DEVELOPMENT OF BIOFILM PROCESS SIMULATOR BASED ON AQUIFAS SEMI-EMPIRICAL MODEL USING MICROSOFT C#.NET PLATFORM.

Abstract

Biofilm processes have seen a revival in recent years. The focus has mainly been on improving the COD (chemical oxygen demand), nitrification and denitrification rates in existing and new wastewater treatment plants (WWTPs). The increased effort in this regard is due to more stringent effluent permits and increased cost of land in many parts of the world requiring smaller foot prints of WWTPs. Modeling biofilm processes is more complicated than conventional activated sludge and only few biofilm modeling simulators are available in the market. Access to these simulators is very limited in low and mid size WWTPs due to their higher price structure. Therefore there is a need for low end simulators for better process understanding of the operators and thus improving the treatment processes of these plants. Aquifas 3.0 was an effort in this direction which was released in public domain by Sen in 2007. This simulator is free of cost and mostly open source, developed in MS Excel using the semi-empirical version of Aquifas model. Several full scale facilities were evaluated using this model and it was able to accurately predict the effluent quality in all of these plants. Since then, this model simulator has been used in designing more than 70 plants worldwide and has a user base of more than 100. However, there were two major limitations in this simulator. Firstly, the unavailability of a graphical user interface (GUI) and secondly, the computational limitations of MS Excel in solving system non-linear semi-empirical equations of the Aquifas model thus having steeper learning curve and longer modeling and calculation time. xii A new version of Aquifas 3.() with an advance GUI and a built in equation solver was considered and developed in the last one year as a part of this study. This software application was developed in Microsoft.NET environment using CH computer language. The software is capable of simulating and solving any complex integrated fixed film activated sludge (IFAS) and conventional activated sludge (CAS) process configuration in steady state conditions. A graphical workspace is provided to model the process by simply dragging and dropping process nodes on the workspace which are graphically connected to each other with pipes to simulate flow streams. The input parameters for each of the node are entered graphically in the associated forms. The solver uses NewtonRaphson method for solving the non-linear equations through linearization. Subsequently, Factorization (LU decomposition) or Gaussian elimination method is used to solve the linearized system of equations iteratively till the solution converges. A separate result window is used to show the results in tabulated form. The output of the software has been tested against Aquifas 3.0 to verity the results which are in full agreement. Aquifas+ has been able to remove two major limitation of Aquifas 3.0 by providing a user friendly interface, and fast and accurate solution of the model. Incomoration of mechanistic model for advance biofilm analysis, preliminary, primary and tertiary treatment and extended period simulation are the future areas of developments envisaged for Aquifas+.