Optimizing waste molasses utilization to enhance electron transfer via micromagnetic carriers: Mechanisms and high-nitrate wastewater denitrification performance

Promotion mechanisms of static magnetic field on sulfide-based partial autotrophic denitrification: Metabolic intermediates, electron behavior, oxidative stress, and microbial community

Sulfide-based Partial Autotrophic Denitrification (SPAD) coupled with anammox is a promising technology for simultaneous sulfide and nitrogen removal. Static magnetic field (SMF) has been recognized to facilitate biological denitrification processes, but the underlying mechanisms remain largely unexplored. In this study, the performance was investigated in long-term operation of SPAD process under SMF, aiming at exploring the potential of SMF to enhance the SPAD process. The results showed that the SMF reactor (R2) achieved 90.14 % nitrite accumulation, while it was 70.54 % in the control reactor (R1). SMF facilitated electron production, transfer and consumption, and increased the activity of Complex Ⅰ, Complex Ⅲ, Cyt.c, sulfide oxidase and nitrate reductase. In addition, SMF alleviated oxidative stress by reducing reactive oxygen species (ROS) production and promoting up-regulation of antioxidant defense systems. Real-time quantitative PCR and reverse transcription PCR combined with high-throughput sequencing analysis showed that SMF promoted the conversion of the dominant genus SOBII (Sulfurimonas) to SOBI (Thiobacillus), and the relative abundance of Thiobacillus in the R2 was 67.64 %, higher than that in the R1 (61.90 %). The study provides a new approach to achieve stable nitrite accumulation by the SPAD process as well as presents new insights into the role of SMF on microorganisms.

Synchronous nitrogen and sulfur removal in sulfur-coated iron carbon micro-electrolytic fillers: Exploring the synergy between sulfur autotrophic denitrification and iron-carbon micro-electrolysis

Sulfur autotrophic denitrification (SAD) is a promising technology for nitrogen removal, particularly suitable for low carbon-to-nitrogen wastewater without additional carbon sources. However, SAD inevitably generates significant amounts of SO42-. To address this issue, combining SAD with iron-carbon micro-electrolysis technology, which can reduce sulfate, provides electron donors for autotrophic denitrification and facilitates sulfur cycling. Nonetheless, extensive iron precipitation can cause clogging and exert toxic effects on microorganisms. Herein, a sulfur-coated iron carbon micro-electrolytic filler (Fe-C@S) was established to achieve higher removal efficiency of NO3--N (97 %) and SO42- (99 %), less NO2--N was produced (<6 mg·L-1), and the role of sulfur shell in Fe-C@S was systematically evaluated. Furthermore, when comparing the Fe-C@S filler with traditional sulfur fillers (TS) and mixed systems combining TS with iron-carbon fillers (TS-ICME), it becomes evident that the Fe-C@S exhibits dual capabilities in nitrogen removal and sulfur recycling. This effectively addresses the issues of excessive SO42- concentration in effluents and the tendency of iron-carbon fillers to harden. Moreover, the Fe-C@S demonstrates nitrogen and sulfur removal performance in continuous landfill leachate experiments. Additionally, the dominant bacteria within the Fe-C@S comprise more electrophilic denitrifying bacteria (18.2 %), its stable and efficient performance in nitrogen and sulfur removal even under low current conditions.

Differences in the efficiency and mechanisms of different iron-based materials driving synchronous nitrogen and phosphorus removal

Iron-dependent denitrification has been substantially investigated worldwide due to the advantages of low cost, high efficiency, and synchronized phosphorous removal. However, differences in nitrogen metabolism processes with different iron-based materials as electron donors have not been systematically studied. This study investigated the efficacy of nitrogen and phosphate removal using various iron-based materials as electron donors. Substantial nitrogen removal was demonstrated, with complete TN removal with Fe/C powder as electron donor, while relatively lower TN removal was achieved in iron scrap, Fe/C granular, and pyrite systems with removal efficiency of 86 ± 3.5%, 78 ± 5.7%, and 61 ± 3.1%, respectively. However, the high efficiency could only be sustained for a short time and further microbial metabolisms were significantly suppressed by microbial encapsulation caused by iron-bearing minerals. The introduction of fresh electron donors revitalized denitrification activity, with TN removal improved back to more than 80%. Similar trends were observed in phosphate removal, with increased efficiencies corresponding to ferrous ion release, reaching the highest level of 94 ± 0.02% with iron scrap as electron donor. Microbial community analysis revealed distinct compositions, with sulfur autotrophic denitrifying bacteria prevailing in pyrite systems, hydrogenotrophic denitrifying bacteria dominating with Fe/C powder, and Fe(II) oxidizing bacteria (FeOB) governing in Fe scrap and Fe/C granular systems for denitrification. Predicted genomic analysis elucidated mechanisms underlying nitrogen and phosphorus removal, emphasizing the importance of direct electron transfer via cytochrome C and ferrous ion transportation. Furthermore, differences in nitrogen metabolism among systems were highlighted, with Fe/C powder facilitating hydrogen oxidation proteins expression, while pyrite systems favored sulfur oxidation process, and iron scrap selected Fe(II) transportation and oxidation. This study provided valuable insights into revealing mechanism for efficient nitrogen and phosphorus removal with iron-based materials as electron donors.

Which biofilm reactor is suitable for degradation of 2,4-dimethylphenol, focusing on bacteria, algae, or a combination of bacteria-algae?

Effectively treating phenolic substances is a crucial task in environmental protection. This study aims to determine whether bacterial-algae biofilm reactors offer superior treatment efficacy compared to traditional activated sludge and biofilm reactors. The average degradation ratios of 2,4-dimethylphenol (40, 70, 150, 300, and 230 mg/L) were found to be 98 %, 99 %, 92.1 %, 84.7 %, and 63.7 % respectively. The bacterial-algae biofilm demonstrates a higher tolerance to toxicity, assimilation ability, and efficacy recovery ability. The cell membrane of Chlorella in the bacteria-algae biofilm is not easily compromised, thus ensuring a stable pH environment. High concentrations of tightly bound extracellular polymers (TB-EPS) enhance the efficacy in treating toxic pollutants, promote the stable structure. Intact Chlorella, bacilli, and EPS were observed in bacterial-algal biofilm. The structural integrity of bacteria-algae consistently enhances its resistance to the inhibitory effects of high concentrations of phenolic compounds. Cloacibacterium, Comamonas, and Dyella were the main functional bacterial genera that facilitate the formation of bacterial-algal biofilms and the degradation of phenolic compounds. The dominant microalgal families include Aspergillaceae, Chlorellales, Chlorellaceae, and Scenedesmaceae have certain treatment effects on phenolic substances. Chlorellales and Chlorellaceae have the ability to convert NH4+-N. The Aspergillaceae is also capable of generating synergistic effects with Chlorellales, Chlorellaceae, and Scenedesmaceae, thereby establishing a stable bacterial-algal biofilm system.

Simultaneous efficient removal of tetracycline and mitigation of antibiotic resistance genes enrichment by a modified activated sludge process with static magnetic field

To address the increasing issue of antibiotic wastewater, this study applied a static magnetic field (SMF) to the activated sludge process to increase the efficiency of tetracycline (TC) removal from swine wastewater and to reveal its enhanced mechanisms. The results demonstrated that the SMF-modified activated sludge process could achieve almost complete TC removal at sludge loading rates of 0.3 mg TC/g MLSS/d. Analysis of zeta potential and extracellular polymeric substances composition of the activated sludge revealed that SMF increased electrostatic interactions between TC and activated sludge and made activated sludge has much more binding sites, finally resulting in the increased TC biosorption. Metagenomic analysis showed that SMF promoted the enrichment of ammonia-oxidizing bacteria, TC-degrading bacteria, and aromatic compounds-degrading bacteria; it also enhanced ammonia monooxygenase- and cytochrome P450-mediated TC metabolism while upregulating functional genes associated with oxidase, reductase, and dehydrogenase - all contributing to increased TC biodegradation. Additionally, SMF mitigated the enrichment and spread of antibiotic resistance genes (ARGs) by decreasing the abundance of potential hosts of ARGs and inhibiting the upregulation of genes encoding ABC transporters and putative transposase. Based on these findings, this study demonstrates that magnetic field is an enhancement strategy with great potential to relieve the harmful impacts of the growing antibiotic wastewater problem on human health and the ecosystem.

Enhanced methane production from anaerobic digestion of waste activated sludge with weak magnetic field: Insights into performances and mechanisms

The impact of weak magnetic field (WMF) on anaerobic digestion (AD) performance of waste activated sludge (WAS) and underlying mechanism were investigated. Results showed that WMF significantly stimulated the methane yield by 12.9∼25.1% with 15 and 30 mT WMF addition, but high WMF (60 mT) attenuated the positive effect. The WMF enriched the anaerobic microbes, especially the acetoclastic and hydrogenotrophic methanogen. Additionally, the WMF dramatically facilitated the metabolic pathways of key enzymes for methanogenesis, which was validated by the significant increase of absolute abundance of anaerobic functional genes (mcrA). The enzyme activities of ATP and F420 were also significantly promoted by 30 mT WMF, but high WMF (60 mT) resulted in increased activity of lactate dehydrogenase. This study reveals that low WMF can promote AD performance of WAS through enhancing microbial activities especially methanogen, but high WMF leads to the loss of cell membrane integrity and attenuates its positive effect.

Investigating the Antibacterial and Anti-inflammatory Potential of Polyol-Synthesized Silver Nanoparticles

Silver nanoparticles (Ag-NPs) were synthesized by using the polyol method. The structural and morphological characteristics of Ag-NPs were studied by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The XRD analysis revealed the formation of single-phase polycrystalline Ag-NPs with an average crystallite size and lattice constant of ∼23 nm and 4.07 Å, respectively, while the FE-SEM shows the formation of a uniform and spherical morphology. Energy-dispersive X-ray spectroscopy confirmed the formation of single-phase Ag-NPs, and no extra elements were detected. A strong absorption peak at ∼427 nm was observed in the UV-vis spectrum, which reflects the surface plasmon resonance (SPR) behavior characteristic of Ag-NPs with a spherical morphology. Fourier-transform infrared (FTIR) spectra also supported the XRD and EDX results with regard to the purity of the prepared Ag-NPs. Anti-inflammatory activity was tested using HRBCs membrane stabilization and heat-induced hemolysis assays. The antibacterial activity of Ag-NPs was evaluated against four different types of pathogenic bacteria by using the disc diffusion method (DDM). The Gram-negative bacterial strains used in this study are Escherichia coli (E. coli), Klebsiella, Shigella, and Salmonella. The analysis suggested that the antibacterial activities of Ag-NPs have an influential role in inhibiting the growth of the tested Gram-negative bacteria, and thus Ag-NPs can find a potential application in the pharmaceutical industry.

Harnessing the potential of ginkgo biloba extract: Boosting denitrification performance through accelerated electron transfer

Ginkgo biloba extract (GBE) had several effects on the human body as one of the widely used phytopharmaceuticals, but it had no application in microbial enhancement in the environmental field. The study focused on the impact of GBE on denitrification specifically under neutral conditions. At the identified optimal addition ratio of 2% (v/v), the system exhibited a noteworthy increase in nitrate reduction rate (NRR) by 56.34%, elevating from 0.71 to 1.11 mg-N/(L·h). Moreover, the extraction of microbial extracellular polymeric substance (EPS) at this ratio revealed changes in the composition of EPS, the electron exchange capacity (EEC) was enhanced from 87.16 to 140.4 μmol/(g C), and the transfer impedance was reduced within the EPS. The flavin, fulvic acid (FA), and humic acid (HA) provided a π-electron conjugated structure for the denitrification system, enhancing extracellular electron transfer (EET) by stimulating carbon source metabolism. GBE also improved electron transfer system activity (ETSA) from 0.025 to 0.071 μL O2/(g·min·prot) and the content of NADH enhanced by 22.90% while significantly reducing the activation energy (Ea) by 85.6% in the denitrification process. The synergy of improving both intracellular and extracellular electron transfer, along with the reduction of Ea, notably amplified the initiation and reduction rates of the denitrification process. Additionally, GBE demonstrated suitability for denitrification across various pH levels, enhancing microbial resilience in alkaline conditions and promoting survival and proliferation. Overall, these findings open the door to potential applications of GBE as a natural additive in the environmental field to improve the efficiency of denitrification processes, which are essential for nitrogen removal in various environmental contexts.