Numerical Simulation For Wastewater Treatment Units And Research On The Improvement Of High-efficient Treatment Units For Overflows

First, we study and discuss the application of commercial software PHOENICS. On the premise of understanding the structure and contents, research the in-line mathematical models and master the application scope of each model systematically.Computational Fluid Dynamics (CFD) technology is used to calculate and simulate the flow pattern of typical wastewater treatment units, including the simulation for single-phase fluid, solid-liquid simulation for two-phase fluid, and taking the CFD technology as the supplementary means, together with the site pilot-scale experiment, to assess and verify the Chemically-Enhanced Primary Treatment Process for Combined Sewer Overflows. Main research contents are as follows:The velocity field inside rectangular sedimentation tank is simulated, and the results show that: the inside velocity distributes unevenly, and there are eddy zones in the front-back of the baffle, which will influence the operating effect seriously;The Peripheral Feed-peripheral Effluent Secondary Clarifier is studied in different reflux ratio, we find the eddy zone exists in the Clarifier, obviously at the center of the tank where the velocity is relatively low;Flow pattern inside a four-tank SBR is studied. Results show that the flow pattern is nearly plug flow in tank 1 and tank 2 at the first stage. However, at the second stage, serious short circuit leading to impact the efficiency and effluent quality in the second stage is found. Therefore, the improving measures are developed, the inflow is changed from tank 2 to tank 3 at the second stage, and the short circuit situation is obviously improved by the simulating results;In several operating conditions, the actual suspended solid concentration in different cross-section of the circular clarifier of Quyang Wastewater Treatment Plant is measured and the simulation for the velocity field and sludge concentration is made, finally the calculated value is compared with the predicted value;Although there exists a certain difference between them, the sludge interface range inside the clarifier can be determined correctly through numerical simulation, which provides the theory basis for optimizing the tank size and improving the settling efficiency.Based on the above simulations for wastewater treatment units, a new Chemically-Enhanced Primary Treatment Process for Combined Sewer Overflows is developed and the flow pattern in reactor and the inclined-tube clarifier is assessed with CFD technology, results show that the process is feasible. In the site pilot-scale experiment, measure the treating ability for the overflow wastewater which can reach: the average removal rate of the SS: 70%, COD: 50%, TP: 85%. Therefore, the feasibility and practicability of the process are verified effectively in such aspects as the CFD flow pattern research and the Pilot-scale experiment.