Ferric chloride (FeCl₃) modified reed straw-based biochar was synthesized to remove nitrate from aqueous solutions and achieve waste recycling. The adsorption of nitrate onto Fe-RBC-600 adsorbents could be described by the pseudo-second-order kinetic model and fitted to Langmuir adsorption, and the maximum adsorption capacity predicted using the Langmuir model was 272.024 mg g⁻¹. The adsorbent characterization indicated that a high temperature of 600 °C and an oxygen-poor environment could develop a hydrophobic surface and O-containing functional groups on the biochar, which provided more binding sites for Fe³⁺/Fe²⁺ attachment and increased the surface functionality of Fe-RBC-600 with iron oxide formation. The increasing surface functionality successfully enhanced the nitrate adsorption property. The mechanism of nitrate adsorption was mainly attributed to the physical adsorption onto the positive surface and sequential chemical reduction by Fe²⁺, and the electrostatic adsorption by protonated amine groups.

Applying microbial fuel cell (MFC) technology for eco-remediation of Cr(VI) pollution from a subsurface environment has great scientific value and practical significance due to its promising advantages of pollutant remediation and renewable energy generation. The aim of the current review is to summarize the migration characteristics of Cr(VI) in a subsurface soil/water environment and investigate the factors affecting the MFC performance for synchronous Cr(VI) remediation and power generation, and sequentially highlight diverse challenges of MFC technology for in situ remediation of subsurface groundwater and soils. The critical review put forward that Cr(VI) removal efficiency and energy production of MFC can be improved by enhancing the adjustability of cathode pH, setting potential, modifying electrode, and incorporating other technologies into MFC. It was recommended that designing typical large-scale, long-term continuous flow MFC systems, adding electron shuttle media or constructing artificial electron according to actual groundwater/soil and Cr(VI) pollution characteristics, site geology, and the hydrogeology condition (hydrochemical conditions, colloid type, and medium) are essential to overcome the limitations of the small size of the laboratory experiments and improve the application of technology to in situ Cr(VI) remediation. This review provided reference and ideas for future research of MFC-mediated onsite Cr(VI) remediation.