Persulfate activation by Fe-rich biochar from sewage sludge digestate for organic pollutants removal: performance and superoxide radical role.

Herein, an innovative methodology aimed at the valorization of sewage sludge through advanced treatment and utilization strategies, thereby fostering a circular economy while attaining both ecological and economic advantages. The research involved a two-step process: an initial Fenton-like chemical pretreatment to enhance sludge biodegradability, followed by anaerobic digestion (AD) to yield methane as an energy source. Subsequently, the iron-rich digestate generated from this process was subjected to pyrolysis, resulting in iron-rich biochar (FBC-600). As a catalyst, FBC-600 accelerated the degradation of Orange G (OG) via persulfate (PS) activation. Under optimized conditions (0.5 g/L FBC-600, 10 mM PS, 50 mg/L OG), 100 % of OG removal was achieved within 60 min. Notably, FBC-600/PS system exhibited remarkable stability and robustness against variations in pH (from 3 to 11), coexisting anions, tap water, and using other common organic pollutants. The FBC-600/PS system exhibited an activation energy of 14.88 kJ/mol and retained 88.9 % OG removal efficiency after five reuse cycles. ensuring consistent performance. Furthermore, mechanistic investigations revealed that the synergistic interaction of oxygen-containing groups (OFGs), iron and nitrogen species, and structural defects synergistically promoted PS activation and enhanced reactive oxygen species (ROS) production. Quenching experiments and electron paramagnetic resonance (EPR) confirmed the predominant role of radical species, particularly O, in the degradation of OG. In the context of the circular economy, the as-developed FBC-600, estimated at $3210 US$/t. Hence, this work highlights a sustainable "waste-to-resource" approach for water treatment, offering both ecological and economic benefits.