Work

Biofilm Accelerates As(III) Oxidation on Reactive MnOx Coated Filter Sand in Groundwater Filters

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Removal of carcinogenic arsenic (As) from groundwater is essential for providing safe drinking water. Arsenate (As(V)) is more effectively removed in groundwater filters than arsenite (As(III)), making the oxidation of As(III) to As(V) a key step in the treatment process. This study distinguishes between surface-catalytic and biological As(III) oxidation on natural manganese oxide (MnO x ) coated filter sand, since it is unknown which pathway dominates in filters. The MnO x coated sand was collected from a full-scale groundwater filter and consisted of a mixture of different abiotically and biologically formed Mn oxides, such as Birnessite and Todorokite. A lab-scale filter setup was operated with As(III)-containing water. Within 3 weeks, a shift from surface-catalytic to biological As(III) oxidation was observed. Initially, surface-catalytic As(III) oxidation ( k CHEM = 0.318 min –1 ) was coupled to Mn(II) release at a ratio of 0.96, approximating the stoichiometric ratio of 1. This coupling disappeared over time, indicating the biological nature of the reaction, as confirmed by microbial inhibition. An increase in relative abundance of the known As-oxidizing families Comamonadaceae, with Polaromonas as the dominant genus, and Microscillaceae were found post experiments. Except for these changes, the microbial community on the sand grains stayed relatively similar prior to and post experiments. No significant changes in the physical-chemical properties of the MnO x coating were found post experiments. A first-order biological As(III) oxidation rate constant k BIO of 4.64 min –1 was found, yielding a half-life of 9 s. This represents a 14-fold acceleration compared with surface-catalytic oxidation, revealing that kinetic limitations rather than surface passivation can be attributed to the loss of surface-catalytic oxidation. Our study demonstrates that biological oxidation of As(III) can outpace the acknowledged oxidizing power of MnO x, offering a potential new pathway for the development of effective As removal systems.

Source: ACS ES&T Water

DOI: 10.1021/acsestwater.5c01031

Authors: Roos Goedhart, Emiel Kruisdijk, Doris van Halem

Institution: Delft University of Technology

Language: English

Topic: Arsenic contamination and mitigation

Subfield: Environmental Chemistry

Field: Environmental Science

Domain: Physical Sciences

SDG: Clean water and sanitation

Open Access status: hybrid

Estimated APC paid: $4,500