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Content archived on 2024-04-19

The demonstration of membrane technology for the recovery & reuse of industrial waste cooling water


Work has been done to demonstrate at both pilot scale and at a prototype scale, the technical feasibility and economic advantages from the utilisation of reverse osmosis membrane technology for the reduction of water usage in closed circuit cooling towers systems.

For potable water the pretreatment requirements were relatively simple and can be met using sand filtration/cartridge filtration for the suspended solids, and softening/antiscalant/acid addition. The silt density index SDI of cooling tower purge water was very much higher than feed water. The pretreatment requirements for purge water were more complex and more costly. Coagulation and microfiltration can be used to reduce the SDI to below 5 as required. As with potable supply the hardness can be dealt with by the same methods.
With respect to membranes, separem clements performed successfully with cooling tower water over a range of conditions and were cleaned successfully after being fouled with feed water and purge water. There was a trade off to be made between pretreatment complexity, cleaning frequency and membrane operating conditions.
It is important to assess the variability in load and cooling tower composition when selecting viable cooling towers for water recovery using reverse osmosis. Voluntary and involuntary losses must be identified from the cooling tower when assessing the impact of reverse osmosis. One must keep within the specified parameters for cooling water chemistry, in particular with respect to the minimum level of hardness and alkalinity.
Reverse osmosis on the cooling tower purge water gave the best economic results for all cases studied. Generally, for places where potable water and water disposal combined costs over 1.00 pound sterling m{-3} h{-1} tower evaporation rate, the reverse osmosis technology offers a compound rate of return in excess of 20% per annum.


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Imperial Chemical Industries plc (ICI)
EU contribution
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The Heath
WA7 4QD Runcorn
United Kingdom

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