Molecular mechanisms through which different carbon sources affect denitrification by Thauera linaloolentis: Electron generation, transfer, and competition

Bioanode boosts efficacy of chlorobenzenes-powered microbial fuel cell: Performance, kinetics, and mechanism

Microbial fuel cell (MFC) is a promising device for water decontamination and energy generation. However, the correlation between power generation and pollutant degradation has not been clarified. Herein, a ruthenium-activated carbon (Ru-AC) bioanode was constructed for chlorobenzenes (CBs) treatment. The pollutant tolerance was improved by Ru-AC anode, and the minimum removal efficiencies of CB and ortho-dichlorobenzene (o-DCB) reached 75.1 % and 69.3 %, respectively, which were considerably higher than those of other MFCs (16.3 %-39.7 %). Correspondingly, the maximum output voltage reached 360.7 mV for the Ru-AC anode, whereas the values obtained from others reached 45.2-149.6 mV. Interaction models were introduced to quantify the relationship between power generation and pollutant degradation. The conversion of highly toxic chlorophenols to organic acids could be accelerated by boosting the mass and electron transfer, thereby simultaneously enhancing CBs removal and power generation. This work provided important insights into pollutant-powered MFC development.

How halogenated aromatic compounds affect the electron supply and consumption in glucose supported denitrification?

Halogenated aromatic compounds possess bidirectional effects on denitrifying bio-electron behavior, providing electrons and potentially interfering with electron consumption. This study selected the typical 4-chlorophenol (4-CP, 0-100 mg/L) to explore its impact mechanism on glucose-supported denitrification. When COD(glucose)/COD(4-CP)=28.70-3.59, glucose metabolism remained the dominant electron supply process, although its removal efficiency decreased to 73.84-49.66 %. When COD(glucose)/COD(4-CP)=2.39-1.43, 4-CP changed microbial carbon metabolism priority by inhibiting the abundance of glucose metabolizing enzymes, gradually replacing glucose as the dominant electron donor. Moreover, 5-100 mg/L 4-CP reduced adenosine triphosphate (ATP) by 15.52-24.67 % and increased reactive oxygen species (ROS) by 31.13-63.47 %, causing severe lipid peroxidation, thus inhibiting the utilization efficiency of glucose. Activated by glucose, 4-CP dechlorination had stronger electron consumption ability than NO2--N reduction (NO3--N > 4-CP > NO2--N), combined with the decreased nirS and nirK genes abundance, resulting in NO2--N accumulation. Compared with the blank group (0 mg/L 4-CP), 5-40 mg/L and 60-100 mg/L 4-CP reduced the secretion of cytochrome c and flavin adenine dinucleotides (FAD), respectively, further decreasing the electron transfer activity of denitrification system. Micropruina, a genus that participated in denitrification based on glucose, was gradually replaced by Candidatus_Microthrix, a genus that possessed 4-CP degradation and denitrification functions after introducing 60-100 mg/L 4-CP.

Exploratory study on the metabolic similarity of denitrifying carbon sources

Mixed carbon sources have been developed for denitrification to eliminate the "carbon dependency" problem of single carbon. The metabolic correlation between different carbon sources is significant as guidance for the development of novel mixed carbon sources. In this study, to explore the metabolic similarity of denitrifying carbon sources, we selected alcohols (methanol, ethanol, and glycerol) and saccharide carbon sources (glucose, sucrose, and starch). Batch denitrification experiments revealed that methanol-acclimated sludge improved the denitrification rate of both methanol (14.42 mg-N/gMLVSS*h) and ethanol (9.65 mg-N/gMLVSS*h), whereas ethanol-acclimated sludge improved the denitrification rate of both methanol (7.80 mg-N/gMLVSS*h) and ethanol (22.23 mg-N/gMLVSS*h). In addition, the glucose-acclimated sludge and sucrose-acclimated sludge possibly improved the denitrification rate of glucose and sucrose, and the glycerol-acclimated sludge improved the denitrification rate of volatile fatty acids (VFAs), alcohols, and saccharide carbon sources. Functional gene analysis revealed that methanol, ethanol, and glycerol exhibited active alcohol oxidation and glyoxylate metabolism, and glycerol, glucose, and sucrose exhibited active glycolysis metabolism. This indicated that the similarity in the denitrification metabolism of these carbon sources was based on functional gene similarity, and glycerol-acclimated sludge exhibited the most diverse metabolism, which ensured its good denitrification effect with other carbon sources.

Thauera sp. for efficient nitrate removal in continuous denitrifying moving bed biofilm reactor

Thauera is the most widely found dominant denitrifying genus in wastewater. In earlier study, MBBR augmented with a specially developed denitrifying five-membered bacterial consortium (DC5) where Thauera was found to be the most abundant and persistent genus. Therefore, to check the functional potential of Thauera in the removal of nitrate-containing wastewater in the present study Thauera sp.V14 one of the member of the consortium DC5 was used as the model organism. Thauera sp.V14 exhibited strong hydrophobicity, auto-aggregation ability, biofilm formation and denitrification ability, which indicated its robust adaptability short colonization and nitrate removal efficiency. Continuous reactor studies with Thauera sp.V14 in 10 L dMBBR showed 91% of denitrification efficiency with an initial nitrate concentration of 620 mg L-1 within 3 h of HRT. Thus, it revealed that Thauera can be employed as an effective microorganism for nitrate removal from wastewater based on its performance in the present studies.

N-methyl pyrrolidone manufacturing wastewater as the electron donor for denitrification: From bench to pilot scale

Actual wastewater generated from N-methylpyrrolidone (NMP) manufacture was used as electron donor for tertiary denitrification. The organic components of NMP wastewater were mainly NMP and monomethylamine (CH3NH2), and their biodegradation released ammonium that was nitrified to nitrate that also had to be denitrified. Bench-scale experiments documented that alternating denitrification and nitrification realized effective total‑nitrogen removal. Ammonium released from NMP was nitrified in the aerobic reactor and then denitrified when actual NMP wastewater was used as the electron donor for endogenous and exogenous nitrate. Whereas TN and NMP removals occurred in the denitrification step, dissolved organic carbon (DOC) and CH3NH2 removals occurred in the denitrification and nitrification stages. The genera Thauera and Paracoccus were important for NMP biodegradation and denitrification in the denitrification reactor; in the nitrification stage, Amaricoccus and Sphingobium played key roles for biodegrading intermediates of NMP, while Nitrospira was responsible for NH4+ oxidation to NO3-. Pilot-scale demonstration was achieved in a two-stage vertical baffled bioreactor (VBBR) in which total‑nitrogen removal was realized sequential anoxic-oxic treatment without biomass recycle. Although the bench-scale reactors and the VBBR had different configurations, both effectively removed total nitrogen through the same mechanisms. Thus, an N-containing organic compound in an industrial wastewater could be used to drive total-N removal in a tertiary-treatment scenario.

Synergistic mechanisms between chlorine-mediated electrochemical advanced oxidation and ultraviolet light for ammonia removal

The combination of chlorine-mediated electrochemical advanced oxidation (Cl-EAO) and ultraviolet (UV) radiation (UV-E/Cl) can efficiently remove ammonia from wastewater. However, the synergistic mechanisms between Cl-EAO and UV need to be explored in more detail. Thus, in this study, the ammonia oxidation performance of Cl-EAO and UV-E/Cl systems were compared, while the synergistic mechanisms were identified by the performance of UV/chlorine oxidation (UV-ClO) system and the results of electron paramagnetic resonance (EPR) analysis, free radical inhibition assays, and determination of steady-state concentration of free radicals. It was found that, compared with the Cl-EAO system, UV increased the ammonia removal rate by 42.85% and reduced the active chlorine concentration (56.64%) and nitrate yield (53.61%). In the Cl-EAO, and UV-E/Cl systems, Cl• were detected, and the free radical inhibition assays and determination of steady-state concentration of free radicals suggested that UV increased the concentration of Cl• by 51.47%, resulting in Cl• becoming the major contributor to ammonia oxidation in the UV-E/Cl system. Besides, UV also increase the concentrations of HO• and Cl2•-, which further promoted the organic matter removal in the real domestic wastewater. This study also discussed the ammonia oxidation performance of the UV-E/Cl system in real domestic wastewater, even with the presence of significant levels of organic and inorganic anions in the wastewater, UV increased the ammonia oxidation by 21.95%. The results of this study thus clarify the mechanisms and potential applications of UV-E/Cl technology.

Metagenomic insights into the nitrogen metabolism, antioxidant pathway, and antibiotic resistance genes of activated sludge from a sequencing batch reactor under tetracycline stress

Tetracycline is prevalent in wastewater treatment plants and poses a potential threat to biological nitrogen removal under long-term exposure. In the present study, the influence of different tetracycline concentrations on the nitrogen removal, bioactivity response, and the spread of antibiotic resistance genes (ARGs) was assessed in sequencing batch reactor (SBR). The nitrogen removal efficiency, nitrification rate, and denitrification rate and their corresponding enzymatic activities gradually decreased with an increase in tetracycline concentration from 0.5 to 15 mg/L. The remarkable toxicity induced by tetracycline led to a significant increase in the peroxidation and the response of antioxidant system, as evidenced by strengthened antioxidant enzymatic activity and abundant genes (SOD12, katG, PXDN, gpx, and apx). Tetracycline addition significantly inhibited the ammonia-oxidizing bacterium Nitrosomonas and functional genes (amoA, amoB, and amoC). The presence of tetracycline decreased the abundance of citrate synthase and genes (CS, IDH3, and acnA) and interfered with carbon source metabolism, leading to impaired bioactivity and treatment performance. In addition, the presence of tetracycline induces diversity and differences in ARGs. The results provide reliable basic data for a deeper understanding of the effects of tetracycline on the nitrogen removal performance of bioreactors and provide a theoretical basis to build a promising strategy for relieving antibiotic-caused process fluctuations.

Novel nitrogen removal process in marine aquaculture wastewater treatment using Enteromorpha ferment liquid as carbon

The process performance of partial denitrification of a novel anaerobic fermentation integrated fixed-film activated sludge (IFAS-AFPD) of Enteromorpha was studied. The response surface method was used to determine the optimal reaction conditions, and the operation experiment was carried out under the optimal conditions. The results showed that the nitrogen removal effect was the best when the salinity was 12.2 g•L^-1, the Carbon-Nitrogen ratio (C/N) was 4, the pH was 8.5, and the Nitrite Accumulation Rate, Nitrate Removal Rate, Chemical Oxygen Demand Utilization Rate could reach 77%, 89% and 51%. Experimental results have shown that the NAR of the Enteromorpha ferment liquid system could be maintained at about 74%, which was noteworthy higher than that of the sodium acetate (CH₃COONa) system at 42%; Microbial community analysis showed that Enteromorpha ferment liquid was more beneficial to the growth of Bacteroidetes than CH₃COONa.

Performance of anammox enchanced by pulsed electric fields under added organic carbon sources using integrated network and metagenomics analyses

This paper aims to investigate the function of a pulsed electric field (PEF) in the anaerobic ammonia oxidation (anammox) process after adding certain chemical oxygen demand (COD) through integrated network and metagenomics analyses. The findings showed that the presence of COD was detrimental to anammox, but PEF could significantly reduce the adverse effect. The total nitrogen removal in the reactor for applying PEF was 16.99% higher on average than the reactor for only dosing COD. Additionally, PEF upgraded the abundance of anammox bacteria subordinate to the phylum Planctomycetes by 9.64%. The analysis of molecular ecological networks promulgated that PEF resulted in an increase in network scale and topology complexity, thereby boosting the potential collaboration of the communities. Metagenomics analyses demonstrated that PEF dramatically promoted anammox central metabolism in the presence of COD, specifically enhancing pivotal N functional genes (hzs, hdh, amo, hao, nas, nor and nos).

Selective pressure of PFOA on microbial community: Enrichment of denitrifiers harboring ARGs and the transfer of ferric-electrons

Perfluorooctanoic acid (PFOA), a class of permanent organic pollutants, is frequently detected in surface and ground water, with the latter made up primarily of porous media (such as soils, sediments, and aquifers) that harbor microbial communities. Therefore, we investigated the effects of PFOA on water ecosystems and found that, under stimulation by 2.4 μM PFOA, denitrifiers were significantly enriched due to their hosting antibiotic resistant genes (ARGs), which were 1.45 times more abundant than the control. Furthermore, denitrifying metabolism was enhanced by Fe(II) electron donation. Specifically, 2.4 μM PFOA significantly enhanced the removal of total inorganic nitrogen by 178.6%. The microbial community became predominated by denitrifying bacteria (67.8% abundance). Notably, the nitrate-reduction ferrous-oxidizing (NRFO) bacteria Dechloromonas, Acidovorax, Bradyrhizorium, etc. were significantly enriched. The selective pressures of PFOA driving the enrichment of denitrifiers were twofold. First, the toxic PFOA induced denitrifying bacteria to produce ARGs, mainly including the efflux (occupying 55.4%) and antibiotic inactivation (occupying 41.2%) types, which improved microbial tolerance to PFOA. The risk of horizontal ARGs transmission was elevated as the overall number of horizontally transmissible ARGs increased by 47.1%. Second, Fe(II) electrons were transported via the porin-cytochrome c extracellular electrons transfer system (EET), promoting the expression of nitrate reductases, which in turn further enhanced denitrification. In summary, PFOA regulated the microbial community structure and influenced microbial TN removal functions and increased the contribution of ARGs by the denitrifier hosts, but the PFOA-induced production of ARGs may pose a serious ecological threat that needs to be comprehensively investigated.