Regeneration of a perchlorate-exhausted highly selective ion exchange resin: Kinetics study of adsorption and desorption processes

Environmental occurrence, toxicity and remediation of perchlorate - A review

Perchlorate (ClO4-) comes under the class of contaminants called the emerging contaminants that will impact environment in the near future. A strong oxidizer by nature, perchlorate has received significant observation due to its occurrence, reactive nature, and persistence in varied environments such as surface water, groundwater, soil, and food. Perchlorate finds its use in number of industrial products ranging from missile fuel, fertilizers, and fireworks. Perchlorate exposure occurs when naturally occurring or manmade perchlorate in water or food is ingested. Perchlorate ingestion affects iodide absorption into the thyroid, thereby causing a decrease in the synthesis of thyroid hormone, a very crucial component needed for metabolism, neural development, and a number of other physiological functions in the body. Perchlorate remediation from ground water and drinking water is carried out through a series of physical-chemical techniques like ion (particle) transfer and reverse osmosis. However, the generation of waste through these processes are difficult to manage, so the need for alternative treatment methods occur. This review talks about the hybrid technologies that are currently researched and gaining momentum in the treatment of emerging contaminants, namely perchlorate.

Impact of Acetate in Reduction of Perchlorate by Mixed Microbial Culture under the Influence of Nitrate and Sulfate

The biological reduction of slow degradation contaminants such as perchlorate (ClO4−) is considered to be a promising water treatment technology. The process is based on the ability of a specific mixed microbial culture to use perchlorate as an electron acceptor in the absence of oxygen. In this study, batch experiments were conducted to investigate the effect of nitrate on perchlorate reduction, the kinetic parameters of the Monod equation and the optimal ratio of acetate to perchlorate for the perchlorate reducing bacterial consortium. The results of this study suggest that acclimated microbial cultures can be applied to treat wastewater containing high concentrations of perchlorate. Reactor experiments were carried out with different hydraulic retention times (HRTs) to determine the optimal operating conditions. A fixed optimal HRT and the effect of nitrate on perchlorate reduction were investigated with various concentrations of the electron donor. The results showed that perchlorate reduction occurred after nitrate removal. Moreover, the presence of sulfate in wastewater had no effect on the perchlorate reduction. However, it had little effect on biomass concentration in the presence of nitrate during exposure to a mixed microbial culture, considering the nitrate as the inhibitor of perchlorate reduction by reducing the degradation rate. The batch scale experiment results illustrated that for efficient operation of perchlorate reduction, the optimal acetate to perchlorate ratio of 1.4:1.0 would be enough. Moreover, these experiments found the following results: the kinetic parameters equivalent to Y = 0.281 mg biomass/mg perchlorate, Ks = 37.619 mg/L and qmax = 0.042 mg perchlorate/mg biomass/h. In addition, anoxic–aerobic experimental reactor results verify the optimal HRT of 6 h for continuous application. Furthermore, it also illustrated that using 600 mg/L of acetate as a carbon source is responsible for 100% of nitrate reduction with less than 50% of the perchlorate reduction, whereas at 1000 mg/L acetate, approximately 100% reduction was recorded.

Perchlorate occurrence in foodstuffs and water: Analytical methods and techniques for removal from water - A review

Perchlorate (ClO₄^-), a type of contaminant with high diffusivity and durability, has been widely detected in water and foodstuffs, arousing a global concern. It can interfere with normal function of the human thyroid gland, affecting human health. Therefore, determination of perchlorate in water and foodstuffs, and removal from water are important. This review focuses on the occurrence of perchlorate, mainly in water and foodstuffs, and provides an overview of analytical methods for determination of perchlorate over the last two decades. In addition, merits and drawbacks of the various methods have been considered. This review also highlights the most commonly used approaches for removal of perchlorate from water. Finally, current trends and future perspectives in determination of perchlorate and removal from water are proposed. This review provided a comprehensive understanding of perchlorate occurrence and its removal from water, and had practical significance in reducing the harm of perchlorate to human.

Preparation of ZnFe2O4/AC composite and its adsorption behaviour for SO2

ZnFe₂O₄/AC composites were prepared by a one-pot hydro-thermal method using the activated carbon as a carrier. The structural, textural and surface properties of the adsorbent have been comprehensively characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra, physical adsorption instrument (BET) and TG-DSC analysis. The removal capacities of the composites were investigated via testing the adsorption capacity at the self-made desulfurization equipment. The process of adsorption for SO₂ was analysed by kinetic model and thermodynamic model. The results show that the adsorption capacity of ZnFe₂O₄/AC composites adsorption kinetics process was conformity with the first kinetics mode1. The adsorption process was in accordance to the Langmuir and Freundlich equation. Additionally, the whole process belonged to spontaneous and exothermic reaction.

Adsorption of low concentration perchlorate from aqueous solution onto modified cow dung biochar: Effective utilization of cow dung, an agricultural waste

In this study, cow dung biochar (CDB) and ferric chloride-modified CDB (Fe@CDB) were synthesized to remove low concentration perchlorate from water. The pseudo-second-order kinetics model was used and satisfactorily described perchlorate removal onto CDB and Fe@CDB. The Langmuir model fit the experimental isotherm data better than the Freundlich model. The maximum adsorption capacity obtained using the Langmuir model was 1787 μg/g for Fe@CDB and 304 μg/g for CDB. The detrimental effects of coexisting anions decreased as: NO₃^- > SO₄^2- > Cl^-. FeCl₃ modification enhanced ion exchange, and this was the main mechanism rather than electrostatic interactions. Also, after modification, the surface area, pore volume, and pore size increased and promoted adsorption. The surface hydrophilicity increased and so did the amounts of the surface oxygenated functional groups OH and COOH, which were responsible for perchlorate adsorption. The materials were further characterized using Brunner-Emmet-Teller (BET) measurements, Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), Scanning Electron Microscopy (SEM), Elemental analysis, X-ray photoelectron spectroscopy (XPS), Boehm titration, Zeta potential and Fourier transform infrared spectroscopy (FTIR).

Capture of perchlorate by a surface-modified bio-sorbent and its bio-regeneration properties: Adsorption, computations and biofouling

A magnetic amine-crosslinked reed (MACR) was synthesized by an insitu precipitation method and used for perchlorate uptake. The morphological properties of clean MACR, perchlorate-saturated MACR and bio-regenerated MACR samples were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. The adsorption capacities of perchlorate by clean and bio-regenerated MACRs were determined. The density functional theory (DFT) method was employed to evaluate the binding free energies between various anions and ammonium/hydroxy groups. The maximum adsorption (Q_max) of perchlorate by MACR was calculated to be 195.5-232.8 mg/g at 30-50 °C. The theoretical computation of adsorption-free energies indicated that ammonium groups were dominant in the process of perchlorate adsorption; other anions, such as [H₂PO₄]^-, [NO₃]^- and [SO₄]^2-, showed relatively higher binding free energies than [ClO₄]^-, which corresponded to the results of competitive adsorption. The spent MACR was then bio-regenerated in a sealed 250-ml conical flask with perchlorate-reducing bacteria (30 °C, 160 rpm) and reached 81.4% of recovery within 3 days. Some hydrophobic macromolecules of extracellular polymeric substances (EPS) might have attached to the surface of MACR, which was validated by the zeta potential, SEM and excitation emission matrix (EEM) fluorescence spectroscopy results.