土壤含水层处理系统对再生水入渗过程中“三氮”去除的柱试验模拟

doi:10.13745/j.esf.sf.2021.2.7

摘要/Abstract

摘要：

土壤含水层处理系统(soil aquifer treatment,SAT)是一种重要的人工回灌地下水方式。以再生水为回灌水源时,水中含有的“三氮”可能会对回灌区地下水造成污染风险。研究各种因素对在SAT中去除再生水中“三氮”的影响具有重要意义。本研究中,通过高200 cm、内径50 cm土柱试验,研究了SAT系统中粒径、干湿比(落干期与淹水期的比值)、在系统表层增加生物炭及渗透流速对实际再生水“三氮”去除效果的影响。结果表明,在干湿比1∶1条件下,实际河道细砂和中细砂柱底部出水中NH₄-N平均去除率分别为73%和66%,去除机理主要为吸附和硝化作用,NO₂-N基本被去除。系统中硝化作用导致NO₃-N浓度升高,出水中NO₃-N浓度平均增长了3.0%4.1%。在深度115 cm以上, 中细砂柱内比细砂柱内的硝化作用更强,这导致了更高的NH₄-N去除率和更低的NO₃-N去除率。延长落干期后(干湿比3∶1),系统具有了更强的复氧能力,促进了硝化作用,使得NH₄-N的平均去除率提高了20%,而NO₃-N的降低了3%4%,增加了NO₃-N污染风险。在中细砂层添加5%重量生物炭后,吸附性能增强,使其对NH₄-N平均去除率增加了20%32%,但对NO₃-N影响不明显。渗透流速与NH₄-N的去除和NO₃-N的增加均呈负相关。综合分析可得出,影响SAT系统去除“三氮”的最主要因素是干湿比和渗透流速,在回补水源中NH₄-N浓度较高时,可考虑在SAT系统表层添加生物炭以增强其去除效果。

关键词: 再生水, 土壤含水层处理, 三氮, 吸附, 硝化作用, 生物炭, 渗透流速

Abstract:

Soil aquifer treatment (SAT) is an important method of artificial groundwater recharge. However, when reclaimed water is used as recharging source, the nitrogen species in water may pose pollution risks to groundwater in the recharging area. It is of great significance, therefore, to study the effects of various factors on nitrogen removal from reclaimed water in SAT. In this study, through soil column experiments (using a column of 200 cm in height and 50 cm in inner diameter), the effects of particle size, dry/wet ratio, biochar addition, temperature and infiltration rates on nitrogen removal were studied. The results showed that under the dry/wet ratio of 1∶1, the average removal efficiencies for NH₄-N in the effluents of fine and medium-fine sand columns were 73% and 66%, respectively, by adsorption and nitrification mainly, while NO₂-N was almost totally removed. Nitrification resulted in a NO₃-N concentration increase in the filtration system by 3.0%-4.1% on average in the effluent. Above the depth of 115 cm, nitrification was stronger in the medium-fine sand column than in the fine sand column, which resulted in a higher NH₄-N and lower NO₃-N removal rates. After prolonging the drying period (using dry/wet ratio 3∶1), the filtration system showed a stronger reoxygenation capacity promoting nitrification. It led to a 20% increase in the average NH₄-N removal rate and 3%-4% reduction of NO₃-N, thus increasing the risk of NO₃-N pollution. After adding 5% biochar (by weight) to the medium-fine sand layer, the adsorption performance was enhanced, and the average NH₄-N removal rate was increased by 20%-32%, but the effect on NO₃-N was not obvious. The infiltration rate was negatively correlated with NH₄-N removal and NO₃-N increase. Based on the comprehensive analysis, it can be concluded that the main factors affecting nitrogen removal in SAT are the dry/wet ratio and infiltration rate. When NH₄-N concentration in the water source is high, biochar can be added to the surface layer in SAT to enhance its nitrogen removal efficiency.

Key words: reclaimed water, soil aquifer treatment, nitrogen, adsorption, nitrification, biochar, infiltration rate

中图分类号:

高珩, 谭行, 任宇, 朱乐诚, 毕二平. 土壤含水层处理系统对再生水入渗过程中“三氮”去除的柱试验模拟[J]. 地学前缘, 2021, 28(5): 125-135.

GAO Heng, TAN Hang, REN Yu, ZHU Lecheng, BI Erping. Nitrogen removal during reclaimed water infiltration in soil aquifer treatment: Experimental simulation using soil column[J]. Earth Science Frontiers, 2021, 28(5): 125-135.

图/表 6

图1 SAT模拟系统示意图

Fig.1 Schematic diagram of the SAT simulation system

图2 再生水及各柱出水中ORP的变化

Fig.2 Changes of ORP in reclaimed water and effluent from each column

图3 再生水及各柱出水“三氮”浓度变化

Fig.3 Concentration changes of nitrogen species in reclaimed water and effluent from each column

图4 不同干湿比条件下细砂(SC1)和中细砂(SC2)柱中各指标去除率随深度变化进水浓度范围:NH4-N 0.150.36 mg/L;NO2-N 0.030.41 mg/L;NO3-N 4.268.01 mg/L。图中误差柱表示标准差。去除率为正表示减小,去除率为负表示增加。

Fig.4 Changes of removal efficiency of nitrogen species with depth in fine sand (SC1) and medium-fine sand (SC2) columns under different dry/wet ratios

图5 不同干湿比条件下SC2和SC3柱15 cm深度处“三氮”与“总氮”浓度及去除率

Fig.5 Concentrations and removal efficiencies of nitrogen species in SC2 and SC3 columns at the depth of 15 cm under different dry/wet ratios

图6 比较两种干湿比条件下SC1、SC2和SC3柱各周期出水中NH4-N和NO3-N的去除率与渗透流速

Fig.6 Comparison of removal efficiencies for NH4-N and NO3-N in effluent and column infiltration rates at each column cycle for SC1, SC2 and SC3 columns under two dry/wet ratios

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