Person: Mahringer, Daniel
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Veröffentlichung Stabilization of chromium (VI) in the presence of iron (II): method development and validation(2020) El-Athman, Fatima; Polenz, Chantal; Mahringer, DanielThe presence of Cr (VI) in drinking water is mainly caused by leaching of chromium-containing aquifer material into groundwater. In contrast to Cr (III), it has been classified as highly toxic. For this reason, the WHO recommends the implementation of separate guideline values, instead of the so far used limit value of total chromium. The separate evaluation of Cr (VI) in raw water and during removal processes requires the Cr (VI) concentration to remain stable after sampling. In the presence of Fe (II), a stabilization of the samples is necessary to inhibit further reduction of Cr (VI) by Fe (II). In this study, two methods of Cr (VI) stabilization in Fe-(II)-containing water samples are investigated: Fe (II) oxidation by oxygen at high pH values in the presence of buffers and Fe (II) complexation by chelating agents. When adding hydrogen carbonate buffer, Cr (VI) recovery reached 100% at pH values of 10 to 12 in the presence of up to 3 mg L-1 Fe (II). Using hydrogen phosphate buffer, Cr (VI) recovery reached 100% only at pH 12 but for a Fe (II) concentration up to 6 mg L-1. Ammonium buffer was found to be less suitable for Cr (VI) stabilization. The addition of EDTA and citrate resulted in low recovery of Cr (VI), whereas citrate was found to accelerate the Cr (VI) reduction. Quelle: https://www.mdpi.comVeröffentlichung Pilot-scale vanadium adsorption onto in-situ biogenic amorphous ferric hydroxide(2023) Mahringer, Daniel; Ruhl, Aki Sebastian; Zerelli, Sami SofieneIn order to reach 4 (micro)g l-1 vanadium in drinking water adsorption onto in-situ biogenic amorphous ferric hydroxide (AFH) is identified as robust new treatment. The evaluation of its technical feasibility and robustness was the aim of this study. As approach at pilot-scale, Fe(II) and oxygen was dosed before pilot waterworks and Fe(II) subsequently biotically oxidized and precipitated in a filter bed. The so in-situ generated biogenic AFH served as adsorbent for vanadium removal. Results show that an initial vanadium concentration of 30 (micro)g l-1 was removed to below 4 (micro)g l-1, if at least 3 mg l-1 Fe(II) were dosed, resulting in a loading of 8.7 mg V per g AFH. A vanadium concentration of 60 (micro)g l-1 with a dosage of 3 mg l-1 Fe(II) was the upper limit for sufficient removal. Vanadium removal increased with increasing pH in the technical setup, due to faster oxidation of Fe(II) in the supernatant, even though adsorption capacity of AFH decreases with increasing pH. A filtration velocity of 20 m h -1 represented the highest velocity to undercut 4 (micro)g l-1 vanadium in the effluent. By mixing Fe(II) containing groundwater with oxygen and vanadium containing water prior to an adsorption filter with AFH sufficient removal was reached, however dependent on the resulting Fe(II) concentration. © 2023 by the authorsVeröffentlichung The fate of selenium in a pilot plant for biological iron and manganese removal(2023) Dippon-Deissler, Urs; Mahringer, Daniel; Ruhl, Aki Sebastian; Steuer, AndreaSelenium (Se) is essential to human health, yet harmful in high doses. Of the water-soluble Se redox species, Se(IV) readily adsorbs onto iron and aluminium oxides. Se(VI), the dominant form in oxygenated waters, is more mobile and less readily adsorbed. In this study, the removal of Se(VI) by reduction with Fe(II) to Se(IV) and subsequent adsorption onto iron hydroxides is investigated in a pilot plant for biological iron and manganese removal from groundwater to investigate an economical approach for Se removal during drinking water production. While Se(IV) is removed by up to 90%, Se(VI) shows no removal over 48 h. In batch-shaking tests, the adsorption of Se(IV) and Se(VI) onto iron hydroxides with and without addition of Fe(II) or dithionite as reducing agents was studied. Se(IV) was removed to a greater extent by adsorption than Se(VI) (7% and 2.6%, respectively, at a starting concentration of 0.1 mg/L) and the addition of reducing agents resulted in no significantly higher removal of Se(VI). Reducing Se(VI) with Fe(II) or dithionite and consequent adsorption onto iron hydroxides can therefore be excluded as viable removal mechanism for Se(VI). © 2023 by the authorsVeröffentlichung Entfernung von Chrom (VI) mit Reduktion, Koagulation, Filtration und biologischer Eisenoxidation (RCbF) im Pilotmaßstab(2021) Dippon-Deissler, Urs; Mahringer, Daniel; Ruhl, Aki Sebastian; Zerelli, Sami SofieneVeröffentlichung Biogenic amorphous ferric hydroxide as adsorbent for vanadium removal in drinking water production(2023) Dippon-Deissler, Urs; Mahringer, Daniel; Ruhl, Aki Sebastian; Zerelli, Sami SofieneVanadium as toxic heavy metal is a drinking water relevant contaminant. However, there is a lack in treatment processes to meet regulatory requirements (e.g. 4 g l-1 in Germany). This study introduces a novel treatment process - the vanadium adsorption onto biogenic amorphous ferric hydroxide (AFH). Basic mechanisms of adsorption onto AFH are described and compared to granular ferric hydroxide (GFH). Adsorption kinetics and pH dependent isotherms in drinking and ultrapure water, parametrization via the empirical Freundlich and Langmuir models, and bond type and strength assessments via sequential extraction are presented. AFH was generated in pilot waterworks in which Fe(II) and oxygen were dosed and subsequently Fe(II) microbiologically oxidized and precipitated in the filter bed. The backwash-water was collected and used for adsorption experiments. Sequential extraction was executed with vanadium loaded AFH produced in the pilot plant. AFH is identified as alternative adsorbent to GFH with similar affinity and capacity. The isotherms cover a concentration range from 10 g l-1 to 4 mg l-1 and the Freundlich model showed a better fit with the experimental data than the Langmuir model. A bidentate mononuclear inner sphere complex is assumed for vanadium adsorption onto AFH, while a bidentate binuclear inner sphere complex is expected for GFH. Sequential extraction showed a strong bond between AFH and vanadium, which was only mobilized by the last extraction step the dissolution of iron particles. A treatment process - adsorption onto biogenic AFH - is suitable for effective vanadium removal and should be further investigated for technical implementation. © 2023 The Author(s).Veröffentlichung Bromat im Trinkwasser: Herkunft, Vorkommen und gesundheitliche Bewertung(2021) Chorus, Ingrid; El-Athman, Fatima; Kämpfe, Alexander David; Mahringer, DanielVeröffentlichung Redox Behavior of Chromium in the Reduction, Coagulation, and Biotic Filtration (RCbF) Drinking Water Treatment(2023) Mahringer, Daniel; Ruhl, Aki Sebastian; Zerelli, Sami SofieneThe chromium (Cr) limit values are currently tightened to 25 (micro)g L-1 (EU), 5 (micro)g L-1 (Germany), and possibly 10 (micro)g L-1 Cr(VI) (California). The combined process of chemical reduction, coagulation, and biotic filtration (RCbF) efficiently removes Cr(VI) in drinking water. In this study, redox-active substances (O2, NO3-, Fe2+, MnO2) were investigated concerning their effect on the RCbF process. The experiments were performed at two-stage pilot waterworks for biological iron and manganese removal. O2 or NO3- as oxidants affected the RCbF process, neither by consumption of the reductant Fe(II) nor by re-oxidation of already formed Cr(III) in the supernatant of the filter bed. However, the oxidation of Cr(III) by O2 to Cr(VI) with MnO2 as a mediator was identified as potential risk for Cr breakthrough. Up to one third of the initial Cr(III) concentration was oxidized to Cr(VI) in the second filter bed within a contact time of only 5 min. The kinetically relevant mechanism seemed to be the formation of Cr(III)Fe(III)-hydroxides and not the reduction of Cr(VI) by Fe(II). Further, the mixing of Cr(VI) containing raw water with Fe(II) containing groundwater was determined as a chemical-free alternative for the RCbF process, depending on the resulting Fe(II) concentration after mixing. © 2023 by the authorsVeröffentlichung Aufbereitung von mit Chrom belastetem Rohwasser für die öffentliche Trinkwasserversorgung(2019) Bartel, Hartmut; Mahringer, Daniel; Deutschland. Umweltbundesamt; Mudra, Rocco; Stützer, Christian; Zerelli, SofianAufgrund neuer Erkenntnisse zum Vorkommen von Chrom und der aktuellen toxikologischen Bewertung wird die Einführung eines Grenzwertes für Chrom VI (Cr (VI)) im Trinkwasser in Deutschland diskutiert. Im Projekt "Aufbereitung von mit Chrom belastetem Rohwasser für die öffentliche Trinkwasserversorgung" wurde die technische Machbarkeit zur Entfernung von Cr(VI) mittels des Aufbereitungsprozesses der biologischen Enteisenung und Entmanganung im halbtechnischen Maßstab untersucht. Reduziertes Eisen-(II)-haltiges Grundwasser enthält aufgrund der thermodynamischen Stabilität kein Cr(VI). Daher wurde das Aufbereitungsverfahren - Reduktion, Coagulation, Filtration (RCF) - im Projekt um die biologische Enteisenung erweitert - im Folgenden als "bio-Fe-RCF" abgekürzt. Bei diesem Verfahren wird Cr(VI)-haltigem Rohwasser Fe(II) zudosiert. Infolgedessen wird Cr(VI) chemisch zu kaum löslichem Chrom III (Cr(III)) reduziert, welches anschließend koaguliert und im nachfolgenden Filtrationsprozess abgetrennt wird. Überschüssiges Fe(II) wird im anschließenden Filtrationsprozess mithilfe der biologischen Enteisenung entfernt. Gegenüber dem RCF-Verfahren bietet "bio-Fe-RCF" folgende Vorteile: Die Oxidation des Fe(II) findet mikrobiologisch katalysiert und (unter-)stöchiometrisch erst nach Eintritt in das Filterbett statt. Auf diese Weise wird die Kontaktzeit zwischen Fe(II) und Cr(VI) vor dem Eintritt ins Filterbett optimiert. Aufgrund der geringen Sauerstoffkonzentration oxidiert soeben entstandenes Cr(III) nicht zurück zu Cr(VI). Ebenfalls wird Cr(VI) als Oxidationsmittel gegenüber gelöstem Sauerstoff begünstigt, um Fe(II) zu oxidieren. Das Aufbereitungsverfahren erreicht zuverlässig Konzentrationen unter 0,5 (mikro)g/L Cr (VI). Konzentrationen unter 0,3 (mikro)g/L Cr (VI) werden mit großem Aufwand und Prozessoptimierung erreicht. Verglichen mit Schwankungen der Randbedingungen wie pH-Wert, Filtrationsgeschwindigkeit, Anwesenheit von Nitrat oder der Cr(VI) -Konzentration ist das Verfahren sehr robust. Die anfängliche Konzentration an Fe(II) erwies sich als wichtigster Parameter für den Aufbereitungserfolg. Ein Durchbruch von Cr(III) durch die Enteisenungsstufe führt unweigerlich zu einer Rückoxidation zu Cr(VI) an der Mangandioxidoberfläche der anschließenden Entmanganungsstufe. Die Entsorgung des Rückspülschlamms über Indirekteinleitung ins Abwasser scheint problematisch, weil die Schwellenwerte der föderalen Gesetzgebung für Chrom übertroffen werden können; hierfür bedarf es noch der Entwicklung eines Lösungsweges. Chrom wird in dreiwertiger Form im Schlamm fest in die Mineralstuktur der Eisenablagerung eingebaut. Die Mischung von Cr(VI)-haltigem, Fe(II)-freiem mit Cr(VI)-freiem und Fe(II)-haltigem Rohwasser mit anschließender Aufbereitung mit der biologischen Enteisenung führt ebenfalls zu einer weitgehenden Entfernung. Quelle: ForshcungsberichtVeröffentlichung Pilot scale hexavalent chromium removal with reduction, coagulation, filtration and biological iron oxidation(2020) Dippon-Deissler, Urs; Mahringer, Daniel; Ruhl, Aki Sebastian; Zerelli, Sami SofieneCr(VI) is identified as highly toxic, therefore a far-reaching limitation of total chromium or Cr(VI) in drinking water was proposed by the Germany Environment Agency. There is a lack in efficient treatment processes to reach Cr(VI) concentrations below 1 (my)g L-1. In this study, the combination of chemical reduction, coagulation and filtration (RCF) was further developed by adding biological iron removal as filtration step (RCbF). The aim of this enhancement was to reach lower effluent concentrations and a higher robustness regarding process parameters. The effectiveness of Cr(VI) removal was investigated using two-stage pilot-scale waterworks. RCbF reaches Cr(VI) effluent concentrations below 0.5 (my)g L-1 despite variations of pH, filtration velocity, or Cr(VI) influent concentrations. Fe(II) dosage and hence molar excess of Fe(II) over Cr(VI) was identified as the key parameter for Cr(VI) removal. Low oxygen dosage for biological iron removal improved the efficiency of RCbF compared to RCF. The co-precipitation of Cr(III) and Fe(III) as solid solution in the supernatant of the filter bed was promoted by low oxygen concentrations making Cr(VI) the preferred oxidant. RCbF was shown to be a suitable treatment process for reaching a low limit value for total chromium or Cr(VI) concerning technical feasibility. © 2020 The Authors.Veröffentlichung Aufbereitung von mit Chrom belastetem Rohwasser für die öffentliche Trinkwasserversorgung(2018) Mahringer, Daniel; Deutschland. Umweltbundesamt