垂向水动力扰动机的蓝藻控制效应数值实验研究

在蓝藻水华的控制研究中,目前的发展趋势是采用快速、生态安全且经济有效的技术,其中使用垂向水动力扰动机抑制蓝藻备受关注,但缺乏深入和定量的工程设计与效果评估研究.针对垂向水动力扰动机的蓝藻抑制效应开展数值实验研究,以三维数值营养盐-藻类动力学模型(EFDC)为框架,定量探讨了扰动机数量及其位置分布对叶绿素、总氮和总磷的影响.模拟结果表明,扰动机的存在对蓝藻抑制具有比较明显的作用,随着扰动机数量由0逐渐增加到20个时,Chl-a峰值浓度共减少了37.695 2μg.L-1,并且扰动机对水质改善的程度与其数量存在很强的非线性关系,即当扰动机数量由无到有并逐渐增加时,藻类抑制的效果明显增强;但当扰动机的数量增加到一定量时,进一步增加数量将不会相应增强蓝藻抑制效果.这表明扰动机存在一个最佳数量问题.此外,本研究发现除了数量之外,扰动机的位置对蓝藻控制的效果也有很大影响.数值实验结果显示如果扰动机放置位置得当,少量的扰动机就可达到甚至超过更多扰动机所能达到的蓝藻控制效果.尤其是优化12个扰动机的位置后,Chl-a峰值浓度比扰动机为20个时减少了7.172 6μg.L-1.这些研究结果验证了国内外相关研究对水动力扰动机蓝藻控制效果的肯定性结果,并进一步表明了在实际应用该项技术时必须因地制宜,结合使用智能工程技术(如:高分辨率数值模型)确定最佳扰动机数量与位置,从而确保以最低成本获取最大的蓝藻控制效果.除蓝藻控制之外,数值实验结果也表明扰动机对营养盐浓度也有一定的降低效果.

Numerical Experiment Study on the Algae Suppression Effect of Vertical Hydrodynamic Mixers

The main technology development on preventing blue-green algae blooms is moving towards developing efficient,ecologically safe,as well as cost-effective measures.Using vertical hydrodynamic mixers to inhibit blue-green algae is a long overlooked approach which deserves more attentions.In this paper,the algae suppression effect of vertical hydrodynamic mixer was studied using a numerical experiment approach,which models the influences of mixers on three water quality constituents Chl-a,TN and TP within a three-dimensional numerical nutrient-algae dynamics framework.The results showed that the presence of mixers had an obvious effect on suppressing blue-green algae.As the number of mixer gradually increased from 0 to 20,the peak concentration of Chl-a totally decreased 37.695 2 μg·L-1,and the magnitude of water quality improvement had a nonlinear relationship with the number of mixers.The nonlinearity is manifested by the results showing that the marginal suppression effect on algae corresponding to an additional mixer is significant when the number of mixers gradually increased from zero,and then became insignificant after the number of mixers reaches a certain threshold value.Therefore,the number of mixers should not exceed an upper threshold value to avoid low economical efficiency and non-optimal design.This study also found that the locations of mixers had significant impacts on the effectiveness of algae suppression.Numerical experiment results showed that if the mixers were placed at proper locations,fewer mixers could produce comparable or even higher algae suppression effect than more mixers that are placed at other locations.Especially when the number of mixer was 12,we maintained the same number but optimized its location,peak concentration of Chl-a reduced 7.172 6 μg·L-1 by comparing with the number of mixer was 20.In general,the numerical experiment results verified the findings of domestic and international researches regarding the algae suppression effect of vertical hydrodynamic mixers,and discovered the important relationship between the algae suppression effectiveness and the number and locations of mixers.This study suggested that allowing cost-effective algae suppression in a specific waterbody,site-specific conditions must be accounted for applying an intelligent design approach with the aid of high-resolution numerical model to determine the optimal number and location of mixers.The numerical experiment also shows that mixers would reduce nutrient concentrations in addition to algae suppression,though at a much less magnitude.