Algae from Cr-containing infiltrate bioremediation for valorised chemical production - Seasonal availability, composition, and screening studies on hydrothermal conversion.

Integrating bioremediation of toxic wastewater with value-added production is increasing interest, but - due to some essential problems - it is hardly applied in industrial practice. The aim of the study was an annual observation of the taxonomic and biochemical composition of various Cr-resistant algal communities grown in the existing Cr-containing infiltrate treatment system, selection of the most suitable algal biomass for infiltrates bioremediation and chromium-loaded algae conversion under mild subcritical conditions. Considering continuous availability and relatively constant chemical composition, Cladophora sp. was selected for utilisation in the chromium bioremediation system, simultaneously as a waste biomass source suitable for hydrothermal conversion. Screening studies conducted in a continuous pilot plant confirmed the possibility of selective extraction of saccharides and their separation from the metals remaining in the solid residual. The negligible concentration of metals in the obtained sugar-rich aqueous phase is essential for its further use in biotechnological processes.

Multifunctional Composite Materials Based on Anion Exchangers Modified with Copper Compounds-A Review of Their Synthesis Methods, Characteristics and Applications.

As copper and its compounds are of fundamental importance for the development of innovative materials, the synthesis of composites intended for water purification was undertaken in which submicron copper containing particles were dispersed within the matrix of a strongly basic anion exchanger, with a macroporous and gel-like structure. Due to their trimethylammonium functional groups, the host materials alone exhibited an affinity to anionic water contaminants and antimicrobial properties. The introduction of such particles as CuO, Cu2O, metallic Cu, CuO/FeO(OH), Cu4O3, Cu(OH)2, Cu4(OH)6SO4, Cu2(OH)3Cl increased these properties and demonstrated new properties. The composites were obtained unconventionally, in ambient conditions, using eco-friendly reagents. Alternative synthesis methods were compared and optimized, as a result of which a new group of hybrid ion exchangers was created (HIXs) containing 3.5-12.5 wt% of Cu. As the arrangement of the inorganic phase in the resin matrix was atypical, i.e., close to the surface of the beads, the obtained HIXs exhibited excellent kinetic properties in the process of oxidation and adsorption of As(III), as well as catalytic properties for the synthesis of triazoles via click reaction, and also antimicrobial properties in relation to Gram-positive Enterococcus faecalis and Gram-negative Pseudomonas aeruginosa and Escherichia coli, preventing biofilm formation. Using thermogravimetry, the effect of the inorganic phase on decomposition of the polymeric phase was evaluated for the first time and comprehensively, confirming the relationship and finding numerous regularities. It was also found that, depending on the oxidation state (CuO, Cu2O, Cu), copper-containing particles affected the textural properties of the polymeric phase endowing a tighter structure, limiting the porosity and reducing the affinity for water.

Natural community of macroalgae from chromium-contaminated site for effective remediation of Cr(VI)-containing leachates.

The natural macroalgal community, which developed in the unique and extremely Cr(VI)-polluted aquatic reservoir situated near a historical chromium-waste landfill, was studied in order to recognize the main mechanisms of Cr(VI) detoxification by the algal species. The conducted taxonomic analysis revealed mixed composition of the filamentous forms of algae and showed that three species of Tribonema, namely T. vulgare, T. microchloron and T. viride, which have not been studied before with regard to the mechanisms of Cr(VI) removal, are likely responsible for the effective bioremediation of this highly Cr(VI)-polluted habitat. The studied algal community, with the ability to grow in extremely high concentrations of Cr(VI), i.e. up to ca. 6150 times the upper limit for surface water, exhibited hyperaccumulative properties for chromium (max 16230 mg/kg dry weight) under the given environmental conditions. We found that the main mechanism of Cr(VI) detoxification was reduction followed by Cr(III) biosorption - feasibly by ion exchange and complexation mechanisms - and that the excellent efficiency of chromium reduction under the given, unfavorable weakly alkaline conditions indicates the biological origin of this process. It was concluded that the examined reservoir inhabited by the algal community can be used, after some modifications, as a simple cost-effective "bioreactor" allowing the reduction of chromium concentration to the desired level. Moreover, the conducted studies are also essential to obtain in-depth knowledge and should also be helpful in the relevance of the community for its further application as a potential biosorbent of Cr(VI) on a global scale.

Cu(II)-Fe(III) oxide doped anion exchangers - Multifunctional composites for arsenite removal from water via As(III) adsorption and oxidation.

The aim of the present study was to investigate As(III) oxidation and adsorption on the surface of hybrid anion exchangers containing Cu(II)-Fe(III) binary oxide deposited in their porous structure with the same Cu:Fe ratio of 1:2 but with different amounts and distribution of inorganic deposit within polymeric beads. The equilibrium studies confirmed high adsorption capacity of the best hybrid polymer: 94.4 mg As/g. Moreover, the adsorption was effective over a wide pH range, selective in the presence of interfering ions, and the material was effectively regenerated. The performance of the hybrid polymer was also confirmed in the column process which enabled both As(III) and As(V) concentrations to be lowered from 500 µg/L to below 10.0 µg/L in a solution with a composition similar to natural groundwater. The breakthrough point of the bed was reached after the solution amounting to 1833 bed volumes passed through the column. Desorbed As speciation, FTIR and XPS studies showed that As(III) was mainly adsorbed on the surface of Cu-Fe oxides followed by its oxidation to As(V). In the oxidation reaction metal oxides acted as catalysts and adsorbents, while the oxidant was probably oxygen dissolved in solution.

Highly efficient arsenic sorbent based on residual from water deironing - Sorption mechanisms and column studies.

The hybrid polymer obtained by entrapment of Fe-Mn waste oxides from water deironing into a chitosan matrix was evaluated as an As(III) and As(V) sorbent. Its maximum adsorption capacity determined from a Langmuir isotherm model was 44.17 mg As(III)/g or 26.80 mg As(V)/g and 50.73 mg As(III)/g or 82.99 mg As(V)/g under neutral and acidic conditions, respectively. The pH markedly influenced the efficiency and the rate of As(V) adsorption, whereas its impact on As(III) removal was slight. The sorbent was simply regenerated using NaOH solution, and no drop in adsorption capacity was observed after 6 cycles. The physical form and the durability of the sorbent enabled continuous work in a fixed-bed system without clogging of the bed. Arsenic concentration in the effluent exceeded 0.01 mg As/L only after passing about 2700 bed volumes. Arsenates formed surface complexes with iron oxides and were bounded by the imine groups of cross-linked chitosan. Arsenites were oxidized by MnO2 before adsorption but, because of the low Mn:Fe ratio, a fraction of them were also directly bound to the iron oxides, especially at neutral pH. The conducted studies confirmed the usability of the examined material as a highly efficient sorbent for arsenic removal from water.

Optimization of hybrid polymer preparation by ex situ embedding of waste Fe/Mn oxides into chitosan matrix as an effective As(III) and As(V) sorbent.

A hybrid polymer for deep removal of arsenic from aqueous solutions was obtained by loading of waste Fe/Mn oxides into a chitosan matrix. The process was optimized by studying the influence of selected individual factors and their reciprocal combinations on the adsorptive and physical properties of the product. The influence of chitosan solution concentration, inorganic load amount, the ratio of Fe/Mn oxides to chitosan, and polymer cross-linking degree on kinetics of As(III) and As(V) adsorption was examined. The optimal values of the parameters were chitosan polymer concentration 1.5% w/w, inorganic load to chitosan ratio 1.67, and glutaraldehyde to chitosan amine groups molar ratio 3:1. The selected products were evaluated in terms of their morphology (scanning electron microscopy (SEM) with EDS analysis), porosity (N2 and CO2 adsorption isotherms), surface properties (Fourier-transform infrared spectroscopy (FTIR), isoelectric point determination) and durability in an acidic environment. The proposed process makes it possible to obtain a product combining beneficial adsorptive properties toward arsenic with the physical form and durability essential in fixed-bed adsorption systems.

Evaluation of hybrid anion exchanger containing cupric oxide for As(III) removal from water.

The aim of this study was investigate of arsenite adsorption on a hybrid polymer based on a polystyrene/divinylbenzene macroporous anion exchanger containing cupric oxide deposited within its porous structure. The study included batch kinetic and equilibrium experiments, and investigation of influence of the pH, regeneration of spent adsorbent and the column process on arsenic(III) adsorption. The experimental data were evaluated using kinetic, isotherm and fixed-bed column models. The adsorption capacity calculated from the Langmuir model was 6.61 mg As(III) g-1. The adsorption rate was controlled by both chemisorption of arsenic on the adsorbent surface and external diffusion, and at a higher initial As(III) concentration also by intraparticle diffusion. The spent adsorbent was easily regenerated with 1.0 M NaOH solution. Based on batch adsorption studies and X-ray photoelectron spectroscopic analyses a mechanism of As(III) adsorption was proposed. Arsenite removal proceeded in two stages: oxidation to arsenate on the CuO surface, followed by an ion exchange reaction. The studied hybrid polymer also showed very good adsorption characteristics under the dynamic regime. The S-shape of breakthrough curves and insignificant influence of bed height, initial concentration and flow rate on the adsorption capacity confirmed its applicability in water treatment.

Callitriche cophocarpa biomass as a potential low-cost biosorbent for trivalent chromium.

The present study focused on the use of the dry mass of the macrophyte Callitriche cophocarpa as an effective biosorbent for chromium removal from concentrated solutions, typical for industrial effluents. In order to evaluate the usability of C. cophocarpa as the Cr(III) sorbent, its detailed physicochemical characterization has been performed as well as the preliminary adsorption studies. The biosorbent was characterized by specific surface area (SSA), porosity, total organic carbon (TOC), inorganic content as well as the cation exchange capacity (CEC), dominant exchangeable cations and anion exchange capacity (AEC), point of zero charge (pHpzc) and buffering capacity. The effect of the initial chromium concentration, solution pH and co-existing anions on the sorption effectiveness have been investigated. Based on theoretical isotherm models, the maximum adsorption capacity of the dry C. cophocarpa has been determined as 77.1 mg Cr(III)/g. Finally, the strength of Cr-binding onto the plant biomass has been evaluated using the BCR extraction method, stating that chromium was strongly and - under environmental conditions - irreversibly bound to the plant biomass.

Alginate beads containing water treatment residuals for arsenic removal from water-formation and adsorption studies.

Water treatment residuals (WTRs) produced in large quantities during deironing and demanganization of infiltration water, due to high content of iron and manganese oxides, exhibit excellent sorptive properties toward arsenate and arsenite. Nonetheless, since they consist of microparticles, their practical use as an adsorbent is limited by difficulties with separation from treated solutions. The aim of this study was entrapment of chemically pretreated WTR into calcium alginate polymer and examination of sorptive properties of the obtained composite sorbent toward As(III) and As(V). Different products were formed varying in WTR content as well as in density of alginate matrix. In order to determine the key parameters of the adsorption process, both equilibrium and kinetic studies were conducted. The best properties were exhibited by a sorbent containing 5 % residuals, formed in alginate solution with a concentration of 1 %. In slightly acidic conditions (pH 4.5), its maximum sorption capacity was 3.4 and 2.9 mg g-1 for As(III) and As(V), respectively. At neutral pH, the adsorption effectiveness decreased to 3.3 mg As g-1 for arsenites and to 0.7 mg As g-1 for arsenates. The presence of carboxylic groups in polymer chains impeded in neutral conditions the diffusion of anions into sorbent beads; therefore, the main rate-limiting step of the adsorption, mainly in the case of arsenates, was intraparticle diffusion. The optimal condition for simultaneous removal of arsenates and arsenites from water by means of the obtained composite sorbent is slightly acidic pH, ensuring similar adsorption effectiveness for both arsenic species.

Iron and aluminium oxides containing industrial wastes as adsorbents of heavy metals: Application possibilities and limitations.

Industrial wastes with a high iron or aluminium oxide content are produced in huge quantities as by-products of water treatment (water treatment residuals), bauxite processing (red mud) and hard and brown coal burning in power plants (fly ash). Although they vary in their composition, the wastes have one thing in common--a high content of amorphous iron and/or aluminium oxides with a large specific surface area, whereby this group of wastes shows very good adsorbability towards heavy metals, arsenates, selenates, etc. But their physical form makes their utilisation quite difficult, since it is not easy to separate the spent sorbent from the solution and high bed hydraulic resistances occur in dynamic regime processes. Nevertheless, because of the potential benefits of utilising the wastes in industrial effluent treatment, this issue attracts much attention today. This study describes in detail the waste generation processes, the chemical structure of the wastes, their physicochemical properties, and the mechanisms of fixing heavy metals and semimetals on the surface of iron and aluminium oxides. Typical compositions of wastes generated in selected industrial plants are given. A detailed survey of the literature on the adsorption applications of the wastes, including methods of their thermal and chemical activation, as well as regeneration of the spent sorbents, is presented. The existing and potential ways of modifying the physical form of the discussed group of wastes, making it possible to overcome the basic limitation on their practical use, are discussed.

Oxidation of As(III) in aqueous solutions by means of macroporous redox copolymers with N-chlorosulfonamide pendant groups.

The possibility of oxidizing As(III) to As(V) in aqueous solutions by means of heterogeneous oxidants, i.e. synthetic macromolecular redox compounds, was studied. The materials contain N-chlorosulfonamide functional groups in the sodium form: [P]-SO(2)NClNa (R/ClNa, 2.1 mmol/g) or in the hydrogen form: [P]-SO(2)NClH (R/ClH, 2.4 mmol/g), attached to a cross-linked macroporous poly(styrene-divinylbenzene) matrix. They were obtained through the transformation of Amberlyst 15 (Rohm and Haas) commercial cation exchanger's sulfonic functional groups. The experiments were conducted in the H(2)O and 0.01 M NaOH environment (R/ClNa) and in the H(2)O and 0.01 M H(2)SO(4) environment (R/ClH), using the batch process and the column process and NaAsO(2) solutions (93-375 mg As(III)/dm(3)). The experiments showed that the two copolymers' capacity to oxidize As(III) is high and depends on the process conditions. In the column process experiments, conducted using NaAsO(2) solutions with a concentration of ∼ 93 mg As(III)/dm(3) at a flow rate of 4 BV/h (R/ClH) and 6 BV/h (R/ClNa), a breakthrough (defined as the exceedance of 0.05 mg As(III)/dm(3) in the effluent) would occur after the solutions amounting to about 400 bed volumes had been passed through the column.