Screening of typical pollutants in groundwater polluted by nitrogen heterocyclic pesticides and removal mechanism of iron-doped biochar.

Pesticide-contaminated sites often contain high concentrations of pollutants, including various unknown nitrogen heterocyclic compounds. Effectively treating pesticide-contaminated groundwater poses a significant challenge. Identifying these unknown pollutants and strategically designing materials in a targeted manner offers insights for groundwater remediation. This study employed liquid chromatography-high resolution mass spectrometry (LCHRMS) to analyze groundwater pollutants from pesticide-contaminated sites. Non-targeted screening techniques were adopted to identify and prioritize pollutants for treatment. The critical pyrolysis parameters of sawdust biochar doped with iron (Fe) prepared through a one-step pyrolysis method were evaluated. A total of 36 pollutants were identified via non-targeted screening. Among these, 2-aminobenzimidazole (2-AB) and 2-hydroxybenzimidazole (2-HB), with concentrations of 214.95 mg/L and 286.57 mg/L, respectively, were selected as the target pollutants due to having the highest concentrations. The biochar prepared with a sawdust-to-iron weight ratio of 5:1 and processed at 800 °C (BC5-Fe-800) achieved the best removal rates: 100 % for 2-AB and 99.89 % for 2-HB in the pesticide-contaminated groundwater and 99.49 % chemical oxygen demand (COD) removal rate. Analysis using FT-IR spectra, XRD patterns, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations revealed that the main adsorption mechanisms of the iron-doped biochar were electrostatic adsorption, π-π interaction, hydrogen bonding, surface complexation, and hydrophobic partitioning. BC5-Fe-800 exhibited high reusability, maintaining over 95 % removal efficiency for 2-AB and 2-HB after five consecutive regeneration cycles. This study successfully identified and treated pollutants in pesticide-contaminated groundwater, providing a reliable solution for treating water bodies with high concentrations of complex pollutants.