The waster water treatment plant in Tunis
In such applications, drive units are often subject to extreme environmental conditions, and must be designed accordingly. But in addition to climatic conditions, other factors also play a great role in the choice of the drive technology supplier. The following article explains how the total cost of ownership needs to be taken into account in this case, and how savings in the wrong place can result in considerable additional efforts and expenses.
The waster water treatment plant in Tunis, which is operated by public enterprise ONAS (Office National de l'Assainissement), has eight pools in which mixers powered by two large geared motors ensure steady circulation. Thereby, the waste water is oxygenated, enabling the decomposition of dirt particles through bacteria. The plant supplies Tunis and its metropolitan area with process water, covering the needs of approx. 2.5 million people. It features drive technology that is nearly 30 years old and must be replaced step by step. A robust design is a must for new drive solutions, since the units are installed outdoors and operate non-stop while the temperature fluctuates considerably. In winter, the temperature can drop to -5 °C, while up to 45 °C is possible in summer. Up to now this has frequently affected the lubrication of the originally installed gear units, requiring maintenance to a problematic extent. The goal was therefore to implement lower-maintenance drive solutions which are well-suited for extreme environmental conditions.