Removal Efficiency Of Heavy Metals Research Articles

Gravity-driven membrane system treating heavy metals-containing secondary effluent: Improved removal of heavy metals and mechanism

This study aimed at investigating the removal performance of the gravity-driven membrane (GDM) system in treating the heavy metals-containing secondary effluent, as well as evaluating the respective roles of Fe and Mn addition on the removal of heavy metals. GDM process with the formation of biocake layer exerted effective removals of Cr, Pb and Cd, with an average removal efficiency of 98%, 95% and 40%, respectively, however, after removing the biocake layer, the removal efficiencies of Cr, Pb and Cd reduced to 59%, 85% and 19%, respectively, indicating that the biocake layer played a fundamental role in removing heavy metals. With the assistance of Fe, the removal efficiency of heavy metals increased, and exhibited a positive response to the Fe dosage, due to the adsorption by the freshly generated iron oxides. On the contrary, the Mn involvement would result in the reduction of Cd removal due to the competitive adsorption of residual dissolved Mn2+ and Cd. Furthermore, the addition of a high dosage of Fe increased the diversity of eukaryotic communities and facilitated the elimination of heavy metals, however, the involvement of Mn would lead to a reduction in microbial diversity, resulting in a decrease of heavy metal removal efficiency. These findings are expected to develop new tactics to enhance heavy metal removal and promote widespread application of GDM technology in the fields of deep treatment of heavy metals-containing wastewater and reclamation of secondary effluent.

Development of a loose powder sintering method for the preparation of porous ceramic from municipal solid waste incineration fly ash

Loose powder sintering was used to prepare porous ceramic from municipal solid waste incineration fly ash (MSWI FA) and waste glass (WG). Sintering experiments at various temperatures, holding times, Al2O3 and SiC were conducted to investigate their effect on the ceramic properties and volatile heavy metal removal efficiency. The results show that increasing temperature from 1100 °C to 1250 °C promoted the transition of the mixtures from loose powder to a densified sintered matrix, with a bulk density increase of 31.10% and an open porosity decrease of 70.41%. The bulk density of the ceramic increased to 2.44 g/cm3 with 3% Al2O3 addition. The removal rates of Pb, Zn, Cu and Cd were higher than 90% at 1200 °C for 90 min, and promoted by the increasing temperature and holding time. Notably, 3% Al2O3 addition inhibited the volatilisation of Zn, Cu and Cd, particularly for Zn, the removal rate of which reduced to 61.66% at 1200 °C. The bulk density of the ceramic decreased to a minimum value of 1.48 g/cm3 with 4% SiC. The ratio of MSWI FA:WG:Al2O3:borax of 28.3:56.7:10:5 was proposed to obtain ceramic with a bulk density of 1.54 g/cm3 and a water absorption rate of 8.59% at 1150 °C. The leaching concentration of the porous ceramic met the Chinese regulatory standard (GB 8978-1996). Preparation of MSWI FA-based porous ceramics using the powder sintering method is a promising route for the harmless utilisation of MSWI FA. The porous ceramic is potentially applicable as a thermal-insulation building material.

An environmentally friendly approach for industrial wastewater treatment and bio-adsorption of heavy metals using Pistacia soft shell (PSS) through flocculation-adsorption process

In this research, the potential application of Pistacia soft shell (PSS) was investigated as a novel bio-based flocculant for pulp and paper wastewater (PPWW) treatment. In line with this, after characterization of the PSS, the removal efficiencies of chemical oxygen demand (COD), turbidity and heavy metals (Cu2+ and Pb2+) from PPWW were investigated with different dosage of PSS. The results were compared with alum as a reference flocculant. In addition, the effect of pH adjustment on the flocculation-adsorption performance of PSS was studied under acidic and alkaline condition. Zeta potential, BET, FTIR and SEM as well as kinetics and isotherm analyses were conducted for mechanistic understanding. According to the results, PSS treatment could remove COD, turbidity, Cu2+ and Pb2+ up to 67%, 87%, 70% and 74%, respectively which were better than alum: 56%, 85%, 31% and 35%. It was observed that, pH adjustment significantly improved the performance of PSS treatment. Maximum removal efficiencies of 92%, 95%, 97% and 98% were achieved for COD, turbidity, Cu2+ and Pb2+, respectively, under optimal condition of using 2 g/L PSS at pH 9. The mechanism analysis revealed that the high removal efficiency of PSS is related to the dual flocculation-adsorption of bridging and sweeping mechanisms. The results of this study suggested PSS as a promising, sustainable and eco-friendly bio-based flocculant and adsorbent for industrial wastewater treatment.

Experimental Analysis of Heavy Metal Contaminated Electroplating Industrial Site Soil Using Tamarind Seed Biochar

Abstract: Biochar application is a promising strategy for the rehabilitation of contaminated soil while ensuring suitable waste management. Biochar is a highly porous organic material derived from wood, manure, or plant-based biomass through pyrolysis in a low-oxygen environment. Pyrolysis is a technique that produces biochar by means of the thermal decomposition of the feedstock in an oxygen-free environment. In this work, tamarind seed was pyrolyzed in a muffle furnace 500 – 700oC to prepare biochar. The soil is contaminated with the electroplating industrial effluent, which is rich in nickel (Ni), copper (Cu), and chromium (Cr) concentrations. In this study, the atomic absorption spectrophotometer (AAS) technique has been used to find the removal efficiency of heavy metals for a curing time of 7, 14 and 28 days soil samples The result obtained from the physicochemical analysis indicated that the contaminated soils recorded an acidic pH. Adding biochar to contaminated soil in different percentages (2%, 4%, 6%, 8%, and 10%) to increase the pH value and using direct shear test, the shear strength of the soil determined different percentage of biochar. The result obtained adding 8% of Biochar to get optimum Shear strength. The functional groups present in the raw biomass and pyrolyzed biochar are determined using fourier transform infrared spectroscopy (FTIR)

Evaluation of the characterization and heavy metals remediation potential of biosurfactant produced by Aeromonas hydrophila S62A

The evaluation of the heavy metals remediation potential and characterization of biosurfactant produced by Aeromonas hydrophilia strain S62A isolated from water and sediment samples of Imo River, Nigeria was studied. In this study, 12 bacterial isolates were isolated from contaminated water and sediment samples using spread plate technique and primarily screened for biosurfactant production using emulsification index, oil displacement and surface tension tests. Secondary biosurfactant production was carried out in a modified mineral salt medium under optimized conditions for 5 days and the produced biosurfactant was characterized and evaluated for its heavy metals removal efficiencies using standard analytical procedures. The result showed that the bacterial strain identified as Aeromonas hydrophilia S62A out of the 12 isolate strains had the highest and lowest values of 66.66 %, 23.76 cm and 90 mN/m for emulsification index, oil displacement and surface tension tests, respectively. The purified biosurfactant was found to be glycophospholipid as confirmed by the gas chromatographic (GC) and Fourier Transformed Infra-Red Spectroscopic (FTIR) profiles with 5 mg/mL critical micelles concentration (CMC). Statistically, significant differences (P < 0.05) were detected among the means of all surfactant CMC treatment in comparison to their untreated controls with 2 × CMC lead having the highest (98.92 %) and control (water) having the lowest (2.09 %) heavy metals removal efficiencies. Therefore, the present study has produced glycophospholipid biosurfactant with unique structural and chemical features and composition and could be exploited in environmental remediation of heavy metals contaminated ecosystems.

Electricity production by Ochrobactrum-related strain CD-1 and pb2+ removal in dual-chamber microbial fuel cell

<p>Dual-chamber microbial fuel cell (MFC) was constructed to treat heavy metal wastewater (Pb2+ solution). The results showed the maximum voltage, the maximum electric power density and pb2+ removal were 9.6 mV, 371.0 mV/m2 and 52.3% respectively. The effects of different cathode chamber environments on the production potential (V, volts) and Pb2+ removal rate of strained CD-1 were investigated. The results show that when the cathode chamber is soil, the maximum voltage is 8.88mV, and when the cathode chamber is solution, the maximum voltage is 12.11mV. The removal efficiency of heavy metals polluted from near to far from the electrode plate in the soil is 68.9%, 62.1%, 57.5%, and the removal efficiency of heavy metals in the solution is 67.46%. It can be concluded that when the soil is the cathode chamber. The removal rate of local heavy metals was the highest. When the solution was used as a cathode chamber, the average removal rate of heavy metals was the highest. The bacteria, named strain CD-1, as the electricity production bacteria (EPB) used in the dual chamber microbial fuel cell (MFC), was isolated from activate sludge and identified on its morphology, physichemical properties and phylogenetic positions. The results indicated that strain CD-1 was Gram-negative, rod. Oxidase and catalase reactions were positive. Strain CD-1 could use gluconate, lactose, D-fructose, L-Arabinose, D-arabinose, acetate, propionate, butyrate, lactate, sucrose and glucose, not use melibiose, galactose, N-acetylglucosamine, ethanol and glycerol.16S rRNA gene sequences analysis showed that strain CD-1 was most related to Ochrobactrum sp. (AJ245941）with the homology similarities of 98%. Based on the above results, strain CD-1 was belonged to the genus of Ochrobactrum and seemed to represent a novel species.</p>

Triggered heavy metals and chlorine simultaneous removal from hazardous waste incineration fly ash

To date, heavy metals and chlorine removal from hazardous waste incineration fly ash (HWI FA) by thermal treatment was scarcely reported. High content of calcium in HWI FA might affect heavy metals chlorination volatilization. The aim of this study was to realize heavy metals and chlorine simultaneous removal from HWI FA triggered by fluidized-bed municipal solid waste incineration fly ash (FBMSWI FA) during sintering. Results showed that the dilemma of low heavy metals removal efficiency was due to the dense structure and the difficulty of transformation of the stable phases including Cu2S, CuSiO3, and Zn2SiO4. By co-sintering with FBMSWI FA at the ratio of 1:1, the removal efficiency of Cu, Zn, Pb, Cd, and Cl reached as high as 84.4%, 92.0%, 99.9%, 99.5%, and 99.7%, respectively. Compared with the control, chlorination volatilization efficiency of Cu and Zn was significantly increased by 210.5% and 89.2%. The favourable promotion could be mainly attributed to Si/Al matrix in FBMSWI FA triggered the following reaction: i) Ca-bearing compounds in HWI FA were activated to destroy the dense structure, which facilitated the transformation of Cu2S to CuO; and ii) the conversion of NaCl and KCl to gaseous chlorine was promoted, which the formation of metal chlorides was accelerated.

Fabrication and Characterization of Magnetic Cellulose-Chitosan-Alginate Composite Hydrogel Bead Bio-Sorbent.

The implementation of inorganic adsorbents for the removal of heavy metals from industrial effluents generates secondary waste. Therefore, scientists and environmentalists are looking for environmentally friendly adsorbents isolated from biobased materials for the efficient removal of heavy metals from industrial effluents. This study aimed to fabricate and characterize an environmentally friendly composite bio-sorbent as an initiative toward greener environmental remediation technology. The properties of cellulose, chitosan, magnetite, and alginate were exploited to fabricate a composite hydrogel bead. The cross linking and encapsulation of cellulose, chitosan, alginate, and magnetite in hydrogel beads were successfully conducted through a facile method without any chemicals used during the synthesis. Energy-dispersive X-ray analysis verified the presence of element signals of N, Ca, and Fe on the surface of the composite bio-sorbents. The appearance and peak's shifting at 3330-3060 cm-1 in the Fourier transform infrared spectroscopy analysis of the composite cellulose-magnetite-alginate, chitosan-magnetite-alginate, and cellulose-chitosan-magnetite-alginate suggested that there are overlaps of O-H and N-H and weak interaction of hydrogen bonding with the Fe3O4 particles. Material degradation, % mass loss, and thermal stability of the material and synthesized composite hydrogel beads were determined through thermogravimetric analysis. The onset temperature of the composite cellulose-magnetite-alginate, chitosan-magnetite-alginate, and cellulose-chitosan-magnetite-alginate hydrogel beads were observed to be lower compared to raw-material cellulose and chitosan, which could be due to the formation of weak hydrogen bonding resulting from the addition of magnetite Fe3O4. The higher mass residual of cellulose-magnetite-alginate (33.46%), chitosan-magnetite-alginate (37.09%), and cellulose-chitosan-magnetite-alginate (34.40%) compared to cellulose (10.94%) and chitosan (30.82%) after degradation at a temperature of 700 °C shows that the synthesized composite hydrogel beads possess better thermal stability, owing to the addition of magnetite and the encapsulation in the alginate hydrogel beads.

Removal of zinc by Selenastrum sp. and simultaneous biodiesel production from metal-resistant biomass for energy and environmental sustainability

In this study, the phycoremediation of zinc by the unicellular green alga, Selenastrum sp. and simultaneous biodiesel production from heavy metal resistant biomass was investigated. The microalga Selenastrum sp. was used to remove the zinc amended at 1, 3, 5, 7 ppm in the BG II medium. In all the tested zinc concentrations (1–7 ppm), there was no noticeable heavy metal stress on the microalga and the algal culture showed a steady and better growth pattern in zinc amended medium than that control (no zinc added). Furthermore, on the 24th day, the biomass concentration was 1.63 g/L for the 5 ppm and 7 ppm zinc dosed experiments, which was higher than the control. Atomic adsorption spectroscopic analysis showed that zinc concentration in the medium (5 and 7 ppm) was reduced to ~0.44 ppm, which is equivalent to 90 % heavy metal removal efficiency. The total lipid content and biodiesel yield from zinc-resistant Selenastrum biomass was 17.6 and 65.1 %, respectively. Finally, test microalga grown in zinc-added media produced beneficial fatty acids such as palmitic, palmitoleic, oleic, stearic, linoleic, and linolenic acid for high-quality biodiesel production.

Calcium-doped magnetic humic acid nano particles for the efficient removal of heavy metals from wastewater: the role of Ca

ABSTRACT Ca doping is an effective method for improving the adsorption capacity of HA–Fe aggregates and regulating their structures. Understanding the structural characteristics of Ca–HA–Fe aggregates can help explore their microscopic adsorption effect on heavy metals. However, the heterogeneity of HA results in an incomplete understanding of the structural characteristics of the ternary system of Ca–HA–Fe aggregates and adsorption of the quaternary system of Ca–HA–Fe–Pb/Cu/Cd. In this study, interactions between Ca–HA–Fe ternary and Ca–HA–Fe–Pb/Cu/Cd quaternary systems were discussed from a molecular perspective. The structures of the basic structural units of HA were identified. Density functional theory (DFT) was employed to calculate the stable states of basic structural units of HA and Ca2+. The results showed that hydroxyl and carboxyl groups exhibited the highest capacity to bind with Ca2+. The interactions among Ca, HA, and Fe led to the formation of network aggregates. The binding energies of functional groups for heavy metals and the feasibility of ion exchange were calculated by the method of experiment and DFT. According to the contribution of functional group complexation and ion exchange, the ion exchange values for Pb2+, Cu2+, and Cd2+ were 66.71%, 62.87%, and 60.79%, respectively, which indicated that Ca2+ ion exchange showed considerable potential in enhancing the adsorption capacity of heavy metals.

Efficient removal of heavy metals from aqueous solutions using Mn-doped FeOOH: Performance and mechanisms

The treatment of heavy metal ion contamination in aquatic ecosystems has been a growing global concern for centuries. Iron oxide nanomaterials are effective in heavy metals removal, but are frequently challenging due to the precipitation of Fe(III) and poor reusability. To improve the removal of heavy metals by iron hydroxyl oxide (FeOOH), the iron-manganese oxide material (FMBO) was separately prepared to remove Cd(II), Ni(II), and Pb(II) in individual and multiple systems. Results revealed that the loading of Mn enlarged the specific surface area and stabilized the structure of FeOOH. FMBO achieved 18%, 17%, and 40% higher removal capacities of Cd(II), Ni(II), and Pb(II) than that of FeOOH, respectively. Besides, mass spectrometry analysis demonstrated that the surface hydroxyls (-OH, Fe/Mn–OH) of FeOOH and FMBO provided the active sites for metal complexation. Fe(III) was reduced by Mn ions and further complexed with heavy metals. Further density functional theory calculations revealed that Mn loading led to the structural reconstruction of the electron transfer, which significantly promoted stable hybridization. This confirmed that FMBO improved the properties of FeOOH and was efficient for removing heavy metals from wastewater.

Efficiency evaluation of titanium oxide nanocomposite membrane in adsorption of chromium from oil effluents.

Reverse osmosis and nanofiltration (NF) are the essential physical separation technologies used to remove contaminants from liquid streams. A hybrid of nanofiltration and forward osmosis (FO) was used to increase the removal efficiency of heavy metals in synthesized oil effluents. Thin-film nanocomposite (TFN) membranes were synthesized by applying surface polymerization on a polysulfone substrate to use in the forward osmosis process. The impact of different membrane fabrication conditions such as time, temperature, and pressure on effluent flux, the effect of different concentrations of the heavy metal solution on adsorption rate and sedimentation rate, the impact of TiO2 nanoparticles on the performance and structure of forward osmosis membranes were investigated. The morphology, composition, and properties of TiO2 nanocomposites made by the infrared spectrometer and X-ray diffraction (XRD) were studied. Kinetic modeling and Langmuir, Freundlich, and Tamkin relationships were used to draw adsorption isotherms and evaluate adsorption equilibrium data. The results indicated that pressure and temperature directly affect water outlet flux, and time affects it indirectly. Evaluating the isothermal relationships revealed that chromium adsorption from the TFN 0.05ppm membrane and thin-film composite (TFC) membrane follows the Langmuir model with correlation coefficients of 0.996 and 0.995, respectively. The significant removal of heavy metals and the acceptable amount of water flux demonstrated the appropriate potential of the titanium oxide nanocomposite membrane, which can be used as an effective adsorbent to remove chromium from aqueous solutions.

Reduction of cadmium content in 29 % and 54 % P2O5 phosphoric acid by manganese oxide material birnessite-type Na-MnO2

This paper presents a new approach for the purification of 29% and 54% P2O5 phosphoric acid contaminated with cadmium ions using synthesized lamellar material based on manganese (Na-MnO2). The removal efficiencies of cadmium ions were 35 % and 31 % for 54% and 29% P2O5 phosphoric acid. The kinetic and isotherm studies of cadmium adsorption were performed. After the phosphoric acid purification process, Na-MnO2 material was characterized by XRD, SEM, and TGA-DTA. All the results enable the refinement of the final phase by the Rietveld method. A proposed mechanism of cadmium ion removal by Na-MnO2 was given. The stability of the material was also controlled in the acid medium 29 % and 54 % P2O5. The results confirmed that Na-MnO2 material could be a potential sorbent for the efficient removal of heavy metals from phosphoric acid solutions. This simple process can be further developed and thus opens an avenue in the industrial sector to process larger quantities using high-performance materials based on manganese. Self-consistent ab initio calculations, based on DFT (Density Functional Theory) approach and using the FLAPW method (Full potential Linear Augmented Plane Wave), were performed to investigate both the electronic and magnetic properties of materials.

Chlorine and heavy metals removal from municipal solid waste incineration fly ash by electric field enhanced oxalic acid washing

Electric field enhanced oxalic acid (H2C2O4) washing was conducted to examine the simultaneously removal efficiency of heavy metals (HMs) and chlorine, especially insoluble chlorine from municipal solid waste incineration fly ash (MSW FA). Results show that chlorine and HMs can be effectively removed with a total chlorine, As, Ni and Zn removal rate of 99.10%, 79.08%, 75.42% and 71.43%, when the electrode exchange frequencies is 40 Hz, current density is 50 mA/cm2, H2C2O4 adding amount is 0.5 mol/L and the reaction time is 4 h. Insoluble chlorine removal efficiency is up to 95.32%, much higher than reported studies. And the chlorine content in the residue is lower than 0.14%. Meanwhile, HMs removal efficiency is remarkable, 41.62%–67.51% higher than that of water washing. The high-efficient removal effect is caused by the constantly changing direction of electrons hitting the fly ash surface, which provides more escape channels for internal chlorine and HMs. These results proved that electric field enhanced oxalic acid washing could be a promising method for removing contaminants from MSWI fly ash.

Low-cost and highly durable kaolin supported CHA zeolite composite membrane for efficient removal of heavy metals from aqueous solution

Low-cost and highly durable kaolin supported CHA zeolite composite membrane for efficient removal of heavy metals from aqueous solution

Isolation and characterization of a plant growth‑promoting rhizobacterium strain MD36 that promotes barley seedlings and growth under heavy metals stress.

Plant growth, promoting, bacteria, (PGPB) can improve plant germination and growth in heavy metal-contaminated land and enhance heavy metal removal efficiency. In this study, we isolated PGPR bacterial strains which can withstand heavy metal pollution and tested their ability to improve barley germination under heavy metal stress. Out of 16 multi-resistant heavy metal isolates, strain MD36 was identified by 16S rRNA sequencing and shared close relation to different species of the genus Glutamicibacter. The new isolated strain showed other important PGPR activities, mainly IAA production and salt tolerance. The effect of adding the strain MD36 to barley grains under heavy metal stress enhanced their germination up to 100%, while the percentage of germination ranged between 0 and 20% for non-inoculated grains. In addition, in these conditions, MD36 can significantly enhance barley growth by reducing the heavy metal effect. This study strongly recommends the use of MD36 as seed coatings trials in the field to enhance growth and yield in soils contaminated with heavy metals, as well as in bioremediation of HM-contaminated salt-containing soils and water.

Highly rapid and efficient removal of heavy metals, heavy rare earth elements, and phenolic compounds using EDTA-cross-linked MXene polymer composite: Adsorption characteristics and mechanisms

Recovery of heavy metals, heavy rare earth elements, and phenolic compounds from industrial water has attracted attention due to their ecological toxicity and their larger demand for advanced technologies. We herein synthesize a novel EDTA-cross-linked MXene polymer composite for the removal of lead (II), holmium (III), and hydroquinone. The structure, morphology, and sorption performance of the EDTA-cross-linked MXene polymer composite were explored comprehensively. The correlation coefficients (R2) of the PSO kinetic model for lead (II), Ho (III), and hydroquinone were 0.9999 and greater than those of the PFO kinetic model when comparing the R2 derived by fitting the two kinetic models. EDTA-cross-linked MXene polymer composite rapidly removed the heavy metals, heavy rare earth metals, and phenolic compounds, such as lead (II), holmium (III), and hydroquinone within 5, 8, and 10 min, respectively. The sorption isotherm of lead (II), holmium (III), and hydroquinone might be explained well by the Langmuir model, and the maximum sorption capabilities (qmax) were derived as 893.92 mg/g for lead (II), 809.37 mg/g for Ho, and 754.09 mg/g for HQ, respectively. The adsorbed composite could easily be regenerated and can be utilized 19 times without a significant impact on its sorption performance. The synthesized adsorbent also exhibits remarkable sorption performance for other heavy metals (Cd, Cr, Ca, Mg, Ba, and Ni), rare earth metals (Eu, Yb, Er, Lu, Tm, and Y), and phenolic compounds (catechol and resorcinol). This research work provides a new EDTA-cross-linked MXene polymer composite for the excellent elimination of lead, holmium (III), and hydroquinone.

Heavy metal remediation using chelator-enhanced washing of municipal solid waste compost based on spectroscopic characterization

Due to high metal toxicity, mixed municipal solid waste (MSW) compost is difficult to use. This study detected the presence of heavy metals (Cd, Cu, Pb, Ni, and Zn) in MSW compost through mineralogical analysis using X-ray diffraction (XRD) and performed topographical imaging and elemental mapping using a scanning electron microscope and energy dispersive X-ray analysis (SEM-EDX). Ethylenediaminetetraacetic acid (EDTA), a typical chelator, is tested to remove heavy metals from Indian MSW compost (New Delhi and Mumbai). It deals with two novel aspects, viz., (i) investigating the influence of EDTA-washing conditions, molarity, dosage, MSW compost-sample size, speed, and contact time, on their metal removal efficiencies, and (ii) maximizing the percentage removal of heavy metals by determining the optimal process control process parameters. These parameters were optimized in a batch reactor utilizing Taguchi orthogonal (L25) array. The optimization showed that the removal efficiencies were 96.71%, 47.37%, and 49.94% for Cd, Pb, and Zn in Delhi samples, whereas 45.55%, 79.52%, 59.63%, 82.31%, and 88.40% for Cd, Cu, Pb, Ni, and Zn in Mumbai samples. Results indicate that the removal efficiency of heavy metals was greatly influenced by EDTA-molarity. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of hydroxyl group, which aids heavy metal chelation. The results reveal the possibility of EDTA to reduce the hazardous properties of MSW compost.

Cyanidiales-Based Bioremediation of Heavy Metals

With growing urbanization and ongoing development activities, the consumption of heavy metals has been increasing globally. Although heavy metals are vital for the survival of living beings, they can become hazardous when they surpass the permissible limit. The effect of heavy metals varies from normal to acute depending on the individual, so it is necessary to treat the heavy metals before releasing them into the environment. Various conventional treatment technologies have been used based on physical, chemical, and biological methods. However, due to technical and economic constraints and poor sustainability towards the environment, the use of these technologies has been limited. Microalgal-based heavy metal removal has been explored for the past few decades and has been seen as an effective, environment-friendly, and inexpensive method compared to conventional treatment technology. Cyanidiales that belong to red algae have the potential for remediation of heavy metals as they can withstand and tolerate extreme stresses of heat, acid salts, and heavy metals. Cyanidiales are the only photosynthetic organisms that can survive and thrive in acidic mine drainage, where heavy metal contamination is often prevalent. This review focuses on the algal species belonging to three genera of Cyanidiales: Cyanidioschyzon, Cyanidium, and Galdieria. Papers published after 2015 were considered in order to examine these species' efficiency in heavy metal removal. The result is summarized as maximum removal efficiency at the optimum experimental conditions and based on the parameters affecting the metal ion removal efficiency. This study finds that pH, initial metal concentration, initial algal biomass concentration, algal strains, and growth temperature are the major parameters that affect the heavy metal removal efficiency of Cyanidiales.

Recyclable Mg-MOF-74@cellulose aerogel composites for efficient removal of heavy metals from wastewater

In this study, Mg-MOF-74, an environmentally friendly metal-organic framework material with non-toxic Mg elements as the framework centers, was loaded onto low-cost and green cellulose aerogels via an in-situ growth approach to construct the Mg-MOF-74@CA composite with a three-dimensional porous structure, overcoming the problems that Mg-MOF-74 nanoparticles tend to agglomerate and cannot be easily recovered. The removal performance of the synthesized Mg-MOF-74@CA composite towards Pb(II), Cd(II), and Cu(II) was evaluated by combining batch experiments, model fittings, and characterization analyses (SEM, XRD, FTIR, MIP, TG, and XPS). The results show that the porosity of Mg-MOF-74@CA is 84.447%. The removal of Pb(II), Cd(II), and Cu(II) by Mg-MOF-74@CA reach the equilibriums at about 5 h. And the removal of Pb(II), Cd(II), and Cu(II) by Mg-MOF-74@CA are strongly influenced by solution pH, while almost independent of ionic strength and humic acid (HA). The strong complexation of Pb(II), Cd(II), and Cu(II) with the surface sites of Mg-MOF-74@CA is the main removal mechanism. The maximum adsorption capacities of Mg-MOF-74@CA towards Pb(II), Cd(II), and Cu(II) at 298 K are 223.555, 160.033, and 74.349 mg/g, respectively. Interestingly, the selective binding order of Mg-MOF-74@CA for Pb(II), Cd(II), and Cu(II) is Cu(II)>Pb(II)>Cd(II). In summary, the Mg-MOF-74@CA composite has good application prospects in practical wastewater treatment.