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Electrochemical nitrate reduction reaction (NITRR) is a promising approach to removing nitrogen pollutants in wastewater. Herein, Pd-Cu2O/CF was synthesized using a two-step method: in situ growth of cubic Cu2O nanoparticles on Cu foam (CF) and electrodeposited palladium (Pd) metal. The cubic Cu2O nanoparticles provide abundant hydrogen/oxygen-adsorbing sites, and Pd sites with outstanding hydrogen adsorption–desorption features generate more active hydrogen (H*), both of which effectively improve the activity for NITRR. It was demonstrated that Pd-Cu2O/CF had excellent performance with nitrate removal of 99.7% within 60 min. To remove total nitrogen (TN) from wastewater, NH4+ was completely oxidized to N2 within 120 min by adding Cl−, and the TN removal was up to 99.9%. Moreover, Pd-Cu2O/CF displayed long-term stability after ten cycle tests. [ABSTRACT FROM AUTHOR]

The relation between the microstructure and sludge conditioning performance and mechanism of cationic polyacrylamide (CPAM) (low charge density (CD) CPAM C1, medium CD CPAM C4, and high CD CPAM C7) was extensively studied and recognized in this study. Igarashi and Pyun models based on reactivity ratio characterized the microstructure of the polymers. Results indicated that the blockness percent and mean sequence length of acrylamide (AM) unit decreased, whereas those of cationic unit increased with CD. Effect of dosage on sludge conditioning performance and mechanism was studied by measuring turbidity, filter cake moisture content (FCMC), specific resistance of filtration (SRF), floc size distribution, and zeta potential. The longest AM unit sequence length and separated cationic unit of C1 were concluded to be responsible for bridging. Moreover, the conditioning disadvantages of AM were as follows: narrow flocculation window, high optimum dosage, and maximum FCMC. On the contrary, the highest cationic blockness percent of C7 favored efficient charge neutralization, which contributed to the generation of the lowest optimum dosage. However, the SRF was significantly high, which posed as a difficulty for future treatments. The medium cationic blockness percent and mean AM unit sequence length of C4 led to the combination of charge neutralization and bridging effect with a wide flocculation window and the lowest FCMC and SRF. [ABSTRACT FROM AUTHOR]

Heavy metal pollution has become one of the most urgent environmental issues, which also poses a potential threat to the human health. This article is suggested to review the advance on the performance of chemical coagulation process in removing heavy metal from water. Chemical coagulation process is considered to be a valid method which is determined by the hydrolyzed species of the inorganic coagulants under different raw water and coagulation conditions. And the main mechanisms of the removal of heavy metals are adsorption, complexation, and coprecipitation. Compared with the aluminum-based coagulants, the iron-based coagulants have better performance due to the use of wide pH range and large surface area of the resulting flocs. During the chemical coagulation process, the valence state of arsenic and antimony could affect the removal efficiency. Thus, the oxidants and reductants are often combined with inorganic coagulants used in this process. It is found that pH is an important factor greatly influencing the performance directly or indirectly. The complex resulting from the interaction between the inorganic/organic pollutant and inorganic coagulant may contribute to the removal of heavy metals. Overall, chemical coagulation is an effective way to control heavy metal pollution with/without other water treatment technologies. [ABSTRACT FROM AUTHOR]

PO43- and SiO32- are often used as modifier to improve stability and aggregating ability of the iron-base coagulants, however, there are few reports about their detailed comparison between the coagulation performance and mechanisms. In this study, three coagulants—polyferric phosphoric sulfate (PFPS), polysilicon ferric sulfate (PFSS), and polyferric sulfate (PFS) were synthesized; their structure and morphology were characterized by Fourier transformed infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and Scanning electron microscope (SEM). Alkali titration and Ferron species analysis were employed to investigate the hydrolysis performance and species distribution. Jar test was conducted to measure their coagulation behaviors at different dosage, pH, and temperatures in which the flocs properties were measured. The results showed that a number of new compounds were formed due to the presence of PO43- and SiO32-. Moreover, PFPS and PFSS had similar level in Fea as well as Feb. Among them, PFPS produced more multi-core iron atoms polymer and content of Feb, and the formed flocs were larger and denser. It exhibited superior coagulation performance in terms of turbidity reduction, UV254 removal and residual ferric concentration. Jar test and floc breakage/regrowth experiments indicated other than charge neutrality, the dominated mechanism involved in PFSS was the adsorption between polysilicic acid and solution particle, while PFPS was sweeping, entrapment/adsorption resulting from larger polymer colloid of Fe-P chemistry bond. [ABSTRACT FROM AUTHOR]