曝气充氧条件下污染河道氨挥发特性模拟

以污染河道为研究对象,模拟研究污染河道在曝气充氧(底泥曝气,ES组；水曝气,EW组)条件下氨挥发的特性,探讨主要影响因素及其作用过程.研究表明,污染河道水体具有一定氨挥发潜力,在实验室模拟条件下,氨挥发速率平均为2.51mg·m-2·h-1,相当于0.50 kgN· hm-2·d-1；曝气污染河道水体的氨挥发有一定的促进作用,与对照相比(EC组)氨挥发速率和累积氨挥发量存在显著差异(P＜ 0.05)；不同曝气方式对氨挥发过程影响不同,氨挥发速率存在显著差异(P＜0.05)；至实验结束,EW组的累积挥发量为2809.76 mg/m2,分别是ES组和EC组的1.17和2.25倍；各实验组的氨挥发累积量用一级动力学方程能很好地拟合,根据模型可以预测氨挥发量；同一温度条件下,pH值、铵氮浓度和通气频率是影响氨挥发的主要因素；曝气可以通过增加通气频率和提高水体pH值来促进氨挥发进行；在曝气作用下随着硝化过程的进行对氨挥发有一定的限制作用；曝气条件下,氨挥发作用在硝化过程启动阶段最为明显.

Characterization of ammonia volatilization from polluted river under aeration conditons: a simulation study

Most surface waters in China are eutrophic because of anthropogenic activities. Eutrophication typically results in algal blooms and can lead to poor water quality. Nitrogen is generally recognized as one of the most influential nutrients limiting productivity within an aquatic ecosystem. Nitrogen is also is one of the main factors affecting water quality. The main reason for this phenomenon is that various organic materials including nitrogen-rich materials that exist widely in the water column and sediments consume oxygen, resulting in a lack of dissolved oxygen. Artificial aeration is a technique used to improve water quality of polluted rivers and is widely used to control river pollution in China and abroad. A large number of studies on aeration have indicated that the nitrification/denitrification pathway is the major reduction mechanism of ammonium nitrogen load within polluted rivers. However, limited information is available on the effect of aeration on ammonia volatilization within urban polluted rivers. Ammonia volatilization is an important pathway facilitating nitrogen removal within aquatic systems. Previous research on characteristics of ammonia volatilization facilitating nitrogen removal from water focused on wastewater with relatively higher concentrations of ammonium. These wastewater types included those originating from dairies, wastewater containing slurry concentrations, and stabilization ponds treating domestic wastewater. Furthermore, studies evaluating of the role of ammonia volatilization in nitrogen removal from polluted rivers through aeration have yet to be conducted. It is important to conduct research that quantifies the extent of ammonia volatilization within polluted urban rivers under different aeration conditions. This knowledge can indicate the extent of nitrogen removal by different widely applied techniques for treating heavily polluted river water. Characteristics of ammonia volatilization within a polluted urban river under different conditions were examined: aerating to sediments (ES) and aerating to water (EW). This study was conducted using the indoor experimental method. Results showed that ammonia volatilization was potentially suitable for polluted municipal river, where the average rate of ammonia volatilization was 0.50 kgN·hm^-2·d^-1 under simulated laboratory conditions. Compared to the control group (EC), aeration could facilitate and significantly accelerate the ammonia volatilization of polluted river water (P < 0.05). The ammonia volatilization rate showed significant differences under varying aeration conditions (P < 0.05). By the end of the experiment, cumulative ammonia volatilization in group EWwas 2809.76 mg/m², which was 1.17 times that in the ES group and 2.25 times what occurred within the EC group.With respect to the ammonia volatilization effect of the two aeration mechanisms, the EW technique is superior to the ES technique with a cumulative ammonia volatilization of 1.17 times that of the Es technique. Moreover, the first order kinetic equation is suitable for describing the cumulative amount of ammonia volatilization under different conditions, by which the ammonia volatilization could be predicted. The main factors affecting ammonia volatilization were analyzed. The key factors influencing ammonia volatilization under a constant temperature were pH, ventilation frequency and ammonium concentration. Aeration could facilitate and accelerate the ammonia volatilization through increasing ventilation frequency and elevating the value of pH in overlying water. Under aeration conditions, the nitrification process could be promoted. However, ammonia volatilization rate would decrease with nitrification. During the period of nitrification start-up, the values of cumulative ammonia volatilization were close to the maximum under aeration conditions.