Nanomembranes - Nanotechnologies for Water Environment Applications - page 389

technologies such as activated sludge systems and secondary clarifier and also as a
pretreatment for RO (Figure 12.12). This endeavor is pursued with the aim of
developing a more compact treatment system while achieving better and more consistent
effluent quality.

Primary
sedimentation

Domestic sewage

MBR
(either using
MF/UF/NF)

Reverse osmosis

Replacing secondary treatment and biofiltration/
MF/UF

UV disinfection

Reclaimed water

Figure 12.12 Domestic sewage treatment and reclamation using MBR-RO system.

An Integrated Membrane Process (IMP) consisted of an MBR (equipped with a
0.4 μm flat sheet membrane) and an RO was shown to be effective for degrading slow-
and hard-to-degrade organic constituents present in the RO concentrate that was
recycled back to the MBR (Lew et al., 2005). Consistent quality of product water for
high value reuse applications was demonstrated in the pilot-scale MBR-RO system
operated at the Bedok Water Reclamation Plant, Singapore (Qin et al., 2006). Better
removal was achieved in terms of total organic carbon (TOC) and nitrogenous
compounds (NH 4 -N and NO 3 ) due to the biological degradation and longer sludge
retention time in the MBR, which provided more efficient nitrogen removal compared
with the conventional secondary treatment process (Table 12.8).

Recently, increased number of R&D on nanomembranes for water reclamation
has been documented. Nanomembranes have the advantage in reducing dissolved
organic matters with molecular weight greater than 200 Da. In a study conducted by
Choi et al. (2007) using NF MBR for water reclamation from domestic sewage, the
polyamide NF membrane was reported to achieve 0.5 to 2.0 mg/L TOC in the permeate
as compared with an average of 5 mg/L for the permeate from MF MBR (Qin et al.,
2006). That is, NF membrane is able to provide better organic matter retention compared