Reuse of microalgae residue after oil production as a Fenton-like catalyst in wastewater treatment: Catalytic performance and mechanism

Efficient and economical catalysts are crucial for activating H 2 O 2 in Fenton-like reactions. Microalgae harvesting by magnetic separation will inevitably result in unrecovered Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) entering the downstream oil production stage. This part of Fe 3 O 4 NPs can play a catalytic role in the co-liquefaction process with microalgae to improve the bio-oil quality, and then be separated from the liquid phase along with microalgae hydrochar (MHC). Herein, this N-rich MHC loaded Fe 3 O 4 NPs composite (Fe 3 O 4 @MHC) as a by-product was recycled without reprocessing to remove Rhodamine B (RhB). Detailed characterization data indicates that Fe 3 O 4 NPs can be well anchored and dispersed on MHC surface after liquefaction . The Fe 3 O 4 @MHC exhibits an outstanding catalytic performance in the activation of H 2 O 2 for RhB degradation, with a removal rate of >97 % within 60 min at a lower dosage (0.17 g/L). MHC act as electron donors due to the abundant oxygen- and nitrogen-containing functional groups to accelerate Fe 2+ /Fe 3+ cycle. OH and O 2 − are the dominant active species in catalytic systems. This study not only provides an economical carbon material with high efficiency for environmental remediation, but also proposes a reliable solution for the disposal of solid residues after microalgae bio-oil production.