Research On Stochastic Model Of Organic Concentration In Municipal Wastewater Treatment Plant

With the development of human society, environmental problems have become more serious, and water shortage has become a serious factor restricting economic and social progress. Recently, our country has increased the construction dynamics of the municipal sewage plant. So, scientifically and rationally simulating and controlling of these sewage treatment processes will not only assure effluents achieve the standards stably, but also lower the operation cost.Modeling of activated sludge process has become a common part of design and operation of wastewater treatment plants all over the world. Furthermore, with the improvement of people's understanding, the uncertainty of sewage treatment system has become a universal attention question. So, we need a comprehensive understanding of treatment uncertainties in the process of organic matter degradation, and through analyzing and builting correct model to provide the theoretical basis for operation and management of sewage treatment system.Stochastic differential equation is an effective tool to solve complex problems about nonlinearity and uncertainty, and its research and application to water pollution control planning are still at the initial stage at home and abroad. In this paper, at first the development process of the activated sludge models are expounded, and the research status of activated sludge models are analyzed at home and abroad. Then, based on stochastic theory, a stochastic model of organic concentration is built, which is mainly used in the simulation and predication of organic concentration in wastewater treatment process. The method and theory of model building, as well as analysis and calculation are researched of exploratory, and also a new approach to the model building and simulation of wastewater treatment system are provided.Based on the Monod equation and material balance, adding a random disturbance term which is recognizd as a wiener process to the deterministic model of organic concentration, a stochastic model of organic concentration is built. After that,through solving stochastic model, organic concentration, expectation function and variance function are obtained, and then its funtion expressions are theoretical analyzed. Parameter sensitivity analysis of expectation function and variance function verifies the stochastic model in theory.Finally, the model is applied to simulate and analyze in the actual sewage plant. Take a municipal sewage plant in Suzhou for example, using Matlab software, the deterministic and stochastic model of organic concentration are programed, and the sumulations show that: The deterministic model of organic concentration not containing the uncertainties of system, so the simulation result does not reflect the disturbance changes of the water quality over time. The simulation result of the stochastic model of organic concentration is more realistic operating conditions, which can reflect random changes of the organic concentration at different times.To a certain municipal sewage treatment plant, if the needed data and parameters can be acquired, the organic concentration and disturbance changes would be predicted rapidly through this stochastic model. And then, through correlation analysis to judge operation condition of the wastewater plant, it also can provide theoretical basis for follow-up operation and control.