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Hghly stable, reusable, and multi-functional biocatalytic microparticles with Laccase (Lac) enzyme (Lac/particles) were synthesized for bisphenol A (BPA) removal from aqueous solution. The Lac/particles were prepared by encapsulating Lac enzymes into poly ethylene glycol (PEG) hydrogel via the UV assisted emulsion polymerization method followed by cross linking with glutaraldehyde (GA). The obtained Lac/particles were spherical and micron sized (137–535 μm), presenting high enzyme entrapment efficiency of 100%, high activity recovery of 18.9%, and great stability at various pHs (3–7) than the free Lac. The Lac/particles could adsorb the BPA into the catalytic particles in a short time, promoting contact between BPA and enzyme, and further enzymatically degrade them without the shaking process and independent surrounding buffer solution. The Lac/particles could be reused for another round BPA adsorption and biotranformation by maintaining over 90% of BPA removal efficiency after seven times reuse. The synergistic effects of adsorption and biocatalytical reaction of Lac/particles have significant values in high efficient and cost-effective BPA removal.

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Zero valent iron (ZVI) applications to remediation of shallow groundwaters can be affected by dissolved oxygen (DO) and organic ligands. To explore the intersection between these complicating factors, this study thoroughly characterized the reactions of nitrobenzene (NB) with ZVI in the presence DO and the model ligand ethylene diamine tetraacetic acid (EDTA). The results showed that NB is degraded by both ZVI reduction and ZVI-induced advanced oxidation under oxygen-limited conditions. The contribution of •OH to the degradation of NB increased with time so that nearly 39% of NB was oxidized by •OH at 15 min (pH = 3), but reduction was still the main pathway of NB transformation throughout. NB reduction products, such as aniline (AN), were also oxidized by •OH. The lower the pH, the greater the contribution of advanced oxidation, but DO was the limiting factor for •OH generation. Only 4.7% NB was fully degraded by ring opening and/or mineralization because the production of •OH was limited by low DO. After the transformation of NB and AN, other benzene ring and nitrogen-containing intermediates were identified (e.g., p-nitrophenol, p-aminophenol, hydroquinone, and p-benzoquinone). The removal of total organic carbon and total organic nitrogen was minimal. The results suggested that the relative doses of ZVI, DO, and iron-complexing ligands can be balanced for the optimal (rapid and deep) removal of organic contaminants.

Tripolyphosphate (TPP) has many advantages as a ligand for the optimization of the Fe 2+ /O 2 system in environmental remediation applications. However, the relationship between remediation performance and the Fe 2+ /TPP ratio in the system has not been previously described. In this study, we report that the degradation mechanism of p-nitrophenol (PNP) in Fe 2+ /O 2 systems is regulated by the Fe 2+ /TPP ratio under neutral conditions. The results showed that although PNP was effectively degraded at different Fe 2+ /TPP ratios, the results of specific reactive oxygen species (ROS) scavenging experiments and the determination of PNP degradation products showed that the mechanism of PNP degradation varies with the Fe 2+ /TPP ratio. When C Fe 2+ ≥ C TPP , the initially formed O 2 •− is converted to •OH and the •OH degrades PNP by oxidation. However, when C Fe 2+ < C TPP , the O 2 •− persists long enough to degrade PNP by reduction. Density functional theory (DFT) calculations revealed that the main reactive species of Fe 2+ in the system include [Fe(TPP)(H 2 O) 3 ] − and [Fe(TPP) 2 ] 4− , whose content in the solution is the key to achieve system regulation. Consequently, by controlling the Fe 2+ /TPP ratio in the solution, the degradation pathways of PNP can be selected. Our study proposed a new strategy to regulate the oxidation/reduction removal of pollutants by simply varying the Fe 2+ / TPP ratio of the Fe 2+ /O 2 system.