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Arsenic (As) is a toxic element, and elevated levels of geogenic As in drinking water pose a threat to the health of several hundred million people worldwide. In this study, we used microfluidics in combination with optical microscopy and X-ray spectroscopy to investigate zerovalent iron (ZVI) corrosion, secondary iron (Fe) phase formation, and As retention processes at the pore scale in ZVI-based water treatment filters. Two 250 μm thick microchannels filled with single ZVI and quartz grain layers were operated intermittently (12 h flow/12 h no-flow) with synthetic groundwater (pH 7.5; 570 μg/L As(III)) over 13 and 49 days. Initially, lepidocrocite (Lp) and carbonate green rust (GRC) were the dominant secondary Fe-phases and underwent cyclic transformation. During no-flow, lepidocrocite partially transformed into GRC and small fractions of magnetite, kinetically limited by Fe(II) diffusion or by decreasing corrosion rates. When flow resumed, GRC rapidly and nearly completely transformed back into lepidocrocite. Longer filter operation combined with a prolonged no-flow period accelerated magnetite formation. Phosphate adsorption onto Fe-phases allowed for downstream calcium carbonate precipitation and, consequently, accelerated anoxic ZVI corrosion. Arsenic was retained on Fe-coated quartz grains and in zones of cyclic Lp-GRC transformation. Our results suggest that intermittent filter operation leads to denser secondary Fe-solids and thereby ensures prolonged filter performance., Environmental Science & Technology, 56 (19), ISSN:0013-936X, ISSN:1520-5851

Synchrotron hard X-ray spectroscopy with focussing optics allows recording X-ray fluorescence (XRF) maps at energies around element specific X-ray absorption edges. Stacking multiple XRF maps along the energy axis yields chemical images that contain spatially resolved information on the speciation of the absorber in the sample matrix at the micrometre scale. Short dwell times needed to keep measurement time and radiation-induced sample changes within acceptable limits result in spectral noise that affects the uncertainty in data analysis. In this study, we develop a model to quantify the uncertainty associated with the processing of XRF image stacks using Bayesian inference. To demonstrate the potential of our approach, the model is applied to stacks of XRF maps collected around the copper (Cu) K-edge (pixel size: 3 × 3 μm2, map sizes: 500 × 500 μm2). The investigated samples include digested sewage sludge spiked with either CuO nanoparticles (NP) or dissolved CuSO4 and their corresponding ashes obtained through incineration. The chemical imaging data reveal differences in species distribution between sludge spiked with CuO NP or dissolved Cu. These differences disappear during the incineration process and the resulting ashes exhibit almost identical Cu species distribution. The uncertainty analysis approach developed in this study can be used for data interpretation, but can also be used for the planning of chemical imaging experiments at synchrotron beamlines., Journal of Analytical Atomic Spectrometry, 35 (3), ISSN:0267-9477, ISSN:1364-5544

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO2) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg−1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg−1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg−1 were incinerated, resulting in SSA with 9 mg kg−1 and 30 mg kg−1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO2-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO2-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds. ISSN:2051-8153 ISSN:2051-8161

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO2) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg−1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg−1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg−1 were incinerated, resulting in SSA with 9 mg kg−1 and 30 mg kg−1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO2-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO2-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds., Conservative engineered nanoparticles (ENPs) that resist transformation during wastewater treatment and sludge incineration can be released from sewage sludge ash. Transient ENPs that undergo transformation are retained in the sewage sludge ash.

Titanium dioxide (TiO

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18–108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10–100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles., Graphical abstract Image 1, Highlights • Characterization of Ce redox speciation in a set of different soils and sewage sludges using XANES. • Oxidation state of Ce from industrial Ce inputs to sludge can vary considerably. • Ce:La ratios in sewage sludge are often distorted by industrial La inputs. • The use of REE patterns yields a robust quantification of industrial Ce. • Ce-bearing particles of industrial origin in the sludge often occur in the nanoscale.

Combustion of sewage sludge has become a viable route for sewage sludge management especially as the agricultural use of sewage sludge has become increasingly difficult due to more stringent requirements regarding the quality of sewage sludge. Combustion of digested sewage sludge in dedicated monocombustion facilities is advantageous, as it substantially reduces the volume of the sludge and still allows for a recovery of phosphorus from the sewage sludge ash at a later stage. Despite increasing amounts of sewage sludge being combusted, knowledge on the respective combustion kinetics is still fragmentary. The goal of this study was, therefore, to identify the major combustion reactions of sewage sludge, assess their Arrhenius parameters (activation energy and pre-exponential factor), and assign suitable reference compounds to the individual reactions. For that purpose, experiments were conducted using a thermogravimetric analyzer (TGA). With matrix inversion, we identified 10 individual reactions. Despite ...

Titanium dioxide (TiO2) (nano)particles are produced in large quantities and their potential impacts on ecosystems warrants investigations into their fate after disposal. TiO2 particles released into wastewater are retained by wastewater treatment plants and accumulate in digested sludge, which is increasingly incinerated in industrialized countries. Therefore, we investigated the changes of the Ti-speciation during incineration of as-received sludge and of sludge spiked with anatase (d=20–50 nm) or rutile (d=200–400 nm) using X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In the as-received sludge, rutile and anatase were the dominant Ti bearing minerals and both remained unaffected by the anaerobic treatment. During incineration, Ti reacts with hematite to members of the hematite-ilmenite solid solution series (Hem-Ilm). Up to 80% of the Ti spiked as anatase transformed into Hem-Ilm, a distorted 6-fold coordinated Ti (Ti(IV)sulfate) and rutile during incineration. Up to 30% and 60% of rutile transformed into Hem-Ilm and Ti(IV)sulfate represented phases in fly and bottom ash, respectively. Fe and Ti were spatially correlated in ash derived from as-received and anatase spiked sludge, whereas only a thin layer of the spiked rutile reacted with Fe, in line with XAS data. This study highlights the transient nature of nano-Ti species during sewage sludge incineration.

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO4, ZnO-NP, or dissolved ZnSO4 into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In t...

Production volumes of cerium dioxide nanoparticles (CeO2 NP) are predicted to increase in the near future, which will result in increasing amounts of CeO2 NP discharged into wastewater systems and their accumulation in the sewage sludge. At the same time, thermal treatments of sewage sludge, especially incineration, are gaining in importance. Therefore, knowledge on the physical–chemical transformations of CeO2 NP during wastewater treatment and sludge incineration is critical for assessing possible (eco-) toxicological effects related to the increased use of CeO2 NP. We, thus, incinerated unspiked municipal sewage sludge as well as sludge spiked with CeO2 of different particle sizes (4 nm (CeO2-s1), 26 nm (CeO2-s2) and >16 μm (CeO2-s3)) in a pilot fluidized bed reactor to investigate the (size dependent) transformation of CeO2 under conditions mimicking full-scale incineration facilities. We used Ce K- and LIII-edge X-ray absorption spectroscopy (XAS) complemented by analytical electron microscopy to assess the changes in Ce speciation and to characterize the morphology of the pristine and the transformed Ce-(nano)particles. After one week of incubation in digested sludge under anaerobic conditions, CeO2-s1 already showed partial reduction (≈40%) to a Ce(III)-phase. Cerium dioxide of larger particle size (CeO2-s2 and -s3) was less reactive and did not show any detectable reduction within the same reaction time. Incineration of the sludge in general led to a further reduction of Ce, irrespective of whether the Ce was spiked (CeO2-s1, CeO2-s2, CeO2-s3) or already present in the sludge. Reduction during incineration was nearly complete for CeO2-s1 but much less pronounced for CeO2-s2 and -s3. Ce(IV) in larger (primary-) particle sizes thus was more resistant to reduction during anaerobic digestion and incineration. In addition, elemental distribution maps of the CeO2-s1 fly ash revealed elevated Ce signal intensities evenly distributed over areas of several 100 nm. The complementary results obtained from spectroscopic and microscopic analyses indicate that incineration led to the reductive decomposition of the initial CeO2-s1 NP and the sequestration of Ce(III) into a mineralogical phase with probably allanite-like local Ce(III) coordination. Our results, thus, highlight the importance of particle size and the surrounding matrix both affecting the transformation of CeO2 during sewage sludge incineration.

Fate and impact of cerium dioxide nanomaterials (CeO2 NM) in soil remains uncertain. Most of the recent environmental studies used high doses of CeO2 NM in short-term laboratory experiments and stated soil as large sink for NM. Recent studies covering the life cycle of plants found evidence for particle uptake in crop plants, and triggered concern about NM entering the food chain. Here, we present a 25 months outdoor lysimeter study that investigates the translocation, biological impact, and transformation of CeO2 NM in soils cultivated with different crops (wheat (Triticum aestivum L.), canola (Brassica napus L.), and barley (Hordeum vulgare L.)). Low doses of CeO2 NM (NM-212, 10 and 50 mg CeO2 NM kg−1 soil) were applied to a Cambisol by sewage sludge or artificial rainwater. To simulate ploughing, the CeO2 NM was mixed into the first 20 cm of the lysimeter soil. Three weeks after the NM application by sewage sludge and five days after the latest NM application by artificial rainwater wheat seeds were sown. We found no vertical Ce translocation to deeper soil layers as well as negligible release of Ce into percolating water, confirming that soil is a sink for CeO2 NM. Furthermore, no inhibition of the NM sensitive ammonium oxidizing bacteria (AOB) was observed which implies a low bioavailability of CeO2 NM in soil. The detected Ce root uptake for canola (Ce Due to negligible mobility in the soil-water interface, as well as non-toxicity to AOB, the environmental risk of the tested CeO2 NM appears to be low, compared to other highly mobile emergent pollutants. Nonetheless, further long-term investigations need to focus on the speciation and localization of NM in plants to clarify uptake and impact of NM to crops.