I CONGRESO NACIONAL COMEII 2015 Reunión Anual de Riego y Drenaje

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1 Artículo: COMEII I CONGRESO NACIONAL COMEII 2015 Reunión Anual de Riego y Drenaje Jiutepec, Morelos, México, 23 y 24 de noviembre EVALUACIÓN EXPERIMENTAL DE UN SISTEMA NF-PV DESTINADO PARA APLICACIONES DE RIEGO AGRÍCOLA Ulises Dehesa Carrasco 1 ; José Javier Ramírez Luna 2 1 CONACYT Research Fellow, Instituto Mexicano de Tecnología del Agua, Paseo Cuauhnáhuac 8532, Col. Progreso, C.P , Jiutepec, Morelos, México. 2 Instituto Mexicano de Tecnología del Agua, Paseo Cuauhnáhuac 8532, Col. Progreso, C.P , Jiutepec, Morelos, México. Resumen La desalinización con energía solar representa una solución atractiva para aplicaciones de riego agrícola en zonas remotas, especialmente en cuencas endorreicas donde los compuestos presentes, tales cómo sulfatos, exceden los límites máximos permisibles para aplicaciones de riego. En éste trabajo se presenta un estudio experimental de un sistema de desalinización de Nano filtración (NF) con paneles fotovoltaicos (PV) que opera sin almacenamiento eléctrico. Con el fin de evaluar el rendimiento del sistema, diferentes concentraciones de S04 fueron analizados. El experimento se llevó a cabo a cielo abierto bajo diferentes condiciones de radiación solar. Con base en los resultados experimentales, la calidad del permeado obtenido satisfice los estándares de la Ley Federal de Derechos en Materia de Agua. Sin embargo, la concentración inicial y el ensuciamiento del sistema de pre-tratamiento juegan un papel importante en el rendimiento del sistema. Se observó una disminución de permeado de 7 lpm cuando la concentración inicial aumenta de 525 mg / l a 2,539 mg / l. Esta disminución representa cerca del 2 kwh / m 3 de consumo de energía. El consumo máximo de energía probado fue 3,4 kwh / m 3 con una concentración de 2,539 mg / l. Se observó una producción de permeado que oscila entre 2,16 a 4,08 m 3 / d, por lo que es posible irrigar entre 1 y 2 hectáreas de cultivos. Palabras clave: Desalinización solar, riego agrícola, aplicaciones de la NF.

2 ABSTRACT Desalination driven with solar energy represent an appealing solution for agricultural irrigation in remote areas. In this work, an experimental study of a NF-PV desalination system without electric storage is presented. In order to evaluate the performance of the system, different salt concentrations (mainly SO4-2 ) was tested. The experiment was conducted at open sky under varying solar radiation conditions. Based on experimental result, the quality of permeated obtained satisfice the standards of Mexican norm for irrigation. However, the initial concentration and fouling play an important role in the performance of the system. Was observed a decrement of permeated of 7 lpm going from 525 mg/l to 2539 mg/l. This decrement represent close of the 2 kwh/m 3 of energy consumption. The maximum energy consumption tested was 3,4 kwh/m 3 with a concentration of 2539 mg/l. Was observed a production of 2,16 4,8 m 3 /d, making it possible to irrigate between 1 and 2 hectares of crops. Keywords: Solar Desalination, agricultural irrigation, applications of NF. 1. Introduction The limited water resources are a real challenge for the actual status of agriculture in the world. The most important drivers for water scarcity are: growing water demands as the population increases, economic development, and the increase water per capita consumption [1]. Experts in the field agree that the production of food locally represents a strategic policy for undeveloped countries [2] In Latin America, in particular the north of Mexico, exist large tracts of land that are potentially productive for crops or pasture management. However, these lands are not exploited because the available groundwater has not the water-quality necessary for agriculture applications [3]. Mainly because the limit maximum permissible of some type of salt, so as, S04-2 are exceeded by 400% as previously was reported by [4]. Without other water sources, brackish groundwater is used directly to irrigate the crops. However, this practice reduces the performance of agricultural production and causes a negative impact on the soil surface by the salt deposition [2]. Desalination of brackish groundwater (BW) is an alternative that has been employed to increase the availability of water, and indirectly reduce the negative impact of contamination of the soil by salt. The quantity and water quality needed for irrigation is defined depending on the crop and soil characteristics [2]. The water for irrigation is classified based on established standards, the most important are: electrical conductivity (EC), total dissolved solids concentration (TDS), sodium risk (as function of the sodium absorption ratio (SAR)), the potential of hydrogen (ph) and the cations (Ca 2+, Mg 2+, Na +, K + ) and anions concentration (HCO3 2-, Cl -, SO4 2-, CO3 2-, and NO3). 2

3 Desalination for agriculture applications is often thought as an unprofitable process, mainly because this is an expensive method (e.i 40-45% of the total cost) [5]. However, in recent years this perception is changing [2],[6]-[7]. Some countries such as Spain, Israel and United Arab Emirates have increased the volume of desalination water for agriculture irrigation [8]. The reverse osmosis (RO) is the technology with major presence in market desalination for large or small applications [2],[8]. Nanofiltration (NF) has been used as one part of the solution for pre-treatment in RO desalination. The NF membrane is used to remove particles with diameters greater than 2 nm such as sulfates, which negatively affect the useful life of the RO membranes. The NF membrane do not prevent entirely the flow of salt through the membrane; monovalent compounds present in the mixture can cross. The presence of these compounds in permeate flow can be beneficial for the crops, because some of this compounds are required for the plant growth appropriately; provided that the maximum permissible limits, stabilized in standardized norm, are not exceed [5]. An NF system works with lower pressures than RO, in consequence the specific energy consumption is lower. This characteristics allow design and build less robust systems where solar energy with photovoltaic panels is very attractive especially for small-scale applications in remote areas [9]. The NF desalination process couplet with solar photovoltaic (NF-PV), has been reported previously in literature [11],[13]. IEA-ETSAP and IRENA, publication demonstrated the feasibility of NF-FV, for treating water in isolated places for human consumption [11]. The results showed that this systems can be used for small scale irrigation. Richards et al., reported a study of desalination by an hybrid membrane configuration (NF,UF and RO). The specific energy consumption ranged from 2 8 kwh per 1 m 3 of disinfected and desalinated drinking water. Ghermandi A. and Massalem R. studied the advantages of NF membranes instead of RO membrane in the production of irrigation water. Based on the simulation of the performance of a solar-assisted pilot plant, the energy consumption by the proposed system was 40% lower than conventional reverse osmosis desalination, reducing in 34% the currently abstracted groundwater volumes, and increasing in 18% the total biomass production of the irrigated crops [5]. Recently, Jasson et al.[4], carried out an experimental study about alternative treatment brackish water for irrigation using a NF-FV system. The study was focused in understanding the behavior of the system, keeping constant the amount of sulfate in the influent (1863 mg/l) which affect mainly the water quality. Authors report a production average of 3.2 m 3 / day with 6.3 solar peak hr, allowing cultivation in the region of study, up to 15 tons of tomatoes to a rate of 35 kg / m 3. Zarzo D. et al. published the Spanish experience in desalination for agriculture applications. The authors concluded that the desalinated water can be more expensive than water from other origins but this depends 3

4 on many factors. However, many agricultural products can support the price of desalinated water without a great impact on the overall price [2] [7]. Application of desalination with PV assisted as previously was described, commonly uses a batteries support system for the storage of the photovoltaic electric energy that is on its turn transformed in AC for powering the pumping system. However, the electricity supplied by PV system can be used directly to energize the pump of the NF system producing permeate only during the sunlight hours and storing the desalinated water instead of the electric energy. The aim of the present study is to evaluate the performance of the NF-PV desalination system as function of exogenous variable. The electricity supplied by PV system is used directly to energize the driven pump of the NF system, without battery support. The system was evaluated as function of energy consumption, recovery rate and quality of the effluent, considering the exogenous variables as irradiance and the salt concentration in the influent. The effect of pressure drop in the system by fouling in the pretreatment filters are discussed. 2. Materials and methods. a) NF-PV System In Fig. 1 the scheme of the experimental device is shown. The system is integrated by one micro filter used for pretreatment of the influent, a stage of Nanofiltration modules (NF), photovoltaic solar cell (PV) and pumping system. The NF stage is composed by four NF polyamide membranes (ESNA1-LF-4040 model) connected in parallel configuration, providing an equivalent area of 30.6 m 2. The prototype was designed to operate with a nominal capacity of permeate close to 12 l / min with a supply of brackish water of 60 l / min. The electric supply was provided by a photovoltaic plant with a nominal power of 1.92 kw integrated by eight polycrystalline silicon modules of 240 W each module which supplies power to a submersible centrifugal pump, model SQFlex 16 SQF-10. The coupling of the PV plant with the pump system was direct (without battery support) and controlled only with an on-off switch. 4

5 Fig. 1. Schematic diagram of the NF-PV system b) Methodology The experiment was carried out under laboratory conditions using a solution with high content of SO4-2 as influent. In order to evaluate the system performance, four different concentrations of the influent were tested. The nominal values of concentrations was 525 mg/l, 1170 mg/l, 1750 mg/l and 2539 mg/l respectively. In each test the concentration was kept constant while solar radiation was a free parameter whit a variation along the solar day in a range of w/m 2. The irradiation was measured over the plane of the PV solar cell with a Kipp & Zone pyranometer of first class with an uncertainty of ± 1.0%. In order to calculate the power supplied by PV plant the voltage and electrical current was directly measured with a 34972A Data Acquisition. The volumetric flow was measured using an AQF flow meter with resolution of 0.25 l / min and the pressure through Ashcroft G2 pressure transducers were installed on the input and output ports of the system. The evaluation of the system consisted in determine the removing effectiveness of SO4-2, the specific energy consumption, the permeate recovery rate and quality of permeate for fertigation. The removal efficiency of SO4-2 was determined under conditions of sunny and cloudy days with a relation of the SDT of the influent and the permeate stream. The energy consumption was defined as the ratio of permeate flow and the electric power supplied to the pumping system according to equation 1. (1) 5

6 Where radiation, and the same time. represent the average permeate flow in the time as function of solar is the average electric power supplied to the pumping system in The quality of permeate for fertigation was evaluated as function of the following parameters: EC, TDS, PH and SAR. The SAR is evaluated with the content of sodium cations, calcium and magnesium according the equation 2, as was reported by [3],[12]. (2) 3. Analysis and discussion of results. The experiment focused in the behavior of the NF-PV desalination unit as function of the influent concentration and solar irradiation. Four sets of experiments were carried out for this purpose. In each set, the concentration of influent was kept constant, varying only the irradiance along the solar day in a range from 300 to1000 w/m 2. The fixed nominal influent concentration corresponding to the four sets were 525 mg / L, 1170 mg / L, 1750 mg / L and 2539 mg / L respectively. As mentioned above, each reported data point corresponds to an average over 3000 measurements, during a 500 min period. The experiment results are discussed in below. a) Water quality In order to quantify the water quality the ph, EC and SDT was measured. In each set, the measurement were carrying out at the start, middle and end of the test. The concentration remained with a maximum standard deviations of ±10 mg / L (± 19.9 µs/cm). The experimental result is shown in table 1. 6

7 Table 1: Evaluation of water quality SDT Test ph CE (µs/cm) (mg/l) T ( C) A B C A B C A B C A B C Influent (A), Effluent (B) and permeated (C) Based on experiment observations, the "fouling in pre-treatment filters, have an important effect on the water quality. The suspended solids eventually can saturate the filters. Consequently, the effective working pressure are drastically reduced as show in the Fig, 2. Fig, 2. Effect of fouling in the pre-treatment filter on the hydraulic head loss. A dirty filter respect to a new one. 7

8 A typical maintenance of the system consists in changing the pre-treatment filter with a new one. This modification led to an increment in the inlet pressure on to NF membrane. The NF membranes do not avoid entirely the flow of salt, monovalent compounds present in the mixture cross through to the membrane. Water and salt have different rates of mass transfer across to NF membrane, it allows the "rejection phenomenon. As the working pressure increases, the rate of water transfer increase also without changing the flow rate of the salt. In consequence, the permeation of the salt through the membrane was lower as is show in the experiment four (table 1). The sulfates remotion effectiveness, based on CE measurement, can be expressed as 100 (3) Where represents the amount of salts rejected and, the influent concentration. It can be observed that the highest efficiency (94%) was obtained in the test 4th. The results are presented in Table 2. Table 2: Efficiency of sulfate remotion Influent (µs/cm) Permeate Efficiency % Test 1 1, Test 2 2, Test 3 3, Test 4 4, In order to quantify the amount of sulfates and chlorides, a detailed study for test 4 was conducted. According with NMX-AA-073-SCFI-2001 (Mexican standard) were determined chlorides and with NMX-AA (Mexican standard) was used for the sulfates. Considering the NMX-AA-051-SCFI-2001 and flame method, the elements useful for the SAR was obtained. The results are presented in Table 3. Table 3 Determination of chlorides, sulfates and SAR chlorides sulfates Ca Mg Na SAR Test (mg/l) (mg/l) A B C

9 b) Solar system The experimental tests runs were conducted under conditions of sunny and cloudy days. During experimental tests the voltage provided by the photovoltaic panels was kept at an average of volts. The graph of Fig. 3 shows a typical day of test. Fig. 3. Solar radiation on PV level (primary axis) and volts provide by panel (secondary axis) Figure 4 shows the power required by the system relative to the incident solar radiation. A linear dependence is observed. However, scattering effects were due to the radiation dispersed by cloudiness and the effects of tilt PV system. 9

10 Fig. 4. Power supplied to system as a function of solar radiation. The test correspond to one day of sparsely cloudiness. c) NF system Permeate flow rate is affected inversely with the influent concentration. This is a characteristic of the NF systems. Figure 5 shows the permeate production with respect to the initial concentration. Based on the experimental results, the production of permeate relative to the supply pressure has a linear trend. Further, the concentration inversely affects permeate production. Observe that the increase of 525 mg / L to 2539 (mg / L) production experienced a decline close to 7 lpm which affects the energy consumption of the system. 10

11 Fig. 5. Production of permeate as a function of the feed pressure. Fig. 6 shows power consumption per unit of permeate volume. It can be observed that the power consumption is a linear function to influent concentration: higher sulfates concentration requires higher energy consumption. The maximum consumption was 3.4 Kwh/m 3. In previous works, has been reported consumption between kwh / m 3 [11]. 11

12 Figura 6 Energy consumption for deferent influent concentration The direct coupled configuration of the NF-PV was established by irrigation requirements. As a general rule, the crops should be irrigated when the irradiance is low, in order to reduce losses of water by vaporization and minimize plant stress. In this context, instead of accumulating electric energy in batteries for later use, treated water during the day can be stored in elevated tanks. In fact, is cheaper store water in tanks that accumulate energy in a batteries. The NF-PV system produce from of m 3 /d, making it possible to irrigate between 1 and 2 hectares of crops. 4. Conclusion An experimental study of a NF-PV desalination system without electrical storage support was presented. Experiments were carried out for different influent concentration and solar radiation. Based on experiment observation, the quality of permeated obtained satisfice the standards of Mexican norm for irrigation. The permeate production is affected inversed to influent concentration. In fact, was observed a decrement of permeated of 7 lpm going from 525 mg/l to 2539 mg/l. The fouling have an important effect on the production, was observed a hydraulic head loss maximum of 20.9 m H20. The energy consumption is affected stronger by the initial concentration as well as fouling in the pretreatment filters. Concern to energy consumption the maximum value was 3.4 Kwh/m 3 with a concentration of 2539 mg/l. The NF-PV system produce from of m 3 /d, making it possible to irrigate between 1 and 2 hectares of crops. 12

13 Acknowledgement The authors appreciate the partial support by 1772 Cátedras CONACYT-Mexico project. U. Dehesa-Carrasco wishes to thanks J.J. Quiñones Aguilar and E. Delgado-Quezada for technical support. Reference [1] Shaffer D. L., Yin Yip N., Gilron J., Elimelech M., Seawater desalination for agriculture by integrated forward and reverse osmosis: Improved product water quality for potentially less energy, Journal of Membrane Science (2012) 1 8. [2] Zarzo D.,Campos E., Terrero P., Spanish experience in desalination for agriculture, Desalination and Water Treatment, / Desalination Publications. [3] Carrera-Villacrés D.V., Crisanto-Perrazo T., Ortega-Escobar H., Ramírez-Garcia J., Salinidad cuantitativa y cualitativa del sistema hidrográfico Santa María-Río verde, México, Tecnología y ciencias del agua, Vol. 6, 2015, pp [4] Flores-Prieto J.J., Ramírez-Luna J.J., Calderón-Mólgora C., Delgado-Quezada, E., Morales-García A.J., Tratamiento de agua salobre mediante nanofiltración solar a baja presión para irrigación, Tecnología y ciencias del agua, (2015). [5] Ghermandi A., Messalem R. The advantages of NF desalination of brackish water for sustainable irrigation: The case of the Arava Valley in Israel, Desalination and Water Treatment, 10 (2009) [6] Garcia C., Molina F., Zarzo D., 7 year operation of a BWRO plant with raw water from a coastal aquifer for agricultural irrigation, Desalin. Water Treat. 31 (2011) [7] Veza J.M., Water desalination for agricultural applications, Chapter in Water Desalination for agricultural Applications,Proceedings of the FAO Expert Consultation on Water Desali- nation for Agriculture Applications, April, Rome, [8] Birnhack L., Shlesinger N., Lahav O., A cost effective method for improving the quality of inland desalinated brackish water destined for agricultural irrigation, Desalination 262 (2010) [9] Richards, B. S. and Schafer, A. I., Photovoltaic-powered desalination system for remote Australian communities, Renewable Energy, Vol. 28, 2003, pp

14 [10] Koyuncu, I., Yazgan, M., Topacik D., and Sarikaya, H. Z., Evaluation of the low pressure RO and NF membranes for an alternative treatment of Buyukcekmece Lake Water Science and Technology: Water Supply IWA Publishing, Vol 1, No1, 2001, pp [11] IEA-ETSAP and IRENA, Water desalination using renewable energy, Technology Brief I12 March [12] Silva, J.T., Montocayo R., Ochoa S., Estrada F., Cruz-Cárdenaz G., Escalera C., Villalpando F., Nava J., Calidad química del agua subterránea y superficial de la cuenca del rio Duero, Michoacán. Water Technology and Sciences, Vol. IV, No. 5, 2013, pp [13] Ludwig, H., Energy consumption of reverse osmosis seawater desalination possibilities for its optimization in design and operation of SWRO plants, Desalination and Water Treatment, Vol. 13, 2010, pp [14] HRAYSHAT E. S., Brackish water desalination by a standalone reverse osmosis desalination unit powered by photovoltaic solar energy, Renewable Energy, Vol. 33, 2008, pp [15] MAC-HARG, J. P., Energy Optimization of Brackish Groundwater Reverse Osmosis Desalination, Final Report for Contract Number ; Texas Water Development Board, 2011, pp