Removal behavior and mechanisms of U(VI) in aqueous solution using aloe vera biochar with highly developed porous structure

Phosphorus-rich biochar modified with Alcaligenes faecalis to promote U(VI) removal from wastewater: Interfacial adsorption behavior and mechanism

Phosphorus-rich biochar (PBC) has been extensively studied due to its significant adsorption effect on U(VI). However, the release of phosphorus from PBC into solution decreases its adsorption performance and reusability and causes phosphorus pollution of water. In this study, Alcaligenes faecalis (A. faecalis) was loaded on PBC to produce a novel biocomposite (A/PBC). After adsorption equilibrium, phosphorus released into solution from PBC was 2.32 mg/L, while it decreased to 0.34 mg/L from A/PBC (p < 0.05). The U(VI) removal ratio of A/PBC reached nearly 100%, which is 13.08% higher than that of PBC (p < 0.05), and it decreased only by 1.98% after 5 cycles. When preparing A/PBC, A. faecalis converted soluble phosphate into insoluble metaphosphate minerals and extracellular polymeric substances (EPS). And A. faecalis cells accumulated through these metabolites and formed biofilm attached to the PBC surface. The adsorption of metal cations on phosphate further contributed to phosphorus fixation in the biofilm. During U(VI) adsorption by A/PBC, A. faecalis synthesize EPS and metaphosphate minerals by using the internal components of PBC, thus increasing the abundance of acidic functional groups and promoting U(VI) adsorption. Hence, A/PBC can be a green and sustainable material for U(VI) removal from wastewater.

The remediation of uranium-contaminated groundwater via bioreduction coupled to biomineralization with different pH and electron donors

Stimulating indigenous microbes to reduce aqueous U(VI) to insoluble U(IV) by adding an electron donor has been applied as an applicable strategy to remediate uranium-contaminated groundwater in situ. However, biogenic U(IV) minerals are susceptible to oxidative remobilization after exposure to oxygen. To enhance the stability of the end product, glycerol phosphate (GP) was selected to treat artificial uranium-containing groundwater at different pH values (i.e., 7.0 and 5.0) with glycerol (GY) as the control group. The results revealed that removal ratios of uranium with GP were all higher than those with GY, and reduced crystalline U(IV)-phosphate and U(VI)-phosphate minerals (recalcitrant to oxidative remobilization) were generated in the GP groups. Although bioreduction efficiency was influenced at pH 5.0, the stability of the end product with GP was elevated significantly compared with that with GY. Mechanism analysis demonstrated that GP could activate bioreduction and biomineralization of the microbial community, and two stages were included in the GP groups. In the early stage, bioreduction and biomineralization were both involved in the immobilization process. Subsequently, part of the U(VI) precipitate was gradually reduced to U(IV) precipitate by microorganisms. This work implied that the formation of U-phosphate minerals via bioreduction coupled with biomineralization potentially offers a more effective strategy for remediating uranium-contaminated groundwater with long-term stability.