Use of Algae for Removing Heavy Metal Ions From Wastewater: Progress and Prospects

Addressing the challenges for sustainable production of algal biofuels: I. Algal strains and nutrient supply

Microalgae hold promise for the production of sustainable replacement of fossil fuels due to their high growth rates, ability to grow on non-arable land and their high content, under the proper conditions, of high energy compounds that can be relatively easily chemically converted to fuels using existing technology. However, projected large-scale algal production raises a number of sustainability concerns concerning land use, net energy return, water use and nutrient supply. The state-of-the-art of algal production of biofuels is presented with emphasis on some possible avenues to provide answers to the sustainability questions that have been raised. Here, issues concerning algal strains and supply of nutrients for large-scale production are discussed. Since sustainability concerns necessitate the use of wastewaters for supply of bulk nutrients, emphasis is placed on the composition and suitability of different wastewater streams. At the same time, algal cultivation has proven useful in waste treatment processes, and thus this aspect is also treated in some detail.

Selecting reliable and robust freshwater macroalgae for biomass applications

Intensive cultivation of freshwater macroalgae is likely to increase with the development of an algal biofuels industry and algal bioremediation. However, target freshwater macroalgae species suitable for large-scale intensive cultivation have not yet been identified. Therefore, as a first step to identifying target species, we compared the productivity, growth and biochemical composition of three species representative of key freshwater macroalgae genera across a range of cultivation conditions. We then selected a primary target species and assessed its competitive ability against other species over a range of stocking densities. Oedogonium had the highest productivity (8.0 g ash free dry weight m⁻² day⁻¹), lowest ash content (3–8%), lowest water content (fresh weigh: dry weight ratio of 3.4), highest carbon content (45%) and highest bioenergy potential (higher heating value 20 MJ/kg) compared to Cladophora and Spirogyra. The higher productivity of Oedogonium relative to Cladophora and Spirogyra was consistent when algae were cultured with and without the addition of CO₂ across three aeration treatments. Therefore, Oedogonium was selected as our primary target species. The competitive ability of Oedogonium was assessed by growing it in bi-cultures and polycultures with Cladophora and Spirogyra over a range of stocking densities. Cultures were initially stocked with equal proportions of each species, but after three weeks of growth the proportion of Oedogonium had increased to at least 96% (±7 S.E.) in Oedogonium-Spirogyra bi-cultures, 86% (±16 S.E.) in Oedogonium-Cladophora bi-cultures and 82% (±18 S.E.) in polycultures. The high productivity, bioenergy potential and competitive dominance of Oedogonium make this species an ideal freshwater macroalgal target for large-scale production and a valuable biomass source for bioenergy applications. These results demonstrate that freshwater macroalgae are thus far an under-utilised feedstock with much potential for biomass applications.

The Genus Cladophora Kützing (Ulvophyceae) as a Globally Distributed Ecological Engineer

The green algal genus Cladophora forms conspicuous nearshore populations in marine and freshwaters worldwide, commonly dominating peri-phyton communities. As the result of human activities, including the nutrient pollution of nearshore waters, Cladophora-dominated periphyton can form nuisance blooms. On the other hand, Cladophora has ecological functions that are beneficial, but less well appreciated. For example, Cladophora has previously been characterized as an ecological engineer because its complex structure fosters functional and taxonomic diversity of benthic microfauna. Here, we review classic and recent literature concerning taxonomy, cell biology, morphology, reproductive biology, and ecology of the genus Cladophora, to examine how this alga functions to modify habitats and influence littoral biogeochemistry. We review the evidence that Cladophora supports large, diverse populations of microalgal and bacterial epiphytes that influence the cycling of carbon and other key elements, and that the high production of cellulose and hydrocarbons by Cladophora-dominated periphyton has the potential for diverse technological applications, including wastewater remediation coupled to renewable biofuel production. We postulate that well-known aspects of Cladophora morphology, hydrodynamically stable and perennial holdfasts, distinctively branched architecture, unusually large cell and sporangial size and robust cell wall construction, are major factors contributing to the multiple roles of this organism as an ecological engineer.

Synthesising acid mine drainage to maintain and exploit indigenous mining micro-algae and microbial assemblies for biotreatment investigations

The stringent regulations for discharging acid mine drainage (AMD) has led to increased attention on traditional or emerging treatment technologies to establish efficient and sustainable management for mine effluents. To assess new technologies, laboratory investigations on AMD treatment are necessary requiring a consistent supply of AMD with a stable composition, thus limiting environmental variability and uncertainty during controlled experiments. Additionally, biotreatment systems using live cells, particularly micro-algae, require appropriate nutrient availability. Synthetic AMD (Syn-AMD) meets these requirements. However, to date, most of the reported Syn-AMDs are composed of only a few selected heavy metals without considering the complexity of actual AMD. In this study, AMD was synthesised based on the typical AMD characteristics from a copper mine where biotreatment is being considered using indigenous AMD algal-microbes. Major cations (Ca, Na, Cu, Zn, Mg, Mn and Ni), trace metals (Al, Fe, Ag, Na, Co, Mo, Pb and Cr), essential nutrients (N, P and C) and high SO(4) were incorporated into the Syn-AMD. This paper presents the preparation of chemically complex Syn-AMD and the challenges associated with combining metal salts of varying solubility that is not restricted to one particular mine site. The general approach reported and the particular reagents used can produce alternative Syn-AMD with varying compositions. The successful growth of indigenous AMD algal-microbes in the Syn-AMD demonstrated its applicability as appropriate generic media for cultivation and maintenance of mining microorganisms for future biotreatment studies.

Sorption of Pb(II) onto a mixture of algae waste biomass and anion exchanger resin in a packed-bed column

Sorption of Pb(II) was studied by using a biosorbent mixture of algae waste biomass and Purolite A-100 resin in a packed-bed column. Mixing these two components was done to prevent the clogging of the column and to ensure adequate flow rates. Increasing of solution flow rate and initial Pb(II) concentration make that the breakthrough and saturation points to be attained earlier. The experimental breakthrough curves were modeled using Bohart-Adams, Thomas and Yoon-Nelson models, and the parameters for all these models were calculated. A regeneration efficiency of 98% was achieved using 0.1 mol L(-1) HCl and not significant changes in lead uptake capacity after three biosorption/desorption cycles were noted. The biosorbent mixture was able to remove Pb(II) from synthetic wastewater at pH 5.0 and flow rate of 3.5 mL min(-1), and the obtained effluent has better quality characteristics. The biosorbent mixture it is suitable for a continuous system for large-scale applications.

Phycoremediation of lead and cadmium by employing Nostoc muscorum as biosorbent and optimization of its biosorption potential

The present study reports the influence of different factors on the sorption of Pb and Cd by Nostoc muscorum. The results showed that extent of Pb and Cd removal by N. muscorum cells increased with increasing biosorbent dose, but exhibited decline in the adsorption capacity. The maximum sorption of Cd (85.2%) and Pb (93.3%) was achieved at 60 and 80 microg/ml concentrations of respective metal, within 30 and 15 min, respectively. The result revealed that optimum biosorption of Pb and Cd occurred at pH 5 and 6, respectively, at 40 degrees C temperature. Presence of binary metals (both Pb and Cd) in a solution showed that the presence of one metal ion resulted into decreased sorption of other metal ion. The presence of Ca and EDTA showed significant decrease in the sorption of Pb and Cd, while other anions and cations did not show significant effect on the biosorption of both the metals. Maximum desorption of Pb and Cd was achieved in the presence of EDTA and HNO3, respectively. Results also showed that the test biosorbent could be repeatedly used up to six biosorption/desorption cycles without significant loss of its initial metal adsorption capacity.

Chemically Modified Lagenaria vulgaris as a Biosorbent for the Removal of CuII from Water

The ability of a biosorbent based on a chemically modified Lagenaria vulgaris shell for CuII ion removal from aqueous solution was studied in batch conditions. The biosorbent was characterized by Fourier-transform infrared spectroscopy and the effect of relevant parameters such as contact time, pH, biomass dosage, and initial metal ion concentration was evaluated. The sorption process was found to be fast, attaining equilibrium within 40 min, and results were found to be best fitted by a pseudo-second order kinetic model. Experimental data showed that the biosorption is highly pH dependent, and the optimal pH was 5.0. Results were analyzed in terms of the following adsorption isotherms: Langmuir, Freundlich, Temkin, and Flory–Huggins, by a linear regression method. The CuII biosorption followed the Langmuir isotherm model (r2 = 0.998) with the maximum sorption capacity of 14.95 mg g–1. The methyl-sulfonated Lagenaria vulgaris biomass investigated in this study exhibited a high potential for the removal of CuII from aqueous solution.

Variation in patterns of metal accumulation in thallus parts of Lessonia trabeculata (Laminariales; Phaeophyceae): implications for biomonitoring

Seaweeds are well known to concentrate metals from seawater and have been employed as monitors of metal pollution in coastal waters and estuaries. However, research showing that various intrinsic and extrinsic factors can influence metal accumulation, raises doubts about the basis for using seaweeds in biomonitoring programmes. The thallus of brown seaweeds of the order Laminariales (kelps) is morphologically complex but there is limited information about the variation in metal accumulation between the different parts, which might result in erroneous conclusions being drawn if not accounted for in the biomonitoring protocol. To assess patterns of individual metals in the differentiated parts of the thallus (blade, stipe, holdfast), concentrations of a wide range of essential and non-essential metals (Fe, Cr, Cu, Zn, Mn, Pb, Cd, Ni and Al) were measured in the kelp Lessonia trabeculata. Seaweeds were collected from three sampling stations located at 5, 30 and 60 m from an illegal sewage outfall close to Ventanas, Chile and from a pristine location at Faro Curaumilla. For the majority of metals the highest concentrations in bottom sediment and seaweed samples were found at the site closest to the outfall, with concentrations decreasing with distance from the outfall and at control stations; the exception was Cd, concentrations of which were higher at control stations. The patterns of metal concentrations in different thallus parts were metal specific and independent of sampling station. These results and the available literature suggest that biomonitoring of metals using seaweeds must take account of differences in the accumulation of metals in thallus parts of complex seaweeds.

Biofilm establishment and heavy metal removal capacity of an indigenous mining algal-microbial consortium in a photo-rotating biological contactor

An indigenous mining algal-microbial consortium was immobilised within a laboratory-scale photo-rotating biological contactor (PRBC) that was used to investigate the potential for heavy metal removal from acid mine drainage (AMD). The microbial consortium, dominated by Ulothrix sp., was collected from the AMD at the Sar Cheshmeh copper mine in Iran. This paper discusses the parameters required to establish an algal-microbial biofilm used for heavy metal removal, including nutrient requirements and rotational speed. The PRBC was tested using synthesised AMD with the multi-ion and acidic composition of wastewater (containing 18 elements, and with a pH of 3.5 ± 0.5), from which the microbial consortium was collected. The biofilm was successfully developed on the PRBC’s disc consortium over 60 days of batch-mode operation. The PRBC was then run continuously with a 24 h hydraulic residence time (HRT) over a ten-week period. Water analysis, performed on a weekly basis, demonstrated the ability of the algal-microbial biofilm to remove 20–50 % of the various metals in the order Cu > Ni > Mn > Zn > Sb > Se > Co > Al. These results clearly indicate the significant potential for indigenous AMD microorganisms to be exploited within a PRBC for AMD treatment.

Growth, composition and metal removal potential of a Phormidium bigranulatum-dominated mat at elevated levels of cadmium

Prompted by the fact that interaction of metals with cyanobacterial mats has been little studied, the present study evaluates the response of a cyanobacterial mat, dominated by Phormidium bigranulatum, to elevated concentrations of Cd²⁺ in the medium. The mat failed to grow at 7 μM of Cd²⁺ when the metal as also the mat inoculum were simultaneously added to the medium right in the beginning of the experiment due to marked sensitivity of P. bigranulatum, the main constituent of the mat, to high concentrations of Cd²⁺. However, the mat previously grown in Cd²⁺-free medium for a time period of 1-4 weeks grew successfully when exposed to media containing very high concentrations of Cd²⁺. Four-week-old mat could grow at 250 μM of Cd²⁺, which has been found toxic to many cyanobacteria and algae by previous researchers. Greater tolerance of older mats to Cd²⁺ may be due to greater proportion of exopolysaccharides, which are well known to sequester metal ions extracellularly, in them. Whereas the relative proportion of P. bigranulatum declined at high concentrations of the test metal that of green algae increased due most likely to their tolerance to Cd²⁺. Air bubbles were seen entrapped in the mat due obviously to photosynthetic activity. Elevated concentrations of Cd²⁺ reduced the number of air bubbles in the mat. Decline in number of air bubbles at high concentrations of metal ions was more prominent in the case of younger mat than in the older one. The present study also evaluated changes in species composition of mats of different age that were subsequently grown in Cd²⁺ enriched culture medium. Younger mats showed change in species composition at very low concentrations of Cd²⁺, but older mats showed little changes even at very high concentrations of the test metal. Hence older mats more strongly resisted to changes in its species composition than the younger ones upon exposure to high concentrations of Cd²⁺. The growing mat successfully removed Cd²⁺ from the medium, which was greater at lower concentrations of Cd²⁺ in the external environment.

Influence of growth phase on harvesting of Chlorella zofingiensis by dissolved air flotation

The effects of changes in cellular characteristics and dissolved organic matter (DOM) on dissolved air flotation (DAF) harvesting of Chlorella zofingiensis at the different growth phases were studied. Harvesting efficiency increased with Al(3+) dosage and reached more than 90%, regardless of growth phases. In the absence of DOM, the ratio of Al(3+) dosage to surface functional group concentration determined the harvesting efficiency. DOM in the culture medium competed with algal cell surface functional groups for Al(3+), and more Al(3+) was required for cultures with DOM than for DOM-free cultures to achieve the same harvesting efficiency. As the culture aged, the increase of Al(3+) dosage due to increased DOM was less than the decrease of Al(3+) dosage associated with reduced cell surface functional groups, resulting in overall reduced demand for Al(3+). The interdependency of Al(3+) dosage and harvesting efficiency on concentrations of cell surface functional groups and DOM was successfully modeled.

Sustainable sources of biomass for bioremediation of heavy metals in waste water derived from coal-fired power generation

Biosorption of heavy metals using dried algal biomass has been extensively described but rarely implemented. We contend this is because available algal biomass is a valuable product with a ready market. Therefore, we considered an alternative and practical approach to algal bioremediation in which algae were cultured directly in the waste water stream. We cultured three species of algae with and without nutrient addition in water that was contaminated with heavy metals from an Ash Dam associated with coal-fired power generation and tested metal uptake and bioremediation potential. All species achieved high concentrations of heavy metals (to 8% dry mass). Two key elements, V and As, reached concentrations in the biomass of 1543 mg.kg⁻¹ DW and 137 mg.kg⁻¹ DW. Growth rates were reduced by more than half in neat Ash Dam water than when nutrients were supplied in excess. Growth rate and bioconcentration were positively correlated for most elements, but some elements (e.g. Cd, Zn) were concentrated more when growth rates were lower, indicating the potential to tailor bioremediation depending on the pollutant. The cosmopolitan nature of the macroalgae studied, and their ability to grow and concentrate a suite of heavy metals from industrial wastes, highlights a clear benefit in the practical application of waste water bioremediation.

Continuous metal removal from solution and industrial effluents using Spirogyra biomass-packed column reactor

The granules of Spirogyra neglecta biomass, diameter 0.2-0.5mm, were successfully prepared by boiling it in urea-formaldehyde mixture. Metal sorption performance of the column packed with Spirogyra granules was assessed under variable operating conditions, such as, different influent metal concentrations, bed heights and flow rates. These conditions greatly influenced the breakthrough time and volume, saturation time and volume, and the ability of the column to attain saturation after reaching the breakthrough. The experimental breakthrough curves obtained under varying experimental conditions were modeled using Bohart-Adams, Wolborska, Thomas, Yoon-Nelson and modified dose-response models. The first two models were valid only in representing the initial part of the breakthrough curves; however, the other three models were good in representing the entire breakthrough curve. The granule-packed column could be successfully used up to 6 and 9 cycles of sorption and desorption for the removal of Cu(II) and Pb(II), respectively. The column could efficiently remove different metals from real industrial effluents, and hence the test biomass (Spirogyra granules) is a good candidate for commercial application.

Modelling growth of, and removal of Zn and Hg by a wild microalgal consortium

Microorganisms isolated from sites contaminated with heavy metals usually possess a higher removal capacity than strains from regular cultures. Heavy metal-containing soil samples from an industrial dumpsite in Northern Portugal were accordingly collected; following enrichment under metal stress, a consortium of wild microalgae was obtained. Their ability to grow in the presence of, and their capacity to recover heavy metals was comprehensively studied; the datasets thus generated were fitted to by a combined model of biomass growth and metal uptake, derived from first principles. After exposure to 15 and 25 mg/L Zn(2+) for 6 days, the microalgal consortium reached similar, or higher cell density than the control; however, under 50 and 65 mg/L Zn(2+), 71% to 84% inhibition was observed. Growth in the presence of Hg(2+) was significantly inhibited, even at a concentration as low as 25 μg/L, and 90% inhibition was observed above 100 μg/L. The maximum amount of Zn(2+) removed was 21.3 mg/L, upon exposure to 25 mg/L for 6 day, whereas the maximum removal of Hg(2+) was 335 μg/L, upon 6 day in the presence of 350 μg/L. The aforementioned mechanistic model was built upon Monod assumptions (including heavy metal inhibition), coupled with Leudeking-Piret relationships between the rates of biomass growth and metal removal. The overall fits were good under all experimental conditions tested, thus conveying a useful tool for rational optimisation of microalga-mediated bioremediation.

Metal uptake by microalgae: underlying mechanisms and practical applications

Metal contamination of a few aquatic, atmospheric, and soil ecosystems has increased ever since the industrial revolution, owing to discharge of such elements via the effluents of some industrial facilities. Their presence to excessive levels in the environment will eventually lead to serious health problems in higher animals owing to accumulation throughout the food web. Current physicochemical methods available for recovery of metal pollutants (e.g., chemical precipitation, oxidation/reduction, or physical ion exchange) are either expensive or inefficient when they are present at very low concentrations. Consequently, removal of toxic metals by microorganisms has emerged as a potentially more economical alternative. Microalgae (in terms of both living and nonliving biomass) are an example of microorganisms suitable to recover metals and able to attain noteworthy percent removals. Their relatively high metal-binding capacities arise from the intrinsic composition of their cell walls, which contain negatively charged functional groups. Consequently, microalgal cells are particularly efficient in uptake of those contaminants when at low levels. Self-defense mechanisms developed by microalgal cells to survive in metal-containing media and environmental factors that affect their removal (e.g., pH, temperature, and biomass concentration) are reviewed here in a comprehensive way and further discussed in attempts to rationalize this form of remediation vis-a-vis with conventional nonbiological alternatives.

Biosorption of copper and zinc by immobilised and free algal biomass, and the effects of metal biosorption on the growth and cellular structure of Chlorella sp. and Chlamydomonas sp. isolated from rivers in Penang, Malaysia

In this study, the biosorption of copper and zinc ions by Chlorella sp. and Chlamydomonas sp. isolated from local environments in Malaysia was investigated in a batch system and by microscopic analyses. Under optimal biosorption conditions, the biosorption capacity of Chlorella sp. for copper and zinc ions was 33.4 and 28.5 mg/g, respectively, after 6 hr of biosorption in an immobilised system. Batch experiments showed that the biosorption capacity of algal biomass immobilised in the form of sodium alginate beads was higher than that of the free biomass. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses revealed that copper and zinc were mainly sorbed at the cell surface during biosorption. Exposure to 5 mg/L of copper and zinc affected both the chlorophyll content and cell count of the algal cells after the first 12 hr of contact time.

Removal of metal ions by Phormidium bigranulatum (cyanobacteria)-dominated mat in batch and continuous flow systems

Live Phormidium bigranulatum-dominated mat successfully removed Pb(II), Cu(II) and Cd(II) from aqueous solution. Percent metal removal approached equilibrium within 4h, independent of mat thickness (0.2-1.6 mm), in batch system. But % metal removal increased with increase in mat thickness due to enhancement of biomass, which provided more metal binding sites. Metal accumulation decreased with increase in mat thickness due to lessened metal availability vis-à-vis biomass. Metal removal (%) increased with increasing mat area, but decreased with increasing metal concentration in the solution. In continuous flow system, metal accumulation increased with increasing volume of single or multi-metal solution passed over the mat. The mat removed all the tested metals from the multi-metal solution with almost the same efficiency. The maximum removal of the test metals occurred at the lowest tested flow rate. Raceway type ponds can be employed for large-scale use of Phormidium mat in bioremediation of metalliferous wastewaters.

Lead (Pb) in biota and perceptions of Pb exposure at a recently designated Superfund beach site in New Jersey

The Raritan Bay Slag Site (New Jersey) was designated a Superfund site in 2009 because the seawall, jetties, and sediment contained lead (Pb). Our objective was to compare Pb and mercury (Hg) levels in biota and public perceptions of exposure at the Superfund and reference sites. Samples (algae, invertebrates, fish) were collected from the Raritan Bay Slag Site and reference sites and analyzed for Pb and Hg. Waterfront users were interviewed using a standard questionnaire. Levels of Pb in aquatic organisms were compared to ecological and human health safety standards. Lead levels were related to location, trophic level, and mobility. Lead levels in biota were highest at the western side of the West Jetty. Mean Pb levels were highest for algae (Fucus = 53,600 ± 6990 ng/g = ppb [wet weight], Ulva = 23,900 ± 2430 ppb), intermediate for grass shrimp (7270 ± 1300 ppb, 11,600 ± 3340 ppb), and lowest for fish (Atlantic silversides 218 ± 44 ppb). Within species, Pb levels varied significantly across the sampling sites. Lead levels in algae, sometimes ingested by individuals, were sufficiently high to exceed human safety levels. Mercury levels did not differ between the Superfund and reference sites. Despite the fence and warnings, people (1) used the Superfund and reference sites similarly, (2) had similar fish consumption rates, and (3) were not concerned about Pb, although most individuals knew the metal was present. The fish sampled posed no apparent risk for human consumers, but the algae did.

Sorption and desorption of Cd, Cu and Pb using biomass from an eutrophized habitat in monometallic and bimetallic systems

This work examines the sorption capacity of a natural biomass collected from an irrigation pond. The biomass mainly consisted of a mixture of chlorophyte algae with caducipholic plants. Biosorption experiments were performed in monometallic and bimetallic solutions containing different metals commonly found in industrial effluents (Cd, Cu and Pb). The biosorption process was slightly slower in the binary system comparing with monometallic system which was related to competition phenomena between metal cations in solution. The biosorbent behaviour was quantified by the sorption isotherms fitting the experimental data to mathematical models. In monometallic systems, the Langmuir model showed a better fit with the following sorption order: Cu ~ Pb > Cd; and biomass-metal affinity order: Pb > Cd ~ Cu. In bimetallic systems, the binary-type Langmuir model was used and the sorption order obtained was: Pb ~ Cu > Cd. In addition, the effectiveness of the biomass was investigated in several sorption-desorption cycles using HCl and NaHCO(3). The recovery of metal was higher with HCl than with NaHCO(3), though the sorption uptake of the biomass was sensitively affected by the former desorption agent in subsequent sorption cycles.

Removal of mercury from sediment by ultrasound combined with biomass (transgenic Chlamydomonas reinhardtii)

As one of the most pervasive environmental problems, Hg pollution in sediment is particularly difficult to remediate because it cannot be decomposed. The application of ultrasound combined with biomass (transgenic Chlamydomonas reinhardtii (C. reinhardtii), a green alga) for the removal of Hg from model and contaminated sediments (Al(2)O(3), α-HgS, and PACS-2 marine sediment) was investigated in this study. Ultrasound was found to enhance Hg release from Al(2)O(3), α-HgS, and PACS-2 marine sediment into the aqueous phase compared to mechanical shaking. A transgenic C. reinhardtii (2AMT-2) expressing a plasmamembrane-anchored metallothionein polymer effectively recovered Hg(II) released into the aqueous phase by sonication over a broad pH range from 2.0 to 9.0. The results showed that this combined technique of ultrasound and alga biomass (2AMT-2) engineered for enhanced metal recovery was effective to remove Hg from solids and sediments, especially from Al(2)O(3) and α-HgS with no natural organic matter. The results of this study are discussed with respect to the development of in situ remediation techniques for Hg-contaminated sediments.

The biosorption of heavy metals from aqueous solution by Spirogyra and Cladophora filamentous macroalgae

The aim of this research was to develop a low cost adsorbent for wastewater treatment. The prime objective of this study was to search for suitable freshwater filamentous algae that have a high heavy metal ion removal capability. This study evaluated the biosorption capacity from aqueous solutions of the green algae species, Spirogyra and Cladophora, for lead (Pb(II)) and copper (Cu(II)). In comparing the analysis of the Langmuir and Freundlich isotherm models, the adsorption of Pb(II) and Cu(II) by these two types of biosorbents showed a better fit with the Langmuir isotherm model. In the adsorption of heavy metal ions by these two types of biosorbents, chemical and physical adsorption of particle surfaces was perhaps more significant than diffusion and adsorption between particles. Continuous adsorption-desorption experiments discovered that both types of biomass were excellent biosorbents with potential for further development.

Accumulation of lead by free and immobilized cyanobacteria with special reference to accumulation factor and recovery

Lead accumulation by free and immobilized cyanobacteria, Lyngbya majuscula and Spirulina subsalsa was studied. Exponentially growing biomass was exposed to 1-20mg L(-1) of Pb(II) solution at pH 6, 7 and 8 for time periods ranging from 10 min to 48 h. L. majuscula accumulated 10 times more Pb (13.5 mg g(-1)) than S. subsalsa (1.32 mg g(-1)) at pH 6 within 3h of exposure to 20mg L(-1) Pb(II) solution and 76% of the Pb could be recovered using 0.1M EDTA. This chelator (2 μM) did not influence Pb accumulation whereas 100 μM citrate increased that of S. subsalsa 6- to 8-fold. L. majuscula filaments enmeshed in a glass wool packed in a column removed 95.8% of the Pb from a 5mg L(-1) Pb solution compared to free and dead biomass which removed 64 and 33.6% Pb respectively. A 92.5% recovery of accumulated Pb from the immobilized biomass suggests that repeated absorption-desorption is possible.

Preparation and characterization of chitosan encapsulated Sargassum sp. biosorbent for nickel ions sorption

A new biosorbent -Sargassum sp. encapsulated with epichlorohydrin (ECH) cross-linked chitosan (CS) was investigated for nickel ions removal. The prepared biosorbent with Sargassum sp. to cross-linked chitosan of 3 (weight ratio) had the highest sorption capacity. The biosorption kinetics can be well fitted by the diffusion-controlled model. The organic leaching of CS was 77-88% less than that of algae at different pH. The biosorption capacity of nickel on CS was much higher than that of cross-linked chitosan (CLC) bead and lower than that of raw algae due to encapsulation. In addition, the reusability of CS was further evaluated and confirmed through five adsorption-desorption cycles. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the nickel ions sequestration mechanism included ion exchange and nickel complexation with the carboxyl, amino, alcoholic and ether groups in CS.

Metal biosorption by two cyanobacterial mats in relation to pH, biomass concentration, pretreatment and reuse

The pH-dependent metal sorption by Oscillatoria- and Phormidium-dominated mats was effectively expressed by the Hill function. The estimated Hill functions can fruitfully predict the amount of metal sorbed at a particular initial pH. Pretreatment of biomass with 0.1 mmol L(-1) HCl was more effective than pretreatment with CaCl(2), HNO(3), NaOH, and SDS in enhancing metal sorption ability of the biomass. Desorption of metal ions in the presence of 100 mmol L(-1) HCl from metal-loaded mat biomass was completed within 1 h. After six cycles of metal sorption/desorption, sorption decreased by 6-15%. Only 6% and 11% of the biomass derived from the Oscillatoria sp.- and Phormidium sp.-dominated mats was lost during the cycling. The cyanobacterial mats seem to have better potential than several biomass types for use in metal sorption from wastewaters as they are ubiquitous, self-immobilized, and have good reusability.

Effect of nutrients on the biodegradation of tributyltin (TBT) by alginate immobilized microalga, Chlorella vulgaris, in natural river water

The removal and degradation of tributyltin (TBT) by alginate immobilized Chlorella vulgaris has been evidenced in our previously published work. The present study was further to investigate the effect of spiked nutrient concentrations on the TBT removal capacity and degradation in the same alginate immobilized C. vulgaris. During the 14-d experiment, compared to the control (natural river water), the spiked nutrient groups (50% or 100% nutrients of the commercial Bristol medium as the reference, marked as 1/2N or 1N) showed more rapid cell proliferation of microalgae and higher TBT removal rate. Moreover, significantly more TBT was adsorbed onto the alginate matrix, but less TBT was taken up by the algal cells of the nutrient groups than that of the control. Mass balance data showed that TBT was lost as inorganic tin in the highest degree in 1N group, followed by 1/2N group and the least was in the control, but the relative abundance of the intermediate products of debutylation (dibutyltin and monobutyltin) were comparable among three groups. In conclusion, the addition of nutrients in contaminated water stimulated the growth and physiological activity of C. vulgaris immobilized in alginate beads and improved its TBT degradation efficiency.

Biosorption of Pb and Zn by Non-Living Biomass of Spirulina sp

Removal of heavy metals (Pb(2+), Zn(2+)) 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 Pb(2+) and Zn(2+) 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 Zn(2+) adsorption was at pH 8 and 10.

Improvement of metal adsorption onto chitosan/Sargassum sp. composite sorbent by an innovative ion-imprint technology

Technology for immobilization of biomass has attracted a great interest due to the high sorption capacity of biomass for sequestration of toxic metals from industrial effluents. However, the currently practiced immobilization methods normally reduce the metal sorption capacities. In this study, an innovative ion-imprint technology was developed to overcome the drawback. Copper ion was first imprinted onto the functional groups of chitosan that formed a pellet-typed sorbent through the granulation with Sargassum sp.; the imprinted copper ion was chemically detached from the sorbent, leading to the formation of a novel copper ion-imprinted chitosan/Sargassum sp. (CICS) composite adsorbent. The copper sorption on CICS was found to be highly pH-dependent and the maximum uptake capacity was achieved at pH 4.7-5.5. The adsorption isotherm study showed the maximum sorption capacity of CICS of 1.08 mmol/g, much higher than the non-imprinted chitosan/Sargassum sp. sorbent (NICS) (0.49 mmol/g). The used sorbent was reusable after being regenerated through desorption. The FTIR and XPS studies revealed that the greater sorption of heavy metal was attributed to the large number of primary amine groups available on the surfaces of the ion-imprinted chitosan and the abundant carboxyl groups on Sargassum sp. Finally, an intraparticle surface diffusion controlled model well described the sorption history of the sorbents.

Chemical reaction- and particle diffusion-based kinetic modeling of metal biosorption by a Phormidium sp.-dominated cyanobacterial mat

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r2=0.932-0.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the kinetics of metal biosorption due either to prefixed order or unjustifiable change in rate constant and reaction order with varying concentrations of metal and biomass in the solution. The diffusion-based models, namely, the intra-particle diffusion model and the external mass transfer model fitted well to the time-course metal sorption data, thus suggesting involvement of both external and intra-particle diffusion processes in sorption of test metals by mat biomass. However, the Boyd kinetic expression clearly showed that the external mass transfer is the dominant process.

Patterned paper as a template for the delivery of reactants in the fabrication of planar materials

This account reviews the use of templates, fabricated by patterning paper, for the delivery of aqueous solutions of reactants (predominantly, ions) in the preparation of structured, thin materials (e.g., films of ionotropic hydrogels). In these methods, a patterned sheet of paper transfers an aqueous solution of reagent to a second phase-either solid or liquid-brought into contact with the template; this process can form solid structures with thicknesses that are typically ≤1.5 mm. The shape of the template and the pattern of a hydrophobic barrier on the paper control the shape of the product, in its plane, by restricting the delivery of the reagent in two dimensions. The concentration of the reagents, and the duration that the template remains in contact with the second phase, control growth in the third dimension (i.e., thickness). The method is especially useful in fabricating shaped films of ionotropic hydrogels (e.g., calcium alginate) by controlling the delivery of solutions of multivalent cations to solutions of anionic polymers. The templates can also be used to direct reactions that generate patterns of solid precipitates within sheets of paper. This review examines applications of the method for: (i) patterning bacteria in two dimensions within a hydrogel film, (ii) manipulating hydrogel films and sheets of paper magnetically, and (iii) generating dynamic 3-D structures (e.g., a cylinder of rising bubbles of O(2)) from sheets of paper with 2-D patterns of a catalyst (e.g., Pd(0)) immersed in appropriate reagents (e.g., 1% H(2)O(2) in water).

Immobilization of Rose Waste Biomass for Uptake of Pb(II) from Aqueous Solutions

Rosa centifolia and Rosa gruss an teplitz distillation waste biomass was immobilized using sodium alginate for Pb(II) uptake from aqueous solutions under varied experimental conditions. The maximum Pb(II) adsorption occurred at pH 5. Immobilized rose waste biomasses were modified physically and chemically to enhance Pb(II) removal. The Langmuir sorption isotherm and pseudo-second-order kinetic models fitted well to the adsorption data of Pb(II) by immobilized Rosa centifolia and Rosa gruss an teplitz. The adsorbed metal is recovered by treating immobilized biomass with different chemical reagents (H₂SO₄, HCl and H₃PO₄) and maximum Pb(II) recovered when treated with sulphuric acid (95.67%). The presence of cometals Na, Ca(II), Al(III), Cr(III), Cr(VI), and Cu(II), reduced Pb(II) adsorption on Rosa centifolia and Rosa gruss an teplitz waste biomass. It can be concluded from the results of the present study that rose waste can be effectively used for the uptake of Pb(II) from aqueous streams.

Evaluation of DNA extraction methods from complex phototrophic biofilms

Phototrophic biofilms are used in a variety of biotechnological and industrial processes. Understanding their structure, ie microbial composition, is a necessary step for understanding their function and, ultimately, for the success of their application. DNA analysis methods can be used to obtain information on the taxonomic composition and relative abundance of the biofilm members. The potential bias introduced by DNA extraction methods in the study of the diversity of a complex phototrophic sulfide-oxidizing biofilm was examined. The efficiency of eight different DNA extraction methods combining physical, mechanical and chemical procedures was assessed. Methods were compared in terms of extraction efficiency, measured by DNA quantification, and detectable diversity (16S rRNA genes recovered), evaluated by denaturing gradient gel electrophoresis (DGGE). Significant differences were found in DNA yields ranging from 116 +/- 12 to 1893 +/- 96 ng of DNA. The different DGGE fingerprints ranged from 7 to 12 bands. Methods including phenol-chloroform extraction after enzymatic lysis resulted in the greatest DNA yields and detectable diversity. Additionally, two methods showing similar yields and retrieved diversity were compared by cloning and sequencing. Clones belonging to members of the Alpha-, Beta- and Gamma- proteobacteria, Bacteroidetes, Cyanobacteria and to the Firmicutes were recovered from both libraries. However, when bead-beating was applied, clones belonging to the Deltaproteobacteria were also recovered, as well as plastid signatures. Phenol-chloroform extraction after bead-beating and enzymatic lysis was therefore considered to be the most suitable method for DNA extraction from such highly diverse phototrophic biofilms.

The role of periphyton in mediating the effects of pollution in a stream ecosystem

The effects of pollutants on primary producers ramify through ecosystems because primary producers provide food and structure for higher trophic levels and they mediate the biogeochemical cycling of nutrients and contaminants. Periphyton (attached algae) were studied as part of a long-term biological monitoring program designed to guide remediation efforts by the Department of Energy's Y-12 National Security Complex on East Fork Poplar Creek (EFPC) in Oak Ridge, Tennessee. High concentrations of nutrients entering EFPC were responsible for elevated periphyton production and placed the stream in a state of eutrophy. High rates of primary production at upstream locations in EFPC were associated with alterations in both invertebrate and fish communities. Grazers represented >50% of the biomass of invertebrates and fish near the Y-12 Complex but <10% at downstream and reference sites. An index of epilithic periphyton production accounted for 95% of the site-to-site variation in biomass of grazing fish. Analyses of heavy metals in EFPC periphyton showed that concentrations of zinc, cadmium, copper and nickel in periphyton decreased exponentially with distance downstream from Y-12. Zinc uptake by periphyton was estimated to reduce the concentration of this metal in stream water approximately 60% over a 5-km reach of EFPC. Management options for mitigating eutrophy in EFPC include additional reductions in nutrient inputs and/or allowing streamside trees to grow and shade the stream. However, reducing periphyton growth may lead to greater downstream transport of contaminants while simultaneously causing higher concentrations of mercury and PCBs in fish at upstream sites.

Quantitative study of Au(III) and Pd(II) ion biosorption on genetically engineered Tobacco mosaic virus

One major obstacle in the mineralization of metal onto biologically derived templates is the lack of fundamental information pertaining to the relationship between metal ion loading and overall metal deposition onto the biotemplate. This study focuses on Au(III) and Pd(II) biosorption on the genetically-modified model biological template Tobacco mosaic virus (TMV1Cys). Metal ion (Au(III) or Pd(II)) loading on the TMV1Cys template was measured as a function of the equilibrium concentration of Au(III) or Pd(II) ions in solution at several temperatures. In addition, the Pd(II) loading on the TMV-wild (wild-type TMV) and TMV1Cys were compared to estimate the improvement of metal ion loading by genetic modification of the biotemplate. The gold or palladium coatings on the TMV1Cys were prepared using various metal ion loadings. Results show, for a range of metal ion loadings, a positive correlation existed between the concentration of the metal ions and the coating density of the metals deposited on the virus surface.

Removal of Cadmium from aqueous solution by polysaccharide produced from Paenibacillus polymyxa

This paper deals with the removal of Cadmium from aqueous solutions by polysaccharide produced from Paenibacillus polymyxa. The effects of contact time, initial metal ions concentration, mass of the polysaccharide and pH were studied. The Freundlich and Dubinin-Radushkevich (D-R) models have been applied and the equilibrium adsorption was found to best fit the Dubinin-Radushkevich adsorption isotherm based on the coefficient of correlation, R(2). The maximum Cd(2+) uptake was 520.09 mg g(-1). An empirical modeling was performed by using a 2(3) full factorial design and a regression equation for adsorption of Cd(2+) was determined from the data. The pH and the initial concentration of Cadmium are the most significant parameters affecting Cd(2+) adsorption followed by the mass of the polysaccharide.