The economic and ecological arguments for water conservation in renal units are undeniable, and thankfully there are now options for addressing it in every situation.
Dialysis facilities are hospitals’ biggest consumers of water, and any wastage is costly both to healthcare budgets and to the environment. As well as increasing bills, excessive consumption exacerbates water scarcity problems which affect natural habitats and people’s quality of life. A related issue is that inefficiencies in water use mean more energy is required by utility companies, to treat and supply extra volumes, and carbon emissions are raised accordingly. The energy efficiency of hospitals’ own water purification systems also needs to be considered.
Reverse osmosis (RO) is a key element of water purification for dialysis. A RO unit’s filter blocks the passage of dissolved substances, while allowing a percentage of the water to pass through as purified dialysate. The rest of the water, which now has a higher concentration of minerals, is rejected. Without a water recovery system, it simply ‘runs to drain’. Some set-ups waste up to two thirds of their input water in this way, and this may go on for 16 hours a day or even 24/7.
There are two main alternatives for recovering that water: re-using it for some other purpose; or re-treating and recirculating it through the purification system.
Re-use for a different purpose
The term ‘grey water’ is often used for water which is no longer of drinking quality but is still suitable for other uses. The ‘concentrate’ rejected by a RO unit falls into this category. Importantly, it has not been in contact with the patient and, despite its higher dissolved content, it can be considered clean. It requires only minimal treatment, in the form of UV radiation and/or chlorination for bacterial control.
Grey water may be used, for instance, in flushing toilets, laundry, cooling equipment or for watering garden areas. For this to be feasible, the hospital must have a use for the quantities that will be produced. If it does, the payback through lower water bills will be quick. There must be enough space in the facility for a collection tank, pipework and pumps, and installation of these will cost less if they are incorporated into a new building design rather than retrofitted.
Recirculation of concentrate
In this type of system there is no need for a tank as the concentrate is continuously recirculated via a ring main. After passing through a second RO unit, the re-treated concentrate is returned to the front end of the purification set-up.
In up to date ROs, water recovery rates are typically around 70% – leaving just 30% to run to drain. The most high-tech systems have additional water-saving and energy-efficient features which boost recovery to 85-90% and further reduce electricity bills. Advanced technology inevitably comes at a higher price, but a straightforward calculation can determine whether its return on investment will be fast enough to justify itself.
Specifications vary according to needs and budgets. At the top end, there are solutions that offer four-way-acting recovery. In addition to concentrate recirculation and re-treatment, as described, the intelligent technology of these systems respond to changes in dialysate demand, conductivity and temperature.
Variable-speed pumps save water and energy by adjusting flow rates according to dialysate needs. If less dialysate is required, they slow down production and send less water to drain. If no dialysate is being used, they shut the system down and no water goes to drain.
When water is being recirculated, but little dialysate is being drawn off, the concentrate’s dissolved content increases. This is detected by monitoring its conductivity. In response, the RO slowly opens its drain valves so some of the concentrate can be ejected and replaced by fresh water to restore an acceptable dissolved content level. Recirculation can also add unwanted heat energy to the concentrate, so the RO monitors temperature and again uses controlled drain valve opening to adjust as necessary.