Metal Biosorption Capacity Research Articles

Microbial bioremediation: unraveling the potential for cleaner environments through comparative analysis

Bioremediation is used to remove toxic environmental waste to nontoxic waste from polluted environment. Bioremediation is the waste management technique with help of isolated microbial stains to neutralize the pollutants from contaminated sites. The primary objective of this study is to find the metal tolerance and biosorption capacity of two microbes isolated that is, Bacillus subtilis and Deinococcus radiouranus in the removal of heavy Metals (Zn, Pb, and Mg). Metal tolerance test was done by using MIC test. The soil sample was taken out from the different intervals of time and analyzed by AAS. Bio-sorption of Bacillus was slightly higher than the bio-sorption of D. radiouranus. Bacillus was able to accumulate 99.39% of Zn, 67.63% of Mg and 99.98% of Pb from the contaminated soil. The Deinococcus was able to accumulate 97.21% of Zn, 79.77% of Mg and 99.9% of Pb from the contaminated soil. Bacillus was more efficient in the removal of Zn and Pb whereas D. radiouranus was more helpful in the removal of Mg but slightly less accumulated Zn and Pb compared to Bacillus.

A comparative study on heavy metal (cadmium) tolerance and biosorption capacity of locally isolated lactic acid bacteria

Heavy metals (HM) have less biological role but show extreme toxicity in living systems. Lactic acid bacteria (LAB) are beneficial microorganisms, some of which have the ability to chelate HM and may be used to treat heavy metals poisoning. The aim of the current study was to select and identify Cd-removing probiotic LAB strains, for future pharmaceutical application. Seventeen LAB strains, from human excretions and animal fecal matter, were initially verified for their probiotic properties. The strains which could survive in the presence of Cd (≥100 ppm) were selected. The metal removal efficiency of isolates was compared, through atomic absorption spectrophotometry (AAS), by measuring the reduction in Cd contents of CdCl2 5 mg/L (3.05 ppm of Cd) supplemented broth following 24 h culturing of the strains. The Cd reduction of 38–75% was recorded in culture broth. The Cd removal ability significantly varied (p < 0.05) with microbial surface charge, incubation period, temperature and pH of media. Levilactobacillus brevis MW362790 and Pediococcus pentosaceus MT323062, identified through 16S rRNA gene sequencing, were recognized as strong Cd chelators. These strains may have application in pharmaceutical or agriculture (farm animals) for protection against cadmium toxicity. Further studies are suggested on in vivo metal detoxification potential.

Heavy metal tolerance, and metal biosorption by exopolysaccharides produced by bacterial strains isolated from marine hydrothermal vents

The present study highlights heavy metal tolerance, EPS production, and biosorption capacity of four hydrothermal vent bacterial strains, namely Exiguobacterium aquaticum, Mammaliicoccus sciuri, Micrococcus luteus, and Jeotgalicoccus huakuii against As, Cd, Cr, Cu, Co, Pb and Ni. The biosorption assay showed high removal efficiency of As (83%) by E. aquaticum, Cd (95%) by M. sciuri, Cu (94%) by M. luteus, and Ni (89%) by J. huakuii and their produced EPS with these metals in aqueous solution were 84%, 85%, 98%, and 91%, respectively. The maximum EPS yield was attained by optimized medium composition consisting of 1% Xylose, and 1% NaCl at pH 7. In metal-amended conditions, the four bacterial strains showed induced EPS production in the initial concentrations. SEM with EDX and CLSM images showed that the growth and EPS production of bacterial strains were affected by metal ion concentrations. A phenol sulphuric acid method and BCA assay were used to identify both the carbohydrate and total protein content of four extracted EPS. A DPPH assay revealed that EPS influences free radical scavenging and has a highly enhanced synergistic effect with its antioxidant activity. FT-IR analysis of four extracted EPS showed the shifting of peaks in the functional groups of EPS before and after adsorption of metal ions. At pH 5 and after 60 min contact time metal removal efficiency and adsorption capacity increased as calculated for As, Cd, Cu, and Ni by four extracted EPS: (86%, 20 mg/g), (74%, 19 mg/g), (94%, 60 mg/g) and (89%, 32 mg/g) and (89%, 16 mg/g), (85%, 16 mg/g), (96%, 22 mg/g) and (91%, 16 mg/g), respectively. The Langmuir compared to the Freundlich model was found to better represent the adsorption by EPS providing maximum adsorption capacities for As (34.65 mg/g), Cd (52.88 mg/g), Cu (24.91 mg/g), and Ni (58.38 mg/g).

Metal tolerance and biosorption capacities of bacterial strains isolated from an urban watershed.

Rapid industrialization and urbanization have led to widespread metal contamination in aquatic ecosystems. This study explores the metal tolerance and biosorption characteristics of four bacterial strains (Serratia sp. L2, Raoultella sp. L30, Klebsiella sp. R3, and Klebsiella sp. R19) isolated from Saint Clair River sediments. These strains effectively removed various metal cations (As3+, Pb2+, Cu2+, Mn2+, Zn2+, Cd2+, Cr6+, and Ni2+) in single and multi-metal solutions. Minimum inhibitory concentration (MIC) assays revealed strain-specific variations in metal tolerance, with L2 and L30 exhibiting higher tolerance. Surprisingly, R3 and R19, despite lower tolerance, demonstrated superior metal removal efficiency, challenging the notion that tolerance dictates removal efficacy. In single-metal solutions, R3 and R19 excelled at extracting various metal ions, while competitive binding in multi-metal solutions hindered removal. However, R3 and R19 retained higher removal efficiencies, possibly due to enhanced flocculation activities facilitating metal-ion contact. Comprehensive Fourier-transform infrared (FTIR) analysis highlighted the strains' metal-binding capabilities, with novel peaks emerging after metal exposure, indicative of extracellular polymeric substance (EPS) production. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed metal accumulation on bacterial surfaces and within cytoplasmic regions and revealed morphological changes and metal adsorption patterns, emphasizing the strains' ability to adapt to metal stress. Scanning transmission microscopy (STEM) and EDX analysis uncovered metal accumulation within bacterial cells, underscoring the complexity of microbial-metal interactions. This study also confirms that the simultaneous presence of an aqueous solution may cause a mutual inhibition in the adsorption of each metal to the EPS resulting in reduced metal uptake, which emphasizes the need to select specific bacterial strains for a given metal-containing effluent. The differences in metal distribution patterns between Klebsiella sp. R19 and Raoultella sp. L30 suggest species-specific metal accumulation strategies driven by environmental conditions and metal availability. The heavy metal-removing capabilities and the ability to grow over a wide range of metal concentrations of the strains used in this study may offer an advantage to employ these organisms for metal remediation in bioreactors or in situ.

Lead biosorption profiling of endophytic Aspergillus flavus SGE34 isolated from Cleome viscosa Linn.

ABSTRACT Lead is an environmental pollutant that causes remarkable damage to various organs in the human body, especially the nervous system. Removal of lead by conventional methods is costly, and therefore, in the current scenario, biosorption using fungi is extensively explored as they provide good metal uptake systems. The present study evaluated the Pb (II) biosorption potential of endophytic fungi Aspergillus flavus SGE34. The fungal isolate was obtained from the root of an indigenous medicinal plant of the Chhattisgarh region named Cleome viscosa Linn. The biosorption potential of dead fungal biomass was optimized at different operating parameters like contact time, pH, and temperature. The maximum biosorption values were found at pH 6.0 with an equilibrium time of 150 minutes at 350C. The Fourier transform infrared spectroscopy study revealed that the pattern of new absorption bands, altered absorption intensity, and shift in wavenumber of functional groups was deduced, due to interaction between metal ions and active sites of biosorbent. The present study concluded that A. flavus SGE34 has high metal tolerance and biosorption capacity; it could effectively remove lead from industrial effluents.

A novel green solution to metal pollution in aquatic environment: Pyracantha coccinea M. J. Roemer

ABSTRACT Metal pollution today has reached the level of a great threat to humans and their environment. A novel green solution was presented for metal pollution in aquatic environment using Pyracantha coccinea M. J. Roemer in the current study. Due to its widespread industrial use, manganese pollution in water environment has become a serious issue in recent years, and for this reason, it was used as a model metal to determine the treatment potential of P. coccinea M. J. Roemer. The results showed that the pseudo-second-order kinetic model and Freundlich isotherm model agreed well with the experimental data, and the biosorption process had a physical, spontaneous and favourable nature. The maximum metal biosorption capacity was determined to be 59.867 mg g−1. This study showed that P. coccinea M. J. Roemer could present an environmentally friendly, cost-effective, effectual solution for the metal issue in aquatic environment.

Eco-friendly approach for tannery effluent treatment and CO2 sequestration using unicellular green oleaginous microalga Tetradesmus obliquus TS03.

The present study explored the process of bioremediation, sequestration of carbon dioxide, and biofuel production using multifarious potent freshwater microalgae Tetradesmus obliquus TS03. The heavy metals were reduced, viz., 8.34mg of cadmium (95.13%), 4.56mg of chromium (97.28%), 1.34mg of copper (98.67%), 1.24mg of cobalt (98.19%), 1.93mg of lead (96.72%), 2.31mg of nickel (97.14%), and 2.23 mgL-1 of zinc (96.59%) using photobioreactor microalgal treatment method. The heavy metal biosorption capacity rate (qmax) was 98.90% determined by the Langmuir and Freundlich isotherm kinetics model at 10days of effluent treatment using Tetradesmus obliquus TS03. The microalgae T. obliquus TS03 utilized 98.34% of carbon dioxide (CO2) enhanced by acetyl CoA carboxylase and RuBisCO enzymes. The biodiesel was extracted from microalga and identified 32 fatty acid methyl ester major compounds viz., tetradecanoate methyl ester, hexadecanoic acid methyl ester, tridecanoic acid methyl ester, heptadecatrienoic acid methyl ester, octadecanoic acid methyl ester, eicosanoic acid methyl ester, pentadecanoic acid methyl ester, and cis-methylicosanoate using gas mass chromatography (GCMS). The biodiesel functional groups were identified, viz., amides, phenols, alcohols, alkynes, carboxylic acids, carbonyls, and ketones groups using Fourier transformation infrared (FTIR). The bioethanol was identified using high-performance liquid chromatography (HPLC) and determined the peak presented at RT of 4.35min (75,693.1046µVs-1).

OPTIMIZATION OF CHROMIUM AND LEAD BIOSORPTION IN WASTEWATER USING 33 FACTORIAL DESIGN

In this study removing heavy metals, Cr (III), and Pb (II) from wastewater, Microorganism Trichoderma sp. biosorption was performed using Cr (III), and Pb (II) removal was taken into account. For this study, 3^3 Factorial Experiment Designs were used, and temperature (°C), biosorbent dosage (g/L), and pH were selected as the main factors for Cr (III), and Pb (II) metals and three levels of these factors were determined as low, medium, and high. In this study, which was carried out to increase the metal removal efficiency and biosorption capacity, the main factors and the significance of each interaction of these factors were examined with 3^3 Factorial Design. For this purpose, by conducting Analysis of Variance (ANOVA) via Response Surface Methodology and optimization, more detailed results were obtained regarding the factors affecting the efficiency of metal removal from wastewater.

Bioremediation Strategies for Mitigation of Heavy Metals: A Critical Review

In normal conditions plants require heavy metals for growth but their accumulation inn bioavailability form in soil and water has harmful effects on all biological systems. The increasing release of HMs from industrial discharge and other anthropogenic activities are threatening sustainable agricultural development, food supply and dairy industry. Under such conditions heavy metal (HM) stress is one of the most destructive abiotic stresses for plants. Anthropogenic activities are the main source of heavy metal (HM) accumulation. Industrial pollution of both water bodies and soil mainly consists of accumulation of Cr, Ni, Cu, Zn, Cd, Pb, Hg, and As. These heavy metals (HMs) non-biodegradable pollutants present in soil and water are not easy to metabolize and their concentration in soil and water increases with time. The conventional methods for removal of heavy metals from the environment involve high costs and are not eco-friendly. In contrast to this phytoremediation is an eco-friendly approach and it can be considered as an alternative to the traditional methods in terms of their cost-effectiveness and maximum recovery of the metal ions. Microbes have greater metal biosorption capacities and various mechanisms of metal sequestration. This review focuses on various aspects of phytoremediation including genetic engineering and microbe-assisted approaches.

Biosorption of nickel, cobalt, zinc and copper ions by Serratia marcescens strain 16 in mono and multimetallic systems

The metallurgical industry is one of the main sources of heavy metal pollution, which represents a severe threat to life. Metals can be removed from aqueous solutions by using microbial biomasses. This paper analyses the heavy metal biosorption capacity of Serratia marcescens strain 16 in single and multimetallic systems. The results obtained show that Co(II), Ni(II) and Zn(II) biosorption in monometallic systems is two to three times higher than in the presence of bi-metallic and multimetallic solutions. Fourier transform infrared spectroscopy confirmed that carbonyl, carboxyl and hydroxyl were the main functional groups, as well as the amide bands I and II involved in metal uptake, which are present in external structures of the bacterial cell. The results obtained demonstrated the viability of S. marcescens strain 16 as a biosorbent for the design of eco-friendly technologies for the treatment of waste liquor.

A new soil microcosm to evaluate the Cd, Cu and Pb biosorption by Absidia cylindrospora

Fungi could be considered as an effective tool for treating metal pollution in soils because of their metal tolerance and biosorption capacity. While most of biosorption studies intended for bioremediation trials are carried out in liquid medium, this study presents the development of a new type of soil microcosm, designed to evaluate the fungal biosorption of metals in a solid medium. The research focused on the bioaugmentation with the fungus Absidia cylindrospora of a soil artificially contaminated by metals (Cd, Cu, and Pb). Soil microcosms were performed in layers, and a separation technique including a centrifugation step was developed. The results showed that the centrifugation step does not cause the leaching of metals from the soil. The developed procedure allows to effectively separate the mycelium from the soil at the end of the experiment. It leads to an accurate evaluation of the metal accumulated by the fungus, by better estimating the bioaccumulation factor (BAF) which was superior to 1 for the metals studied. In addition, Absidia cylindrospora was viable after 30 days experiment, and able to biosorb considerable amounts of the metals studied from the contaminated soil; it accumulates 171 mg.kg−1 of Cu, 146 mg.kg−1 of Cd and 119 mg.kg−1 of Pb. These results confirm the ability of the fungal strain to be used for bioremediation studies.

The use of Phanerochaete chrysosporium for modification of bentonite for preconcentration and determination of heavy metals

In this study, a solid phase extraction method was successfully applied in the preconcentration and determination of trace levels of Cu(II) and Cd(II) ions and Phanerochaete chrysosporium (white rot fungus) modified bentonite was used as adsorbent. After the biosorption of Cu(II) and Cd(II) ions, metal concentrations in the samples were determined by atomic absorption spectrophotometry. pH, adsorbent amount, eluent type, sample volume, and flow rate, which are effective in the adsorption of metal ions, have been studied. 1 M HCl was used for desorption of these metal ions retained (recovery 95–100%). In addition, the effect of interfered ions has also been investigated. Sorption data were examined according to Langmuir and Freundlich adsorption equations. The results obtained show that the applied method has a high metal biosorption capacity, and Cu(II) and Cd(II) ions are successfully recovered. It was also successful in applying the proposed enrichment method to real water samples.Recovery values between 92.3% and 97.3% were obtained for the studied metal ions. According to the results, the proposed method can be successfully applied to water analysis at 95% confidence interval.

Heavy metals biosorption mechanism of partially delignified products derived from mango (Mangifera indica) and guava (Psidium guiag) barks.

This paper evaluates the biosorption of toxic metal ions onto the bioadsorbents derived from mango (Mangifera indica) and guava (Psidium guiag) barks and their metal fixation mechanisms. Maximum metal biosorption capacities of the mango bioadsorbent were found in the following increasing order (mg/g): Hg (16.24) < Cu (22.24) < Cd (25.86) < Pb (60.85). Maximum metal biosorption capacities of guava bioadsorbent follow similar order (mg/g): Hg (21.48) < Cu (30.36) < Cd (32.54) < Pb (70.25), but with slightly higher adsorption capacities. The removal mechanisms of heavy metals using bioadsorbents have been ascertained by studying their surface properties and functional groups using various spectrometric, spectroscopic, and microscopic methods. Whewellite (C2CaO4·H2O) has been identified in bioadsorbents based on the characterization of their surface properties using X-ray techniques (XPS and XRD), facilitating the ion exchange of metal ions with Ca2+ bonded with carboxylate moieties. For both the bioadsorbents, the Pb2+, Cu2+, and Cd2+ are biosorbed completely by ion exchange with Ca2+ (89-94%) and Mg2+ (7-12%), whereas Hg2+ is biosorbed partially (57-66%) by ion exchange with Ca2+ (38-42%) and Mg2+ (19-24%) due to involvement of other cations in the ion exchange processes. Bioadsorbents contain lignin which act as electron donor and reduced Cr(VI) into Cr(III) (29.87 and 37.25 mg/g) in acidic medium. Anionic Cr(VI) was not adsorbed onto bioadsorbents at higher pH due to their electrostatic repulsion with negatively charged carboxylic functional groups.

Recent Advances in Biosorption of Copper and Cobalt by Filamentous Fungi.

Copper (Cu) and Cobalt (Co) are among the most toxic heavy metals from mining and other industrial activities. Both are known to pose serious environmental concerns, particularly to water resources, if not properly treated. In recent years several filamentous fungal strains have been isolated, identified and assessed for their heavy metal biosorption capacity for potential application in bioremediation of Cu and Co wastes. Despite the growing interest in heavy metal removal by filamentous fungi, their exploitation faces numerous challenges such as finding suitable candidates for biosorption. Based on current findings, various strains of filamentous fungi have high metal uptake capacity, particularly for Cu and Co. Several works indicate that Trichoderma, Penicillium, and Aspergillus species have higher Cu and Co biosorption capacity compared to other fungal species such as Geotrichum, Monilia, and Fusarium. It is believed that far more fungal species with even higher biosorption capability are yet to be isolated. Furthermore, the application of filamentous fungi for bioremediation is considered environmentally friendly, highly effective, reliable, and affordable, due to their low technology pre-requisites. In this review, we highlight the capacity of various identified filamentous fungal isolates for biosorption of copper and cobalt from various environments, as well as their future prospects.

Efficient recovery of metal tolerant fungi from the soil of industrial area and determination of their biosorption capacity

Due to various anthropogenic activities, different heavy metals like arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg) and nickel (Ni) accumulate in the soils of industrial areas. In the current study, contaminated soil was collected from Yuepu industrial area of Shanghai, China. Soil analysis revealed the presence of Pb and Cu in high concentrations, ranging from 125.9–128.0 mg/kg and 98.4–100.2 mg/kg, respectively. These soil samples were further used to isolate metal tolerant microbes. Subsequent screening resulted in the isolation of four major fungal species including Fusarium fujikuroi, Fusarium solani, Trichoderma citronoviridae and Trichoderma reesei. Molecular characterization of isolated fungi was performed and amplified sequences were deposited in GenBank NCBI database. Metal tolerance and biosorption capacity of these fungal strains towards lead and copper were tested. Fungal strains were exposed to increasing concentrations (100–1000 ppm) of chlorides of lead and copper and the tolerance of the selected fungi was evaluated by measuring the minimum inhibitory concentrations (MIC). The range of MIC values was found to be 400 ppm to 1000 ppm. The tolerance index of all the tested fungi was calculated and T. citronoviridae was observed to be tolerant at 1 mM concentration of lead while F. solani was the most tolerant species at 1 mM concentration of copper. The highest biosorption capacity of Pb was exhibited by T. citronoviridae, while T. reesei showed the best absorption capacity of Cu followed by F. solani. Scanning electron microscopy (SEM) showed visible adsorption of metal on fungal mycelia and suggested it to be the mechanism of metal removal. On the basis of these findings, it could be concluded that T. citronoviridae and F. solani are the potential mycoremediation microbes in Pb and Cu contaminated soils, respectively.

Efficacy of two seaweeds dry mass in bioremediation of heavy metal polluted soil and growth of radish (Raphanus sativus L.) plant.

This study investigated the effect of Ulva fasciata and Sargassum lacerifolium seaweeds as heavy metal remediators for soil and on the growth of radish (Raphanus sativus L.). The soil was inoculated by dry biomass of each seaweed alone and by their mixture. Seaweeds inoculation increased the organic matter content, clay-size fraction, and nutrients in the soil.Seaweeds mixture treatment caused a significant reduction in the contents of Pb, Cu, Zn and Ni in the soil samples and reduced them to the tolerable limits (40.2, 49.3, 43.8 and 1.1 mg kg-1, respectively), while Cd, Cr, Fe, and Mn contents were closely decreased to the tolerable limits. Biosorption of soil heavy metals by seaweeds decreased the bioaccumulated concentrations of metals in radish plant roots and/or translocated to its shoots compared to control. For seaweeds mixture-treated soil, cultivated radish roots were able to phyto-extract Cd, Cu, Cr, and Ni from the soil (bioaccumulation factor values > 1) of 7.45, 1.18, 3.13, and 26.6, respectively. Seaweeds inoculation promoted the growth of cultivated radish and improved the germination percentage and the morphological and biochemical growth parameters compared to control plants. The achieved soil remediation by dried seaweeds might be due to their efficient metal biosorption capacity due to the existence of active functional groups on their cell wall surfaces. Increased growth observed in radish was as a result of nutrients and growth hormones (gibberellins, indole acetic acid, and cytokinins) present in dried seaweeds. This study shows the efficiency of seaweeds as eco-friendly bioremediators for controlling soil pollution.

Influence of zinc and manganese enrichments on growth, biosorption and photosynthetic efficiency of Chlorella sp.

Treating biosolids from industrial, urban, and agricultural plants produces high amounts of water. After organic pollutants and non-essential heavy metals have been removed, these wastewaters are still rich in trace elements such as zinc (Zn), copper, or manganese (Mn) and have high conductivity and extremely variable pH. In this study, an isolated Chlorella sp. strain was grown for 21days in nutrient solutions enriched with known amounts of Zn or Mn to obtain concentrations three (4.0mgL-1)- and six (1.0mgL-1)-fold higher than the basal medium levels, respectively, and over the limits permitted in aquatic environments. The green alga exhibited high tolerance to Zn and Mn, with the maximum abatement of Zn (28-30%) and Mn (60-63.5%) after 14 and 7days of culture, respectively. Mn stimulated the growth rate and biomass production of Chlorella, which showed the highest carbon levels just in the first week. In both treatments, the nitrogen and protein contents remarkably increased. The photosynthetic pigments increased until the 14th day, with a higher extent in the Zn-enriched solution. An increasing photochemical efficiency was observed after 7days of treatment, when the microalgae grown in Zn- and Mn-enriched solutions showed a slightly higher maximum photochemical efficiency than control. The autotrophic and controlled growth system adopted was designed to monitor the dynamic balance of Zn and Mn contents in the solutions and in the algal biomass. This system has proved to be useful in identifying the optimal nutritional conditions of the microalgae, along with the optimal temporal patterns of both metal biosorption capacity for water remediation and element bioaccumulation in the algal biomass.

Microbes used as a tool for bioremediation of heavy metal from the environment

Heavy metal pollution poses a serious threat to all forms of life in the environment due to the toxic effects of long-term environmental pollution. These metals are extremely sensitive at low concentrations and can be stored in food webs, posing a serious public health risk. Different organic pollutants and metals are not degradable and remain in their environment for a long time. Remediation using conventional physical and chemical methods is uneconomical and produces large volumes of chemical waste. The balance of hazardous metals has shown a strong and growing interest over the years. The use of biosensor microorganisms is eco-friendly and cost-effective. Therefore, microorganisms have a variety of mechanisms of metal sequestration that hold greater metal biosorption capacities. Finally, we provide suggestion from microbial tools to remove, recover metals, and metalloids from solutions using living or dead biomass and their components.

Influence of organic matter and CO2 supply on bioremediation of heavy metals by Chlorella vulgaris and Scenedesmus almeriensis in a multimetallic matrix

This research evaluated the influence of organic matter (OM) and CO2 addition on the bioremediation potential of two microalgae typically used for wastewater treatment: Chlorella vulgaris (CV) and Scenedesmus almeriensis (SA). The heavy metal (HM) removal efficiencies and biosorption capacities of both microalgae were determined in multimetallic solutions (As, B, Cu, Mn, and Zn) mimicking the highest pollutant conditions found in the Loa river (Northern Chile). The presence of OM decreased the total biosorption capacity, specially in As (from 2.2 to 0.0 mg/g for CV and from 2.3 to 1.7 mg/g for SA) and Cu (from 3.2 to 2.3 mg/g for CV and from 2.1 to 1.6 mg/g for SA), but its influence declined over time. CO2 addition decreased the total HM biosorption capacity for both microalgae species and inhibited CV growth. Finally, metal recovery using different eluents (HCl, NaOH, and CaCl2) was evaluated at two different concentrations. HCl 0.1 M provided the highest recovery efficiencies, which supported values over 85% of As, 92% of Cu, and ≈100% of Mn and Zn from SA. The presence of OM during the loaded stage resulted in a complete recovery of As, Cu, Mn, and Zn when using HCl 0.1 M as eluent.

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Effluents containing heavy metals are hazardous to human health and the environment even at low concentrations. It is costly and unsustainable to use conventional methods to remove heavy metals from dilute effluents. Microalgal biomass owing to its high metal biosorption capacity, is a promising alternative biosorbent for treating dilute heavy metal solutions. However, the application of freely suspended algal biomass for metal removal has a number of drawbacks such as small particle size, low chemical resistance, low mechanical strength, and difficulty in separation of biomass and effluent. The present article reviews the techniques used to address these drawbacks. It also discusses the key factors affecting biosorption efficiency including initial concentration of metal ions, contact time, solution pH, solution temperature, biosorbent concentration, agitation rate, and competing ions. Biomass cross-linking with appropriate agents such as polysolfane, formaldehyde, or chlorohydrin could improve mechanical strength, chemical resistance, and separation of the biomass from the effluent. However, cross-linked biomass usually shows low sorption capacity and slow rate of metal uptake. These disadvantages could be minimized by using physical and/or chemical pretreatments prior to biomass cross-linking. Alkaline detergent, sodium hydrogen carbonate without autoclaving, sodium hydroxide or sodium carbonate plus autoclaving, or supercritical carbon dioxide at mild conditions are among the most effective pretreatments. Apart from liberating more latent metal binding sites on the biomass, supercritical CO2 could also improve the porosity of the biomass thereby improving sorption rate of the cross-linked biomass. High sorption capacity and rapid metal uptake will allow substantial reduction in size of biosorption columns, which will consequently improve the economic and sustainability features of algal-based metal biosorption processes.