Nanomembranes - Nanotechnologies for Water Environment Applications - page 376

interactions. Fouling can be controlled by altering the operating conditions, chemicals
addition, or by pretreatment like cartridge filtration, coagulation/flocculation, activated
carbon adsorption, etc. Costa and Norberta de Pinho (2006) studied NF of Tagus River
and found that membrane permeation fluxes were 15-19% lower than that of pure water
under the same operating conditions. Permeation fluxes decreased slightly with water
recovery rates (WRR) due to the increase in concentration polarization and reversible
deposition of organic material on the membrane surface.

Mijatovi et al. (2004) conducted pilot tests for NOM removal in treatment of
water from Lake Butoniga near the town of Buzet, Croatia, using NF and different UF
membranes. Since most of the organic matter in the lake water was smaller than 6-8 kD,
they recommended a NF membrane after flocculation and filtration in a trial plant to
avoid fouling of the NF membrane. The process in the trial pilot plant including
ozonation, flocculation and filtration was chosen on the basis of preliminary work with a
capacity of 10 m 3 h -1 . This combination (Figure 12.5) produced water of high quality
while process parameters remained stable over 3 months of investigation. The NF
membrane with low inorganic rejection showed very good removal of NOM with
negligible tendency toward scaling. A NF plant with three permeation stages was
designed to operate at 6 bar and at a WRR of 90%. In summary, the compliance of NF
with surface water requirements appears unproblematic.

Coagulant

H 2 SO 4

B ackwas h Tank

Lake
water

DMF
Filter

Coagulation /
Flocculation / Flotation

Pre-
Ozonation

Slow
Sand
Filter

UF/NF Main Ozonation

Product
Water

Figure 12.5 Scheme of conventional trial plant and membrane technique.