Simultaneous adsorption of chromate and arsenate onto ferrihydrite/alginate composite beads: Competition and mechanism.

Ferrihydrite is an effective adsorbent of chromate and arsenate. In order to gain insight into the application of ferrihydrite in water treatment, macroporous alginate/ferrihydrite beads, synthesized using two different methods (internal and encapsulation processes), were used in this work. The properties of the ferrihydrite were assessed using various techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) theory, and zetametry. The results showed that the specific surface area of the ferrihydrite was 242 m2/g, and the PZC was pH8. The kinetic and isotherm adsorption properties of the ferrihydrite were evaluated in this study. The results indicate that the pseudo second-order and Freundlich models accurately describe the kinetic and isotherm adsorption properties of chromates and arsenates. For chromate removal, ferrihydrite exhibited a relatively high adsorption capacity (40.7 mgCr/g) compared to other adsorbents. However, the arsenate adsorption capacity of MFHB-SI (140.8 mgAs/g) was shown to be the most optimal. The internal synthesis process was suitable for arsenate retention due to the resulting arsenate precipitation. The competitive adsorption analyses indicated that the presence of chromate does not limit the adsorption of arsenate. However, the presence of arsenate almost completely inhibits the adsorption of chromate when the arsenate concentration is above 50 mg/L, due to the precipitation reaction of arsenate.

Identification of functional groups of Opuntia ficus-indica involved in coagulation process after its active part extraction.

Opuntia ficus-indica that belongs to the Cactaceae family and is a member of Opuntia kind has received increasing research interest for wastewater treatment by flocculation. The objectives of this study were (i) to provide more information regarding the active constituents of Opuntia spp. and (ii) to improve the extracting and using conditions of the flocculant molecules for water treatment. A classic approach by jar test experiments was used with raw and extracted material by solubilization and precipitation. The surface properties of solid material were characterized by FTIR, SEM, zeta potential measurement, and surface titration. The splitting based on the solubility of the material with pH and the titration of functional groups completed the method. The optimal pH value for a coagulation-flocculation process using cactus solid material (CSM) was 10.0 and a processing rate of 35 mg L-1. The alkaline pH of flocculation suggests an adsorption mechanism with bridging effect between particles by water-soluble extracted molecules. To validate this mechanism, an extraction water was carried out at pH = 10 (optimum of flocculation) and the solution was acidified (pH = 7) to allow precipitation of so considered active flocculant molecules. The strong flocculant property of this extract was verified, and titration of this solution showed at least one specific pKa of 9.0 ± 0.6. This pKa corresponds to phenol groups, which could be assigned to lignin and tannin.

Phosphate removal from aqueous solution using ZVI/sand bed reactor: Behavior and mechanism.

This research reports on phosphate removal from aqueous solution using ZVI/sand packed columns. The influence of column preconditioning, consisting of ZVI pre-oxidation before feeding the columns with phosphate solution, revealed that a column aged for 1 day was more efficient than un-conditioned column, 5-days and 10-days preconditioned columns. The distribution of phosphate trapped inside the columns was evaluated by measuring phosphate concentration in the solids at different levels (P1, P2 and P3) along the depth of the columns. The distribution of phosphate inside the columns was determined for a time period up to 46 days, corresponding to column saturation. Results showed heterogeneous trapping along the column before saturation and homogeneous distribution upon saturation. The maximum cumulative trapped phosphate after column dismantling was determined before saturation (after 17 days running) at 130, 68 and 31 mgP/gFe at the inlet-P1, P1-P2 and P2-P3 layers, respectively, whereas the homogeneous distribution of phosphate upon saturation was determined at 132 mgP/gFe throughout the column. Solid supports were characterized using SEM, XRD and XPS. Lepidocrocite and maghemite/magnetite were the only iron oxidation products identified at the different layers inside the columns. XPS results confirmed the sorption of phosphate at the surface of ZVI and its oxidation products and highlighted the formation of an iron phosphate complex.

Influence of humic acids on the adsorption of Basic Yellow 28 dye onto an iron organo-inorgano pillared clay and two hydrous ferric oxides.

Effect of humic acids (HAs), macromolecules from natural organic matter, on the adsorption of Basic Yellow 28 is the aim of the present work. Three adsorbents were investigated in this study: an iron organo-inorgano pillared clay and two synthetic Hydrous Iron Oxide (Goethite and HFO). The surface charge was positive in the pH range of this study for the pillared clay; in contrast, it changes from positive to negative when the pH value increased (pH>9) for the two (oxy)hydroxides. Pseudo-first order kinetic rate constants and adsorption capacities increase from humic acid to BY 28. Adsorption isotherms of BY 28 and HA in single component were analysed using the Freundlich equation. Adsorption capacities increased sharply when the pH value of the dye solution was raised from 3 to 9. Increasing the pH medium from 3 to 9 reduces the HA adsorption capacities onto Fe-SMPM and iron oxyhydroxides, respectively. Fitting between measured and predicted sorption capacities of BY 28 and HA in a binary component system indicates that the Sheindorf-Rebuhn-Sheintuch (SRS) model, an extended Freundlich model, is able to describe the simultaneous adsorption of BY 28 and HA. Humic acids favourably affect the adsorption of BY 28, and a cooperative mechanism could be suggested. The synergetic effect existing between BY 28 and HA is shown by the interaction coefficients η12, which are generally high and increase with pH. Some phenomena have been advanced to explain this mechanism.

Fixed-bed column studies of pentachlorophenol removal by use of alginate-encapsulated pillared clay microbeads.

Columns were packed with two alginate/pillared clays microbeads (aluminium-pillared clay and surfactant-modified aluminium-pillared clay). Pentachlorophenol sorption performance was assessed under variable operating conditions: different bed heights, influent pentachlorophenol concentrations and flow rates. These conditions greatly influenced the breakthrough time/volume, the saturation time/volume and the uptake capacity. Higher values of experimental uptake capacities were obtained for the encapsulated surfactant-modified aluminium-pillared clay compared with the encapsulated aluminium-pillared clay, and the values were compared with those obtained with other low-cost sorbents. The experimental breakthrough curves were modelled using Bed Depth Service Time (BDST), Wolborska and Thomas models. Linear relationship was obtained for the BDST model, indicating the suitability of this model; bed capacity increased sharply with the introduction of CTAB in the inorgano-pillared clay. Wolborska model was applied only to the initial part of the curves. Thomas model was no doubt the most suitable description of the adsorption mechanisms for the entire breakthrough curves. Experimental and Thomas model-predicted equilibrium uptake capacities were in accordance.

Adsorption of basic dyes in single and mixture systems on granular inorganic-organic pillared clays.

The adsorption of two basic dyes, CI Basic Yellow 28 and CI Basic Green 4, was studied in single and binary solute systems using two classes of inorganic-organic pillared clay granules as sorbents (300-400 microm and 700-800 microm). These were prepared by high-shear wet granulation from an Al cetyltrimethylammonium bromide intercalated clay powder (particle diameter < 50 microm). Adsorption rate data indicate that BY 28 adsorbs more rapidly than BG 4 and a pseudo-first-order model was found to fit the kinetic curves, with regression coefficients above 0.98. Adsorption isotherms in single solute systems at pH 3 and pH6 were respectively analysed according to the Langmuir and Freundlich models using non-linear regression. Best fits were obtained with the Langmuir model. In binary dye systems the adsorption at three molar ratios (1:9, 1:1 and 9:1) demonstrated that the adsorption of BG 4 was greater than that of BY 28 on all the sorbents studied; this was in agreement with the results obtained for single solute systems. Increasing the granule size decreased dye adsorption, an effect in accordance with the Sheindorf-Rebuhn-Sheintuch model.

Cooperative coadsorption of 4-nitrophenol and basic yellow 28 dye onto an iron organo-inorgano pillared montmorillonite clay.

Sorption properties of an iron surfactant-modified pillared montmorillonite (Fe-SMPM) toward two organic pollutants, basic yellow 28 dye (BY28) and 4-nitrophenol (4-NP), were studied at different pH values in both single component and binary pollutant systems. The pseudo-first-order model fits well with the kinetic data obtained in single component studies and sorption capacities of both BY28 and 4-NP increased with the pH value. A sorption synergetic mechanism was observed in binary systems; 4-nitrophenol adsorption was enhanced by the presence of BY28 in the mixture and increased with dye concentrations. Isotherms were described using the Freundlich model in single component systems and the Sheindorf-Rebhun-Sheintuch (SRS) model, an extended Freundlich model, in binary mixtures systems. Hydrophobic interactions between the surfactant-modified pillared clay and the pollutants were suggested to explain the sorption mechanisms.

Short term copper toxicity on Microcystis aeruginosa and Chlorella vulgaris using flow cytometry.

Copper sulphate is a common algaecide applied to ponds in order to keep phytoplanktonic blooms under control, especially those prone to cyanobacterial development. The copper toxicity was evaluated for two phytoplanktonic species with the same size and shape: one cyanobacteria Microcystis aeruginosa and one chlorophyceae Chlorella vulgaris. Under controlled conditions in order to keep free copper concentration constant, three bioassays were carried out: growth inhibition tests and two sets of flow cytometric analysis (autofluorescence and esterase activity inhibition). The results showed: (1) that regardless of the cell type, as copper concentrations increased, cell division rate and autofluorescence decreased, (2) a difference in sensitivity according to the length of exposure to copper: 24 or 48 h, and (3) that M. aeruginosa showed a greater sensitivity than C. vulgaris in the 24h copper exposure assay according to esterase activity data.

Copper and nitrophenol pollutants removal by Na-montmorillonite/alginate microcapsules.

The use of renewable bioresources allows the development of low cost adsorbents that are versatile. In the present paper, the affinity and the removal capacity of montmorillonite/alginate microcapsules for a hydrophobic organic pollutant (4-nitrophenol) and an inorganic pollutant (copper) were evaluated. The physicochemical processes through sorption and kinetic experiments under different ratios of montmorillonite vs. alginate and initial contaminant concentrations were investigated. The total weight loss and diameter decrease during the drying process were 90-96% and 64%, respectively. A significant decrease in beads diameter, related to water elimination, has been observed during the first 24h. Structural modifications that occur during the drying process were evaluated using thermal analysis. From correlation coefficients, the second-order equation depicts properly the adsorption of copper by the microbeads adsorption capacity increases to saturation with time; 3 and 6h were needed to reach equilibrium on wet and dry mixed microcapsules. The pseudo-second order model properly depicts the adsorption process of 4-NP onto Na-mont and (Na-mont/SA) mixed microcapsules but failed to reproduce the data observed for the alginate beads. Isotherms data were fitted with good correlation using the Langmuir model; alginate and montmorillonite adsorption capacities (q(m)/wet beads) agree with those obtained by various studies.

Wastewater treatment in a hybrid activated sludge baffled reactor.

A novel hybrid activated sludge baffled reactor (HASBR), which contained both suspended and attached-growth biomass perfect mixing cells in series, was developed by installing standing and hanging baffles and introducing plastic brushes into a conventional activated sludge (CAS) reactor. It was used for the treatment of domestic wastewater. The effects on the operational performance of developing the suspended and attached-growth biomass and reactor configuration were investigated. The change of the flow regime from complete-mix to plug-flow, and the addition of plastic brushes as a support for biofilm, resulted in considerable improvements in the COD, nitrogen removal efficiency of domestic wastewater and sludge settling properties. In steady state, approximately 98+/-2% of the total COD and 98+/-2% of the ammonia of the influent were removed in the HASBR, when the influent wastewater concentration was 593+/-11 mg COD/L and 43+/-5 mg N/L, respectively, at a HRT of 10 h. These results were 93+/-3 and 6+/-3% for the CAS reactor, respectively. Approximately 90+/-7% of the total COD was removed in the HASBR, when the influent wastewater concentration was 654+/-16 mg COD/L at a 3h HRT, and in the organic loading rate (OLR) of 5.36kgCOD m(-3) day(-1). The result for the CAS reactor was 60+/-3%. Existing CAS plants can be upgraded by changing the reactor configuration and introducing biofilm support media into the aeration tank.

Planktonic microbial community responses to added copper.

It is generally agreed that autotrophic organisms and especially phytoplanktonic species can be harmed by copper through its effect on photosystem. However, the impact of copper on other components of the pelagic food web, such as the microbial loop (autotrophic and heterotrophic picoplankton, pigmented and non-pigmented flagellates and ciliates) has received little attention. Indoor experiments were conducted to evaluate the direct and indirect effects of copper, supplied in the range of concentrations used to control cyanobacteria growth in ponds, on non-targeted organisms of natural microbial loop communities sampled in spring and summer. Two copper concentrations were tested (80microgL(-1) and 160microgL(-1) final concentrations), set, respectively, below and above the ligand binding capacity of the water samples. Both caused a significant decrease in the biomass and diversity of pigmented organisms (picophytoplankton and pigmented flagellates). Conversely, the heterotrophic bacterioplankton and the heterotrophic flagellates did not seem to be directly affected by either copper treatment in terms of biomass or diversity, according to the descriptor chosen. The ciliate biomass was significantly reduced with increasing copper concentrations, but differences in sensitivity appeared between spring and summer communities. Potential mixotrophic and nanoplanktorivorous ciliates appeared to be more sensitive to copper treatments than bacterivorous ciliates, suggesting a stronger direct and (or) indirect effect of copper on the former. Copper sulphate treatments had a significant restructuring effect on the microbial loop communities, resulting in a dominance of heterotrophic bacterioplankton among microbial microorganisms 27 days after the beginning of the treatment. The spring microbial communities exhibited a greater sensitivity than the summer communities with respect to their initial compositions.

Myriophyllum alterniflorum DC., biomonitor of metal pollution and water quality. Sorption/accumulation capacities and photosynthetic pigments composition changes after copper and cadmium exposure.

Watermilfoil genus Myriophyllum could be used in ecological surveys as in-situ biomonitors of metal pollution and water quality due to its ability to accumulate chemicals. The copper and cadmium sorption characteristics of Myriophyllum alterniflorum have been investigated. The Langmuir and Freundlich isotherms were used to model the metal sorption isotherms and the monolayer sorption capacities, as obtained by the Langmuir isotherm, were determined to be 13.9 mg/g and 11.1 mg/g for Cu2+ and Cd2+ respectively. Results have been compared with previous works on watermilfoils and are in accordance with those obtained on Myriophyllum spicatum. The sorption of the two metals was time-dependent and the kinetics fitted the pseudo-second-order equation well. The data were discussed in terms of ionic radii and HSAB concept. The phytotoxic effects assessed by classical (i.e. changes in biomass, node length) and photosynthetic pigments content endpoints have been investigated using chemometric techniques leading to an effect of cadmium onto photosynthetic pigments.

Effect of extraction method on EPS from activated sludge: an HPSEC investigation.

The extracellular polymeric substances (EPS) contained in activated sludge flocs resulting from two-sewage treatment plants were extracted according to eight methods referred to in the bibliography. Extracted EPS were characterized by their extraction yield, carbon concentration, their biochemical composition, their HPSEC chromatograms and, where possible, molecular weight (MW) distributions. With HPSEC chromatograms, the use of the mobile phase containing methanol allowed a hydrophobic mechanism for EPS, extracted partly by chemical methods, to be identified. An MW distribution (from 0.1 to 600kDa) was established for EPS extracted by control and physical methods only, from calibration. Except for the resin and heating extraction methods, the EPS extracted from the two sludges displayed the same trend in their HPSEC fingerprints but not in their MW distribution. Results show that the extraction methods using chemical reagents strongly affected the HPSEC fingerprints of EPS, whereas, the physical methods influenced only MW distribution but not HPSEC fingerprints. The use of heat to extract EPS seems to induce hydrolysis of a part of EPS. The HPSEC fingerprint is a good indicator for the appreciation of the consequences of EPS extraction methods on the EPS extracted and the distribution of EPS with low MW in particular.

Effect of copper sulphate treatment on natural phytoplanktonic communities.

Copper sulphate treatment is widely used as a global and empirical method to remove or control phytoplankton blooms without precise description of the impact on phytoplanktonic populations. The effects of two copper sulphate treatments on natural phytoplanktonic communities sampled in the spring and summer seasons, were assessed by indoor mesocosm experiments. The initial copper-complexing capacity of each water sample was evaluated before each treatment. The copper concentrations applied were 80 microg l(-1) and 160 microg l(-1) of copper, below and above the water complexation capacity, respectively. The phytoplanktonic biomass recovered within a few days after treatment. The highest copper concentration, which generated a highly toxic environment, caused a global decrease in phytoplankton diversity, and led to the development and dominance of nanophytoplanktonic Chlorophyceae. In mesocosms treated with 80 microg l(-1) of copper, the effect on phytoplanktonic community size-class structure and composition was dependent on seasonal variation. This could be related to differences in community composition, and thus to species sensitivity to copper and to differences in copper bioavailability between spring and summer. Both treatments significantly affected cyanobacterial biomass and caused changes in the size-class structure and composition of phytoplanktonic communities which may imply modifications of the ecosystem structure and function.

Laboratory investigation of the phosphorus removal (SRP and TP) from eutrophic lake water treated with aluminium.

Mechanisms involved in phosphorus (P) removal from eutrophic lake water with aluminium (Al) were assessed by jar tests. For this purpose, eutrophic lake water enriched with soluble reactive phosphorus (SRP), algae or sediments in order to mimic the various conditions found in shallow eutrophic lakes was studied. Total phosphorus (TP) removal was reached after floc settling, the maximal TP removal efficiency (90-95%) was obtained for an Al concentration ranging from 2 to 5 mg L(-1), depending on the organic matter (OM) origin (algae or sediments). Algae appeared to limit macro-floc formation (those able to settle). In contrast, in the presence of sediments, macro-floc formation was favoured at low Al dose (2-3 mg L(-1) Al). High SRP removal was obtained with the lowest Al dose (1 mg L(-1) Al) and remained greater than 60% for an SRP concentration up to 350 microg L(-1). SRP removal was not influenced by the OM origin. The experimental data and literature were used to suggest a hypothetical model for floc formation and P removal with Al under the conditions observed in treated lakes.

Toxicity of copper excess on the lichen Dermatocarpon luridum: antioxidant enzyme activities.

The aim of this study was to investigate the toxicity of copper on the aquatic lichen Dermatocarpon luridum focusing on the activities of some antioxidant enzymes. Investigations were conducted using increasing copper concentrations (0.00, 0.25, 0.50, 0.75 and 1.00 mM CuSO(4) x 5H(2)O) in synthetic freshwater that emulated the major ion compositions of its natural water biota; time course measurement was 0, 3, 6, 12, 24 and 48 h. The copper concentration in thalli increased with its increase in the medium and the duration of treatment. Copper induced lipid peroxidation, measured using the hydroperoxi-conjugated dienes (HPCD) concentration. The decrease in the protein concentrations was similar in thalli exposed to copper concentrations above 0.50 mM and the decrease was twice lower in thalli exposed to 0.25 mM copper. The activities of antioxidant enzymes measured were differently affected by copper excess. For 0.25 mM copper, the activities of SOD (superoxide dismutase) and APX (ascorbate peroxidase) were unchanged when compared with unstressed thalli whereas the CAT (catalase) activity increased and the GR (glutathione reductase) activity decreased. The activities of SOD and APX increased in thalli exposed to concentrations above 0.50mM copper. The CAT activity increased after the first 3h of experiments at these concentrations and then decreased with the duration of treatment at an activity lower than in the unstressed plant. Whereas the APX activity increased, the GR activity similarly decreased for the copper concentration tested whatever the duration of the experiment.

Use of the aquatic lichen Dermatocarpon luridum as bioindicator of copper pollution: accumulation and cellular distribution tests.

Laboratory experiments were conducted to investigate the potential use of the aquatic lichen Dermatocarpon luridum as bioindicator of copper pollution. Lichen thalli were exposed to 0.00, 0.25, 0.50, 0.75 and 1.00 mM copper in synthetic freshwater to solve the problems of metal bioavailability. The mineral composition of this media was prepared so that it corresponded to the ion composition of natural waters in D. luridum ecosystems. Sequential elution procedures using NiCl2 or Na2-EDTA (20 mM) were used to determine the distribution of metals at different cellular sites. The copper concentration extracted from thalli was correlated with pollution intensity, the greater correlation being with the Na2-EDTA extractant. The malondialdehyde concentration in thalli can be used as indicator of copper pollution; however, similar membrane degradation was observed for 0.25 and 0.50 mM copper and for 0.75 and 1.00 mM copper.

Comparison of the complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and produced by pure bacteria strains, for cadmium, lead and nickel.

This paper provides information on the metal complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and from eight pure cultures of bacteria isolated from the same activated sludge. The EPS extracted from pure bacteria cultures are mainly composed of proteins and low quantities of polysaccharides and uronic acids in comparison with EPS extracted from activated sludges. The EPS studied present two apparent pK(a) and the IR spectra show the presence of the same functional groups on all the EPS studied. The ability of EPS to complex Cd, Pb and Ni, was studied at pH 7 with Chau and Ruzic's models using polarography titration. All of the EPS exhibited a greater ability to complex Pb than Ni, Cd showing the weakest affinity overall. The EPS extracted from the pure cultures of bacteria were less able to complex the metals than that extracted from activated sludges. Literature data, IR data and EPS phosphorous content, supported by the EPS pK(a), revealed that carboxylic and phosphoric groups may play a major role in binding to metals at pH 7. This study underlines the importance of metal exposure in order for bacteria to secrete or modify EPS. After exposure, the EPS then exhibit the greatest capacity to bind metal in order to protect bacteria from harmful effects of heavy metals.

Environmental impact of two successive chemical treatments in a small shallow eutrophied lake: Part I. Case of aluminium sulphate.

This paper deals with the efficiency and effects of addition of aluminium sulphate on soft water quality of a shallow eutrophic lake. Almost all the controlled variables improved with treatment, especially nutrient concentrations such as soluble reactive phosphorus (SRP) and transparency. However, aluminium sulphate was not added in sufficient quantity to reduce the total phosphorus content. SRP concentration was significantly reduced in the short term. Moreover, external loading of phosphorus was high and not taken into account by the in-lake treatments. Finally, resuspension of sediment (polymictic lake) removed the alum hydroxide layer on the sediment surface, which reduced treatment effectiveness. No significant pH decrease was noted following alum addition. According to bibliographical toxicological data, monomeric aluminium content does not show any toxic effect on aquatic fauna and flora. In spite of low SRP in the water column, the treatment did not prevent appearance of Microcystis sp. colony (> 10 colony per ml) approximately 30 days after alum application.

Environmental impact of two successive chemical treatments in a small shallow eutrophied lake: Part II. Case of copper sulfate.

The appearance of cyanobacteria ( > 10 colony per ml) was not prevented after alum treatment. In order to prevent cyanobacteria efflorescences in a small shallow polymictic lake (Courtille, France), copper sulfate was applied. Treatment level was 63 microg 1(-1) as Cu2+ from CUSO4, 5 H2O. Cyanobacteria were kept under control during the summer. Microcystis sp. completely disappeared, which allowed swimming in the lake throughout the tourist season. Microcystis only reappeared 2 months after the treatment. Copper content in the water column only returned to its background level 2 months after copper addition. This high residence time of copper in the water might have been caused by complexation and adsorption of copper on natural organic matter, whose level was high in the ecosystem studied. A mechanism of transfer of 'truly' dissolved copper towards particulate copper has been underlined and explains the disappearance of this fraction of copper in the water column.