A sulfate reducing bioreactor controlled by an electrochemical system enables near-zero chemical treatment of metallurgical wastewater.

Metallurgical wastewaters are characterized by a low pH (<4), high concentrations of sulfate (15 gSO42- L-1), and metal(loid)s. Current treatment requires the consumption of chemicals such as alkali and high levels of waste sludge generation. In this study, we have shown that combining water electrolysis and sulfate reducing bioreactors enables the in-situ generation of base and H2, eliminating the need for base and electron donor addition, resulting in the near-zero treatment of metallurgical wastewater. By extracting cations from the effluent of the system to the bioreactor, the bioreactor pH could be maintained by the in-situ production of alkali. The current for pH control varied between 112-753 mol electrons per m³ wastewater or 5-48 A m-2 electrode area. High concentrations of sulfate in the influent and addition of CO2 increased the current required to maintain a steady bioreactor pH. On the other hand, a high sulfate reduction rate and increased influent pH lowered the current required for pH control. Moreover, the current efficiency varied from 14% to 91% and increased with higher pH and cation (Na+, NH4+, K+, Mg2+, Ca2+) concentrations in the middle compartment of the electrochemical cell. The salinity was lowered from 70-120 mS cm-1 in the influent to 5-20 mS cm-1 in the system effluent. The energy consumption of the electrochemical pH control varied between 10 and 100 kWh m-3 and was affected by the conductivity of the wastewater. Industrial wastewater was treated successfully with an average energy consumption of 39 ± 7 kWh m-3, removing sulfate from 15 g SO42- L-1 to 0.5 ± 0.5 g SO42- L-1 at a reduction rate of 20 ± 1 gSO42- L-1 d-1..Metal(loid)s such as As, Cd, Cu, Pb, Te, Tl, Ni and Zn were removed to levels of 1-50 µg L-1.

High rate production of concentrated sulfides from metal bearing wastewater in an expanded bed hydrogenotrophic sulfate reducing bioreactor.

Metallurgical wastewaters contain high concentrations of sulfate, up to 15 g L-1. Sulfate-reducing bioreactors are employed to treat these wastewaters, reducing sulfates to sulfides which subsequently co-precipitate metals. Sulfate loading and reduction rates are typically restricted by the total H2S concentration. Sulfide stripping, sulfide precipitation and dilution are the main strategies employed to minimize inhibition by H2S, but can be adversely compromised by suboptimal sulfate reduction, clogging and additional energy costs. Here, metallurgical wastewater was treated for over 250 days using two hydrogenotrophic granular activated carbon expanded bed bioreactors without additional removal of sulfides. H2S toxicity was minimized by operating at pH 8 ± 0.15, resulting in an average sulfate removal of 7.08 ± 0.08 g L-1, sulfide concentrations of 2.1 ± 0.2 g L-1 and peaks up to 2.3 ± 0.2 g L-1. A sulfate reduction rate of 20.6 ± 0.9 g L-1 d-1 was achieved, with maxima up to 27.2 g L-1 d-1, which is among the highest reported considering a literature review of 39 studies. The rates reported here are 6-8 times higher than those reported for other reactors without active sulfide removal and the only reported for expanded bed sulfate-reducing bioreactors using H2. By increasing the influent sulfate concentration and maintaining high sulfide concentrations, sulfate reducers were promoted while fermenters and methanogens were suppressed. Industrial wastewater containing 4.4 g L-1 sulfate, 0.036 g L-1 nitrate and various metals (As, Fe, Tl, Zn, Ni, Sb, Co and Cd) was successfully treated with all metal(loid)s, nitrates and sulfates removed below discharge limits.

Valorization of selenium-enriched sludge and duckweed generated from wastewater as micronutrient biofertilizer.

Selenium (Se) is an essential trace element for humans and animals with a narrow window between deficiency and toxicity levels. Application of conventional chemical Se fertilizers to increase the Se content of crops in Se deficient areas could result in environmental contamination due to the fast leaching of inorganic Se. Slow-release Se-enriched biofertilizers produced from wastewater treatment may therefore be beneficial. In this study, the potential of Se-enriched biomaterials (sludge and duckweed) as slow-release Se biofertilizers was evaluated through pot experiments with and without planted green beans (Phaseolus vulgaris). The Se concentration in the bean tissues was 1.1-3.1 times higher when soils were amended with Se-enriched sludge as compared to Se-enriched duckweed. The results proved that the Se released from Se-enriched biomaterials was efficiently transformed to health-beneficial selenoamino acids (e.g., Se-methionine, 76-89%) after being taken up by beans. The Se-enriched sludge, containing mainly elemental Se, is considered as the preferred slow-release Se biofertilizer and an effective Se source to produce Se-enriched crops for Se-deficient populations, as shown by the higher Se bioavailability and lower organic carbon content. This study could offer a theoretical reference to choose an environmental-friendly and sustainable alternative to conventional mineral Se fertilizers for biofortification, avoiding the problem of Se losses by leaching from chemical Se fertilizers while recovering resources from wastewater. This could contribute to the driver for a future circular economy.

Oxygen-rich poly-bisvanillonitrile embedded amorphous zirconium oxide nanoparticles as reusable and porous adsorbent for removal of arsenic species from water.

A new oxygen-rich porous polymer based on bisvanillonitrile was synthesized and characterized. This polymer was employed as support for the anchoring of 14.5 w% amorphous zirconium oxide nanoparticles. The formation of homogeneously dispersed nanoparticles in the poly-bisvanillonitrile (PBVN) host material was confirmed using N2-sorption, XRPD, XPS and electron microscopy. The combination of zirconium oxide nanoparticles having active adsorption sites with the porous supporting material showed excellent adsorption of arsenic species. The resulting adsorption capacities of the hybrid material extend to 245 mg g-1 for arsenite (AsIII) and 115 mg g-1 for arsenate (AsV). Moreover, adsorption kinetics showed a fast removal of both arsenic species with initial adsorption rate h of 0.0646 mg g-1 min-1 for arsenite and 0.0746 mg g-1 min-1 for arsenate. The immobilization was not interfered by the presence of other compounds in solution, indicating the applicability in real working environments. The material could be regenerated in a continuous mode using a 0.1 mol L-1 sodium hydroxide solution at 70 °C to desorb arsenic.

Rational design of lanthanide nano periodic mesoporous organosilicas (Ln-nano-PMOs) for near-infrared emission.

We present three Periodic Mesoporous Organosilica (PMO) materials: a PMO material functionalized with pyridine dicarboxamide (DPA-PMO) and two amine functionalized PMO materials (Am-PMO and Am-ePMO). The pyridine dicarboxamide ligands in the DPA-PMO material provide the tethering sites for Ln3+-coordination. A Schiff base reaction was carried out on the amine functionalized PMOs to introduce similar lanthanide coordination sites. The Nd and Yb modified nano-PMOs are evaluated as near-infrared (NIR) emitting luminescent materials. The DPA-PMO and Am-ePMO materials can act as good platforms for NIR luminescence. A significant enhancement in the decay time can be observed upon grafting an Yb(hfa)3 complex to the PMO materials instead of YbCl3. All of the DPA-PMO@Ln(hfa)3 and Am-ePMO@Ln(hfa)3 materials show characteristic NIR emission performance both in the solid state and in aqueous suspension.

Effect of speciation and composition on the kinetics and precipitation of arsenic sulfide from industrial metallurgical wastewater.

Precipitation of arsenic as As2S3 produces little waste sludge, has the potential for low chemical consumption and for selective metal(loid) removal. In this study, arsenic removal from acidic (pH 2), metallurgical wastewater was tested in industrially relevant conditions. Sulfides added at a S:As molar ratio of 2.5 and 5 resulted in removal of 99% and 84% of As(III) and As(V). Precipitation of As2S3 from the As(III) and industrial wastewater containing 17% As(V) was nearly instantaneous. For the synthetic As(V) solution, reduction to As(III) was the rate limiting step. At a S:As ratio of 20 and an observed removal rate (k2 = 4.8 (mol L-1) h-1), two hours were required to remove of 93% of arsenic from a 1 g As L-1 solution. In the case of As(V) in industrial samples this time lag was not observed, showing that components in the industrial wastewater affected the removal and reduction of arsenate. Speciation also affected flocculation and coagulation characteristics of As2S3 particles: As(V) reduction resulted in poor coagulation and flocculation. Selective precipitation of arsenic was possible, but depended on speciation, S:As ratio and other metals present.

Removal of arsenic and mercury species from water by covalent triazine framework encapsulated γ-Fe2O3 nanoparticles.

The covalent triazine framework, CTF-1, served as host material for the in situ synthesis of Fe2O3 nanoparticles. The composite material consisted of 20 ±â€¯2 m% iron, mainly in γ-Fe2O3 phase. The resulting γ-Fe2O3@CTF-1 was examined for the adsorption of AsIII, AsV and HgII from synthetic solutions and real surface-, ground- and wastewater. The material shows excellent removal efficiencies, independent from the presence of Ca2+, Mg2+ or natural organic matter and only limited dependency on the presence of phosphate ions. Its adsorption capacity towards arsenite (198.0 mg g-1), arsenate (102.3 mg g-1) and divalent mercury (165.8 mg g-1) belongs amongst the best-known adsorbents, including many other iron-based materials. Regeneration of the adsorbent can be achieved for use over multiple cycles without a decrease in performance by elution at 70 °C with 0.1 M NaOH, followed by a stirring step in a 5 m% H2O2 solution for As or 0.1 M thiourea and 0.001 M HCl for Hg. In highly contaminated water (100 µg L-1), the adsorbent polishes the water quality to well below the current WHO limits.

Partitioning of Ag and CeO2 nanoparticles versus Ag and Ce ions in soil suspensions and effect of natural organic matter on CeO2 nanoparticles stability.

This study examined the solid-liquid distribution of 14.8-nm Ag and 6.2-nm CeO2 nanoparticles in soil suspensions and compared it to that of Ag+ and Ce3+ ions, to better understand their environmental behaviour and fate. After 24 h incubation, more than 51% or 29% of the spiked amounts of Ag or CeO2 nanoparticles, respectively, can be retrieved in the liquid phase of (re)suspended soils. The Ag or Ce concentration remaining in solution depends on the incubation time and was influenced by soil properties. Significant correlations are obtained between, on the one hand, the relative amounts of Ag or CeO2 nanoparticles in suspension and the soil-pH, CEC, texture, suspended matter, nitrogen, phosphorus, TOC and main and trace elements content on the other hand. The presence of dissolved natural organic matter stabilizes CeO2 nanoparticles in the aqueous phase. In soil suspensions, Ag+ and Ce3+ ions seemingly interact more strongly with soil constituents compared to their nanoparticle counterparts, rendering the Ag and CeO2 nanoparticles to be more stable and potentially bioavailable.

Identification of platinum nanoparticles in road dust leachate by single particle inductively coupled plasma-mass spectrometry.

Elevated platinum (Pt) concentrations are found in road dust as a result of emissions from catalytic converters in vehicles. This study investigates the occurrence of Pt in road dust collected in Ghent (Belgium) and Gothenburg (Sweden). Total Pt contents, determined by tandem ICP-mass spectrometry (ICP-MS/MS), were in the range of 5 to 79ngg-1, comparable to the Pt content in road dust of other medium-sized cities. Further sample characterization was performed by single particle (sp) ICP-MS following an ultrasonic extraction procedure using stormwater runoff for leaching. The method was found to be suitable for the characterization of Pt nanoparticles in road dust leachates. The extraction was optimized using road dust reference material BCR-723, for which an extraction efficiency of 2.7% was obtained by applying 144kJ of ultrasonic energy. Using this method, between 0.2% and 18% of the Pt present was extracted from road dust samples. spICP-MS analysis revealed that Pt in the leachate is entirely present as nanoparticles of sizes between 9 and 21nm. Although representing only a minor fraction of the total content in road dust, the nanoparticulate Pt leachate is most susceptible to biological uptake and hence most relevant in terms of bioavailability.

UiO-66-(SH)2 as stable, selective and regenerable adsorbent for the removal of mercury from water under environmentally-relevant conditions.

The dithiol functionalized UiO-66-(SH)2 is developed as an efficient adsorbent for the removal of mercury in aqueous media. Important parameters for the application of MOFs in real-life circumstances include: stability and recyclability of the adsorbents, selectivity for the targeted Hg species in the presence of much higher concentrations of interfering species, and ability to purify wastewater below international environmental limits within a short time. We show that UiO-66-(SH)2 meets all these criteria.

Dispersion and solubility of In, Tl, Ta and Nb in the aquatic environment and intertidal sediments of the Scheldt estuary (Flanders, Belgium).

Certain specialty elements are indispensable in modern technologies for their particular properties. Yet, potential risks associated to the release of these elements at any stage, remains unknown. Therefore, the dispersion of indium (In), thallium (Tl), tantalum (Ta) and niobium (Nb) in the aquatic environment of the Scheldt estuary (Flanders, Belgium) was studied. Maximum concentrations in intertidal sediments of 101 ± 15 µg kg-1 for In, 481 ± 37 µg kg-1 for Tl, 88 ± 19 µg kg-1 for Ta and 1162 ± 4 µg kg-1 for Nb appeared on the sampling location closest to the river mouth, i.e. 57.5 km upstream. Their distribution in the intertidal sediments depends on the physicochemical sediment characteristics along the flow of the river Scheldt. The same was the case for most other metals and aluminum as their occurrence also correlated (p < 0.05) with the occurrence of In, Tl and Nb. While in general, studied elements correlate to the OM content and sulfur and phosphorus herein included, a relative enrichment of In, Tl and Nb was seen at Rupelmonde (92.0 km from the river mouth). Mainly the intertidal sediment silt fraction is capable of retaining the elements by exchanging with other ions in the mineral interlayer. Increasing salinity towards the river mouth can furthermore induce the formation of insoluble chloride species. Overall, the solubility of In, Tl, Ta and Nb appeared extremely low upon extraction of pore water from intertidal sediments saturated to 100% field capacity.

Ship-in-a-bottle CMPO in MIL-101(Cr) for selective uranium recovery from aqueous streams through adsorption.

Mesoporous MIL-101(Cr) is used as host for a ship-in-a-bottle type adsorbent for selective U(VI) recovery from aqueous environments. The acid-resistant cage-type MOF is built in-situ around N,N-Diisobutyl-2-(octylphenylphosphoryl)acetamide (CMPO), a sterically demanding ligand with high U(VI) affinity. This one-step procedure yields an adsorbent which is an ideal compromise between homogeneous and heterogeneous systems, where the ligand can act freely within the pores of MIL-101, without leaching, while the adsorbent is easy separable and reusable. The adsorbent was characterized by XRD, FTIR spectroscopy, nitrogen adsorption, XRF, ADF-STEM and EDX, to confirm and quantify the successful encapsulation of the CMPO in MIL-101, and the preservation of the host. Adsorption experiments with a central focus on U(VI) recovery were performed. Very high selectivity for U(VI) was observed, while competitive metal adsorption (rare earths, transition metals...) was almost negligible. The adsorption capacity was calculated at 5.32mg U/g (pH 3) and 27.99mg U/g (pH 4), by fitting equilibrium data to the Langmuir model. Adsorption kinetics correlated to the pseudo-second-order model, where more than 95% of maximum uptake is achieved within 375min. The adsorbed U(VI) is easily recovered by desorption in 0.1M HNO3. Three adsorption/desorption cycles were performed.

Technologies for Arsenic Removal from Water: Current Status and Future Perspectives.

This review paper presents an overview of the available technologies used nowadays for the removal of arsenic species from water. Conventionally applied techniques to remove arsenic species include oxidation, coagulation-flocculation, and membrane techniques. Besides, progress has recently been made on the utility of various nanoparticles for the remediation of contaminated water. A critical analysis of the most widely investigated nanoparticles is presented and promising future research on novel porous materials, such as metal organic frameworks, is suggested.