潜流人工湿地系统停留时间分布与N、P浓度空间变化

Residence Time Distributions and Spatial Variation of N,P in the Subsurface-flow Constructed Wetlands for Purification of Eutrophic Aquaculture Water

通过人工湿地小试装置,研究了风车草和香蒲水平潜流人工湿地处理富营养化养殖水体过程中水力停留时间分布(RTD)特征和系统内N、P浓度空间变化规律.结果表明,供试的香蒲潜流湿地和风车草潜流湿地系统RTD曲线特征值σ2分别为0.3246和0.4108,表明水流流态介于推流与混合流之间,风车草潜流湿地系统RTD曲线较香蒲潜流湿地平滑,水流混合流动程度较弱.2种植物类型湿地床体总氮(TN)和氨氮(NH4+-N)浓度在垂直方向上的分层现象明显,尤其在湿地床体前端;TN浓度随着取样点深度增加而上升,而NH4+-N浓度则以中层取样点为最低;对于总磷(TP)和正磷酸盐(PO43--P)浓度,2种植物类型湿地系统内均表现为随取样点深度增加而上升,但这种差异随沿程而降低.与香蒲湿地相比较,风车草潜流湿地系统N、P浓度分层现象更为明显.风车草湿地系统后端各层取样点TN和TP平均浓度较香蒲湿地系统分别下降了19.8%和12.3%,说明风车草潜流湿地系统对富营养化养殖水体中氮、磷的去除效果优于香蒲湿地.

Hydraulic residence time distributions （RTD） and spatial variations of N, P were studied in a small-scale horizontal subsurface-flow constructed wetlands （HSFCWs） planted with Cyperous alternifolius and Typha angustifolia respectively for purification of eutrophic aquaculture water. The results show that the residence time distribution curves of the investigated HSFCWs lie between plug-flow and completely mixed model with characteristic values （ σ2 ） of 0. 324 6 and 0.410 8, respectively. Compared with Typha angustifolia, Cyperous alternifolius wetland shows fine flow pattern with characteristics of smoother RTD curve and weaker vertical mixed flow. Total nitrogen （TN） and ammonia nitrogen （NH4^＋ -N） show stratified distributions in the two HSFCWs, especially in the front end of the wetland beds. TN in the lower layer is higher than that in the upper, while NH4^＋ -N in the middle layer is the lowest in all the sampling layers. Total phosphorus （TP） and phosphate （PO4^3- -P） increases with sampling depth. Differences in TP and PO4^3- -P between the layers decrease gradually along distance. Cyperous alternifolius wetland shows better stratification distributions of N, P, as compared with Typha angustifolia, which is mainly contributed to the difference in flow patterns between the two HSFCWs. On average, concentrations of TN and TP in the rear end of the Cyperous alternifolius wetland are 19.3 % and 12.5 % lower, respectively, as compared to the Typha angustifolia wetland, suggesting that removal efficiencies of the Cyperous alternifolius wetland for purification of eutrophic aquaculture water is higher than those of the Typha angustifolia.