High recovery reverse osmosis

Situations in which the high costs of disposal of reverse osmosis brines might tilt the economic balance in favour of the costs of increasing the units water recovery rate and paying for whatever additional chemical engineering was required to permit such raising, are surveyed. The calculations start from the premise that the volume of brine to be conveyed, treated and disposed of at an 80 per cent recovery rate was double that at 90 per cent. Pre- and post-treatments that might be needed and which would be dictated by the composition of the groundwater feed, to avoid membrane scaling and injection well plugging include softening, sulphate removal and brine concentration. No attempt was made to cost these options, as they were site-specific.