Metabolic and Proteomic Responses to Salinity in Synthetic Nitrifying Communities of Nitrosomonas spp. and Nitrobacter spp

Metal sulfides in aged-coarse sands tailings facilitate naphthenic acids removal from oil sands process water

The use of natural substrates for oil sands process water (OSPW) reclamation offers advantages such as onsite availability and scalability. This study evaluated potential of aged and fresh coarse sand tailings (CST) towards removal of classical naphthenic acids (NAs) from a real OSPW obtained from an oil sands' tailing ponds in Alberta (NAs: 4.87 mg/L). Aged-CST achieved superior removal efficiencies of NAs (96.5 %), aromatics (>90 %), and acid-extractable organics (∼95 %), compared to fresh-CST, which showed limited removal (∼34.3 %) similar to conventional slow sand filters (∼30-45 %). Although limited surface area of both CST materials (∼1.82 m2/g) was not conducive to physical adsorption, the oxidation of metal sulfides in aged-CST enhanced the chemical reactivity, surface heterogeneity, and microbial activity, facilitating efficient adsorption, precipitation, and biodegradation of NAs. Kinetics modelling indicated that aged-CST strongly fit the pseudo-second order (R² = 0.969, k₂ = 0.003 g mg⁻¹ h⁻¹) and Elovich model (R² = 0.876, 1/b = 1.713 mg g⁻¹), indicating chemisorption as dominant removal mechanism, while fresh-CST exhibited poor fits and limited performance. Fourier-transform infrared spectroscopy and synchronous fluorescence spectroscopy analyses revealed that intensities of hydroxyl groups, aliphatic, carboxylic, and ester compounds significantly increased in aged-CST after filtration. A labelled isotope desorption study using Lauric-D23 acid cross-verified that adsorption and precipitation (∼65 %) with metal sulfides were key mechanisms, while remaining ∼35 % were chemically transformed by-products, as indicated by mass balance. Microbial community analysis showed that aged-CST had higher microbial richness (Chao1 ∼1000) compared to fresh-CST (∼500, respectively). Hydrocarbon-degrading bacteria (e.g., Rhodococcus and Sphingomonas) and acidophilic bacteria (Bryobacter, Candidatus Solibacter) were dominant in aged-CST, facilitating NAs biodegradation. BE-SPME analysis confirmed successful removal (∼86 %) of bioavailable organics removing toxicity. This study highlights aged-CST as a viable natural substrate for OSPW reclamation, offering insights into its fate and opportunities for resource recovery.

Long-term stability of comammox Nitrospira under weakly acidic conditions and their acid-adaptive mechanisms revealed by genome-centric metatranscriptomics

Despite their widespread presence in acidic environments, the stability and adaptative mechanisms of complete ammonia oxidization (comammox) bacteria remain poorly understood. In this three-year study, comammox Nitrospira consistently dominated both abundance and activity in an acidic nitrifying reactor (pH = 6.3-6.8), as revealed by metagenomic and cDNA-based 16S rRNA sequencing. Batch tests demonstrated their decent nitrification down to pH 4.7, while ceasing at pH 4.2. Genome-centric metatranscriptomics revealed that comammox Nitrospira upregulated a Rh-type ammonium transporter to enhance substrate uptake under acidic conditions. Active proton transport, mediated by NADH dehydrogenases and F-type ATPase, was identified as a primary strategy for maintaining pH homeostasis in comammox Nitrospira. Genes associated with carbon acquisition, chemotaxis, and DNA repair were upregulated at low pH, suggesting these processes play roles in acid adaptation. These findings enhance the understanding of ecological roles and adaptive mechanisms of comammox bacteria in acidic environments.

Integrating Genome-Resolved Metagenomics with Trait-Based Process Modeling to Determine Biokinetics of Distinct Nitrifying Communities within Activated Sludge

Conventional bioprocess models for wastewater treatment are based on aggregated bulk biomass concentrations and do not incorporate microbial physiological diversity. Such a broad aggregation of microbial functional groups can fail to predict ecosystem dynamics when high levels of physiological diversity exist within trophic guilds. For instance, functional diversity among nitrite-oxidizing bacteria (NOB) can obfuscate engineering strategies for their out-selection in activated sludge (AS), which is desirable to promote energy-efficient nitrogen removal. Here, we hypothesized that different NOB populations within AS can have different physiological traits that drive process performance, which we tested by estimating biokinetic growth parameters using a combination of highly replicated respirometry, genome-resolved metagenomics, and process modeling. A lab-scale AS reactor subjected to a selective pressure for over 90 days experienced resilience of NOB activity. We recovered three coexisting Nitrospira population genomes belonging to two sublineages, which exhibited distinct growth strategies and underwent a compositional shift following the selective pressure. A trait-based process model calibrated at the NOB genus level better predicted nitrite accumulation than a conventional process model calibrated at the NOB guild level. This work demonstrates that trait-based modeling can be leveraged to improve our prediction, control, and design of functionally diverse microbiomes driving key environmental biotechnologies.

Effective mechanisms of water purification for nitrogen-modified attapulgite, volcanic rock, and combined exogenous microorganisms

The study tested the water purification mechanism of the combination of microorganisms and purification materials via characteristic, enzymatic, and metagenomics methods. At 48 h, the removal rates of total nitrogen, total phosphorous, and Mn chemical oxygen demand in the combination group were 46.91, 50.93, and 65.08%, respectively. The alkaline phosphatase (AKP) activity increased during all times tested in the volcanic rock, Al@TCAP, and exogenous microorganism groups, while the organophosphorus hydrolase (OPH), dehydrogenase (DHO), and microbial nitrite reductase (NAR) activities increased at 36-48, 6-24, and 36-48 h, respectively. However, the tested activities only increased in the combination groups at 48 h. Al@TCAP exhibits a weak microbial loading capacity, and the Al@TCAP removal is primarily attributed to adsorption. The volcanic rock has a sufficient ability to load microorganisms, and the organisms primarily perform the removal for improved water quality. The predominant genera Pirellulaceae and Polynucleobacter served as the sensitive biomarkers for the treatment at 24, 36-48 h. Al@TCAP increased the expression of Planctomycetes and Actinobacteria, while volcanic rock increased and decreased the expression of Planctomycetes and Proteobacteria. The growth of Planctomycetes and the denitrification reaction were promoted by Al@TCAP and the exogenous microorganisms. The purification material addition group decreased the expression of Hyaloraphidium, Chytridiomycetes (especially Hyaloraphidium), and Monoblepharidomycetes and increased at 36-48 h, respectively. Ascomycota, Basidiomycota, and Kickxellomycota increased in group E, which enhanced the nitrogen cycle through microbial enzyme activities, and the growth of the genus Aspergillus enhanced the phosphorous purification effect.

Anoxic storage to promote arsenic removal with groundwater-native iron

Storage containers are usually used to provide a constant water head in decentralized, community groundwater treatment systems for the removal of iron (Fe) and arsenic (As). However, the commonly practiced aeration prior to storage assists in rapid and complete Fe²⁺ oxidation, resulting in poor As removal, despite sufficient native-Fe²⁺ in the source water. In this study, it was found that application of anoxic storage enhanced As removal from groundwater, containing ≥300 µg/L of As(III) and 2.33 mg/L of Fe²⁺ in an As affected village of Rajshahi district in Bangladesh. Although the oxidation of Fe²⁺ and As(III) during oxic storage was considerably faster, the As/Fe removal ratio was higher during anoxic storage (61-80±5 µgAs/mgFe) compared to the oxic storage (45±5 µgAs/mgFe). This higher As removal efficacy in anoxic storage containers could not be attributed to the speciation of As, since As(V) concentrations were higher during oxic storage due to more favorable abiotic (As(III) oxidation by O₂ and Fenton-like intermediates) and biotic (As(III) oxidizing bacteria, e.g., Sideroxydans, Gallionella, Hydrogenophaga) conditions. The continuous, in-situ hydrous ferric oxide floc formation during flow-through operation, and the favorable lower pH aiding higher sorption capacities for the gradually formed As(V) likely contributed to the improved performance in the anoxic storage containers.

Insight into functionally active bacteria in nitrification following Na+ and Mg2+ exposure based on 16S rDNA and 16S rRNA sequencing

Despite increasing interests in osmotic membrane bioreactors, the information regarding the bacterial toxicity effects of reversely transported draw solute (RTDS) is limited. In this study, two representative draw solutes (NaCl and MgCl₂) were used at different concentrations (0, 2.5, 5.0, 7.5 and 10.0 g/L) to evaluate their toxicity in a continuous nitrifying bioreactor. Notably, Mg²⁺ selectively inhibited the activity of ammonia-oxidizing bacteria (AOB), which decreased to 11.3% at 7.5 g-Mg²⁺/L. The rRNA-based analysis was more effective than the rDNA-based analysis to elucidate the relationship between active communities of nitrifying bacteria and the actual nitrifying performance. Nitrosomonas europaea, a representative AOB, was vulnerable to Mg²⁺ in comparison to Na⁺. In contrast, the dominant nitrite-oxidizing bacteria (NOB), Nitrobacter winogradskyi and Nitrolancea hollandica, maintained a relevant level of relative abundance for achieving nitrite oxidation after exposure to 10 g/L Na⁺ and Mg²⁺. This fundamental inhibition information of the draw solute can be applied to set the operational regime preventing the critical solute concentration in mixed liquor of nitrifying OMBRs.