Search Results (2)

A mechanistic model was developed to simulate one-dimensional pesticide transport in two-stage vertical flow constructed wetland. The two pesticides taken under study were carbendazim and chlorothalonil. The water flow patterns within the constructed wetland were simulated using the Richards equation. Water content and vertical flux, which are the outputs of the substrate water flow model, were used to calculate the substrate moisture-related parameters and advection term in the solute transport model. The governing solute transport equation took into account a total of six processes: advection, molecular diffusion, dispersion, adsorption to the solid surface, degradation and volatilization. A total of 14 simulation cases, corresponding with available experimental data, were used to calibrate the model, followed by further simulations with standardized influent pesticide concentrations. The simulations indicated that the constructed wetland reached a steady state of pesticide removal after 7 days of operation. Two distinct water flow patterns emerged under saturated and unsaturated conditions. The patterns observed while varying the hydraulic loading rates were similar for each individual saturation condition. Two-factor ANOVA of the simulated data further revealed that the carbendazim and chlorothalonil removal was dependent on the hydraulic loading rates, but it was independent of the influent pesticide concentration. Analysis of the simulated pesticide removal showed that degradation emerged as the predominant removal process over time for both the pesticides. The model developed in this study can be an important tool for the design and construction of treatment wetlands for pesticide removal from wastewater. Full article

The Ethiopian floriculture industry produces large amounts of wastewater, which requires treatment systems with lower retention times, higher hydraulic flow, and higher hydraulic loading rates (HLRs). Unsaturated vertical flow constructed wetlands (UVF-CWs), which represent these characteristics, have not been studied in depth for chlorothalonil remediation from wastewater. In this study, six UVF-CWs and nine pumping stations were organized into three experimental groups as three independent two-stage CW systems. The influent was pumped into the first vertical-flow stage, after which the effluent was collected and pumped into the second vertical-flow stage. The stage A and stage B effluents were tested for chlorothalonil removal at three different HLR of 50, 200, and 400 L d⁻¹ m⁻² and two influent chlorothalonil concentrations of 100 and 500 µg L⁻¹. The chlorothalonil levels for the stage A effluent at an HLR of 50 L d⁻¹ m⁻² for both influent chlorothalonil concentrations were below the detection limit of 0.08 µg L⁻¹. A maximum chlorothalonil concentration of 7.9 and 196 µg L⁻¹ was observed in the stage A effluent for influent concentrations of 100 and 500 µg L⁻¹, respectively. The chlorothalonil levels for the stage B effluent were all below the detection limit of 0.08 µg L⁻¹. A final chlorothalonil removal efficiency of at least 99.9% was observed for both influent chlorothalonil concentrations at the three HLRs used. These results demonstrated that UVF-CWs represent a viable solution for chlorothalonil remediation in the Ethiopian floriculture industry. Full article