Heavy Metals In Wastewater Research Articles

A new eco-friendly fluorescent microcapsules for effective and selective detection of Hg(II)&Cu(II)

The detection of heavy metals in wastewater with eco-friendly materials and sustainable processes is extremely important for the environment and human health. In this study, sporopollenin, which is a natural polymer material, was derivatized with an innovative macrocyclic compound, and then fluorescence property was acquired. Bodipy and Pillar[5]arene were used to prepare fluorescent microcapsules (Sp-P[5]-bodipy) based on organic compounds. The compounds used in the preparation of fluorescent microcapsules were synthesized by conventional procedures and characterized by several methods such as NMR, FT-R, mass spectroscopy, elemental analysis, and melting point. The characterization of the obtained surfaces was carried out with TGA, FT-IR and SEM device in the determination of the surface morphology and the functional groups. The target fluorescent microcapsules, Sp-P[5]-bodipy, were performed using fluorescence spectroscopy to detect metal ions in aqueous solutions that the modified surfaces encapsulated Hg(II) and Cu(II) ions, respectively. Moreover, some parameters such as pH, temperature, response time, limit of detection (LOD) and binding stoichiometry were examined for practical chemo-sensor applications that Sp-P[5]-bodipy have a low LOD for both Cu(II) (6.16 µM) and Hg(II) ions (3.42 µM).

Synthesis and characterization of pectin-xanthate and their application in heavy metal and lignin enriched paper industry wastewater treatment

ABSTRACT Three grades of pectin xanthates (PX1, PX2, and PX3) have been prepared by the reaction of pectin with carbon disulfide (CS2) in an alkaline medium using NaOH, via the xanthation process. The percentage yield of prepared pectin xanthates has been found to be 87.06%, 90.38%, and 93.80% for PX1, PX2, and PX3, respectively. Prepared pectin xanthates and raw pectin were utilized for heavy metals (Cu(II) and Ni(II)) and lignin enriched paper industry wastewater (LEPIW) treatment. The removal percentage of pectin, PX1, P X2, and PX3 for Cu removal at optimum condition (adsorbent dose: 5.14 g/L, pH: 5 for Cu and 7 for Ni, optimum temperature: 50°C and time: 80 min for Cu(II) and 100 min for Ni(II)) has been found as 85%, 92.33%, 93.5%, and 94.66% and 76.66%, 89.44%, 91.66%, and 93.33%, respectively, for Ni removal. The LEPIW treatment efficacy for pectin, PX1, PX2, and PX3 has been found to be 54%, 77%, 83%, and 86% for the initial COD: 2000 mg/L, pH: 7, optimum temperature: 40°C in 105 min operation time. Adsorption isotherm studies suggest that Langmuir isotherm is most appropriate which indicates adsorption follows chemisorption. The adsorption capacities of PX1, PX2, and PX3 are found as 309.59, 352.11, and 380.22 mg/g for Cu(II) and 299.40, 315.45, and 328.94 mg/g and for Ni(II), respectively, which is very high in comparison with many other recent literature studies.

Key operational parameters assessment for a chromium (VI)-reducing annular upflow microbial fuel cell

Development of upflow microbial fuel cells (MFCs) is of importance since these types of MFCs can be integrated in wastewater treatment plants for the provision of continuous treatment and energy recovery. In this study, key operational parameters were assessed for a hexavalent chromium [Cr(VI)] reducing annular upflow MFC (approximately 5 L total liquid volume). The optimized operational parameters were cathode and anode hydraulic retention times of 2 days, temperature of 34 °C, influent Cr(VI) concentration of 800 mg L−1, and anode and cathode pH of 7 and 4 respectively. This study demonstrated that a parallel configuration is advantageous since it leads to a high current and power density operation due to low internal resistance when compared to series configuration. The precipitation of Cr(III) over time was demonstrated to have a potential to reduce MFC performance and operating at high influent Cr(VI) pHs (7–10) should be avoided. The optimized peak output potential difference and maximum power density achieved under parallel configuration were 896 mV and 994 mW m−3 respectively, at a current density of 1191 mA m−3. This study provides a step into developing continuous metal reducing MFCs for use in simultaneous treatment of heavy metals in wastewater and energy recovery.

The Effect of Chemical Treated Okra Waste for Heavy Metal Adsorption from Natural Gas Production Wastewater

Nowadays, one of the leading environmental pollutants is heavy metals. Hence, heavy metals in wastewater must be removed before discharge because they are toxic even at low concentrations. This research aims to evaluate the efficiency of okra waste as an adsorbent for heavy metals removal from wastewater in natural gas production. In this study, chemical activation of okra adsorbent was processed to increase the surface area of okra adsorbent for better adsorption, whenever the impregnation of the powdered okra waste was performed using phosphoric acid (H3PO4) as the impregnating agent. The okra powder was impregnated at a rate of 4: 1 (v / m). The FTIR was used to characterize the okra-activated carbon and the peaks showed the presence of functional groups such as Hydroxyl (OH), Amino (N-H), Carboxyl (C=O, C-O-C), C-0 stretching and M-O at 3390.05, 2905.5, 1640-1658, 1050.05 and 650 stretching bands respectively. Furthermore, the batch adsorption experiments were conducted via varying agitation speed, contact time, adsorbent dose and adsorbent particle sizes. The results showed that the maximum removal percent of Cd2+, Cu2+, Pb2­+, Zn 2+, Ag2+ and Ba2+metal ions had been observed to be at an agitation speed of 1000 rpm, contact time of 90 min­, okra adsorbent dose of 0.25 g and particle size of 1.00mm. The experimental findings show that okra wastes from agricultural by-products may be a low-cost adsorbent for future research to remove additional heavy metals owing to their high effectiveness in removing Cd2+, Cu2+, Pb2+, and Zn2+ ions from wastewater.

Chloride ion enhanced oxidant-free in situ degradation of Ni-EDTA by electrochemical process with boron-doped diamond electrodes

Conventional advanced oxidation processes were used to treat heavy metal complexes. However, a considerable amount of oxidants was required to enable effective oxidative degradation, which led to a significant increase of the treatment costs and subsequent difficulties in the sludge disposal. Based on the abundance of anions in heavy metal wastewater, the effects of anions on the in-situ degradation of Ni-EDTA in an oxidant-free electrochemical system with boron-doped diamond (BDD) as the anode were investigated. The presence of Cl- was found to exert a significant effect on improving the degradation process. Moreover, pH had little effect on the removal of nickel (Ni) and Ni-EDTA within a specific pH range (1 < pH < 9). The removal efficiencies of Ni and TOC reached 100 % and 77.45 %, respectively, at pH 2.16 with 0.4 M NaCl electrolyte, 2 mM Ni-EDTA concentration, and a current density of 50 mA/cm2. •OH and Cl• played crucial roles in the removal of Ni-EDTA by disrupting the chelation sites of Ni and EDTA molecules. The released Ni2+ ions could active the H2O2 in-situ generated at the cathode to produce •OH. The formation of the precipitation products such as NiOOH, Ni(OH)2, and NiCO3 in the Cl-/BDD system were conform based on the XRD and XPS analyses, which suggested the possible pathways for the removal of Ni2+ and Ni3+. Finally, the possible degradation pathways of Ni-EDTA were proposed based on the identification of intermediate products using UPLC-MS.

In situ polymerization of three-dimensional polypyrrole aerogel for efficient solar-driven interfacial evaporation and desalination

Solar-driven interfacial evaporation (SIE) and desalination is a promising approach to mitigate the scarcity of freshwater resources. Here, a three-dimensional polypyrrole (3D PPy) aerogel was prepared by in situ polymerization of pyrrole to serve as an independent evaporator. The interconnected pore structure and super-hydrophilicity enabled PPy evaporators with rapid water transport to the top interface (< 5 s). The hydrogen interaction between polymer chains and water molecules induced large amount of intermediate water, thereby reducing the evaporation enthalpy of water in PPy aerogels. As a result, the optimized PPy aerogel attained an evaporation rate of 2.90 kg m−2 h−1 and an energy conversion efficiency of 114% under 1 sun irradiation. Moreover, the generated steam can be accelerated by the convection and an evaporation rate as high as 6.10 kg m−2 h−1 was realized at 2.5 m s−1. The rapid water transport also enabled PPy aerogel with high-efficiency of self-salt-discharge and efficient desalination for 3.5 wt% brine under 2.5 m s−1. In the outdoor SIE experiment, the excellent evaporation performance was achieved at 12:40 (7.04 kg m−2 h−1 under 74.2 mW cm−2 of solar intensity and 2.5 m s−1 of convective flow), and the cumulative evaporation of 41.50 kg m−2 for successive 9 h was obtained. After the evaporation of simulated seawater and heavy metal wastewater, the concentration of collected fresh water could be reduced about 2–3 orders of magnitude. This 3D PPy evaporation platform with high light absorption, porous structure, super-hydrophilic property, effective steam diffusion, and excellent salt resistance provides an effective way to develop advanced solar-driven water treatment technology.

Supplementation of strigolactone analog for enhancing the removal of nutrient and heavy metal by microalgae-fungi symbionts

The purification effects of Chlorella vulgaris and Chlorella vulgaris-Clonostachys symbionts on nutrients and heavy metals in wastewater were investigated to determine the optimal symbiotic treatment technology and the suitable concentration of GR24. The results showed that exogenous GR24 not only promoted the formation of uniform green spheres in microalgae-fungi symbionts, but also increased its photosynthetic performance and growth. At 10−7 M GR24 addition concentration, the specific growth rate of microalgae-fungi symbionts was 0.367 ± 0.04 d−1, the maximum removal efficiency of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were 81.96 ± 7.93 %, 80.26 ± 7.91 % and 82.96 ± 8.05 %, respectively. When the concentration of exogenous GR24 was 10−5 M, the removal efficiency of heavy metals was the best at both low and high pollution levels. It was worth noting that the removal efficiency of Zn at low concentration pollution levels (1 mg L−1) was 99.32 ± 0.43 %, nearly 100 %. This study promoted the development of microalgae-fungal symbionts in the field of wastewater treatment.

Efficient Hg(Ⅱ) adsorption of polyphenol functionalized Poly(pyrrole methane)s: The role of acid doped ions

A series of doped and dedoped polyphenol functionalized poly(pyrrole methane)s (234HBAs) were designed to investigate the impact of various dopants on mercury adsorption in water. The adsorption performance of dedoped 234HBAs showed no significant difference (ranging from 2961 to 3004 mg·g−1 at 318 K). However, the adsorption capacities of doped 234HBAs for mercury exhibited significant optimization and varied among different dopants (ranging from 3676 to 4103 mg·g−1 at 318 K). In addition to ultra-high adsorption capacity, 234HBAs also exhibited broad working pH range (2–11), fast kinetics (adsorption equilibrium within 10 min), good anti-ion interference and selectivity (Kd > 7.1 × 105 mL·g−1), and excellent regeneration ability (little attenuation of adsorption capacity after 20 cycles). Furthermore, through characterization techniques (FT-IR, XPS) and the density functional theory (DFT) calculation, it was discovered that the presence of doped acid ions enhanced the capture and immobilization of mercury to varying extents besides the robust chelation binding of mercury by the adjacent phenolic hydroxyl groups. Among these ions, oxygen-containing citrate and sulfate exhibited a stronger ability to facilitate the removal of mercury compared with chloride ions. More importantly, this straightforward approach to fabricating functionalized adsorbents for the remediation of mercury-containing wastewater holds significant guiding implications for the treatment of other heavy metal and organic wastewater.

Bioremediation of industrial wastewater heavy metals using solo and consortium Enterobacter spp.

Heavy metals are considered the most common pollutants in industrial wastewater areas. Out of thirty bacterial isolates, only 3 isolates sighted the highest metal resistance activity for Zn+2, Fe+2, Pb+2, Co+2, Mn+2, Ni+2, and Cd+2. The biochemical and DNA homology identification with similarities 99.58%, 99.79%, and 99.86% of those isolates was identified and deposited in WDCM, respectively, as Enterobacter kobei OM144907 SCUF0000311, Enterobacter cloacae OM180597 SCUF0000312, and Enterobacter hormaechei OM181067 SCUF0000313. The minimum tolerance activity (MIC) of heavy metal concentrations against E. kobei and E. cloacae was 25, 15, and 15 mmol/l for Ni+2, Fe+2, and Mn+2, respectively, and 10 mmol/l for Zn+2, Pb+2, Co+2, and Cd+2, while against E. hormaechei, it is 15 mmol/l for Ni+2, Fe+2, and Mn+2 and 10 mmol/l for Zn+2, Pb+2, Co+2, and Cd+2. The consortium and solitary application of bacterial isolates towards heavy metal removal at 100%, 200%, and 300% industrial wastewater concentrations were conducted and showed that more than 90% removal of Zn+2, Fe+2, Pb+2, Mn+2, Ni+2, and Cd+2 from a non-concentrated polluted sample (100%) was reported by the three strains. With doubling the polluted sample concentration (200%), the highest removal efficiency for Zn+2, Pb+2, Mn+2, Ni+2, and Cd+2 was reported by E. cloacae as 70. 75, 66, 65, and 57%, respectively. Removal efficiency after increasing the polluted sample concentration to 300% showed that E. cloacae removed above 45% of all tested heavy metals except Pb+2. Ultimately, E. cloacae exposed the highest efficiency with recommendations for heavy metals removal under higher concentrations.

Functionalized UiO-67-Rhodanine-3-acetic acid (Rd) composites efficiently trapping Pb (II) in wastewater

Metal organic frameworks (MOFs) have the advantages of large specific surface area, high porosity, controlled structures and strong stability, and were excellent adsorbents for the efficient trapping of heavy metals. In this work, two morphologies of Zr-MOF composites (UiO-67-AC-Rd and UiO-67-FA-Rd) under different solvent conditions were synthesized by a sequential solvothermal process. The properties of the composites were characterized by SEM, TEM, XRD, XPS, and BET, and the adsorption capacities of Pb (II) were investigated in detail. The excellent performance of UiO-67-AC-Rd exhibited superfast removal efficiencies for Pb (II), ascribing to its surface contains plentiful oxygen, nitrogen and sulfur functional groups and large specific surface area, which makes it have fascinating properties in removing Pb (II), and the maximum adsorption capacity of Pb (II) was 309.8 mg g−1. Chelation and electrostatic adsorption were considered as the main adsorption mechanisms. Adsorption isotherms were fitted well using the Langmuir and Freundlich model, and the adsorption thermodynamics indicated that the adsorption process was endothermic and spontaneous. The UiO-67-AC-Rd composites maintained excellent adsorption capacity for Pb (II) after four consecutive cycles, and the removal efficiency was above 74 %. The study will further provide a new pathway to the application of UiO-67-Rd composites in the adsorption of heavy metals in wastewater.

Extraction of heavy metals from wastewater using amine-modified mesoporous silica.

Presence of heavy metals in wastewater is a critical environmental issue, and efficient extraction of the metals remains a challenging task. In this study, the adsorption behavior of Ce(III), Hg(II), and Cu(II) metal ions using MCM-48 material modified with acid and base functional groups was examined. The modified materials were characterized using various techniques, including XRD, BET, FT-IR, NMR, and SEM, which revealed that the materials' properties remained unchanged after modification. The adsorption capacity of the modified materials for metal ions was then evaluated and was found that the amine-modified MCM-48 material exhibited the highest adsorption efficiency. Precisely, the amine-modified material achieved an adsorption capacity of 97% for Ce(III), 98% for Hg(II), and 90% for Cu(II) after 180min of adsorption. These results highlight the effectiveness of amine functionalization in enhancing the adsorption capacity of silica material for heavy metals.

Photoelectrochemical advanced oxidation processes for simultaneous removal of antibiotics and heavy metal ions in wastewater using 2D-on-2D WS2@CoFe2O4 heteronanostructures

The presence of antibiotics in water poses significant threats to both human health and the environment. Addressing this issue requires the effective treatment of medical wastewater. Photoelectrochemical advanced oxidation processes (PEAOPs) are emerging as promising solutions for wastewater treatment. This process utilizes photocatalysts to convert charge carriers into reactive species such as hydroxyl radicals and superoxide ions, which are essential for degrading pollutants in wastewater. However, limitations in charge carrier separation and transport have hindered the efficiency of photoelectrochemical advanced oxidation processes. To overcome these limitations, we designed WS2@CoFe2O4 heterojunctions, optimizing their energy levels to enhance charge transport and separation. This improvement significantly increased the oxidation of antibiotics such as amoxicillin and azithromycin. Multiple reactions occurred at the WS2@CoFe2O4 heterojunctions during photoelectrochemical advanced oxidation processes, leading to the impressive degradation of up to 99% of antibiotics under visible light irradiation at 0.8 V. Urea and H2O2 acted as oxidation agents within photoelectrochemical advanced oxidation processes, amplifying the generation of hydroxyl radicals and superoxide ions, further enhancing antibiotic oxidation. Moreover, the WS2@CoFe2O4 photoanode efficiently oxidized toxic antibiotics while converting As(III) into the less harmful As(V). Crucially, recyclability tests confirmed the robustness of the WS2@CoFe2O4 photoanode, ensuring its suitability for prolonged use in photoelectrochemical advanced oxidation processes. Integrating WS2@CoFe2O4 photoanodes into water purification systems can enhance efficiency, reduce energy consumption, and improve economic viability. This technology's scalability and its ability to protect ecosystems while conserving water resources make it a promising solution for addressing the critical issue of antibiotic pollution in water environments.

Application of common industrial solid waste in water treatment: a review.

Industrial solid waste has a wide range of impacts, and it is directly or indirectly related to land, atmosphere, water, and other resources. Industrial solid waste has a large amount of production, complex and diverse components and contains a variety of harmful substances. However, as industrial by-products, it also has a lot of available value. Industrial solid waste has been continuously studied in water treatment due to its special composition and porous and loose structure. It is known that there are few reviews of various industrial solid wastes in the field of wastewater treatment, and most of them only discuss single industrial solid waste. This paper aims to sort out the different studies on various solid wastes such as fly ash, red mud, wastewater sludge, blast furnace slag and steel slag in dyeing, heavy metal, and phosphorus-containing wastewater. Based on the modification of industrial solid waste and the preparation of composite materials, adsorbents, coagulants, catalysts, filtration membranes, geological polymers, and other materials with high adsorption properties for pollutants in wastewater were formed; the prospect and development of these materials in the field of wastewater were discussed, which provides some ideas for the mutual balance of environment and society. Meanwhile, some limitations of solid waste applications for wastewater treatment have been put forward, such as a lack of further researches about environment-friendly modification methods, application costs, the heavy metal leaching, and toxicity assessment of industrial solid waste.

Advances, challenges, and prospects in microalgal-bacterial symbiosis system treating heavy metal wastewater

Heavy metal (HM) pollution, particularly in its ionic form in water bodies, is a chronic issue threatening environmental security and human health. The microalgal-bacterial symbiosis (MABS) system, as the basis of water ecosystems, has the potential to treat HM wastewater in a sustainable manner, with the advantages of environmental friendliness and carbon sequestration. However, the differences between laboratory studies and engineering practices, including the complexity of pollutant compositions and extreme environmental conditions, limit the applications of the MABS system. Additionally, the biomass from the MABS system containing HMs requires further disposal or recycling. This review summarized the recent advances of the MABS system treating HM wastewater, including key mechanisms, influence factors related to HM removal, and the tolerance threshold values of the MABS system to HM toxicity. Furthermore, the challenges and prospects of the MABS system in treating actual HM wastewater are analyzed and discussed, and suggestions for biochar preparation from the MABS biomass containing HMs are provided. This review provides a reference point for the MABS system treating HM wastewater and the corresponding challenges faced by future engineering practices.

Response of anammox to long-term stress of Ni(II): Nitrogen removal, microbial products and microbial community

Anaerobic ammonium oxidation (anammox) has been successfully applied to the practical wastewater treatment due to a high nitrogen removal performance, low sludge yield and low operating cost. Heavy metals in wastewater have received extensive attention because of their non-degradability and biotoxicity. In order to apply anammox system to treat wastewater containing heavy metals and explore the anammox system recovery to complex engineering environments, Ni(II) was used as representative substance to investigate its long-term effects on the anammox process in continuous flow reactors. The self-recovery ability of the anammox system after long-term exposure to Ni(II) was also investigated. The results showed that low concentrations of Ni(II) (≤ 5 mg/L) had a slight inhibitory effect on the anammox system, while high concentrations of Ni(II) (≥ 10 mg/L) could lead to the deterioration of the anammox system. Extracellular polymeric substance (EPS) content increased with increasing Ni(II) concentration. High-throughput sequencing results showed that Ni(II) severely impacted the microbial community of the anammox system, especially Candidatus Kuenenia. The abundance of Candidatus Kuenenia decreased from 32.11% to 13.99% with increasing Ni(II) concentration from 0 mg/L to 15 mg/L. After stopping Ni(II) addition, EPS and functional bacterial abundance recovered to some extent, and nitrogen removal efficiency (NRE) only returned to 44.53% of normal levels. The self-recovery of the anammox system was a longer process.

Nanoscale Zero-Valent Iron (nZVI) for Heavy Metal Wastewater Treatment: A Perspective

Industries such as non-ferrous metal smelting discharge billions of gallons of highly toxic heavy metal wastewater (HMW) worldwide annually, posing a severe challenge to conventional wastewater treatment plants and harming the environment. HMW is traditionally treated via chemical precipitation using lime, caustic, or sulfide, but the effluents do not meet the increasingly stringent discharge standards. This issue has spurred an increase in research and the development of innovative treatment technologies, among which those using nanoparticles receive particular interest. Among such initiatives, treatment using nanoscale zero-valent iron (nZVI) is one of the best developed. While nZVI is already well known for its site-remediation use, this perspective highlights its application in HMW treatment with metal recovery. We demonstrate several advantages of nZVI in this wastewater application, including its multifunctionality in sequestrating a wide array of metal(loid)s (> 30 species); its capability to capture and enrich metal(loid)s at low concentrations (with a removal capacity reaching 500 mg·g−1 nZVI); and its operational convenience due to its unique hydrodynamics. All these advantages are attributable to nZVI’s diminutive nanoparticle size and/or its unique iron chemistry. We also present the first engineering practice of this application, which has treated millions of cubic meters of HMW and recovered tons of valuable metals (e.g., Cu and Au). It is concluded that nZVI is a potent reagent for treating HMW and that nZVI technology provides an eco-solution to this toxic waste.

A novel double-network hydrogel made from electrolytic manganese slag and polyacrylic acid-polyacrylamide for removal of heavy metals in wastewater

Electrolytic manganese slag (EMS), a bulk waste generated in industrial electrolytic manganese production, can be a cost-effective adsorbent for heavy metals removal after appropriate modification. In this study, EMS was activated by NaOH and then used to make the EMS-based double-network hydrogel (an EMS/PAA hydrogel) via a one-pot method. The results showed that the EMS/PAA hydrogel exhibits a high selective adsorption capacity of 153.85, 113.63 and 54.35 mg·g−1 for Pb (II), Cd (II) and Cu (II), respectively. In addition, Density Functional Theory (DFT) suggests that the adsorption energies (Ead) of Pb, Cd and Cu on SiO2/PAA of the EMS/PAA gels are − 4.15, − 1.96, and − 2.83 eV, respectively, and SiO2/PAA, with a strong affinity to Pb2+, is one of the reasons for the selective adsorption capacity of EMS/PAA gel for Pb2+. The removal efficiency of the EMS/PAA gel for Pb2+, Cd2+, Cu2+ decreased after four adsorption-desorption cycles by 20.00 %, 24.56 % and 46.56 %, respectively. Mechanism studies suggested that the elimination of the heavy metals by EMS/PAA gels mainly involves electrostatic attraction, inner-sphere complexation, and coordination interactions. The EMS/PAA hydrogels not only have high adsorption capacity, but are also easy to prepare and circulate, making them ideal for practical applications.

Bentonite Clay as an Alternative Adsorbent for Removal of Heavy Metals in wastewater

This study investigates the potential of bentonite clay as an alternative adsorbent for removing heavy metals from abattoir wastewater. Laboratory experiments were conducted to evaluate the effectiveness of bentonite clay in removing six heavy metals, including Lead, Chromium, Arsenic, Cadmium, Zinc and Iron. Results show that bentonite clay effectively removed all heavy metals, with removal efficiencies ranging from 75% to 95%. The study also found that the adsorption efficiency of bentonite clay increased with increasing initial metal concentration and decreasing pH of the solution. Freundlich and Langmuir models were used to predict the adsorption process, and the R2 values for both models were similar. This suggests that both models were equally adequate or inadequate in describing the process. The study concludes that bentonite clay is a promising adsorbent for removing heavy metals from wastewater. It is recommended that the use of bentonite clay as an alternative adsorbent for heavy metal removal should be further explored and optimized, particularly in terms of operating conditions such as pH, contact time, and adsorbent dosage.

Zwitterionic cyclodextrin membrane with uniform subnanometre pores for high-efficient heavy metal ions removal

Polymer nanofiltration (NF) membranes have been widely applied in the desalination, resource substances purification and separation, and wastewater treatment. Nevertheless, direct construction of subnanometre channel polymer membranes for achieving high-efficient metal ions separation is still challenging because of the complicated membrane preparation and difficultly manipulating the membrane pore-size in sub-nanometer. Herein, we exploited a novel subnanometre channel membrane with zwitterionic β-cyclodextrins (ZCDs) by interfacial polymerization. Wherein ZCDs act as building blocks with hydrophobic inner subnanometre cavities and hydrophilic outer rims, allowing for simultaneously improved water permeability and metal ions selectivity. By modulating the zwitterionic monomer grafting ratio of ZCDs and their loading content in the membrane, the ZCDM membrane exhibits high water permeance (J = 21.7 L m−2 h−1∙bar−1) and heavy metal ions rejection, e.g., RCr3+ = 99.8%, RFe3+ = 98.9%, respectively, these values outperform the state-of-the-art NF membranes. Moreover, the ZCDM membrane has good stability and anti-fouling/-bacterial properties, e.g., the water flux recovery ratio and anti-bacterial ratio is >97% and >99%, in the long-term running process. This work offers a feasible strategy for constructing polymer membranes with uniform subnanometre pore, and demonstrates their potential for the heavy metal separation and wastewater treatment.

Research progress on using biological cathodes in microbial fuel cells for the treatment of wastewater containing heavy metals.

Various types of electroactive microorganisms can be enriched to form biocathodes that reduce charge-transfer resistance, thereby accelerating electron transfer to heavy metal ions with high redox potentials in microbial fuel cells. Microorganisms acting as biocatalysts on a biocathode can reduce the energy required for heavy metal reduction, thereby enabling the biocathode to achieve a lower reduction onset potential. Thus, when such heavy metals replace oxygen as the electron acceptor, the valence state and morphology of the heavy metals change under the reduction effect of the biocathode, realizing the high-efficiency treatment of heavy metal wastewater. This study reviews the mechanisms, primary influencing factors (e.g., electrode material, initial concentration of heavy metals, pH, and electrode potential), and characteristics of the microbial community of biocathodes and discusses the electron distribution and competition between microbial electrodes and heavy metals (electron acceptors) in biocathodes. Biocathodes reduce the electrochemical overpotential in heavy metal reduction, permitting more electrons to be used. Our study will advance the scientific understanding of the electron transport mechanism of biocathodes and provide theoretical support for the use of biocathodes to purify heavy metal wastewater.