The impact of biochar and activated carbon on the purification efficiency of two wetland systems under varying pollution loads

The water quality purification of constructed wetlands (CWs) with adsorbent materials has been extensively studied, yet the impact on the improvement in water quality of natural sediment wetlands (SWs) remains unclear. In this study, CWs and SWs were established with biochar and activated carbon substrates, and high and low nitrogen (N) and phosphorus (P) pollution loads were applied. Additionally, relevant studies on the purification efficiencies of artificial wetlands under different pollution loads were reviewed. Results showed that the purification capacities of biochar and activated carbon were affected by the pollution load, and that there was significant interaction between the pollution load and wetland type (P = 0.000). The removal efficiencies of NH₄⁺, NO₃^-, and total P in CWs were significantly higher than those in SWs. In particular, the removal stability of NO₃^- was higher in the BCW (77.12%) and ACW (75.94%) under high pollution loads (P = 0.000). As the pollution load increased, the TP removal efficiency of SWs decreased from 86.56% to 75.97%, while the addition of biochar significantly enhanced removal efficiency (94.57%). The BSW experiment was more efficient in purifying P and NH₄⁺ than ASW or SW. ACWs presented lowest microbial diversity and richness while higher metabolism of chemoheterotrophy and nitrate reduction. This study confirms that the addition of B can promote the sustainability of SW purification, and that both biochar and activated carbon exhibited varying adsorption characteristics in different wetland types. It demonstrates the improved purification potential in biochar added SWs.