强化浅基质层干植草沟对道路径流的脱氮效果

搭建6个不同结构和介质组成的浅基质层干植草沟模拟柱,在基质层添加较多发酵木屑,利用进水期的脱氮作用,并设置饱水层提高设施落干期脱氮能力,从而强化设施全周期脱氮效果.以半人工道路径流作为进水,考察各模拟柱运行效果,并结合分层取样水质检测结果和模拟柱内体积含水率、ORP的变化过程,分析氮素在不同模拟柱内的去除机制.结果表明:在运行参数相对实际应用环境更为不利的条件下,设置饱水层的模拟柱的TN去除率在67%～78%; TN去除过程主要发生在进水期,且在含较多发酵木屑的基质层即被大量去除;设置饱水层不仅可提高落干期设施脱氮能力,还可保证较浅的基质层在进水期快速达到适宜反硝化的缺氧条件,从而保证进水期设施的脱氮效果;设置持水性过渡层并在其中放置有机质可以有效平衡饱水层碳源补给并控制有机质淋失的问题.

Nitrogen Removal Efficiencies from Road Runoff by Dry Grass Swales with a Shallow Substrate Layer

To investigate nitrogen removal efficiencies and mechanisms from road runoff by dry grass swales with a shallow substrate layer, we constructed six dry grass swale columns with different structures and media composition. In order to enhance the nitrogen removal efficiencies during the whole process, fermented woodchips were added into the substrate layer, and saturated zones were established. Semi-synthetic road runoff was used as the influent water. The influent and effluent quality were analyzed, and the change in volumetric water content and ORP of the media were monitored. The results showed significant nitrogen removal by these columns under unfavorable conditions. The range of the average removal rate of TN by the dry grass swales with saturated zones was 67%-78%. The nitrogen removal process mainly occurred during the wet period of the substrate layer. The saturated zones enhanced nitrogen removal efficiencies during the dry period, and also promoted the quick establishment of anoxic conditions in the substrate layer during the wet period. The water-holding transition layer with organic matter was effective at providing a carbon source for denitrification in the saturated zone, and for avoiding the leaching of pollutants caused by organic decomposition.