Abstract
The Beirut, Lebanon, Water Treatment Plant is of conventional design, and processes between 147,000 and 190,000 cu m of water per day. Algae grow abundantly in the various treatment units of the plant, particularly during spring and summer. Algae in the water entering the plant and algae growing within the plant cause severe management and operational difficulties. A study was conducted to determine the dose of chlorine lethal to the algae which were causing operational difficulties. In laboratory experiments, a single dose of 1.8 mg/l of chlorine was sufficient to kill all the algal taxa growing in the plant. If the chlorine dose was regenerated to the original concentration every 24 hours, then a dose of 1.2 mg/l was sufficient. In field studies, continuous dosing of chloride to maintain a residual chlorine level of 0.8 mg/l was found lethal to the algal taxa. Prechlorination is therefore recommended as an effective method for the control of algal growth in conventional water treatment plants in the tropics. (Moore-IVI)