Organic micropollutants (OMPs) are a threat to aquatic environments, and wastewater treatment plants may act as a source or a barrier of OMPs entering the environment. Understanding the fate of OMPs in wastewater treatment processes is needed to establish efficient OMP removal strategies.Enhanced OMP biotransformation has been documented during biological nitrogen removal and has been attributed to the cometabolic activity of ammonia oxidizing bacteria (AOB) and, specifically, to the ammonia monooxygenase (AMO) enzyme. Yet, the exact mechanisms of OMP biotransformation are often unknown. This review aims to fundamentally and quantitatively evaluate the role of ammonia oxidation in OMP biotransformation during wastewater treatment processes. OMPs can be transformed by AOB via direct and indirect enzymatic reactions: AMO directly transforms OMPs primarily via hydroxylation, while biologically produced reactive nitrogen species (hydroxylamine (NH2OH), nitrite (NO2 − ) and nitric oxide (NO)) can chemically transform OMPs through nitration, hydroxylation and deamination and can contribute significantly to the observed OMP transformations. OMPs containing alkyl-, aliphatic hydroxyl-, ether-, and sulfide functional groups as well as substituted aromatic rings and aromatic primary amines can be biotransformed by AMO, while OMPs containing alkyl groups, phenols, secondary amines and aromatic primary amines can undergo abiotic transformations mediated by reactive nitrogen species.Higher OMP biotransformation efficiencies and rates are obtained in AOB-dominant microbial communities, especially in autotrophic reactors performing nitrification or nitritation, than in non-AOB-dominant microbial communities. The biotransformations of OMPs in wastewater treatment systems can often be linked to ammonium (NH4 + ) removal following two central lines of evidence:(i) similar transformation products (i.e. hydroxylated, nitrated and desaminated TP) are detected in wastewater treatment systems as in AOB pure cultures; (ii) consistency in OMP biotransformation (rbio, µmol/g VSS/d) to NH4 + removal (rNH4+, mol/g VSS/d) rate ratios (rbio/rNH4+) are observed for 3 individual OMPs across different systems with similar rNH4+ and AOB abundances. In this review, we conclude that AOB are the main driver of OMP biotransformation during wastewater treatment processes. The importance of biologically driven abiotic OMP transformation is quantitatively assessed and functional groups susceptible to transformations by AMO and reactive nitrogen species are systematically classified. This review will improve the prediction of OMP transformation and facilitate the design of efficient OMP removal strategies during wastewater treatment.

Dissolved organic matter (DOM) is linked to the heterogeneous distribution of elevated arsenic (As) in groundwater used for drinking and irrigation purposes, but the relationship between DOM characteristics and arsenic mobility has yet to be fully understood. Here, DOM from groundwater sampled in the Bengal Basin region was characterized using both conventional bulk emission-excitation (EEM) spectroscopy and high-performance size exclusion chromatography coupled to spectroscopy (HPSEC-EEM). Notably, application of the novel HPSEC-EEM approach permitted the total fluorescence of individual samples to be independently resolved into its underlying components. This allowed the external validation of the bulk-sample fluorescence decomposition and offered insight into the molecular size distribution of fluorescent DOM. Molecular size distributions were similar for the UVA fluorescent (C 310 , C 340) as well as the three visible fluorescent (C 390 , C 440 C 500) components. There was a greater visible fluorescence in shallow aquifer samples (10-33 m) with high As (SH, up to 418µg/L) than in samples from the same depth with lower As (up to 40µg/L). This indicated a link between DOM quality and As mobility within the shallow aquifer. The deep aquifer samples (170-200 m) revealed DOM characteristics similar to SH samples but had low As concentrations (<4µg/L), signifying that the deep aquifer is potentially vulnerable to As contamination. These findings pave the way for a more comprehensive assessment of the susceptibility of drinking water aquifers, thereby supporting the management of groundwater resources.

Natural dissolved organic matter (DOM) can serve as an additional substrate for organic micropollutant (OMP) degrading bacteria, thus influencing OMP biodegradation in aquatic systems. DOM biodegradation depends on the OMP...

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