1080th General Monthly Meeting
Challenge in the Provision of Drinking Water for Cities;
Risk Management and Clever Science
Engineering Aspects (Mr Colin Nicholson)
Challenges to Diagnostic Technologies (Dr Peter Cox)
Australian Water Technologies
Date: May 5th, 1999
ABSTRACT
Challenges to Diagnostic Technologies (Dr Peter Cox)
Currently we monitor the microorganisms in drinking water largely by culturing Escherichia coliand its close relatives. This test has the advantages of testing for live microorganisms, being quantitative and taking advantage of the rapid replication of these bacteria in overnight culture to be very sensitive. New technologies such as Polymerase Chain Reaction offer the hope of rapid detection of mircoorganisms in less than a day. However, in practice they have been affected by inhibitors in the sample or by being prone to false positive tests (often described as too "sensitive"). As we have seen recently, too, it is not enough mearly to count microbes in water. Ultimately we have to know whether microbes in drinking water correlate with illness in the consumer. This requires close liason with the Health Department officials. We then have to develop tests that selectively identify microbes that are alive and likely to cause illness in consumers. In many cases tests are not yet available to tell this. In these cases do we still want to know if they are there? Does the consumer?
Water - What's in it for us ?
A report on addresses presented to the 1080th General Monthly Meeting of the Societyby Dr Edmund Potter
When the number of chemical elements passed 100 and their isotopes exceeded 2,500, I warmed to the far-off days of just four elements, only two of which (air and water) were really vital anyway. Not surprising then that, when the 1080th General Monthly Meeting of the Society on 5th May 1999 offered two speakers addressing "Challenge in the Provision of Drinking Water for Cities", I was in my element.
Immediate Past-President Dr.D.J.O'Connor was in the Chair and introduced the first speaker, microbiologist Dr. Peter Cox (Australian Water Technologies, owned by Sydney Water Corporation). He explained five broad steps in the detection of water-borne microbes in terms relevant to human health: sample, enrich, separate, identify and enumerate, and confirm. The testing seeks three features: indicators of recent faecal contamination such as E. coli, indicators of pathogens (disease-causing bugs), and identification of the pathogens themselves, examples being viruses (0.05-0.1 um), bacteria (0.5-1.5 um), parasitic protozoa, plus giardia (5-8 um).
Acceptance criteria for any new technology (including control) are tough to satisfy but must include details of: accuracy and limit of detection or effectiveness, reliability, predictive value, and cost (it is cheaper to indicate than to observe pathogens). Quality Assurance for potable water implies: identification of contamination sources, application of preventative measures, followed by monitoring, validation, and verification of consequent effects.
The second speaker, Mr. Colin Nicholson (Manager, Operational Services, Sydney Water) reviewed the past and current water-treatment practices for the Sydney region and referred to possible future developments.
Sydney's first water supply (1788) was the Tank stream, then Busby's Bore, and Botany swamps. In modern times water has been stored in large dams, initially the Southern Dams (Cataract, Nepean, etc.), supplemented later by Warragamba and the Shoalhaven scheme. In addition there are now 11 water filtration/treatment plants and 20,000 km of pipeline to conduct the product to us consumers, who currently draw an average of 410 L/d each. The main treatment is based on ferric chloride addition, which instantly produces a ferric hydroxide floc that envelops raw-water turbidity. The clear water is decanted from the floc, further clarified by sand filtration, disinfected with chlorine, and fluoridated. If necessary chemical additions are made to control black manganese deposits or serious corrosion of brass fittings.
Long-term concerns regarding drinking water quality include giardia (destroyed by chlorine), cryptosporidium (resistant to chlorine), other protozoa, viruses, algae, and disinfection residues (chlorinated organics). Future controls for these problems could include replacement of chlorine by ozone and ultraviolet radiation, and various degrees of membrane filtration (even down to 10-9 um particles). The introduction of such measures must await consideration of suitability and costs, and public awareness of related issues such as the acceptance and provision of water re-use and industrial-quality water.
After some searching questions were admirably handled by both speakers, Dr E.C.Potter proposed the vote of thanks, which was keenly supported.