Page 300 - Membranes for Industrial Wastewater Recovery and Re-Use

Case studies 269

water is ultimately produced with a resistivity of 18.2 MQ cmP2. Some 58% of
the high-purity water is reclaimed and recycled to the ultrapure water plant. The
remaining water is sent to the effluent treatment facility with the RO concentrate
and the brine regenerate. Under these conditions 54% of the production flow is
generated from recycled flow.
Included in the reclamation strategy is the utilisation of waste heat through a
heat exchange network. Hot reclaim drains are used to preheat the supply of
high purity DI. This represents a huge energy saving by increasing the cold DI
from 2 5 to 5 5°C and has a dual benefit as it cools the wastewater prior to being
treated in the reclaim plant.
There is a significant financial saving from using reclaim water as 83% of the
treatment cost is associated with bringing raw water on site and then disposing
of it (Table 5.18). The reclaim water costs only 12% that of treating raw water
generating a saving of 20% on the total operating and maintenance budget for
the DI water treatment plant. The main economic decision is concerned with
determining the amount of reclaim water to recycle. Zero reclaim incurs high
operational costs due to raw water price but 100% reclaim incurs excessive
additional up front capital investment. Between the two extremes is an economic
optimum, which depends largely on the utility cost of the local region (Fig. 5.26).
In order for the reclaim percentage to increase the cost curve needs to change
such that the capital cost in relation to the raw water/discharge costs will
decrease. The major barrier to this is the rapid changes that can occur in
microprocessor production which means new chemical pollutant can be
generated which the original plant is incapable of treating.

5.12 Discussion
The case studies featured have not only demonstrated that reuse of industrial
waste water is technically feasible but economically viable. In all cases the
installation of a membrane system for recycling water has resulted in an overall
saving to the company involved. Annual savings have ranged from $102 282 to
$642240 (Table 5.19) and have paid back the initial capital from within 8
months (automotive) to 6 years (power). The most cost-effective of the schemes
has been the automotive plant (internal loop) which generates an annual return

Table 5.18 Water treatment cost breakdown
Raw water Reclaim water

Raw water (%) 67.2 0
Electricity (%) 13.4 9.47
Chemicals (%) 3.2 2.28
Discharge (%) 16.1 0
Total (YO) 100 11.7
Excludes labour and media replacement.