Simulation Of Algal Inhibition Using In-situ Water-lifting Aeration Technology In Deep-water Reservoirs

Water-lifting aeration technology is an effective in-situ algal growth inhibitiontechnology for source water reservoirs. Based on the typical operational conditions ofthe water-lifting aeration system used to improve the water quality of the JinpenReservoir, fields of flow and algal concentration outside the water-lifting aerator weresimulated with FLUENT software in order to determine the appropriate intervalbetween two water-lifting aerators and predict the effect of the algal growth inhibition,and the effects of temperature gradient and water depth on the radius of in-situ algalinhibition zone and mixing characteristics of the algae were mainly studied, the mainconclusions can be drawn as follows:(1) The flow field outside the water-lifting aerator changed periodically as thevelocity of the outflow of the water-lifting aerator changed periodically. Taking the ratioof the algal inhibition zone to the whole flow domain as a target, the worst moment ofthe algal-growth inhibition in one period was determined and the research method ofalgal-growth inhibition using water-lifing aeration technology was established.(2) When the temperature gradient was between0.17°C/m and0.73°C/m, theclockwise flow near the inlet and counter-clockwise flow in other domains coexisted;with the increase of the temperature gradient, buoyancy resistance acting on the waternear the water-inlet of the simulation region increased, zone and strength of inletcirculation became weakened, and the time required for flow outside water-liftingaerator reaching stable state increased.; flow velocity decreased with the distance fromthe water-lifting aerator.(3) When the temperature gradient was increased from0.17°C/m to0.73°C/m, the shape of the core algal growth inhibition zone was almost the same under the waterdepth of80m, however, the radius of the core algal growth inhibition zone wasincreased from100m to150m, and the ratio of the algal growth inhibition zone to thewhole flow domain was increased from25.16%to28.60%. The design intervals ofwater-lifting aerators,250m-300m, in reservoirs were proved to be proper.(4) When the water depth was increased from50m to110m, the shape of the corealgal growth inhibition zone was irrelevant to the water depth under the temperaturegradient of0.47°C/m, however, the radius of the core algal growth inhibition zone wasincreased from60m to175m that are1.2times and1.6times of the correspondingwater depth, and the ratio of the algal growth inhibition zone to the whole flow domainwas increased from12.5%to30.6%.(5) Taking the algae at the growth compensation point into consideration,characteristic of the algae transported passively outside the water-lifting aerator wasanalyzed. Algal transport mainly contains horizontal move, downward move, move nearthe bottom and upward move. Algae suspended in the non-core zone can be transportedpassively to the core zone; the time algae grew below growth compensation pointincreased, as the time for algae transporting below the growth compensation point wasmuch longer than that for algae transporting in the growth area, and it was increasedwith the temperature gradient and water depth indicating the effect of algal inhibitionbecame better.(6) As the operational time of water-lifting aerator was increased, algaeconcentration near the surface of water outside the water-lifting aerator was decreased,however, algae concentration at the bottom area of the reservoir was increased gradually;when the flow outside the water-lifting aerator got stable, algae concentration at thesurface water could be20%of the initial algae concentration. Simulated results agreedwell with the field measured ones.