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Nano zero-valent iron (NZVI) with high chemical reactivity and environmental friendliness had recently become one of the most efficient technologies for wastewater restoration. However, the unitary NZVI system had not met practical requirements for wastewater treatments. Expectantly, the development of NZVI would prefer multifunctional NZVI-based composites, which could be prepared and optimized by the combined methods and technologies. Consequently, a systematic and comprehensive summary from the perspective of multifunctional NZVI-composite had been conducted. The results demonstrated that the advantages of various systems were integrated by multifunctional NZVI-composite systems with a more significant performance of pollutant removal than those of the bare NZVI and its composites. Simultaneously, characteristics of the product prepared by the incorporation of numerous methods were superior to those by a simple method, resulting in the increase of the entirety efficiency. By comparison with other preparation methods, the ball milling method with higher production and field application potential was worthy of attention. After combining multiple technologies, the effect of NZVI and its composite systems could be dramatically strengthened. Preparation technology parameters and treatment effect of contaminants could be further optimized using more comprehensive experimental designs and mathematical models. The mechanism of the multifunctional NZVI system for contaminants treatment was primarily focused on adsorption, oxidation, reduction and co-precipitation. Multiple techniques were combined to enhance the dispersion, alleviating passivation, accelerating electron transfer efficiency or mass transfer action for optimizing the effect of NZVI composites.

The removal of arsenic(III), one of the most poisonous wastewater pollutants, was investigated using nanoscale zero-valent iron supported onto pumice and modified by chitosan (CS-P-NZVI). Scanning electron microscopy (SEM) analysis revealed that NZVI was distributed dispersedly on CS-P-NZVI without being oxidized. As(III) could be removed by adsorption on CS-P-NZVI in a very short time (minute scale) with high removal rates (more than 99.5%) over a wide range of pH (2.01–12.54) and concentration (20–100 mg/L). The removal of As(III) by CS-P-NZVI agreed well with the pseudo-first-order reaction kinetics and pseudo-second-order reaction kinetics. Reaction rate constants (Kobs) ranged from 0.27 to 0.96 min−1 at varied NZVI dosage. Freundlich isotherm provided a good model of the sorption system, indicating that CS-P-NZVI was heterogeneous in the surface properties. The thermodynamic parameters suggested that As(III) adsorption by CS-P-NZVI was a spontaneous and exothermic process. X-ray photoelectron spectroscopy (XPS) and atomic fluorescence spectrophotometer (AFS) analyses indicated that As(III) was only physically adsorbed on the surface of CS-P-NZVI within 60 min. Our results indicated that CS-P-NZVI might be an effective material for both in situ and ex situ remediation.

Sediment contamination by heavy metals has become a widespread problem that can affect the normal behaviors of rivers and lakes. After chitosan/Fe0-nanoparticles (CS-NZVI) beads were cross-linked with glutaraldehyde (GLA), their mechanical strength, stability and separation efficiency from the sediment were obviously improved. Moreover, the average aperture size of GLA-CS-NZVI beads was 20.6 μm and NZVI particles were nearly spherical in shape with a mean diameter of 40.2 nm. In addition, the pH showed an insignificant effect on the removal rates from the sediment. Due to the dissolution of metals species into aqueous solutions as an introduction of the salt, the removal rates of all heavy metals from the sediment were increased with an increase of the salinity. The competitive adsorption of heavy metals between the sediment particles and GLA-CS-NZVI beads became stronger as the sediment particles became smaller, leading to decreased removal rates. Therefore, the removal efficiency could be enhanced by optimizing experimental conditions and choosing appropriate materials for the target contaminants.

The removal of heavy metals from wastewater is one of the most important issues for the world, especially from industrial effluents. Pumice-nanoscale zero-valent iron (P-NZVI) was successfully prepared in different experimental conditions. Meanwhile, the shape, size and distribution of NZVI on P-NZVI were evaluated using a scanning electron microscope (SEM). At the optimum condition, NZVI with a mean diameter of 20.2 nm was distributed uniformly and consistently on the surface of pumice. Freundlich isotherm analysis suggested that the surface property of P-NZVI were heterogeneous. The removal of Hg (II) and Cr (VI) by P-NZVI could be well described by pseudo-first-order kinetic model. At equilibrium qmax of Hg (II) and Cr (VI) was 107.1 and 106.9 mg/g, respectively. Thermodynamic investigation suggested that the removal of Hg (II) and Cr (VI) by P-NZVI was an endothermic and spontaneous process. The less values of ΔH0 for Hg (II) than those for Cr (VI) demonstrated that more thermal energy was needed to remove Cr (VI) than Hg (II) at the same reaction rate.

Nanoscale zero-valent iron successfully supported on pumice (P-NZVI) was used to remove heavy metals from wastewater with a higher removal capacity and efficiency. NZVI particles with a mean diameter of 30.6 nm are distributed uniformly on the surface of P-NZVI. The thermal stability and mechanical strength of P-NZVI were also obviously enhanced. P-NZVI with a 7.7% NZVI mass fraction had a specific surface area (SBET) of 32.2 m2/g. The removal capacity of Hg (II) and Cr (VI) by P-NZVI was 332.4 mg Hg/g Fe and 306.6 mg Cr/g Fe, respectively. As an increase of pH, the removal rates of Hg (II) increased but those of Cr (VI) decreased gradually. P-NZVI is a regenerated material. The X-ray photoelectron spectroscope analysis (XPS) results indicated that Hg (II) and Cr (VI) were removed by a rapid physical adsorption in the first 0.5 min and predominantly by reduction. In terms of the efficiency and speed, P-NZVI was a promising candidate for applications to in situ environmental remediation, especially to the heavy metals pollution incidents with an extremely high concentration of heavy metals.

Surface water and groundwater are the main water resources used for drinking and production. Assess- ments of the relationship between surface water and groundwater provide information for water resource man- agement in Sanjiang plain, Northeast China. The surface water (river, lake, and wetland) and groundwater were sampled and analyzed for stable isotopic (dD, d 18 O) composition, tritium, and chlorofluorocarbons concentra- tions. The local meteoric water line is dD = 7.3d 18 O-6.7. The tritium (T) and chlorofluorocarbon (CFC) contents in groundwater were analyzed to determine the groundwater ages. Most groundwater were modern water with the ages \50 years. The groundwaters in mountain area and near rivers were younger than in the central plain. The oxygen isotope (d 18 O) was used to quantify the relationship between surface water and groundwater. The Songhua, Heilongjiang, and Wusuli rivers were gaining rivers, but the shallow groundwater recharged from rivers at the confluence area of rivers. At the confluence of Songhua and Heilongjiang rivers, 88 % of the shallow groundwater recharged from Songhua river. The combination of stable isotopes, tritium, and CFCs was an effectively method to study the groundwater ages and interrelation between sur- face water and groundwater. Practically, the farmlands near the river and under foot of the mountain could be culti- vated, but the farmlands in the central plain should be controlled.

The synergistic effect of two different advanced oxidation technologies, heterogeneous sulfate radical based Fenton and TiO2 photocatalysis, was observed through a drastic enhancement of Rhodamine B removal in Co–TiO2/Oxone/Photo process. Our catalysts were obtained by a citric acid-assisted sol–gel method and Rhodmine B was used as model organic pollutant. The cobalt species in Co–TiO2 play a crucial role of integration Fenton with TiO2 photocatalysis in one heterogeneous hybrid system that not only active Oxone to produce SO4-, but also enhance the photocatalytic activity of TiO2 as well as extend its absorption spectrum to visible region, thus it can be defined as a type of bifunctional catalyst. The influence of the pH, [Oxone]/[RhB] molar ratio and catalyst concentration of the catalytic performance were investigated. The Rhodamine B can be eliminated 100% and TOC removal of solution can reach 68% at the optimum conditions by Photo/Co–TiO2/Oxone process. Moreover, the catalyst was demonstrated to have good stability and reusability.

Fe0 nanoparticles (NZVI) were successfully immobilized on epichlorohydrin/chitosan beads (ECH–CS–NZVI beads) for reduction of Cr(VI) from wastewater. Characterization with scanning electron microscope (SEM) showed that ECH–CS–NZVI beads with an average aperture size of 23.2 μm mainly consisted of Fe, O, C and N. Fourier transform infrared (FTIR) spectrum suggested that ECH could be grafted to CS–NZVI beads. A marked decrease in crumpling ratios indicated that the mechanical strength of Fe0-nanoparticles–chitosan (CS–NZVI) beads was obviously enhanced by cross-linking of epichlorohydrin (ECH). The thermal stability of ECH–CS–NZVI beads was also enhanced. Cr(VI) concentration, NZVI dosage, pH values and reaction temperature played an important role in the lifetime and using efficiency of ECH–CS–NZVI beads. Under all experimental conditions, the removal of Cr(VI) using ECH–CS–NZVI beads was consistent with pseudo first-order reaction kinetics. A removal rate could be maintained as high as 76.6% and 48.2% on the second and third runs, respectively, which hinted that ECH–CS–NZVI beads could be regenerated. The study demonstrates that ECH–CS–NZVI beads could become an effective and promising technology for in situ remediation of Cr(VI).

Nanoscale zero-valent iron (NZVI) was successfully entrapped in chitosan (CS) beads for reduction of Cr (VI) from wastewater. The removal mechanism may include both physical adsorption of Cr (VI) on the surface or inside of CS-NZVI beads and subsequent reduction of Cr (VI) to Cr (III). The free amino groups and hydroxyl groups on CS may contribute little to hinder the formation of Fe(III)–Cr(III) precipitate. Entrapment of NZVI in CS beads prevents the particles from aggregation and oxidation. The results indicate that there is no significant difference between the reaction rates of bare NZVI and entrapped NZVI. Cr (VI) reduction kinetics follows a pseudo-first-order rate expression. The reduction capacity for Cr (VI) increases with increasing temperature and NZVI dosage but decreases with the increase in initial concentration of Cr (VI) and pH values. This study demonstrates that entrapment of NZVI in CS beads has the potential to become a promising technique for in situ groundwater remediation.