Producing the 120 litres of dialysate required for a typical four hour haemodialysis session requires approximately 400 litres of mains water. Reverse osmosis is an important step in the purification process that this water undergoes. Reverse osmosis systems vary in efficiency, but commonly reject up to [two thirds] of the water presented to them. Termed ‘reject water’, this high grade grey water does not come into contact with the patient at any stage and poses no infection risk, yet it is needlessly ‘lost to drain’ in almost all dialysis facilities. Two case studies from East Kent - one in a main dialysis unit and one in a new-build satellite unit, outline a simple methodology for salvaging reject water so that it can be put to an alternative use.
CASE STUDY 1: Canterbury Dialysis Unit
When the Canterbury dialysis unit updated its water purification system with the installation of a new reverse osmosis plant in 1997, it was soon apparent that large volumes of reject water were being ‘lost to drain’. Within two years, and with the help of the hospital’s Estates Department, a simple system capable of recycling 800 litres of this water per hour was installed at a cost of £15,000. The system has now been running for over ten years, saving the Trust £7,500 each year on mains water and sewerage costs.
The salvaged reject water is directed to a recovery tank in the basement. From there it is pumped up to the grey water tank on the roof, which then supplies the water to the hospital toilets.
CASE STUDY 2: Ashford Dialysis Unit
A similar system was included in a new-build satellite dialysis unit in Ashford, where the conserved water feeds into the local laundry room. Because water recovery was designed in from the start, the costs were much lower: just £2500.
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