Immobilization of blue green microalgae on loofa sponge to biosorb cadmium in repeated shake flask batch and continuous flow fixed bed column reactor system

Summary An indigenous strain of blue green microalga, Synechococcus sp., isolated from wastewater, was immobilized onto loofa sponge discs and investigated as a potential biosorbent for the removal of cadmium from aqueous solutions. Immobilization has enhanced the sorption of cadmium and an increase of biosorption (21%) at equilibrium was noted as compared to free biomass. The kinetics of cadmium biosorption was extremely rapid, with (96%) of adsorption within the first 5 min and equilibrium reached at 15 min. Increasing initial pH or initial cadmium concentration resulted in an increase in cadmium uptake. The maximum biosorption capacity of free and loofa immobilized biomass of Synechococcus sp. was found to be 47.73 and 57.76 mg g⁻¹ biomass respectively. The biosorption equilibrium was well described by Langmuir adsorption isotherm model. The biosorbed cadmium was desorbed by washing the immobilized biomass with dilute HCl (0.1 M) and desorbed biomass was reused in five biosorption–desorption cycles without an apparent decrease in its metal biosorption capacity. The metal removing capacity of loofa immobilized biomass was also tested in a continuous flow fixed-bed column bioreactor and was found to be highly effective in removing cadmium from aqueous solution. The results suggested that the loofa sponge-immobilized biomass of Synechococcus sp. could be used as a biosorbent for an efficient removal of heavy metal ions from aqueous solution.     

Enhancement of Lead(II) Biosorption by Microalgal Biomass Immobilized onto Loofa (Luffa cylindrica) Sponge

A unicellular green microalga, Chlorella sorokiniana, was immobilized on loofa (Luffa cylindrica) sponge and successfully used as a new biosorption system for the removal of lead(II) ions from aqueous solutions. The biosorption of lead(II) ions on both free and immobilized biomass of C. sorokiniana was investigated using aqueous solutions in the concentration range of 10–300 mg/L. The biosorption of lead(II) ions by C. sorokiniana biomass increased as the initial concentration of lead(II) ions increased in the medium. The maximum biosorption capacity for free and immobilized biomass of C. sorokiniana was found to be 108.04 and 123.67 mg lead(II)/g biomass, respectively. The biosorption kinetics were found to be fast, with 96 % of adsorption within the first 5 min and equilibrium reached at 15 min. The adsorption of lead(II) both by free and immobilized C. sorokiniana biomass followed the Langmuir isotherm. The biosorption capacities were detected to be dependent on the pH of the solution; and the maximum adsorption was obtained at a solution pH of about 5. The effect of light metal ions on lead(II) uptake was also studied and it was shown that the presence of light metal ions did not significantly affect lead(II) uptake. The loofa sponge‐immobilized C. sorokiniana biomass could be regenerated using 0.1 M HCl, with up to 99 % recovery. The desorbed biomass was used in five biosorption‐desorption cycles, and no noticeable loss in the biosorption capacity was observed. In addition, fixed bed breakthrough curves for lead(II) removal were presented. These studies demonstrated that loofa sponge‐immobilized biomass of C. sorokiniana could be used as an efficient biosorbent for the treatment of lead(II) containing wastewater.     

Cadmium uptake by non-viable biomass from a marine brown algaEcklonia radiata turn

Biomass of non-viable and dried brown marine algaeEcklonia radiata Turn. was used to examine its cadmium uptake capability. Twelve different pretreatments on the algal biomass were prepared. Among these pretreatments, the algal biomass, which treated with 0.1 M NaOH and kept in water bath (100°C, 18 h) followed by washing with distilled water and squeezing, showed the highest amount of cadmium uptake as 1634±195 mg/g dry biomass at pH 4.0 and 50°C. Adsorption temperatures and pH levels played some important role in cadmium uptake. However, cadmium uptake decreased dramatically at a lower pH than 4.0. Freundlich adsorption isotherm showed potent cadmium uptake capacity of the non-viable biomass. Pretreatments on the nonviable algal biomass shown in this study may enhance the cadmium removal in the industrial wastewater.     

Biosorption of Copper(II) by Live and Dried Biomass of the White Rot Fungi Phanerochaete chrysosporium and Funalia trogii

Biosorption is an innovative and alternative technology to remove heavy metal pollutants from aqueous solution using live, inactive and dead biomasses such as algae, bacteria and fungi. In this study, live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was applied as heavy metal adsorbent material. Biosorption of copper(II) cations in aqueous solution by live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was investigated to study the effects of initial heavy metal concentration, pH, temperature, contact time, agitation rate and amount of fungus. Copper(II) was taken up quickly by fungal biomass (live or dried) during the first 15 min and the most important factor which affected the copper adsorption by live and dried biomass was the pH value. An initial pH of around 5.0 allowed for an optimum adsorption performance. Live biomass of two white rot fungi showed a high copper adsorption capacity compared with dried biomass. Copper(II) uptake was found to be independent of temperature in the range of 20–45 °C. The initial metal ion concentration (10–300 mg/L) significantly influenced the biosorption capacity of these fungi. The results indicate that a biosorption as high as 40–60 % by live and dried biomass can be obtained under optimum conditions.     

Biosorption of lead, cadmium, and zinc by Citrobacter strain MCM B-181: characterization studies

The biosorption process for removal of lead, cadmium, and zinc by Citrobacter strain MCM B-181, a laboratory isolate, was characterized. Effects of environmental factors and growth conditions on metal uptake capacity were studied. Pretreatment of biomass with chemical agents increased cadmium sorption efficiency; however, there was no significant enhancement in lead and zinc sorption capacity. Metal sorption by Citrobacter strain MCM B-181 was found to be influenced by the pH of the solution, initial metal concentration, biomass concentration, and type of growth medium. The metal sorption process was not affected by the age of the culture or change in temperature. Equilibrium metal sorption was found to fit the Langmuir adsorption model. Kinetic studies showed that metal uptake by Citrobacter strain MCM B-181 was a fast process, requiring <20 min to achieve >90% adsorption efficiency. The presence of cations reduced lead, zinc, and cadmium sorption to the extent of 11. 8%, 84.3%, and 33.4%, respectively. When biomass was exposed to multimetal solutions, metals were adsorbed in the order Co2+ < Ni2+ < Cd2+ < Cu2+ < Zn2+ < Pb2+. Among various anions tested, only phosphate and citrate were found to hamper metal sorption capacity of cells. Biosorbent beads prepared by immobilizing the Citrobacter biomass in polysulfone matrix exhibited high metal loading capacities. A new mathematical model used for batch kinetic studies was found to be highly useful in prediction of experimentally obtained metal concentration profiles as a function of time. Metal desorption studies indicated that Citrobacter beads could, in principle, be regenerated and reused in adsorption-desorption cycles. In an expanded scale trial, biosorbent beads were found to be useful in removal/recovery of metals such as lead from industrial wastewaters.     

Removal of cadmium by Pleurotus sajor-caju basidiomycetes

The bioaccumulation of cadmium by the white rot fungus Pleurotus sajor-caju onto dry biomass was investigated using aqueous media with concentrations in the range of 0.125 mM–1.0 mM The highest cadmium uptake (between 88.9 and 91.8%) was observed with aerobic fungal biomass from the exponential growth phase. Up to 1.0 mM cadmium gradually inhibited mycelium development, but never blocked it completely. Freeze-dried, oven-dried and non-metabolizing live Pleurotus sajor-caju biomass types were tested for their capacity to adsorb the test ion Cd²⁺ within the pH range of 4.5 to 6.0. Freeze–dried biomass proved to be the most efficient biomass type for Cd²⁺ metal adsorption. Therefore, Pleurotus sajor-caju may be used for heavy metal removal and bioremediation.     

Immobilization of microbial cells and enzymes with hydrophobic photo-crosslinkable resin prepolymers

Summary The accumulation of cadmium from aqueous systems by various green microalgae was investigated with focus, on Chlorella regularis as it is known to concentrate large amounts of heavy metals. The amount of cadmium absorbed by Chlorella cells was rapid during the first 30 min following addition of cadmium and then continued to be absorbed more slowly. The uptake of cadmium by Chlorella was not markedly affected by temperature or metabolic inhibitors. Most of the cadmium absorbed by Chlorella cells was easily released by EDTA. The amount of cadmium absorbed differed markedly with the pH value of the solution and was inhibited by the presence of other divalent cations. Heat-killed Chlorella cells took up cadmium to a greater degree than living ones. From these results, it was considered that the uptake of cadmium into Chlorella cells was not directly mediated by metabolic processes, rather it appeared completely dependent upon physico-chemical adsorption on the cell surface.The ability to accumulate cadmium was species specific and found to be (in decreasing order); Chlamydomonas reinhardtii>Chlorella regularis> Scenedesmus bijuga>Scenedesmus obliquus>Chlamydomonas angulosa> Scenedesmus chlorelloides.Studies on the Accumulation of Heavy Metal Elements in Biological Systems Part XIV     

Cadmium biosorption by <Emphasis Type="Italic">Bacillus</Emphasis><Emphasis Type="Italic"> circulans</Emphasis> strain EB1

Summary A heavy metal resistant bacterium, Bacillus circulans strain EB1 showed a high cadmium biosorption capacity coupled with a high tolerance to this metal when grown in its presence. Bacillus circulans EB1 cells grown in the presence of 28.1 mg cadmium/l were capable of removing cadmium with a specific biosorption capacity of 5.8 mg Cd/g dry wt biomass in the first 8 h. When the cells were pre-conditioned with low concentrations of cadmium in pre-grown medium, the uptake was increased to 6.7 mg Cd/g dry wt biomass. The maximum uptake of␣cadmium was during mid-logarithmic phase of growth. The resting cells (both wet and dry) of EB1 were also able to biosorb cadmium. Specific biosorption capacities of wet and dry biomass were 9.8 and 26.5 mg Cd/g dry wt biomass, respectively. Maximum cadmium removals by both wet and dry cells were at pH 7.0. The results showed that the cadmium removal capacity of resting cells was markedly higher than that of growing cells. Since both growing and resting cells had a high biosorption capacity for cadmium, EB1 cells could serve as an excellent biosorbent for removal of cadmium from natural environments.     

Mechanism of cadmium uptake by activated sludge

Summary The significance of metabolic activity in cadmium uptake by unacclimated activated sludge was studied. Below 30 mg/l cadmium in solution, biosorption was found to follow the Freundlich isotherm, which is the most common pattern for physico-chemical adsorption. More than 95% of total cadmium uptake was achieved within 5 min metal-sludge contact time. Biosorption increased strongly when the initial cadmium concentration in solution was raised from 10 to 100 mg/l, whereas in the same concentration range the metabolic activity of the sludge, as measured by respiratory activity and extracellular protein production, was very significantly inhibited. The addition of nutrients at low but significant levels failed to increase cadmium uptake in 2 h contact time, while in 24 h the addition of nutrients caused the biosorption to increase by only 5–10% without any significant growth of the biomass. Biosorption was found to increase with temperature between 5° C and 40° C, in correlation with an increase in the metabolic activity of the sludge. Pretreatment of the sludge with metabolic inhibitors (NaN₃ and UV rays) appeared to cause only a very slight decrease (5–10%) of biosorption. These results suggest that metabolic uptake of cadmium was low and that adsorption to the surface of the cells was the major mechanism of uptake.Offprint requests to: S. S. Sofer     

Kinetic modeling and equilibrium studies during cadmium biosorption by dead Sargassum sp. biomass

A basic investigation on the removal of cadmium(II) ions from aqueous solutions by dead Sargassum sp. was conducted in batch conditions. The influence of different experimental parameters; initial pH, shaking rate, sorption time, temperature and initial concentrations of cadmium ions on cadmium uptake was evaluated. Results indicated that cadmium uptake could be described by the Langmuir adsorption model, being the monolayer capacity negatively affected with an increase in temperature. Analogously, the adsorption equilibrium constant decreased with increasing temperature. The kinetics of the adsorption process followed a second-order adsorption, with characteristic constants increasing with increasing temperature. Activation energy of biosorption could be calculated as equal to 10 kcal/mol. The biomass used proved to be suitable for removal of cadmium from dilute solutions. Its maximum uptake capacity was 120 mg/g. It can be considered an optimal result when compared to conventional adsorbing materials. Thus Sargassum sp. has great potential for removing cadmium ions especially when concentration of this metal is low in samples such as wastewater streams.     

Use of Phanerochaete chrysosporium biomass for the removal of textile dyes from a synthetic effluent

Summary The use of Phanerochaete chrysosporium biomass for the removal of Reactofix Golden Yellow from aqueous solution and eight textile dyes (four azo and four anthraquinone) from a synthetic effluent (0.6 g/l) at different pH, temperature and biomass concentrations was studied. Adsorption was maximum at pH 2.0 and 40 °C using 2.45 g mycelial biomass. The rate constant of adsorption was 1.95×10⁻¹/min for Reactofix Golden Yellow and 1.64×10⁻¹/min for synthetic effluent. In both cases, the equilibrium data fitted well in the Langmuir but not the Freundlich model of adsorption, and the adsorption was biphasic. Adsorption decreased the COD of Reactofix Golden Yellow and synthetic effluent by 54 and 57%, respectively. Desorption (80–84%) of dyes from P. chrysosporium mycelial surface occurred as the pH increased from 2 to 10.     

Biosorption of Pb<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Non-Living Biomass of <Emphasis Type="Italic">Spirulina</Emphasis> sp.

Removal of heavy metals (Pb²⁺, Zn²⁺) from aqueous solution by dried biomass of Spirulina sp. was investigated. Spirulina rapidly adsorbed appreciable amount of lead and zinc from the aqueous solutions within 15 min of initial contact with the metal solution and exhibited high sequestration of lead and zinc at low equilibrium concentrations. The specific adsorption of both Pb²⁺ and Zn²⁺ increased at low concentration and decreased when biomass concentration exceeded 0.1 g l⁻¹. The binding of lead followed Freundlich model of kinetics where as zinc supported Langmuir isotherm for adsorption with their r ² values of 0.9659 and 0.8723 respectively. The adsorption was strongly pH dependent as the maximum lead biosorption occurred at pH 4 and 10 whereas Zn²⁺ adsorption was at pH 8 and 10.     

Iron and cadmium uptake by duodenum of hypotransferrinaemic mice

Absorption from food is an important route for entry of the toxic metal, cadmium, into the body. Both cadmium and iron are believed to be taken up by duodenal enterocytes via the iron regulated, proton-coupled transporter, DMT1. This means that cadmium uptake could be enhanced in conditions where iron absorption is increased. We measured pH dependent uptake of ¹⁰⁹Cd and ⁵⁹Fe by duodenum from mice with an in vitro method. Mice with experimental (hypoxia, iron deficiency) or hereditary (hypotransferrinaemia) increased iron absorption were studied. All three groups of mice showed increased ⁵⁹Fe uptake (p<0.05) compared to their respective controls. Hypotransferrinaemic and iron deficient mice exhibited an increase in ¹⁰⁹Cd uptake (p<0.05). Cadmium uptake was not, however, increased by lowering the medium pH from 7.4 to 6. In contrast, ⁵⁹Fe uptake (from ⁵⁹FeNTA₂) and ferric reductase activity was increased by lowering medium pH in control and iron deficient mice (p<0.05). The data show that duodenal cadmium uptake can be increased by hereditary iron overload conditions. The uptake is not, however, altered by lowering medium pH suggesting that DMT1-independent uptake pathways may operate.     

The recovery of heavy metals using encapsulated microbial cells

We prepared capsules containingSaccharomyces cerevisiae andZoogloea ramigera cells for the removal of lead (II) and cadmium ions. Microbial cells were encapsulated and cultured in the growth medium. TheS. cerevisiae cells grown in the capsule did not leak through the capsule membrane. The dried cell density reached to 250 g/l on the basis of the inner volume of the 2.0 mm diameter capsule after 36 hour cultivation. The dry whole cell exopolymer density of encapsulatedZ. ramigera reached to 200 g/L. The capsule was crosslinked with triethylene tetramine and glutaric dialdehyde solutions. The cadmium uptake of encapsulated whole cell exopolymer ofZ. ramigera was 55 mg Cd/g biosorbent. The adsorption line followed well Langmuir isotherm. The lead uptake of the encapsulatedS. cerevisiae was about 30 mg Pb/g biomass. The optimum pH of the lead uptake using encapsulatedS. cerevisiae was found to be 6. Freundlich model showed a little better fit to the adsorption data than Langmuir model. 95 percent of the lead adsorbed on the encapsulated biosorbents was desorbed by the 1 M HCl solution. The capsule was reused 50 batches without loosing the metal uptake capacity. And the mechanical strength of the crosslinked capsule was retained after 50 trials.     

Accumulation of zinc and cadmium by Cytophaga johnsonae

Passive and active accumulation of zinc and cadmium by a common soil and freshwater bacterium, Cytophaga johnsonae, was studied using a radio-tracer batch distribution technique. The effects of variation of pH (3–10), as well as of ionic strength (0.007 and 0.07 m) on passive accumulation of the metals were examined. For both zinc and cadmium, accumulation was mainly due to passive processes, such as surface adsorption and/or diffusion into the periplasm. However, at low zinc concentrations, accumulation increased when glucose was added, suggesting an active uptake; at higher zinc concentrations such uptake was not detected, probably because it was masked by the stronger sorption properties of the cell wall. Adsorption of the metals was pH dependent: at higher ionic strength, accumulation was enhanced at pH values above 7; at lower ionic strength, adsorption differed and was markedly higher, with increased accumulation between pH 5 and 8.     

Biosorption of uranium by Myxococcus xanthus

This paper deals with uranium biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 2.4 mM of uranium g⁻¹, is demonstrated to be a more efficient biosorbent than wet biomass. For uranium concentrations of 0.1–0.3 mM, between 95.79% and 95.99% of the uranium was taken up from the solution. Dry biomass biosorption was found to be relatively rapid, reaching equilibrium after 5–10 min. In addition, the pH influenced biosorption, pH 4.5 promoting maximum uptake. It was also established that the biosorbed uranium is located on the cellular wall and within the extracellular mucopolysaccharide of this microorganism. Furthermore, using sodium carbonate as a desorbent agent, 80.82% of the biosorbed uranium could be recovered. The results obtained indicate the possible utilization of M. xanthus biomass to solve some problems of the water contaminated by uranium.     

Implication of distinct proteins in cadmium uptake and transport by intestinal cells HT-29

The mechanisms of intestinal absorption have not been clearly elucidated for cadmium, a toxic metal. In this work, we show the implication of distinct proteins in cadmium transport, and the transport step where these proteins are involved. We first validated the HT-29 model by evaluating nontoxic doses of cadmium (ranging from 1 to 20 μmol/L), and by quantifying metal uptake and transepithelial transport. The time-course of 1 μmol/L cadmium uptake at pH 7.5 showed three steps: a rapid one during the first 4 min, probably due to cadmium binding to the membrane; a slower one, characterized by K _m of 1.65±0.54 μmol/L and V _max of 3.9±0.3 pmol/min per mg protein; and a third, corresponding to slow accumulation that was not equilibrated even after 48 h of cadmium exposure. Intracellular metallothionein content following 1 or 5 μmol/L cadmium exposure showed a significant increase after 6 h of exposure, and was not equilibrated even after 72 h, allowing cadmium accumulation. After 24 h of exposure, metallothionein content was 5-fold, 14-fold, 26-fold, and 50-fold, respectively, for cells grown in the presence of 1, 5, 10, and 20 μmol/L cadmium, compared to control cells. The second step of uptake, characterized by carrier-mediated transport, was markedly increased at pH 5.5, compared to pH 7.5, and strongly inhibited by the metabolic inhibitor dinitrophenol. Moreover Nramp2 transporter cDNA was present in HT-29 cells. These data suggest the involvement of a proton-coupled transporter, which may be the divalent cation transporter Nramp2 (natural resistance-associated macrophage protein 2). Cadmium uptake was also inhibited by copper, zinc, and para-chloromercuribenzenesulfonate (pCMBS), but not by verapamil or ouabain. Taken together, our results indicate that cadmium could enter HT-29 cell by Nramp2 proton-coupled active transport and by diffusion, and accumulates in the cell as long as it binds to metallothionein. Cadmium toxicity could depend partly on the activity of Nramp2, and partly on metallothionein content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biosorption of Cr, Cu and Al bySargassum biomass

The biosorption and desorption of Cr, Cu and Al were carried out using brown marine algaeSargassum fluitans biomass, known as the good biosorbent of heavy metals. The content of alginate bound to light metals could be changed by physical and chemical pretreatment. The maximum uptake of Cr, Cu and Al was independent of the alginate content. The maximum uptake of Al was two times(mole basis) than those of Cu and Cr. The aluminum-alginate complex was found in the sorption solution of raw and protonated biomass. Most of Cu, Al and light metals sorbed in the biomass were eluted at pH 1.1. However, only 5 to 10% of Cr sorbed was eluted at pH 1.1. The stoichometric ion exchange between Cu and Ca ion was observed on Cu biosorption with Ca-loaded biomass. A part of Cr ion was bound to biomass as Cr(OH)₂ ⁺ or Cr(OH)²⁺. Al was also bound to biomass as multi-valence ion and interfered with the desorbed Ca ion. The behavior of rawS. fluitans in ten consecutive sorption-desorption cycles has been investigated in a packed bed flow-through-column during a continuous removal of copper from a 35 mg/L aqueous solution at pH 5. The eluant used was a 1%(w/v) CaCl/HCl solution at pH3.     

Cadmium adsorption by the non-living biomass of microalgae grown in axenic mass culture

The freeze-dried (extracted and non-extracted) biomass of 15 microalgal species grown in axenic mass culture and belonging to the Cyanobacteria, Chloro-, Eustigmato-, Phaeo-, Rhodo- and Tribophyceae were investigated for their ability to adsorb cadmium (Cd) ions from aqueous solutions. For comparison, other standard adsorbing materials (activated carbon, silica gel, siliceous earth) were included in the studies. The biomass of 11 microalgae exhibited a higher Cd adsorption than the standard materials. Extraction of the algal biomass increased the Cd adsorption capability of some, but not all microalgae. High Cd adsorption was found inAnabaena lutea, Nodularia harveyana, andNostoc commune (Cyanobacteria),Chlamydomonas sp. (Chlorophyceae),Bumilleriopsis filiformis (Tribophyceae), and inEctocarpus siliculosus, Halopteris scoparia andSpermatochnus paradoxus (Phaeophyceae). The specific surface (m² cm^–3) of the various microalgae was determined by means of laser diffractometry.Anabaena inaequalis andA. lutea (Cyanobacteria) and the Phaeophyceae had especially high Cd adsorption per surface unit. Most of the Cd adsorbed to these various materials could be desorbed subsequently with diluted mineral acid (pH 2).