March 07, 2024

What is a CSSD RO?

CSSD (Central Sterile Supply Department) Sterilisation units are used to supply healthcare facilities with water with reduced hardness and bacterial load to be used in sterilisers and washer-disinfectors.

Water quality requirements for the final rinse water for washer-disinfectors and manual disinfection are a pH between 5.5 and 8.0, conductivity below 30 µS/cm, total hardness below 10 ppm, chloride below 10 ppm, silicates below 1 ppm and endotoxin of less than 0.25 EU/ml.

The water quality requirements for steam sterilizers are more stringent than that for washer disinfectors. The pH needs to be between 5 and 7.5, conductivity below 5 µS/cm, total hardness below 2 pm, chlorides below 0.5 ppm and silicates below 1 ppm.

Given the water quality requirements, Reverse Osmosis is generally the main technology used to produce compliant water for CSSDs – hence why CSSD water treatment systems are termed CSSD ROs.


Why Reverse Osmosis?

Given the various species that require removal to achieve compliant water, the best combination of technologies is bulk demineralisation combined with disinfection. Given Reverse Osmosis is the most energy efficient bulk demineralisation process, this is what is used for the first stage of CSSD water treatment. There are two main configurations of Reverse Osmosis used to achieve the water purity for washer disinfectors and steam sterilisers:

  • Two pass Reverse Osmosis
  • Single pass Reverse Osmosis with mixed bed resin polishing

Each technology has its advantages and disadvantages. Two pass Reverse Osmosis requires more power and has a larger physical footprint but readily produces high purity water. Single pass Reverse Osmosis with resin polishing produces a lower volume waste stream but requires resin changeouts when it becomes depleted. Regardless of whether single or two pass Reverse Osmosis is selected, the membrane filtration systems can also be operated in a duplex formation to allow for duty/standby/assist configuration giving the client maximum flexibility.


What additional treatment is required?

Given membrane filtration is the main bulk demineralisation step, a pre-treatment system will in most cases be required to ensure membrane longevity. If chlorinated tap water is used as the feedwater, which is very common for metropolitan hospitals and clinics, then a dechlorination system will be required as well as a softening system as antiscalants cannot be used for CSSD ROs. This protects the membranes from oxidative attack by the chlorine and from scale formation due to multivalent ions in the feedwater. The dechlorination system will usually consist of a granular activated carbon filter which can be setup in lead-lag formation to ensure the membranes are constantly protected from chlorine. Water softeners are generally setup in twin alternating fashion to allow for sufficient time for regeneration of the resin. Multimedia filters are only required in the pre-treatment system if ground or surface water is used in place of tap water and there is a significant level of suspended solids present.

Achieving the required conductivity is only part of creating a compliant water stream. Following demineralisation, the water will be disinfected (usually using UV disinfection) and then heat treated to ensure the ring main temperature is maintained at 65 °C. The UV lamps used for disinfection can either be standard mercury-based lamps or the latest generation UV-LED lamps which have instantaneous warmup and are heavy metal free. UV is preferred to other disinfection methods as it does not require chemicals to operate. Endotoxins, toxins which are released from bacteria when they are destroyed, are removed by endotoxin filters installed downstream of the UV lamps. Washer-disinfectors have an upper limit of endotoxins in the treated water – so regular sampling is required.


Supplying and Monitoring Compliant Water

Following disinfection, the ultrapure water is heat treated and pumped through a ring main to washer-disinfectors and steam sterilisers situated around the hospital. Alongside the hot water ring main, a cold water ring main is increasingly being installed. To ensure constant supply, the hot and cold storage tanks are fitted with non-contact level sensors and are pumped through the ring mains by duty/standby pumps to ensure there is constant supply. Booster pumps can also be included on the front end of the CSSD RO, prior to pre-treatment, if there is insufficient mains pressure available. All pumps can also be fitted as hot swap pumps to allow for easy changeouts during servicing.

To ensure the correct operation of a CSSD RO, the pressures, conductivity, temperatures, pH and flow rates all need to be carefully monitored. Remote monitoring and control can allow offsite engineers to rapidly remedy any issues with the water treatment system. CSSD ROs require continual monitoring and regular maintenance to ensure they continually produce compliant water. Mimic panels and lockout valves can also be installed at the nurses station to allow for additional control and automation.

Moerk Water has extensive experience in the design and construction of CSSD ROs.  Contact Moerk Water to make sure your CSSD water supply is AS4187/AS5369 compliant.