EXPERIMENTAL AND NUMERICAL SIMULATION OF THREE-PHASE FLOW IN AN AERATION TANK

Aeration plays an important role in the treatment of activated sludge due tothe interactions among bubbles, sewage and activated sludge in an aeration tank. The aerationperformance is directly concerned with the efficiency of sewage disposal. So the three-dimensionaltwo-fluid model was established with emphasis on the phase interaction terms in this paper. Thismodel, as an extension of the two-phase flow model, involved the motion laws of three-phases, andwas compared with experimental studies. The finite volume method was used in the numericalsimulation of gas-liquid two-phase flow and gas-liquid-solid three-phase flow. In order to discussthe influence of gas-phase, liquid-phase and solid-phase motions in an aeration tank on the sewagedisposal, three kinds of boundary and initial conditions were adopted. The simulated results of theflow structure show qualitatively good agreement with the experimental data. And the theoreticalbasis for designing the best aeration tank was discussed according to the simulated results.

Evaluation and improvement of wastewater treatment plant performance using BioWin

In this study,the activated sludge model implemented in the BioWin software was validated against full-scale wastewater treatment plant data. Only two stoichiometric parameters(Y p /acetic and the heterotrophic yield(Y H)) required calibration. The value 0.42 was used for Yp /acetic in this study,while the default value of the BioWin software is 0.49,making it comparable with the default values of the corresponding parameter(yield of phosphorus release to substrate uptake(YPO4)) used in ASM2,ASM2 d,and ASM3 P,respectively. Three scenarios were evaluated to improve the performance of the wastewater treatment plant,the possibility of wasting sludge from either the aeration tank or the secondary clarifier,the construction of a new oxidation ditch,and the construction of an equalization tank. The results suggest that construction of a new oxidation ditch or an equalization tank for the wastewater treatment plant is not necessary. However,sludge should be wasted from the aeration tank during wet weather to reduce the solids loading of the clarifiers and avoid effluent violations. Therefore,it is recommended that the design of wastewater treatment plants(WWTPs) should include flexibility to operate the plants in various modes. This is helpful in selection of the appropriate operating mode when necessary,resulting in substantial reductions in operating costs.

EXPERIMENTAL STUDY ON GAS-LIQUID TWO-PHASE FLOWS IN AN AREATION TANK BY USING IMAGE TREATMENT METHOD

Particle Image Velocimetry （PIV） technique was employed to study experimentally gas-liquid two-phase flow in an aeration tank. In terms of the PIV principles, an algorithm of PIV based on the Fast Fourier Transformation （FFT） was worked out. The PIV program was developed and verified, and then was used to measure three kinds of states in the testing device. The program was also used to calculate and analyze the related parameters. The experimental data indicate that the bubbles in testing device have the longest resident time and stronger turbulent intensity for the gas-liquid two-phase flow in a special case （Case 3）, resulting in great increase of the oxygen transferring speed and efficiency, whereby providing the basis for the selection design of aeration tank.

The effect of bubble plume on oxygen transfer for moving bed biofilm reactor

The movement of the bubble plume plays an important role in the operation of a moving bed biofilm reactor （MBBR）, and it directly affects the contact and the mixture of the gas-liquid-solid phases in the aeration tank and also the oxygen transfer from the gas phase to the liquid phase. In this study, the velocity field is determined by a 4-frame PTV as well as the time-averaged and timedependent velocity distributions. The velocity distribution of the bubble plume is analyzed to evaluate the operating efficiency of the MBBR. The results show that the aeration rate is one of the main factors that sway the velocity distribution of the bubble plumes and affect the operating efficiency of the reactor.