MODELING OF DISSOLVED OXYGEN DEFICIT IN RIVER WATER SYSTEM A NEW DISSOLVED OXYGEN DEFICIT MODEL FOR RIVERS

Abstract

deficit in river water system due to organic pollution from point sources and non point sources has been developed after thorough investigation of the limitations with existing models and applying the fundamental principles of Reynolds transport theorem, material balance equation and Fick's law in one-dimensional space. The model consider the effects of de-oxygenation due to carbonaceous and nitrogenous organic matter releases from point and non point sources, settling of carbonaceous and nitrogenous organic matter, strewn flow driven atmospheric re-aeration, hydrodynamic dispersion, periphyton and phytoplankton photosynthesis, endogenous respiration of phytoplankton and periphyton algal species, and total sediment oxygen demand due to oxidation of algal carbon and other possible processes in sediment deposit of rivers. The second-order first-degree total derivative for dissolved oxygen deficit has first been written for steady-state flow conditions, considering the spatial variations of DOD in uniform flow regime, and considering reaction terms. The total derivative of dissolved oxygen deficit is then directly integrated in two steps involving four auxiliary functions of dissolved oxygen deficit. A complete model to simulate the dissolved oxygen deficit responses in the river water environment has been developed The effect of oxidation of sediment algal carbon has been accounted with a second model that simulates settling of phytoplankton species and the subsequent sediment oxygen demand due to oxidation of sediment algal carbon in river beds. The first-order. first-degree sediment algal carbon derivative has been solved in single step applying two auxiliary functions to get a sediment algal carbon equation. Then the. two sediment oxygen demand equations are taken as additive terms and the total sediment oxygen demand model has been written. This sediment algal carbon model has been used in the total derivative for dissolved oxygen deficit to account sediment oxygen demands. A different approach has also been developed to take into account the non point source effects on dissolved oxygen level in rivers. A first-order kinetics representing addition, oxidation and settling of non-point organic substances in the river water environment has been developed from the fundamental principle of continuity. The non point sources are characterized in terms of equivalent oxygen demands of carbonaceous and nitrogenous substances and their effects on dissolved oxygen in rivers have been determined based on ultimate oxygen demands and material loads. The first-order kinetic , equations of remaining carbonaceous and nitrogenous substances of non point sources have been used in the reaction terms of total derivative for dissolved oxygen deficit. 99 This thesis work also discusses detail literature review on processes and parameters estimation. The main natural processes accounted in the dissolved oxygen deficit derivative as reaction terms and estimation of their parameters have been discussed. In the absence of parameter measurements, the parameter estimation has been accomplished with the help of selected equations. The re-aeration coefficients have been estimated using a widely used O'Connor's approach and measured values of dispersion coefficients has been adopted in the simulation of dissolved oxygen deficit. The oxygen production due to phytoplanlaon algal species has been accounted on the basis of total gross daily average production for maximum growth rates. The effects of nutrient, temperature and light limiting conditions on growth of phytoplankton algal species have been considered to adjust the maximum growth rate. The periphyton oxygen production has been estimated based on effects of atmospheric re-aeration and measurements of diurnal dissolved oxygen range. Measured values of nutrients, temperature, de-oxygenation rate constants, biochemical oxygen demands, algal species, dispersion coefficients, stream flow and hydraulic parameters have been used in parameter estimation. Other parameter values required in the new model, have been adopted from literature. Detail algorithm has been written for the model to develop computational programs with Microsoft Excel Application. Two different dissolved oxygen simulators have been developed. The first one, DO-BALANCE-01, simulates the dissolved oxygen deficit and other system variables of rivers accounting the effects of point sources. and residual sediment oxygen demands of non-point pollution sources during worst condition in rivers... The second one,.-DO-BALANCE-02,. simulates they.:, effects of point sources and.non point sources of pollution during high: flow seasons.;:.. The validity of the model has been tested in the main tributary of ' upper Willamette River basin, the McKenzie River, in the State of Oregon in USA. The dissolved oxygen deficits, have been simulated using DO-BALANCE-01 in two river reaches of McKenzie River, from river mile 47.7 to 19.3 and river mile 19.3 to mouth.. at - Eugene , of .McKenzie,.. for the worst conditions during. August .22-27 1994.The model: estimates. achieved coefficients- of correlation. of 0.76,,.and. 0.90.when mixing .: locations dissolved oxygen levels and deficit values are compared with observed values respectively. The standard deviations of observed dissolved oxygen level and deficit sample values are 0.05 and 0.12 respectively. The corresponding standard deviation of simulated sample values in the two river reaches is 0.59 in both variables. The sample simulated values of dissolved oxygen concentration and deficit in the two reaches have shown more deviation from their mean values of 13.27 and 1.15 respectively. These simulated sample values have shown coefficient of variations (CV) of 0.05 and 0.52 respectively. The simulated ~,;~ .._ : deficit values have shown more variation than the dissolved oxygen concentrations. vii The correlations achieved between observed and simulated values have testified that the model is valid and mathematically sound to simulate dissolved oxygen deficit during worst condition at the McKenzie River Reaches. The sensitivity of model responses to changes in measurements of periphyton and phytoplankton algal species, hydraulic characteristics, estimates of dispersion-and re-aeration coefficients, sediment oxygen. demand measurements and diurnal dissolved oxygen ranges in terms of dissolved oxygen deficit and dissolved oxygen concentration have been statistically analyzed.The results has shown that the model responses have shown enormous error when very high. dispersion coefficients estimated with Fischer et al are used in simulation.The model results have shown tolerable errors in case of the other sensitivity analysis parametr values at McKenzie River. The effects of hydrodynamic dispersion, stream flow driven re-aeration, dilution, settling processes, residual sediment load, and oxidation of sediment algal carbon, Periphyton and Phytoplankton algae photosynthetic activities and endogenous respiration of these species on dissolved oxygen deficit responses have been observed to be highly significant at McKenzie.