Enhanced virus reduction in constructed wetlands with quaternized biochar: Performance and mechanism

Enteric viruses in wastewater pose a challenge to water reuse safety, and conventional constructed wetlands (CWs) provide insufficient virus reduction. To address this challenge, we developed quaternized biochar (BCQA) as a dual-function antiviral material capable of both virus adsorption and capsid structural disruption. The BCQA-amended constructed wetland (BCQA-CW) achieved a 3.24-log higher virus reduction than the CW without BCQA during long-term operation. Compared with unmodified biochar, the higher positive surface charge of BCQA strengthened virus-surface adsorption, while transmission electron microscopy (TEM) and circular dichroism (CD) spectroscopy provided direct evidence of capsid structural damage following contact with BCQA. Molecular docking and molecular dynamics simulations revealed that the quaternary ammonium groups (QAG) engaged in multiple non-covalent interactions with viral outer capsid proteins. These interactions involved hydrogen bonds, halogen bonds, and salt bridges with valine, glutamine, and aspartic acid residues of protein F, identifying key interaction hotspots responsible for capsid destabilization. When tested with real secondary effluent, BCQA-CW achieved high levels of virus reduction (4.02 ± 0.23 log reduction), while toxicity assessment indicated enhanced ecological safety of the treated water. Overall, this study demonstrates a substrate-based strategy for effective virus reduction in CWs, supporting the safe reuse of treated wastewater.