Metal Removal Research Articles

Effects of Biological and Enzymatic Ageing on the Surface Properties of Mg-modified Biochar

The excellent surface properties of Mg-modified biochar have highlighted a broad application prospect for soil heavy metal mitigation. However, the soil biotic aging process can have an impact on the physical and chemical properties of biochar as well as the heavy metal removal performance. Therefore, MgCl2-modified biochar was subjected to a six-month microbial and enzymatically aged test to explore the effects of different biotic aging processes on the physical and chemical properties. The Pb2+ adsorption performance of Mg-modified biochar that experienced different aging processes was compared using isothermal adsorption experiments. The results showed that after microbial aging, the Mg-modified biochar pyrolyzed at 700 ℃ displayed a low persistent free radical signal, with the biofilm secreted by microorganisms wrapped on the surface of the biochar, leading to the increase in the oxygen-containing functional groups on the biochar surface and the increase in the maximum adsorption capacity of Pb2+ from 55.31 mg·g-1 to 86.27 mg·g-1. In contrast, a higher free radical signal of 500 ℃ pyrolyzed biochar suggested that the free radical inhibited the growth and reproduction of microorganisms on the biochar surface, resulting in an insignificant enhancement in maximum adsorption capacity to Pb2+ compared to that with unmodified biochar. The pores of the Mg-modified biochar were severely damaged during the enzymatically aged process, resulting in a decrease in the adsorption capacity of Pb2+ to 22.18 mg·g-1, which was significantly lower than that of the unmodified biochar. Therefore, the adsorption capacity of microbially aged Mg-modified biochar is superior to that of enzymatically aged Mg-modified biochar, mainly because the oxygen-containing functional groups exhibited on the surface of the biochar covered by microorganisms come from the extracellular secretions of microorganisms, which promote the removal of Pb2+.

Highly selective and effective copper removal from wastewater by magnetic precipitation separation

The presence of heavy metals in wastewater poses a substantial threat to both public health and the environment. However, the selective removal and separation of heavy metal ions at ultra-low concentrations from wastewater remains a considerable challenge. In this paper, we innovatively proposed a magnetic precipitation separation method to remove Cu (II) from wastewater using Fe3O4 nanoparticles and Na2S. In this process, the Cu (II) was reduced to CuS by Na2S, which then rapidly aggregated with Fe3O4 nanoparticles to form Fe3O4-CuS nanoclusters. SEM, DLS, XRD, VSM and XPS studies demonstrated that the removal of Cu (II) was related to the formation of Fe3O4-CuS nanoclusters. The results indicated that the removal efficiency of Cu (II) from wastewater could reach 99.75 % within 30 s. In contrast, the removal efficiencies of Co (II), Ni (II), and Zn (II) were 7.64 %, 6.14 %, and 8.41 %, respectively. In addition, the Fe3O4 nanoparticles were easily regenerated from Fe3O4-CuS nanoclusters using ultrasound, maintaining 98 % removal efficiency of Cu (II) after six consecutive cycles. These results suggested that this method held great potential for the removal of heavy metals from wastewater.

Azolla pinnata and Lemna minor as comparative hyperaccumulators for livestock wastewater treatment: morpho-physiological and genetic approach.

The potential of two different aquatic macrophytes, Azolla pinnata R.Br. and Lemna minor L., to treat livestock wastewater through phytoremediation was investigated. The physiological analysis includes the removal efficiency of manganese (Mn) from livestock wastewater by AAS. Morphological observation was performed by using a scanning electron microscope (SEM) and visual observation. RAPD analysis was applied to observe the DNA profile. It was observed that the removal efficiency of Mn was higher in L. minor with a 92% removal rate, while in A. pinnata RE, it was at a 77% rate. The higher removal rate of Mn by L. minor showed that plants had a significant impact on the removal of heavy metals, with a p ≤ 0.05. Retention time and the removal of heavy metals were found to be positively correlated. As early as 24h after exposure to livestock wastewater (LW), the stomata on the leaves of A. pinnata and L. minor have both shrunk, and the root surfaces have shortened. According to the RAPD analysis, A. pinnata only shows an increase in band intensities and no polymorphism, whereas L. minor has 19% polymorphisms that indicate higher tolerance as hyperaccumulators. As a conclusion, L. minor showed no signs of necrosis and performed more efficiently as a hyperaccumulator in LW, with a higher removal efficiency.

Harnessing the Power of Plants: Innovative Approaches to Pollution Prevention and Mitigation

Innovative and sustainable environmental management strategies are urgently required to address the escalating global pollution crisis. Phytoremediation, which involves using plants to mitigate, remediate, or contain environmental contaminants, is a promising, cost-effective, and environmentally friendly alternative to conventional remediation methods. This review summarizes current research to elucidate the multifaceted roles of plants in pollution mitigation, detailing mechanisms such as phytoextraction, phytostabilization, phytodegradation, and rhizofiltration; we highlight successful case studies that demonstrate practical applications across diverse environments, such as the use of hyperaccumulator plants for heavy metal removal and genetically engineered species for organic pollutant degradation. Furthermore, this review explores recent technological advancements that have enhanced the effectiveness of phytoremediation, such as the integration of nanotechnology and genetic engineering. It also analyzes the economic and social implications of adopting plant-based pollution control strategies, emphasizing their potential for community involvement and socioeconomic benefits. Despite the promising outlook, we acknowledge the inherent challenges and limitations of phytoremediation, including public acceptance and scalability issues. Finally, we identify key opportunities for future research and innovative approaches that could expand the scope and impact of phytotechnologies in pollution mitigation. This comprehensive review underscores the potential of plants as both agents of environmental restoration and essential components of sustainable pollution management systems.

Contamination characteristics of heavy metals and enrichment capacity of native plants in soils around typical coal mining areas in Gansu, China

Exploitation of mineral resources is a vital backbone of a country’s socio-economic development. However, the coal exploration would cause ecological and environmental problems such as pollutions of water, soils and atmosphere. Especially, the pollution of heavy metals of soil has become increasingly severity. Plant enrichment and tolerance to heavy metals are crucial for the phytoremediation of coal gangue mountain. In phytoremediation, phytostabilization which can reduce the metal contamination of soil by uptake and burn-off of heavy metals with highly accumulating plants, is one of the most effective techniques of eco-remediation treatment. In present work, heavy metals contamination of soil and plants in the Yaojie mining which located in arid and semi-arid area of northwest China were investigated through field investigation. To identify the suitable plants for the remediation and ecological reclamation of heavy metal contaminated soil in typical mining area, the contamination characteristics of heavy metals in the above-ground parts of 27 native plants and their surrounding non-rhizosphere soils were analyzed. After eliminated by wet digestion and high-pressure closed digestion, the mass fractions of Zinc (Zn), cadmium (Cd), chromium (Cr) and copper (Cu) were determined with inductively coupled plasma emission spectrometer, and the contents of Hydrargyrum (Hg) and Arsenic (As) were analyzed with atomic fluorescence spectrophotometer. The Nemerow pollution index showed that in the surrounding soil, the pollution index of heavy metal was 6.32, which reached the extreme severe pollution level. Among the 6 heavy metals, the most severe contamination being Hg (Pi = 8.50) and had particularly strong Coefficient of variation (CV = 105.8%), which is more likely to be caused by anthropogenic activities. In the aboveground parts of 27 plants, except for Zn, other metals exceeded the standard level, and the exceedance rates in descending order were As, Hg, Cr, Cd, and Cu. The most severe exceedance of As was found in C. virgata, which was as high as 19.20, and the average exceedance rate of As in all plants was 2.79. Bioconcentration Factor (BCF) was utilized as an indicator of the enrichments of various metals in 27 plants. The maximum value of BCF for As and Hg in C. virgata were 1.52 and 2.50, Cr and Cu in X. sibiricum were 0.72 and 2.32, Cd and Zn in S. glauca were 3.33 and 1.82. As revealed, except Cr, all the BCF of other metals are greater than 1, indicating that the three plants exhibited a strong accumulation capacity of heavy metal and are potential candidate pioneer species for the removal of heavy metals from the contaminated soil in the Yaojie mining area. This study provides a basis for plant selection for ecological restoration of contaminated soils in arid and semi-arid regions.

Nanocomposite membrane for simultaneous removal of dye and heavy metal ions from wastewater.

A catalytic 2D nanocomposite membrane (CNC) was fabricated and used for the simultaneous removal of methylene blue (MB) and heavy metal ions in aqueous solution. Both molybdenum disulfide (MoS2) and graphene oxide (GO) were incorporated in a chitosan polymer matrix, and the fabricated CNC membrane exhibited performance as a nanofiltration membrane. Here MoS2 activated H2O2 to generate very reactive oxygen species (ROS), such as hydroxyl radicals, allowing the catalytic breakdown of the organic dye contaminants and reducing heavy metal ions. Greater than 99% efficiencies were achieved for the simultaneous removal of methylene blue (MB) and the heavy metal Co2+. Moreover, significant removal efficiencies in the 89-96% range were demonstrated for other heavy metal ions of Cu2+, Pb2+, and Ni2+. The generated ROS were trapped by terephthalic acid (TA) and confirmed by fluorescence emission spectroscopy. The used membrane was regenerated and reused with a flux recovery rate of more than 91% after 4 experimental cycles. These promising results indicated that the novel catalytic 2D nanocomposite membrane showed a high potential for the simultaneous removal of organic contraminants and heavy metal ions from textile industry wastewater.

Treatment of digested blackwater using a submerged microfiltration membrane system or a drum filter

After energy recovery from blackwater via anaerobic digestion, technologies such as struvite precipitation and ammonia stripping can be used to enhance nutrient recovery. However, the presence of suspended solids, organics and metals, can negatively impact the nutrient recovery processes. This study examined the treatment of digested blackwater, applying either a ceramic microfiltration membrane or a drum filter, operating in parallel in a source-separated wastewater plant. The digestate as well as the permeates from the membrane and drum filter were sampled regularly and evaluated. In general, the ceramic membrane proved to be more efficient in improving the quality of digested blackwater in comparison to the drum filter. The ceramic membrane reduced total suspended solids to below the detection limit, while the drum filter achieved 74 % removal. The membrane removed 74 %, 85 % and 76 % of TOC, BOD7 and COD-Cr, respectively, higher than the corresponding treatment with the drum filter, which removed 41 %, 42 % and 34 %, respectively. No significant differences in phosphate and ammonium concentrations (P-value = 0.05), before and after both treatment methods were observed. The membrane removed particulate-bound metals (As, Cd, Cr, Cu, Ni, Pb and Zn) up to 25 %, 95 %, 87 %, 95 %, 66 %, 90 % and 98 %, respectively. The drum filter achieved lower removal for particulate-bound As, Cd, Ni, Pb and Zn for 25 %, 79 %, 44 %, 56 % and 86 %, respectively. The removal of metals is critical to maintain struvite purity and prevent the struvite contamination due to co-precipitate of these metals.

Two-step process to recover metal and mineral residues from municipal solid waste incinerated (MSWI) ashes

The utilization potential of mineral fractions after metal recovery from fly ash and air pollution control residues from a municipal solid waste incineration plant was studied. Chemical leaching using acidic (H2SO4), and alkaline (NaOH) solutions was applied for metal recovery from fly ash and air pollution control residues from a municipal solid waste incineration plant. Subsequently, the feasibility of recycling both untreated and treated samples in cementitious materials was evaluated. This study aims to investigate the influences of chemical leaching on the structures and properties of MSWI residues as well as examine the utilization potential in cementitious materials of mineral residues after leaching, and their environmental risk. The use of acidic and alkaline leachants had good efficiency in critical metal recovery and unvalued/hazardous metal removal: 99 % of As, 72–80 % of Cd, 47–60 % of Zn, Cu, Co or Mn. After leaching, the chemical composition, physical properties, and mineralogical phases of the incinerated residues were substantially modified. The postleaching mineral residues showed potential for use in supplementary cementitious materials with enhanced reactivity and control of hydration kinetics. The compressive strength of cement pastes using 20 % of MSWI residues can obtain 14 MPa after 7 days. Detrimental impacts from potential toxic elements in incinerated residues can be alleviated through chemical leaching.

Constructing positively charged hollow fiber nanofiltration membranes with high performance for the treatment of wastewater containing heavy metal ions

The presence of heavy metal ions in wastewater has been identified as a significant environmental and human health concern. Positively charged hollow fiber (HF) Nanofiltration (NF) membranes show great promise and excellent potential for the removal of heavy metal ions due to Donnan exclusion effect. Nevertheless, the current limitations of positively charged HF NF membranes, including complex preparation process, low flux and poor selectivity, continue to impede their broader implementation. In this work, a high flux HF NF membrane with positively charged surface was fabricated via doping piperazine in the aqueous-phase solution of polyethyleneimine to modulate the interfacial polymerization and to adjust the structure of the subsequent polyamide skin layer. Subsequently, the surface of this nascent skin layer was modified with diethylenetriamine/ethanol solution to increase its positive charge density, and thus to improve the rejection of multivalent cations. The optimal HF NF membrane shows a pure water permeability of 160 LMH/MPa and a MgCl2 rejection of higher than 97 %. In addition, it shows a rejection of higher than 95 % for heavy metal salts such as CoCl2, MnCl2, NiCl2, CuCl2 and Cr2(SO4)3, and a rejection of more than 98 % for antibiotics such as tetracycline hydrochloride, oxytetracycline and levofloxacin. It also possesses good resistance to acid and contamination. In addition, the optimal HF NF membrane has been successfully scaled up to a module of 20 filaments and still shows excellent separation performance, suggesting its vast potential for industrial application.

Nanoparticles for treatment of cadmium-contaminated cocoa-growing soils and beans: Performance on metal immobilization and removal.

Some areas of tropical soils where cocoa grows contain high cadmium (Cd) concentrations. The cocoa plant's need for nutrition causes the reticular system to uptake the toxic metal, translocate it, and accumulate it in roots, stems, and other edible parts such as cocoa beans and shells, threatening the health of cocoa consumers. To cope with this difficulty, different treatments have been applied to cadmium-contaminated soils, but they showed limited success. In this study, we prepared multicomponent nanoparticles (MCNPs) to treat cocoa soils in fixed-bed columns and field tests. Also, MCNPs were mixed with two varieties of cocoa beans, CNN51 and Fino de Aromain, during the fermentation, aiming to capture the cadmium. Our field investigations began by collecting soil samples from three Ecuadorian cocoa-producing farms to determine their physicochemical properties, cadmium, and iron contents. A few weeks later, a home-built prototype was installed in a cocoa plantation to fabricate the nanomaterials using commercial-grade chemicals and rainwater. Scanning Electron Microscope (SEM) images showed MCNPs with an average size of 65.21 nm and the formation of chain-like aggregates. In contrast, MCNPs size was 76.6 nm, measured with Dispersed Light Scattering (DLS). The chemical composition of MCNPs was 90.7% Fe0 and 1.81% sulfur (S), analyzed by energy dispersal X-ray (EDX) and confirmed by X-ray diffraction (XRD) spectrometer measurements. Regarding the treatments, for the fixed-bed column tests, 0.28-1.08 L/kg was dosed into the soil, while for field treatments, 250, 500, and 835 mL/min MCNPs were injected in soil areas of 5 m2 surrounding each cocoa tree (0.5-4.5 mg MCNPs/kg soil) at depths between 0 and 5 cm. Test results revealed that the procedure applied in the field did not reproduce the metal’s immobilization (∼22%) as in the fixed-bed columns (∼80%). Moreover, cadmium removal was ∼ 20% and ∼75% after treating CCN51 and Fino de Aroma cocoa beans with 0.112 kg MCNPs/kg in the fermentation on-site and 0.034 kg MCNPs/kg in the laboratory. In this study, the size and chain-like aggregates of MCNPs notably influenced the field treatments as they precluded the filtration of MCNPs downwards. However, immobilizing cadmium could be more effective in soils with higher concentrations of the metal and multicomponent nanoparticles of smaller size, expanding our research scope and offering a practical solution to pollution issues in cocoa-growing regions.

Three-dimensionally assembled polyelectrolyte multilayers-functionalized silica nanowire membrane for highly-efficient adsorptive separation of copper ions from water

High-performance materials for heavy metal ion removal are highly demanded in environmental treatment. Membrane adsorption has the advantages of being easy to operate and avoiding secondary pollution. It remains challenging to prepare adsorption membranes with both high removal rate and high permeability. Here, we present a novel strategy for preparing poly(acrylic acid) (PAA) and polyethyleneimine (PEI) multilayer-assembled silica nanowires (SiO2 NWs) membrane with abundant, multiple functional groups on a highly porous network for Cu(II) capture. The SiO2 NWs in the hybrid membranes serve as a rigid 3D framework to improve membrane porosity and water flux, while the polyelectrolyte multilayers assembled on the SiO2 NWs provide abundant, highly accessible adsorption sites for Cu(II) uptake. The adsorption capacity of the membranes can be tuned by changing the dosage of the assembled SiO2 NWs and the PAA/PEI pair layers. The maximum adsorption capacity of the active polyelectrolyte layer for SiO2 NWs@(PAA/PEI)4 composite membrane was 272.5 mg/g toward Cu(II), outperforming the counterpart (PAA/PEI)4 membrane (97.5 mg/g) after removal of the SiO2 NWs framework. The hybrid membrane shows excellent adsorption performance for the removal of low concentrations of Cu(II) in a dynamic adsorption mode, and the removal rate is maintained at above 90% after eight recycles.

Homogeneous Crystallization of Nickel as Ni₃S₄ in a Fluidized Bed Reactor with Supersaturation Control

This study investigates the recovery of nickel sulfide (NiS) using fluidized bed homogeneous crystallization (FBHC), emphasizing the process from nucleation to crystallization. Sludge production in conventional chemical precipitation becomes a drawback in treating wastewater economically and efficiently. FBHC offers a promising alternative by minimizing sludge generation. The study examines various operational parameters, including hydraulic retention times (HRT), reflux ratio (R), initial nickel concentration, and static bed height (SBH), to optimize NiS recovery. Results show that FBHC achieves high total removal efficiency (TR) and crystallization ratio (CR), under the optimum condition of HRT = 15min, R = 8.3, initial nickel concentration = 147mg/L, and SBH = 35cm. The agglomeration of Ni(OH)2 was found to be crucial for the crystal growth during the surface oxidation of Ni3S4. This technological approach to wastewater treatment offers highly efficient heavy metal removal from wastewater.

Biosynthesis and Application of Biological Thin Films for Heavy Metal Ion Biosorption from Aqueous Solution

This study investigates the biosynthesis and application of Mycelium Bio-Films (MBFs) derived from pure Common oyster mushroom (COM) for heavy metal ion biosorption from aqueous solutions. The research focuses on the growth mechanism of MBFs and their potential for Cu (II) ions removal. MBFs were synthesized through a hyphae cultivation process and characterized using Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), and Energy-Dispersive X-ray Spectroscopy (EDS) mapping. Batch biosorption experiments were conducted to determine optimal operational parameters and adsorption mechanisms. Key findings reveal optimal biosorption conditions at pH 5, with a 40-minute contact time, and 100mg/L initial Cu (II) concentration using 0.2g of biosorbent in 10mL aqueous solution at room temperature with 150rpm agitation. Under these conditions, a maximum adsorption efficiency of 82.8% was achieved. The adsorption process best fits Pseudo-second-order kinetics and Langmuir isotherm, indicating chemisorption, complexation, and ion exchange as primary mechanisms. Functional groups involved in biosorption include carboxyl, hydroxyl, and amide groups. Importantly, MBFs demonstrate high reusability potential through diluted acid elution. This research contributes to environmental remediation by presenting a novel, sustainable biosorbent for heavy metal removal. The MBFs show promise for industrial wastewater treatment applications, offering an eco-friendly alternative to conventional adsorbents and contributing to filling the lack of biobank collections. Future studies could explore the efficacy of MBFs with other heavy metals and investigate potential scale-up for large-scale implementation.

Expression of Concern: “Enlightening the characteristics of bioflocculant of endophytic actinomycetes from marine algae and its biosorption of heavy metal removal” [Environmental Research 200 (2021) 111708

Expression of Concern: “Enlightening the characteristics of bioflocculant of endophytic actinomycetes from marine algae and its biosorption of heavy metal removal” [Environmental Research 200 (2021) 111708

A multifunctional coconut shell biochar modified by titanium dioxide for heavy metal removal in water/soil and tetracycline degradation

Heavy metals and tetracycline pollute the environment and endanger human health. This work prepared a multifunctional coconut shell biochar (Ti-XBC) through NaHCO3 activation and TiO2 modification. The modified coconut shell biochar was characterized by various methods. Ti-4BC exhibited excellent removal performance for heavy metals. The maximum adsorption capacity of Ti-4BC on Cd2+, Pb2+, Cr3+, and Cr6+ reached 104.2, 136.8, 101.2, 112.4 mg/g in water. The adsorption of Ti-4BC for four metal ions had a competitive effect in the binary metal system. It also reduced the mobility of four heavy metal ions in soil. Density functional theory (DFT) calculations were employed to explain the mechanism of heavy metal removal. Additionally, the degradation performance and mechanism of Ti-4BC towards tetracycline were investigated. The results indicated that the maximum degradation rate was 99.4%. Overall, this work developed a multifunctional material capable of both removing heavy metals and degrading antibiotics, addressing the issue of single-function in biochar. This provided a novel approach for tackling complex and diverse environmental pollution scenarios.

Clay-Based Materials for Heavy Metals Adsorption: Mechanisms, Advancements, and Future Prospects in Environmental Remediation

Given the severe threats posed by heavy metal pollution to ecological environments and human health, developing effective remediation technologies is of paramount importance. This review delves into the mechanisms, recent advancements, and future prospects of clay mineral-based materials in the adsorption of heavy metals. Clay minerals such as kaolinite, montmorillonite, and bentonite have demonstrated immense potential for the removal of heavy metals from water and soil due to their natural abundance, low cost, and high efficiency. This article summarizes the latest advancements in the adsorption of heavy metals like chromium, copper, lead, cadmium, arsenic and hydrargyrum by clay minerals, while examining how chemical and physical modifications can enhance the adsorption capacity, selectivity, and stability of these minerals. Furthermore, this review discusses how factors such as pH, temperature, and ionic strength affect adsorption efficiency and outlines challenges and future research directions for optimizing clay-based adsorbents in environmental applications.

A novel and facile method for the synthesis of rGO/ZnO nanocomposite and its versatile use in water treatment

We introduce a novel, rapid, and environmentally friendly method for synthesising reduced graphene oxide (rGO)/ZnO nanocomposite. This single-step synthesis involves the pyrolytic decomposition of sucrose to produce rGO, simultaneously with zinc acetate to produce the rGO/ZnO nanocomposite. Unlike conventional methods, this approach is distinguished by its environmental sustainability, avoiding the use of toxic chemicals and generating no harmful byproducts. This method advances the development of sustainable technologies by providing a green alternative for the cost-effective production of rGO/ZnO composites from inexpensive precursors. The process enables bulk production within minutes, making it suitable for industrial-scale applications. Various characterisation techniques confirmed the successful formation of rGO and rGO/ZnO nanocomposites. The materials were then evaluated for their efficacy as a comprehensive water purification solution, demonstrating effectiveness in heavy metal removal, photodegradation of organic pollutants, and bacterial disinfection.

Electrocoagulation for nickel, chromium, and iron removal from mine water using aluminum electrodes

High global demand for nickel metal has contributed significantly to the growth of the nickel mining industry in Indonesia. This growth has a positive multiplier effect on the economy, with the potential to affect aquatic life and humans owing to the high levels of chromium, nickel, and iron in mine water. Therefore, this study aims to develop an electrocoagulation (EC) reactor to remove nickel, chromium, and iron from mine water. This study used a continuous reactor and aluminum electrodes with variations in current density (3.378, 6.757, and 10.135 mA/cm2) and inflow (0.3, 0.5, and 1 L/min). The results showed that the operating scenario with a current strength of 6 A and an inflow of 0.3 L/min had a removal efficiency of 86.89 % nickel, 99.51 % chromium, and 80.61 % iron with a charge loading value of 11,194 F/ma3 and Reynolds number of 39. These results are expected to provide valuable information for the development of an effective EC technology, thereby demonstrating its potential for the removal of metals from nickel mine water.

Removal of Pb(II), Cr(III), Co(II), Cu(II) cations from aqueous solutions using tetraethylenepentamine-functionalized HY cubic zeolite: optimization, characterization, and mechanistic insights.

This research utilized tetraethylenepentamine-functionalized HY cubic zeolite as an adsorbent to effectively remove heavy metals from aqueous solutions. The adsorbent was characterized using FT-IR, XRD, TGA, FE-SEM, and EDS-MAP techniques. The synthesis aimed to optimize and evaluate the removal efficiency of Pb(II), Cr(III), Co(II), and Cu(II) from aqueous solutions by investigating key parameters, including initial pH, concentration, adsorbent dosage, and contact time. The results indicate that the highest adsorption capacities for each metal follow the order: Pb(II) > Cr(III) > Co(II) > Cu(II), with respective percentages of 99.7%, 98.2%, 95.1%, and 92.4%. Analysis of the batch systems reveals that the equilibrium data for Pb(II), Cr(III), Co(II), and Cu(II) align well with the Langmuir and Freundlich isotherms also show a good fit, with correlation coefficients (R2) higher than 0.9335 and 0.9478, respectively. The maximum adsorption capacities (181.82, 175.44, 169.49, and 158.73mg/g) reflect the nature of the adsorption process. Kinetic studies for Pb(II), Cr(III), Cu(II), and Cu(II) yielded correlation coefficients (R2) higher than 0.9971. These high R2 values suggest that the experimental data closely fit a pseudo-second-order model, indicating a two-step adsorption mechanism. Heavy metal removal is attributed to ion exchange and chemisorption within the zeolite pores, involving interactions with nitrogen lone pairs.

Treatment performance of different units in the anaerobic-anoxic-aerobic process of landfill leachate under antibiotic exposure

ABSTRACT The effectiveness of three different treatment units (anaerobic, anoxic, and aerobic) in A/A/O reactors when treating landfill leachate that contained varying concentrations of tetracycline (TC) was evaluated. The effluent quality, sludge performance, and removal rates of COD, TN, TP, and NH3-N of the reactors were investigated. The results showed that in the three treatment units (anaerobic, anoxic, and aerobic), when the TC dosage was 10 mg/L, the removal rates of NH3-N continued to decrease to 6.9%, 16.3%, and 32.8%, and the removal rates of COD, TN, and TP in the three treatment units reached their maximum values, which were 37.5%, 57.4%, and 69.6%; 21.1%, 37.1%, and 41.0%; 13.0%, 16.2%, and 27.4%, respectively. During the reactor's operation, the heavy metal content in the treatment units initially increased followed by a decrease, especially for Mn and Zn. This was due to the production of more EPS by microorganisms, resulting in more active sites for heavy metal adsorption. In addition, with the increase of TC concentration, TC removal rate was always positively correlated with PN, COD, TN and heavy metals removal rates, and negatively correlated with NH3-N, TP, pH, and PS. Further analysis revealed that TC was toxic to microorganisms, leading to a decrease in biodiversity and microbial community diversity among the three treatment units in the reactor. This article analyzed the treatment effects of different treatment units in leachate under antibiotic exposure conditions, to explore better external conditions for sewage biological treatment facilities.