Manganese-mediated ammonium removal by a bacterial consortium from wastewater: Experimental proof and biochemical mechanisms

Adsorption and nitrogen removal of NH4+-N based on Mn (II)/α-MnO2 cycle in bio-electrochemical system

This paper developed a single-chamber α-MnO2-coupled microbial electrolysis cell (α-MnO2-MEC) system to enhance the oxidation denitrification rate of ammonia nitrogen (NH4+-N) in order to overcome the electrode repulsion problem between NH4+ and the anode. The α-MnO2 material with an equilibrium adsorption capacity of 10.6 mg·g-1 for NH4+-N was developed. The removal rate of total nitrogen in the α-MnO2-MEC reactor is 95.8 %, and NH4+ oxidation efficiency is 100 % in 20 h, which is 78.7 % and 47.8 % higher than in the α-MnO2 reactor and the MEC reactor, respectively. The Mn(II)/α-MnO2 cycle was realized in α-MnO2-MEC reactor, avoiding the loss of the Mn(II). The 16S rRNA gene sequencing identified key microbial genera involved in the ammonia removal are Candidatus_Brocadia, SC-I-84, and Thauera. This study demonstrates that combining α-MnO2 with bioelectrochemistry provides a novel strategy for ammonia nitrogen wastewater treatment, offering a new insight for optimizing electrochemical-microbial coupled nitrogen removal.

Simultaneous removal of ammonia, cadmium, and oxytetracycline via a double-layer immobilized bioreactor driven by manganese redox: Optimization and potential mechanism

The coexistence of ammonia nitrogen (NH4+-N), heavy metals and antibiotics in composite polluted wastewater has garnered significant attention. This study developed a novel double-layer biological carrier using sodium alginate, diatomite, polyvinyl alcohol, manganese-modified biochar, and pyrolusite, loaded with strains YZ8 and MA23 to form an efficient bioreactor (M1). Under conditions of a hydraulic retention time of 24 h, the carbon to nitrogen ratio and pH were 1.5 and 6.5, M1 achieved an average NH4+-N removal efficiency of 99 %. Additionally, the average removal efficiencies of cadmium and oxytetracycline by M1 through biosorption, co-precipitation and Mn(Ⅲ) oxidation reached 90 % and 85 %, respectively. High-throughput results indicated that M1 had a relatively high abundance of functional bacterial genera. Comparative KEGG analysis revealed that M1 promoted the expression of functional genes involved in N cycling and Mn transformation. This study offers new perspectives on tackling the issue of composite water environmental pollution.

Autotrophic ammonium nitrogen removal process mediated by manganese oxides: Bioreactors performance optimization and potential mechanisms

Manganese(IV) (Mn(IV)) reduction coupled with ammonium (NH4+-N) oxidation (Mnammox) has been found to play a significant role in the nitrogen (N) cycle within natural ecosystems. However, research and application of the autotrophic NH4+-N removal process mediated by manganese oxides (MnOx) in wastewater treatment are currently limited. This study established autotrophic NH4+-N removal sludge reactors mediated by various MnOx types, including δ-MnO2 (δ-MSR), β-MnO2 (β-MSR), α-MnO2 (α-MSR), and natural Mn ore (MOSR), investigating their NH4+-N removal performances and mechanisms under different initial N loading and pH conditions. During the 330 d operation, the reactors exhibited NH4+-N removal efficiencies in the order of δ-MSR > α-MSR > β-MSR > MOSR. Notably, metal-reducing bacteria (Candidatus Brocadia, Dechloromonas, and Rhodocyclaceae) and Mn(II) oxidizing bacteria (Pseudomonas and Zoogloea) were enriched in the reactors, especially in the δ-MSR. The presence of these microorganisms facilitated the reduction of Mn(IV) and utilized the generated Mn(II) to drive autotrophic denitrification (MnOAD), thereby completing the Mn(IV)/Mn(II) cycle and enhancing N removal in the system. An active Mn cycle displayed in δ-MSR, which could be demonstrated by the formation of petal-shaped biogenic MnOx and the increased abundance of Mn cycling genes (MtrCDE, MtrA, MtrB, and CotA, etc.). Meanwhile, genes involved in N metabolism were enriched, particularly functional genes associated with nitrification and denitrification. In this study, the coupling of Mnammox and MnOAD was realized via the Mn cycle, providing a new perspective on the application of autotrophic N removal technologies in wastewater treatment.

Simultaneous removal of ammonia, copper ions and sulfamethoxazole from aquaculture wastewater with low carbon to nitrogen ratio enhanced by manganese redox driven by a two-stage synergistic bioreactor: Optimization and potential mechanism

The problem of low carbon-nitrogen ratio (C/N) in wastewater is a major challenge for biological treatment, especially the complex pollution of ammonia nitrogen (NH4+-N), sulfamethoxazole (SMX), and copper ions (Cu(II)). Herein, a strain of Pseudoxanthomonas sp. MA23 with manganese (Mn) reduction-coupled ammonia oxidation properties was isolated. Subsequently, kaolin and bentonite were used as the main raw materials, and a mixture of coconut shell biochar (CSBC) and different Mn ores were added to make ceramsite carriers to load the target strain MA23. To achieve complete N removal and Mn redox process, Dechloromonas sp. YZ8 with Mn redox and denitrification performance was introduced, and a second-stage bioreactor was constructed with volcanic rock as the biocarrier. The results showed that the bioreactor was most effective when the hydraulic retention time (HRT) was 20.0 and 2.0 h, C/N was 1.5, and pH was 6.5. The response of the bioreactors was investigated by inflowing different concentrations of Cu(II) and SMX. Appropriate Cu(II) concentrations promoted the electron transfer in the system, and Cu(II) and SMX were together removed by biological action and chemisorption. Furthermore, genes involved in N metabolism were enriched in the bioreactors and the microorganisms responded to environmental changes by up or down-regulating relevant metabolic genes. The synergistic system proposed in this study provided a promising attempt to simultaneously address NH4+-N-Cu(II)-SMX pollution in low C/N wastewater.

Efficient manganese ammonia oxidation (Mnammox) and its influencing factors at low temperature: Metal oxide-mediated denitrification process in water bodies

This study explores the metal oxide-mediated NH4+-N reduction process: manganese ammonia oxidation efficiency, influencing factors and its resistance to low-temperature environments in water bodies. After 177d of stabilized startup of an up-flow reactor, NH4+-N removal efficiency was 63.51 %, total nitrogen (TN) removal rate was 0.021 kg/(m3.d), and effluent Mn2+ concentration was 1.503 mg/L, which was in dynamic equilibrium. X-ray photoelectron spectroscopy exhibited manganese valence state 3.29, similar to biological manganese oxidation. High-throughput sequencing revealed that phyla's denitrification function increased relative abundance, and manganese-reducing bacterial genera appeared. The batch test showed that 5 mg MnO2 had NH4+-N removal at 85.01 %. After 44 days, NH4+-N removal efficiency was 77.47 %, effluent Mn2+ concentration was 3.280 mg/L, TN removal rate was 0.063 kg/(m3.d). The long-term effect of the influent load change on the denitrification and Mnammox efficiency at 25 ∼ 15 °C was examined. Effluent Mn2+ concentration was 1.811 mg/L was relatively stable. Manganese valence decreased from 3.29 to 3.20, Mn4+ decreased by 9.58 %, while Mn3+ and Mn2+ increased by 10.94 % and 1.37 %, respectively. A new phylum Thermotogota and genus SBR1031 appeared in the microbial community.

Enhanced nitrogen removal in constructed wetlands with multivalent manganese oxides: Mechanisms underlying ammonium oxidation processes

The ammonium (NH4+) removal efficiency in constructed wetlands (CWs) is often limited by insufficient oxygen. In this study, an extract of Eucalyptus robusta Smith leaves was used to prepare multivalent manganese oxides (MVMOs) as substrates, which were used to drive manganese oxide (MnOx) reduction coupled to anaerobic NH4+ oxidation (Mnammox). To investigate the effects and mechanisms of MVMOs on ammonium nitrogen (NH4+-N) removal, four laboratory-scale CWs (0 %/5 %/15 %/25 % volume ratios of MVMOs) were set up and operated as continuous systems. The results showed that compared to controlled C-CW (0 % MVMOs), Mn25-CW (25 % MVMOs) improved the average NH4+-N removal efficiency from 24.31 % to 80.51 %. Furthermore, N2O emissions were reduced by 81.12 % for Mn25-CW. Isotopic tracer incubations provided direct evidence of Mnammox occurrence in Mn-CWs, contributing to 18.05-43.64 % of NH4+-N removal, primarily through the N2-producing pathway (73.54-90.37 %). Notably, batch experiments indicated that Mn(III) played a predominant role in Mnammox. Finally, microbial analysis revealed the highest abundance of the nitrifying bacteria Nitrospira and Mn-cycling bacteria Pseudomonas, Geobacter, Anaeromyxobacter, Geothrix and Novosphingobium in Mn25-CW, corresponding to its superior NH4+-N removal efficiency. The enhancement of NH4+ oxidation, first to hydroxylamine and then to nitrite, in Mn25-CW was attributed to the upregulation of ammonia monooxygenase genes (amoABC and hao). This study enhanced our understanding of Mnammox and provided further support for the use of manganese oxide substrates in CWs for efficient NH4+-N removal.

Plant-microbe involvement: How manganese achieves harmonious nitrogen-removal and carbon-reduction in constructed wetlands

Carbon deficits in inflow frequently lead to inefficient nitrogen removal in constructed wetlands (CWs) treating tailwater. Solid carbon sources, commonly employed to enhance denitrification in CWs, increase carbon emissions. In this study, MnO2 was incorporated into polycaprolactone substrates within CWs, significantly enhancing NH4+-N and NO3--N removal efficiencies by 48.26-59.78 % and 96.84-137.23 %, respectively. These improvements were attributed to enriched nitrogen-removal-related enzymes and increased plant absorption. Under high nitrogen loads (9.55 ± 0.34 g/m3/d), emissions of greenhouse gases (CO2, CH4, and N2O) decreased by 147.23-202.51 %, 14.53-86.76 %, and 63.36-87.36 %, respectively. N2O emissions were reduced through bolstered microbial nitrogen removal pathways by polycaprolactone and MnO2. CH4 accumulation was mitigated by the increased methanotrophs and dampened methanogenesis, modulated by manganese. Additionally, manganese-induced increases in photosynthetic pigment contents (21.28-64.65 %) fostered CO2 sequestration through plant photosynthesis. This research provides innovative perspectives on enhancing nitrogen removal and reducing greenhouse gas emissions in constructed wetlands with polymeric substrates.

Biomineralized manganese oxide mediated nitrogen-contained wastewater treatment

In recent years, manganese (Mn) has emerged as an accelerator for nitrogen metabolism. However, the bioactivity of manganese is limited by the restricted contact between microbes and manganese minerals in the solid phase and by the toxicity of manganese to microbes. To enhance the bioactivity of solid-phase manganese, biomineralized manganese oxide (MnOx) modified by Lactobacillus was introduced. Nitrogen removal performance have confirmed the effective role of biomineralized MnOx in accelerating the removal of total inorganic nitrogen (TIN). Metagenomic analysis has confirmed the enhancement of the nitrogen metabolic pathway and microbial extracellular electron transfer (MEET) in biomineralized MnOx treatment group (BIOA group). Additionally, the enrichment of manganese oxidation and denitrification genus indicates a coupling between nitrogen metabolism and manganese metabolism. One point of views is that biomineralized MnOx-mediated nitrogen transformation processes could serve as a substitute for traditional nitrogen removal processes.