In-situ degradation of soil-sorbed 17β-estradiol using carboxymethyl cellulose stabilized manganese oxide nanoparticles: Column studies

Efficient remediation of mercury-contaminated groundwater using MoS2 nanosheets in an in situ reactive zone

Mercury contamination in groundwater is a serious global environmental issue that poses threats to human and environmental health. While MoS2 nanosheets have been proven promising in removing Hg from groundwater, an effective tool for in situ groundwater remediation is still needed. In this study, we investigated the transport and retention behavior of MoS2 nanosheets in sand column, and employed the formed MoS2in situ reactive zone (IRZ) for the remediation of Hg-contaminated groundwater. Breakthrough test revealed that high flow velocity and MoS2 initial concentration promoted the transport of MoS2 in sand column, while the addition of Ca ions increased the retention of MoS2. In Hg removal experiments, the groundwater flow velocity did not influence the Hg removal capacity due to the fast reaction rate between MoS2 and Hg. With an optimized MoS2 loading, MoS2IRZ effectively reduced the Hg effluent concentration down to <1 μg/L without apparent Hg remobilization. Additionally, flake-like MoS2 employed in this study showed much better Hg removal performance than flower-like and bulk MoS2, as well as other reported materials, with the Hg removal capacity a few to tens of times higher than those materials. These results suggest that MoS2 nanosheets have the potential to be an efficient IRZ reactive material for in situ remediation of Hg in contaminated groundwater.

Bioaugmented removal of 17β-estradiol, nitrate and Mn(II) by polypyrrole@corn cob immobilized bioreactor: Performance optimization, mechanism, and microbial community response

The coexistence of nitrate and endocrine substances (EDCs) in groundwater is of global concern. Herein, an efficient and stable polypyrrole@corn cob (PPy@Corn cob) bioreactor immobilized with Zoogloea sp. was designed for the simultaneous removal of 17β-estradiol (E2), nitrate and Mn(II). After 225 days of continuous operation, the optimal operating parameters and enhanced removal mechanism were explored, also the long-term toxicity and microbial communities response mechanisms under E2 stress were comprehensively evaluated. The results showed that the removal efficiencies of E2, nitrate, and Mn(II) were 84.21, 82.96, and 47.91%, respectively, at the optimal operating conditions with hydraulic retention time (HRT) of 8 h, pH of 6.5 and Mn(II) concentration of 20 mg L^-1. Further increased of initial E2 (2 and 3 mg L^-1) resulted in the inhibiting effect of denitrification and manganese oxidation, but excellent E2 removal efficiencies maintained, which were associated with the formation and continuous accumulation of biomanganese oxides (BMO). Characterization analysis of biological precipitation demonstrated that adsorption and redox conversion on the BMO surface played key roles in the removal of E2. In addition, different levels of E2 exposure are decisive factors in community evolution, and bioaugmented bacterial communities with Zoogloea as the core group can dynamically adapt to E2 stress. This study offers the possibility to better utilize microbial metabolism and to advance opportunities that depend on microbial physiology and material characterization applications.

Applications and Biological Activity of Nanoparticles of Manganese and Manganese Oxides in In Vitro and In Vivo Models

The expanding applications of nanotechnology seem to be a response to many technological, environmental, and medical challenges. The unique properties of nanoparticles allow for developing new technologies and therapies. Among many investigated compounds is manganese and its oxides, which in the form of nanoparticles, could be a promising alternative for gadolinium-based contrast agents used in diagnostic imaging. Manganese, which is essential for living organisms as an enzyme cofactor, under excessive exposure-for example, due to water contamination or as an occupational hazard for welders-can lead to neurological disorders, including manganism-a condition similar to Parkinson's disease. This review attempts to summarise the available literature data on the potential applications of manganese and manganese oxide nanoparticles and their biological activity. Some of the published studies, both in vitro and in vivo, show negative effects of exposure to manganese, mainly on the nervous system, whereas other data suggest that it is possible to develop functionalised nanoparticles with negligible toxicity and novel promising properties.

Environment-Friendly Removal Methods for Endocrine Disrupting Chemicals

In the past few decades, many emerging pollutants have been detected and monitored in different water sources because of their universal consumption and improper disposal. Among these, endocrine-disrupting chemicals (EDCs), a group of organic chemicals, have received global attention due to their estrogen effect, toxicity, persistence and bioaccumulation. For the removal of EDCs, conventional wastewater treatment methods include flocculation, precipitation, adsorption, etc. However, there are some limitations on these common methods. Herein, in order to enhance the public’s understanding of environmental EDCs, the definition of EDCs and the characteristics of several typical EDCs (physical and chemical properties, sources, usage, concentrations in the environment) are reviewed and summarized in this paper. In particular, the methods of EDC removal are reviewed, including the traditional methods of EDC removal, photocatalysis, biodegradation of EDCs and the latest research results of EDC removal. It is proposed that photocatalysis and biodegradation could be used as an environmentally friendly and efficient EDC removal technology. Photocatalytic technology could be one of the water treatment methods with the most potential, with great development prospects due to its high catalytic efficiency and low energy consumption. Biodegradation is expected to replace traditional water treatment methods and is also considered to be a highly promising method for efficient removal of EDCs. Besides, we summarize several photocatalysts with high catalytic activity and some fungi, bacteria and algae with strong biodegradability.

Efficient removal of mercury from simulated groundwater using thiol-modified graphene oxide/Fe-Mn composite in fixed-bed columns: Experimental performance and mathematical modeling

Mercury contamination in groundwater has been considered as an environmental and public health issue all over the world. Yet, effective in situ remediation techniques have been lacking. A thiol-modified graphene oxide/Fe-Mn composite (SGO/Fe-Mn) was employed as a reactive sorbent of permeable reactive barrier (PRB) for in situ remediation of mercury contaminated groundwater using fixed-bed columns. Mercury existed as HgCl₂, Hg(OH)₂, and HgClOH, and was mainly removed through surface complexation. The Brunauer-Emmett-Teller sorption isotherm model provided adequate fitting of the sorption isotherm data with a maximum monolayer sorption capacity of 112.03 ± 16.59 mg g^-1. Breakthrough time, the time when 5% of initial Hg concentration is measured in the effluent, increased with the decrease of influent mercury concentration, pore velocity, dissolved oxygen (DO), and dissolved organic matter (DOM). The resultant column sorption capacity was enhanced at higher influent mercury concentration, lower groundwater pore velocity, lower DOM and DO. Moreover, when the SGO/Fe-Mn was thoroughly mixed with quartz sand in the column, the breakthrough time was increased and the resultant sorption capacity was improved compared to the case that SGO/Fe-Mn was packed between two layers of quartz sand. Mathematically, the Adams-Bohart model satisfactorily reproduced the initial behavior of mercury breakthrough curves (<40 pore volumes). Yan model adequately simulated the breakthrough curves. The results reveal the potential of SGO/Fe-Mn as an efficient PRB reactive material for in situ remediation of mercury in contaminated groundwater.

Transformation of m-aminophenol by birnessite (δ-MnO2) mediated oxidative processes: Reaction kinetics, pathways and toxicity assessment

The m-aminophenol (m-AP) is a widely used industrial chemical, which enters water, soils, and sediments with waste emissions. A common soil metal oxide, birnessite (δ-MnO₂), was found to mediate the transformation of m-AP with fast rates under acidic conditions. Because of the highly complexity of the m-AP transformation, mechanism-based models were taken to fit the transformation kinetic process of m-AP. The results indicated that the transformation of m-AP with δ-MnO₂ could be described by precursor complex formation rate-limiting model. The oxidative transformation of m-AP on the surface of δ-MnO₂ was highly dependent on reactant concentrations, pH, temperature, and other co-solutes. The UV-VIS absorbance and mass spectra analysis indicated that the pathway leading to m-AP transformation may be the polymerization through the coupling reaction. The m-AP radicals were likely to be coupled by the covalent bonding between unsubstituted C2, C4 or C6 atoms in the m-AP aromatic rings to form oligomers as revealed by the results of activation energy and mass spectra. Furthermore, the toxicity assessment of the transformation productions indicated that the toxicity of m-AP to the E. coli K-12 could be reduced by MnO₂ mediated transformation. The results are helpful for understanding the environmental behavior and potential risk of m-AP in natural environment.

Reaction of bisphenol A with synthetic and commercial MnOx(s): spectroscopic and kinetic study

The reaction of bisphenol A (BPA) using laboratory synthesized (Syn-MnOx) and commercially available (Com-MnOx) MnOx(s) media was investigated using spectroscopic and aqueous chemistry methods. The surface area of Syn-MnOx (128 m2 g-1) and Com-MnOx (13.6 m2 g-1) differed by an order of magnitude. The impurities were less than 1% by weight for Syn-MnOx while Com-MnOx contained 29% impurity by weight, mainly Al, Si and Fe. The removal of 99.7% BPA was observed applying Syn-MnOx, while 71.2% BPA removal was observed applying Com-MnOx after 44 hours of reaction of 10 mM MnOx(s) media with 1 mM BPA at pH 5.5. The reduction of Mn was detected in the surface of both BPA reacted media, but a higher content of reduced Mn was observed in Syn-MnOx (52% in Syn-MnOx compared to 29% in Com-MnOx). The release of soluble Mn was an order of magnitude higher in batch experiments reacting BPA with Syn-MnOx compared with Com-MnOx. The C 1s and O 1s XPS high resolution spectral analyses identified the presence of functional groups that likely correspond to BPA oxidation products, such as dimers and quinones associated with MnOx(s) surfaces on both reacted media. The reaction of BPA with Syn-MnOx fit the electron transfer-limited model (R2 = 0.96), while the reaction of BPA with Com-MnOx had a better fit for surface complex formation-limited model (R2 = 0.95). These results suggest that BPA removal and the reactivity of MnOx(s) are affected by the differences in surface area and impurities present in these media. Thus, this study has relevant implications for the reaction of MnOx(s) with emerging organic contaminants in natural biogeochemical processes and water treatment applications.

Transport of multi-walled carbon nanotubes stabilized by carboxymethyl cellulose and starch in saturated porous media: Influences of electrolyte, clay and humic acid

This study investigated the transport behaviors of carboxymethyl cellulose (CMC) and starch stabilized multi-walled carbon nanotubes (MWNTs) through a saturated quartz sand column in the presence of electrolytes, model clays, and natural organic matter (humic acid) through column breakthrough experiments and model simulations. Both stabilizers, CMC and starch, greatly enhanced the breakthrough of MWNTs, with a full breakthrough plateau (C/C₀) ranging from 0.69 to 0.90 at ionic strength from 0.3 to 10mM. Between the two stabilizers, CMC was more effective in resisting particle deposition, and thus CMC-stabilized MWNTs were more transportable through the medium. While non-stabilized MWNTs were much less transportable and were vulnerable to electrolyte effects (especially Ca²⁺), the stabilized counterparts were much more resistant to the coagulation effects of electrolytes. The presence of colloidal clay particles showed contrasting effects on the transport of bare and stabilized MWNTs. The full breakthrough C/C₀ of bare MWNTs was suppressed by kaolinite and montmorillonite particles from 0.33 to <0.15 with 5mg/L clay, indicating that the presence of both clays enhanced the aggregation and deposition of MWNTs. However, kaolinite particles facilitated the transport of stabilized-MWNTs, while montmorillonite weakened the breakthrough of stabilized MWNTs. Humic acid had less effect on the mobility of stabilized-MWNTs than that of bare MWNTs. The advection-dispersion transport model incorporated with the filtration theory was able to simulate the breakthrough curves and quantitatively interpret the particle deposition. The results can facilitate our understanding of fate and transport of stabilized carbon nanotubes in the environment.