氮负荷波动下污水地下渗滤系统除污及释放N2O的特征

通过实验室模拟试验分析了进水氮负荷对污水地下渗滤系统出水水质及N2O产生的影响。结果表明:随进水氮负荷升高,系统对NH_4~+-N、COD等污染物的去除率呈下降趋势,而对TN的去除率呈先增加后降低的趋势;在低进水氮负荷(≤1.6 g/(m~2·d))和高进水氮负荷(≥6.4 g/(m~2·d))时,生物脱氮作用的N_2O气体产率相对较低,不超过(31.8±2.7)mg/(m~2·d);在中等进水氮负荷(2.4~5.6g/(m~2·d))时,N_2O气体产率最大值达到(60.6±2.0)mg/(m~2·d);N_2O的转化率也呈先升高后降低的变化趋势,在氮负荷为2.4 g/(m~2·d)时,转化率达到最大值,即1.33%±0.03%。综合考虑地下渗滤系统处理效果及N_2O产率等方面的要求,建议在工程应用中,污水地下渗滤系统的进水氮负荷为4.0~5.6 g/(m~2·d)。在该负荷区间下,N_2O主要产生在地下渗滤系统的下层,即厌氧区域是N_2O的主要释放源,占总体的70%以上。

On the decontamination efficiency and N2O release features in the subsurface infiltration system under varying nitrogen loads

The purpose of this paper is to make an exploration of the influence of the different affecting nitrogen loads on the pollutant removal and N2O release in the SWIS (short for Subsurface Wastewater Infiltration System) as one of the sources of N2O emission.In the paper,we have brought about a related suggestion in the regard to the optimal engineering application of the nitrogen ranges.That is to say,we have arranged a set of rough simulation experiments including 6 runs with different nitrogen loads known as 1.6 g/(m2 · d),2.4 g/(m2 · d),4.0 g/(m2·d),5.6 g/(m2·d),6.4 g/(m2 · d) and 7.2 g/(m2· d).The resnlts of our simulated experiment indicate that,with the increase of the influent nitrogen load,it is possible to decrease the removal rate of NH4+-N,COD and the other pollutants contained,whereas the removal rate of TN tends to increase first and then decrease.Literally speaking,when the influent nitrogen load is 4.0 g/(m2 · d),it would be possible to achieve the greatest TN removal rate.It also suggests that,the lower (≤ (31.8 ± 2.7) g/(m2 · d)) the TN removal rate under the conditions of low load (≤ 1.6 g/(m2 · d)),the higher the production rate of N2O (≥6.4 g/(m2 · d)) under the influent nitrogen loads would be.On the other hand,under the condition of the medium nitrogen load (2.4-5.6 g/(m2 · d)),the maximum N2O emission rate can be made as high as(60.6 ± 2.0)mg/(m2· d) in accordance with our observation.Thus,an increasing trend tends to be followed by a decrease so as to reach the maximum rate (1.33％ ±0.03％) on the condition when the nitrogen load gets to 2.4 g/(m2 · d),as the conversion rate of N2O has also been indicated.Nevertheless,when the nitrogen load increases greater than 4.0 g/(m2 · d),the N2O conversion rate would begin to drop significantly.Therefore,taking into consideration the treating efficiency and N2 O emission rate,it is recommended to adopt the influent nitrogen load in a range from 4.0 g/(m2 · d) to 5.6 g/(m2 · d) in case when it is necessary to lay out a subsurface infiltration system for engineering applications.Under such a load condition,N2O can be produced mainly from the lower layer of SWIS,that is,the anaerobic layer,as a main contributor,which may account for over 70％ of the total N2O emission.