•Catastrophe of heavy metal pollution in environment is discussed in terms of remediation through bacterial Exopolysaccharide.•Biosynthesis of polymer, mechanism of action and metal remediation ...through polymer has been expounded deeply.•Wide range of bacterial cells and their EPS in diverse forms have been critically analyzed.•Challenges that still lie in the path of commercialization has been scrutinized.
Heavy metal contamination has been recognized as a major public health risk, particularly in developing countries and their toxicological manifestations are well known. Conventional remediation strategies are either expensive or they generate toxic by-products, which adversely affect the environment. Therefore, necessity for an environmentally safe strategy motivates interest towards biological techniques. One of such most profoundly driven approach in recent times is biosorption through microbial biomass and their products. Extracellular polymeric substances are such complex blend of high molecular weight microbial (prokaryotic and eukaryotic) biopolymers. They are mainly composed of proteins, polysaccharides, uronic acids, humic substances, lipids etc. One of its essential constituent is the exopolysaccharide (EPS) released out of self defense against harsh conditions of starvation, pH and temperature, hence it displays exemplary physiological, rheological and physio-chemical properties. Its net anionic makeup allows the biopolymer to effectively sequester positively charged heavy metal ions. The polysaccharide has been expounded deeply in this article with reference to its biosynthesis and emphasizes heavy metal sorption abilities of polymer in terms of mechanism of action and remediation. It reports current investigation and strategic advancements in dealing bacterial cells and their EPS in diverse forms – mixed culture EPS, single cell EPS, live, dead or immobilized EPS. A significant scrutiny is also involved highlighting the existing challenges that still lie in the path of commercialization. The article enlightens the potential of EPS to bring about bio-detoxification of heavy metal contaminated terrestrial and aquatic systems in highly sustainable, economic and eco-friendly manner.
Among the many heavy metal pollution treatment agents, carbonate materials show strong flexibility and versatility by virtue of their high adsorption capacity for heavy metals and the characteristics ...of multiple and simple modification methods. It shows good potential for development. This review summarizes the application of carbonate materials in the treatment of heavy metal pollution according to the research of other scholars. It mainly relates to the application of surface-modified, activated, and nano-sized carbonate materials in the treatment of heavy metal pollution in water. Natural carbonate minerals and composite carbonate minerals solidify and stabilize heavy metals in soil. Solidification of heavy metals in hazardous waste solids is by MICP. There are four aspects of calcium carbonate oligomers curing heavy metals in fly ash from waste incineration. The mechanism of treating heavy metals by carbonate in different media was discussed. However, in the complex environment where multiple types of pollutants coexist, questions on how to maintain the efficient processing capacity of carbonate materials and how to use MICP to integrate heavy metal fixation and seepage prevention in solid waste base under complex and changeable natural environment deserve our further consideration. In addition, the use of carbonate materials for the purification of trace radioactive wastewater and the safe treatment of trace radioactive solid waste are also worthy of further exploration.
Environmental Monitoring Device
In article number 2303871, Chien‐Fu Chen and co‐workers developed an electric‐free, semi‐automatic environmental monitoring device for on‐site detection of harmful ...heavy metal ions in water. All users can repeatably extract the fix‐volume sample solutions and then release them to complete the detection process automatically. This device is valid for on‐site multiple heavy metal ion pollution screenings in resource‐constrained settings.
Lead (Pb), one of the pervasive and protracted environmental heavy metals, is believed to affect the female reproductive system in many species. The Nrf2 and NF-kappaB are the two key transcriptional ...factors regulating cellular redox status and response against stress and inflammation respectively, showing an interaction between each other. The aim of this study is to investigate the effect of Pb on bovine granulosa cells (GCs) and its association with the regulation of Nrf2 and NF-kappaB pathways. For this, bovine GCs were cultured in vitro and exposed to different doses of Pb for 2 h. Cellular response to Pb insult was investigated 24 h post treatment. Results showed that exposure of GCs to Pb-induced ROS accumulation and protein carbonylation. Additionally, GCs exhibited reduction in cell viability and decrease in the expression of cell proliferation marker genes (CCND2 and PCNA). This was accompanied by cell cycle arrest at G0/G1 phase. Moreover, Pb downregulated both Nrf2 and NF-kappaB and their downstream genes. Lead increased the expression of endoplasmic reticulum (ER) stress marker genes (GRP78 and CHOP) and the proapoptotic gene (caspase-3) while the antiapoptotic gene (BCL-2) was reduced. Our findings suggest that Pb-driven oxidative stress affected GCs proliferation, enhances ER stress, induces cell cycle arrest and mediates apoptosis probably via disruption of Nrf2/NF-kappaB cross-talk. However, further functional analysis is required to explain different aspects of Nrf2 and NF-kappaB interactions under metal challenge.
Globally there are over 20millionha of land contaminated by the heavy metal(loid)s As, Cd, Cr, Hg, Pb, Co, Cu, Ni, Zn, and Se, with the present soil concentrations higher than the geo-baseline or ...regulatory levels. In-situ and ex-situ remediation techniques have been developed to rectify the heavy metal-contaminated sites, including surface capping, encapsulation, landfilling, soil flushing, soil washing, electrokinetic extraction, stabilization, solidification, vitrification, phytoremediation, and bioremediation. These remediation techniques employ containment, extraction/removal, and immobilization mechanisms to reduce the contamination effects through physical, chemical, biological, electrical, and thermal remedy processes. These techniques demonstrate specific advantages, disadvantages, and applicability. In general, in-situ soil remediation is more cost-effective than ex-situ treatment, and contaminant removal/extraction is more favorable than immobilization and containment. Among the available soil remediation techniques, electrokinetic extraction, chemical stabilization, and phytoremediation are at the development stage, while the others have been practiced at full, field scales. Comprehensive assessment indicates that chemical stabilization serves as a temporary soil remediation technique, phytoremediation needs improvement in efficiency, surface capping and landfilling are applicable to small, serious-contamination sites, while solidification and vitrification are the last remediation option. The cost and duration of soil remediation are technique-dependent and site-specific, up to $500ton−1 soil (or $1500m−3 soil or $100m−2 land) and 15years. Treatability studies are crucial to selecting feasible techniques for a soil remediation project, with considerations of the type and degree of contamination, remediation goals, site characteristics, cost effectiveness, implementation time, and public acceptability.
Display omitted
•Various remediation methods have been developed for heavy metal-contaminated soils.•In-situ, contaminant removal/extraction remediation techniques are more favorable.•The methods landfilling, soil washing, and solidification are well established.•Electrokinetic extraction, chemical stabilization, and phytoremediation are immature.•Treatability studies are crucial to selecting feasible soil remediation techniques.
Display omitted
•nZVI is able to perform fast and simultaneous removal of different heavy metal ions.•Fast separation and seeding effect of nZVI facilities its application in wastewater.•A novel ...process of Eh-controlled reactor, nZVI separator and reuse is proposed.•Eh-controlled system and nZVI recirculation increase material efficiency of nZVI.•The process produces stable effluent and is effective in wastewater treatment.
Treatment of wastewater containing heavy metals requires considerations on simultaneous removal of different ions, system reliability and quick separation of reaction products. In this work, we demonstrate that nanoscale zero-valent iron (nZVI) is an ideal reagent for removing heavy metals from wastewater. Batch experiments show that nZVI is able to perform simultaneous removal of different heavy metals and arsenic; reactive nZVI in uniform dispersion brings rapid changes in solution Eh, enabling a facile way for reaction regulation. Microscope characterizations and settling experiments suggest that nZVI serves as solid seeds that facilitate products separation. A treatment process consisting of Eh-controlled nZVI reaction, gravitational separation and nZVI recirculation is then demonstrated. Long-term (>12 months) operation shows that the process achieves >99.5% removal of As, Cu and a number of other toxic elements. The Eh-controlled reaction system sustains a highly-reducing condition in reactor and reduces nZVI dosage. The process produces effluent of stable quality that meets local discharge guidelines. The gravitational separator shows high efficacy of nZVI recovery and the recirculation improves nZVI material efficiency, resulting in extraordinarily high removal capacities ((245mg As+226 mg-Cu)/g-nZVI). The work provides proof that nanomaterials can offer truly green and cost-effective solutions for wastewater treatment.
China is a large agricultural country that produces a large amount of crop straw every year. Thus, the development of cost-effective and economic application of invasive plants is warranted. Biochars ...derived from crop straw have been proven to be promising for adsorbent materials. However, less studies have focused on biochar derived from different types of crop straw as adsorbent under the same conditions to compare their adsorption performance. Here, we characterized the five biochars in the same system (600 °C). In results, GBC has higher ash content, pH, CEC, specific surface area, mineral composition and oxygen-containing functional groups. The adsorption kinetics can be explained adequately by the pseudo-second-order model and the Langmuir model, indicating that the adsorption behavior of the biochar is both physical adsorption and chemical adsorption; the adsorption process includes complexation reaction, cationic π bond, ion precipitation and electrostatic adsorption. In conclusion, GBC exhibited higher metal equilibrium adsorption capacities (125 mg·gsup.−1 for Pbsup.2+, 29 mg·gsup.−1 for Cdsup.2+). The solution pH, biochar dosing, pyrolysis temperature and the properties of these heavy metals were responsible for adsorption capacity, thus showing stronger affinity and better adsorption effect. Our results are important for the selection and utilization of plant-based biochar for different heavy metals.
Display omitted
•Pyrolysis of oil-based drill cuttings was studied by TGA and fixed-bed reactor.•The reaction model of oil-based drill cuttings pyrolysis depends on the degree of conversion.•High ...heating rate was preferentially selected to predict the reaction mechanism.•500℃ was considered the optimum temperature for oil recovery from oil-based drill cuttings pyrolysis.•Possible reaction pathways during oil-based drill cuttings pyrolysis were proposed.
Oil-based drill cuttings (OBDC), as a by-product produced from the exploration and extraction of shale gas fields, have received increasing attention as both hazardousness and potential energy resources. In this study, the pyrolysis performance of OBDC was investigated using a thermogravimetric analyzer (TGA) and fixed-bed reactor. Results showed that the primary decomposition of OBDC occurred at 85–360 °C. The average activation energy calculated by model-free methods Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (OFW), Starink, and Friedman (FM) models were 53.11, 57.87, 53.38, and 64.23 kJ/mol, respectively. The reaction model depended on the degree of conversion. Moreover, high heating rates were conductive to predict the reaction mechanism. The analysis results of pyrolysis products showed that with the temperature increased from 450 °C to 600 °C, the oil yield presented a first increased and then decreased tendency, and reached the highest (14.94%) at 500 °C, then decreased to 12.10% at 600 °C. The oil was mainly composed of diesel fraction (C12-C22), which can be used as a fuel or raw material. Moreover, the lower heating value (LHV) of gaseous products was the highest (31.80 MJ/Nm3) at 600 °C. In addition, the oil content of char was far below 0.3%, and the heavy metal content in char was below the national standards (CJ/T 362–2011, China), suggesting that OBDC pyrolysis could achieve energy recovery and harmless treatment simultaneously. The results can provide a theoretical basis and data support for optimizing and developing OBDC pyrolysis reactors and processes.
Mixed metal oxide composites have been widely used as adsorbents for the removal of heavy metal ions from wastewater. In this work, Fesub.2Osub.3/TiOsub.2 composite was sustainably prepared via the ...treatment of titanium slag with a low-concentration sulfuric acid solution (20%) and used for the removal of As(V) from aqueous solutions. The resulting products were characterized by X-ray diffraction (XRD), N2 adsorption−desorption, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The batch adsorption was employed to investigate the removal efficiency of the Fesub.2Osub.3/TiOsub.2 adsorbent toward As(V). The Langmuir and Freundlich isotherms were plotted in order to study the adsorption process. The adsorption of As(V) on FeOsub.3/TiOsub.2 fitted well with the Freundlich isotherm model, suggesting a multilayer adsorption process with an adsorption capacity of 68.26 mg·gsup.−1. The adsorption kinetics study demonstrated that the adsorption behavior of the Fesub.2Osub.3/TiOsub.2 composite for the As(V) was pseudo-second-order. With low-cost preparation and high adsorption capacity, the prepared Fesub.2Osub.3/TiOsub.2 adsorbent could be used as an effective adsorbent for As(V) removal from contaminated water sources. The approach utilized in this research is viewed as a sustainable route for creating a proficient adsorbent for the purification of water.
PDF
