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Economical evaluation of the fluoride removal by nanofiltration
Desalination 249 (2009) 154–157
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Economical evaluation of the fluoride removal by nanofiltration F. Elazhar a, M. Tahaikt a, A. Achatei a, F. Elmidaoui a, M. Taky a, F. El Hannouni a, I. Laaziz a, S. Jariri b,1, M. El Amrani a, A. Elmidaoui a,⁎ a b
Laboratory of Separation Processes, Department of Chemistry, Ibn Tofail University, BP 1246 Kenitra, Morocco Office National de l'Eau Potable (ONEP), Rabat, Morocco
a r t i c l e
i n f o
Article history: Accepted 28 June 2009 Available online 4 October 2009 Keywords: Defluoridation Nanofiltration Membrane Cost Capital cost Operating cost
a b s t r a c t Economic evaluation was carried out for a plant of fluoride removal by nanofiltration having a capacity of 2400 m3/d (100 m3/h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium. The design of this plant was carried out for the predetermined optimized conditions corresponding to a recovery rate of 84%, a fluoride rejection of 97.8% and a pressure pump of 10 bar. The capital cost was estimated to 748,003 € and the calculated operating cost to 0.212 €/m3. These costs were briefly compared to other ones. © 2009 Elsevier B.V. All rights reserved.
1. Introduction During the last decade the removal of low-molecular weight compounds and the removal of salts with different valences from ground and surface waters for drinking water production were carried out by nanofiltration (NF) increasingly [1]. In North America, Scandinavia, Great Britain and France nanofiltration is already up todate-technique [2,3]. In developing countries such as in Morocco, the nanofiltration is in the step of research-development. Many studies were conducted by the National Office of Potable Water (ONEP) in Morocco in collaboration with Ibn Tofail University to remove lowmolecular weight such as nitrate or fluoride by membrane processes especially nanofiltration [4–8]. The water in many regions in Morocco usually exceeds the standards for fluoride and is sometimes brackish. The dental fluorosis as a harmful effect is widespread among the population such as in the centre of Morocco especially the plateau of Benguerir where the work was conducted. To prevent these adverse effects, the World Health Organization fixed the maximum acceptable concentration of fluoride ions in drinking water as 1.5 mg/l. The same standards are adopted in Morocco. When NF is applied the process should be technically and economically feasible and the best performing and the most economical options of process design and operation should be found. The cost of the NF process is largely a function of the module
⁎ Corresponding author. Tel./fax: +212 37373033. E-mail address: [email protected] (A. Elmidaoui). 1 Tel.: +212 7759600; fax: +212 7752377. 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.017
design, membrane flux, system operation conditions and plant capacity. In previous works [4,5,8], various technical aspects of the application of nanofiltration in fluoride removal were studied and optimized. Moreover a preliminary economical study on the basis of two adopted models was carried out [8]. In this work, economical study was conducted to evaluate the real costs of the nanofiltration technology on the basis of real industrial and economical data. The economical evaluation was carried out for a production capacity of 2400 m3/d (100 m3/h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium (consumption for domestic use of 50 l per capita per day). The design of this plant was carried out for the predetermined optimized conditions [4] corresponding to a recovery rate of 84% and a fluoride rejection of 97.8%. 2. Description of the nanofiltration unit The proposed design for the nanofiltration unit is shown in Fig. 1. The characteristic of well feed water is shown in Table 1. The drilling water is pumped from the reservoir T1 (150 m3) to the pre-treatment section by low pressures pumps (P1 and P2). The pretreated water was pumped up with high pressure pumps to the NF unit. Because it's low mineralization [4], the permeate is then remineralized by a lime saturator. The treated water is stored in the product water tank T3 and then distributed to the city of Benguerir. The produced brine was collected in the tank and discharged on a surface for spreading and evaporation. The solid residues were evacuated by truck.
F. Elazhar et al. / Desalination 249 (2009) 154–157
155
Fig. 1. Design of the treatment unit. (F1) and (F2) sand filter, (F3) cartridge filter, (T1) tank of pre-treated water, (T2) tank of preparation of sequestering, (T3) tank of storage of treated water, (P1, P2, P3, P4, P5, P6, P9) pumps, (R1) hopper Storage of lime, (C1) lime milk preparation tank, (C2) antiscalant preparation tank (C3) acid storage tank; (P7) milk injection pump (in the saturator), (S1) saturator, (C4, P8) silicate storage tank and pump.
2.1. Pre-treatment unit
2.2. Nanofiltration unit
The pre-treatment unit is composed of two sand filters (F1 and F2); one of which is in operation, the other being on rinsing. The capacity of each filter is of 125 m3/h filled with sand, to retain the suspended solids that might be present. The speed of filtration of this underground water is 30 m/h. The water undergoes a microfiltration on cartridge of polypropylene with 30 m/h of velocity, to remove particles larger than 10 µm and provide a final protection and to conform the pre-treated water to the nanofiltration membranes requirements. A commercial sequestering reagent prepared in the tank T2 is fed with the network of piping by the pump P4 to attenuate the risk of salt precipitations.
The pre-treated water is pumped from the reservoir (T1) to the NF group by high pressure pump (10 bars) (P3). The NF group is composed of 10 pressure tube containing 70 Film-Tec spiral wound membranes (NF90 8040) made in polyamide and having each one 6.7 m2 of area. 2.3. Post treatment unit The post-treatment of the NF permeate, includes remineralisation using a lime saturator, suitable to increase the temporary hardness to 1 meq/l (81 mg/l) of calcium bicarbonate in order to decrease the
Table 1 Characteristics of the feed water. Temperature °C Conductivity µS/cm pH pHs (saturation pH) TH °F TA °F TAC °F Ca2+ ppm Mg2+ ppm NO− 3 ppm Cl− ppm F− ppm ppm SO2− 4 Langelier Index
29 1492 7.41 7.80 44.2 0 32 108 38.5 20 560 2.32 116 0.39
The main treatment unit comprises:
▪ ▪ ▪
Pre-treatment post. Nanofiltration unit. Post-treatment.
Fig. 2. Schematic diagram of the lime saturator. (R1) hopper storage of lime, (C1) lime milk preparation tank, (P7) milk injection pump (in the saturator), (S1) saturator, (C4, P8) silicate storage tank and pump.
156
F. Elazhar et al. / Desalination 249 (2009) 154–157
Table 2 cost of the various equipments of the pre-treatment.
Table 4 Cost of various components of the post-treatment.
Materials
Cost (€)
Materials
Cost (€)
Filtration on sand Filtration on cartridge Air compressor Water pump of washing Raw water storage tank Antiscalant preparation tank Treated water storage tank Brine tank Brine transfer pump Total
30,000 3000 5000 3000 9000 9000 15,000 10,000 4000 88,000
Acid storage tank Acid pump Hopper storage of lime Lime milk preparation tank Milk injection pump (in the saturator) Saturator Silicate storage tank Permeate feed pump (to saturator) Total
8500 700 1180 1300 400 10,000 8000 700 30,780
3.4. Dimensioning and cost of nanofiltration unit corrosion risks. This method was chosen because it appears less expensive. Fig. 2 shows the schematic diagram of the lime saturator. After saturation, the equilibrated water was stored in the product water tanks (T3) and pumped to the Benguerir city. 3. Economic evaluation Cost is a major factor in implementing membrane technologies. Several factors affect the cost for NF process such as the raw water quality, the plant capacity, the recovery rate and the desired produced water quality. The economical evaluation of the cost of the produced cubic meter requires the calculation of the investment cost and the operating cost.
The NF group is composed of 10 pressure tube containing 70 FilmTec spiral wound membranes (NF90 8040) corresponding to 7 membranes per tube. The calculation of the Nanofiltration group was carried out on the basis of result obtained by using the software ROSA 6.1.4 program elaborated by DOW Chemical Corp. The software of dimensioning gave 67 membranes which were brought to 70 to have 7 membranes per tube of pressure. Table 3 gives the cost of nanofiltration group. 3.5. Post-treatment cost The various components of the post treatment and their prices are given in Table 4.
3.1. Capital cost Total capital costs include manufactured equipments, concrete, steel, membranes, pumps (feed, recycle and backflush) electrical and control instrumentations, pipes, valves, tanks, frames, and miscellaneous item (including building, electrical supply, treated water storage and pumping, etc.). All capital costs components were annualized considering an amortization factor calculated as a function of the interest rate for capital investments (6.7%) and for a design life of the plant of 15 years. Total capital costs of the various materials have been evaluated according to the reported international price and of the local market price, which is the price that has been evaluated net of tax and except expenses of the customs. 3.2. Pre-treatment cost Table 2 summarizes the various equipments of the pretreatment and their costs. 3.3. Construction and building cost The cost of the building construction and metal frames was calculated on the basis of a concrete price of 215 €/m2 and a girder and duckboards price of 15 €/kg. The total price was estimated to 429 500 € including site works and engineering costs (excavation works, ballasting of soil, concreting of soil, control room, storeroom, support girder and duckboards …).
Table 3 Cost of the NF group.
3.6. Auxiliary equipments and various costs The costs of the auxiliary equipments were calculated on the basis of percent cost of the heavy material including the NF group and the post-treatment. Table 5 gives the various equipments and the total cost. The costs of the various services contributing to the realization of the installation were expressed in percent cost of the heavy material. Table 6 gives the ratios and the costs of these services. 3.7. Operating cost The operating costs include the consumable, the energetic cost and the installation maintenance. Costs of energy, labour, amortization, chemicals, membrane replacement, consumables, spare parts, and major replacements or refurbishment required over the lifetime of the plant are included in operational and maintenance costs. Information relating to the items and current cost evaluate are provided below.
▪ ▪
The expected price of electricity in this case was 0.1 €/kWh. The total energy consumed by the operation of defluoridation by nanofiltration was estimated to 0.4 kWh/m3 [8]. The depreciation period was fixed to 15 years. The annual exploitation was fixed to 334 days and 24 h/d. The calculated
Table 5 Cost of the auxiliary equipments.
Nanofiltration group
Numbers
Unit price (€)
Cost (€)
Equipment
Ratio
Cost (€)
High pressure pump Pressure tube Membranes Tube support Diaphragms and joins Total (€)
1 10 70 – –
7800 1000 500 1600 700 55,100
7800 10,000 35,000 1600 700
Piping and taps Equipment for regulation Instrumentation of measure and control Power electric installation Command electric installation Total (€)
32% 18% 7% 20% 5%
55,161 31,028 12,066 34,476 8619 141,350
F. Elazhar et al. / Desalination 249 (2009) 154–157 Table 6 Cost of the various services.
157
Table 8 comparison of capital and operating costs for the tow calculations.
Nature of services
Ratio
Cost (€)
Assembly Transport Spar part Assurance of building site Total (€)
10% 3% 5% 1%
1723 517 861 172 3273
On the basis of the model On the basis of really data
Capital cost (€)
Operating cost (€/m3)
1,344,009 748,003
0.160 0.212
4. Conclusion
The total cost of the installation all included is of 748,003 €.
▪ ▪
▪ ▪
amortization rate was of 0.060 €/m3. Typically, the amortization rate for the NF process is around 0.050 €/m3. The interest on capital was fixed at 3% per year for a reimbursing period of 15 years. The calculated value was of 0.026 €/m3. Chemical use depends mainly on feed water quality and degree of pre-/post-treatment and cleaning process. In our case where the feed water quality is good, the major chemicals used for pretreatment were sulphuric acid and antiscalant agents. For the post-treatment the used chemicals were lime and silicates. The cost of chemicals was estimated to 0.05 €/m3. Membranes life was estimated to 5 years for an exploitation of 8000 h and for this good quality feed water. The cost of maintenance was estimated at 3% per year of the capital cost.
The technical and the economical data for the calculated operating and maintenance costs for the NF plant are given in Table 7. Table 8 compares the costs calculated in a previous work [8] on the basis of an adopted model and the costs evaluated in this work. The capital cost calculated on the basis of the adopted model appears largely higher than that calculated on the basis of the real data. But the operating costs are comparable despite the slightly higher value of the real cost.
Table 7 Summary data and costs of the NF plant.
High quality requirement for NF feed water, membrane fouling, high energy consumption, large volume of water lost as retentate and overall cost of the NF process are the main barriers that arise when considering NF for improving conventional ground water treatment. However the capital and operating costs are still the major factors in implementing NF technology for production of drinking water. In this work economical evaluation of the fluoride removal by NF was carried out by calculation of the capital and the operating costs on the basis of real industrial and economical data. The capital cost for a plant of 2400 m3/d was estimated to 748.003€ and the operating cost to 0.212€/m3. It is difficult to analyse and to compare the capital costs of different NF plants which are based on the operating conditions (production capacity, recovery rate, amortization period …) and the quality of product water. Moreover there are not enough experiences in desalination of brackish water or in specific treatment, such as fluoride removal, by NF to make it. Concerning the operating cost, the estimated one in this case is comparable to many other costs evaluated for production of drinking water by NF. For an existing NF plant in Florida with a capacity of 53,000 m3/d for groundwater, Bergman [9] gave a total treatment cost of 0.25 US$/m3 (0.23 €/m3). For several plant capacities, For several plant capacities, Wiesner et al. [10] have estimated to 0.30–0.40 US$/ m3 (0.24 €/m3, 0.32 €/m3) the costs of the treatment of surface water for drinking water production by NF. The capital cost calculated on the basis of the adopted model appears largely higher than the calculated one on the basis of the real data. But the operating costs are comparable. Acknowledgements
Operating conditions Drinking water production capacity Recovery rate Fluoride rejection Pressure Total membrane area Pump efficiency Power demand Energy cost Amortization period
2400 m3/d 84% 97.8% 10 bar 509.2 m2 85% 400 Wh/m3 0.1 € 15 (year)
Product water quality Conductivity Fluoride (mg/l) Alkalinity (°F) Total hardness (°F) Aggressiveness
20 µS/cm < 0.7 8 8 >0
Capital Cost (€) Pre-treatment Building and construction NF group Post-treatment Auxiliary equipments Various services Total capital cost
88,000 429,500 55,100 30,780 141,350 3273 748,003
Operating Cost (€/m3) Depreciation of the installation Interest on capital Membranes replacement Energy Maintenance Chemical Total operating cost
0.062 0.026 0.009 0.040 0.025 0.050 0.212
This work was supported by ONEP Co. (Morocco), TIA Company (Technologies Industrielles Appliquées, France). The authors express their thanks for this support. References [1] R. Rautenbach, A. Gröschl, Separation potential of nanofiltration membranes, Desalination 77 (1990) 73. [2] T. Thorsen, Membrane filtration of humic substances — state of the art, Wat. Sci. Tech. 40 (9) (1999) 105–112. [3] C. Ventresque, V. Gisclon, G. Bablon, G. Chagneau, An outstanding feat of modern technology: the Mery-sur-Oise Nanofiltration Treatment Plant (340,000 m3/d), Desalination 131 (2000) 1–16. [4] M. Tahaikt, R. El Habbani, A. Ait Haddou, I. Achary, Z. Amor, M. Taky, A. Alami, A. Boughriba, M. Hafsi, A. Elmidaoui, Fluoride removal from groundwater by nanofiltration, Desalination 212 (2007) 46–53. [5] M. Tahaikt, I. Achary, M.A. Menkouchi Sahli, Z. Amor, M. Taky, A. Alami, A. Boughriba, M. Hafsi, A. Elmidaoui, Defluoridation of Moroccan groundwater by electrodialysis: continuous operation, Desalination 189 (2006) 215–220. [6] M.A. Menkouchi Sahli, M. Tahaikt, I. Achary, M. Taky, F. Elhanouni, M. Hafsi, M. Elmghari, A. Elmidaoui, Technical optimization of nitrate removal for groundwater by ED using a pilot plant, Desalination 189 (2006) 200–208. [7] A. Elmidaoui, F. Elhannouni, M.A. Menkouchi Sahli, L. Chay, H. Elabbassi, M. Hafsi, D. Largeteau, Pollution of nitrate in Moroccan groundwater. Removal by electrodialysis. Desalination 136 (2001) 325–332. [8] M. Tahaikt, R. El Habbani, A. Ait Haddou, M. Taky, M. El Amrani, M. Kharif, A. Boughriba, M. Hafsi, A. Elmidaoui, Comparison of the performances of electrodialysis and nanofiltration in fluoride removal, Oral communication in Desalination and the Environment, 2007, pp. 22–25, April Halkidiki, Greece. [9] R.A. Bergman, Membrane softening versus lime softening in Florida: a cost comparison update, Desalination 102 (1995) 11–24. [10] M.R. Wiesner, J.H. Hackney, S. Sethi, J.G. Jacangelo, J.M. Laîné, Cost estimates for membrane filtration and conventional treatment, J. AWWA 86 (12) (1994) 33–41.
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Economical evaluation of the fluoride removal by nanofiltration F. Elazhar a, M. Tahaikt a, A. Achatei a, F. Elmidaoui a, M. Taky a, F. El Hannouni a, I. Laaziz a, S. Jariri b,1, M. El Amrani a, A. Elmidaoui a,⁎ a b
Laboratory of Separation Processes, Department of Chemistry, Ibn Tofail University, BP 1246 Kenitra, Morocco Office National de l'Eau Potable (ONEP), Rabat, Morocco
a r t i c l e
i n f o
Article history: Accepted 28 June 2009 Available online 4 October 2009 Keywords: Defluoridation Nanofiltration Membrane Cost Capital cost Operating cost
a b s t r a c t Economic evaluation was carried out for a plant of fluoride removal by nanofiltration having a capacity of 2400 m3/d (100 m3/h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium. The design of this plant was carried out for the predetermined optimized conditions corresponding to a recovery rate of 84%, a fluoride rejection of 97.8% and a pressure pump of 10 bar. The capital cost was estimated to 748,003 € and the calculated operating cost to 0.212 €/m3. These costs were briefly compared to other ones. © 2009 Elsevier B.V. All rights reserved.
1. Introduction During the last decade the removal of low-molecular weight compounds and the removal of salts with different valences from ground and surface waters for drinking water production were carried out by nanofiltration (NF) increasingly [1]. In North America, Scandinavia, Great Britain and France nanofiltration is already up todate-technique [2,3]. In developing countries such as in Morocco, the nanofiltration is in the step of research-development. Many studies were conducted by the National Office of Potable Water (ONEP) in Morocco in collaboration with Ibn Tofail University to remove lowmolecular weight such as nitrate or fluoride by membrane processes especially nanofiltration [4–8]. The water in many regions in Morocco usually exceeds the standards for fluoride and is sometimes brackish. The dental fluorosis as a harmful effect is widespread among the population such as in the centre of Morocco especially the plateau of Benguerir where the work was conducted. To prevent these adverse effects, the World Health Organization fixed the maximum acceptable concentration of fluoride ions in drinking water as 1.5 mg/l. The same standards are adopted in Morocco. When NF is applied the process should be technically and economically feasible and the best performing and the most economical options of process design and operation should be found. The cost of the NF process is largely a function of the module
⁎ Corresponding author. Tel./fax: +212 37373033. E-mail address: [email protected] (A. Elmidaoui). 1 Tel.: +212 7759600; fax: +212 7752377. 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.017
design, membrane flux, system operation conditions and plant capacity. In previous works [4,5,8], various technical aspects of the application of nanofiltration in fluoride removal were studied and optimized. Moreover a preliminary economical study on the basis of two adopted models was carried out [8]. In this work, economical study was conducted to evaluate the real costs of the nanofiltration technology on the basis of real industrial and economical data. The economical evaluation was carried out for a production capacity of 2400 m3/d (100 m3/h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium (consumption for domestic use of 50 l per capita per day). The design of this plant was carried out for the predetermined optimized conditions [4] corresponding to a recovery rate of 84% and a fluoride rejection of 97.8%. 2. Description of the nanofiltration unit The proposed design for the nanofiltration unit is shown in Fig. 1. The characteristic of well feed water is shown in Table 1. The drilling water is pumped from the reservoir T1 (150 m3) to the pre-treatment section by low pressures pumps (P1 and P2). The pretreated water was pumped up with high pressure pumps to the NF unit. Because it's low mineralization [4], the permeate is then remineralized by a lime saturator. The treated water is stored in the product water tank T3 and then distributed to the city of Benguerir. The produced brine was collected in the tank and discharged on a surface for spreading and evaporation. The solid residues were evacuated by truck.
F. Elazhar et al. / Desalination 249 (2009) 154–157
155
Fig. 1. Design of the treatment unit. (F1) and (F2) sand filter, (F3) cartridge filter, (T1) tank of pre-treated water, (T2) tank of preparation of sequestering, (T3) tank of storage of treated water, (P1, P2, P3, P4, P5, P6, P9) pumps, (R1) hopper Storage of lime, (C1) lime milk preparation tank, (C2) antiscalant preparation tank (C3) acid storage tank; (P7) milk injection pump (in the saturator), (S1) saturator, (C4, P8) silicate storage tank and pump.
2.1. Pre-treatment unit
2.2. Nanofiltration unit
The pre-treatment unit is composed of two sand filters (F1 and F2); one of which is in operation, the other being on rinsing. The capacity of each filter is of 125 m3/h filled with sand, to retain the suspended solids that might be present. The speed of filtration of this underground water is 30 m/h. The water undergoes a microfiltration on cartridge of polypropylene with 30 m/h of velocity, to remove particles larger than 10 µm and provide a final protection and to conform the pre-treated water to the nanofiltration membranes requirements. A commercial sequestering reagent prepared in the tank T2 is fed with the network of piping by the pump P4 to attenuate the risk of salt precipitations.
The pre-treated water is pumped from the reservoir (T1) to the NF group by high pressure pump (10 bars) (P3). The NF group is composed of 10 pressure tube containing 70 Film-Tec spiral wound membranes (NF90 8040) made in polyamide and having each one 6.7 m2 of area. 2.3. Post treatment unit The post-treatment of the NF permeate, includes remineralisation using a lime saturator, suitable to increase the temporary hardness to 1 meq/l (81 mg/l) of calcium bicarbonate in order to decrease the
Table 1 Characteristics of the feed water. Temperature °C Conductivity µS/cm pH pHs (saturation pH) TH °F TA °F TAC °F Ca2+ ppm Mg2+ ppm NO− 3 ppm Cl− ppm F− ppm ppm SO2− 4 Langelier Index
29 1492 7.41 7.80 44.2 0 32 108 38.5 20 560 2.32 116 0.39
The main treatment unit comprises:
▪ ▪ ▪
Pre-treatment post. Nanofiltration unit. Post-treatment.
Fig. 2. Schematic diagram of the lime saturator. (R1) hopper storage of lime, (C1) lime milk preparation tank, (P7) milk injection pump (in the saturator), (S1) saturator, (C4, P8) silicate storage tank and pump.
156
F. Elazhar et al. / Desalination 249 (2009) 154–157
Table 2 cost of the various equipments of the pre-treatment.
Table 4 Cost of various components of the post-treatment.
Materials
Cost (€)
Materials
Cost (€)
Filtration on sand Filtration on cartridge Air compressor Water pump of washing Raw water storage tank Antiscalant preparation tank Treated water storage tank Brine tank Brine transfer pump Total
30,000 3000 5000 3000 9000 9000 15,000 10,000 4000 88,000
Acid storage tank Acid pump Hopper storage of lime Lime milk preparation tank Milk injection pump (in the saturator) Saturator Silicate storage tank Permeate feed pump (to saturator) Total
8500 700 1180 1300 400 10,000 8000 700 30,780
3.4. Dimensioning and cost of nanofiltration unit corrosion risks. This method was chosen because it appears less expensive. Fig. 2 shows the schematic diagram of the lime saturator. After saturation, the equilibrated water was stored in the product water tanks (T3) and pumped to the Benguerir city. 3. Economic evaluation Cost is a major factor in implementing membrane technologies. Several factors affect the cost for NF process such as the raw water quality, the plant capacity, the recovery rate and the desired produced water quality. The economical evaluation of the cost of the produced cubic meter requires the calculation of the investment cost and the operating cost.
The NF group is composed of 10 pressure tube containing 70 FilmTec spiral wound membranes (NF90 8040) corresponding to 7 membranes per tube. The calculation of the Nanofiltration group was carried out on the basis of result obtained by using the software ROSA 6.1.4 program elaborated by DOW Chemical Corp. The software of dimensioning gave 67 membranes which were brought to 70 to have 7 membranes per tube of pressure. Table 3 gives the cost of nanofiltration group. 3.5. Post-treatment cost The various components of the post treatment and their prices are given in Table 4.
3.1. Capital cost Total capital costs include manufactured equipments, concrete, steel, membranes, pumps (feed, recycle and backflush) electrical and control instrumentations, pipes, valves, tanks, frames, and miscellaneous item (including building, electrical supply, treated water storage and pumping, etc.). All capital costs components were annualized considering an amortization factor calculated as a function of the interest rate for capital investments (6.7%) and for a design life of the plant of 15 years. Total capital costs of the various materials have been evaluated according to the reported international price and of the local market price, which is the price that has been evaluated net of tax and except expenses of the customs. 3.2. Pre-treatment cost Table 2 summarizes the various equipments of the pretreatment and their costs. 3.3. Construction and building cost The cost of the building construction and metal frames was calculated on the basis of a concrete price of 215 €/m2 and a girder and duckboards price of 15 €/kg. The total price was estimated to 429 500 € including site works and engineering costs (excavation works, ballasting of soil, concreting of soil, control room, storeroom, support girder and duckboards …).
Table 3 Cost of the NF group.
3.6. Auxiliary equipments and various costs The costs of the auxiliary equipments were calculated on the basis of percent cost of the heavy material including the NF group and the post-treatment. Table 5 gives the various equipments and the total cost. The costs of the various services contributing to the realization of the installation were expressed in percent cost of the heavy material. Table 6 gives the ratios and the costs of these services. 3.7. Operating cost The operating costs include the consumable, the energetic cost and the installation maintenance. Costs of energy, labour, amortization, chemicals, membrane replacement, consumables, spare parts, and major replacements or refurbishment required over the lifetime of the plant are included in operational and maintenance costs. Information relating to the items and current cost evaluate are provided below.
▪ ▪
The expected price of electricity in this case was 0.1 €/kWh. The total energy consumed by the operation of defluoridation by nanofiltration was estimated to 0.4 kWh/m3 [8]. The depreciation period was fixed to 15 years. The annual exploitation was fixed to 334 days and 24 h/d. The calculated
Table 5 Cost of the auxiliary equipments.
Nanofiltration group
Numbers
Unit price (€)
Cost (€)
Equipment
Ratio
Cost (€)
High pressure pump Pressure tube Membranes Tube support Diaphragms and joins Total (€)
1 10 70 – –
7800 1000 500 1600 700 55,100
7800 10,000 35,000 1600 700
Piping and taps Equipment for regulation Instrumentation of measure and control Power electric installation Command electric installation Total (€)
32% 18% 7% 20% 5%
55,161 31,028 12,066 34,476 8619 141,350
F. Elazhar et al. / Desalination 249 (2009) 154–157 Table 6 Cost of the various services.
157
Table 8 comparison of capital and operating costs for the tow calculations.
Nature of services
Ratio
Cost (€)
Assembly Transport Spar part Assurance of building site Total (€)
10% 3% 5% 1%
1723 517 861 172 3273
On the basis of the model On the basis of really data
Capital cost (€)
Operating cost (€/m3)
1,344,009 748,003
0.160 0.212
4. Conclusion
The total cost of the installation all included is of 748,003 €.
▪ ▪
▪ ▪
amortization rate was of 0.060 €/m3. Typically, the amortization rate for the NF process is around 0.050 €/m3. The interest on capital was fixed at 3% per year for a reimbursing period of 15 years. The calculated value was of 0.026 €/m3. Chemical use depends mainly on feed water quality and degree of pre-/post-treatment and cleaning process. In our case where the feed water quality is good, the major chemicals used for pretreatment were sulphuric acid and antiscalant agents. For the post-treatment the used chemicals were lime and silicates. The cost of chemicals was estimated to 0.05 €/m3. Membranes life was estimated to 5 years for an exploitation of 8000 h and for this good quality feed water. The cost of maintenance was estimated at 3% per year of the capital cost.
The technical and the economical data for the calculated operating and maintenance costs for the NF plant are given in Table 7. Table 8 compares the costs calculated in a previous work [8] on the basis of an adopted model and the costs evaluated in this work. The capital cost calculated on the basis of the adopted model appears largely higher than that calculated on the basis of the real data. But the operating costs are comparable despite the slightly higher value of the real cost.
Table 7 Summary data and costs of the NF plant.
High quality requirement for NF feed water, membrane fouling, high energy consumption, large volume of water lost as retentate and overall cost of the NF process are the main barriers that arise when considering NF for improving conventional ground water treatment. However the capital and operating costs are still the major factors in implementing NF technology for production of drinking water. In this work economical evaluation of the fluoride removal by NF was carried out by calculation of the capital and the operating costs on the basis of real industrial and economical data. The capital cost for a plant of 2400 m3/d was estimated to 748.003€ and the operating cost to 0.212€/m3. It is difficult to analyse and to compare the capital costs of different NF plants which are based on the operating conditions (production capacity, recovery rate, amortization period …) and the quality of product water. Moreover there are not enough experiences in desalination of brackish water or in specific treatment, such as fluoride removal, by NF to make it. Concerning the operating cost, the estimated one in this case is comparable to many other costs evaluated for production of drinking water by NF. For an existing NF plant in Florida with a capacity of 53,000 m3/d for groundwater, Bergman [9] gave a total treatment cost of 0.25 US$/m3 (0.23 €/m3). For several plant capacities, For several plant capacities, Wiesner et al. [10] have estimated to 0.30–0.40 US$/ m3 (0.24 €/m3, 0.32 €/m3) the costs of the treatment of surface water for drinking water production by NF. The capital cost calculated on the basis of the adopted model appears largely higher than the calculated one on the basis of the real data. But the operating costs are comparable. Acknowledgements
Operating conditions Drinking water production capacity Recovery rate Fluoride rejection Pressure Total membrane area Pump efficiency Power demand Energy cost Amortization period
2400 m3/d 84% 97.8% 10 bar 509.2 m2 85% 400 Wh/m3 0.1 € 15 (year)
Product water quality Conductivity Fluoride (mg/l) Alkalinity (°F) Total hardness (°F) Aggressiveness
20 µS/cm < 0.7 8 8 >0
Capital Cost (€) Pre-treatment Building and construction NF group Post-treatment Auxiliary equipments Various services Total capital cost
88,000 429,500 55,100 30,780 141,350 3273 748,003
Operating Cost (€/m3) Depreciation of the installation Interest on capital Membranes replacement Energy Maintenance Chemical Total operating cost
0.062 0.026 0.009 0.040 0.025 0.050 0.212
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