Influence of electrodes and media saturation in horizontal flow wetlands employed for municipal sewage treatment: A comparative study

This study reports organic matter, nutrient, coliform removal performance in microbial fuel cell (MFC)-based, normal (without electrodes) horizontal flow (HF) constructed wetlands that were filled with stone-aggregate and dosed with municipal wastewater. The HF constructed wetlands were operated as monoculture plant-based shallow bed-fully saturated or polyculture plant-based deep bed-partially saturated systems. The HF wetlands were operated under two hydraulic loading (HL) rates: 29.3 and 58.6 mm/d. The MFC-based, normal HF constructed wetlands achieved 80 to 100% organic, 55 to 92% nitrogen removal percentage throughout the experimental campaign. Organic removal was influenced by the organic biodegradation ratio (BOD/COD) profiles of municipal wastewater, particularly in the MFC-based systems. Nitrogen removal was achieved through media-based adsorption and microbial nitrification–denitrification. The wetland systems achieved ≥93% phosphorus and ≥83% coliform removal through media-based adsorption, filtration, and oxidation kinetics. Nutrient accumulation percentage in plants tissue was <1% with respect to total removal. HL and pollutant removal rates increment were positively correlated. Maximum power density production rates were 10.6, and 38.6 mW/m² in shallow bed-fully saturated and deep bed-partially saturated HF constructed wetlands, respectively. The deep bed-partially saturated MFC-based, normal HF wetlands achieved higher pollutant removal, bioenergy production because of better atmospheric oxygen transmission capacity.