Existing Assets: To Be or Not To Be

Model-assisted design of wastewater treatment systems has grown substantially in the past three decades. Modelling technology has enabled more comprehensive understanding of unit process interactions and more efficient designs. In addition, with the development of increased computational power and model-based analytical tools, the possibility exists to use models to address the concepts of design uncertainty and risk assessment (Belia et al., 2009; Belia et al., 2011). This paper addresses two recent design projects in which original comprehensive demolition and reconstruction designs were reconsidered and eventually altered in favour of smaller high rate processes coupled to existing assets. The risk-based design approach and this change in thinking has resulted in projected capital savings of 20 million pounds.