In Genetic Algorithms mutation probability is usually assigned a constant value, therefore all chromosome have the same likelihood of mutation irrespective of their ®tness. It is shown in this paper that making mutation a function of ®tness produces a more ef®cient search. This function is such that the least signi®cant bits are more likely to be mutated in high-®tness chromosomes, thus improving their accuracy, whereas low-®tness chromosomes have an increased probability of mutation, enhancing their role in the search. In this way, the chance of disrupting a high-®tness chromosome is decreased and the exploratory role of low-®tness chromosomes is best exploited. The implications of this new mutation scheme are assessed with the aid of numerical examples.

The innovative nutrient removal process scheme DEPHANOX proved to be very efficient because it maximises the utilisation of organic substrate for phosphorus and nitrogen removal. The process solves the competition for organic substrates among Poly-P organisms and denitrifiers as well as the problem of overgrowing of slow nitrifiers by faster organotrophs, typical of activated sludge. In experiments, DEPHANOX showed better P removal efficiency than a JHB configuration, working with a very low influent COD/TKN ratio. This paper reports the results of a simulation study that has been carried out to better understand the behaviour of the two configurations with a wide variety of influent wastewater characteristics and under dynamic conditions. The results of the simulation confirmed the high P removal capacity of the DEPHANOX configuration with low influent COD/TKN ratios.

An enhanced process model for SBRs has been developed. Though the basic mechanism largely draws on the Activated Sludge Model n. 2d, its new features are the splitting of the nitrification stage in a two-step process, according to the well known Nitrosomonas -Nitrobacter oxidation sequence, and an improved X PAO dynamics, involved in the anaerobic/aerobic phosphorus removal process.The model was implemented through the DLL technique allowing complied C++ modules to be linked to an ordinary Simulink block diagram. The static sensitivity study revealed that if the parameter vector is partitioned into subsets of biologically related parameters and calibrated separately, the calibration procedure does not present particularly difficult aspects. Trajectory sensitivity showed also to which extent data collection could be optimised in order to improve calibration accuracy.The study of the shape of the error functional generated by parameters couples allows a much more effective calibration strategy.

No abstract

No abstract