The good, the bad and the ugly: process modelling for design

Severn Trent Water has considerable experience in process modelling of activated sludge systems. Using three case studies, this paper highlights some of the pitfalls as well as the successes encountered in Severn Trent's modelling history. The three case studies highlighted show when modelling has proven to be a great success; when modelling would have worked had all the relevant information been known and included; and when modelling simply does not appear to be the way forward. Reference is made to Minworth sewage treatment works serving Birmingham, the Milcote biological nutrient removal plant serving Stratford-upon-Avon, and Toton wastewater treatment works serving South West Nottingham. Alpha factors are shown as a key concern when providing suitable information for process design, and the use of pilot work as a means of verifying and backing up model results is also highlighted.