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Potential risk of calcium carbonate precipitation in agricultural drain envelopes in arid and semi-arid areas
Agricultural Water Management 97 (2010) 1602–1608
Contents lists available at ScienceDirect
Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Potential risk of calcium carbonate precipitation in agricultural drain envelopes in arid and semi-arid areas M. Ghobadi Nia a,∗ , H. Rahimi b , T. Sohrabi b , A. Naseri c , H. Tofighi d a
Water Engineering Dept., Shahrekord University, Shahrekord, Iran Irrigation and Reclamation Engineering Dept., University of Tehran, Karaj, Iran Water Eng. Dept., Ahvaz University, Ahvaz, Iran d Soil Science Dept., University of Tehran, Karaj, Iran b c
a r t i c l e
i n f o
Article history: Received 19 September 2009 Accepted 18 May 2010 Available online 11 June 2010 Keywords: Drain envelope clogging Chemical precipitation Precipitation indices
a b s t r a c t Soil particle deposition and/or chemical precipitation can reduce the permeability of drain envelopes and filters. The first step in recognizing clogging phenomena is the identification of the nature of the precipitating materials. Calcium carbonate is a substance of low solubility that precipitates rapidly, forming a hard pan layer in the soil and/or clogging drain envelopes. The main objective of the present study is to investigate the precipitation risk of calcium carbonate in agricultural drain envelopes in the Khuzestan province of Iran. In this study, three indicators namely Ryznar, Langelier and Stiff-Davis indices were employed to assess the precipitation risk of calcium carbonate in agricultural drainage water. Results showed that all agricultural drainage systems in the study area give evidence of a potential risk of calcium carbonate precipitation, but the severity of the problem is different. The results also showed that the Ryznar and Stiff-Davis indices provide a better estimation of the potential precipitation risk of calcium carbonate than the Langelier index. Analyses of soil samples and drain envelopes from a drainage system, installed in the Abadan palm grove, showed that the main chemical component was calcium carbonate. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Clogging of subsurface drainage systems due to precipitation of different substances is responsible for the reduction of drainage capacity and considered to be as a major problem in many countries, including Iran. This problem may develop due to soil particle invasion, and chemical and/or organic precipitation. Therefore, clogging can be a physical, chemical, biochemical or biological process. Chemical clogging occurs due to precipitation of salts, such as calcium carbonate, calcium sulfate, magnesium carbonate, calcium–magnesium carbonate and metals like iron (Vlotman et al., 2001). The type of substances, having potential clogging risk, varies in different areas depending on climate condition and soil properties. Clogging by iron ochre formation is most common in humid areas. However, alkaline soils are most common in arid and semi-arid areas and the groundwater has a low iron content, thus, clogging is mostly the result of the precipitation of different salts (Stuyt et al., 2005). Salt precipitation normally happens due to changes in pH (more than 7.5), pressure, temperature and/or evapotranspiration (Vlotman et al., 2001). Salts in arid and semi-arid areas are classified into five groups in respect
∗ Corresponding author. Tel.: +98 3814425541, fax: +98 381 4424428. E-mail address: [email protected] (M. Ghobadi Nia). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.05.014
to their anions, including carbonates, sulfates, chlorides, nitrates and borates (FAO/UNESCO, 1973). Salts of low solubility will precipitate and develop a hard pan or clog drain envelopes. The three most common salts in arid and semi-arid areas are calcium carbonate, calcium sulfate and magnesium carbonate with a solubility of 0.013, 1.9 and 2.5 g/l, respectively. Among these salts, magnesium carbonate is less common, while the other two are more frequently observed. Calcium carbonate (CaCO3 ), which has the lowest solubility, comprises 80% of the total salt precipitation in arid areas. Due to its low solubility, calcium carbonate rapidly precipitates in the soil and forms a hard pan layer (FAO/UNESCO, 1973). Precipitation of calcium carbonate has also been observed in many subsurface drainage systems around the world. It has been responsible for cementation and clogging of a gravel envelope around a drain pipe under a road bed in Belgium. A similar process has been observed in France, where the groundwater contained a substantial amount of soluble calcium (Stuyt et al., 2005; Vlotman et al., 2001). Precipitation of calcium carbonate in soils depends on soil water velocity, CO2 content produced by plant roots and bacteria, changes in CO2 partial pressure in the atmosphere and Ca2+ concentration in the soil. Calcium carbonate has an inverse solubility which means its solubility decreases with increasing temperature (Lindsay, 1979; Sheikholeslami, 2005). In an aquatic environment, calcium carbonate equilibrium relations are (Tchobanoglous et al.,
M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608
2004; Sheikholeslami, 2005): (CO2 )g ⇔ (CO2 )aq
(1)
(CO2 )aq + H2 O ⇔ (H2 CO3 )aq
(2)
+
−
(3)
+
2−
(4)
(H2 CO3 )aq ⇔ (H )aq + (HCO3 )aq −
(HCO3 )aq ⇔ (H )aq + (CO3 (CO3
2−
)aq + (Ca
2+
)aq
)aq ⇔ (CaCO3 )s ↓
(5)
where the subscripts ‘g’, ‘aq’ and ‘s’ refer to gaseous environment (atmosphere), aquatic environment and solid state, respectively. The equilibrium relation of calcium carbonate composition in an aquatic environment can be defined as: (Ca2+ )aq + (HCO3 − )aq ⇔ (H+ )aq + (CaCO3 )s ↓
(6)
If in an aquatic environment the bicarbonate concentration is more than 1 mmol/l, then calcium is more than 1–1.5 mmol/l and at pH > 7.5 precipitation of calcium carbonate will occur. The rate of calcium carbonate precipitation depends on the amount of bicarbonate and calcium ions (Rogers et al., 2003). Iron precipitation and ochre formation is a common problem in temperate-humid areas. This phenomenon has extensively been investigated for several decades while, precipitation of low soluble salts such as calcium carbonate and calcium sulfate in drain pipes and envelopes has not been fully studied (Stuyt et al., 2005). The main objective of the present investigation is to study the potential precipitation risk of calcium carbonate in agricultural drainage systems of the Khuzestan province in South-west Iran. The paper includes an introduction on the calcium carbonate precipitation indices, the determination of potential precipitation risk in the area, and typical field measurements in order to validate the results.
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Sheikholeslami, 2005) present C as a function of temperature and total dissolved salts (TDS). It can also be presented as a function of the electrical conductivity (EC) which is commonly measured in drainage studies. Eq. (9) is derived from the Debye–Huckel theory and known as the Guntelberg approximation. The activity coefficients can be calculated using the Debye–Huckel equation (Lindsay, 1979; Tchobanoglous et al., 2004): log =
0.5(Zi )2 I 0.5 1 + I 0.5
(10)
where is the activity coefficient, I is the ionic strength of the solution, Zi is the charge of the ionic species. The Debye–Huckel’s equation is valid for solution of ionic strength up to 0.2 mol/l (Lindsay, 1979). For higher ionic strength the right hand side of Eq. (10) is reduced with 0.3I. Griffin and Jurinak (1973) analyzed 27 samples of saturated soil extracts and 124 samples of river water and obtained the following equation for the ionic strength (Lindsay, 1979): I = 0.013EC
(11)
where EC is the electrical conductivity (dS/m) and I is ionic strength (mol/l). The equilibrium constant (Ka2 ) and solubility product constant (Ksp ) are functions of the temperature. Values of these coefficients at different temperatures are given by Tchobanoglous et al. (2004). Different equations have been proposed to express the relationship between temperature and equilibrium constant, and between temperature and solubility product constant, different equations have been proposed. The best fitted relationship between temperature and product solubility is the quadratic equation: Ksp = (0.0024T 2 − 0.2519T + 9.325)10−9
(12)
2. Materials and methods
and between temperature and equilibrium constant the linear equation:
2.1. Calcium carbonate precipitation indices
Ka2 = 9.21 × 10−13 T + 2.3 × 10−11
To determine the precipitation risk of calcium carbonate in water conveyance pipes, heating systems of industrial plants and trickle irrigation systems, various indices have been proposed based on the saturation concept of calcium carbonate. The most common indices for the evaluation of the potential precipitation risk of calcium carbonate are Ryznar Saturation Index (RSI), Langelier Saturation Index (LSI) and Stiff-Davis Saturation Index (S-DSI). These indices can also be used to evaluate precipitation risks of calcium carbonate in agricultural drains and envelopes. Ryznar Saturation Index (RSI): Ryznar (1944) presented this index for determining the potential precipitation risk of calcium carbonate. This index is based on the saturation concept of calcium carbonate in water at a given pH and is given by:
where T is the temperature (◦ C). Substituting Eqs. (10)–(13) in Eq. (9) gives:
RSI = 2pHs − pH
(7)
where pH is the measured pH of the water sample and pHs is the saturation pH for calcium carbonate which can be computed using the following expressions: −
pHs = p[Ca2+ ] + p[HCO3 ] + C
(8)
C = pKa2 − pKsp − log Ca2+ − log HCO
3
−
(9)
where pKa2 is the negative logarithm of the equilibrium constant for the dissociation of bicarbonate, pKsp is the negative logarithm of the solubility product constant for the dissociation of calcium carbonate, Ca2+ is the activity coefficient of the calcium ion, HCO3 is the activity coefficient of the bicarbonate ion, [Ca2+ ] is the calcium and [HCO3 − ] is the bicarbonate ion concentration in mol/l. Other research workers (Langelier, 1946; Tchobanoglous et al., 2004;
C = log
0.0024T 2 − 0.2519T + 9.325 9.21 × 10−4 T + 2.3 × 10−2
(13)
+ 2.5
(0.013EC)0.5
1 + (0.013EC)0.5 (14)
Langelier Saturation Index (LSI): The Langelier Saturation Index is one of the most common methods for predicting calcium carbonate precipitation (Langelier, 1946). This index has also been derived from the theoretical saturation concept. Initially, this method was employed for predicting calcium carbonate precipitation in steam boilers. For the first time Wilcox et al. (1954) used this index to predict the precipitation of calcium carbonate in soils. LSI is defined as (Bresler et al., 1982; Langelier, 1946; Tchobanoglous et al., 2004): LSI = pH − pHs
(15)
Positive values of LSI and RSI less than 7 indicate the tendency of calcium carbonate to precipitate and its magnitude shows the severity of potential precipitation risk (Carrier Air Conditioning Company, 1965; Tchobanoglous et al., 2004). The RSI estimates a smaller precipitation risk than the LSI. Potential precipitation risks of calcium carbonate according to LSI and RSI are shown in Tables 1 and 2, respectively. Stiff-Davis Saturation Index (S-DSI): Since Langelier Saturation index is a better indicator for the potential precipitation risk of calcium carbonate in water with lower TDS values (TDS < 10,000 mg/l),
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M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608 Table 1 Potential precipitation risk according to the Langelier Index (after Carrier Air Conditioning Company, 1965). LSI
Precipitation risk
<0 0–0.5 0.5–1 1–2 >2
No Low Moderate High Very high
Table 2 Potential precipitation risk according to the Ryznar Index (after Carrier Air Conditioning Company, 1965). RSI
Precipitation risk
>7 6–7 5–6 4–5 <4
No Low Moderate High Very high
Stiff-Davis Saturation Index has been proposed for water with high TDS-concentration. This index is identical with LSI, S-DSI = pH − pHs
(16)
however, the solubility constant for predicting the saturated pH (pHs ) is modified experimentally (Stiff and Davis, 1952) and reads: pHs = p[Ca2+ ] + p[HCO3 − ] + K
(17)
where K is a function of the ionic strength and temperature, and obtained from the Stiff-Davis Chart (Stiff-Davis, 1952). Similar to the Langelier Index, the precipitation risk of calcium carbonate according to S-DSI can be obtained from Table 1. 2.2. Field measurements In order to determine the potential risk of calcium carbonate precipitation in agricultural drainage systems in Khuzestan, 19 drainage locations in various parts of the province were selected. Fig. 1 shows the locations of the selected drains. At the selected drain of each drainage location, the parameters required for calculating the saturation indices such as the needed anions and cations, EC, pH and the drainage water temperature were measured. The measured parameters are shown in Table 3. Subsequently, the Ryznar, Langelier, and Stiff-Davis indices were calculated using Eqs. (7), (15) and (16). To determine the type and amount of the possi-
Fig. 1. Location of the investigated agricultural drains in the Khuzestan province.
Table 3 Chemical parameters and calculated calcium carbonate precipitation indices for the studied drainage waters. No.
Drain location
EC (dS/m)
pH
T (◦ C)
Ca2+ (mmol/l)
HCO3 − (mmol/l)
p[Ca2+ ]
p[HCO3 − ]
C
K
LSI
RSI
S-DSI
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Dehkhoda Shoaibieh Haft Tappeh Kahang Amir Kabir (Field 2-2) Amir Kabir (Field 2-10) Karun Industrial (M) Jannat Makan Gotvand Aghili Loureh Ajirob–Salimeh Saghari Drain Haft Tappeh (Riahi) Kamp neibari Shadeghan Plain Shordasht (Salt Plain) Karun Industrial to Shatit Drain Abadan Palms field
19.21 7.02 1.75 1.65 11.60 13.60 2.41 3.02 1.71 1.25 1.22 0.64 0.57 0.67 1.04 9.15 31.00 2.49 15.09
8.1 7.7 7.4 7.8 7.7 7.8 7.7 8.2 7.7 7.6 7.9 7.9 8.5 7.6 7.7 7.9 7.9 7.9 7.96
31.4 22.9 25.9 26.2 25.0 24.5 25.4 27.4 24.5 25.2 24.5 23.7 22.2 23.0 23.6 25.0 31.2 25.0 20.0
8.59 9.03 6.32 3.28 16.00 19.00 6.64 5.32 3.91 2.56 3.03 1.41 1.98 2.02 3.19 19.00 16.55 6.80 9.00
2.59 3.72 7.20 4.13 7.00 5.00 4.76 4.48 4.23 4.47 4.70 4.20 3.10 5.01 5.58 4.00 1.58 4.54 10.40
2.07 2.04 2.20 2.48 1.80 1.72 2.18 2.27 2.41 2.59 2.52 2.85 2.70 2.69 2.50 1.72 1.78 2.17 2.05
2.59 2.43 2.14 2.38 2.15 2.30 2.32 2.35 2.37 2.35 2.33 2.38 2.51 2.30 2.25 2.40 2.80 2.34 1.98
2.51 2.62 2.30 2.29 2.68 2.74 2.36 2.36 2.33 2.27 2.28 2.23 2.25 2.25 2.28 2.63 2.53 2.37 2.72
2.75 2.50 2.15 2.13 2.55 2.59 2.22 2.23 2.17 2.10 2.11 2.03 2.05 2.05 2.10 2.50 2.92 2.24 2.90
0.94 0.61 0.76 0.65 1.06 1.03 0.84 1.22 0.59 0.39 0.77 0.44 1.04 0.36 0.67 1.20 0.78 1.02 1.21
6.22 6.48 5.89 6.51 5.59 5.73 6.02 5.76 6.52 6.83 6.36 7.02 6.43 6.89 6.37 5.56 6.33 5.87 5.54
0.70 0.73 0.91 0.81 1.20 1.19 0.98 1.35 0.75 0.56 0.94 0.64 1.24 0.55 0.85 1.33 0.40 1.15 1.03
M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608
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Fig. 2. Calculated Langelier saturation index (LSI) and Stiff-Davis saturation index (S-DSI) for the drainage water of the investigated drains.
ble precipitated substances in the drains, the drains at locations 5, 6, 16 and 19 were selected as they show a higher precipitation risk. In order to determine the characteristic salt content of the soils, two soil samples were taken from drain depth. Among these drains, drains at location 19, which is an experimental field with both granular and synthetic drain envelopes, were studied in more detail. The drain pipes in this field were covered with four different envelopes including two synthetic types of Pre-wrapped Loose Materials (PLM) and two types of mineral envelopes. The investigation was conducted for 3 years after the drainage system was installed. For the analysis of the precipitated substances, the synthetic envelopes were considered as it was possible to remove the drain pipe along with its envelope. According to the types of synthetic envelopes, two drain pipes were selected. From each drain pipe, two samples of drainage water were taken from the drain outlet, as well as from the installed piezometers near the location of excavation. Then, samples of the drain pipes with their envelopes were taken by excavating a length of 50 cm.
more appropriate for EC values less than 15 dS/m and the Stiff-Davis index for EC values beyond 15 dS/m. Considering this fact, the two mentioned indices were combined and presented in Fig. 2. Comparison of the results shows that, in general, the Ryznar index estimates less severe calcium carbonate precipitation than the other two indices for ECs less than 20 dS/m, while for higher EC values up to 30 dS/m, the Ryznar index is the same as the Stiff-Davis index. However, the Stiff-Davis index indicates a lower precipitation potential for ECs greater than 30 dS/m. Based on the Ryznar index, the drainage water has a higher potential precipitation risk of calcium carbonate if pH, bicarbonate and calcium quantities are higher, while the Langelier index mostly depends on the pH and at high pH, even if bicarbonate and calcium amounts are low, it shows a higher estimation of precipitation risk. In this context, the Ryznar index presents a more logical estimation compared with the Langelier index. Thus, based on the results of the analysis of estimating the precipitation risk of calcium carbonate the Ryznar index should be considered for ECs less than 20 dS/m and the Stiff-Davis index for ECs higher than 20 dS/m.
3. Results and discussion 3.2. Effect of temperature on calcium carbonate precipitation risk 3.1. Drainage water analysis Calculated values of Langelier and Stiff-Davis, and Ryznar indices for drainage water samples are shown in Figs. 2 and 3, respectively. As can be seen from these figures, based on the defined precipitation standards for each index, there is precipitation risk of calcium carbonate in all drains. However, the severity of precipitation differs for each drain and depends on the index used. The Ryznar index estimated a lower precipitation potential compared with the other two indices for EC values less than 30 dS/m. As already mentioned, Langelier index is suitable for solutions of lower TDS values. The results of this study confirm this. As the results show, for EC values less than 15 dS/m, the Stiff-Davis index is higher than the Langelier index, while the Langelier index is higher for EC values greater than 15 dS/m. Thus, the Langelier index is
Temperature is a time-dependent factor which affects the chemical reactions, including salt precipitation. The effect of temperature on precipitation risk of calcium carbonate was investigated and Figs. 4 and 5 show the Langelier and Stiff-Davis, and the Ryznar indices, respectively, for temperature rises of 5, 10 and 15 ◦ C. It can be seen that the precipitation risk increases with increasing temperature. For Langelier and Stiff-Davis indices, a temperature increase of 15 ◦ C does rise the number of drainage water locations with high calcium carbonate precipitation risk from 20% to 60%. Fig. 6 shows the effect of increasing temperature on the Langelier index. The figure clearly depicts that the slope of the curve decreases with increasing temperate. When the water temperature changes from 5 to 10 ◦ C, the Langelier index change is 0.14, while for a temperature rise from 55 to 60 ◦ C, its change is only 0.01. This
Fig. 3. Calculated Ryznar saturation index (RSI) for the drainage water of the investigated drains.
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Fig. 4. Variation of Langelier saturation index (LSI) and Stiff-Davis saturation index (S-DSI) at temperature rises of 5, 10 and 15 ◦ C.
Fig. 5. Variation of Ryznar saturation index (RSI) at temperature rises of 5, 10 and 15 ◦ C.
Fig. 6. Langelier saturation index (LSI) versus temperature.
fact indicates that calcium carbonate precipitation is more likely at temperature variation in the lower than in the higher temperature ranges. Analysis of the Ryznar index shows the same trend. 3.3. Concentration of calcium carbonate in drainage envelopes As the chemical analysis of the drainage water shows (Table 3), the investigated areas have high potential for calcium carbonTable 4 Percentage of calcium carbonate and calcium sulfate in soil samples taken at drain depth. Number of drain location
Calcium carbonate (%)
Calcium sulfate (%)
5 6 16 19
45.2 45.3 44.5 37.25
– – 2.1 –
ate precipitation. Table 4 shows the measured amount of calcium carbonate and calcium sulfate in the soil samples taken from drain depth for four drainage systems. The results showed that a high percentage of calcium carbonate was precipitated at drain depth. In order to determine the rate and distribution of calcium carbonate precipitation in the drainage envelopes of the drain at field 19, some samples were taken from different envelope sections (on and between drainage pipe holes). Analysis of these samples showed that precipitation of calcium carbonate is present over the whole depth of the envelope layer. The rate of calcium carbonate accumulation was nearly the same for all samples and it was not possible to determine a specified area with higher or lower calcium carbonate precipitation. Electronic microscope analysis was carried out to determine the type of precipitation compound around and between the envelope fibers. The results of the analysis are shown in Fig. 7 and Table 5. Based on the obtained results, the main components of the precipitated materials in the envelope samples are silica, calcium and oxygen. This means that the precipitated materials are either soil particles or calcium carbonate. Qualitative analysis indicated that the amount of calcium is the same or higher than the silica. Therefore, calcium is considered as the main component of
Table 5 Percentage of different elements in the precipitated material of the envelope fibers at drain location 19. Element
Calcium Silica Oxygen Magnesium Others
Sample no. 1
2
3
18.57 15.96 59.17 5.32 0.98
57.34 3.04 36.62 Negligible 3
13.55 18.79 60.88 6.78 0
M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608
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Fig. 7. Electronic microscope images of synthetic fibers surrounded by calcium carbonate precipitation. Table 6 Magnitude of precipitated calcium carbonate in synthetic envelopes at drain location 19. Sample no.
Calcium carbonate precipitation (% by weight)
Total precipitation (% by weight)
Ratio of calcium carbonate by weight to total precipitation by weight (%)
1 2 3
20.2 13.1 6.3
48.6 27.6 6.3
41.7 47.3 100
the precipitated material in the envelopes. As Table 6 shows, calcium carbonate precipitate in samples comprises more than 40% of the total precipitation by weight. Results indicated that more calcium carbonate precipitated where the amount of soil particles in the envelope material was high, while less calcium carbonate was found where the envelope contained few or no soil particles. In the absence of soil particles, calcium carbonate formed the total available precipitation. Therefore, presence of soil particles around the envelope increases the potential for calcium carbonate precipitation. 4. Conclusions The present research was carried out to assess the chemical clogging risk of agricultural drain envelopes in the Khuzestan province using three available indices including Ryznar, Langelier and StiffDavis. Based on the research findings the following conclusions can be drawn:
• All drainage systems of that area are subjected to potential calcium carbonate precipitation risk. • The Ryznar index presented a better estimation of calcium carbonate precipitation risk for EC < 20 dS/m, while for EC > 20 dS/m the Stiff-Davis index was more appropriate. However, further study is required to find the proved link between the introduced indices, including their categories and the actual clogging hazard in drain plots. • Temperature changes have a considerable effect on precipitation risk of calcium carbonate and should be considered in the decision-making on the construction of a drainage system. • Calcium carbonate is considered as a main chemical precipitation compound in the drainage envelopes of the investigated area. • The amount of calcium carbonate precipitation in a drainage system is a function of the drained surface area: the larger the drained surface, the higher the precipitation may be. • Considering prevailing environmental factors in the investigated area, there is a high potential risk for the precipitation
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of calcium carbonate and, consequently, for clogging of drainage envelopes. Acknowledgments This research was fully financially supported by the University of Tehran and The Ministry of Energy. The authors wish to express their deep gratitude for this support. References Bresler, E., Mcneal, B.L., Carter, D.L., 1982. Saline and Sodic Soil (Principles-DynamicsModeling). Springer-Velarg, Berlin, 236 pp. Carrier Air Conditioning Company, 1965. Handbook of Air Conditioning System Design. McGraw-Hill, Mei Ya Publication Co, 750 pp. FAO/UNESCO, 1973. Irrigation, Drainage and Salinity—An International Source Book. Hutchinson and Co LTD, London, 510 pp. Griffin, R.A., Jurinak, J.J., 1973. Estimation of activity coefficients from the electrical conductivity of natural aquatic systems and soil extracts. J. Soil Sci. 116, 26–30.
Langelier, W., 1946. Chemical equilibria in water treatment. J. Am. Water Work Assoc. 38 (2), 169–178. Lindsay, W.L., 1979. Chemical Equilibria in Soils. Wiley–Interscience, New York, 448 pp. Rogers, D.H., Lamm, F.R., Alam, M., 2003. Subsurface drip irrigation systems (SDI) water quality assessment guidelines. Rep. MF2575. Kansas State University, Kansas. Ryznar, J.W., 1944. A new index for determining amount of calcium carbonate scale formed by water. J. Am. Water Work Assoc. 36, 472–486. Sheikholeslami, R., 2005. Scaling potential index (SPI) for CaCO3 based on Gibbs free energies. AIChE 51 (6), 1782–1789. Stiff, J.H.A., Davis, L.E., 1952. A method for predicting the tendency of oil field water to deposit calcium carbonate. Pet Trans. AIME 195, 213–216. Stuyt, L.C.P.M., Dierickx, W., Beltrán, J.M., 2005. Materials for Subsurface Land Drainage Systems. FAO Irrigation and Drainage Paper 60 Rev. 1. Rome, 183 pp. Tchobanoglous, G., Burton, F.L., Stensel, H.D., Inc Metcalf & Eddy, 2004. Wastewater Engineering: Treatment and Reuse, 4th ed. McGraw-Hill, New York, 1820 pp. Vlotman, W.F., Willardson, L.S., Dierickx, W., 2001. Envelope Design for Subsurface Drains. International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands (Publication 56). Wilcox, L.V., Blair, G.Y., Bower, C.A., 1954. Effect of bicarbonate on suitability of water for irrigation. Soil Sci. 77, 259–266.
Contents lists available at ScienceDirect
Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Potential risk of calcium carbonate precipitation in agricultural drain envelopes in arid and semi-arid areas M. Ghobadi Nia a,∗ , H. Rahimi b , T. Sohrabi b , A. Naseri c , H. Tofighi d a
Water Engineering Dept., Shahrekord University, Shahrekord, Iran Irrigation and Reclamation Engineering Dept., University of Tehran, Karaj, Iran Water Eng. Dept., Ahvaz University, Ahvaz, Iran d Soil Science Dept., University of Tehran, Karaj, Iran b c
a r t i c l e
i n f o
Article history: Received 19 September 2009 Accepted 18 May 2010 Available online 11 June 2010 Keywords: Drain envelope clogging Chemical precipitation Precipitation indices
a b s t r a c t Soil particle deposition and/or chemical precipitation can reduce the permeability of drain envelopes and filters. The first step in recognizing clogging phenomena is the identification of the nature of the precipitating materials. Calcium carbonate is a substance of low solubility that precipitates rapidly, forming a hard pan layer in the soil and/or clogging drain envelopes. The main objective of the present study is to investigate the precipitation risk of calcium carbonate in agricultural drain envelopes in the Khuzestan province of Iran. In this study, three indicators namely Ryznar, Langelier and Stiff-Davis indices were employed to assess the precipitation risk of calcium carbonate in agricultural drainage water. Results showed that all agricultural drainage systems in the study area give evidence of a potential risk of calcium carbonate precipitation, but the severity of the problem is different. The results also showed that the Ryznar and Stiff-Davis indices provide a better estimation of the potential precipitation risk of calcium carbonate than the Langelier index. Analyses of soil samples and drain envelopes from a drainage system, installed in the Abadan palm grove, showed that the main chemical component was calcium carbonate. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Clogging of subsurface drainage systems due to precipitation of different substances is responsible for the reduction of drainage capacity and considered to be as a major problem in many countries, including Iran. This problem may develop due to soil particle invasion, and chemical and/or organic precipitation. Therefore, clogging can be a physical, chemical, biochemical or biological process. Chemical clogging occurs due to precipitation of salts, such as calcium carbonate, calcium sulfate, magnesium carbonate, calcium–magnesium carbonate and metals like iron (Vlotman et al., 2001). The type of substances, having potential clogging risk, varies in different areas depending on climate condition and soil properties. Clogging by iron ochre formation is most common in humid areas. However, alkaline soils are most common in arid and semi-arid areas and the groundwater has a low iron content, thus, clogging is mostly the result of the precipitation of different salts (Stuyt et al., 2005). Salt precipitation normally happens due to changes in pH (more than 7.5), pressure, temperature and/or evapotranspiration (Vlotman et al., 2001). Salts in arid and semi-arid areas are classified into five groups in respect
∗ Corresponding author. Tel.: +98 3814425541, fax: +98 381 4424428. E-mail address: [email protected] (M. Ghobadi Nia). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.05.014
to their anions, including carbonates, sulfates, chlorides, nitrates and borates (FAO/UNESCO, 1973). Salts of low solubility will precipitate and develop a hard pan or clog drain envelopes. The three most common salts in arid and semi-arid areas are calcium carbonate, calcium sulfate and magnesium carbonate with a solubility of 0.013, 1.9 and 2.5 g/l, respectively. Among these salts, magnesium carbonate is less common, while the other two are more frequently observed. Calcium carbonate (CaCO3 ), which has the lowest solubility, comprises 80% of the total salt precipitation in arid areas. Due to its low solubility, calcium carbonate rapidly precipitates in the soil and forms a hard pan layer (FAO/UNESCO, 1973). Precipitation of calcium carbonate has also been observed in many subsurface drainage systems around the world. It has been responsible for cementation and clogging of a gravel envelope around a drain pipe under a road bed in Belgium. A similar process has been observed in France, where the groundwater contained a substantial amount of soluble calcium (Stuyt et al., 2005; Vlotman et al., 2001). Precipitation of calcium carbonate in soils depends on soil water velocity, CO2 content produced by plant roots and bacteria, changes in CO2 partial pressure in the atmosphere and Ca2+ concentration in the soil. Calcium carbonate has an inverse solubility which means its solubility decreases with increasing temperature (Lindsay, 1979; Sheikholeslami, 2005). In an aquatic environment, calcium carbonate equilibrium relations are (Tchobanoglous et al.,
M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608
2004; Sheikholeslami, 2005): (CO2 )g ⇔ (CO2 )aq
(1)
(CO2 )aq + H2 O ⇔ (H2 CO3 )aq
(2)
+
−
(3)
+
2−
(4)
(H2 CO3 )aq ⇔ (H )aq + (HCO3 )aq −
(HCO3 )aq ⇔ (H )aq + (CO3 (CO3
2−
)aq + (Ca
2+
)aq
)aq ⇔ (CaCO3 )s ↓
(5)
where the subscripts ‘g’, ‘aq’ and ‘s’ refer to gaseous environment (atmosphere), aquatic environment and solid state, respectively. The equilibrium relation of calcium carbonate composition in an aquatic environment can be defined as: (Ca2+ )aq + (HCO3 − )aq ⇔ (H+ )aq + (CaCO3 )s ↓
(6)
If in an aquatic environment the bicarbonate concentration is more than 1 mmol/l, then calcium is more than 1–1.5 mmol/l and at pH > 7.5 precipitation of calcium carbonate will occur. The rate of calcium carbonate precipitation depends on the amount of bicarbonate and calcium ions (Rogers et al., 2003). Iron precipitation and ochre formation is a common problem in temperate-humid areas. This phenomenon has extensively been investigated for several decades while, precipitation of low soluble salts such as calcium carbonate and calcium sulfate in drain pipes and envelopes has not been fully studied (Stuyt et al., 2005). The main objective of the present investigation is to study the potential precipitation risk of calcium carbonate in agricultural drainage systems of the Khuzestan province in South-west Iran. The paper includes an introduction on the calcium carbonate precipitation indices, the determination of potential precipitation risk in the area, and typical field measurements in order to validate the results.
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Sheikholeslami, 2005) present C as a function of temperature and total dissolved salts (TDS). It can also be presented as a function of the electrical conductivity (EC) which is commonly measured in drainage studies. Eq. (9) is derived from the Debye–Huckel theory and known as the Guntelberg approximation. The activity coefficients can be calculated using the Debye–Huckel equation (Lindsay, 1979; Tchobanoglous et al., 2004): log =
0.5(Zi )2 I 0.5 1 + I 0.5
(10)
where is the activity coefficient, I is the ionic strength of the solution, Zi is the charge of the ionic species. The Debye–Huckel’s equation is valid for solution of ionic strength up to 0.2 mol/l (Lindsay, 1979). For higher ionic strength the right hand side of Eq. (10) is reduced with 0.3I. Griffin and Jurinak (1973) analyzed 27 samples of saturated soil extracts and 124 samples of river water and obtained the following equation for the ionic strength (Lindsay, 1979): I = 0.013EC
(11)
where EC is the electrical conductivity (dS/m) and I is ionic strength (mol/l). The equilibrium constant (Ka2 ) and solubility product constant (Ksp ) are functions of the temperature. Values of these coefficients at different temperatures are given by Tchobanoglous et al. (2004). Different equations have been proposed to express the relationship between temperature and equilibrium constant, and between temperature and solubility product constant, different equations have been proposed. The best fitted relationship between temperature and product solubility is the quadratic equation: Ksp = (0.0024T 2 − 0.2519T + 9.325)10−9
(12)
2. Materials and methods
and between temperature and equilibrium constant the linear equation:
2.1. Calcium carbonate precipitation indices
Ka2 = 9.21 × 10−13 T + 2.3 × 10−11
To determine the precipitation risk of calcium carbonate in water conveyance pipes, heating systems of industrial plants and trickle irrigation systems, various indices have been proposed based on the saturation concept of calcium carbonate. The most common indices for the evaluation of the potential precipitation risk of calcium carbonate are Ryznar Saturation Index (RSI), Langelier Saturation Index (LSI) and Stiff-Davis Saturation Index (S-DSI). These indices can also be used to evaluate precipitation risks of calcium carbonate in agricultural drains and envelopes. Ryznar Saturation Index (RSI): Ryznar (1944) presented this index for determining the potential precipitation risk of calcium carbonate. This index is based on the saturation concept of calcium carbonate in water at a given pH and is given by:
where T is the temperature (◦ C). Substituting Eqs. (10)–(13) in Eq. (9) gives:
RSI = 2pHs − pH
(7)
where pH is the measured pH of the water sample and pHs is the saturation pH for calcium carbonate which can be computed using the following expressions: −
pHs = p[Ca2+ ] + p[HCO3 ] + C
(8)
C = pKa2 − pKsp − log Ca2+ − log HCO
3
−
(9)
where pKa2 is the negative logarithm of the equilibrium constant for the dissociation of bicarbonate, pKsp is the negative logarithm of the solubility product constant for the dissociation of calcium carbonate, Ca2+ is the activity coefficient of the calcium ion, HCO3 is the activity coefficient of the bicarbonate ion, [Ca2+ ] is the calcium and [HCO3 − ] is the bicarbonate ion concentration in mol/l. Other research workers (Langelier, 1946; Tchobanoglous et al., 2004;
C = log
0.0024T 2 − 0.2519T + 9.325 9.21 × 10−4 T + 2.3 × 10−2
(13)
+ 2.5
(0.013EC)0.5
1 + (0.013EC)0.5 (14)
Langelier Saturation Index (LSI): The Langelier Saturation Index is one of the most common methods for predicting calcium carbonate precipitation (Langelier, 1946). This index has also been derived from the theoretical saturation concept. Initially, this method was employed for predicting calcium carbonate precipitation in steam boilers. For the first time Wilcox et al. (1954) used this index to predict the precipitation of calcium carbonate in soils. LSI is defined as (Bresler et al., 1982; Langelier, 1946; Tchobanoglous et al., 2004): LSI = pH − pHs
(15)
Positive values of LSI and RSI less than 7 indicate the tendency of calcium carbonate to precipitate and its magnitude shows the severity of potential precipitation risk (Carrier Air Conditioning Company, 1965; Tchobanoglous et al., 2004). The RSI estimates a smaller precipitation risk than the LSI. Potential precipitation risks of calcium carbonate according to LSI and RSI are shown in Tables 1 and 2, respectively. Stiff-Davis Saturation Index (S-DSI): Since Langelier Saturation index is a better indicator for the potential precipitation risk of calcium carbonate in water with lower TDS values (TDS < 10,000 mg/l),
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M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608 Table 1 Potential precipitation risk according to the Langelier Index (after Carrier Air Conditioning Company, 1965). LSI
Precipitation risk
<0 0–0.5 0.5–1 1–2 >2
No Low Moderate High Very high
Table 2 Potential precipitation risk according to the Ryznar Index (after Carrier Air Conditioning Company, 1965). RSI
Precipitation risk
>7 6–7 5–6 4–5 <4
No Low Moderate High Very high
Stiff-Davis Saturation Index has been proposed for water with high TDS-concentration. This index is identical with LSI, S-DSI = pH − pHs
(16)
however, the solubility constant for predicting the saturated pH (pHs ) is modified experimentally (Stiff and Davis, 1952) and reads: pHs = p[Ca2+ ] + p[HCO3 − ] + K
(17)
where K is a function of the ionic strength and temperature, and obtained from the Stiff-Davis Chart (Stiff-Davis, 1952). Similar to the Langelier Index, the precipitation risk of calcium carbonate according to S-DSI can be obtained from Table 1. 2.2. Field measurements In order to determine the potential risk of calcium carbonate precipitation in agricultural drainage systems in Khuzestan, 19 drainage locations in various parts of the province were selected. Fig. 1 shows the locations of the selected drains. At the selected drain of each drainage location, the parameters required for calculating the saturation indices such as the needed anions and cations, EC, pH and the drainage water temperature were measured. The measured parameters are shown in Table 3. Subsequently, the Ryznar, Langelier, and Stiff-Davis indices were calculated using Eqs. (7), (15) and (16). To determine the type and amount of the possi-
Fig. 1. Location of the investigated agricultural drains in the Khuzestan province.
Table 3 Chemical parameters and calculated calcium carbonate precipitation indices for the studied drainage waters. No.
Drain location
EC (dS/m)
pH
T (◦ C)
Ca2+ (mmol/l)
HCO3 − (mmol/l)
p[Ca2+ ]
p[HCO3 − ]
C
K
LSI
RSI
S-DSI
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Dehkhoda Shoaibieh Haft Tappeh Kahang Amir Kabir (Field 2-2) Amir Kabir (Field 2-10) Karun Industrial (M) Jannat Makan Gotvand Aghili Loureh Ajirob–Salimeh Saghari Drain Haft Tappeh (Riahi) Kamp neibari Shadeghan Plain Shordasht (Salt Plain) Karun Industrial to Shatit Drain Abadan Palms field
19.21 7.02 1.75 1.65 11.60 13.60 2.41 3.02 1.71 1.25 1.22 0.64 0.57 0.67 1.04 9.15 31.00 2.49 15.09
8.1 7.7 7.4 7.8 7.7 7.8 7.7 8.2 7.7 7.6 7.9 7.9 8.5 7.6 7.7 7.9 7.9 7.9 7.96
31.4 22.9 25.9 26.2 25.0 24.5 25.4 27.4 24.5 25.2 24.5 23.7 22.2 23.0 23.6 25.0 31.2 25.0 20.0
8.59 9.03 6.32 3.28 16.00 19.00 6.64 5.32 3.91 2.56 3.03 1.41 1.98 2.02 3.19 19.00 16.55 6.80 9.00
2.59 3.72 7.20 4.13 7.00 5.00 4.76 4.48 4.23 4.47 4.70 4.20 3.10 5.01 5.58 4.00 1.58 4.54 10.40
2.07 2.04 2.20 2.48 1.80 1.72 2.18 2.27 2.41 2.59 2.52 2.85 2.70 2.69 2.50 1.72 1.78 2.17 2.05
2.59 2.43 2.14 2.38 2.15 2.30 2.32 2.35 2.37 2.35 2.33 2.38 2.51 2.30 2.25 2.40 2.80 2.34 1.98
2.51 2.62 2.30 2.29 2.68 2.74 2.36 2.36 2.33 2.27 2.28 2.23 2.25 2.25 2.28 2.63 2.53 2.37 2.72
2.75 2.50 2.15 2.13 2.55 2.59 2.22 2.23 2.17 2.10 2.11 2.03 2.05 2.05 2.10 2.50 2.92 2.24 2.90
0.94 0.61 0.76 0.65 1.06 1.03 0.84 1.22 0.59 0.39 0.77 0.44 1.04 0.36 0.67 1.20 0.78 1.02 1.21
6.22 6.48 5.89 6.51 5.59 5.73 6.02 5.76 6.52 6.83 6.36 7.02 6.43 6.89 6.37 5.56 6.33 5.87 5.54
0.70 0.73 0.91 0.81 1.20 1.19 0.98 1.35 0.75 0.56 0.94 0.64 1.24 0.55 0.85 1.33 0.40 1.15 1.03
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Fig. 2. Calculated Langelier saturation index (LSI) and Stiff-Davis saturation index (S-DSI) for the drainage water of the investigated drains.
ble precipitated substances in the drains, the drains at locations 5, 6, 16 and 19 were selected as they show a higher precipitation risk. In order to determine the characteristic salt content of the soils, two soil samples were taken from drain depth. Among these drains, drains at location 19, which is an experimental field with both granular and synthetic drain envelopes, were studied in more detail. The drain pipes in this field were covered with four different envelopes including two synthetic types of Pre-wrapped Loose Materials (PLM) and two types of mineral envelopes. The investigation was conducted for 3 years after the drainage system was installed. For the analysis of the precipitated substances, the synthetic envelopes were considered as it was possible to remove the drain pipe along with its envelope. According to the types of synthetic envelopes, two drain pipes were selected. From each drain pipe, two samples of drainage water were taken from the drain outlet, as well as from the installed piezometers near the location of excavation. Then, samples of the drain pipes with their envelopes were taken by excavating a length of 50 cm.
more appropriate for EC values less than 15 dS/m and the Stiff-Davis index for EC values beyond 15 dS/m. Considering this fact, the two mentioned indices were combined and presented in Fig. 2. Comparison of the results shows that, in general, the Ryznar index estimates less severe calcium carbonate precipitation than the other two indices for ECs less than 20 dS/m, while for higher EC values up to 30 dS/m, the Ryznar index is the same as the Stiff-Davis index. However, the Stiff-Davis index indicates a lower precipitation potential for ECs greater than 30 dS/m. Based on the Ryznar index, the drainage water has a higher potential precipitation risk of calcium carbonate if pH, bicarbonate and calcium quantities are higher, while the Langelier index mostly depends on the pH and at high pH, even if bicarbonate and calcium amounts are low, it shows a higher estimation of precipitation risk. In this context, the Ryznar index presents a more logical estimation compared with the Langelier index. Thus, based on the results of the analysis of estimating the precipitation risk of calcium carbonate the Ryznar index should be considered for ECs less than 20 dS/m and the Stiff-Davis index for ECs higher than 20 dS/m.
3. Results and discussion 3.2. Effect of temperature on calcium carbonate precipitation risk 3.1. Drainage water analysis Calculated values of Langelier and Stiff-Davis, and Ryznar indices for drainage water samples are shown in Figs. 2 and 3, respectively. As can be seen from these figures, based on the defined precipitation standards for each index, there is precipitation risk of calcium carbonate in all drains. However, the severity of precipitation differs for each drain and depends on the index used. The Ryznar index estimated a lower precipitation potential compared with the other two indices for EC values less than 30 dS/m. As already mentioned, Langelier index is suitable for solutions of lower TDS values. The results of this study confirm this. As the results show, for EC values less than 15 dS/m, the Stiff-Davis index is higher than the Langelier index, while the Langelier index is higher for EC values greater than 15 dS/m. Thus, the Langelier index is
Temperature is a time-dependent factor which affects the chemical reactions, including salt precipitation. The effect of temperature on precipitation risk of calcium carbonate was investigated and Figs. 4 and 5 show the Langelier and Stiff-Davis, and the Ryznar indices, respectively, for temperature rises of 5, 10 and 15 ◦ C. It can be seen that the precipitation risk increases with increasing temperature. For Langelier and Stiff-Davis indices, a temperature increase of 15 ◦ C does rise the number of drainage water locations with high calcium carbonate precipitation risk from 20% to 60%. Fig. 6 shows the effect of increasing temperature on the Langelier index. The figure clearly depicts that the slope of the curve decreases with increasing temperate. When the water temperature changes from 5 to 10 ◦ C, the Langelier index change is 0.14, while for a temperature rise from 55 to 60 ◦ C, its change is only 0.01. This
Fig. 3. Calculated Ryznar saturation index (RSI) for the drainage water of the investigated drains.
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Fig. 4. Variation of Langelier saturation index (LSI) and Stiff-Davis saturation index (S-DSI) at temperature rises of 5, 10 and 15 ◦ C.
Fig. 5. Variation of Ryznar saturation index (RSI) at temperature rises of 5, 10 and 15 ◦ C.
Fig. 6. Langelier saturation index (LSI) versus temperature.
fact indicates that calcium carbonate precipitation is more likely at temperature variation in the lower than in the higher temperature ranges. Analysis of the Ryznar index shows the same trend. 3.3. Concentration of calcium carbonate in drainage envelopes As the chemical analysis of the drainage water shows (Table 3), the investigated areas have high potential for calcium carbonTable 4 Percentage of calcium carbonate and calcium sulfate in soil samples taken at drain depth. Number of drain location
Calcium carbonate (%)
Calcium sulfate (%)
5 6 16 19
45.2 45.3 44.5 37.25
– – 2.1 –
ate precipitation. Table 4 shows the measured amount of calcium carbonate and calcium sulfate in the soil samples taken from drain depth for four drainage systems. The results showed that a high percentage of calcium carbonate was precipitated at drain depth. In order to determine the rate and distribution of calcium carbonate precipitation in the drainage envelopes of the drain at field 19, some samples were taken from different envelope sections (on and between drainage pipe holes). Analysis of these samples showed that precipitation of calcium carbonate is present over the whole depth of the envelope layer. The rate of calcium carbonate accumulation was nearly the same for all samples and it was not possible to determine a specified area with higher or lower calcium carbonate precipitation. Electronic microscope analysis was carried out to determine the type of precipitation compound around and between the envelope fibers. The results of the analysis are shown in Fig. 7 and Table 5. Based on the obtained results, the main components of the precipitated materials in the envelope samples are silica, calcium and oxygen. This means that the precipitated materials are either soil particles or calcium carbonate. Qualitative analysis indicated that the amount of calcium is the same or higher than the silica. Therefore, calcium is considered as the main component of
Table 5 Percentage of different elements in the precipitated material of the envelope fibers at drain location 19. Element
Calcium Silica Oxygen Magnesium Others
Sample no. 1
2
3
18.57 15.96 59.17 5.32 0.98
57.34 3.04 36.62 Negligible 3
13.55 18.79 60.88 6.78 0
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Fig. 7. Electronic microscope images of synthetic fibers surrounded by calcium carbonate precipitation. Table 6 Magnitude of precipitated calcium carbonate in synthetic envelopes at drain location 19. Sample no.
Calcium carbonate precipitation (% by weight)
Total precipitation (% by weight)
Ratio of calcium carbonate by weight to total precipitation by weight (%)
1 2 3
20.2 13.1 6.3
48.6 27.6 6.3
41.7 47.3 100
the precipitated material in the envelopes. As Table 6 shows, calcium carbonate precipitate in samples comprises more than 40% of the total precipitation by weight. Results indicated that more calcium carbonate precipitated where the amount of soil particles in the envelope material was high, while less calcium carbonate was found where the envelope contained few or no soil particles. In the absence of soil particles, calcium carbonate formed the total available precipitation. Therefore, presence of soil particles around the envelope increases the potential for calcium carbonate precipitation. 4. Conclusions The present research was carried out to assess the chemical clogging risk of agricultural drain envelopes in the Khuzestan province using three available indices including Ryznar, Langelier and StiffDavis. Based on the research findings the following conclusions can be drawn:
• All drainage systems of that area are subjected to potential calcium carbonate precipitation risk. • The Ryznar index presented a better estimation of calcium carbonate precipitation risk for EC < 20 dS/m, while for EC > 20 dS/m the Stiff-Davis index was more appropriate. However, further study is required to find the proved link between the introduced indices, including their categories and the actual clogging hazard in drain plots. • Temperature changes have a considerable effect on precipitation risk of calcium carbonate and should be considered in the decision-making on the construction of a drainage system. • Calcium carbonate is considered as a main chemical precipitation compound in the drainage envelopes of the investigated area. • The amount of calcium carbonate precipitation in a drainage system is a function of the drained surface area: the larger the drained surface, the higher the precipitation may be. • Considering prevailing environmental factors in the investigated area, there is a high potential risk for the precipitation
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of calcium carbonate and, consequently, for clogging of drainage envelopes. Acknowledgments This research was fully financially supported by the University of Tehran and The Ministry of Energy. The authors wish to express their deep gratitude for this support. References Bresler, E., Mcneal, B.L., Carter, D.L., 1982. Saline and Sodic Soil (Principles-DynamicsModeling). Springer-Velarg, Berlin, 236 pp. Carrier Air Conditioning Company, 1965. Handbook of Air Conditioning System Design. McGraw-Hill, Mei Ya Publication Co, 750 pp. FAO/UNESCO, 1973. Irrigation, Drainage and Salinity—An International Source Book. Hutchinson and Co LTD, London, 510 pp. Griffin, R.A., Jurinak, J.J., 1973. Estimation of activity coefficients from the electrical conductivity of natural aquatic systems and soil extracts. J. Soil Sci. 116, 26–30.
Langelier, W., 1946. Chemical equilibria in water treatment. J. Am. Water Work Assoc. 38 (2), 169–178. Lindsay, W.L., 1979. Chemical Equilibria in Soils. Wiley–Interscience, New York, 448 pp. Rogers, D.H., Lamm, F.R., Alam, M., 2003. Subsurface drip irrigation systems (SDI) water quality assessment guidelines. Rep. MF2575. Kansas State University, Kansas. Ryznar, J.W., 1944. A new index for determining amount of calcium carbonate scale formed by water. J. Am. Water Work Assoc. 36, 472–486. Sheikholeslami, R., 2005. Scaling potential index (SPI) for CaCO3 based on Gibbs free energies. AIChE 51 (6), 1782–1789. Stiff, J.H.A., Davis, L.E., 1952. A method for predicting the tendency of oil field water to deposit calcium carbonate. Pet Trans. AIME 195, 213–216. Stuyt, L.C.P.M., Dierickx, W., Beltrán, J.M., 2005. Materials for Subsurface Land Drainage Systems. FAO Irrigation and Drainage Paper 60 Rev. 1. Rome, 183 pp. Tchobanoglous, G., Burton, F.L., Stensel, H.D., Inc Metcalf & Eddy, 2004. Wastewater Engineering: Treatment and Reuse, 4th ed. McGraw-Hill, New York, 1820 pp. Vlotman, W.F., Willardson, L.S., Dierickx, W., 2001. Envelope Design for Subsurface Drains. International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands (Publication 56). Wilcox, L.V., Blair, G.Y., Bower, C.A., 1954. Effect of bicarbonate on suitability of water for irrigation. Soil Sci. 77, 259–266.