Environmental Engineering Reference
In-Depth Information
The membrane material for treatment of textile effluent would need to be
carefully selected as color dyes tend to absorb onto most of the membrane materials. The
polyamide material in NF-70 membrane can be colored by most dyes present in the
textile effluent, and this had led to severe fouling and declination of flux during
operation. The new type of membranes developed by Akbari et al. (2007) has provided
an alternative to membrane selection for treating textile effluent. Through UV-grafting
using sodium p -styrene sulfonate (NaSS) as a vinyl monomer, Akbari et al. (2007)
developed two new hollow fiber (negatively charged) NF membranes, 1AG and 2AG,
with molecular weight cut off of 4600 and 2000 Da, respectively. The average
permeability of 1AG and 2AG were 15 and 4 l/m 2 ·Pa, respectively. Four types of dyes
along with their respective characteristics and the retentions at 3 bars are summarized in
Table 12.13 (extracted from Akbari et al., 2007).
Table 12.13 Characteristics of the dyes and the respective retentions at 3 bars by hollow
fiber NF membrane (extracted from Akbari et al., 2007).
Retention
Dye
Symbol
MW (Da)
Charge
1AG
2AG
Acid Orange
AO10
452
-2
96.4
98.0
Direct Red 80
DR80
1373
-6
99.6
-
Direct Yellow 8
DY8
518
-1
99.8
-
Reactive Orange 16
RO16
617
-1
94.0
-
The sieving mechanism has played an important role in the retention of the dyes.
This is clearly noted by the high retention (99.6%) of DR80 which has the highest
molecular weight among the dyes tested. Ionic exclusion mechanism is more prominent
than the sieving mechanisms in causing the difference in retention between AO10 and
DY8, and DR80. DY8 with a molecular weight of 518 Da has a very high retention
despite a molecular weight lower than DR80, which could be due to the retention of
colloids formed (which would absorb most of the soluble dyes) in the present of salts
(NaCl and MgSO 4 ). The flux of 1AG operating at 2 bars decreased by about 10% within
the first 9 hours and remained constant thereafter, while the dye retention (DR80) was
more than 97%. The stabilized flux was at approximately 34 l/m 2 ·h. This is twice the
flux reported by Fersi et al. (2005) using the NF 270 polyamide membrane to treat
biologically treated effluent of the textile wastewater. This work has made one step
forward in the development of NF membranes for reclamation and reuse of textile
effluents.
12.4 Nanomembranes in Seawater Desalination
 
 
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