Transactions Template JOURNAL OF ENGINEERING RESEARCH AND TECHNOLOGY, VOLUME 1, ISSUE 1, MARCH 2014 32 Use of Nanofiltration for Nitrate Removal from Gaza Strip Groundwater Yunes Mogheir, Ahmed Albahnasawi Abstract— Due to excessive usage of nitrate fertilizer in agriculture and discharging of wastewater from treatment plants, and leakage of wastewater form cesspools, nitrate level in the groundwater has increased. Elevated nitrate in water resources could lead to serious problem including eutrophication, and potential hazards for human and animal health. The aim of this study is to investigate the use of Nanofltraiton for nitrate removal in Gaza Strip as case study. One commercial membrane (NF90) was used in this study. The stirred dead end flow model was used. In addition, two types of water were used: Aqueous solution and real water. The performance of the tested membrane was measured in terms of flux rate and nitrate rejection under different operation conditions: nitrate concentration was varied between 50-400mg/L, applied pressure (6-12) bar and TDS concentration (500-3570) mg/l. The percentage of nitrate removal was in the range of 0.62% and 66.68% and the flux rate ranges between 2.61 and 30.12 L/m2.hr. These values depend on operation conditions such as nitrate concentration, TDS compostion and operation pressure. In real water, the percentage of nitrate removal was influenced by TDS value in general, but to be more specific, it was found that the concentration of sulphat has a great effect on nitrate removal, as the sulphat concentration increased the nitrate removal decreased. NF90 was observed to be an effective membrane for nitrate removal of Gaza Strip at higher permeate flux and lower applied pressure, especially in North Gaza Strip were low TDS and Sulphat concentration were observed. Index Terms— Nanofiltration, Nitrate, Rejection, Flux Rate, Well, Total dissolved solids and Pressure. I INTRODUCTION Water is essential to sustain life, and a satisfactory (ade- quate, safe and accessible) supply must be available to all. Improving access to safe drinking water can result in tangi- ble benefits to health. The Gaza Strip is a highly populated, small area in which the groundwater is the main water source. During the last few decades, groundwater quality has been deteriorated to a limit that the municipal tap water became brackish and un- suitable for human drinking consumption in most parts of the Strip. The aquifer is intensively exploited through more than four thousands of pumping wells. As a result of its in- tensive exploitation, the aquifer has been experiencing sea- water intrusion in many locations in the Gaza Strip; In addi- tion high nitrate is measured in many places in Gaza strip aquifer [1].Nitrate in the groundwater in the Gaza Strip has become a serious problem in the last decade. As a result of extensive use of fertilizers, discharging of wastewater from treatment plants, and leakage of wastewater form cesspools, increased levels of nitrate, up to 400 mg/L, have been de- tected in groundwater. Nitrate concentrations more than 50 mg/L are very harmful to infant, fetuses, and people with health problems. To overcome this serious situation, the reverse osmosis (RO) technology is used to replace the tap water or to im- prove its quality. Several private Palestinian water investing companies established a small-scale reverse osmosis (RO) desalination plants to cover the shortage of good quality drinking water in the whole Gaza Strip. Desalination is a considerable alternative for water sup- ply in order to improve the quality of water in the area. So, desalination plants began to be established in Gaza strip using RO technique. The shortage of energy source become a big constrain facing desalination plants of which these plants are operating at limited operational hours, The need to find more choices to develop water sector in Gaza Strip be- come an essential priority. Thinking of innovative actions for desalination sector needs balance and acceptable deci- sions [2]. New technologies including nanofiltration membrane (NF) application will be considered and experimentally in- vestigated to measure the possibility of enhancing the per- formance of the desalination plants and increasing produc- tion in the near future. In addition, effluent brine treatment technology prior to disposal may be studied and recom- mended [3]. Nanofiltration (NF) is a suitable method for the removal of a wide range of pollutants from groundwater or surface water. The major application of NF is softening, but NF is usually applied for the combined removal of NOM (Natural Use Nanofiltration for Nitrate Elimination from Gaza Strip Ground Water, Yunes Mogheir, Ahmed Albahnasawi ( 2014) 33 organic material), micropollutants, viruses and bacteria, ni- trates and arsenic, or for partial desalination. Industrial full- scale installations have proven the reliability of NF in these areas [4]. In the Gaza Strip there is no desalination plant using nan- otechnology, the aim of this research to test if Nanofiltration membrane is suitable for nitrate removal from groundwater. II Experimental Setup A Materials NF90 (DOW Filmtec) nanofiltration element is a high ar- ea, high productivity element designed to remove a high percentage of salts, nitrate, iron and organic compounds such as pesticides, herbicides and THM precursors. The high active area membrane combined with low net driving pres- sure of the membrane allows the removal of these com- pounds at low operating pressure. The system consists of HP4750 stainless cylindrical cell purchased from Steirlitech - UK with volume of 300mL. The cell is pressurized via Nitrogen Gas supplied by Gas cylinder with a manual pres- sure regulator. The experiments are conducted at room tem- perature and at pressure range of (6 – 12) bar; Figure 1 shows the system component. Figure 1 system component. B Sampling The filtration experiments were carried out on different samples: 1) Pure sample: deionized water with EC=7μS/cm 2) Synthesis standard solutions: (50-10-150-200-250- 300-350-400) ppm as NO3 Solution. 3) Real sample: Water samples were collected from dif- ferent municipal wells distributed on all Gaza Strip gover- norates and divided based on the concentration of Nitrates, the sample Nitrates concentrates are chosen every fifteen mg/L, the concentrations of Nitrates varied between (32- 364) mg/L. The water samples were collected based on Pal- estine Water Authority (PWA) chemical tests results in 2011. C Methods After collecting the samples, major chemical analysis were performed for these samples such as (pH, TDS, and NO3). Nitrate Measurement 4500-NO3 nitrogen (nitrate) method was used in nitrate measurement. Nitrate concentration was determined by CT- 2600 Spectrophotometer. TDS Measurement Concentration of TDS was determined by Conductivity meter (Microprocessor conductivity meter BODDS-307W, which measures the EC. To get the approximare TDC value we multiply EC by (0.6). PH Measurement PH is a logarithmic notation used to measure hydrogen activity (i.e., whether a solution is acid or basic). pH = - log [H+](1) As a simplification, it is assumed that pH is a function of the hydrogen ion concentr tion {[H+]} when in reality it is related to the hydrogen ion activity H+. Since pure water is slightly ionized, it is expressed as an equilibrium equation termed the ion product constant of water. The concentration of these two ions is relatively small and is expressed as a simple logarithmic notation. pH is the negtive log of the hydrogen ion[5] . The pH was measured with (pH/ORP/ISE Graphic LCD pH Bench top Meter, HANNA instrument) pH meter. D Tested parameter Flux Rate Flux rate Represent the volume of liquid passing through specific area of membrane at certain operating pressure dur- ing a period of time. The flux rate of a filter is important in determining how rapidly filtration can be completed. If there is nothing in the sample stream to clog the pores, the flux rate should remain constant. Flux rate = V/A.t (l/m2.hr) (2) Where; V: volume of water permeated at the time (t) (l). A: surface area of membrane (0.00146 m2). t: time of filtration(hr). Note that these tests were carried out at different pres- sures (6, 8, 10, 12 bar), because this pressure ranges are lie in the operation pressure range of NF membrane (Filmtec membranes product information). Rejection The same meaning of removal efficiency, represent the ability of membrane to reject salts and impurities from feed water. This is one of the most important characteristics of membrane; that’s depended on the feed water characteristics, membrane characteristics and applied pressure. The ability of membrane to reject TDS & NO3 was measured using the following equation: %R= (1-Cp/Cf)*100 (3) Where; Cp: salt concentration in permeate (mg/l). Cf: salt concentration in feed water (mg/l). III Result and discussion Use Nanofiltration for Nitrate Eliminati on from Gaza Strip Ground Water, Yunes Mogheir, Ahmed Albahnasawi (2014) 34 A Flux rate 1 A queues solution Many factor influence the flux rate such as operation pressure and ionic concentration Figure 2 illustrate the rela- tion between flux rate and operation pressure for pure water sample. Flux rate dos not only depend on the operating pres- sure but also on the influent concentration.as ionic concen- tration increase the flux rate will be decrease as show in Figure 3 the effect of operating pressure and ionic concen- tration on flux rate in nitrate solution sample. For each pres- sure, a linear relation can be obtained for flux rate against the feed nitrate concentration with high correlation ranges between (0.94 to 0.97). This reduction in flux crossing is increased when the ions is added, probably due to increasing solution osmotic pressure. Figure 2 pure water flux rate with different pressure. Figure 3 Effect of feed nitrate concentration and opreat- ing pressure on flux rate (nitrate sample (50,100,150,200,250,300,350 and 400 mg/l as NO3. 2 Real water sample. As in case of a queues solution, the flux rate increases linearly with increase of applied pressure Figure 4 and Table 1 show the effect of TDS concentration and operating pres- sure on flux rate, the general trend is as TDS concentration increases the flux rate decrease B Rejection of ionic component 1 A queues solution Figure 4 Effect of TDS concentrations on flux. The nitrate removal (rejection rate) of solution at differ- ent pressure were analyzed Figure 5 shows the effect of operation pressure and ionic concentration on nitrate rejec- tion, as pressure increased nitrate rejection increased on the contrary as nitrate feed concentration increases nitrate rejec- tion decreases. This can be explained by considering salt transport through the membrane as a result of diffusion and convection, which are respectively due to a concentration and a pressure gradient across the membrane. At low trans- membrane pressure Figure 5 Effect of feed nitrate concentration and opreat- ing pressure on nitrate rejection rate(nitrate sample (50,100,150,200,250,300,350 and 400 mg/l as NO3). (TMP), diffusion contributes substantially to the salt transport resulting in a lower retention. With increasing TMP, the salt transport by diffusion becomes relatively less important, so that salt retention is higher [6] [7]. Use Nanofiltration for Nitrate Elimination from Gaza Strip Ground Water, Yunes Mogheir, Ahmed Albahnasawi ( 2014) 35 Table 1 Flux rate and TDS concentration. Well ID. TDS(mg/L) Pressure (Bar) 6 Bar 8 Bar 10 Bar 12 Bar Flux rate (L/m2.hr) A211 500 12.82 18.45 22.29 30.12 D75 630 12.57 17.37 21.95 29.87 D60 950 7.94 12.01 17.24 28.48 W2 970 9.22 13.93 18.54 28.86 Darage 1200 6.42 10.6 16.17 23.98 Hera 1350 7.79 11.69 17.13 28.24 S69 1506 5.57 9.6 13.72 20.16 R306 1587 5.55 10.18 15.64 21.1 C79A 1600 6.36 10.37 15.94 22.8 P145 1650 5.4 8.98 13.95 18.92 R25A 1900 6.04 10.28 15.85 21.82 L127 1950 5.35 9.69 14.19 18.26 R25B 2020 5.35 9.07 13.59 19.65 L198 2100 5.18 7.27 11.82 17.96 R74 2200 4.78 7.06 10.56 15.62 L87 2450 4.61 6.53 9.73 14.7 H104 2454 3.11 6.4 8.7 14.12 R311 2570 3.35 6.7 9.73 14.4 Shoot 2574 5.03 6.72 10.33 15.38 Seka 2673 2.92 6.53 8.81 14.12 Astath 2900 3.11 5.97 8.7 13.7 G49 3010 2.9 5.78 8.66 13.7 E124A 3140 2.61 4.65 7.55 10.71 L190 3570 3.61 6.49 8.53 13.61 2 Real water samples. As observed in aqueous solutions the effect of operating pressure was evaluated. In real water there were many fac- tors that influenced the rejection percentage such as TDS concentration and other chemical concentration. The result show that as operation pressure increases the removal of nitrate increases. However, for other wells, the operating pressure was not the main influencing factor. TDS concentration plays an important role. Table 2 shows the results of nitrate removal and operating pressures, the max- imum rejection percentage at 12 bar was 55.56% at well A211 and the minimum nitrate rejection was zero at many wells when operating pressures was 6 bars depending to TDS concentration and composition and nitrate concentra- tion in feed water The result in Figure 6 showed that in general that a rela- tion between TDS concentration and nitrate rejection, when we fixed the nitrate concentration in feed water. As shown in Figure 6 there are drop in curve, but when the effect of ni- trate concentration is fixed and plot the nitrate removal and sulphate concentration, a strong relation between sulphate concentration and nitrate rejection was found (Figure 7). Figure 6 and Figure 7 show the nitrate rejection results against TDS and sulphat concentration. To show this rela- tion, Nitrate concentration must be fixed. For example E124A well have 3140 mg/l as TDS concentration and S69 Use Nanofiltration for Nitrate Eliminati on from Gaza Strip Ground Water, Yunes Mogheir, Ahmed Albahnasawi (2014) 36 well has 1506 mg/l as TDS concentration, but nitrate rejec- tion in E124A is higher than S69, although nitrate concentra- tion in E124A is higher than in S68. This was due to that the sulphate concentration in E124A was 149 mg/L but in S69 was 240 mg/L. That means the sulphate concentration plays important role in NF90 nitrate rejection percentage. Because of high removal of sulphate, because of their valance, nitrate is forced to pass through the membrane. The removal of monovalent such as nitrate was greatly decreased under the presence of sulphate ions. Retention of the nega- tive sulphate ion in concentration water disturbed the elec- trical equilibrium on both sides of the membrane that the nitrate ions was forced through the membrane in permeate water to maintain electric equilibrium [8]. It was also observed that an increase of sulphate concen- tration generally decreases the chloride rejection. The reten- tion of chloride anion is lower for the salt mixtures than for single salts experiment. It seems that the presence of high valance anion (SO4) drives more chloride into membrane, thus decreasing its retention [9]. The sequence of rejection of monovalent anions can be written as R (F)> R (Cl)> R (NO3), the observed retention of the three ions is similar to the ionic order and opposite to the hydration energy order for the monovalent ions, the F which has higher hydration energy is better retained than Cl and NO3 [10] [11]. From the above two paragraph it can be conclude that the chloride is better than nitrate in rejection according to rejec- tion sequence, while sulphat has negative effect on chloride rejection so sulphate has negative effect on nitrate rejection. Figure 6 Relation between TDS concentration and nitrate rejection. Use Nanofiltration for Nitrate Elimination from Gaza Strip Ground Water, Yunes Mogheir, Ahmed Albahnasawi ( 2014) 37 Table 2 Nitrate rejection result with sulphate and TDS concentration. Well No. TDS Nitrate NO3 (mg/LNO3) Sulphate SO4 (mg/L) 6 Bar 8 Bar 10 Bar 12 Bar A211 500 45 22 33.33 42.22 48.89 55.56 W2 970 71 108 18.31 28.17 39.44 42.85 E124A 3140 80 149 75 21.25 27.5 35 S69 1506 32 240 8.23 15.63 22.32 28.13 H104 2454 76 394 5.35 10.6 15.15 18.5 D75 630 133 41 42.87 48.12 50.38 52.63 R306 1587 136 155 8.09 14.71 19.85 23.53 R74 2200 120 219 5 10.83 15 18.33 R25A 1900 146 269 4.79 10.27 14.38 17.81 Astath 2900 140 407 0.71 2.14 5.73 8.57 G49 3010 138 550 0.96 1.79 5.17 6.79 C79A 1600 190 105 16.84 19.47 24.21 36.63 Darage 1200 178 111 16.85 23.6 27.53 34.27 L198 2100 185 375 1.62 4.86 8.11 10.81 L190 3570 193 628 0.52 1.04 1.55 2.07 D60 950 211 90 36.49 39.81 41.71 43.6 P145 1650 206 213 6.31 13.59 23.3 30.1 R25B 2020 226 280 7.52 12.83 16.81 21.24 Seka 2673 230 359 2.17 10 12.61 15.22 R311 2570 217 444 1.38 3.23 8.76 12.44 Hera 1350 273 135 21.61 31.87 36.26 45.42 L127 1950 364 157 18.68 23.9 29.67 32.97 L87 2450 304 271 4.61 9.21 14.47 17.76 Shoot 2574 332 356 0.60 1.2 7.83 14.16 Use Nanofiltration for Nitrate Eliminati on from Gaza Strip Ground Water, Yunes Mogheir, Ahmed Albahnasawi (2014) 38 Figure 7 Relation between nitrate rejection and sulphate concentration. IV Comparison between Real water and Aque- ous Solutions: 1) Flux Rate The performance of NF90 membrane varied in terms of flux rate. Consequently, the pure water flux rate was higher than the real water flux rate. As the water contains more salts or other substances, the flux rate decreases. At this pattern the membrane perfor- mance, so the pure flux rate was higher than of real water flux. Also complexity of water character play a good role in membrane behavior and that is why the queues solution flux rate is higher than real water flux rate. The maximum flux rate for aqueous solution was ob- tained at 12 bar (34.13 L/m2.hr) for pure water and minimum flux rate was obtained at 6 bar (16.31 L/m2.hr). The maximum flux rate for real water was obtained at 12 bar (30.12 L/m2.hr) for A211 and minimum flux rate was obtained at 6 bar (2.61 L/m2.hr) for E142A. 2) Nitrate Rejection Generally, the overall rejection percentages of the NF90 membrane of aqueous solutions were found to be higher than the rejection of real water. For aqueous solution the maximum and minimum nitrate rejection of aqueous solu- tion was 66.68% and 21.67% respectively, while for real water the maximum and minimum nitrate rejection of were 55.56% and 0 % respectively. The characteristics of feed water significantly affect the membrane rejection such as the content of sulphate and hardness. This explains the difference of rejection between real water and aqueous solution. In addition, real water may contain some colloids and many other substances that can negatively affect the membrane rejection. Conclusion NF90 membrane showed good result for nitrate removal in real water, which varied between 0.62% and 55%, and flux rate between 2.61 and 30.12 L/m2.hr, when the operat- ing pressure varied between 6 and 12 bar. It can be concluded that the sulphate has negative effect on chloride rejection and on nitrate rejection. As the real water contains more salts or other substance, the flux rate decrease. At this pattern the membrane performance, so the pure flux rate was higher than of real water flux. Also com- plexity of water character play a good role in membrane behavior and that is why the nitrate solutions flux rate are higher than real water flux rate. NF90 was observed to be an effective method to nitrate removal of Gaza Strip at higher permeate flux and lower applied pressure, especially in North Gaza Strip were low TDS and Sulphat concentration were observed. In other Ga- za Strip places TDS and sulphat should be removed before using nanofiltration to nitrate removal. The characteristics of feed water significantly affect the membrane rejection such as the content of sulphate and hardness. This explains the difference of rejection between real water and aqueous solution. Sensitivity of the system to the circumstances like tem- perature, quality of deionized water used in system flushing, regular insurance of zero leakage of pressure , the period of using membrane, using tools washed by deionized water , all these restriction make the test harder. The importance of testing Nanofiltration membranes as new emerging technology in Gaza strip is to improve the overall desalination quality with acceptable cost; carrying out tests helps to understand the behavior of NF90 for nitrate removal. 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