Nanomembranes - Nanotechnologies for Water Environment Applications - page 388

Biofiltration has been used for decades prior to the application of membrane for
domestic sewage reclamation. The quality produced is generally sufficient to meet the
requirement for non-potable reuse. Further treatment of biofiltration effluent could
produce high quality reuse water. Biofiltration columns that acted as a pretreatment
process prior to a lab-scale RO system with an empty bed contact time of 30 minutes
was able to prolong the RO operation time by 5 times compared with the corresponding
system where no biofilters were used (Hu et al., 2005).
Figure 12.11 MF (left) and RO (right) membrane systems used at the Ulu Pandan
NEWater Plant, Singapore (Photo courtesy of Keppel Seghers Engineering Singapore).
The introduction of membrane processes to water reclamation has provided a
breakthrough both in terms of quality of the product and production rates. The use of a
0.2 μm polypropylene hollow fiber MF membrane and a patented compressed air
backwash system tested at Water Factory 21, Orange County, California was able to
produce 5 times more product water and with 42% lower operating and maintenance
cost as compared with the system using the lime pretreatment method (Guendert, 2003).
With the advancement in technology, suitable type of pre-treatment membranes could be
developed to achieve a high organic matter rejection efficiency in order to reduce the
fouling rate on RO membrane while sustaining a high operating flux. Many studies have
investigated the potential of submerged membrane bioreactors (MBR) incorporating
MF/UF/NF membranes to replace the conventional domestic sewage treatment