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Water pollution is a major environmental issue with the rapid development of industry. Therefore, advanced technologies and materials are needed to remove pollutants from contaminated waters. The adsorption process displays many advantages such as high adaptability and removal efficiency for water sources of varying quality. Hydrogels have recently attracted attention due to their high adsorption capacity and structural stability, yet several issues remain to be explored, such as the number of reuse and engineering applications. Here, we review hydrogels for the removal of methylene blue from wastewater, with focus on hydrogel preparation and properties, adsorption performance and mechanisms, reusability and comparison with biological and chemical oxidation methods. [ABSTRACT FROM AUTHOR]

Activated carbon fiber (ACF) was used as a green catalyst to activate persulfate (PS) for oxidative decolorization of azo dye. ACF demonstrated a higher activity than activated carbon (AC) to activate PS to decolorize Orange G (OG). The decolorization efficiency of OG increased as ACF loading, PS dosage, and temperature increased. OG decolorization followed a pseudo first-order kinetics, and the activation energy was 40.902 kJ/mol. pH had no apparent effect on OG decolorization. Radical quenching experiments with various radical scavengers (e.g., alcohols, phenol) showed that radical-induced decolorization of OG took place on the surface of ACF, and both SO and HO· were responsible for OG decolorization. The impact of inorganic salts was also evaluated because they are important compositions of dye wastewater. Cl and SO exhibited a promoting effect on OG decolorization, and the accelerating rate increased with elevating dosage of ions. Addition of Cl and SO could increase the adsorption of OG on ACF surface, thus favorable for OG decolorization caused by the surface-bound SO and HO·. Conversely, HCO and humic acid (HA) slightly inhibited OG decolorization. The azo band and naphthalene ring on OG were remarkably destructed to other intermediates and finally mineralized to CO and HO. [ABSTRACT FROM AUTHOR]

• nCuO exhibited the highest reactivity in PAA activation among nMOPs. • High reactivity of Cu(I) in PAA activation was unveiled. • A new scavenging experiment was developed to distinguish CH 3 C(O)OO●. • Co-existing H 2 O 2 played a significant role in Cu(II)/Cu(I) conversion. • The nCuO/PAA process is promising in real wastewater decontamination. Peracetic acid (PAA)-based advanced oxidation processes (AOPs) has attracted increasing attentions towards contaminant degradation in the wastewater treatment. Herein, we report the efficient activation of PAA by nano-CuO (nCuO/PAA) to degrade carbamazepine (CBZ) for the first time. Rapid degradation of CBZ was observed in the nCuO/PAA system at neutral initial pH. A new scavenging experiment with Mn2+ as a specific scavenger was developed to distinguish the dominant role of CH 3 C(O)OO● for CBZ degradation in the nCuO/PAA process. The oxidation of CBZ by CH 3 C(O)OO● was verified to proceed via the electrons transfer, and the acute and chronic toxicity of the transformation products was significantly reduced. The efficient activation of PAA by nCuO was found to be realized through continuous conversion of Cu(II) to Cu(I), which was significantly boosted by co-existing H 2 O 2. The nCuO/PAA process was slightly affected by the water matrices, and maintained high efficiency in real water samples. The findings obtained in this study provide new insights into the catalytic formation of CH 3 C(O)OO● from PAA and facilitate the development and application of PAA-based AOPs in wastewater treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • nTiO 2 in anatase (A_nTiO 2) enhances the decomposition of PAA. • A_nTiO 2 catalyzed decomposition of PAA proceeds via a non-radical process. • The unsaturated Ti atoms (Ti 5c) on {0 0 1} facets act as the reactive sites for PAA decomposition. • The interaction process enhances the stability of A_nTiO 2. While peracetic acid (PAA) are known to be susceptible to decomposition by metals for radical generation, herein we report a novel decomposition process of PAA with TiO 2 nanoparticle (nTiO 2) for the first time. nTiO 2 in anatase (A_nTiO 2) could significantly enhance the decomposition of PAA, whereas, nTiO 2 in rutile phase had no impact on the stability of PAA. Electron paramagnetic resonance (EPR) technique and a radical quenching study indicated lack of involvement of reactive radicals. In-depth investigation revealed that the {0 0 1} facets of A_nTiO 2 with high surface free energy were especially reactive for the catalytic decomposition of PAA. Theoretical calculations proved the adsorption of PAA onto A_nTiO 2 {0 0 1} surface was much more favorable than the predominated {1 0 1} facets. The unsaturated five coordinated Ti (Ti 5c), typical Lewis acid sites on A_nTiO 2 {0 0 1} surface, were further confirmed as the dominant active sites for catalyzing PAA decomposition. This novel decomposition process could enhance the stability and migration of A_nTiO 2 , increasing the potential environmental risk. Meanwhile, the disinfection of PAA was inhibited by introducing A_nTiO 2. The new findings of this study broaden the knowledge on PAA decomposition process, and have an important implication for PAA disinfection and environmental behavior of TiO 2 nanoparticle. [ABSTRACT FROM AUTHOR]

• Selective elimination of TCs by PMS in livestock wastewater. • A kinetic model describes TCs oxidation in real livestock wastewater. • PMS-promoted TCs oxidation proceeds via non-radical process. • Theoretical calculations reveal the electrophilic attacks at ring B of TCs. • Hydroxylation dominates in the PMS-induced oxidation of TCs. Tetracyclines (TCs) discharged from livestock wastewater have received worldwide concerns owing to their potential threats to the ecosystem and human health. Advanced oxidation processes always exhibit low efficiency to remove TCs in livestock wastewater due to the radical scavenging by water matrices. Herein, we report selective elimination of TCs by peroxymonosulfate (PMS) in livestock wastewater. A kinetic model was developed to describe the rapid degradation of TCs by PMS in the real livestock wastewater. The radical scavenging study and electron paramagnetic resonance (EPR) technique excluded the contribution of radical species (e.g., SO 4 −) in the PMS-promoted oxidation of TCs. Theoretical calculations revealed the electrophilic attacks of PMS most likely located on the B-ring of TCs. Transformation product analysis further elucidated that hydroxylation dominated in the PMS-promoted oxidation of TCs, and N-demethylation also significantly contributed to chlorotetracycline (CTC) oxidation by PMS. These results demonstrate a promising strategy to eliminate TCs in livestock wastewater, because PMS shows specific reactivity towards TCs, and thus suffers less interference from the complicated water matrices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cr, Cu, Zn and Cd could be removed simultaneously by nZVI@SBC. • NO 3 – and HA promote the removal of Cr, Cu, Zn and Cd. • Cr and Cu were reduced by nZVI and then removed through co-precipitation. • The removal of Cd and Zn were driven by alkali precipitation and complexation. Cr, Cu, Zn, and Cd commonly coexisted in the electroplating wastewater with high salinity and organics, while their removal was often investigated individually. In this study, the simultaneous removal of Cr, Cu, Zn, and Cd was investigated by nano zero-valent iron modified sludge biochar (nZVI@SBC). The results showed that nZVI@SBC could significantly improve the removal efficiency of the four heavy metals (HMs) in high salinity wastewater. NO 3 – (N-NO 3 –) and humic acid (HA) could promote the removal of Cr, Cu, Zn, and Cd, and PO 4 3- (P-PO 4 3-) could enhance the removal of Cd. EPR analysis demonstrated the generation of 1O 2 in different water matrices. The 1O 2 intensity increased in the presence of NO 3 – and HA, which indicated the acceleration of the nZVI corrosion and the promoted electron transfer in the system. To further understand the reaction mechanism, the variation of nZVI@SBC structures and compositions during the treatment process were characterized by SEM-EDS, XRD, BET, and XPS. Cr and Cu were removed through adsorption and co-precipitation after reduction by nZVI, while Cd and Zn were removed by alkali precipitation and complexation. This work improves the understanding of simultaneous removal of HMs by nZVI@SBC and provides a cost-effective approach for the electroplating wastewater treatment. [ABSTRACT FROM AUTHOR]

High strength hydrothermal liquefaction wastewater (HTL-WW) is produced during the hydrothermal liquefaction of biowaste into bio-oil. The presence of complex and refractory organics in HTL-WW limited the conversion efficiency during the anaerobic digestion. An anaerobic biofilm reactor, packed with granular activated carbon (GAC) and polyethylene (PE) rings, was continuously operated over 160 days for HTL-WW treatment in this study. The performance was higher than previous researches in terms of organic loading and methane production, resulting in 285 ± 22 mL/g COD (83.4% of theoretic value) methane yield when operated at a concentration of 10 g COD/L under a 1.7 d HRT. The potential role of GAC on HTL-WW conversion, including absorption, microbial enrichment, and metabolic flux variation via enhancement of direct interspecies electron transfer (DIET), was also discussed. It was found that the GAC played a very important role in the beginning, acting as an adsorbent for the reduction of inhibitors and color. In addition, biofilms developed on the GAC enriched the syntrophic metabolism of bacteria responsible for inhibitors degradation. Over 80% of the COD and 75% of color in HTL-WW were removed by microbes. Furthermore, the difference in microbial structure between the PE and GAC biofilms revealed the potential of establishing DIET on the GAC via enrichment of Anaerolineaceae , Syntrophomonas and Methanosaeta. Image 1 • HTL-WW was continuously treated by anaerobic biofilm reactor over 160 days. • GAC acted as adsorbent reducing inhibitors and color in the beginning. • Inhibitors degraders and syntrophic metabolism bacteria were enriched in biofilms. • Potential of established DIET on the GAC was discussed. [ABSTRACT FROM AUTHOR]