Potential Risk of Calcium Carbonate Precipitation in Agricultural Drain Envelopes in Arid and Semi-Arid Areas

Agricultural Water Management 97 (2010) 1602–1608

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Agricultural Water Management

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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 b Irrigation and Reclamation Engineering Dept., University of Tehran, Karaj, Iran c Water Eng. Dept., Ahvaz University, Ahvaz, Iran d Soil Science Dept., University of Tehran, Karaj, Iran article info abstract

Article history: Soil particle deposition and/or chemical precipitation can reduce the permeability of drain envelopes and Received 19 September 2009 filters. The first step in recognizing clogging phenomena is the identification of the nature of the precip- Accepted 18 May 2010 itating materials. Calcium carbonate is a substance of low solubility that precipitates rapidly, forming a Available online 11 June 2010 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 Keywords: province of Iran. In this study, three indicators namely Ryznar, Langelier and Stiff-Davis indices were Drain envelope clogging employed to assess the precipitation risk of calcium carbonate in agricultural drainage water. Results Chemical precipitation Precipitation indices 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 to their anions, including carbonates, sulfates, chlorides, nitrates and borates (FAO/UNESCO, 1973). Salts of low solubility will pre- Clogging of subsurface drainage systems due to precipitation of cipitate and develop a hard pan or clog drain envelopes. The three different substances is responsible for the reduction of drainage most common salts in arid and semi-arid areas are calcium carbon- capacity and considered to be as a major problem in many coun- ate, calcium sulfate and magnesium carbonate with a solubility of tries, including Iran. This problem may develop due to soil particle 0.013, 1.9 and 2.5 g/l, respectively. Among these salts, magnesium invasion, and chemical and/or organic precipitation. Therefore, carbonate is less common, while the other two are more frequently clogging can be a physical, chemical, biochemical or biological observed. Calcium carbonate (CaCO3), which has the lowest solu- process. Chemical clogging occurs due to precipitation of salts, bility, comprises 80% of the total salt precipitation in arid areas. such as calcium carbonate, calcium sulfate, magnesium carbon- Due to its low solubility, calcium carbonate rapidly precipitates ate, calcium–magnesium carbonate and metals like iron (Vlotman in the soil and forms a hard pan layer (FAO/UNESCO, 1973). Pre- et al., 2001). The type of substances, having potential clogging cipitation of calcium carbonate has also been observed in many risk, varies in different areas depending on climate condition and subsurface drainage systems around the world. It has been respon- soil properties. Clogging by iron ochre formation is most com- sible for cementation and clogging of a gravel envelope around a mon in humid areas. However, alkaline soils are most common drain pipe under a road bed in Belgium. A similar process has been in arid and semi-arid areas and the groundwater has a low iron observed in France, where the groundwater contained a substan- content, thus, clogging is mostly the result of the precipitation tial amount of soluble calcium (Stuyt et al., 2005; Vlotman et al., of different salts (Stuyt et al., 2005). Salt precipitation normally 2001). happens due to changes in pH (more than 7.5), pressure, tem- Precipitation of calcium carbonate in soils depends on soil perature and/or evapotranspiration (Vlotman et al., 2001). Salts in water velocity, CO2 content produced by plant roots and bacteria, 2+ arid and semi-arid areas are classiﬁed into ﬁve groups in respect changes in CO2 partial pressure in the atmosphere and Ca concentration in the soil. Calcium carbonate has an inverse solubility which means its solubility decreases with increasing temperature ∗ Corresponding author. Tel.: +98 3814425541, fax: +98 381 4424428. (Lindsay, 1979; Sheikholeslami, 2005). In an aquatic environment, E-mail address: [email protected] (M. Ghobadi Nia). calcium carbonate equilibrium relations are (Tchobanoglous et al.,

2004; Sheikholeslami, 2005): Sheikholeslami, 2005) present C as a function of temperature and total dissolved salts (TDS). It can also be presented as a function (CO ) ⇔ (CO ) (1) 2 g 2 aq of the electrical conductivity (EC) which is commonly measured in

(CO2)aq + H2O ⇔ (H2CO3)aq (2) drainage studies. Eq. (9) is derived from the Debye–Huckel theory and known as the Guntelberg approximation. The activity coefﬁ- (H CO ) ⇔ (H+) + (HCO −) (3) 2 3 aq aq 3 aq cients can be calculated using the Debye–Huckel equation (Lindsay, − + 2− (HCO3 )aq ⇔ (H )aq + (CO3 )aq (4) 1979; Tchobanoglous et al., 2004):

2− 2+ 2 0.5 (CO3 )aq + (Ca )aq ⇔ (CaCO3)s↓ (5) 0.5(Zi) I log = (10) + I0.5 where the subscripts ‘g’, ‘aq’ and ‘s’ refer to gaseous environment 1 (atmosphere), aquatic environment and solid state, respectively. where is the activity coefficient, I is the ionic strength of the The equilibrium relation of calcium carbonate composition in solution, Zi is the charge of the ionic species. The Debye–Huckel’s an aquatic environment can be defined as: equation is valid for solution of ionic strength up to 0.2 mol/l 2+ − + (Lindsay, 1979). For higher ionic strength the right hand side of (Ca )aq + (HCO3 )aq ⇔ (H )aq + (CaCO3)s↓ (6) Eq. (10) is reduced with 0.3I. Griffin and Jurinak (1973) analyzed 27 If in an aquatic environment the bicarbonate concentration is samples of saturated soil extracts and 124 samples of river water more than 1 mmol/l, then calcium is more than 1–1.5 mmol/l and and obtained the following equation for the ionic strength (Lindsay, at pH > 7.5 precipitation of calcium carbonate will occur. The rate of 1979): calcium carbonate precipitation depends on the amount of bicarbonate and calcium ions (Rogers et al., 2003). I = 0.013EC (11) Iron precipitation and ochre formation is a common problem where EC is the electrical conductivity (dS/m) and I is ionic strength in temperate-humid areas. This phenomenon has extensively been (mol/l). investigated for several decades while, precipitation of low soluble The equilibrium constant (K ) and solubility product constant salts such as calcium carbonate and calcium sulfate in drain pipes a2 (K ) are functions of the temperature. Values of these coefficients and envelopes has not been fully studied (Stuyt et al., 2005). sp at different temperatures are given by Tchobanoglous et al. (2004). The main objective of the present investigation is to study the Different equations have been proposed to express the relationship potential precipitation risk of calcium carbonate in agricultural between temperature and equilibrium constant, and between tem- drainage systems of the Khuzestan province in South-west Iran. perature and solubility product constant, different equations have The paper includes an introduction on the calcium carbonate pre- been proposed. The best fitted relationship between temperature cipitation indices, the determination of potential precipitation risk and product solubility is the quadratic equation: in the area, and typical field measurements in order to validate the 2 −9 results. Ksp = (0.0024T − 0.2519T + 9.325)10 (12)

2. Materials and methods and between temperature and equilibrium constant the linear equation:

2.1. Calcium carbonate precipitation indices −13 −11 Ka2 = 9.21 × 10 T + 2.3 × 10 (13)

To determine the precipitation risk of calcium carbonate in where T is the temperature (◦C). water conveyance pipes, heating systems of industrial plants and Substituting Eqs. (10)–(13) in Eq. (9) gives: trickle irrigation systems, various indices have been proposed . based on the saturation concept of calcium carbonate. The most . T 2 − . T + . . 0 5 C = 0 0024 0 2519 9 325 + . (0 013EC) log − − 2 5 . common indices for the evaluation of the potential precipitation 9.21 × 10 4T + 2.3 × 10 2 1 + (0.013EC)0 5 risk of calcium carbonate are Ryznar Saturation Index (RSI), Lange- (14) lier 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. Langelier Saturation Index (LSI): The Langelier Saturation Index Ryznar Saturation Index (RSI): Ryznar (1944) presented this is one of the most common methods for predicting calcium carbon- index for determining the potential precipitation risk of calcium ate precipitation (Langelier, 1946). This index has also been derived carbonate. This index is based on the saturation concept of calcium from the theoretical saturation concept. Initially, this method was carbonate in water at a given pH and is given by: employed for predicting calcium carbonate precipitation in steam boilers. For the ﬁrst time Wilcox et al. (1954) used this index to pre- RSI = 2pHs − pH (7) dict the precipitation of calcium carbonate in soils. LSI is deﬁned as where pH is the measured pH of the water sample and pHs is the (Bresler et al., 1982; Langelier, 1946; Tchobanoglous et al., 2004): saturation pH for calcium carbonate which can be computed using the following expressions: LSI = pH − pHs (15)

2+ − pHs = p[Ca ] + p[HCO3 ] + C (8) Positive values of LSI and RSI less than 7 indicate the tendency of calcium carbonate to precipitate and its magnitude shows the C = pKa2 − pKsp − log 2+ − log − (9) Ca HCO3 severity of potential precipitation risk (Carrier Air Conditioning where pKa2 is the negative logarithm of the equilibrium constant Company, 1965; Tchobanoglous et al., 2004). The RSI estimates for the dissociation of bicarbonate, pKsp is the negative logarithm of a smaller precipitation risk than the LSI. Potential precipitation the solubility product constant for the dissociation of calcium car- risks of calcium carbonate according to LSI and RSI are shown in + bonate, Ca2 is the activity coefﬁcient of the calcium ion, HCO3 is Tables 1 and 2, respectively. the activity coefﬁcient of the bicarbonate ion, [Ca2+] is the calcium Stiff-Davis Saturation Index (S-DSI): Since Langelier Saturation − and [HCO3 ] is the bicarbonate ion concentration in mol/l. Other index is a better indicator for the potential precipitation risk of cal- research workers (Langelier, 1946; Tchobanoglous et al., 2004; cium carbonate in water with lower TDS values (TDS < 10,000 mg/l), 1604 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 No 0–0.5 Low 0.5–1 Moderate 1–2 High >2 Very high

Table 2 Potential precipitation risk according to the Ryznar Index (after Carrier Air Conditioning Company, 1965).

RSI Precipitation risk

>7 No 6–7 Low 5–6 Moderate 4–5 High <4 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:

2+ − pHs = p[Ca ] + 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 calcu- lating the saturation indices such as the needed anions and cations, EC, pH and the drainage water temperature were measured. The Fig. 1. Location of the investigated agricultural drains in the Khuzestan province. measured parameters are shown in Table 3. Subsequently, the Ryz- nar, Langelier, and Stiff-Davis indices were calculated using Eqs. (7), (15) and (16). To determine the type and amount of the possi-

Table 3 Chemical parameters and calculated calcium carbonate precipitation indices for the studied drainage waters.

◦ 2+ − 2+ − No. Drain location EC (dS/m) pH T ( C) Ca (mmol/l) HCO3 (mmol/l) p[Ca ] p[HCO3 ] C K LSI RSI S-DSI 1 Dehkhoda 19.21 8.1 31.4 8.59 2.59 2.07 2.59 2.51 2.75 0.94 6.22 0.70 2 Shoaibieh 7.02 7.7 22.9 9.03 3.72 2.04 2.43 2.62 2.50 0.61 6.48 0.73 3 Haft Tappeh 1.75 7.4 25.9 6.32 7.20 2.20 2.14 2.30 2.15 0.76 5.89 0.91 4 Kahang 1.65 7.8 26.2 3.28 4.13 2.48 2.38 2.29 2.13 0.65 6.51 0.81 5 Amir Kabir (Field 2-2) 11.60 7.7 25.0 16.00 7.00 1.80 2.15 2.68 2.55 1.06 5.59 1.20 6 Amir Kabir (Field 2-10) 13.60 7.8 24.5 19.00 5.00 1.72 2.30 2.74 2.59 1.03 5.73 1.19 7 Karun Industrial (M) 2.41 7.7 25.4 6.64 4.76 2.18 2.32 2.36 2.22 0.84 6.02 0.98 8 Jannat Makan 3.02 8.2 27.4 5.32 4.48 2.27 2.35 2.36 2.23 1.22 5.76 1.35 9 Gotvand 1.71 7.7 24.5 3.91 4.23 2.41 2.37 2.33 2.17 0.59 6.52 0.75 10 Aghili 1.25 7.6 25.2 2.56 4.47 2.59 2.35 2.27 2.10 0.39 6.83 0.56 11 Loureh 1.22 7.9 24.5 3.03 4.70 2.52 2.33 2.28 2.11 0.77 6.36 0.94 12 Ajirob–Salimeh 0.64 7.9 23.7 1.41 4.20 2.85 2.38 2.23 2.03 0.44 7.02 0.64 13 Saghari Drain 0.57 8.5 22.2 1.98 3.10 2.70 2.51 2.25 2.05 1.04 6.43 1.24 14 Haft Tappeh (Riahi) 0.67 7.6 23.0 2.02 5.01 2.69 2.30 2.25 2.05 0.36 6.89 0.55 15 Kamp neibari 1.04 7.7 23.6 3.19 5.58 2.50 2.25 2.28 2.10 0.67 6.37 0.85 16 Shadeghan Plain 9.15 7.9 25.0 19.00 4.00 1.72 2.40 2.63 2.50 1.20 5.56 1.33 17 Shordasht (Salt Plain) 31.00 7.9 31.2 16.55 1.58 1.78 2.80 2.53 2.92 0.78 6.33 0.40 18 Karun Industrial to Shatit Drain 2.49 7.9 25.0 6.80 4.54 2.17 2.34 2.37 2.24 1.02 5.87 1.15 19 Abadan Palms ﬁeld 15.09 7.96 20.0 9.00 10.40 2.05 1.98 2.72 2.90 1.21 5.54 1.03 M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608 1605

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, more appropriate for EC values less than 15 dS/m and the Stiff-Davis 6, 16 and 19 were selected as they show a higher precipitation risk. index for EC values beyond 15 dS/m. Considering this fact, the two In order to determine the characteristic salt content of the soils, mentioned indices were combined and presented in Fig. 2. Compar- two soil samples were taken from drain depth. ison of the results shows that, in general, the Ryznar index estimates Among these drains, drains at location 19, which is an exper- less severe calcium carbonate precipitation than the other two imental field with both granular and synthetic drain envelopes, indices for ECs less than 20 dS/m, while for higher EC values up to were studied in more detail. The drain pipes in this field were cov- 30 dS/m, the Ryznar index is the same as the Stiff-Davis index. How- ered with four different envelopes including two synthetic types ever, the Stiff-Davis index indicates a lower precipitation potential of Pre-wrapped Loose Materials (PLM) and two types of mineral for ECs greater than 30 dS/m. envelopes. The investigation was conducted for 3 years after the Based on the Ryznar index, the drainage water has a higher drainage system was installed. For the analysis of the precipitated potential precipitation risk of calcium carbonate if pH, bicarbon- substances, the synthetic envelopes were considered as it was pos- ate and calcium quantities are higher, while the Langelier index sible to remove the drain pipe along with its envelope. According mostly depends on the pH and at high pH, even if bicarbonate and to the types of synthetic envelopes, two drain pipes were selected. calcium amounts are low, it shows a higher estimation of precipi- From each drain pipe, two samples of drainage water were taken tation risk. In this context, the Ryznar index presents a more logical from the drain outlet, as well as from the installed piezometers estimation compared with the Langelier index. Thus, based on the near the location of excavation. Then, samples of the drain pipes results of the analysis of estimating the precipitation risk of calcium with their envelopes were taken by excavating a length of 50 cm. 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 Temperature is a time-dependent factor which affects the chem- Calculated values of Langelier and Stiff-Davis, and Ryznar ical reactions, including salt precipitation. The effect of temperature indices for drainage water samples are shown in Figs. 2 and 3, on precipitation risk of calcium carbonate was investigated and respectively. As can be seen from these figures, based on the defined Figs. 4 and 5 show the Langelier and Stiff-Davis, and the Ryznar precipitation standards for each index, there is precipitation risk indices, respectively, for temperature rises of 5, 10 and 15 ◦C. It of calcium carbonate in all drains. However, the severity of pre- can be seen that the precipitation risk increases with increasing cipitation differs for each drain and depends on the index used. temperature. For Langelier and Stiff-Davis indices, a temperature The Ryznar index estimated a lower precipitation potential com- increase of 15 ◦C does rise the number of drainage water locations pared with the other two indices for EC values less than 30 dS/m. with high calcium carbonate precipitation risk from 20% to 60%. As already mentioned, Langelier index is suitable for solutions of Fig. 6 shows the effect of increasing temperature on the Lange- lower TDS values. The results of this study confirm this. As the lier index. The figure clearly depicts that the slope of the curve results show, for EC values less than 15 dS/m, the Stiff-Davis index is decreases with increasing temperate. When the water temperature higher than the Langelier index, while the Langelier index is higher changes from 5 to 10 ◦C, the Langelier index change is 0.14, while for EC values greater than 15 dS/m. Thus, the Langelier index is 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. 1606 M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608

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.

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 enve- Fig. 6. Langelier saturation index (LSI) versus temperature. lope fibers. The results of the analysis are shown in Fig. 7 and fact indicates that calcium carbonate precipitation is more likely at Table 5. Based on the obtained results, the main components of temperature variation in the lower than in the higher temperature the precipitated materials in the envelope samples are silica, cal- ranges. Analysis of the Ryznar index shows the same trend. cium 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 3.3. Concentration of calcium carbonate in drainage envelopes silica. Therefore, calcium is considered as the main component of As the chemical analysis of the drainage water shows (Table 3), the investigated areas have high potential for calcium carbon- Table 5 Percentage of different elements in the precipitated material of the envelope fibers at drain location 19. Table 4 Percentage of calcium carbonate and calcium sulfate in soil samples taken at drain Element Sample no. depth. 12 3 Number of drain location Calcium carbonate (%) Calcium sulfate (%) Calcium 18.57 57.34 13.55 5 45.2 – Silica 15.96 3.04 18.79 6 45.3 – Oxygen 59.17 36.62 60.88 16 44.5 2.1 Magnesium 5.32 Negligible 6.78 19 37.25 – Others 0.98 3 0 M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608 1607

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 20.2 48.6 41.7 2 13.1 27.6 47.3 3 6.3 6.3 100 the precipitated material in the envelopes. As Table 6 shows, cal- • All drainage systems of that area are subjected to potential calcium carbonate precipitate in samples comprises more than 40% of cium carbonate precipitation risk. the total precipitation by weight. Results indicated that more cal- • The Ryznar index presented a better estimation of calcium car- cium carbonate precipitated where the amount of soil particles in bonate precipitation risk for EC < 20 dS/m, while for EC > 20 dS/m the envelope material was high, while less calcium carbonate was the Stiff-Davis index was more appropriate. However, further found where the envelope contained few or no soil particles. In the study is required to ﬁnd the proved link between the introduced absence of soil particles, calcium carbonate formed the total avail- indices, including their categories and the actual clogging hazard able precipitation. Therefore, presence of soil particles around the in drain plots. envelope increases the potential for calcium carbonate precipita- • Temperature changes have a considerable effect on precipitation. tion risk of calcium carbonate and should be considered in the decision-making on the construction of a drainage system. • 4. Conclusions Calcium carbonate is considered as a main chemical precipitation compound in the drainage envelopes of the investigated area. • The present research was carried out to assess the chemical clog- The amount of calcium carbonate precipitation in a drainage ging risk of agricultural drain envelopes in the Khuzestan province system is a function of the drained surface area: the larger the using three available indices including Ryznar, Langelier and Stiff- drained surface, the higher the precipitation may be. • Davis. Based on the research ﬁndings the following conclusions can Considering prevailing environmental factors in the investi- be drawn: gated area, there is a high potential risk for the precipitation 1608 M. Ghobadi Nia et al. / Agricultural Water Management 97 (2010) 1602–1608

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