Anna Kieniewicz
TRITA LWR Master Thesis 06:08
VRF:
35
2
5
10 2030
1000
30
800
NO3 -N (mg/l)
flux (l/hm2)
25 20 15 10
400 200
5 0
Theoretical NO3-N Actual NO3 -N
0
0
20
40
60
80
100
0
water recovery rate (%)
300 250 200 150 100 Theoretical PO4-P Actual PO4-P
0 5
10
15
20
VRF
25
15
20
25
30
35
(Fig. 30) probably due to precipitation of different phosphate compounds. During the test the nitrate nitrogen separation did not act in the same manner as indicated by theory. Consequently, lower than expected concentrations of NO3-N were found in the concentrate stream (Fig.31) The phosphorous limit was already reached at VRF=10 in the permeate stream, while in the mixed permeate the phosphorous and nitrogen concentration were still below 0.15mg/l and 6 mg/l, respectively. During the experiment phosphorous reduction came to 99.9% and for nitrogen (NO3-N+NH4-N) it was equal to 99.3%. After the test, the membrane chemical cleaning procedure (pH=11) was carried out. During the water test the permeate flow raised to 90l/h. The salt reduction remained at the same level as before the experiment (99%). Test 4, line 2 The aim of the fourth test was to examine if it is possible to further concentrate the feed water from line 2 (up to VRF=50) and at the same time receive the required permeate quality. Like in previous tests the water flux was gradually declining due to the increasing salt content in the feed tank during the concentration process (Fig.32). The estimated average flux in the experiment was marginally lower than during the previous tests. The samples from the concentrate stream, permeate stream and the tank with mixed permeate were taken only at VRF=20 and 50 during the last test. The analyses of phosphate phosphorous and nitrate nitrogen showed a difference between the actual concentrations in the concentrate stream and the theoretical ones. The biggest variation was noticed at VRF=50, where 67% and 69% of the theoretical phosphate phosphorous and nitrate nitrogen concentrations respectively were found in the residual stream.
350
0
10
Fig. 31 NO3-N concentration in the concentrate stream vs. VRF, test 3, line 2.
400
50
5
VRF
Fig. 29 Permeate flux vs. recovery rate, test 3, line 2.
PO4-P (mg/l)
600
30
35
Fig. 30 PO4-P concentration in the concentrate stream vs. VRF, test 3, line 2.
The concentration of phosphorous and nitrogen in both permeate stream and mixed permeate was below set limits even at VRF=30. The reduction efficiency amounted to 99.9% for phosphorous and 99.5% for nitrogen (NO3-N+NH4-N). After the experiment the membrane was cleaned with acid chemicals (pH=2). During the water test permeate flow increased from 84 to 86l/h. The salt reduction was estimated to 99%. Test 3, line 2 The third test was executed in order to verify the results obtained in the previous experiment. During the concentration process a slightly better flux was noticed at each volume reduction step, with the average flux higher than 29 l/m2h (Fig.29). As in the second experiment, the phosphate phosphorous concentration in the concentrate stream at VRF=20 and 30 were lower than the theoretical
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