The 11th International Conference on Water Resource and Environment (WRE 2025)

Abstract: Bench-scale plug-flow type reactor with Spirodela polyrhiza and Lemna aequinoctialis duckweeds was applied to treat low-strength municipal wastewater. The experimental unit was operated at a constant hydraulic retention time of 4 days, during which duckweed was initially provided at 100% of the water surface area. During continuous operation, growing duckweed biomass was harvested twice a week to maintain the original coverage condition of duckweed on the water surface, and the amount of excess duckweed biomass was monitored. Municipal wastewaters containing different organic (COD) and nitrogen (TKN) concentrations, with their average values ranging from 45-118 mg/l and 17-70 mg/l, respectively, were examined on their effect on the treatment performance, duckweed biomass production, and associated microbial communities. The experimental results revealed the highest average biomass production of 6.5 g dry mass/m2/day of Spirodela polyrhiza duckweed over 72 days of operation when influent wastewater with the highest COD concentrations was applied. At lower organic concentrations, lower average duckweed biomass production rates, ranging from 3-4 g/m2/day for Spirodela polyrhiza and 0.2-1.5 g/m2/day for Lemna aequinoctialis were observed. During the treatment of wastewaters, moderate average COD removal of 37-59% and TKN 22-47% were achieved. Microbial community analyses revealed predominance of Burkholderiales, Pirellulales, Verrucomicrobiales, and Rhizobiales bacterial consortium associated with Spirodela polyrhiza duckweed under high growth yield conditions, whereas Cyanobacteriales were found predominant on duckweeds cultivated under low COD conditions.