Evaluation of the Impact of Return Flows on the Operation of a Wastewater Treatment Plant

A systemic analysis of a wastewater treatment plant quickly reveals that return flows from the sludge treatment line affect the water treatment process. These return flows have a maximum value that is characteristic of a steady state of plant operation and the effects are detectable at several levels. It can, for example, influence the operation of the clarifier indicated by changes in the Sludge Volume Index, induce anaerobiosis in the separation works that stems from excess sludge production or decrease the dewatering of sludges. All these observations lead to the conclusion that the sludge treatment line should be designed that it could take up production overloads. It was also found that it is indispensible to monitor the water treatment line operation step by step in order to detect rapidly any drift of the operating parameters from their normal values.