Comparison of water-lifting aerator type for algae inhibition in stratified source water reservoirs

Non-submerged and submerged water-lifting aerators have been recently developed to improve the water quality of source water reservoirs, but the non-submerged aerator has the drawbacks of higher initial investment and being more difficult to operate and maintain compared with the submerged aerator. To explore whether the submerged water-lifting aerator also has better performance on in-situ algae inhibition in source water reservoirs, the effects of submerged and non-submerged water-lifting aerators on algae inhibition were numerically investigated under different hydrological and operational conditions. Taking Jinpen Reservoir as a study case, under different conditions of water depth, temperature gradient and inlet velocity period, the flow outside the aerators, core algae inhibition zones and mixing of algae were numerically analyzed, and the simulated results were validated against the measured data. Simulated results showed that the flow outside any water-lifting aerator was characterized as one large clockwise circulation under a stable state, but the circulated flow was developed further for the submerged case. When the water depths were 77.25 m, 87.25 m and 97.25 m, the percentages of the core algae inhibition zone to the whole flow domain were 39.71%, 41.14% and 42.73% respectively, which were 5.88%, 3.68% and 1.15% larger than those for the non-submerged case; the periods required for complete mixing of algae were 10 days, 12 days and 14 days respectively for the submerged case, which were 8 days, 7 days and 6 days shorter than those for the respective non-submerged cases. Algae were transported from the surface layer to the bottom layer mainly by advection generated from the circulated flow arising from water-lifting aeration. Under similar hydrological and operational conditions, the core algae inhibition zones were larger and the mixing of algae was quicker for the submerged case. Submerged water-lifting aerators have advantages over the non-submerged aerators in the investment required and the operation and performance of algae inhibition and are recommended for in-situ algae inhibition in stratified source water reservoirs.