Filter by Themen
Abwasserbehandlung
Analytik & Hygiene
Digitalisierung
Events
Nachhaltigkeit & Umweltschutz
Netze
Wasser & Abwasser
Wasseraufbereitung
Wassergewinnung
Wasserstress
Water Solutions
Filter by Kategorien
Advertorial
Branche
Events
Forschung & Entwicklung
Leute
News
People
Products & Solutions
Produkte & Verfahren
Publications
Publikationen
Sonstiges
Trade & Industry
Filter by Veranstaltungsschlagworte
abwasser
ACHEMA
Automatisierung
FDBR
Hydrologie
kanalnetze
MSR
Talsperren
trinkwasser
wasseraufbereitung
wasserbau
Wassernetze
Wasserversorgung

How rusting iron removes arsenic from water

Kategorie:
Thema:
Autor: Franziska Betz

How rusting iron removes arsenic from water
The researchers were able to use the experiment to show when and where arsenic and other elements from the water were bound to the iron. photo: Eawag

November 2, 2022 | In many regions of the world, groundwater is contaminated with arsenic of natural origin. The harmful substance can be filtered out of water with the help of iron. Eawag researchers have for the first time made visible exactly what happens in this process in a new type of experimental set-up.

When metallic iron corrodes, i.e. rusts, iron oxides are formed that can strongly bind pollutants such as arsenic. Simple and inexpensive water filters are based on this principle, which people in the affected regions of Africa and Asia can use to treat arsenic-contaminated drinking water. Iron powder, iron filings or iron nails are used, often in combination with sand. Much research has been done in recent years on the efficiency of these filter methods, including at Eawag in Bangladesh.

“Previous studies on this topic have one drawback, however,” says Andreas Voegelin, head of the Molecular Environmental Geochemistry group in Eawag’s Water Resources and Drinking Water (W + T) department. “The reactions between arsenic and iron are usually investigated in suspensions in which the filter material is floating in the water. However, the results do not show which processes take place in the pore space, i.e. the cavities between the individual solid particles of a filter.+ The researchers from the W +T department were particularly interested in how arsenic removal is influenced by the periodic operation of a water filter, i.e. when water flow and water accumulation alternate.

The work groups of Andreas Voegelin, Joaquin Jimenez-Martinez, Stephan Hug and Michael Berg wanted to explore this question in a joint experiment that combined all their expertise. Environmental engineer Jonas Wielinski, who did his doctorate at Eawag, took on the challenging tasks and developed an experimental set-up that reproduces the conditions in an arsenic filter as well as possible and makes them visible.

“Our objective was to observe and understand the geochemical processes in the pore space between iron particles and sand grains on the scale of micrometres,” says Wielinski, who is now a postdoctoral researcher at Carnegie Mellon University in the USA.

Miniature filters under the microscope

Under an optical microscope in Jimenez-Martinez’s microfluidics laboratory, Wielinski examined an arsenic filter in miniature: a channel only 250 micrometres deep and 45 millimetres long, filled alternately with strips of quartz sand and iron grains. The researchers added arsenic and other elements to the water used to run the filter model in concentrations typical of groundwater in Bangladesh. The pump connected to the filter pumped water through the system for twelve hours at a time, followed by a twelve-hour break, during which the water rested in the filter.

Wielinski regularly sampled the filtered water during the experiment, which lasted several weeks, to determine the removal of the arsenic. With the optical microscope, he automatically took a picture of the filter model every 30 minutes. Played back in fast motion, these images show in detail how the metallic iron corrodes and how the newly-formed iron oxides change colour in cycles – from green-black to orange-red and brown when the water is flowing and vice.-versa when the water stops. These colour changes are a consequence of the corrosion processes, in the course of which various iron oxides are formed and cyclically transformed.

Alternation between water flow and water accumulation favours filtration

After the end of the experiment, the filter model was analysed by X-ray microscopy to determine the type and distribution of the iron oxides and the arsenic bound to them. By combining these results with the colour changes observed in the optical microscope, the researchers were able to understand in detail the dynamic formation and transformation of the iron oxides in the filter and their effect on arsenic removal.

“With this new experimental set-up, we were able to visually demonstrate how the distribution of the iron and quartz sand grains and the water flow through the filter influence the spatial and temporal sequence of the arsenic removal,” says Wielinski. In particular, the alternation between water flow and water accumulation had a positive effect on the filter performance. “A realisation that is useful in the further optimisation of such filters,” he notes and adds: “The set-up developed in this study also has great potential for researching other biogeochemical processes in porous media such as groundwater aquifers or soils.

Original Publication

Wielinski, J.; Jimenez-Martinez, J.; Göttlicher, J.; Steininger, R.; Mangold, S.; Hug, S. J.; Berg, M.; Voegelin, A. (2022) Spatiotemporal mineral phase evolution and arsenic retention in microfluidic models of zerovalent iron-based water treatment, Environmental Science and Technology, 56(19), 13696-13708,

Das könnte Sie auch interessieren:

New research shows even a wastewater plant can catch a cold
An integrated modeling framework to assess surface and ground water resources
Arctic lakes act as chimneys for carbon dioxide

Passende Firmen zum Thema:

Publikationen

Water Sensitive Urban Design as a Role Model for Water Management in Germany?

Water Sensitive Urban Design as a Role Model for Water Management in Germany?

Autor: Jacqueline Hoyer / Juliane Ziegler
Themenbereich: gwf - Wasser|Abwasser
Erscheinungsjahr: 2013

“Water Sensitive Urban Design” (WSUD), originally developed in Australia, is a planning and design approach combining the functionality of water management with principles of urban design. WSUD is mainly used in the development of integrated ...

Zum Produkt

Tertiary Filtration with Ultrafiltration Membranes in Municipal Wastewater Treatment Plants

Tertiary Filtration with Ultrafiltration Membranes in Municipal Wastewater Treatment Plants

Autor: Martin Wett and Eberhard Back
Themenbereich: gwf - Wasser|Abwasser
Erscheinungsjahr: 2011

During the operation of tertiary filtration stages in a dead-end-mode, retentate concentrate and rinsing water from membrane cleaning accrue naturally. Work on process solutions for these process waters with no additional particle loads for the ...

Zum Produkt

Water Solutions – 01 2017

Water Solutions – 01 2017

Themenbereich: Water Solutions
Erscheinungsjahr: 2017

The leading professional magazine for water and wastewater ...

Zum Produkt

Sie möchten die gwf Wasser + Abwasser testen

Bestellen Sie Ihr kostenloses Probeheft

Überzeugen Sie sich selbst: Gerne senden wir Ihnen die gwf Wasser + Abwasser kostenlos und unverbindlich zur Probe!

Finance Illustration 03