Water-based Fe3O4 magnetic fluid-coated Aspergillus niger spores for treating liquid contaminated with Cr(VI)

Preparation of smart magnetic fluids and application in sewage treatment: Copper adsorption, kinetic and isotherm study

The effective removal of heavy metal ions from sewage remains a critical issue, and applying the operability of magnetic materials to large volume wastewater treatment has been a significant challenge. In this paper, metal ions adsorption induced aggregation strategy is proposed to solve this contradiction. The intelligent magnetic fluid designed in this study is a well-dispersed fluid state when treating sewage, and can efficiently adsorb heavy metal ions in wastewater with high adsorption capacity and ultra-fast adsorption kinetics. More importantly, after saturation of adsorption, the magnetic fluid will transform from a well-dispersed fluid state to an agglomeration state which is easy to precipitate and separate via external magnetic field. In a simple and effective way, the particles size of magnetic nanoparticles was precisely controlled by cellulose derivatives modification to obtain a stable magnetic fluid in water. The Freundlich model best described Cu2+ adsorption on magnetite nanoparticles, the correlation coefficients from the Cu2+ adsorption on the two magnetic fluids are 0.9554 and 0.9336, n are 1.868 and 2.117, revealing a favorable adsorption of Cu2+ onto magnetic fluids. The pseudo second-order model fitted the adsorption kinetic data better, the qe are 0.1948 and 0.1315 mmol/g and the R2 are 0.9999, indicating that the adsorption of Cu2+ onto the magnetic fluid was dominated by chemisorption. Moreover, the removal rate of Cu2+ in tap water and lake water was more than 97.1%, and the removal rate of large volume sewage was 81.7%. The synthetic magnetic fluid has high adsorption capacity, ultra-fast adsorption kinetics, reusability and easy separation, indicating its potential application for the removal of heavy metal ions from large-volume sewage.

Cr(VI) reduction by Agrobacterium sp. Cr-1 and Lysinibacillus sp. Cr-2, novel Cr(VI)-reducing strains isolated from chromium plant soil

The bioremediation of Cr(VI)-contaminated soil is a promising strategy; however, the performance of Cr(VI)-reducing bacteria is limited by the toxicity of Cr(VI). In this study, two novel Cr(VI)-reducing bacteria were isolated from a Cr salt plant and identified as Agrobacterium sp. and Lysinibacillus sp. The Cr(VI) reduction conditions of the two strains were optimized. At a Cr(VI) concentration of 500 mg/L, Agrobacterium sp. Cr-1 reduced Cr(VI) with a removal rate of 96.91%, while that for Lysinibacillus sp. Cr-2 was 92.82%. First-order reaction kinetic equations simulated the positive relationship between time and Cr(VI) concentration during Cr(VI) reduction in these two strains. Agrobacterium sp. Cr-1 was further studied, and the effects of different cell components on Cr(VI) reduction were detected. The extracellular extracts of Agrobacterium sp. Cr-1 played a major role in Cr(VI) reduction, followed by intracellular extracts and cell membranes. The scanning electron microscope-energy dispersive spectrometer (SEM-EDS) images show that the precipitation was Cr. The high Cr(VI) reducing ability of Agrobacterium sp. Cr-1 suggests that this strain is promising for the remediation of Cr(VI)-contaminated sites.

Anchored growth of highly dispersed LDHs nanosheets on expanded graphite for fluoride adsorption properties and mechanism

In this study, a new composite with layered double hydroxides (LDHs) anchored grown on expanded graphite (EG) interlayers was prepared by vacuum-assisted intercalation and hydrothermal method. Both sides of EG were completely covered by highly dispersed LDHs nanosheets and formed a sandwich-like structure. The unique structure made expanded graphite/layered double hydroxides (EG/LDHs) composites which had excellent F^- adsorption performance. The adsorption performance of F^- on EG/LDHs was evaluated, and the results indicated that the adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir model. Pseudo-second-order kinetic model indicated that the adsorption sites were the main factor in the adsorption process. Moreover, the maximum adsorption capacity (Q_m) reached 63.21 mg·g^-1 at 30 min at room temperature, which was better than most of the same type of adsorbents. The highly dispersed of LDHs anchored growth on EG overcame the disadvantage of aggregation, which exposed more adsorption sites and improved the removal efficiency of F^-. In addition, the effects of pH, anion interference, different water quality, and regeneration tests on the EG/LDHs composites were also analyzed, showing that the composites have good stability.

Biosorption of Cr (VI) by acid-modified based-waste fungal biomass from Calocybe indica fruiting bodies production

The world is going through a colossal drinking water scarcity. Unchecked discharge (even at trace levels) of Cr (VI) from industries into water bodies is a serious environmental concern. Here, we report waste fungal biomass (WFB) for the detoxification and removal of chromium ions. Biomass understudy was collected from Calocybe indica fruiting bodies. WFB was used after drying and pretreatment with two distinctive chemical methods, which improved the remediation effectiveness of Cr (VI). Light microscope and Field emission Scanning microscope (FESEM) were employed to elucidate the surface morphology of waste fungal biomass. While Fourier-Transform Infrared-Spectroscopy (FTIR) and Energy Dispersive X-Ray analysis (EDAX) were deployed to explore the mechanism of interaction between Cr (VI) anion and waste fungal biomass. X-ray Photoelectron Spectroscopy (XPS) analyses demonstrated considerable conversion of Cr (VI) into nontoxic Cr (III) species. The most favorable condition for optimum Cr (VI) remediation of 99.66% by treated waste fungal biomass (TWFB) occurred at pH 3, contact time 10 min, adsorbent dosage 3 gL^-1, Cr (VI) concentration 4 mgL^-1, stirring speed 140 rpm, and temperature 320 K, where for untreated waste fungal biomass (UWFB) the optimum of 85% remediation occurred at a contact time 15 min, and adsorbent dosage 2 gL^-1 whereas other experimental conditions remained identical as TWFB biosorbent. Pseudo-second-order kinetics (R² > 0.99) model matched the adsorption rate. And, the Freundlich isotherm model (R² > 0.99) is shown to be a better match for the experimental data. The optimum amount of Cr (VI) adsorbed by the TWFB and UWFB were 205.8 ± 10.1 and 72.85 ± 2.36 mgg^-1, respectively. Thermodynamic parameters revealed that the adsorption was spontaneous (ΔG ˂ 0), endothermic (ΔH > 0), and entropy-driven (ΔS > 0). The generated WFB adsorbent also has significant recycling potential. After five cycles of regeneration and adsorption. It can still keep up good remediation effectiveness of Cr (VI) ions to 85.5.