平流式二沉池三维数值模拟分析

采用Fluent15.0软件对城市污水处理厂的平流式二沉池进行模拟分析。选取RNG k-ε模型和欧拉双流体模型,利用加拿大温莎大学Imam实验数据验证了该模型的准确性。基于该模型,以出水悬浮物浓度(ESS)和异重流比例为表征指标,对影响二沉池沉淀效率的3个因素——污泥颗粒粒径、表面溢流率和挡板比例进行分析。结果表明:污泥颗粒粒径影响泥水分离的效果,模拟实验得到的最佳颗粒粒径为300μm。表面溢流率对出水悬浮物浓度值影响较大,随表面溢流率增大出水悬浮物浓度值和异重流比例呈非线性急剧增加。同时,二沉池中最佳的挡板比例为60%,此结构不仅有利于能量的耗散和异重流比例的减小,而且能保证较低的出水悬浮物浓度值。

THREE-DIMENSIONAL NUMERICAL SIMULATION ANALYSIS ON RECTANGULAR SECONDARY SETTLING TANKS

The numerical simulation analysis of rectangular settling tanks was carried out in wastewater treatment plants( WWTPs) by using the Fluent15. 0． The RNG k － ε and eulerian two-fluid models were selected． The reliability of theselected model was verified by the experimental results of Imam in the University of Windsor in Canada． Two indicators wereselected including the concentration of effluent suspended solids and the proportion of density flow． Three factors were analyzedincluding the size of sludge particle，the surface overflow rate and the proportion of baffle． The results showed that the effect ofseparation between sludge and water was influenced by the size of sludge particle． Moreover，the optimized particle size was300 μm． The surface overflow rate influenced the concentration of effluent suspended solids intensively． The concentration ofthe effluent suspended solids and the proportion of density flow were increased by nonlinear with the increase of surfaceoverflow rate． In addition，the optimized proportion of baffle was 60% in the rectangular settling tanks． At this proportion，theenergy dissipation was increased，the proportion of density flow was decreased． Meanwhile，the concentration of effluentsuspended solids was lower．