Systematic Optimisation with Serial Simulations
If hydraulic simulations are conducted to optimise a planned or an operating tank as a service, as it is the case up to now, it has to be decided whether average or maximum loadings are chosen. The consideration of average values allows to predict the behaviour during normal operation but no information is gained about what conditions can arise at limit loadings. It remains unknown whether a tank is able to treat the maximum loadings. A statement on this can be made only if the simulations are computed with extremal input parameters, as it is usually done. With this prediction concerning the security of the operation no information can be gained about what situations will arise in normal operation and which specific circumstances apply there.
This dilemma can be overcome by conducting serial simulations. Particularly well-founded predictions about the situation in the tank can be made on the basis of a number of simulations for which the loading parameters Q, SVI and X are varied from minimum to maximum in sensible steps. By means of simulations at varying recycle ratios it is possible to optimise the operation of secondary settling tanks in a degree of detail not known so far. The software hydrograv proload.cfd enables its users to set secondary objectives like maximisation of sludge storage volume or sludge displacement from the secondary clarifier into the aeration tank (to support the main goal of a good effluent quality) and to evaluate the achievement of these objectives for the first time. These serial simulations can be conducted automatically and therefore require particularly little user effort.