3种生物滞留设计对城市地表径流溶解性氮的去除作用

城市地表径流溶解性氮(N)的有效控制具有挑战性.2015构建了3种不同设计的生物滞留设施:壤砂种植紫穗狼尾草(CB)、壤砂种植紫穗狼尾草设置饱和带(MB1)、壤砂种植紫穗狼尾草设置饱和带并添加10%木块(MB2).在模拟城市地表径流水文、水质变化条件下,研究3种生物滞留种植植物、设置饱和带以及添加碳源对城市地表径流溶解性N(NH_4~+-N、NO_3~--N)的去除作用.通过为期1年试验监测表明,在进水NH_4~+-N浓度平均值为(5.45±2.21)mg·L-1情况下,3种生物滞留对NH_4~+-N均具有显著的去除作用(去除率95%).基质吸附、硝化与植物吸收是生物滞留有效去除城市地表径流NH_4~+-N的主要途径.在进水NO_3~--N平均值为(5.88±2.32)mg·L-1情况下,CB、MB1和MB2出水NO_3~--N浓度的平均值分别为(4.04±2.64)、(0.84±1.18)和(0.26±0.48)mg·L-1,相应去除率分别为31.3%、85.7%和95.6%.生物滞留种植紫穗狼尾草、设置饱和带以及添加碳源均可显著降低出水NO_3~--N浓度,减少NO_3~--N淋溶输出,提高NO_3~--N去除率.植物吸收和微生物反硝化是生物滞留去除NO_3~--N的主要途径.进水NO_3~--N浓度、水量、间隔天数是影响生物滞留出水NO_3~--N浓度的主要因素.生物滞留种植紫穗狼尾草、设置饱和带并添加碳源,在水文、水质变化情况下,仍可有效去除城市地表径流溶解性N.

Effects of Three Bioretention Configurations on Dissolved Nitrogen Removal from Urban Stormwater

Multiple chemical forms of nitrogen in urban storm water make its management challenging. Three types of bioretention systems were constructed in 2015 with loamy sand as filter media, including a conventional freely drained bioretention (CB), a modified bioretetion incorporated a submerged zone (MB1), and a modified bioretention incorporating a submerged zone with woodchips addition (MB2). This study investigated the role of vegetation, the use of submerged zone and carbon addition in achieving co-optimized dissolved nitrogen removal in bioretention systems. Twelve bioretention columns were monitored over a 12-month period of dosing with synthetic storm water under varying hydrology and nitrogen loading rates. All the studied bioretention systems could achieve very good ammonia removal (more than 95%) at an average inflow ammonia concentration of (5.45±2.21) mg·L^-1. The filter media sorption, nitrification and plants uptake were the main removal pathways for incoming ammonia. The effluent nitrate concentrations of the CB, MB1 and MB2 were (4.04±2.64)mg·L^-1 (31.3%), (0.84±1.18) mg·L^-1 (85.7%), and (0.26±0.48) mg·L^-1 (95.6%), respectively, at the average inflow nitrate concentration of (5.88±2.32) mg·L^-1. The use of the native species P. alopecuroides, a submerged zone and woodchips addition could effectively decrease the effluent nitrate concentration, reduce the washout and achieve high nitrate removal. Both plants uptake and denitrification were the two major pathways for removal of inflow nitrate. Inflow magnitude, antecedent dry days and inflow nitrate concentration were the main factors influencing the effluent nitrate concentrations for the three bioretention systems. The results highlighted that the bioretention design of the native species P. alopecuroides incorporated a submerged zone with 10% woodchips addition could consistently and effectively remove storm water nitrate under hydrological regime and nitrogen loading rates.