Insights into microbial and sorptive regulation of chlorpyrifos-bispyribac dissipation in floating treatment wetlands

Agricultural runoff remains one of the most persistent threats to water quality worldwide. Floating wetlands (FWs), when designed appropriately, offer a promising nature-based solution. Here, we show how biologically and sorptively active FWs can remove two agrochemicals—chlorpyrifos (CPF) and bispyribac‑sodium (BIS), under response surface methodology (RSM)‑backed optimal operation (pH 8; 35 °C; 10 mg L⁻¹ each; 1 % glucose). FWs built with Phragmites australis (common reed) were amended with a defined consortium (CB2H, 1 % v/v), plant‑derived biochar (1.5 % w/v), biochar‑immobilized CB2H (1.5 % w/v), and nutrients (N 25 mg L⁻¹, P 25 mg L⁻¹, K 20 mg L⁻¹). CPF and BIS declined exponentially, fitting pseudo‑first‑order kinetics with adsorption component (high S, K d in the immobilized system). CPF disappeared fastest in the consortium‑only and biochar‑immobilized treatments (k = 0.07 and 0.09 day⁻¹), resulting in > 99 % removal (>9.9 mg L⁻¹) by day 20; BIS peaked at > 84 % (8.4 mg L⁻¹) with immobilized cells. FTIR shifts (∼2920–2840, 2800 cm⁻¹) and new C O bands (1600–1800 cm⁻¹) indicated hydrogen bonding in the Phragmites biochar. Approximately 40 % of the CPF loss in the controls was abiotic (sorption/photolysis/hydrolysis). Chemical oxygen demand and ancillary pollutants also declined. Enhanced performance was supported by microbial colonization within biochar pores. The study provides key design constants (k, K d ), positioning engineered FWs as a scalable nature-based technology for pesticide-laden agricultural runoff.