Effect of electrode coupling and external circuit connection variations on pollutant removal with biochar-packed...

Six biochar media and Canna indica plant-based constrfigucted wetlands were developed to treat municipal wastewater; these systems differed in terms of electrode coupling and external circuit configurations. The hydraulic dosing included sequential constant (stable period) and rapid load shifting cycles (unstable period), which were artificially controlled and repeated. The mean percentages of organic matter, nitrogen, phosphorus, and coliform removal ranged from 89 to 98%, 47 to 65%, 82 to 90%, and 41 to 90%, respectively, in both normal (without electrode coupling) and electrode-dependent constructed wetlands. Electrochemical oxidation and electrochemically inactive pathways improved pollutant removal in electrode-embedded constructed wetlands; power density generation ranged from 120 to 298 mW/m³. The electrodes and circuit configurations were critical operational factors for improving pollutant removal and energy recovery in electrode-based systems. The use of multiple anode-cathode electrodes and parallel circuit connections improved operational performance. Plant nutrient uptake was not dominant; the accumulation percentage ranges were 0.3-3%. Higher nutrient concentrations of the biochar media (extracted from the wetland systems) compared to the fresh samples elucidate the effect of media-based adsorption. The normal and electrode-based constructed wetlands achieved 2-9% higher organic matter removal during the unstable period compared to the total removal during the stable period. However, a 1-7% decrease in nitrogen and coliform removal percentage was observed during the unstable period. This study demonstrates the impact of plants, media, electrode, and circuit connection configurations on the overall performance of the conventional and electrode-embedded constructed wetlands operated under sequential fluctuating input loadings.