DOI: https://doi.org/10.55373/mjchem.v28i1.189

Keywords: Constructed wetlands, caffeine, Canna indica, micropollutants, ornamental plants

Abstract

Micropollutants (MPs) such as caffeine in untreated wastewater pose ecological and human health risks, and conventional treatments often fail to remove them effectively. This study evaluated mesocosm-scale horizontal subsurface flow constructed wetlands (CWs) planted with Canna indica under monoculture and polyculture conditions for caffeine and nutrient removal. The CWs contained layered substrates (pebble, sand, gravel, cocopeat, activated carbon, and soil) to enhance contaminant retention. Wastewater spiked with 200 mg L⁻¹ caffeine was introduced, and parameters including ammoniacal nitrogen (AN), biochemical oxygen demand (BOD), total nitrogen (TN), caffeine concentration and plant physiological indicators were analyzed. Monoculture Canna indica reduced caffeine concentration to 46.20 ± 0.09 mg L⁻¹, AN to 5.80 ± 1.98 mg L⁻¹, BOD to 36.50 ± 2.12 mg L⁻¹, and TN to 12.00 ± 1.41 mg L⁻¹. Polyculture CWs showed slightly better performance, lowering caffeine concentration to 45.83 ± 0.51 mg L⁻¹ and achieving greater BOD and TN removal, likely due to synergistic plant microbe interactions enhancing biodegradation. The activated carbon and cocopeat layers contributed to adsorption followed by microbial degradation. Lipid peroxidation indicated the highest malondialdehyde (MDA) concentration in Heliconia spp. (0.0155 mM g⁻¹), whereas in Canna indica grown in polyculture exhibited the lowest (0.0070 mM g⁻¹), indicating reduced physiological stress, likely associated with improved nutrient cycling. Overall, Canna indica, particularly when cultivated in polyculture systems, demonstrates strong potential for decentralised wastewater treatment, supporting Sustainable Development Goals (SDGs) 6 and 14.