Evaluating biochar-filled normal and electrode-embedded constructed wetlands: The impact of loading rates and plant diversity on septic effluent treatment

Abstract

This study evaluated the effectiveness of biochar-filled, electrode-integrated constructed wetlands using Phragmites and Canna indica plants for treating septic tank effluent. Systems operated across varied hydraulic loads (0.25-1.0 m/d) and showed 93-98% chemical oxygen demand, 69-91% nitrogen, and 88-99% phosphorus removals. Electrodes enhanced pollutant removal by initiating bioelectrochemical reactions, while biochar media supported nutrient adsorption. Rhizosphere-dependent oxygen leakage capacities of the Phragmites and Canna indica plant species induced redox potential variations inside the wetland media. Microbial-based degradation primarily contributed to organic and nitrogen removals. A maximum of 4400 mg/kg nitrogen and 1400 mg/kg phosphorus concentrations were quantified with the wetland biochar, exceeding the fresh media's composition. These data profiles imply the influence of adsorption on nutrient removals. Plant-based nutrient accumulation percentages were negligible, ranging between 0.01 and 3%. Organic and nutrient removal percentage increase or decrease magnitude was <= 11% because of input load increment. The power density production with the Phragmites and Canna indica-based electrode-integrated wetlands ranged between 2674 and 63288 milliwatts (mW)/m3; the Phragmites-based system showed greater power density production. The findings of this study will allow the design of low-cost, natural systems to produce better effluent and energy recovery in decentralized clusters.