Iron-Modified Biochar and Plant Species in Enhancing Wastewater Treatment in Constructed Wetlands

Constructed wetlands (CWs) are an effective wastewater treatment technology, with biochar addition believed to further enhance their performance. This study investigated the effects of different ‘tea leaf-derived biochar loaded with Fe’ (TBC-Fe) addition levels (0%, 1%, 2%) on wastewater treatment performance in CWs planted with three wetland plant species: Cyperus alternifolius (CA), Acorus calamus (AC) and Canna indica (CI). Through controlled experiments, we evaluated the effects of TBC-Fe on the removal efficiency of COD, TN, NH₄⁺-N, NO₃⁻-N and TP, while also evaluating plant physiological responses. Results demonstrated that the appropriate biochar addition level (1%) significantly enhanced water quality improvement of CWs and promoted plant growth, root metabolic activity and nutrient uptake (N and P). Among the plant species, the CA system showed the highest potential for pollutant removal. However, its dosage effect is significant; excessive addition of biochar (2%) led to reduced biomass, lower chlorophyll and carotenoid concentration and decreased photosynthesis efficiency, thereby impairing the CW performance. These findings suggest that TBC-Fe can significantly boost the water purification efficiency of CWs, but optimal dosages must be tailored to specific plant species and biochar characteristics for maximum effectiveness in both wastewater purification and plant growth.