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

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