RECYCLING OF RAINWATER FOR COOLING TOWER OPERATIONKatayon Saed and Sathananthan Selvadurai
This project evaluated the feasibility of recycling rainwater as make up water for cooling tower operation. The system, which was installed on the rooftop of one the Ngee Ann Polytechnic's building, is intended to replace the normal city water supply from PUB. In this project rainwater was collected from the roof gutter, subsequently filtered and disinfected and then sent to nearby cooling tower to replace and eliminate the need from city water. A solenoid valve triggered supply of city water in the absence of rain or dry season. A comprehensive monitoring system was implemented whereby rainwater samples in the storage tanks and the cooling tower basin were taken regularly to determine their chemical, biological and physical properties. This is to determine that the rainwater quality would not cause operational problems for the cooling tower system such as corrosion, scaling and breakout of the Legionella bacteria. In general, results showed that values of conductivity, alkalinity, Chloride, silica, standard plate count, Legionella bacteria, total dissolved solids, total suspended solids, phosphate and Aluminum were well within the control limits practiced in Singapore, USA and Hong Kong. However, values of pH, hardness and Iron concentrations didn't comply with the recommended control limits, occasionally. During 3 months of operation and actual installation, results indicated an effective saving of 40% of the water used, in terms of volume, the volume of which did not have to come from city water. As a result of savings in terms of water, energy costs, and deferred capital, the cost of collected roof water was calculated to be S$0.20 per cubic meter.
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