Enhanced efficiencies on purifying acid mine drainage in constructed wetlands based on synergistic adsorption of attapulgite-soda residue composites and microbial sulfate reduction.

Constructed wetlands (CWs) are a promising approach for treating acid mine drainage (AMD). However, the extreme acidity and high loads of heavy metals in AMD can easily lead to the collapse of CWs without proper pre-treatment. Therefore, it is considered essential to maintain efficient and stable performance for AMD treatment in CWs. In this study, pre-prepared attapulgite-soda residue (ASR) composites were used to improve the substrate of CWs. Compared with CWs filled with gravel (CWs-G), the removal efficiencies of sulfate and Fe, Mn, Cu, Zn Cd and Pb in CWs filled with ASR composites (CWs-ASR) were increased by 30% and 10-70%, respectively. These metals were mainly retained in the substrate in stable forms, such as carbonate-, Fe/Mn (oxide)hydroxide-, and sulfide-bound forms. Additionally, higher levels of photosynthetic pigments and antioxidant enzyme activities in plants, along with a richer microbial community, were observed in CWs-ASR than in CWs-G. The application of ASR composites alleviated the adverse effects of AMD stresses on wetland plants and microorganisms. In return, the increased bacteria abundance, particularly SRB genera (e.g., Thermodesulfovibrionia and Desulfobacca), promoted the formation of metal sulfides, enabling the saturated ASR adsorbed with metals to regenerate and continuously capture heavy metals. The synergistic adsorption of ASR composites and microbial sulfate reduction maintained the stable and efficient operation of CWs. This study contributes to the resource utilization of industrial alkaline by-products and promotes the breakthrough of new techniques for low-cost and passive treatment systems such as CWs.

Effective Removal of Different Heavy Metals Ion (Cu, Pb, and Cd) from Aqueous Solutions by Various Molecular Weight and Salt Types of Poly-γ-Glutamic Acid.

In light of industrial developments, water pollution by heavy metals as hazardous chemicals has garnered attention. Addressing the urgent need for efficient heavy metal removal from aqueous environments, this study delves into using poly-γ-glutamic acid (γ-PGA) for the bioflocculation of heavy metals. Utilizing γ-PGA variants from Bacillus subtilis with different molecular weights and salt forms (Na-bonded and Ca-bonded), the research evaluates their adsorption capacities for copper (Cu), lead (Pb), and cadmium (Cd) ions. It was found that Na-bonded γ-PGA with a high molecular weight showed the highest heavy metal adsorption (92.2-98.3%), particularly at a 0.5% concentration which exhibited the highest adsorption efficiency. Additionally, the study investigated the interaction of γ-PGA in mixed heavy metal environments, and it was discovered that Na-γ-PGA-HM at a 0.5% concentration showed a superior adsorption efficiency for Pb ions (85.4%), highlighting its selectivity as a potential effective biosorbent for wastewater treatment. This research not only enlightens the understanding of γ-PGA's role in heavy metal remediation but also underscores its potential as a biodegradable and non-toxic alternative for environmental cleanup. The findings pave the way for further exploration into the mechanisms and kinetics of γ-PGA's adsorption properties.

Optimization and mechanism of the novel eco-friendly additives for solidification and stabilization of dredged sediment.

Solidification/stabilization technology is commonly used in the rehabilitation of dredged sediment due to its cost-effectiveness. However, traditional solidification/stabilization technology relies on cement, which increases the risk of soil alkalization and leads to increased CO2 emissions during cement production. To address this issue, this study proposed an innovative approach by incorporating bentonite and citrus peel powder as additives in the solidifying agent, with the aim of reducing cement usage in the dredged sediment solidification process. The research results showed that there is a significant interaction among cement, bentonite, and citrus peel powder. After response surface methodology (RSM) optimization, the optimal ratio of the cementitious mixture was determined to be 14.86 g/kg for cement, 5.85 g/kg for bentonite, and 9.31 g/kg for citrus peel powder. The unconfined compressive strength (UCS) of the solidified sediments reached 3144.84 kPa. The reaction products of the solidification materials, when mixed with sediment, facilitated adsorption, gelation, and network structure connection. Simultaneously, the leaching concentration of heavy metals was significantly decreased with five heavy metals (Zn, As, Cd, Hg, and Pb) leaching concentrations decreasing by more than 50%, which met the prescribed thresholds for green planting. This study demonstrated the ecological benefits of employing bentonite and citrus peel powder in the solidification process of dredged sediment, providing an effective solution for sediment solidification.

Two-stage hydrothermal oxygenation for efficient removal of Cr(VI) by starch-based polyporous carbon: Wastewater application and removal mechanism.

Cr(VI) is of concern because of its high mobility and toxicity. In this work, a two-stage hydrothermal strategy was used to activate the O sites of starch, and by inserting K-ion into the pores, starch-based polyporous carbon (S-PC) adsorption sites was synthesized for removal of Cr(VI). Physicochemical characterization revealed that the O content of the S-PC reached 20.66 % after activation, indicating that S-PC has excellent potential for adsorption of Cr(VI). The S-PC removal rate for 100 mg/L Cr(VI) was 96.29 %, and the adsorption capacity was 883.86 mg/g. Moreover, S-PC showed excellent resistance to interference, and an equal concentration of hetero-ions reduced the activity by less than 5 %. After 8 cycles of factory wastewater treatment, the S-PC maintained 81.15 % of its original activity, which indicated the possibility of practical application. Characterization and model analyses showed that the removal of Cr(VI) from wastewater by the S-PC was due to CC, δ-OH, ν-OH, and C-O-C groups, and the synergistic effect of adsorption and reduction was the key to the performance. This study provides a good solution for treatment of Cr(VI) plant wastewater and provides a technical reference for the use of biological macromolecules such as starch in the treatment of heavy metals.

Roles of red mud in remediation of contaminated soil in mining areas: Mechanisms, advances and perspectives.

Red mud (RM) is a kind of strong alkaline solid waste produced from the aluminum industry, which contributes significantly to environmental pollution and can cause severe health issues.Currently, RM is widely recognized as a potential material for soil remediation because of its rich metal oxide content, such as Fe/Al oxides. However, there is no comprehensive description on the roles of RM in passivation remediation of contaminated soil in mining areas. This review summarizes the mechanisms of passivation of heavy metals (HMs) in contaminated soil by RM, including precipitation, adsorption and ion exchange. Besides the effects of adding RM on soil physicochemical properties, heavy metal forms and ecological environment are further elaborated. Moreover, using the co-hydrothermal carbonization of RM and biomass for enhancing the efficiency of contaminated soil remediation is proposed as the main prospective research. This paper provides technical references for the resource utilization of RM and the treatment of heavy metal-contaminated soil.

Applications of hollow nanostructures in water treatment considering organic, inorganic, and bacterial pollutants.

One of the major issues of modern society is water contamination with different organic, inorganic, and contaminants bacteria. Finding cost-effective and efficient materials and methods for water treatment and environment remediation is among the scientists' most important considerations. Hollow-structured nanomaterials, including hollow fiber membranes, hollow spheres, hollow nanoboxes, etc., have shown an exciting capability for wastewater refinement approaches, including membrane technology, adsorption, and photocatalytic procedure due to their extremely high specific surface area, high porosity, unique morphology, and low density. Diverse hollow nanostructures could potentially eliminate organic contaminants, including dyes, antibiotics, oil/water emulsions, pesticides, and other phenolic compounds, inorganic pollutants, such as heavy metal ions, salts, phosphate, bromate, and other ions, and bacteria contaminations. Here, a comprehensive overview of hollow nanostructures' fabrication and modification, water contaminant classification, and recent studies in the water treatment field using hollow-structured nanomaterials with a comparative attitude have been provided, indicating the privilege abd detriments of this class of nanomaterials. Eventually, the future outlook of employing hollow nanomaterials in water refinery systems and the upcoming challenges arising in scaling up are also propounded.

Stabilization of heavy metals in solid waste and sludge pyrolysis by intercalation-exfoliation modified vermiculite.

Increasing amounts of solid waste and sludge have created many environmental management problems. Pyrolysis can effectively reduce the volume of solid waste and sludge, but there is still the problem of heavy metal contamination, which limits the application of pyrolysis in environmental management. The intercalated-exfoliated modified vermiculite (IEMV) by intercalators of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide were used to control the release of Cd, Cr, Cu, Zn and Pb during pyrolysis process of sludge or solid waste. The retention of heavy metals in sludge was generally better than that in solid waste. The IEMV by octadecyltrimethylammonium bromide as the intercalator calcined 800 °C (STAB-800) was the best additive for heavy metal retention, and the retention of Cr, Cu and Zn was significantly better than that of Pb and Cd. Cr, Cu, Zn and Pb were at low risk, while Cd had considerable risk under certain circumstances. New models were proposed to comprehensively evaluate the results of the risk and forms of heavy metals, and the increasing temperature was beneficial in reducing the hazards of heavy metals by the addition of STAB-800. The reaction mechanism of heavy metals with vermiculite was revealed by simulation of reaction sites, Fukui Function and Frontier Molecular Orbital. Thermal activation-intercalated-exfoliated modified vermiculite (T-IEMV) is more reactive and had more active sites for heavy metals. Mg atoms and outermost O atoms are the main atoms for T-IEMV to react with heavy metals. The Cr, Cu and Zn have better adsorption capacity by T-IEMV than Pb and Cd. This study provides a new insight into managing solid waste and sludge and controlling heavy metal environmental pollution.

Silicon a key player to mitigate chromium toxicity in plants: Mechanisms and future prospective.

Chromium is a serious heavy metal (HM) and its concentration in plant-soil interface is soaring due to anthropogenic activities, unregulated disposals, and lack of efficient treatments. High concentration of Cr is toxic to ecosystems and human health. Cr stress also diminishes the plant performance by changing the plant's vegetative and reproductive development that ultimately affects sustainable crop production. Silicon (Si) is the second-most prevalent element in the crust of the planet, and has demonstrated a remarkable potential to minimize the HM toxicity. Amending soils with Si mitigates adverse effects of Cr by improving plant physiological, biochemical, and molecular functioning and ensuring better Cr immobilization, compartmentation, and co-precipitation. However, there is no comprehensive review on the role of Si to mitigate Cr toxicity in plants. Thus, in this present review; the discussion has been carried on; 1) the source of Cr, 2) underlying mechanisms of Cr uptake by plants, 3) how Si affects the plant functioning to reduce Cr toxicity, 4) how Si can cause immobilization, compartmentation, and co-precipitation 5) strategies to improve Si accumulation in plants to counter Cr toxicity. We also discussed the knowledge gaps and future research needs. The present review reports up-to-date knowledge about the role of Si to mitigate Cr toxicity and it will help to get better crop productivity in Cr-contaminated soils. The findings of the current review will educate the readers on Si functions in reducing Cr toxicity and will offer new ideas to develop Cr tolerance in plants through the use of Si.

Eco-friendly nanoparticles: mechanisms and capacities for efficient removal of heavy metals and phosphate from water using definitive screening design approach.

Can nano-zero-valent iron, synthesized using oak leaf extract, be the key solution for water preservation, efficiently removing heavy metal ions and phosphate anions simultaneously? This research unveils how this technology not only promises high efficiency in the remediation of water resources, but also sets new standards for environmentally friendly processes. The high antioxidant capacity and high phenol content indicate suggest the possibility of oak-nZVI synthesis using oak leaf extract as a stable material with minimal agglomeration. The simultaneous removal of Cd and phosphates, as well as and Ni and phosphates was optimized by a statistically designed experiment with a definitive screening design approach. By defining the key factors with the most significant impact, a more efficient and faster method is achieved, improving the economic sustainability of the research by minimizing the number of experiments while maximizing precision. In terms of significance, four input parameters affecting process productivity were monitored: initial metal concentration (1-9 mg L-1), initial ion concentration (1-9 mg L-1), pH value (2-10), and oak-nZVI dosage (2-16 mL). The process optimization resulted in the highest simultaneous removal efficiency of 98.99 and 87.30% for cadmium and phosphate ions, respectively. The highest efficiency for the simultaneous removal of nickel and phosphate ions was 93.44 and 96.75%, respectively. The optimization process fits within the confidence intervals, which confirms the assumption that the selected regression model well describes the process. In the context of e of the challenges and problems of environmental protection, this work has shown considerable potential and successful application for the simultaneous removal of Cd(II) and Ni(II) in the presence of phosphates from water.

Insights into the Mechanism of Selective Removal of Heavy Metal Ions by the Pulsed/Direct Current Electrochemical Method.

Heavy metal pollution treatment in industrial wastewater is crucial for protecting biological and environmental safety. However, the highly efficient and selective removal of heavy metal ions from multiple cations in wastewater is a significant challenge. This work proposed a pulse electrochemical method with a low-/high-voltage periodic appearance to selectively recover heavy metal ions from complex wastewater. It exhibited a higher recovery efficiency for heavy metal ions (100% for Pb2+ and Cd2+, >98% for Mn2+) than other alkali and alkaline earth metal ions (Na+, Ca2+, and Mg2+ were kept below 3.6, 1.3, and 2.6%, respectively) in the multicomponent solution. The energy consumption was only 34-77% of that of the direct current electrodeposition method. The results of characterization and experiment unveil the mechanism that the low-/high-voltage periodic appearance can significantly suppress the water-splitting reaction and break the mass-transfer limitation between heavy metal ions and electrodes. In addition, the plant study demonstrates the feasibility of treated wastewater for agricultural use, further proving the high sustainability of the method. Therefore, it provides new insights into the selective recovery of heavy metals from industrial wastewater.

Mineralogical and sorption characterization of lateritic soils from Southwestern Nigeria for use as landfill liners.

Lateritic soils are prevalent in the tropical regions, and they are used for various construction purposes including landfill liner applications. However, their contaminant attenuation potentials through sorption and the influence of parent rocks on this property are poorly understood. This study investigates lateritic soils from southwestern Nigeria as barrier to leachate migration in engineered landfills and related waste containment facilities. The lateritic soils were investigated through X-ray diffraction (XRD), geochemical analysis and batch equilibrium sorption test to evaluate the competitive sorption of Mn, Cd, Pb, Cu and Cr which are common in landfill leachates. The XRD analysis shows that the kaolinite and dickite are the dominant clay minerals present in the lateritic soils, implying low desiccation cracking and low shrink-swell behaviour. The geochemical analysis indicate that the lateritic soils are silico-alumino-feruginuous with average major oxide composition of SiO2, Al2O3and Fe2O3 of 50.86 wt%, 29.83 wt% and 14.29 wt%), respectively. Additional oxides with lower abundance include TiO2 (1.55 wt%), Na2O (0.01 wt%), MgO (0.36 wt%), CaO (0.15 wt%) and K2O (1.52 wt%). The lateritic soils contain trace amount of heavy metals with average concentrations of Cd (0.039 ppm), Pb (0.548 ppm), Cr (0.189 ppm), Cu (0.964 ppm), Mn (0.145 ppm). Furthermore, the low abundance of sodium oxide in the lateritic soils indicates that the soil particles are not susceptible to dispersion while the presence of considerable amount of iron and manganese oxides signify its good heavy metal retention. The batch equilibrium sorption analysis shows that the lateritic soils derived from granite-gneiss and charnockite exhibit better sorption potential than those derived from schist and quartzite. This high sorption capacity is intricately related to the presence of goethite in the soils. The sorption of these trace metals onto the lateritic soils follows Langmuir type isotherm and these isotherms deviate from the corresponding desorption isotherms to different degrees indicating various extents of hysteresis. The sorption hysteresis indices for these trace metals range from 0.63 to 0.99 and imply that the trace metals may re-leached to the surrounding soils and groundwater. Thus, it is recommended that landfill liners utilizing these lateritic soils are design as a composite containment facility by integrating compacted soil liners, leachate collection systems and monitoring networks to ensure effective environmental protection.

Transport and transformations of cadmium in water-biofilm-sediment phases as affected by hydrodynamic conditions.

Hydrodynamic conditions play a crucial role in governing the fate, transport, and risks of metal elements. However, the contribution of hydrodynamic conditions to the fate and transport of heavy metals among water, sediment, and biofilm phases is poorly understood. In our study, we conducted experiments in controlled hydrodynamic conditions using a total of 6 two-phase and 9 three-phase mesocosms consisting of water, biofilm, and sediment. We also measured Cd (cadmium) specification in different phases to assess how hydrodynamic forces control Cd bioavailability. We found that turbulent flow destroyed the surface morphology of the biofilm and significantly decreased the content of extracellular polymeric substances (p < 0.05). This led to a decrease in the biofilm's adsorption capacity for Cd, with the maximum adsorption capacity (0.124 mg/g) being one-tenth of that under static conditions (1.256 mg/g). The Cd chemical forms in the biofilm and sediment were significantly different, with the highest amount of Cd in the biofilm being acid-exchangeable, accounting for up to 95.1% of the total Cd content. Cd was more easily released in the biofilm due to its weak binding state, while Cd in the sediment existed in more stable chemical forms. Hydrodynamic conditions altered the migration behavior and distribution characteristics of Cd in the system by changing the adsorption capacity of the biofilm and sediment for Cd. Cd mobility increased in laminar flow but decreased in turbulent flow. These results enhance our understanding of the underlying mechanisms that control the mobility and bioavailability of metals in aquatic environments with varying hydrodynamic conditions.

In-situ registration subtraction image segmentation algorithm for spatiotemporal visualization of copper adsorption onto corn stalk-derived pellet biochar by micro-computed tomography.

The non-homogeneous structure and high-density ash composition of biochar matrix pose significant challenges in characterizing the dynamic changes of heavy metal adsorption onto biochar with micro-computed tomography (Micro-CT). A novel in-situ registration subtraction image segmentation method (IRS) was developed to enhance micro-CT characterization accuracy. The kinetics of Cu(II) adsorption onto pellet biochar derived from corn stalks were tested. Respectively, the IRS and traditional K-means algorithms were used for image segmentation to the in-situ three-dimensional (3D) visual characterization of the Cu(II) adsorption onto biochar. The results indicated that the IRS algorithm reduced interference from high-density biochar composition, and thus achieved more precise results (R2 = 0.95) than that of K-means (R2 = 0.72). The visualized dynamic migration of Cu(II) from surface adsorption to intraparticle diffusion reflexed the complex mechanism of heavy metal adsorption. The developed Micro-CT method with high generalizability has great potential for studying the process and mechanism of biochar heavy metal adsorption.

Contrasting fate and binding behavior of Mn and Cu with dissolved organic matter during in situ remediation using multicomponent capping in malodorous black water.

The common use of peroxides in the remediation of malodorous black water may lead to the activation of heavy metals in sediment when eliminating black and odorous substances. The mechanisms of heavy metal interactions with dissolved organic matter (DOM) in response to in situ capping have not been elucidated, but this information could guide the optimization of capping materials. We developed a capping material consisting of hydrothermally carbonized sediment (HCS), hydrated magnesium carbonate (HMC) and sodium percarbonate (SPC) and used microcosm experiments to investigate the dynamics of Mn and Cu at the sediment-water interface in malodorous black water. The results showed that HCS, HMC and SPC contributed multiple functions of mechanical protection, chemical isolation and oxygen provision to the new caps. HMC promoted the conversion of Mn/Cu into carbonate minerals. The optimal mass proportions were 25 % HCS, 60 % HMC and 15 % SPC based on the mixture design. In situ capping altered the fate and transformation of metals in the sediment-overlying water profile in the short term through Mn immobilization and Cu activation. The complexation of Cu(II) ions was significantly stronger than that of Mn(II) ions. In situ capping had a significant effect on the order of complexation of different fluorescent DOM molecules with Mn(II)/Cu(II) ions: microbial byproducts and fulvic acid-like components were preferentially complexed with Cu(II) ions after capping, while phenolic and humic acid-like components preferentially interacted with Mn(II) ions. Humic-like components bound to Cu were affected the most by capping treatment, whereas protein-like components were relatively weakly affected. Our study provides valuable knowledge on the impact of in situ capping on DOM-metal complexes.

Spectroscopic insights into the binding characteristics of heavy metals to dissolved organic matter in landfill leachate.

Landfill leachate is produced in the process of sanitary landfilling, which contains significant amounts of dissolved organic matter (DOM) and heavy metal contaminants. Insights into the interactions between heavy metals and DOM in landfill leachate are beneficial for the understanding of heavy metal fates and optimization of landfill leachate treatment. In this work, the coherent structural changes of landfill leachate DOM during binding with various heavy metals were explored through the integration of molecular spectroscopic methods with chemometrics and statistic correlation analyses. The results indicate that protein substances, phenolic and discrete carboxyl groups in landfill leachate DOM were involved in the complexation with heavy metals, resulting in the formation of conjugated macromolecules/aggregates with high aromaticity and molecular weight/size. The fluorescent protein-like, fulvic acid-like, and humic-like fractions in DOM were engaged in the interaction, which were closely related to phenolic-like and carboxylic-like structure. Compared to membrane concentrates DOM, raw leachate DOM exhibited a higher binding affinity to heavy metals (especially for Cu2+, whilst the weakest was Cd2+). The integrated approach provides useful information in elucidating the binding processes of metals with landfill leachate DOM, including site heterogeneity, binding strength and functional group sequences.

Preparation and characterization of P-type zeolite for adsorption of Cr3+, Ni2+, and Co2.

Acid-washed coal fly ash (AW-CFA) was subjected to wet grinding activation followed by hydrothermal crystallization to synthesize P zeolite (FAZ-P). The FAZ-P obtained at 120 °C for 24 h exhibited a maximum relative crystallinity of 93.15% and was employed for the adsorption of Cr3+, Ni2+, and Co2+ from aqueous solutions. The zeolitization of coal fly ash (CFA) leads to an increase in specific surface area to 44.00 m2/g, resulting in the formation of nano-sized P zeolite crystals with uniformly narrow fissures and sizes within the range of 10-30 nm. Adsorption experimental results indicate that FAZ-P exhibits maximum adsorption capacities of 49.03 mg/g for Cr3+, 22.20 mg/g for Ni2+, and 27.25 mg/g for Co2+. The adsorption equilibrium data for both mixed and single-metal ion solutions conform to the Langmuir model, with the affinity sequence for heavy metal ions being Cr3+ > Co2+ > Ni2+. The pseudo-first-order and pseudo-second-order kinetic models effectively described the adsorption behavior of Cr3+, Ni2+, and Co2+. Increasing the initial pH value of the solution significantly enhanced the adsorption capacity of the adsorbent for heavy metal ions. The removal mechanism of metal ions involves both adsorption and ion exchange processes. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic.

Attempts to obtain clean biochar from hyperaccumulator through pyrolysis: Removal of heavy metals and transformation of phosphorus.

The sound disposal of the ensuing heavy metal-rich plants can address the aftermath of phytoremediation. In this study, the first attempt was made to obtain heavy metals-free and phosphorus-rich biochar from phytoremediation residue (PR) by pyrolysis, and the effects of chlorinating agent type, chlorine dosage, and pyrolysis residence time on heavy metal removal, phosphorus (P) transformation, and biochar properties were investigated. The results showed that as chlorine dosage and pyrolysis residence time increased, added polyvinyl chloride (PVC) reduced the concentration of Zn in biochar to one-tenth of that in PR by intensified chlorination, where both Zn concentration (2727.50 mg/kg) and its leaching concentration (29.13 mg/L) met the utilization requirements, in which the acid-base property of biochar plays a key role in heavy metal leaching. Meanwhile, more than 90% of P in PR remained in biochar and the bioavailability of P in biochar enhanced with the decomposition of organic P to inorganic P, where the concentration of plant-availability P (Pnac) expanded from 1878.40 mg/kg in PR to 8454.00 mg/kg in biochar. This study demonstrated that heavy metal hyperaccumulator can be converted into heavy metal-free and phosphorus-rich biochar with promising applications, which provides new perspectives for the treatment of such hazardous wastes.

Migration and morphological transformation patterns of heavy metals on sludge cells and extracellular polymeric substances (EPS) under the influence of different treatments.

The impediment of sludge resource utilization stems from the presence of heavy metals within the sludge matrix. To optimize heavy metal removal techniques from undried sludge, it is essential to study the distribution of heavy metals in the sludge flocs structure and the changes in morphology in the sludge cells after different treatments. In this study, the sludge was subjected to chemical treatments using citric acid (CA), EDTA, and saponin, as well as electrokinetic treatment at 2 V/cm. The distribution and migration of Cu, Ni, and Zn in sludge flocs after various treatment methods were analyzed. The heavy metals were found to migrate from intracellular to extracellular polymeric substances (EPS) without causing extensive sludge cell lysis. They gradually diffused outward with the dispersion of the EPS layer. The migration efficiency of the three heavy metals in the sludge flocs was Zn, Ni, and Cu. This was mainly related to the initial distribution and morphology of the heavy metals. Under the influence of chemicals and an electric field, the acid-soluble and reducible heavy metals in the cells partially migrated to the EPS, while the stable heavy metals transformed into an unstable state. Furthermore, the order of chemical reagents in terms of their effect on the migration efficiency of heavy metals was CA > EDTA > Saponin, owing to the varying binding strengths of heavy metals and their impact on the degree of loosening of the EPS. Especially after CA treatment a greater proportion of Cu, Ni, and Zn were transferred from the cells to the EPS. The acidification effect near the anode during electrokinetic treatment intensifies the migration of heavy metals. This study provides basic research for subsequent engineering optimization aimed at removing heavy metals from sludge.

The interfacial interaction between typical microplastics and Pb2+ and their combined toxicity to Chlorella pyrenoidosa.

Microplastics (MPs), a new type of pollutant, have attracted much attention worldwide. MPs are often complexed with other pollutants such as heavy metals, resulting in combined toxicity to organisms in the environment. Studies on the combined toxicity of MPs and heavy metals have usually focused on the marine, while on the freshwater are lacking. In order to understand the combined toxic effects of MPs and heavy metals in the freshwater, five typical MPs (PVC, PE, PP, PS, PET) were selected to investigate the adsorption characteristics of MPs to Pb2+ before and after the MPs aging by ultraviolet (UV) irradiation through static adsorption tests. The results showed that UV aging enhanced adsorption of Pb2+ by MPs. It is noteworthy that MPs-PET had the highest adsorption capacity for Pb2+, and the interaction between MPs-PET and Pb2+ was the strongest. We specifically selected MPs-PET to study its combined toxicity with Pb2+ to Chlorella pyrenoidosa. In the combined toxicity test, MPs-PET and Pb2+ had significant toxic effects on Chlorella pyrenoidosa in the individual exposure, and the toxicity of individual Pb2+ exposure was greater than that of individual MPs-PET exposure. In the combined exposure, when MPs-PET and Pb2+ without adsorption (MPs-PET/Pb2+), MPs-PET and Pb2+ had a synergistic effect, which would produce strong physical and chemical stress on Chlorella pyrenoidosa simultaneously, and the toxic effect was the most significant. After the adsorption of MPs-PET and Pb2+ (MPs-PET@Pb2+), the concentration and activity of Pb2+ decreased due to the adsorption and fixation of MPs-PET, and the chemical stress on Chlorella pyrenoidosa was reduced, but the physical stress of MPs-PET still existed and posed a serious threat to the survival of Chlorella pyrenoidosa. This study has provided a theoretical basis for further assessment of the potential environmental risks of MPs in combination with other pollutants such as heavy metals.

Wood fly ash and blast furnace slag management by alkali-activation: Trace elements solidification and composite application.

Wood and biomass are burned in many industries as a sustainable energy source. The large quantities of fly ash produced must be landfilled, leading to environmental concerns. Precipitator wood fly ash (PFA) and ground granulated blast furnace slag (BFS) have been used in this study to prepare alkali-activated composites to manage and recycle the fly ash. After an essential characterization, the influence of parameters such as PFA and BFS content, alkaline activator content (silica moduli of 0, 0.82, 1.32), curing method, and curing duration on the mechanical, chemical, and microstructural properties of the samples have been studied through compressive strength, density, FTIR, and SEM-EDS investigations. The environmental safety and influence of polycondensation on heavy metal stabilization have been examined through ICP-MS. The results prove that oven and hydrothermal curing obtain the early age strength. Despite the variations of strength with duration and type of curing, the compressive strength of samples after 28 days of curing tends to close values for a constant PFA/BFS ratio, due to which the need for energy-intensive curing methods is addressed. ICP-MS shows that the composites can suitably solidify As, Cd, Ba, Cr, Pb, Mo, Se, Hg, Sr, Cu, and Zn. On the other hand, the composites were almost incapable of stabilizing Co and V. Unlike the case for mechanical properties; higher PFA content favours hazardous metal stabilization through polycondensation.