Rama Rao Karriand Venkateswarlu Chimmiri
Petroleum and Chemical Engineering, Insitut Teknologi of Brunei, Brunei Darussalam, Brunei
Waste water treatment has become a necessary and mandatory to reduce the effects of polluting the soil and water bodies. Especially the effluent waste water produced from a pharmaceutical industry consists of harmful chemical and toxins which retains in the earth and has long term lethal effects changing the biological cycle of vegetation and human mankind. Many techniques and processes are being in use around the world, among these biofilm processes are increasingly gaining more importance as they are environmental friendly and less energy intensive. The behavior of a biofilm is determined by a variety of biological, chemical and physical processes internal to the film as well as interactions between the biofilm and its environment. The excellent biomass retention with reasonable hydraulic retention times of biofilm processes make them attractive. Fixed bed biofilm reactors are increasingly used for anaerobic treatment of effluent waste waters. The main advantage of the fixed bed processes is that high volumetric densities of microorganisms can be accumulated by natural attachment as biofilms. The high density of biomass accumulation allows excellent treatment performance in fairly small reactor volumes, which is economically beneficial. Since the biofilm and its environment form a complex system, it is often difficult to analyze the biofilm reactors experimentally. Mathematical models could be very helpful in analyzing such processes. Mathematical and kinetic modeling of biofilm reactors involving complex biological reactions for the conversion of substrates by microorganisms is a difficult task. The application of biofilm reactor models to real practical problems suffers due to the lack of knowledge of accurate kinetic models and uncertainty in the model parameters. Successful modeling of bioreactors, therefore, requires selecting an appropriate kinetic model and accurate determination of its parameters. Inverse estimation of model parameters via mathematical modeling route known as inverse modeling (IM) is an attractive alternative to the experimental methods. In this approach, the parameters are determined as a consequence of the validation of the process model with the aid of measured data. Parameter estimation by IM involves minimization of an objective function and thus needs the support of efficient optimization algorithms. In this study, a novel optimization method is proposed based on ant colony optimization (ACO) and applied for the determination of kinetic and film thickness parameters of biofilm models of an experimental fixed bed anaerobic reactor used in the treatment of pharmaceutical waste water. The results of this study are evaluated with respect to mathematical models, optimization methods, kinetic and film thickness expressions and reactor bed packing. These results have explained the complexity of the numerical model, the type of kinetic and film thickness models and the suitability of packing to be used with the biofilm reactor.
Keywords: Bio film reactor, fixed bed anaerobic reactor, mathematical model, ant colony optimization, Inverse modeling, Kinetic parameters.