With the UK water companies under increasing financial and environmental pressures they are having to look for innovative options to provide lower capital and operational cost solutions to asset management in order to maintain profits. Process modelling provides a tool which can be used to help identify more cost effective options through a better understanding of processes and their limitations. Although modelling can be used in this way, sound judgement needs to be applied in using models as misinterpretation of simulated results could lead to the wrong option being selected. Processes which combine fixed and suspended biomass have been used to improve the performance of existing wastewater treatment works which previously had either a fixed or a suspended growth process only. In addition to improved efficiency, the processes have been found to be more robust. Full scale trials of a fixed film / activated sludge hybrid process, supported by model simulation, have shown that the hybrid process would enable a 120 000 PE sewage treatment works to meet a new, stricter effluent discharge consent without the construction of new tanks.