Mechanistic insights into polyhydroxyalkanoate-enhanced denitrification capacity of microbial community: Evolution of community structure and intracellular electron transfer of nitrogen metabolism

Regulation of microcurrent on carbon and nitrogen metabolism in denitrification under low carbon-to-nitrogen ratio: Optimizing carbon flux distribution

Synergy of autotrophic and heterotrophic denitrification can achieve low-carbon and high-efficient nitrogen removal. However, it remains unclear how microcurrent-driven hydrogen autotrophic denitrification regulates carbon flux distribution (nitrogen reduction, poly-β-hydroxyalkanoate (PHA) storage, and cell growth) in heterotrophic denitrification. This work compared biofilm reactor with biofilm electrode reactor under different carbon-to-nitrogen (C/N) ratios (10 - 3). At C/N ratio of 3, microcurrent accelerated nitrate reduction rate by 0.35 mg/(L·min) and reduced nitrite accumulation by 10.29 mg/L, thus decreasing nitrogen reduction proportion by 11.21%. Meanwhile, PHA storage and cell growth proportions increased by 0.03% and 11.18%, respectively. PHA was initially synthesized and subsequently utilized for nicotinamide adenine dinucleotide and energy production, while cell growth preferentially utilized limited carbon sources to maintain system stability. Increased abundance of hydrogen autotrophic denitrifiers, heterotrophic denitrifiers, and PHA storage bacteria confirmed optimization of microcurrent on carbon flux distribution. These findings advanced the understanding of microcurrent regulation on carbon flux.

Enhancing the efficacy of synthesising PHA from nitrogen-limited activated sludge using magnetic field

Polyhydroxyalkanes (PHA) is a biodegradable biopolyester. In this study, we introduced the biological effects of magnetic field into a sequencing batch reactor (SBR) for PHA production to evaluate the effect of different strength of magnetic field on the efficacy of PHA synthesis by activated sludge and used the magnetic field to enhance the PHA synthesis capacity of nitrogen-limited activated sludge and to optimise the percentage of the content of the two monomers in PHA. The results showed that the magnetic field of appropriate strength was favourable to increase the production of PHA and to increase the percentage of PHV. In addition, microbial community analysis showed that there was an obvious succession of key functional bacteria under different strength of magnetic field. The highest PHA accumulation was achieved after the magnetic field of 16 mT, which reached 57.65% of the dry weight of sludge. In addition, the PHV monomers were more sensitive to the response of the magnetic field, and the magnetic field of 8mT and 16mT positively promoted the synthesis of PHV. It is worth noting that too high a magnetic field would have an inhibitory effect on the synthesis of PHA.

Simultaneous deep removal of nitrate and tetrabromobisphenol A in microbial electrochemical system-constructed wetland

Microbial electrochemical system-constructed wetland (MES-CW) is environmentally friendly in removing organic contaminants from wastewater. Tetrabromobisphenol A (TBBPA) is an emerging pollutant that is inefficiently removed in conventional wastewater treatment. The feasibility of deep removal of TBBPA and nitrate and the related mechanism in MES-CW remains unclear. This study demonstrated the enhanced TBBPA detoxification in MES-CW accompanied by nitrate removal. Nitrate significantly suppressed the TBBPA reductive debromination and methane generation. It altered the microbial community and enriched Acinetobacter in the electrode, stimulating the TBBPA hydrolytic debromination and metabolite oxidation. The biocathode supplied electrons for dehalogenators in TBBPA reductive debromination, while the anode served as the electron acceptor for function bacteria in TBBPA metabolite oxidation. Nitrate and anodic electricity optimized the microbial community and provided electron acceptors for TBBPA metabolites oxidation in MES-CW, guiding the deep removal of nitrate and emerging pollutants in wastewater.

Evaluating AGS efficiency in PHA synthesis and extraction integrated with nutrient removal: The impact of COD concentrations

As natural and biodegradable biopolymers, Polyhydroxyalkanoates (PHA) were synthetized by aerobic granules sludge (AGS) in a sequential batch reactor in this study. The effect of different COD concentrations on PHA accumulation and nutrients removal were investigated. At the same time, different pretreatment methods for PHA extraction, including NaClO pretreatment for extracellular polymeric substances (EPS) removal, Na2CO3 pretreatment for EPS recovery, and grinding pretreatment to reduce particle size and augment the surface area available for interaction with the extraction solvent, were compared. The results showed that the PHA yield increased more than 2 times (from 91.1 to 233.3 mgPHA/gCDW (cell dry weight)) when COD concentration increased from 800 to 1600 mg/L. Polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) both accounted for half of the total, while PHB fraction rose to 71% when COD concentration went up to 1600 mg/L. The PHB can be consumed 3 times faster than PHV. High COD concentration (1600 mg/L) adversely impacted the structure stability of AGS and the phosphorus removal efficiency, while the system consistently exhibited robust nitrogen removal capabilities, with ammonium and TN removal efficiencies exceeding >90%. The dominant bacteria shifted from Flavobacterium to Halomona and Hydrogenophaga as the COD concentration increased. In terms of PHA extraction, Na2CO3 pretreatment, which was used for EPS recovery, had the best PHA recovery with nearly 100% purity and EPS removal efficiency compared with NaClO and grinding pretreatments.

New insight into the metabolic mechanism of a novel lipid-utilizing and denitrifying bacterium capable of simultaneous removal of nitrogen and grease through transcriptome analysis

Introduction

Issues related to fat, oil, and grease from kitchen waste (KFOG) in lipid-containing wastewater are intensifying globally. We reported a novel denitrifying bacterium Pseudomonas CYCN-C with lipid-utilizing activity and high nitrogen-removal efficiency. The aim of the present study was aim to explore the metabolic mechanism of the simultaneous lipid-utilizing and denitrifying bacterium CYCN-C at transcriptome level.

Methods

We comparatively investigated the cell-growth and nitrogen-removal performances of newly reported Pseudomonas glycinae CYCN-C under defined cultivation conditions. Transcriptome analysis was further used to investigate all pathway genes involved in nitrogen metabolism, lipid degradation and utilization, and cell growth at mRNA levels.

Results

CYCN-C could directly use fat, oil, and grease from kitchen waste (KFOG) as carbon source with TN removal efficiency of 73.5%, significantly higher than that (60.9%) with sodium acetate. The change levels of genes under defined KFOG and sodium acetate were analyzed by transcriptome sequencing. Results showed that genes cyo, CsrA, PHAs, and FumC involved in carbon metabolism under KFOG were significantly upregulated by 6.9, 0.7, 26.0, and 19.0-folds, respectively. The genes lipA, lipB, glpD, and glpK of lipid metabolic pathway were upregulated by 0.6, 0.4, 21.5, and 1.3-folds, respectively. KFOG also improved the denitrification efficiency by inducing the expression of the genes nar, nirB, nirD, and norR of denitrification pathways.

Conclusion

In summary, this work firstly provides valuable insights into the genes expression of lipid-utilizing and denitrifying bacterium, and provides a new approach for sewage treatment with reuse of KFOG wastes.

Electrospinning micro-nanofibers immobilized aerobic denitrifying bacteria for efficient nitrogen removal in wastewater

Electrospinning micro-nanofibers with exceptional physicochemical properties and biocompatibility are becoming popular in the medical field. These features indicate its potential application as microbial immobilized carriers in wastewater treatment. Here, aerobic denitrifying bacteria were immobilized on micro-nanofibers, which were prepared using different concentrations of polyacrylonitrile (PAN) solution (8%, 12% and 15%). The results of diameter distribution, specific surface area and average pore diameter indicated that 15% PAN micro-nanofibers with tighter surface structure were not suitable as microbial carriers. The bacterial load results showed that the cell density (OD₆₀₀) and total protein of 12% PAN micro-nanofibers were 107.14% and 106.28% higher than those of 8% PAN micro-nanofibers. Subsequently, the 12% PAN micro-nanofibers were selected for aerobic denitrification under the different C/N ratios (1.5-10), and stable performance was obtained. Bacterial community analysis further manifested that the micro-nanofibers effectively immobilized bacteria and enriched bacterial structure under the high C/N ratios. Therefore, the feasibility of micro-nanofibers as microbial carriers was confirmed. This work was of great significance for promoting the application of electrospinning for microbial immobilization in wastewater treatment.