Remediation of trichloroethylene-contaminated groundwater by three modifier-coated microscale zero-valent iron

Green preparation of regenerable biohybrids with xanthan gum-stabilized biogenic mackinawite nanoparticles for efficient treatment from high-concentration uranium wastewater

The high efficiency, economy, sustainability and no secondary pollution of U(VI) removal is an important and challenging topic for U(VI) wastewater treatment. Here, the regenerable biohybrids with xanthan gum (XG) stabilized biogenic mackinawite nanoparticles (BX-FeS) were prepared, where XG acted as carrier facilitated the Fe2+ attachment and induced the low size, high stability and activity of nearly spherical FeS nanoparticles. Results showed that BX-FeS kept high activity after storing two years and good performance for U(VI) removal in broad pH range and co-existence of ions, and had greater removal efficiency (97.9 %) than biogenic B-FeS (67.1 %). Moreover, BX-FeS preformed high adsorption capacity in uranium wastewater (658.0 mg/g), and lower cost compared with zerovalent-iron and silica gel. Importantly, BX-FeS maintained high activity within three regeneration cycles driven by Desulfovibrio desulfuricans, inhibited the secondary pollution (Fe3+, SO42-) of reaction. This study provides a new strategy for sustainable and efficient treatment of U(VI) wastewater.

Tannic acid promotes the activation of persulfate with Fe(ii) for highly efficient trichloroethylene removal

Trichloroethylene (TCE) is an Environmental Protection Agency (EPA) priority pollutant that is difficult to be removed by some remediation methods. For instance, TCE removal using persulfate (PS) activated by ferrous iron (Fe(ii)) has been tested but is limited by the unstable Fe(ii) concentration and the initial pH of contaminated water samples. Here we reported a new TCE removal system, in which tannic acid (TA) promoted the activation of PS with Fe(ii) (TA-Fe(ii)-PS system). The effect of initial pH, temperature, and concentrations of PS, Fe(ii), TA, inorganic anions and humic acid on TCE removal was investigated. We found that the TA-Fe(ii)-PS system with 80 mg L-1 of TA, 1.5 mM of Fe(ii) and 15 mM of PS yielded about 96.2-99.1% TCE removal in the pH range of 1.5-11.0. Radical quenching experiments were performed to identify active species. Results showed that SO4˙- and ˙OH were primarily responsible for TCE removal in the TA-Fe(ii)-PS system. In the presence of TA, the Fe-TA chelation and the reduction of TA could regulate Fe(ii) concentration and activate persulfate for continuously releasing reactive species under alkaline conditions. Based on the excellent removal performance for TCE, the TA-Fe(ii)-PS system becomes a promising candidate for controlling TCE in groundwater.

Green Synthesis of Nano-Zero Valence Iron with Green Tea and It's Implication in Lead Removal

The nano-zero valence iron (nZVI) via green synthesis for heavy metal remediation has attracted many attentions due to its low-cost, environmental-safety, relative reproductivity, and high stability. However, influence of synthesis conditions on the physiochemical properties of nZVI via green tea extracts and the responding suspensibility, which is required for high reactivity, has not been fully elucidated. In this study, we investigated the zeta potentials, sedimentation and lead (Pb²⁺) removal capacity of various nZVIs synthesized using green tea extracts. The results showed that the tea extracts extracted at 80^oC presented an excellent activity, which contributed to the outstanding suspensibility and reaction activity of nZVI synthesized in a volume ratio of 1:1 (tea extraction versus Fe²⁺ solution). Thus, the optimized nZVI was successfully prepared with a Pb²⁺ removal capacity (377.3 mg/g), which was seven times stronger than 50.31 mg/g of traditional chemical synthesized nZVI.

Polyacrylic acid-b-polyptyrene covered Ni/Fe nanoparticles to remove 1,1,1-trichloroethane in water

A new material, polyacrylic acid-b-polyptyrene (PAA-b-PS) covered Ni/Fe nanoparticles (PAA-b-PS-nZVI-Ni), was developed and evaluated for the selective dechlorination of 1,1,1-trichloroethane (1,1,1-TCA) in the presence of potential interferents. The average size of the PAA-b-PS coated Fe/Ni bimetallic nanoparticles was approximately 50 nm, which resulted from agglomeration prevention by PAA-b-PS. The removal efficiency of 1,1,1-TCA by an optimal dose with a 1.0 g/L Fe/Ni (Ni/Fe = 2 wt%) and 0.5 g/L PAA-b-PS-coated concentration was higher (87.5%) than that of bare Fe/Ni (60%). The pseudo-first-order rate constant (K_obs) of 1,1,1-TCA removal by PAA-b-PS-nZVI-Ni was 0.0142 min^-1 within 240 min. Comparatively, the K_obs values of 1,1,1-TCA removal by other materials (Fe, pure bimetallic Fe/Ni, PAA-b-PS-Fe) were only 0.003, 0.0052 and 0.0103 min^-1, respectively. The 1,1,1-TCA removal efficacy by PAA-b-PS-nZVI-Ni showed no obvious gap regardless of pH or various common inorganic anions (NO₃^-, HCO₃^- and SO₄^2-) at different concentrations. However, humic acid (HA) had great influence on the degradation of 1,1,1-TCA. In conclusion, PAA-b-PS-covered Ni/Fe nanoparticles with its selectivity high effectiveness could be used as one remedial agent for the degradation of 1,1,1-TCA in water.

Biotechnology and nanotechnology for remediation of chlorinated volatile organic compounds: current perspectives

Chlorinated volatile organic compounds (CVOCs) are persistent organic pollutants which are harmful to public health and the environment. Many CVOCs occur in substantial quantities in groundwater and soil, even though their use has been more carefully managed and restricted in recent years. This review summarizes recent data on several innovative treatment solutions for CVOC-affected media including bioremediation, phytoremediation, nanoscale zero-valent iron (nZVI)-based reductive dehalogenation, and photooxidation. There is no optimally developed single technology; therefore, the possibility of using combined technologies for CVOC remediation, for example bioremediation integrated with reduction by nZVI, is presented. Some methods are still in the development stage. Advantages and disadvantages of each treatment strategy are provided. It is hoped that this paper can provide a basic framework for selection of successful CVOC remediation strategies.

Characterization of bimetallic Fe/Ni nanoparticles supported by amphiphilic block copolymer and its application in removal of 1,1,1-trichloroethane in water

The iron and nickel bimetallic nanoparticles supported by the block copolymer polystyrene-block-poly (acrylic acid) (PS-b-PAA-nZVI-Ni) were synthesized successfully and were applied to assess the degradation of 1,1,1-trichloroethane (1,1,1-TCA) in water. An optimal dose of Ni loading was 2 wt%, while an optimal mass ratio of PS-b-PAA to Ni/Fe, i.e., 0.5:1, at which the dechlorination efficiency was a maximum. The size of PS-b-PAA-nZVI-Ni nanoparticles (average size ~ 50 nm) was three times smaller than that of nZVI-Ni due to the prevention of agglomeration of the resultant zerovalent iron nanoparticles by PS-b-PAA. In the applying aspect, the pseudo-first-order rate constant (Kobs) of 1,1,1-TCA removal by PS-b-PAA-nZVI-Ni was 0.0142 min-1 within 240 min, which was approximately five times higher than nZVI. Meanwhile, PS-b-PAA-supported nZVI-Ni nanoparticles penetrated much deeper in quartz sand columns than nZVI-Ni nanoparticles, indicating PS-b-PAA had significant influence on nZVI transport. The findings from this study suggested that PS-b-PAA-nZVI-Ni, with its high reactivity, selective screening for 1,1,1-TCA, could be one significant potential for use as remedial agent to treat chlorinated solvents in water.

Elucidating the dechlorination mechanism of hexachloroethane by Pd-doped zerovalent iron microparticles in dissolved lactic acid polymers using chromatography and indirect monitoring of iron corrosion

The degradation mechanism of the pollutant hexachloroethane (HCA) by a suspension of Pd-doped zerovalent iron microparticles (Pd-mZVI) in dissolved lactic acid polymers and oligomers (referred to as PLA) was investigated using gas chromatography and the indirect monitoring of iron corrosion by continuous measurements of pH, oxidation-reduction potential (ORP), and conductivity. The first experiments took place in the absence of HCA, to understand the evolution of the Pd-mZVI/PLA/H₂O system. This showed that the evolution of pH, ORP, and conductivity is related to changes in solution chemistry due to iron corrosion and that the system is initially cathodically controlled by H⁺ mass transport to Pd surfaces because of the presence of an extensive PLA layer. We then investigated the effects of Pd-mZVI particles, temperature, initial HCA concentration, and PLA content on the Pd-mZVI/PLA/HCA/H₂O system, to obtain a better understanding of the degradation mechanism. In all cases, HCA dechlorination first requires the production of atomic hydrogen H^*-involving the accumulation of tetrachloroethylene (PCE) as an intermediate-before its subsequent reduction to non-chlorinated C₂ and C₄ compounds. The ratio between Pd-mZVI dosage, initial HCA concentration, and PLA content affects the rate of H^* generation as well as the rate-determining step of the process. A pseudo-first-order equation can be applied when Pd-mZVI dosage is much higher than the theoretical stoichiometry (600 mg for [HCA]₀ = 5-20 mg L^-1). Our results indicate that the HCA degradation mechanism includes mass transfer, sorption, surface reaction with H^*, and desorption of the product.

Carbon Nanotube Based Groundwater Remediation: The Case of Trichloroethylene

Adsorption of chlorinated organic contaminants (COCs) on carbon nanotubes (CNTs) has been gaining ground as a remedial platform for groundwater treatment. Applications depend on our mechanistic understanding of COC adsorption on CNTs. This paper lays out the nature of competing interactions at play in hybrid, membrane, and pure CNT based systems and presents results with the perspective of existing gaps in design strategies. First, current remediation approaches to trichloroethylene (TCE), the most ubiquitous of the COCs, is presented along with examination of forces contributing to adsorption of analogous contaminants at the molecular level. Second, we present results on TCE adsorption and remediation on pure and hybrid CNT systems with a stress on the specific nature of substrate and molecular architecture that would contribute to competitive adsorption. The delineation of intermolecular interactions that contribute to efficient remediation is needed for custom, scalable field design of purification systems for a wide range of contaminants.