Microbiological evaluation of nano-Fe3O4/GO enhanced the micro-aerobic activate sludge system for the treatment of mid-stage pulping effluent

Enhanced tetracycline degradation through electron transfer activated by Bacillus cereus synthesized bio-FeS nanoparticles

The synthesis of bio-FeS nanoparticles (NPs) was generally using Gram-negative bacteria and mostly in anaerobic systems, thus limiting their application in the degradation of toxic wastewater. In this study, we successfully synthesized bio-FeS NPs for the first time using the resilient Gram-positive bacterium Bacillus cereus, with the objective of investigating the mechanism of promoting electron transfer in the aerobic/anaerobic degradation of tetracycline (TC). The degradation efficiency of TC was increased by 2.84 and 4.74 times, respectively, under aerobic and anaerobic conditions. Furthermore, the bio-FeS NPs were observed to significantly reduce the activation energy and Gibbs free energy, especially under aerobic conditions. It was found that bio-FeS NPs promoted intracellular electron transfer mainly through activating or replacing the Fe-S centers. The bio-FeS NPs significantly increased ETS activity and NADH levels, indicating that the dehydrogenase activity and intracellular electron transfer efficiency were increased. The bio-FeS NPs formed electron transfer channels inside and outside the cell, provided an effective way for the transfer of electron shuttles from intracellular to extracellular, and improved the extracellular redox activity. This study offered new insights and theories into the role of Gram-positive bacteria in the synthesis of bio-FeS NPs for the remediation of toxic wastewater.

Profiling and metabolic analysis of microorganisms in bioretention cells vegetated with vetiver and cattail species treating nitrogen and phosphorous

Bioretention cells (BRCs) are increasingly used to treat nutrients in stormwater runoff, with plants known to enhance nitrogen (TN) and phosphorus (TP) uptake. This study investigated the role of rhizosphere microbial communities in TN, TP, and COD removal across three BRCs: an unvegetated control (CP), one vegetated with vetiver (P1), and another with cattail (P2). Detailed microbiome profiling revealed key taxa across phylum, family, and genus levels contributing to nutrient cycling, with P2 showing the highest species richness and diversity based on OTU counts and diversity indices. Proteobacteria, Acidobacteria, and Verrucomicrobiota were the most prominent phyla, aligning with their known roles in nutrient uptake. Key functional taxa included denitrifiers (e.g., Ramlibacter, TRA3-20), Ammonia Oxidizing Bacteria (AOBs) (e.g., MND1, Ellin 6067), and Phosphate Accumulating Organisms (PAOs) (e.g., Comamonadaceae, Vicinamibacteria), supporting TN (>79%) and TP (>84%) removal rates. Distinct microbial compositions between vegetated BRCs confirmed the role of root exudates in microbial selection and enhanced nutrient removal. These findings emphasize the importance of plant-specific rhizosphere effects and microbial selection in optimizing BRC design for stormwater treatment applications.

Biodegradation of organosulfur with extra carbon source: Insights into biofilm formation and bacterial metabolic processes

Organosulfur compounds are prevalent in wastewater, presenting challenges for biodegradation, particularly in low-carbon environments. Supplementing additional carbon sources not only provides essential nutrients for microbial growth but also serves as regulators, influencing adaptive changes in biofilm and enhancing the survival of microorganisms in organosulfur-induced stress bioreactors. This study aims to elucidate the biodegradation of organosulfur under varying carbon source levels, placing specific emphasis on functional bacteria and metabolic processes. It has been observed that higher levels of carbon supplementation led to significantly improved total sulfur (TS) removal efficiencies, exceeding 83 %, and achieve a high organosulfur CH3SH removal efficiency of ~100 %. However, in the reactor with no external carbon source added, the oxidation end-product SO42- accumulated significantly, surpassing 120 mEq/m2-day. Furthermore, the TB-EPS concentration consistently increasedwith the ascending glucose concentration. The analysis of bacterial community reveals the enrichment of functional bacteria involved in sulfur metabolism and biofilm formation (e.g. Ferruginibacter, Rhodopeudomonas, Gordonia, and Thiobacillus). Correspondingly, the gene expressions related to the pathway of organosulfur to SO42- were notably enhanced (e.g. MTO increased by 27.7 %). In contrast, extra carbon source facilitated the transfer of organosulfur into amino acids in sulfur metabolism and promoted assimilation. These metabolic insights, coupled with kinetic transformation results, further validate distinct sulfur pathways under different carbon source conditions. The intricate interplay between bacteria growth regulation, pollutant biodegradation, and microbial metabolites underscores a complex network relationship that significantly contributes to efficient operation of bioreactors.

The microplastics distribution characteristics and their impact on soil physicochemical properties and bacterial communities in food legumes farmland in northern China

Microplastics (MPs) pose a threat to farmland soil quality and crop safety. MPs exist widely in food legumes farmland soil due to the extensive use of agricultural film and organic fertilizer, but their distribution characteristics and their impact on soil environment have not been reported. The abundance and characteristics of MPs, soil physical and chemical properties, and bacterial community composition were investigated in 76 soil samples from five provinces in northern China. The results showed that the abundance of MPs ranged from 1600 to 36,200 items/kg. MPs in soil were mostly fibrous, less than 0.2 mm, and white. Rayon, polyester and polyethylene were the main types of MPs. The influences of MPs on soil physicochemical properties and bacterial communities mainly depended on the type of MPs. Notably, polyethylene significantly decreased the proportion of silt particles, and increased the nitrate nitrogen content as well as the abundance of MPs-degrading bacteria Paenibacillus (p < 0.05). Moreover, bacteria were more sensitive to polyesters in soil with low concentration of organic matter. This study indicated that MPs in food legumes farmland soil presented a higher-level. And, they partially altered soil physicochemical properties, and soil bacteria especially in soil with low organic matter.

Response of nitrite accumulation, sludge characteristic and microbial transition to carbon source during the partial denitrification (PD) process

Partial denitrification (PD, nitrate (NO3--N) → nitrite (NO2--N)) as a novel pathway for NO2--N production has been widely concerned, but the specific conditions for highly efficient and stable nitrite maintenance are not yet fully understood. In this study, the effects of carbon sources (acetate, R1; propionate, R2; glucose, R3) on NO2--N accumulation was discussed without seeding PD sludge and the mechanism analysis related to sludge characteristic and microbial evolution were elucidated. The optimal NO2--N, nitrate-to-nitrite transformation ratio (NTR) and nitrite removal efficiency (NRE) reached up to 32.10 mg/L, 98.01 %, and 86.95 % in R1. However, due to the complex metabolic pathway of glucose, the peak time of NO2--N production delayed from 30 min to 60 min. The sludge particle size decreased from 154.2 μm (R1), 130.8 μm (R2) to 112.6 μm (R3) with the increasing extracellular polymeric substances (EPS) from 80.75-85.44 mg/gVSS, 82.68-92.75 mg/gVSS to 106.31-110.25 mg/gVSS, where the ratio of proteins/polysaccharides (PN/PS) was proved to be closely associated with NO2--N generation. For the microbial evolution, Saccharimonadales (70.42 %) dominated the glucose system, while Bacillus (7.42-21.63 %) and Terrimonas (4.24-5.71 %) were the main contributors for NO2--N accumulation in the acetate and propionate systems. The achievement of PD showed many advantages of lower carbon demand, minimal sludge production, lesser greenhouse gas emission and prominent nutrient removal, offering an economically and technically attractive alternative for NO3--N containing wastewater treatment.

Enhanced removal of sulfur-containing organic pollutants from actual wastewater by biofilm reactor: Insights of sulfur transformation and bacterial metabolic traits

Sulfur-containing organic pollutants in wastewater could threaten human health due to their high malodor and toxicity, and their conversion processes are more complex than inorganic sulfur compounds. Membrane aerated biofilm reactor (MABR), as a novel and environmentally-friendly biofilm-based technology, is able to remove inorganic sulfur in synthetic wastewater. However, it is unknown how sulfur-containing organic pollutants in actual wastewater are transformed in MABR system. This work demonstrated the feasibility of MABR to eliminate sulfur-containing organic pollutants in actual wastewater, and the removal efficiency could be reached at approximately 100%. Meanwhile, over 70% of sulfur-containing organic contaminants were transformed to SO₄^2- during the long-term operation. Further analysis indicated that the functional bacteria that participated in sulfur transformation and carbohydrates degradation (e.g., Chujaibacter, Microscillaceaesp., and Thiobacillus) were evidently enriched when treating actual wastewater. Moreover, the critical metabolic pathways (e.g., sulfur metabolism, glycolysis metabolism, and pyruvate metabolism), and the corresponding genetic expressions (e.g., nrrA, tauA, tauC, sorA, and SUOX) were evidently up-regulated during long-term operation, which was beneficial for the transformation of sulfur-containing organic pollutants in actual wastewater by MABR. This work would expand the application of MABR for treating the actual sulfur-containing organic wastewater and provide an in-depth understanding of the organic sulfur transformation in MABR.

Deciphering physicochemical properties and enhanced microbial electron transfer capacity by magnetic biochar

Magnetic biochar is important for improving the electron transfer capacity (ETC) of microorganisms in wastewater treatment. In this study, three magnetic biochar under different pyrolysis temperatures (300, 500 and 700 °C) were prepared by co-precipitation, and their characteristics and impacts on mediating microbial ETC were investigated. Results indicated that magnetic biochar had a higher capacitance and conductivity than pyrolytic biochar, with the largest specific capacitance of 14.7F/g for FCS700 (magnetic biochar prepared at 700 °C). The addition of magnetic biochar could improve the nitrogen removal efficiency of a sludge-biochar system. The electron transfer resistance (R_ct) of magnetic biochar was lower than pyrolytic biochar by 25.5 % (300 °C), 19.7 % (500 °C), and 11.6 % (700 °C), respectively. The structure of the microbial community in the sludge-biochar system differed significantly. Spearman correlation suggested that the electrochemical properties of biochar were an important factor affecting the structure of the microbial community.

Nitrite accumulation, denitrification kinetic and microbial evolution in the partial denitrification process: The combined effects of carbon source and nitrate concentration

The combined effects of carbon source (HAc, HPr, Glu, Glu + HAc) and nitrate concentration (40, 80 mg/L labeling as R₄₀, R₈₀) on partial denitrification (PD) were discussed at C/N ratio of 2.5 (COD = 100, 200 mg/L). The optimal NO₂^--N and NTR reached to 67.03 mg/L, 99.14% in HAc-R₈₀ system, and denitrification kinetics revealed the same conclusion, corresponding to higher COD utilization rate (CUR: 58.46 mgCOD/(gVSS·h)), nitrate reduction rate (N_aRR: 29.94 mgN/(gVSS·h)) and nitrite accumulation rate (N_iAR: 29.68 mgN/(gVSS·h)). The preference order was HAc > HPr > Glu + HAc > Glu in both R₄₀ and R₈₀ systems due to different metabolic pathways, however, the NO₂^--N accumulation and kinetic parameters of R₈₀ group were dramatically higher than those in R₄₀ for the same carbon source. The R₈₀ group facilitated more concentrated biodiversity (607-808 OTUs) with Terrimonas and norank_f_Saprospiraceae responsible for high NO₂^--N accumulation in HAc and HPr served systems, while norank_f_norank_o_Saccharimonadales and OLB13 dominated the Glu containing systems.