This section includes a schematic description of the various components that are currently installed in the NF pilot desalination plant in Hatzeva and an overview of the experimental results obtained from operation of the pilot unit with grid electricity.
 
figb1.png

 
System details

Membranes

Membrane elements:                Two Dow Filmtec NF90-4040
Salt rejection:                         99.2% (99.0% minimum)
Configuration:                         Spiral wound
Polymer:                                Composite polyamide
Total membrane active area:     15.8 m2

HP feed pump

Pump model:                      Grundfos SQFlex 1.2-2
Maximum current:               8.4 A
Supply voltage:                  30-300 VDC, PE
                                       1 x 90-240 V -10%/+6%, 50/60 Hz, PE
Maximum flow rate:             1.4 m3/hour
Maximum pressure head:      120 m

Renewable energy system

Maximum power:                 4 kWp (15 x 280W)
Battery capacity:               12 rechargeable batteries, 2V 750 Ah
Control unit:                      2.1 kWh inverter to provide constant V to the pump
MPPT:                              TriStar MPPT 60 Amp
 
Table B1 shows the flows and pressures measured in the pilot desalination unit between November 2010 and February 2011. During this period, the NF pilot desalination unit has achieved the objectives and exceeded the expectations for faultless operation, permeate production and energy consumption. The NF pilot has been in operation for 24 h/d over the whole period and without any interruption due to defective operation.
 
Table 8. Operation parameters of NF desalination unit between November and February
 
Date
 
Flows
 
 
Pressures
 
Permeate
Recycle
Brine
Blending
Feed
Before NF
Brine
 
L/h
L/h
L/h
L/h
bar
bar
bar
29/11/10
270
900
200
25
2.0
4.2
4.0
2/12/10
280
900
200
25
2.2
4.3
4.0
6/12/10
270
800
200
25
2.0
4.4
4.1
9/12/10
280
900
200
25
2.3
4.2
4.2
12/12/10
260
1000
200
25
2.0
4.3
4.1
16/12/10
260
900
200
25
1.8
4.3
3.9
20/12/10
270
800
200
25
1.8
4.2
4.1
24/12/10
270
800
220
25
1.5
4.3
4.1
27/12/10
270
800
200
25
1.8
4.2
4.0
30/12/10
260
900
220
25
1.6
4.3
4.2
3/1/11
270
900
200
25
1.7
4.2
4.0
5/1/11
270
900
200
25
1.6
4.2
4.0
10/1/11
270
900
220
50
1.7
4.3
4.3
13/1/11
280
1000
220
50
1.8
4.4
4.2
17/1/11
270
900
200
50
1.8
4.3
4.2
20/1/11
260
900
200
50
1.7
4.2
4.2
24/1/11
270
1000
220
50
1.6
4.4
4
27/1/11
280
900
220
50
1.8
4.3
4.1
31/1/11
260
900
210
50
1.7
4.3
4.2
3/2/11
280
800
200
50
1.6
4.4
4.1
7/2/11
270
900
220
50
1.8
4.2
4.1
10/2/11
280
800
200
50
2.0
4.3
4.2
14/2/11
280
900
220
50
1.7
4.4
4.1
17/2/11
270
900
220
50
1.8
4.2
3.9
21/2/11
280
800
200
50
1.6
4.3
4.0
24/2/11
280
900
220
50
1.7
4.3
3.9
28/2/11
270
900
220
50
1.7
4.2
4.1
 
The NF pilot consistently produced a permeate flow of 271 L/h (± 7 L/h) during the period of observation, corresponding to a daily production of 6.5 m3. This is notably higher than what expected when the system was installed (5 m3/d) and mainly due to a higher feed inflow (480 L/h). To ensure smooth operation of the NF membranes, the recovery rate was maintained at a conservative level (57%). Chemicals to prevent scaling for pH control were nevertheless continuously added. Due to the higher feed flow and conservative recovery rate, the brine flow was higher than in the design scheme (209±10 L/h ). The operating pressure of the NF membranes was stable in the range 4.2-4.4 bar and did not show any increase over the period of operation. The blending flow was initially set at 25 L/h and subsequently raised to 50 L/h on January 19 in order to increase the concentration of micronutrients (Ca2+ and Mg2+) in the permeate flow. The specific energy consumption of the pilot plant was 1.37±0.02 kWh/m3. The pilot desalination plant worked with grid electricity during this period of operation.
 
Samples of feed water, permeate, and brine were collected on a weekly basis and analyzed in the laboratories of the Ben-Gurion University of the Negev for the concentration of the ions of principal interest to this study (Ca2+, Mg2+, SO42-, Cl-, HCO3-), pH and electro-conductivity (EC). In addition to these measurements, the concentration of K+ and NO3- was measured on a non-regular basis. Table B2-B4 show the results of the chemical analyses.
 
 
Table 9. Chemical composition of feed water between November and March
 
 
Ca2+
Mg2+
SO42-
Cl-
HCO3-
K+
NO3-
 
ppm
ppm
ppm
ppm
ppm
ppm
ppm
29/11/10
190
90
560
350
235
 
 
6/12/10
185
90
555
320
215
 
 
12/12/10
185
90
560
330
215
 
 
19/12/10
185
90
560
325
215
 
 
27/12/10
170
82
409
277
254
9.6
 
6/1/11
208
95
526
331
245
10.3
 
16/1/11
215
100
547
376
230
10.6
33.8
30/1/11
170
81
490
321
232
 
 
7/2/11
186
91
513
427
280
 
 
13/2/11
165
78
487
302
250
 
 
27/2/11
162
85
550
360
215
 
 
6/3/11
151
79
516
360
210
 
 
Average
181
88
523
340
233
10.2
33.8
 
 
Table 10. Chemical composition of permeate between November and March
 
 
Ca2+
Mg2+
SO42-
Cl-
HCO3-
K+
NO3-
 
ppm
ppm
ppm
ppm
ppm
ppm
ppm
29/11/10
28
14
85
120
52
 
 
6/12/10
25
13
80
110
45
 
 
12/12/10
27
14
85
115
46
 
 
19/12/10
26
14
80
115
47
 
 
27/12/10
17
8
35
78
37
3.2
 
6/1/11
21
9
43
93
41
3.8
 
16/1/11
20
9
43
93
35
3.3
20.1
30/1/11
44
21
120
126
75
 
 
7/2/11
53
27
146
162
66
 
 
13/2/11
36
18
110
102
67
 
 
21/2/11
44
21
135
130
72
 
 
27/2/11
50
27
172
164
77
 
 
6/3/11
43
24
150
154
73
 
 
Average
33
17
99
120
56
3.4
20.1
 
Table 11. Chemical composition of brine between November and March
 
 
Ca2+
Mg2+
SO42-
Cl-
HCO3-
K+
NO3-
 
ppm
ppm
ppm
ppm
ppm
ppm
ppm
6/12/10
430
210
1290
780
490
 
 
12/12/10
455
215
1320
810
495
 
 
19/12/10
460
220
1360
780
525
 
 
27/12/10
410
193
1054
619
532
20.4
 
6/1/11
425
200
1110
654
493
19.1
 
16/1/11
498
230
1347
778
524
20.1
49.1
30/1/11
426
203
1220
714
546
 
 
7/2/11
462
231
1280
860
450
 
 
13/2/11
400
192
1216
622
567
 
 
27/2/11
390
208
1420
760
486
 
 
6/3/11
384
208
1330
780
500
 
 
Average
431
210
1268
742
510
19.9
49.1
 
The chemical analyses of the feed water show that little variation occurred during the period of observation in the inflow concentrations of the monitored ions with the exception of Ca2+, which shows a decreasing trend from the first measurement in November (190 ppm) to the latest measurement in March (151 ppm) that is statistically significant at the 10% level (p­value = 0.07). A corresponding decreasing Ca2+ concentration is observed in the brine.
 
The desalination unit has performed according to model forecasts regarding the removal of the monitored ions. Retention of Cl- ranged between 54% (February 27) and 75% (January 16), corresponding to an average Cl- concentration in the permeate of 120±26 ppm. With the initial blending flow set at 25 L/h, the concentrations of Ca2+ and Mg2+ in the permeate were, respectively, 23 ppm and 12 ppm, values which are lower than the recommended minimum concentration of these nutrients for agricultural use. Consequently the blending flow was increased on January 19 to 50 L/h, raising the average concentration of Ca2+ and Mg2+ in the permeate to 45 ppm and 23 ppm, respectively. Such values are well within or even above the recommended range of concentrations (32-48 ppm for Ca2+; 12-18 ppm for Mg2+). The concentration of SO42- was well above the minimum recommended value of 30 ppm during the whole period.
 
The EC of the feed water shows little variation over the whole period, averaging 2.32 dS/m (±0.15 dS/m) and with no trend towards increase or decrease over time. Similarly, the EC of the brine is relatively constant at 4.73 dS/m (±0.25 dS/m) as it is unaffected by the change in the blending rate on January 19. The EC of the permeate flow averaged 0.71 dS/m (±0.18 dS/m) over the whole period of measurements. Before the increase in blending flow, the average EC of the permeate is 0.58 dS/m (±0.09 dS/m); after January 19 the average EC increases to 0.86 dS/m (±0.12 dS/m), a value that is satisfactory since it is still within the range tolerated by the most salt-sensitive crops.