Presentation Overview • Water quality requirement of draft AS/NZS 4187 • Issues and concerns in a poorly designed water treatment plant • Design to achieve compliance
Biofilm • Microorganisms in fluid colonise surfaces results in biofilm formation even when levels of microbial contamination are low. • Microorganisms living within biofilms produce a slime matrix which protects them against disinfection. Therefore all strategies for microbial control of the water treatment system should be proactive in order to limit microbial growth and biofilm formation (biofouling). • In order to control the formation of biofilm within a water treatment system, disinfection procedure should be applied from the start of the operation. • Once formed biofilm is difficult, if not impossible, to eradicate.
Endotoxin “Endotoxin” is a toxin that is released from the cell surface of Gram-negative bacteria either through its growth and cell division (small amounts) or on the cell's death (large quantities). Chemical disinfection, steam sterilization or hot water sanitisation of equipment, which are contaminated with Gram-negative bacteria, will generate endotoxins. Endotoxins when introduced into human body, can cause a fever-like reaction and other adverse effects. They are not readily inactivated by chemicals. They are extremely heat stable, remaining viable even after conventional autoclaving, and have been shown to require a temperature of 180°C for at least 3 h or 250°C for 30 min to be destroyed.
Endotoxin Continue… A paper by I. P. Lipscomb et al, ‘Comparative Study of Surgical Instruments from Sterile-Service Departments for Presence of Residual Gram Negative Endotoxin and Proteinaceous Deposits’ published in the Journal of Clinical Microbiology (2006), 44 states: In studies of patients admitted to a general hospital in UK, 17.6% displayed bacteremic episodes, with the most prevalent being caused by Escherichia coli, Klebsiellapneumoniae, Enterobacter, and Salmonella. These gram-negative bacteria have lipopolysaccharide molecules or endotoxin on their cell surface, which has been associated with systemic inflammatory infections, such as sepsis.
Issues and concerns of a poorly designed water treatment plant (Bio-Film in Plastic Pipe Work) (“Dam” Type Endotoxin Filter) (Heat Build Up) (Dead Leg Between RO & Tank) (Poorly Designed Plastic Tank) D. Distribution System B. RO Unit A. Pre-treatment C. Storage Tank 10 10
Biofilm Formation Testing Study Methodology The number of colony-forming units (CFU/m2) were determined and the piping was examined under a scanning electron microscopy (SEM) in order to visualise potential biofilm residues on the pipe internal surface. At 3 water treatment systems with hygienically designed RO unit, treated water distribution loop piping with PE-Xa with hot water sanitisation (HWS) were used. Results were recorded after: HWS once per week HWS twice per week HWS 3 times per week One (1) water treatment system with hygienically designed RO unit, treated water distribution loop piping with PE-Xa without hot water sanitisation. 12
SEM Results No disinfection 1 x HWS / week 2 x HWS / week 3 x HWS / week 14
Compliance Testing at Two Hospitals in QLD Study Methodology Water treatment systems at two different hospitals in Queensland were tested for compliance: Case Study 1 – Hospital with a industrial water treatment plant (included RO, off the shelf 1,000 l tank with a lid, pump and ringmain) which was not designed for bacterial control Case Study 2 – Hospital with a purpose built water treatment plant to meet EN15883 compliance
Results – Case Study 1 * - Maximum permitted values for final rinse
Results – Case Study 2 * - Maximum permitted values for final rinse
Conclusion – Design of RO unit to meet compliance Stage by stage removal of impurities
Conclusion – Design of RO unit to meet compliance It should be emphasised that if the rinsewater systems (i.e. RO system) is not designed adequately for the control of bacteria (with a minimum ringmain velocity, minimum dead leg for bacteria / biofilm growth) and is not regularly disinfected and validated (i.e. Water samples should be routinely taken to demonstrate compliance), meeting the draft AS/NZS 4187 microbial specification is a “hit and miss”. Instead, the proliferation of bacteria is not uncommon in a poorly designed and maintained water treatment and distribution system. The system has to be designed to be simple and easily sanitised (chemically or using heat) by the CSSD manager when or if required. This is critical as there might be times when a unexpected high microbial count is found in the town water supply (can occur in an event of a natural disaster such as floods), the CSSD manager should be able to carry out the sanitisation process to resolve this (without relying on the equipment supplier). 21
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