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SILICON SILIC CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Mauro Grassi, B.Sc. (Hons), Ph.D Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Kevin Poulter Stan Swan SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Noble Park, Victoria. Distribution: Network Distribution Company. Subscription rates: $94.50 per year in Australia. For overseas rates, see the order form in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. Fax (02) 9939 2648. E-mail: silicon<at>siliconchip.com.au Publisher’s Letter Desalination plants make heavy reliance on technology Back in July 2009, we featured an article on how desalination plants work, with a particular emphasis on the Sydney desal plant at Kurnell. This plant has been working for over a year now and apparently supplies about 1.5 million homes. And while there was opposition to the plant at the time of construction, it was and is a necessary adjunct to Sydney’s water supply, especially as there is no prospect of extra dams being built. The big drawback of desalination is that it is so energy-intensive. It requires a lot of electricity to make fresh water from sea water – about 5kWh per thousand litres. That is one reason why Sydney residents are now paying more for their water. The demand from the desalination plant has also added to the constant load on Sydney’s electricity supplies. However, a growing population requires more fresh water and apart from advocating domestic water tanks for gardening etc, the state government is caught in a dilemma. Recently, there was a report from Sydney Water on E-coli contamination in the output of the Kurnell desalination plant and as you imagine, this caused considerable consternation. Apparently though, the report was erroneous and the NSW state government was quick to negate the impression that the desalinated water was unsafe to drink. Unfortunately, that is not the end of the matter. The only way that the safety of the water can be guaranteed is constant vigilance on the part of the operators of the plant and also Sydney Water which conducts rigorous testing on the whole of Sydney’s water. There are two reasons for such vigilance. The first is that the membranes used for the reverse osmosis process can fail. While ever they are working perfectly, no contamination can get through. But why would the seawater be contaminated? Apparently, there is a sewage outfall some 2.5km to the south of the seawater inlet. So while it is unlikely, it is still possible for ocean currents to move contaminated seawater to the inlet for the plant. How could such a situation have come about? The sewage plant in question serves the population of Sutherland Shire and it discharges relatively small amounts of sewage compared to Sydney’s deep water sewage outfalls at North Head, Bondi and Malabar. As well, the sewage from Cronulla is subject to tertiary treatment compared to the basic primary treatment of the major outfalls. On that basis, the authorities were probably correct in making the judgement that the situation was safe. However, all the circumstances must always be favourable. First, there can be no failures at the Cronulla sewage plant. This is a pretty difficult requirement, especially since heavy storms in the district could overwhelm the plant, as they sometimes do for Sydney’s other plants. Second, ocean currents must not ever carry sewage-contaminated seawater from Cronulla or any of Sydney’s 10 other outfalls to the inlet of the desalination plant. Third, and most vital, Sydney Water must always be rigorous in testing. It all comes down to technology doesn’t it? While it is all working correctly, the water will be OK. But if there are plant failures and human error, those assurances do not apply. No wonder some people resort to bottled water! Leo Simpson ISSN 1030-2662 Recommended and maximum price only. 2  Silicon Chip siliconchip.com.au