Urban wastewater treatment in Europe: from operational problems to plant design

Purpose - The paper seeks to review some of the main operational problems of wastewater treatment plants designed for nutrient removal. It aims to pay particular attention to bulking and foaming due to massive growth of filamentous organisms, failure or non-optimal operation of secondary settling tanks, and compliance with more stringent effluent requirements. Design/methodology/approach - The discussion of the major operational problems is based on a thorough review of the available literature and own experiences with more than 80 wastewater treatment plants. Findings - To suppress the undesirable growth of filamentous organisms and to achieve an all-year round stable operation of secondary settling tanks several design options for improvement have been developed based on the experience gained so far. The most desirable option for improving the operation of a single treatment plant is to a large extent site specific. Beside adopting the design procedures also operational measures are possible. Practical implications - The paper recommends several practical options for optimising the performance of wastewater treatment plants with regard to the aforementioned problems. These recommendations are based on proved practical experience and, therefore, may act as a flexible toolbox for an individually tailored design or operation of the plant in order to avoid and/or combat the problems during operation. Originality/value - The described options for improvement the operation are based on long lasting practical experience with large scale wastewater treatment plants. They can be used by any operator of such plants for solving some of the major problems of modern wastewater treatment plants.