Drinking Water Quality for the 21 st Century
293
PAC Ammonia CoagulanULIme
I IChlorine
1 ! . --------"----,
PAC
Sludge
CleanveU
1 - - - -..... DISTRIBUTION SYSTEM
Fig. 5. Settled water ozonation with micro- and nano-filtration streams
In the latter configuration, a dual stream operation is shown that permits
switching between a biofiltration train (upper) and a membrane scheme (lower). If
membrane filtration is used for iron and manganese precipitate separation, it is
likely that full disinfection credits would also be granted by the regulatory agency.
The capital cost of membrane facilities is greatly dependent upon the feed-water
quality. However, the cost of membrane filtration facilities is typically greater
than that of pressure granular media filters. UF and MF membrane systems
commercially available in the United States vary greatly in characteristics from
manufacturer to manufacturer. Pilot testing of all available membrane system
types is not practical and would be extremely expensive. As a result, a
preselection of applicable membrane system(s) should be performed prior to
initiating any pilot testing. As many polymeric membranes are sensitive to
oxidants, a membrane resistant to low levels of oxidants such as chlorine,
potassium permanganate, or eventually ozone should be preferably selected.
NF membranes can effect a 90% rejection of alkaline-earth metals without the
same effect on sodium (which is achieved by RO) and can remove a similar
proportion of NOM. For the latter reason, this technology is an effective treatment
for the removal of color as well as DBP precursors material (Chellam et al. 1997).