Towards sustainable development of microalgal biosorption for treating effluents containing heavy metals

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

Metabolism-dependent bioaccumulation of uranium by Rhodosporidium toruloides isolated from the flooding water of a former uranium mine

Remediation of former uranium mining sites represents one of the biggest challenges worldwide that have to be solved in this century. During the last years, the search of alternative strategies involving environmentally sustainable treatments has started. Bioremediation, the use of microorganisms to clean up polluted sites in the environment, is considered one the best alternative. By means of culture-dependent methods, we isolated an indigenous yeast strain, KS5 (Rhodosporidium toruloides), directly from the flooding water of a former uranium mining site and investigated its interactions with uranium. Our results highlight distinct adaptive mechanisms towards high uranium concentrations on the one hand, and complex interaction mechanisms on the other. The cells of the strain KS5 exhibit high a uranium tolerance, being able to grow at 6 mM, and also a high ability to accumulate this radionuclide (350 mg uranium/g dry biomass, 48 h). The removal of uranium by KS5 displays a temperature- and cell viability-dependent process, indicating that metabolic activity could be involved. By STEM (scanning transmission electron microscopy) investigations, we observed that uranium was removed by two mechanisms, active bioaccumulation and inactive biosorption. This study highlights the potential of KS5 as a representative of indigenous species within the flooding water of a former uranium mine, which may play a key role in bioremediation of uranium contaminated sites.This work was supported by the Bundesministerium für Bildung und Forschung grand nº 02NUK030F (TransAqua). Further support took place by the ERDF-co-financed Grants CGL2012-36505 and 315 CGL2014-59616R, Ministerio de Ciencia e Innovación, Spain

Biochemical and molecular mechanisms of plant-microbe-metal interactions: relevance for phytoremediation

Plants and microbes coexist or compete for survival and their cohesive interactions play a vital role in adapting to metalliferous environments, and can thus be explored to improve microbe-assisted phytoremediation. Plant root exudates are useful nutrient and energy sources for soil microorganisms, with whom they establish intricate communication systems. Some beneficial bacteria and fungi, acting as plant growth promoting microorganisms (PGPMs), may alleviate metal phytotoxicity and stimulate plant growth indirectly via the induction of defense mechanisms against phytopathogens, and/or directly through the solubilization of mineral nutrients (nitrogen, phosphate, potassium, iron, etc.), production of plant growth promoting substances (e.g., phytohormones), and secretion of specific enzymes (e.g., 1-aminocyclopropane-1-carboxylate deaminase). PGPM can also change metal bioavailability in soil through various mechanisms such as acidification, precipitation, chelation, complexation, and redox reactions. This review presents the recent advances and applications made hitherto in understanding the biochemical and molecular mechanisms of plant-microbe interactions and their role in the major processes involved in phytoremediation, such as heavy metal detoxification, mobilization, immobilization, transformation, transport, and distribution.info:eu-repo/semantics/publishedVersio

Removal of Arsenic (III) and Chromium (VI) from The Water Using Phytoremediation and Bioremediation Techniques

Advancement in science and technologies parallel to industrial revolution has opened new vistas to exploit the inherent traits of natural resources including green plants and microorganisms to overcome the damage to the environment by pollutants. The present work was aimed to develop the phytoremediation potential of the aquatic plant Eichhornia crassipes for arsenic (III) and chromium (VI) from water. The accumulation, relative growth and bio-concentration factor of plant on treatment with different concentrations of arsenic(III) and chromium(VI) solution significantly increased (P<0.05) with the passage of time. Plants treated with 0.100 mg/L arsenic (III) accumulated the highest concentration of arsenite in roots (7.20 mg kg-1, dry weight) and shoots (32.1 mg kg-1, dry weight); while those treated with 4.0 mg/L of chromium (VI) accumulated the highest concentration of hexavalent chromium in roots (1320 mg/kg, dry weight) and shoots (260 mg/kg, dry weight) after 15 days. The plant biomass was characterized by SEM, EDX, FTIR and XRD techniques. Microwave-assisted extraction efficiency is investigated for extraction of arsenic from plant materials by comparison of the results by three extractant solutions: (i) 10% (v/v) tetramethylammonium hydroxide (TMAH) (ii) Deionized water and (iii) Modified protein extracting solution at different temperature and times. Extraction of chromium ions was carried by same procedure from plant materials using three extractant solutions: (i) 0.02 M ethylenediaminetetraacetic acid (EDTA), (ii) Deionized water and (iii) HCl solution at different temperature and times. Chromatograms are obtained for arsenic and chromium species in plant shoot biomass by using HPLC-ICP-MS. The biosorption of arsenic (III) and chromium (VI) from water is studied by living cells of Bacillus cereus biomass as bioremediation. Bacillus cereus biomass is characterized, using SEM-EDX, AFM and FTIR. Dependence of biosorption was studied with variation of various parameters to achieve the optimum condition. The maximum biosorption capacity of living cells of Bacillus cereus for arsenic (III) and chromium (VI) was found to be 32.42 mg/g and 39.06 mg/g at pH 7.5, at optimum conditions of contact time of 30 min, biomass dosage of 6 g/L, and temperature of 30 ± 2°C. Biosorption data of arsenic (III) chromium (VI) are fitted to linearly transformed Langmuir isotherm and pseudo-second-order model with R2 (correlation vi vii coefficient) > 0.99. Thermodynamic parameters reveal the endothermic, spontaneous, and feasible nature of sorption process of arsenic (III) chromium (VI) onto Bacillus cereus biomass. The arsenic (III) and chromium (VI) ions are desorbed from Bacillus cereus using both 1M HCl and 1M HNO3. The biosorption data of both arsenic (III) and chromium (VI) ions collected from laboratory scale experimental set up is used to train a back propagation (BP) learning algorithm having 4-7-1 architecture. The model uses tangent sigmoid transfer function at input to hidden layer whereas a linear transfer function is used at output layer. The removal of chromium (VI) from aqueous solutions by activated carbon prepared from the Eichhornia crassipes root biomass. The maximum removal capacity of activated carbon was found to be 36.34 mg/g for chromium (VI), at pH 4.5, contact time of 30 min, biomass dosage of 7 g/L, and temperature of 25 ± 2 °C. The adsorption mechanisms of chromium (VI) ions onto activated carbon prepared from the Eichhornia crassipes root biomass are also evaluated in terms of thermodynamics, equilibrium isotherm and kinetics studies. Column studies are also performed to know the breakthrough point with an initial concentration of 10 mg/L

Cadmium resistant bacteria mediated cadmium removal: a systematic review on resistance, mechanism and bioremediation approaches

Cadmium-resistant bacteria that are used to remove cadmium (Cd) are becoming increasingly of the most important and hygienic method. Resistant mechanisms are involved in different ways, and some of them which can be used in cadmium removal techniques based on their molecular mechanisms and minimum inhibitory concentration (MIC). This review summarises recent improvements in understanding the mechanisms by which bacteria are either intrinsically resistant or acquire resistance to cadmium to be used as a way for cadmium removal

Novel bionanocatalysts for green chemistry applications

Desulfovibrio desulfuricans have been known to synthesize good catalysts in a number of industrially and environmentally relevant reactions but the underlying reasons and/or mechanisms for such catalysis have largely remained elusive. This study has shown that in addition to nanoparticle (NP) size, the catalytic properties of D. desulfuricans is hinged on several factors such as the textural surface of the bacterial support, binding mechanism to surface functional groups (amine, carboxyl, phosphoryl and sulfuryl groups) and the crystal structure of the resulting catalyst NPs. In this study, various characterization techniques: AFM, EDX, SEM, HAADF-STEM, HRTEM, XRD and XPS and catalytic hydrogenation of soybean oil. The concept of intracellular trafficking of palladium into the cells of both Gram-negative (Desulfovibrio desulfuricans) and Gram-positive (Bacillus benzeovorans) bacteria was pioneered against previously known extracellular NP deposition. The membrane integrity and membrane potentials of “palladized” cells (‘bio-Pd’) were found to be retained through flow cytometry analysis. Bio-supported bimetallic (bio-Pd/Pt) catalyst from D. desulfuricans and B. benzeovorans demonstrated comparable catalytic properties to a commercial catalyst (Ni-Mo/Al$_2$O$_3$) as a potential ‘green’ alternative. Generally, the extent of viscosity reduction was: 98.7% (thermal), 99.2% (bio-NPs) and 99.6% (Ni-Mo/Al$_2$O$_3$) below 1031 mPa.s of the feed heavy oil. Also the bimetallic bio-NPs produced an increment of ~2$^o$ in API (American petroleum institute) gravity (~9.1$^o$) than monometallic (~7.6$^o$) on average while the API gravity using thermal was lower (6.3$^o$) while that of a commercial catalyst was 11.1$^o$. Finally, the concept of tandem (one-pot) catalysis was pioneered as a potential platform for the remediation of chlorinated benzenes

Applications of Biosorption in Wastewater Treatment

This book examines the state of the art of biosorption as an economical and environmentally friendly technique for pollutant removal in wastewater. Several articles are included that develop the applications of biosorption showing the high efficiency and versatility of this process, as well as showing recent advances in this field. Different modalities of biosorption are demonstrated from free biomass to immobilized biomass, as well as the combination of biomass with modern materials to form composites, emphasizing the significant versatility of this technique. In addition, different examples with biomasses of very different natures are also included and discussed, as are the factors that influence biosorption processes. Other contributions offer some examples of apparently useless materials that are reused and applied in the elimination of pollutants. Therefore, this book is an excellent complement for those researchers who work on biosorption as well as a starting point for those who want to begin research on this topic

Möjligheter med odling av mikroalger för rening av bekämpningsmedelsrester i vatten

Every year, pesticides are found in surface and ground waters in Sweden. Fungicides are in common usage and applied in high amounts against potato late blight. The present thesis examined the possible removal of four fungicides (metalaxyl, cyprodinil, propamocarb and mandipropamid) from water using the microalgae Chlorella vulgaris. Microorganisms are capable of decomposing a range of organic pollutants and the main focus in previously published studies has been on bacteria and fungi. Microalgae are mostly studied due to their high capacity in biosorbing heavy metals. Removal of organic pollutants such as pesticides has been reported, however in fewer studies. The work was divided into two main experiments; one short-term experiment (60 min) using dead and living cells, and one long-term experiment (4 days) using growing cells. In the long-term experiment, the presence of growing algae resulted in around 50% lower propamocarb concentration in the medium compared with final concentration in the control without algae. In the short-term study, the presence of live algae cells led to a 30% reduction of propamocarb, compared to the concentration in the control. The main mechanism behind the reduction of propamocarb in the water phase is proposed to be biosorption onto the algal cells. This conclusion is based on the short duration required for removal to occur. For the other three studied fungicides no removal from the water phase by the algal treatments was observed.Varje år detekteras pesticidrester i yt- och grundvattnet i Sverige. Fungicider används i stor skala mot potatisbladmögel. Mikroorganismer är kapabla att bryta ner en rad olika organiska föroreningar och fokus på den här typen av studier har oftast legat på bakterier och svampar. När liknande studier gjorts på mikroalger har fokus legat på deras goda förmåga att biosorbera tungmetaller. Dock har rening av vatten från organiska föroreningar såsom pesticider rapporterats men dessa har varit få. Detta uppsatsarbete undersökte därför möjligheterna att minska mängden av fyra fungicider (metalaxyl, cyprodinil, propamocarb and mandipropamid) lösta i vatten med hjälp av mikroalgen Chlorella vulgaris. Uppsatsarbetet var uppdelat i två delar; ett korttids-experiment (60 min) med biomassa från levande och döda mikroalger, och ett långtids-experiment (4 dagar) med levande alger. I långtids-experimentet sjönk koncentrationen av propamocarb i lösningen med ca 50% i närvaro av levande alger jämfört med kontrollen där inga alger fanns närvarande. I korttids-experimentet minskade koncentrationen av propamocarb med ungefär 30% i närvaron av levande alger jämfört med kontrollen utan alger. Huvudorsaken till minskningen av propamocarbs beror troligtvis på biosorption som sker på algernas cellväggar. Denna slutsats har dragits baserat på den korta tidsperiod för under vilken minskningen av propamocarb sker. Ingen av de övriga tre fungiciderna minskade i koncentration på grund av mikroalgens närvaro