不同质量浓度硝态氮在潮白河模拟河床中去除效果研究

近年来再生水逐渐成为城市景观河流的主要用水来源,但再生水含有较高氮元素,容易造成水体与地下水污染。河床底泥对NO₃^--N有一定的截留与去除作用,本实验通过河槽装置模拟潮白河河床,探究低、中、高3种NO₃^--N质量浓度水平下河槽系统中底泥对NO₃^--N的去除效果。结果表明:水体中NO₃^--N质量浓度为5、10、20 mg·L^-1时NO₃^--N去除率分别为67.8%、63.0%、55.0%。河槽10 cm处和下部70 cm处对NO₃^--N去除效果较好。底层排出水中pH与NO₃^--N质量浓度相关性较强,底泥中50 cm与70 cm处反硝化作用强度与溶解氧质量浓度紧密相关;随着温度降低,溶解氧质量浓度升高,反硝化作用减弱,NO₃^--N去除效果变差。底泥中NO₃^--N的去除主要通过土壤淋溶作用、同化作用、反硝化作用与异化还原作用等共同作用;部分氮素以同化作用形成的有机氮和异化还原作用形成的NH₄⁺-N留存于底泥中。研究表明,河床底泥对再生水河道具有一定的净化效果。

Removal effect of nitrate nitrogen at different concentrations in a simulated riverbed of the Chaobai River

In recent years, reclaimed water has gradually become the primary water source for urban landscape rivers; however, reclaimed water contains high nitrogen contents, which can cause water and groundwater pollution. The riverbed sediment exhibits an interception and removal effect on NO₃^--N. In this experiment, a channel device was used to simulate the riverbed of Chaobai River to explore the removal effect of the channel system on NO₃^--N under three NO₃^--N concentration levels: low, medium, and high. The results showed that the removal efficiencies of NO₃^--N were 67.8%, 63.0%, and 55.0% when the concentrations of NO₃^--N were 5, 10 mg·L^-1, and 20 mg·L^-1, respectively. The removal effect on NO₃^--N was improved at 10 cm and 70 cm below the river channel, with a strong correlation between pH and NO₃^--N concentration in the bottom effluent. The denitrification intensity at 50 cm and 70 cm in sediment was closely related to the concentration of dissolved oxygen. As the temperature decreased, the dissolved oxygen concentration increased, denitrification decreased, and the removal effect of NO₃^--N worsened. The removal effect of NO₃^--N was primarily caused by soil leaching, assimilation, denitrification, and dissimilatory reduction. Some nitrogen was retained in the sediment as organic nitrogen formed by assimilation and NH₄⁺-N produced by dissimilatory reduction. The study shows that the riverbed sediment exhibits a purification effect on the reclaimed water channel, which can provide a reference for the safe recharge of reclaimed water to rivers and lakes.