Nanomembranes - Nanotechnologies for Water Environment Applications - page 387

Generally, secondary treated effluent is subjected to advance treatment
consisting of biofiltration, MF or UF, RO and UV disinfection before it is directed for
reuse. The flow chart of a typical treatment system for domestic sewage reclamation is
illustrated in Figure 12.10. Development in membrane technology has also reduced the
cost of water reclamation in recent years. This observation has been clearly
demonstrated in the case of NEWater production. The cost including production,
transmission and distribution was reduced by approximately 12% from the original
S$1.30 per cubic meter in 2003 to S$1.15 per cubic meter in 2005 and further another
13% to S$1.00 per cubic meter in April 2007 (PUB, 2007a).
Table 12.7 Cost of reclaim water in different cities and the intended use.
Cities Costs (USD/m 3 )

Intended Use

Riqqa, Kuwait 1 0.07 Non-potable reuse-supply to farm

Non-potable reuse - i.e., watering
golf course, street landscaping.

Tucson, Arizona, USA 2 0.46

Potable water for recharge into
reservoir

Singapore 3 0.66

Potable water quality for
groundwater quality

Sulaibiyah, Kuwait 1 1.2

1 Dotson (2007). 2 Asano et al. (2007). 3 PUB (2007a).

The cost of reclaimed water is also dependent on the degree of treatment and the
required water quality for its intended use. Table 12.7 provides a comparison on the cost
of reclaim water and the usage. It is clearly noted that reclamation to potable water
quality would require a higher production cost. The cost of non-potable reuse of
reclaimed water in Tucson, Arizona, by treating secondary effluent using filtration and
through recharge and recovery is only slightly lower than the cost required for
production of NEWater (suitable for in-direct potable reuse) in Singapore which utilizes
membrane technology and UV disinfection. Hence, membrane technology has provided
a cost-effective mean in producing high quality reclaimed water.

Pretreatment technologies prior to RO prove to be important in maintaining
better effluent quality and reduction of the cost, energy consumption and fouling
potential. Different methods of pretreatment have been tested and applied. Among them
are biofilters, MF, UF and NF. Figure 12.11 shows the MF and RO systems used at the
Ulu Pandan NEWater Plant, Singapore (courtesy of Keppel Seghers Engineering
Singapore Pte Ltd). The main problem commonly encountered in reclamation of
domestic sewage is biofouling, especially in the RO membranes which eventually
reduces the flux and increases the required frequency for membrane cleaning.