Purification efficiency of ecological spur dikes for river pollutants in different geometric arrangements:Experiments and numerical modeling

The traditional ecological spur dike is improved,by using the biological fillers such as the plant materials,combined with microorganisms,to obtain a larger water purification capacity.Most of the researches on spur dikes focused on the hydrodynamic force and the migration and the diffusion of the pollutants,but not so much on the effects of the spur dike materials and the arrangement parameters on the water purification capacity.In this paper the biological zeolite is used to make ecological spur dikes.The laboratory flume experiment shows that compared with the natural zeolite spur dike,the purification effect of the biological zeolite spur dike is significantly improved,and the average removal rate of the NH3-N is kept at 6.8%after 24 h compared with 3.5%of the natural zeolite spur dike.The NH3-N removal rates of a single spur dike,the counterpart spur dikes and the staggered spur dikes decrease with the increase of the inlet flow,and the staggered spur dikes have the best purification effect.Secondly,a numerical model based on the MIKE21 is verified by the experimental results and applied for the Tangjiali Section of the Xutangqiao River in Xinwu District,Wuxi City,Jiangsu Province.The orthogonal test shows that the length of the spur dike has the most important effect on the interception of pollutants and the purification,followed by the angle of the spur dike and the spacing of the spur dikes has the least important effect.The geometric arrangement parameters of the ecological spur dike group with the highest efficiency on the pollutant interception and the purification are:60°(angle),6.7 m(length)and 20 m(spacing).