Influence of intermittent aeration and organic loading rate on lab-scale constructed wetland systems treating synthetic wastewater

Abstract

By coupling the intermittent characteristics of rural sewage discharge and solar energy density, the performance responses of lab-scale tidal flow constructed wetland (TF) and conventional vertical flow constructed wetland (VF) to different organic loading rates (OLRs) (166.3, 300.9, 451.2, 602.4, and 751.2 g/m2 d) in synthetic domestic sewage treatment were investigated to study its feasibility to replace conventional aeration and reduce the dependence of wastewater treatment plants on the grid in this study. Artificial aeration was conducted based on simulating photovoltaic aeration. The increase in OLR promoted the removal performances for the chemical oxygen demand (COD) and ammonia–nitrogen (NH4+-N) in TF, which could be up to 95.7 and 97.2%, respectively, under OLR of 751.2 g/m2 d. Excess organic carbons inhibited NH4+-N removal through competition for oxygen available in VF, where the COD removal efficiency could be 89.6% while low NH4+-N removal (40%) was obtained under OLR 751.2 g/m2 d. With the increase in OLR, the removal of total nitrogen (TN) was enhanced. A higher OLR can not only provide enough electron donors but also produce more anoxic regions for denitrification. The best TN removal was 77.5% in TF and 49.8% in VF, which occurred at OLR of 751.2 and 602.4 g/m2 d, respectively. A drop of TN removal in VF was attributed to the lack of nitrate–nitrogen (NO3--N) when reaching OLR of 751.2 g/m2 d. The removal efficiency for total phosphorus was increased gradually with the increase in OLR. This paper suggests that appropriate control of OLR can achieve the optimal effect of pollutants removal, especially the elimination of TN.