Process And Optimization Of Algae Control Using Water-circulating Aeration In A Eutrophicated Source Water Reservoir

Water-lifting aeration is an effective technology of layered water reservoir in situalgae.Based on the working condition of water-lifting aerator to improve water qualityin xi ’an Shibianyu Reservoir, fields of velocity and algae concentration outside thewater-lifting aerator were numerically simulated and validated against the field data,process and effectiveness of alage control was numerically analyzed with the simulateddata, operational conditions for algae control were optimized with the simulated data.The main conclusions were drawn as follows:(1) Using the species transport model and RNG k-ε turbulence model, aFluent-based numerical method coupling the hydrodynamics and water quality wasdeveloped, the fields of velocity and algae concentration outside the water-liftingaerator were numerically simulated with this developed method, the simulated resultsagreed well with the field data of Shibianyu Reservoir.(2) Periodical outflow from the aerator can be generated by running the aerator,flow field outside the aerator varied with time and reached a quasi-stable state after acertain time period, the flow was characterized as the clockwise circulation near theaerator and the counter-clockwise circulation far from the aerator. As the water depthincreased, the radius of the clockwise circulated flow domain increased, and this willenable more algae to move downwards which is beneficial to algae inhibition.(3) Under the conditions of water depth of50m and air slug period of170s, whenthe temperature gradient was increased from0.17℃/m to0.73℃/m, the shapes of the core algae inhibition were roughly the same, the radius of the core algaeinhibition zone was increased from210m to210m, the ratio of the area of the corealgae inhibition zone to that of the whole domain was only increased from47.3%to47.3%. The simulated results shows that the effectiveness of algae inhibition was notgreatly sensitive to the temperature gradient.(4) Under the same conditions of temperature gradient and air slug period, whenthe water depth was increased gradually, the interval required for reaching quasi-stablestate of flow outside the aerator was lengthened gradually, the radius of the core algaeinhibition zone was also increased. When the water depth was increased from27.5meters to65meters, the algae mass fraction at the algae growth compensation pointwas decreased from82%to about42%.（5）The air slug period of the water-lifting aerator not only influenced the flowfield outside the aerator, but also influenced the core algae inhibition zone. When theair slug period was increased from80s to320s, the area ratio of the core algaeinhibition zone was increased from61.08%to41.22%, but the interval required forreaching quasi-stable state of flow outside the aerator was lengthened.（6）Taking the average algae mass fraction within the water depth of5m as thecriterion for optimizing the operational condition of aerator, based on the simulatedresults of algae concentration, the optimized operation conditions were achieved forthe efficient algae inhibition by running the water-lifting aerator.