Enhanced adsorptive removal of hexavalent chromium in aqueous media using chitosan-modified biochar: Synthesis, sorption mechanism, and reusability.

Hexavalent chromium (Cr(VI)) is deemed a priority contaminant owing to its carcinogenicity, teratogenicity, and mutagenicity towards flora and fauna. A novel Chitosan-modified Mimosa pigra biochar (CMPBC) was fabricated and the efficiency of Cr(VI) oxyanion removal in aqueous systems was compared with the pristine biochar. The instrumental characterization of X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) confirmed the amino modification of MPBC when treated with chitosan. Characteristic features of the Cr(VI) sorptive process by CMPBC and MPBC were examined by performing batch sorption studies. Experimental data suggested that sorption is heavily dependent on pH and the highest adsorption occurred at pH 3.0. The maximum adsorption capacity of CMPBC was 14.6 ± 1.07 mg g-1. It was further noted that the removal efficiency of CMPBC (92%) was considerably greater than that of MPBC (75%) when the solution pH, biochar dose, and initial concentration of Cr(VI) are 3.0, 1.0 g L-1 and 5.0 mg L-1 respectively. The kinetic data were best interpreted by the power function model (R2 = 0.97) suggesting a homogenous chemisorption process. The isotherm data for the removal of Cr(VI) by CMPBC was inferred well by Redlich Peterson (R2 = 0.96) and Temkin (R2 = 0.96) isotherms. Results of sorption-desorption regeneration cycles indicated that the Cr(VI) uptake by CMPBC is not fully reversible. The coexistence of Cr(VI) and Cr(III) on CMPBC was confirmed through the XPS analysis. The electrostatic attractions between cationic surface functionalities and Cr(VI) oxyanions, the partial reductive transformation of Cr(VI) species to Cr(III), as well as complexation of Cr(III) onto CMPBC were identified as the possible mechanisms of mitigation of Cr(VI) by CMPBC. The results and outcomes of this research suggest the possibility of utilizing the CMPBC as an easily available, environmentally sustainable, and inexpensive sorbent to decontaminate Cr(VI) from aqueous media.

Environmental challenges of COVID-19 pandemic: resilience and sustainability - A review.

The emergence of novel respiratory disease (COVID-19) caused by SARS-CoV-2 has become a public health emergency worldwide and perturbed the global economy and ecosystem services. Many studies have reported the presence of SARS-CoV-2 in different environmental compartments, its transmission via environmental routes, and potential environmental challenges posed by the COVID-19 pandemic. None of these studies have comprehensively reviewed the bidirectional relationship between the COVID-19 pandemic and the environment. For the first time, we explored the relationship between the environment and the SARS-CoV-2 virus/COVID-19 and how they affect each other. Supporting evidence presented here clearly demonstrates the presence of SARS-CoV-2 in soil and water, denoting the role of the environment in the COVID-19 transmission process. However, most studies fail to determine if the viral genomes they have discovered are infectious, which could be affected by the environmental factors in which they are found.The potential environmental impact of the pandemic, including water pollution, chemical contamination, increased generation of non-biodegradable waste, and single-use plastics have received the most attention. For the most part, efficient measures have been used to address the current environmental challenges from COVID-19, including using environmentally friendly disinfection technologies and employing measures to reduce the production of plastic wastes, such as the reuse and recycling of plastics. Developing sustainable solutions to counter the environmental challenges posed by the COVID-19 pandemic should be included in national preparedness strategies. In conclusion, combating the pandemic and accomplishing public health goals should be balanced with environmentally sustainable measures, as the two are closely intertwined.

Phytoremediation prospects of per- and polyfluoroalkyl substances: A review.

Extensive use of per- and polyfluoroalkyl substances (PFASs) in various industrial activities and daily-life products has made them ubiquitous contaminants in soil and water. PFAS-contaminated soil acts as a long-term source of pollution to the adjacent surface water bodies, groundwater, soil microorganisms, and soil invertebrates. While several remediation strategies exist to eliminate PFASs from the soil, strong ionic interactions between charged groups on PFAS with soil constituents rendered these PFAS remediation technologies ineffective. Pilot and field-scale data from recent studies have shown a great potential of PFAS to bio-accumulate and distribute within plant compartments suggesting that phytoremediation could be a potential remediation technology to clean up PFAS contaminated soils. Even though several studies have been performed on the uptake and translocation of PFAS by different plant species, most of these studies are limited to agricultural crops and fruit species. In this review, the role of both aquatic and terrestrial plants in the phytoremediation of PFAS was discussed highlighting different mechanisms underlying the uptake of PFASs in the soil-plant and water-plant systems. This review further summarized a wide range of factors that influence the bioaccumulation and translocation of PFASs within plant compartments including both structural properties of PFASs and physiological properties of plant species. Even though phytoremediation appears to be a promising remediation technique, some limitations that reduced the feasibility of phytoremediation in the practical application have been emphasized in previous studies. Additional research directions are suggested, including advanced genetic engineering techniques and endophyte-assisted phytoremediation to upgrade the phytoremediation potential of plants for the successful removal of PFASs.

Amino-functionalized biochars for the detoxification and removal of hexavalent chromium in aqueous media.

The objectives of the study were to evaluate and compare the efficacy of hexavalent chromium (Cr(VI)) removal by amino-modified (HDA-MPBC) and pristine biochar (MPBC) derived from an invasive plant Mimosa pigra. Prepared biochars were characterized and batch experiments were conducted to check the performance and the mechanisms of Cr(VI) removal. FTIR spectra revealed that the surface of HDA-MPBC is abundant with amino functional groups which was further confirmed by XPS analysis. The highest Cr(VI) removal for both HDA-MPBC (76%) and MPBC (62%) was observed at pH 3.0. The batch sorption data were well fitted to the Freundlich isotherm model and pseudo-second-order kinetic model, suggesting the involvement of both physisorption and chemisorption mechanisms for Cr(VI) removal. X-ray photoelectron spectroscopy studies showed that both Cr(VI) and Cr(III) were presented at the modified biochar surface after adsorption. These results indicated that the electrostatic attraction of Cr(VI) coupled with reduction of Cr(VI) to Cr(III) and complexation of Cr(III) ions with functional groups on HDA-MPBC as the most plausible mechanism for removal of Cr(VI) by modified biochar. Regeneration experiment concluded that adsorbed Cr(VI) onto the surface of HDA-MPBC had the least tendency of being desorbed in basic conditions. HDA-MPBC showed a high performance in adsorptive removal of Cr(VI) compared to pristine biochar signifying the amino modification to enhance adsorption performance of biochar in Cr(VI) removal from wastewater.

A systematic review on adsorptive removal of hexavalent chromium from aqueous solutions: Recent advances.

The contamination of natural resources by hexavalent chromium (Cr(VI)) originating from natural and anthropogenic activities is a serious environmental concern. Although many articles on chromium remediation have been published, a comprehensive understanding of the mechanisms involved in remediation with different sorbents is not yet available. In this systematic review, the performance and applicability of several adsorptive materials for Cr(VI) removal from aqueous media are discussed, along with a detailed analysis of the mechanisms involved. Statistical analysis is applied to compare the efficacies of different adsorbents, while a similar approach is used to determine the effects of sorbent properties and experimental conditions on the adsorption capacity. A detailed analysis of the factors involved in fixed-bed column studies is also presented. A suitable desorption approach to the regeneration of the spent adsorbent and its adsorption performance in reuse is also examined. Among the different sorbents, nanoparticles and mineral-doped biochar were found to be the most effective sorbents, while the adsorption was higher at low pH (~4.0) than that at intermediate pH (6-8). Contrary to our expectation, adsorption was high for sorbents with low specific surface areas, suggesting that the adsorption of Cr(VI) is largely influenced by the chemical properties of the sorbents. The optimum adsorption in fixed-bed column systems is obtained at a lower Cr(VI) ion concentration, a lower influent flow rate, and a higher bed height. Since most of the studies reviewed herein were merely experimental and utilized ideal conditions with the presence of a single contaminant, i.e. Cr(VI) in water, further studies on adsorption dynamics with the presence of other interfering ions are suggested. This review is promising for the further development of Cr(VI) removal strategies and closes the research gaps pertaining to their challenges.