Biosorption Of Metals Research Articles

Bioprospecting of cowdung microflora for sustainable agricultural, biotechnological and environmental applications.

The review aims at highlighting the manifold applications of cow dung (CD) and CD microflora covering agricultural, biotechnological and environmental applications. The update research on CD microflora and CD in agricultural domain such as biocontrol, growth promotion, organic fertilizer, sulfur oxidation, phosphorus solubilization, zinc mobilization and underlying mechanisms involved in these processes are discussed. The significance of CD applications in tropical agriculture in context to climate change is briefly emphasized. The advances on genomics and proteomics of CD microflora for enhanced yield of enzymes, organic acids, alternative fuels (biomethane and biohydrogen) and other biocommodities, and environmental applications in context to biosorption of heavy metals, biodegradation of xenobiotics, etc. have been given critical attention.

Effects of Heat and Chemical Pretreatments of Banana Peels for Metal Removal in Single and Multimetal Systems

This study investigated and compared the influence of pretreatments (heat and chemical) on banana peels and their subsequent efficacy in removing toxic metals (Cu, Pb, Zn, Cd) from single and multimetal systems. Banana peels were pretreated using heat (autoclaving, microwaving, boiling) and chemical (acetic acid, nitric acid, NaOH, detergent, methanol, and DMSO) treatments, prior to biosorption tests. Results revealed that pretreatment using detergent enabled banana peels to biosorb metals at relatively higher amounts in both single (Cu-96.26%, Pb-96.72%, Zn-95.75%, Cd-96.92%) and multimetal (Cu-92.43%, Pb-95.91%, Zn-91.88%, Cd-94.42%) systems. Biosorption by detergent-treated peels were profoundly effective when 0.10 g was used, with initial metal concentration of 10 mg/l, agitation speed of 120 rpm and a solution with pH 5. Characterization of detergent pretreated banana peels via FTIR analysis showed that different pretreatments applied did not significantly modify the presence of functional groups. As such, the preexisting functional groups such as hydroxyl, amino, carboxyl, and carbonyl groups were deemed responsible for metal removal. SEM-EDX analysis on detergent pretreated peels suggested that improvement to metal removal may be attributed to enlarged pore size. This suggested that pretreatment with detergent, and as with most chemicals, presented a more feasible and economical approach than heat treatments to successfully enhance metal biosorption by banana peels for wastewater treatment.

A meta-analysis of metal biosorption by suspended bacteria from three phyla

Biosorption of heavy metals by bacterial biomass has been the subject of significant research interest in last decades due to its efficiency, relatively low cost and minimal negative effects for the surrounding environment. In this meta-analysis, the biosorption efficiencies of different bacterial strains for Cu(II), Cd(II), Zn(II), Cr(III), Mn(II), Pb(II) and Ni(II) were evaluated. Optimum conditions for the biosorption process such as initial metal concentration, temperature, pH, contact time, metal type, biomass dosage and bacterial phyla, were evaluated for each heavy metal. According to the results, the efficiencies of bacterial biomass for removal of heavy metal were as follows: Cd(II) > Cr(III) > Pb(II) > Zn(II) > Cu(II) > Ni(II) > Mn(II). Firmicute phyla showed the highest overall (living and dead) biosorption efficiency for heavy metals. Living biomass of Proteobacteria had the best biosorption performance. Living bacterial biomass was significantly more efficient in biosorption of Cu(II), Zn(II) and Pb(II) than dead biomass. The maximum biosorption efficiency of bacterial strains for Cd(II), Pb(II) and Zn(II) was achieved at pH values between 6 and 7.5. High temperatures (>35 °C) reduced the removal efficiencies for Cu(II) and Zn(II) and increased the efficiencies for Cd(II) and Cr(III) ions. The maximum biosorption efficiency of non-essential heavy metals occurred with short contact times (<2 h). Essential metals such as Zn and Cu were more efficiently removed with long biosorption durations (>24 h). The mean biosorption capacity of bacterial biomass was between 71.26 and 125.88 mg g−1. No publication bias existed according to Egger’s and Begg’s test results.

Biosorption: A Review of the Latest Advances

Biosorption is a variant of sorption techniques in which the sorbent is a material of biological origin. This technique is considered to be low cost and environmentally friendly, and it can be used to remove pollutants from aqueous solutions. The objective of this review is to report on the most significant recent works and most recent advances that have occurred in the last couple of years (2019–2020) in the field of biosorption. Biosorption of metals and organic compounds (dyes, antibiotics and other emerging contaminants) is considered in this review. In addition, the use and possibilities of different forms of biomass (live or dead, modified or immobilized) are also considered.

Biosorption of heavy metals by dry biomass of metal tolerant bacterial biosorbents: an efficient metal clean-up strategy.

Heavy metals discharge at an unrestrained rate from various industries into the environment pose serious human health problems. Considering this, the present study aimed at exploring the metal biosorbing potentials of bacterial strains recovered from polluted soils. The bacterial strains (CPSB1, BM2 and CAZ3) belonging to genera Pseudomonas, Bacillus and Azotobacter expressing multi-metal tolerance ability were identified to species level as P. aeruginosa, B. subtilis and A. chroococcum, respectively, by 16S rRNA partial gene sequence analysis. The biosorption of cadmium, chromium, copper, nickel, lead and zinc by three dead bacterial genera were studied as a function of metal concentration, variable pH of the medium and reaction (contact) time. The three bacterial strains exhibited a tremendous metal removal ability which continued even at the highest tested concentration of some metals. Later, a decline in the percentage of biosorbed metals was recorded as the metal concentration was increased with the simultaneous generation of a driving force to overcome mass transfer resistance for movement of metal ions between the solution and the surface of adsorbent. Among test bacteria, B. subtilis biosorbed a maximum of 96% chromium at 25μgmL-1 while the maximum percentage (91%) of biosorbed metals recorded at 400μg CdmL-1 was observed for P. aeruginosa. The sorption of metal ions by dead biomass of three bacterial genera at optimum conditions followed the order-(i) B. subtilis BM2: Pb > Cu > Ni > Cd > Cr, (ii) A. chroococcum CAZ3: Cr > Cd > Cu > Ni > Pb and (iii) P. aeruginosa CPSB1: Cd > Cr > Ni > Cu > Pb > Zn. It was found that the optimum pH for metal adsorption ranged between pH8 and 9 which, however, declined substantially at pH5.0 for all three bacterial strains. In general, the biosorption of Cd, Cr, Cu, Ni and Pb by B. subtilis and A. chroococcum and such metals along with Zn by P. aeruginosa occurred maximally up to 60min of bacterial growth. The adsorption data with regard to five metals provide an outstanding fit to the Langmuir and Freundlich isotherms. The biosorptive ability of three bacterial genera correlated strongly (r2 > 0.9) with each metal. The bacteria belonging to two Gram-negative genera Pseudomonas (P. aeruginosa) and Azotobacter (A. chroococcum) and one Gram-positive genus Bacillus (B. subtilis) demonstrated exceptional metal removal efficiency and, hence, provides a comprehensive understanding of metal-bacteria sorption process which in effect paves the way for detoxifying/removing metals from contaminated environment.

Using Amaranthus green proteins as universal biosurfactant and biosorbent for effective enzymatic degradation of diverse lignocellulose residues and efficient multiple trace metals remediation of farming lands

Improving biomass enzymatic saccharification is effective for crop straw utilization, whereas phytoremediation is efficient for trace metal elimination from polluted agricultural soil. Here, we found that the green proteins extracted from Amaranthus leaf tissue could act as active biosurfactant to remarkably enhance lignocellulose enzymatic saccharification for high bioethanol production examined in eight grassy and woody plants after mild chemical and green-like pretreatments were performed. Notably, this study estimated that total green proteins supply collected from one-hectare-land Amaranth plants could even lead to additional 6400–12,400 tons of bioethanol, being over 10-fold bioethanol yield higher than those of soybean seed proteins and chemical surfactant. Meanwhile, the Amaranth green proteins were characterized as a dominated biosorbent for multiple trace metals (Cd, Pb, As) adsorption, being 2.9–6 folds higher than those of its lignocellulose. The Amaranth plants were also assessed to accumulate much more trace metals than all other plants as previously examined from large-scale contaminated soils. Furthermore, the Amaranth green proteins not only effectively block lignin to release active cellulases for the mostly enhanced biomass hydrolyzes, but also efficiently involve in multiple chemical bindings with Cd, which should thus address critical issues of high-costly biomass waste utilization and low-efficient trace metal remediation.

Extraction of Bioactive Nano Particles from Seaweed for Heavy Metals Removal and Antibacterial Agent

The environmental impact and building up toxicity of heavy metals have been a cause of great concern in recent years. This has given rise to a significant increase of studies with the objective of effectively developing alternative technologies for the removal of substances from industrial effluents that are potentially noxious to the environment. Biosorption can be a piece of the arrangement. A few sorts of biosorbents, for example, ocean growth, molds, yeasts, microorganisms or crab shells are instances of biomass tried for metal biosorption with empowering results. Ocean growth offer points of interest for biosorption on the grounds that their naturally visible structures offer an advantageous reason for the creation of biosorbent particles appropriate for sorption process applications. In the present paper a detailed study has been carried out to find a suitable bionano absorbent extracted from various seaweeds which is abundantly available in the coastal area of Thondi and characterized by UV and FTIR and TEM techniques.

Biosorption of heavy metals by Talaromyces helicus: a trained fungus for copper and biphenyl detoxification

At present, it is common to observe environments with organic and inorganic pollution, defined as co-contamination. Most industrial and urban effluents releases both pollutant types, leading to a complex environmental problem, as the biota must be tolerant to both xenobiotics. T. helicus, an efficient strain to degrade biphenyl, was trained with high copper levels, and became co tolerant to cobalt, lead and cadmium when was cultured in their presence. The copper adaptation was the result of physiological mechanisms, and the activated biochemical processes conferred resistance to Cu2+ as well as to other heavy metals. Furthermore, the Cu2+ adaptation of the mycelium was also transferred to the spores, that removed twice as much copper from solution than those of the no trained parentals. Interestingly, metals combinations were less toxic than single ones, and co tolerance development indicated that the cellular mechanisms that conferred resistance were non-specific, so the micobiota isolated from co contaminated environments often exhibited resistance to more than one ions. These results emphasized the detoxification abilities of T. helicus and the adaptation to heavy metals and biarylic compounds. This data is significant for the environmental biotechnology, suggesting that such tolerance and co tolerance could be acquired in natural environments. So a simple bioremediation strategy could enhance the detoxification of these polluted areas, as the degrader organisms could be present.

Biosorption and removal of toxic heavy metals by metal tolerating bacteria for bioremediation of metal contamination: A comprehensive review

Heavy metal pollution caused due to the industrialization has been considered as a significant public health hazard, and these heavy metals exhibit various types of toxicological manifestations. Conventional remediation methods are expensive and also yield toxic by-products, which negatively affect the environment. Hence, a green technology employing various biological agents, predominantly bacteria, algae, yeasts, and fungi, has received more attention for heavy metal removal and recovery because of their high removal efficiency, low cost, and availability. However, bacterial biosorption is the safest treatment method for the toxic pollutants that are not readily biodegradable such as heavy metals. Metal biosorption by bacteria has received significant attention due to a safe, productive, and feasible technology for the heavy metal-containing wastewater treatment. These metal tolerating bacteria can bind the cationic toxic heavy metals with the negatively charged bacterial structures and live or dead biomass components. Due to the large surface area to volume ratio, these bacterial biomasses efficiently act as the biosorbent for metal bioremediation under multimetal conditions. This review summarizes the biosorption potentials of bacterial biomass towards different metal ions, cell wall constituent, biofilm, extracellular polymeric substances (EPS) in metal binding, and the effect of various environmental parameters influencing the metal removal. Suitable mathematical models of biosorption and their application have been discussed to understand and interpret the adsorption process. Furthermore, different desorbing agents and their utilization in heavy metals recovery and regeneration of biosorbent have been summarized.

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.

Optimization of cadmium and lead biosorption onto marine Vibrio alginolyticus PBR1 employing a Box-Behnken design

Microorganisms are well capable of removing heavy metals by different mechanisms especially where the process of biosorption has attracted researchers in the recent years. Various bacteria and fungi are currently being used for biosorption of heavy metals, however, reports suggesting the use of bioluminescent Vibrio sp. for metal biosorption are rare. In this study, the dead biomass of Vibrio alginolyticus PBR1 was employed to remove two metals, cadmium (Cd) and lead (Pb) from a single aqueous system. The Box-Behnken design (BBD), a Response Surface Method (RSM), was used to optimize biosorption of metals by V. alginolyticus PBR1. The three major factors; pH, biosorbent dosage and metal concentration were optimized to remove the metals efficiently. The optimum conditions for V. alginolyticus PBR1 were pH 5.7, biosorbent dosage of 2.0 g L−1 and metal concentration of 50 mg L−1 for each metal showed to have removal efficiencies of 59.78 % and 82.20 % for Cd and Pb, respectively. Furthermore, the possible interactions between functional groups present on cell surface and metals were studied using Fourier Transform Infrared (FTIR) spectroscopy. The study provides potential application of bioluminescent Vibrio sp. for removing two metals simultaneously from heavy metal contaminated aqueous solution.

Biosorption of Heavy Metals from Aqueous Solutions:Insight and Review

Contamination of water bodies by industrial and domestic effluents containing heavy metals is today considered a big threat to man, flora and fauna. Solving this problem resulting from rapid industrialization has been a challenge over time. From different experimental results obtained, biosorption is considered a part of the solution to this problem. Removal of heavy metals from aqueous solutions is an alternative technique that is cost-effective due to availability of large amount of sorption materials and low or no chemical/energy demand. In this article, a review of past and current outcomes of biosorption studies using different biomaterials was carried out. This review also looked into various factors affecting heavy metals biosorption, adsorption isotherm, kinetics and thermodynamics.

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.

Bio-sorption of toxic metals from industrial wastewater by algae strains Spirulina platensis and Chlorella vulgaris: Application of isotherm, kinetic models and process optimization

The present study evaluates the effect of an acidic treatment on the improvement of the percentage removal of toxic metal (%TMrem) from wastewater by algae strains (Spirulina platensis (SP) and Chlorella vulgar (CV)) under different adsorbent dosages (0.2–2.5 g), a pH of (4–8) and contact time (5–100 min). The acidic treatment (Ac-T) altered the functional groups on the surface of algae promoting more electronegative groups and improved the %TMrem of Al, Ni and Cu. Treated SP removed up to 95.0 ± 0.3% (Std. Dev = 0.24), 87.0 ± 0.2% (Std. Dev = 0.34)%, and 63.0 ± 0.3% (Std. Dev = 0.14) of Al, Ni, and Cu at the optimum pH of 5.5, 6.0, and, 7.0 and an adsorbent dosage of = 2.5 ± 0.1 g/L (Std. Dev = 0.14) g/L, respectively. Lower %TMrem of 87.0% ± 0.2 (Std. Dev = 0.09), 79.1 ± 0.4% (Std. Dev = 0.08), and 80.0 ± 0.2% (Std. Dev = 0.04) were achieved with treated CV, respectively. The optimum operational conditions for maximum %TMrem were determined at (Calgae = 4.8 ± 0.2 gMNPs.L−1, Ct = 88 ± 1, and pH = 6) using the response surface methodology (RSM). The adsorption of TMs on algae is endothermic, spontaneous, and follows Langmuir and second-order kinetics. Zeta potential measurements indicated that the adsorption mechanism between the toxic metal (TM) and algal strains is controlled by electrostatic interaction. As such, bio-sorption is a sustainable and efficient technology for the removal of TM from wastewater.

Enhancement of lead (Pb) biosorption by Gamma irradiated Aspergillus japonicus

Among the different types of microorganisms; the fungal biomass is considered as an effective mediator for bioremediation of heavy metals, due to its higher surface area and extensive hyphal density in the soil. About seven fungal spp. were isolated from the soil garden of the Middle Eastern Regional Radioisotope Center for Arab Countries (MERRCAC); however, a single isolate of Aspergillus japonicus with high potential of metals biosorption was selected for further research during this work. Soil analysis revealed that lead concentration was 5.25 mg/ l. The aims of the present study were to gamma irradiate A. japonicus with low doses of 50 to 250Gy, in order to enhance its heavy metal tolerance ability, and to increase its efficacy for removal of lead (Pb) from the soil. Results indicated that combined treatments of A. japonicus with lead and gamma irradiation doses displayed more enhancements of its biosorption capacity and gain in dry biomass than single treatment. Treatment with Pb (1950 mg/ l) in combination with gamma irradiation (100 Gy) proved to be optimum for increasing the biosorption capacity of this isolate. However, Pb at 650 mg/ l combined with gamma irradiation at 100 Gy was the optimum for gain in dry biomass. Fourier Transform Infrared Spectroscopic (FTIR) analysis showed that the fungal biomass includes in its surface hydroxyl, carboxyl and amine groups. On the other hand, Transmission electron microscope (TEM) examination of the irradiated A. japonicus cells demonstrated accumulation of electron dense Pb on the cell wall and within the fungal cells, this indicate that Pb2+ accumulation by fungi occurs by two methods absorption inside the cell and adsorption on the cell wall. The current study expressed a potential new method for enhancing microbial biosorption using low doses of gamma radiation.

Isolation, identification and heavy metals biosorption of a lead and cadmium-tolerant strain

Adding biological passivation agent during composting is one of the most effective ways to reduce the toxicity of heavy metals in contaminated livestock manure. To further improve biological passivation, we obtained a strain with high-heavy metal compounds tolerance to passivate heavy-metal contaminated manure and to characterize heavy-metal biosorption. High-tolerance microorganisms for lead and cadmium were isolated and screened from swine manure composting samples. The strain was identified by its morphology and molecular biology. After the influence of different pH, temperature and salt concentrations on growth of the strain were investigated, the optimal growth conditions were obtained for further analysis of its biosorption characteristics of lead and cadmium. The bacterium with tolerance to lead and cadmium termed SC19 was obtained, whose lead resistance was 600 mg/L and cadmium resistance was 120 mg/L. The isolate was further identified as Cedecea sp., and then its optimum pH was 7.0, temperature was 37 °C, and salt concentration was 0.5%. Lead removal was highest after 30 min of adsorption by the SC19 strain cultured for the stationary phase 36 h, and the maximum removal rate and biosorption capacity of lead were 60.7% and 329.13 mg/g, respectively. Meanwhile, cadmium removal was highest after 30 min of adsorption by the strain cultured for the logarithmic phase 8 h, and the maximum removal rate and biosorption capacity of cadmium were 51.0% and 126.19 mg/g, respectively. Fourier Transform InfraRed (FT-IR) results revealed that the biosorption process mainly happened on the surface of SC19 cell and many active groups on the cell surface could chelate the Pb²⁺ and Cd²⁺. By comprehensive comparison, it was showed that strain SC19 shared a certain capacity of Pb²⁺ and Cd²⁺ biosorption, and the bacterium provided precious microbial germplasm resources for biological passivation of heavy metal contaminated manure.

Biosorption of Cr (VI) from aqueous solution by extracellular polymeric substances (EPS) produced by Parapedobacter sp. ISTM3 strain isolated from Mawsmai cave, Meghalaya, India

In the current study, EPS producing strain Parapedobacter sp. ISTM3 was isolated from Mawsmai cave, Meghalaya, India. The strain ISTM3 showed enhanced EPS production (4.65 ± 0.10 g L−1) at optimized parameters, i.e., pH 8 and 3% molasses as a carbon source. The extracted EPS was structurally characterized by GC-MS, NMR, and FTIR analysis to investigate its monomer compositions, functional groups, and linkage analysis. GC-MS study confirmed the heteropolymeric nature of EPS, whereas the FTIR study confirmed the presence of an aliphatic group, amine group, uronic acid, and saccharides group in the EPS structure. Biosorption of heavy metals by EPS from an aqueous solution was investigated by using heavy metals mixture (Zn2+, Cu2+, Pb2+, Cr6+, Fe2+, and Cd2+) with 20 mg L−1 concentration of each metal. EPS showed the highest removal efficiency and metal adsorption capability for Cr6+ as compared to other heavy metals studied. Also, metal adsorption capability (19.032 mg g−1) and removal efficiency (95.10%) of Cr6+ by EPS were further increased in acidic conditions (pH 5.0). FTIR and SEM-EDX analysis confirmed the biosorption mechanism of EPS. The Freundlich and Langmuir adsorption isotherms were employed to discover the biosorption parameters for Cr6+ uptake with a concentration range of 10–200 mg L−1 by EPS (1 g L−1). The Langmuir model was found to better fit the Cr6+ adsorption by EPS having a maximum adsorption capacity of 33.783 mg g−1. With this, the present study highlights the EPS production potential of Parapedobacter sp. ISTM3, as well as the potential of extracted EPS for heavy metals removals via adsorption.

Optimization study of biosorption of toxic metals from mining wastewater using Azadirachta indica bark adsorbents.

The effectiveness of two Azadirachta indica bark activated carbons (ABAC) for the removal of selected toxic metals from mining wastewater and the attendant challenge of multivariate factors in the process were enhanced through optimization studies. Experimental design was carried out using adsorbent dosage, agitation rate, contact time, grain size, pH and temperature as independent variables. Batch adsorption experiments were conducted using the experimental design result, then the experimental data obtained were optimized using Design-Expert software and the results validated. Optimum values for ABAC-NaOH adsorbent were 1.999 g of adsorbent dosage, 149.73 rpm agitation rate, 119.55 min contact time, 2 mm grain size, pH of 7 and 30 °C temperature; while for ABAC-HCl adsorbent the optimum values were 3.993 g of adsorbent dosage, 150 rpm agitation rate, 120 min contact time, 2 mm grain size, pH of 7.001 and 30 °C temperature. These resulted in 100% removal efficiencies for all the selected toxic metals with standard errors of between 0.02 and 2.72%. So the optimization process is a very useful tool in adsorption studies. It has the merits of being economical, energy and time saving, and is therefore strongly recommended for the biosorption of toxic metals from mining wastewater using Azadirachta indica adsorbent.

Lead and cadmium biosorption from milk by Lactobacillus acidophilus ATCC 4356.

The food and water contamination with heavy metals is increasing due to the environmental pollutions. Lead and cadmium are the toxic heavy metals for humans that can be found in air, soil, water, and even food. Lactic acid bacteria have the ability to remove and diminish the level of heavy metals. In this study, Lactobacillus acidophilus was used to remove lead and cadmium in milk and the capability of this valuable bacterium in biosorption of these metals low concentrations (µg/L or ppb) in milk was evaluated. First, the variables on lead and cadmium removal by this bacterium have been studied by Plackett–Burman design. Then, the bioremoval process was optimized and the three main factors, the bacterium concentration, contact time, and the initial heavy metal concentration were chosen by using a central composite design. The optimum lead and cadmium bioremoval yield of 80% and 75% were observed, respectively, at 1 × 1012 CFU of L. acidophilus in milk at the 4th day and the initial ion concentration of 100 µg/L. The 3D plots analysis showed the interaction effects on metal biosorption. This study showed that L. acidophilus is a natural effective biosorbent for lead and cadmium removal from milk.