The Ingenieur Vol 57 January-March 2014 The Ingenieur Vol 57 January-March 2014 | Page 46

INGENIEUR with regards to proper maintenance of cooling towers. However, developing countries including Malaysia do not have any such legislation and relies on the designers and operators to be aware of the risk of Legionnaires and to mitigate against it. Nonetheless, local designers and operators are able to refer to the numerous available international codes and guides for cooling towers and hot water systems relating to good practice to mitigate against Legionnaires. Even the Malaysia Standard on Code of Practice on Energy Efficiency for Cooling Towers (expected to be published in early 2014), stipulates the minimum distance apart for cooling tower to any outdoor intake, as well as types of water treatment requirement. In general, the risk from exposure to Legionnaires can be controlled by measures which do not allow the proliferation of Legionella bacteria in the system and reduce exposure to water droplets and aerosol. Precautions include the following; Controlling the release of water spray; Avoidance of water temperatures (25-45°C) and conditions that favour the proliferation of Legionella bacteria and other micro-organisms; Avoidance of water stagnation which may encourage the growth of bio film; Avoidance of the use of materials that harbour bacteria and other micro-organisms, or provide nutrients for microbial growth; Maintenance of the cleanliness of the system and the water in it; Use of water treatment techniques. For cooling towers, apart from traditional chemical treatment, use of non-chemical means of changing water chemistry have gained traction in recent years led no doubt by the sustainability a.k.a. green agenda. These non-chemical means in turn, may be grouped into five basic categories: magnetic, alternating-current (AC) induction, electrostatic, ultrasonic, and mechanical energy (cavitation); and Action to ensure the correct and safe operation and maintenance of the water system. RECOMMENDED CHECKLISTS Monitoring The composition of the make-up of cooling water should be routinely monitored to ensure the continued effectiveness of the treatment programme. The frequency and extent will depend on the operating characteristics of the system; the minimum recommended frequency being once a week to ensure that dosage and bleed rates is correct (see Table A). Table A: On-site Monitoring checks recommended for Good Operating Practice Parameter Timing Make-up water Calcium hardness as mg/l CaCO3 Magnesium hardness as mg/l CaCO3 Total hardness as mg/l CaCO3 Total alkalinity as mg/l CaCO3 Chloride as mg/l Cl Sulphate as mg/l SO4 Conductivity µs (Total dissolved solids) Suspended solids mg/l Inhibitor(s) level mg/l Oxidising biocide mg/l Temperature °C pH Soluble iron as mg/l Fe Total iron as mg/l Fe Concentration factor Microbiological activity Legionella 6 44 VOL 57 JANUARY-MARCH 2014 VOL 55 JUNE 2013 Cooling water Monthly Monthly Monthly Quarterly Monthly Quarterly Monthly Quarterly Quarterly Quarterly Quarterly Quarterly - Monthly Monthly Monthly Quarterly Monthly Quarterly Weekly Quarterly Monthly Weekly Quarterly Weekly Quarterly Quarterly Monthly Weekly Quarterly