OsomoTech proposed the use of reverse osmosis to treat the DNS effluent in Jan 98. At the time they did not supply equipment with sufficient capacity to deal with the 165t effluent produced daily. They go on to say that a 70t set-up would cost £495K including installation. Assuming a 165t set up would cost double, this would cost £990K. Osomotech advice using membrane modules at a cost of £3800 that have an unknown working life and may need changing frequently. Sodium Sulphate may also cause problems with the membranes resulting in appriciable downtime.
In terms of colour reduction, reverse osmosis is efficient and meets the EA quota but in terms of COD it does not meet the guidlines (report uses conc factor vol/vol 1, 2 and 5.9). This may be improved by using a lower conc factor.