Choosing suitable substrate is key to improving the efficiency of wetland decontamination. However, little is known about the effect of particle size. In order to study the effect of substrate type and size on COD, TN, and TP removal from sewage, 1-2, 2-4, and 4-8 mm zeolite, 2-4, 4-8, and 8-16 mm gravel, and 2-4, 3-5, and 6-8 mm anthracite were selected for establishment of the constructed system of experimental media with three replications. Results showed that removal efficiency of COD, TN, and TP varied with different particle sizes of the same material. The greatest COD removal was achieved with 4-8 mm zeolite and gravel and 6-8 mm anthracite, with removal rates of 53.74%, 60.76%, and 62.93%, respectively. Denitrification is the main pattern of nitrogen removal in the artificial test column; results show that smaller particle size is more effective for removal of TN. The removal rate of TP is also higher with smaller sizes of gravel and anthracite, but the opposite pattern occurred with zeolite. The removal of COD, TP, and TN also varied by substrate type. Anthracite led to good removal of COD, TP, and TN. Zeolite was most effective for removal of TN but had lower removal of TP. Gravel has high removal rate for COD, and has a general removal effect on TP.
Keywords: chemical oxygen demand; constructed wetlands; substrate; total nitrogen; total phosphorus.