The effects of hydraulic retention time on coupled pilot-scale

constructed wetlands in removing nutrients

Lijun Ren, Xiaoyan Wang, Shuqing An*

Department of Wetland Ecology, School of Life Science, Nanjing University, Nanjing 210093, China

As most of the wastewaters are difficult to treat in single-stage constructed wetlands, it is necessary to find the optimal CW design characteristics and various types of CWs may be combined in order to achieve higher wastewater treatment effects. 4 types of combined constructed wetland systems, series constructed wetland, parallel constructed wetland, series-parallel constructed wetland and parallel-series constructed wetland treating simulated wastewaters were studied in our trial.

The aim of the study was to examine the effect of hydraulic retention time (HRT) and combined types on the removal of nitrogen and phosphorus by pilot-scale constructed wetlands, in an effort to describe the function of these systems in controlled experiments.

The results implied that coupled pilot-scale constructed wetlands may be used effectively for nutrients removal, especially the parallel-series system. A 5-hour HRT is too long to observe a deleterious effect on TN, and it seemed that a HRT of 4 hours was adequate to result in an acceptable removal efficiency. The different wetland system did not generally show significant difference in TP removal efficiency.