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Abstract
A mathematical model of rock-bed filtration process was formulated and a numerical computation scheme was developed. Eight physical and biological processes, namely, reaeration, sedimentation of organic and inert particulate matter, oxic decomposition of dissolved organic matter, nitrification, and oxic, anoxic, and anaerobic decomposition of organics in sediments were incorporated in the model. The functions describing the qchange in concentrations of six water quality indices and two sediment fractions were obtained from the conversion rate functions based on the IAWPRC approach in a matrix format. The respective differential equations were then solved sequentially using the numerical solution scheme with known initial conditions for a given time step along the reactor length. The simulated changes in the concentrations of water quality indices and sediment fractions were compared with the results of the Inagawa river project for evaluating the model performance. It was possible to obtain a reasonable agreement between the simulated and observed results through the adjustment of kinetic and stoichiometric parameters. The model predicted results for the long term performance of rock-bed filtration systems for four selected cases and indicated that the method could be suitable for the treatment of low strength wastewaters.