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

Saeed, Tanveer; Salam, Md. Abdus; Kumar Yadav, Asheesh

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DOI: https://doi.org/10.4491/eer.2025.017

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

Tanveer Saeed¹^†, Md. Abdus Salam¹, and Asheesh Kumar Yadav²

¹Department of Civil Engineering, University of Asia Pacific, Dhaka 1205, Bangladesh.
²Department of Environment and Sustainability, CSIR-Institute Minerals and Materials Technology, Bhubaneswar, India

Corresponding Author: Tanveer Saeed ,Tel: +8802-58157091-4, Email: dr.tanveer@uap-bd.edu

Received: January 8, 2025; Accepted: April 19, 2025.

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.

Keywords: Adsorption | Biochar | Bioelectrochemical oxidation | Natural technologies | Removal stability