations (Fig. 9). The order of the strength of the relationship followed the trend of Na vs. SO4 (R2 = 0.989)>K vs. SO4 (R2 = 0.949)>Mg vs. SO4 (R2 = 0.787)>Ca vs. SO4 (R2 = 0.572) at different locations along the main drain D-2. The drainage water in the D-2 drain was dominated by Na2SO4, K2SO4 and Mg SO4 salt ion pairs compared to the CaSO4 salt ion pair which may be due to the low solubility constant of CaSO4 salt compared to other highly soluble salts in the drainage water.
|Fig. 9:|| Relationship between SO4 vs. major cations D-2 drain
|Fig. 10:|| Relationship between HCO3 vs. major cations D-2 drain
HCO3 vs. major cations (Na, Ca, Mg and K): Data in Fig. 10 showed a strong relationship between HCO3 and Na (R2 = 0.860) and Ca (R2 = 0.728) and K (R2 = 0.862), except Mg which had a low R2 value of 0.498 in the drainage water. This weak relationship between HCO3 and Mg may be because Mg(HCO3)2 is unstable and quickly converted to the more stable CO3 form in the soil-water solution.
EC vs. different SARs of drainage waters:A very strong relationship was observed between the EC and different SAR values of drainage waters (Fig. 11).
|Fig. 11:|| Relationship between EC vs. different SARs of drainage waters
|Fig. 12:|| Relationship between ESP vs. SARs of D-2 drainage waters
The values of the coefficient of determination (R2) were 0.909, 0.922 and 0.932 for EC vs. adj.SAR, EC vs. adj. Rna and EC vs. SAR, respectively, at different locations of the drain. The SAR values linearly increased with the corresponding increase in the EC (total water salinity).
ESP vs. different SARs of drainage water: The regression analysis showed a poor relationship between the ESP and different SAR values of the drainage water (Fig. 12). The R2 values were 0.057, 0.034 and 0.051 for ESP vs. adj.SAR, ESP vs adj.RNa and SAR, respectively.
|Fig. 13:|| Piper diagram for the classification of D-1 drainage waters
The predicted value of ESP from different SARs was well below the hazardous limit of 15 which can cause deterioration of the soil physical and chemical properties, resulting in loss of land productivity.
Classification of the drainage water: It can be seen from the piper diagrams (Fig. 13 and 14) that drainage water from both the D-1 and D-2 main drains is Na-Cl-HCO3 water. The drainage water was dominated by the Na ion, followed by Ca, Mg and K in descending order as well as by different anions (Cl>HCO3>SO4). It is well known that the ion pairs formed in the drainage waters are NaCl>CaCl2>MgCl2>KCl due to the salt solubility constants.
Main drain D-1: The count of the total coliforms bacteria ranged between 7.0 and 118 for the total bacteria count (MPN colonies/100 mL water sample) and the E. coli ranged between 0.0 and 56.3 (MPN colonies/100 mL water sample) at various locations of the main drain D-1 (Table 6). The main source of bacterial contamination, especially of E. coli, in the drainage water seems to be the household sewage effluent containing human waste (main source of E. coli bacteria) that flows into these drains. D1 samples show that the E. coli that are present are those collected downstream, after the wastewater treatment plant (WWP).
Main drain D-2: The count of the total coliform bacteria ranged between 4.0 and 62.0 (MNP) for the total coliform bacteria and the E. coli ranged between 4.0 and 41.0 (MNP) at various locations of the main D-2 drain (Table 7). As stated earlier, the presence of E. coli indicates the disposal of household sewage effluent containing human waste (main source of E. coli).
|Fig. 14:|| Piper diagram for the classification of D-2 drainage waters
|Table 6:|| Total coliform and E. coli count in the main drain D-1
Overall, the level of E. coli was significantly high in the main D-2 drain compared to the main D-1 drain. This significant difference in E. coli may be due to the disposal of sewage effluent from the main city of Hofuf into the main D-2 drain containing mostly human waste, the main source of E. coli. In D2, all of the samples showed the presence of E. coli because of the supply of untreated wastewater from the WWP at the beginning of D1.
|Table 7:|| Total coliform and E. coli count in main drain D-2
The study results indicated that the drainage water of D-1 belongs to the C4S4 category of very high salinity and very high sodium water, while the drainage water of D-2 falls in the category of C4S3 to C3S2 category with a very high salinity and high sodium water to high salinity and medium sodium water. The relationship between Cl and Na was very strong followed by a weak relationship between Cl and other major cations (Ca, Mg and K in the drainage water. Most of the drainage water salinity is dominated by the Cl ion compared to the sulfate ion. The study results agree with the findings of many investigators who reported the effect of quality of groundwater for deteriorating the quality of drainage water due to excessive use of groundwater for irrigation (Raveendran and Madany, 1991a, b; Madany and Akhter, 1990). Also, El-Din et al. (1993) and Hejazi (1989) observed that seepage of waste effluent from septic tanks and cesspools was responsible for the deterioration of drainage water.
In this study, the NO3 content of drainage water ranged between 60 and 110 mg L-1 which is considered to be high according to the safe limits for irrigation purpose. Previously, many researchers found the concentration of nitrate (NO3) in the groundwater varied from 50-30 mg L-1 in the croplands irrigated with wastewater. On the other hand, the NO3 concentrations were less than 35 mg L-1 in well water irrigated croplands according to Tang et al. (2004) and Bae and Lee (2008). The drainage water in the D-2 drain was dominated by Na2SO4, K2SO4 and MgSO4 salt ion pairs compared to the CaSO4 salt ion pair. The drainage water from both the D-1 and D-2 main drains is Na-Cl-HCO3 water.
Overall, the level of E. coli was significantly high in the main D-2 drain compared to the main D-1 drain. The drainage water in D-1 is classified as C4S4 (very high salinity and very high sodium water), while D-2 drainage water is classified as C4S3 to C3S2 (very high salinity-high sodium water to high salinity-medium sodium water). The nitrate (NO3) concentration is above the recommended limit for irrigation use. The bacterial contamination is very high in the drainage water of both drains and not fit for irrigation. Similar results were reported by Ghafari et al. (2008) who studied aquaculture wastewaters and industrial wastewater containing high levels of nitrate for groundwater contamination.
The drainage water in D-1 is classified as C4S4 (very high salinity and very high sodium water), while D-2 drainage water is classified as C4S3 to C3S2 (very high salinity-high sodium water to high salinity-medium sodium water). The order of abundance of different salts with respect to Cl in the D-1 drainage water was NaCl >CaCl2>MgCl2>KCl; with respect to SO4 salt, it was MgSO4>CaSO4>Na2SO4>K2SO4 and for HCO3, t was Ca(HCO3)2>NaHCO3>Ca(HCO3)2>KHCO3. The drainage waters of both D-1 and D-2 drains are free of sodicity hazards because of the low SAR values. The Na salts dominate in most of the drainage water compared to other cations, such as Ca, Mg and K.
All of the trace elements in the drainage water of both of the drains are within the permissible limits for irrigation purposes. The nitrate (NO3) concentration is above the recommended limit for irrigation use. The bacterial contamination is very high in the drainage water of both drains and it was not fit for irrigation without proper treatment. The concentration of trace and heavy metal ions was within the permissible limits.
Based on the chemistry, the drainage water is not fit for irrigation due to the high total water salinity which could deteriorate the soil physico-chemical characteristics after irrigation. In conclusion, if drainage water is intended for reuse, certain precautionary measures, such as leaching requirements, selection of salt tolerant crop plants and advanced irrigation (drip irrigation), need to be considered to avoid the loss of land productivity.
This research was financially supported by King Abdulaziz City for Science and Technology under Project number 28-125.