Pollutant Removal Efficiency of Vertical Sub-surface Upward Flow Constructed Wetlands for Highway Runoff Treatment

Comprehensive evaluation of substrate materials for contaminants removal in constructed wetlands

Considerable number of studies have been carried out to develop and apply various substrate materials for constructed wetlands (CWs), however, there is a lack of method and model for comprehensive evaluation of different types of CWs substrates. To this end, this article summarized nearly all the substrate materials of CWs available in the literatures, including natural materials, agricultural/industrial wastes and artificial materials. The sources and physicochemical properties of various substrate materials, as well as their removal capacities for main water contaminants including nutrients, heavy metals, surfactants, pesticides/herbicides, emerging contaminants and fecal indicator bacteria (FIB) were comprehensively described. Further, a scoring model for the substrate evaluation was constructed based on likely cost, availability, permeability, reuse and contaminant removal capacities, which can be used to select the most suitable substrate material for different considerations. The provided information and constructed model contribute to better understanding of CWs substrate for readers, and help solve practical problems on substrates selection and CWs construction.

Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

The work presented in this paper is based on the pilot study that was performed to investigate the role of flow pattern in the constructed wetlands (CWs) on the treatment performance of real low-strength municipal wastewater. Four identical pilot-scale horizontal sub-surface flow constructed wetlands (HSSF-CWs) were installed, out of which three beds were planted with a common macrophyte, whereas one was kept as a control. The distinction in the hydraulic design was baffles, vertical up-down (CW2) and side slits (CW3), and the third bed (CW1) was kept horizontal plain type (without baffles). The filter media used in all the beds was dual type, coarse and fine gravel. Monitoring was carried out to determine BOD₅, COD, TSS, NH₄⁺-N, TN, and TP concentrations at different sampling points. Results show that the baffled beds performed better compared to the non-baffled in the order of CW2 > CW3 > CW1 > Control. The highest removal efficiency was measured in the CW2 with a reduction in BOD₅ (86%), COD (77%), TSS (80%), NH₄⁺-N (59%), TN (66%), and TP (64%). The statistical method used also showed that the flow pattern has an impact on the treatment performances of the CWs.

Treatment for domestic wastewater from university dorms using a hybrid constructed wetland at pilot scale

A hybrid constructed wetland (CW) system was operated at pilot scale to evaluate the treatment of domestic wastewater from university dorms in Hubei province, China. The hybrid system consisted of an integrated vertical flow constructed wetland (IVF CW) (a down-flow VF CW and an up-flow VF CW) and a horizontal subsurface flow constructed wetland (HSF CW). The influent for the hybrid CW containing chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonium nitrogen (NH₄⁺-N) with mean concentrations of 152, 0.75, 18.9, and 8.9 mg L^-1, respectively, was purified by the hybrid CW system to achieve mean removal efficiencies of 59.0% COD, 82.8% TP, 57.7% TN, and 79.2% NH₄⁺-N over a 9-month period. The nitrification intensity of the media in the down-flow VF CW was the highest compared to the other CWs, whereas the denitrification intensity of the media in the HSF CW was significantly higher than the IVF CW. The abundance of nitrifying bacteria in the media of the IVF CW was higher than in the HSF CW, while a higher abundance of denitrifying bacteria was found in the HSF CW compared to the IVF CW, suggesting that the HSF CW was more suitable for the growth of denitrifying bacteria.

Modeling organic matter and nitrogen removal from domestic wastewater in a pilot-scale vertical subsurface flow constructed wetland

Constructed wetlands have become an attractive alternative for wastewater treatment. However, there is not a globally accepted mathematical model to predict their performance. In this study, the VS2DTI software was used to predict the effluent biochemical oxygen demand (BOD) and total nitrogen (TN) in a pilot-scale vertical flow constructed wetland (VFCW) treating domestic wastewater. After a 5-week adaptation period, the pilot system was monitored for another 6 weeks. Experiments were conducted at hydraulic retention times (HRTs) in the range of 2-4 days with Typha latifolia as the vegetation. The raw wastewater concentrations ranged between 144-430 and 122-283 mg L(-1) for BOD5 and TN, respectively. A first-order kinetic model coupled with the advection/dispersion and Richards' equations was proposed to predict the removal rates of BOD5 and TN from domestic wastewater. Two main physical processes were modeled in this study, porous material water flow and solute transport through the different layers of the VFCW to simulate the constructed wetland (CW) conditions. The model was calibrated based on the BOD5 and TN degradation constants. The model indicated that most of BOD and TN (88 and 92%, respectively) were removed through biological activity followed by adsorption. It was also observed that the evapotranspiration was seen to have a smaller impact. An additional data series of effluent BOD and TN was used for model validation. The residual analysis of the calibrated model showed a relatively random pattern, indicating a decent fit. Thus, the VS2DTI was found to be a useful tool for CW simulation.