分层水库水深对扬水曝气原位控藻效果的影响

Effects of water depth on algae control in stratified reservoirs by in-situ waterlifting aeration technology

扬水曝气是分层水源水库原位藻类控制的有效技术.针对西安金盆水库扬水曝气水质改善工程典型设计工况,采用商业化Fluent软件模拟计算了不同水深条件下扬水曝气器的外围流场,分析了水深对扬水曝气控藻区域和效果的影响.结果表明,当扬水曝气器外围流场稳定时,进水口附近的顺时针环流和其他区域的逆时针环流共存,进水口顺时针环流范围和强度不受水深影响,水流速度沿扬水曝气器径向减小.当水深从50 m逐渐增加到110 m时,扬水曝气核心控藻区域的百分比从12.5%增大到30.6%,核心控藻区域半径从60 m增加到175 m,藻类完全混合的时间从16 d增加到30 d.当水深不浅于65 m时,藻类在补偿点以下的停留时间均大于48 h,且随水深的增加而延长.非核心控藻区域内的藻类随逆时针环流被动迁移至核心区域,最终悬浮并滞留在扬水曝气器底部附近.分层水库中扬水曝气器合理设计间距为水深的1.2~1.6倍.

Water-lifting aeration is an effective technology for in-situ algae control in source water reservoirs. Based on the typical design conditions of water-lifting aeration project for water quality improvement in Jinpen Reservoir,Xi’an,flow outside the water-lifting aerator under various water depths was modeled using commercial software of Fluent to numerically analyze the effects of water depth on the algae control zone and control effectiveness. When the flow outside the water-lifting aerator reached quasi-steady state,the clockwise flow near the inlet and counter-clockwise flow in other domains coexisted.Zone and strength of inlet circulation were not sensitive to the water depth,and flow velocity decreased as the distance from the water-lifting aerator increased. When the water depth increased from 50 m to 110 m,the ratio of the algal growth control zone to the whole flow domain increased from 12. 5% to 30. 6%,the radius of the core algal growth control zone increased from 60 m to 175 m,and time required for complete mixing of algae increased from 16 days to 30 days. Algae suspended at the non-core inhibition zone was transported passively to the core inhibition region,where it finally settled and stayed near the bottom of the water-lifting aerator. Under water depth higher than 65 m,the residence time of algae under the compensation point was longer than 48 hours,and increased with the water depth. The proper design intervals of water-lifting aerators in stratified reservoirs can be proposed as 1.2 ~ 1. 6 times the water depth.