Free Nitrous Acid Inhibits Atenolol Removal during the Sidestream Partial Nitritation Process through Regulating Microbial-Induced Metabolic Types

Unveiling transformation processes of cardiovascular pharmaceuticals in wastewater based on nontarget screening

Cardiovascular pharmaceuticals were extensively detected and generally coexist with their transformation products (TPs) in wastewater. However, knowledges on TPs and transformation processes for cardiovascular pharmaceuticals remained largely unclear. To fill this knowledge gap, nontarget screening combined with batch experiments were employed to reveal the transformation of five cardiovascular pharmaceuticals (atenolol, metoprolol, propranolol, bezafibrate and candesartan) in aerobic activated sludge. The removal rate constants per unit of biomass ranged from 0.0105 to 0.0571 L g SS-1 h-1 for five cardiovascular pharmaceuticals. Atenolol and bezafibrate exhibited more excellent removal efficiency (over 99 %) than other three cardiovascular pharmaceuticals. Subsequently, 33 TPs were tentatively identified and 16 of them were not reported in previous studies. Based on identified TPs, transformation pathways of five cardiovascular pharmaceuticals were proposed, which suggested acetylation, ammoniation, carboxylation, dealkylation, decarboxylation, dihydroxylation, demethylation, epoxidation, formylation, hydrogenation, hydrolysis, hydroxylation, methylation and oxidation were involved in the transformation of cardiovascular pharmaceuticals in wastewater. Notably, N- dealkylation at the site of secondary and tertiary amine, acetylation at the site of primary amine and dehydrogenation at the site of linear alkyl were summarized as the specific transformation patterns across different cardiovascular pharmaceuticals. Furthermore, the predicted results suggested that about 30 % TPs have higher persistence and bioaccumulation than parent compounds while about 40 % TPs harbored higher toxicity than parent compounds of cardiovascular pharmaceuticals. Collectively, this study unveiled the fate and transformation pathways of five cardiovascular pharmaceuticals and summarized the specific transformation patterns for them in aerobic activated sludge, which is theoretically useful to effectively remove pharmaceuticals from wastewater.

Characterization of a rapid 17β-estradiol-degrading strain, Microbacterium proteolyticum ZJSU01

Estrogens, particularly 17β-estradiol, are prevalent endocrine-disrupting chemicals in aquatic environments, posing risks to ecosystems and human health. Biodegradation is considered one of the most effective and environmentally friendly methods for removing estrogen. In this study, a novel bacterial strain, Microbacterium proteolyticum ZJSU01, was isolated from pig manure. It completely degraded 5 mg/L of 17β-estradiol (E2) within 4 h, as well as its major transformation product, estrone (E1). The strain ZJSU01 displayed strong adaptability to high temperatures (37℃, 42℃) and a broad pH range (6-11), E2 (5 mg/L) could be completely removed by the strain under these conditions. Transformation intermediates were analyzed using UHPLC and HPLC-Q-TOF-MS to identify key metabolites and trace the degradation pathways. Four potential degradation pathways were identified, including the 4,5-seco pathway, which is widely conserved in most E2-degrading bacteria. Whole-genome sequencing predicted a chromosome with a size of 3,828,432 bp, and a series of functional genes, and transcriptomics analysis identified several genes involved in E2 degradation. The budC gene, a member of the short-chain dehydrogenases/reductases (SDRs) family, was identified as critical for E2 degradation and exhibited a nearly 170-fold upregulation. Meanwhile, genes such as fdeE and catA were associated with downstream degradation. Microbacterium proteolyticum ZJSU01 demonstrated strong acid-base and high-temperature resilience, highlighting its strong potential for practical applications due to its degradation capability and adaptability. This strain could be applied in wastewater treatment to effectively remove estrogenic pollutants from contaminated water. KEY POINTS: • Microbacterium proteolyticum ZJSU01 removed 100% of E2 (10、5、1 mg/L) within 4 h. • Strain ZJSU01 showed great tolerance to high temperature and acid-base conditions. • A novel gene, budC, was identified as the primary driver of E2 degradation by ZJSU01.

Biotic and abiotic removal of acetaminophen during sidestream partial nitritation processes: Underlying mechanisms and transformation pathways

Pharmaceutical residues in sidestream wastewater pose the hazardous threats to ecosystem and human health. In this work, the biotic and abiotic degradation of acetaminophen were investigated during the sidestream partial nitritation process. Results demonstrated that the abiotic removal efficiency of acetaminophen was positively correlated with nitrite concentration, whereas the biotransformation of acetaminophen was mainly dependent on metabolic types and free nitrous acid (FNA) concentrations. 91.6 % of acetaminophen, acting as the sole carbon and/or energy source to support the growth of ammonia-oxidizing bacteria (AOB) and heterotrophs, was removed by adsorption (6.2 %) and biotransformation (consisting of 49.4 % AOB-induced metabolism and 36.0 % heterotrophs-induced metabolism) when lacking nitrite and FNA. Increasing FNA from 0.03 mg N L-1 to 0.15 mg L-1 led to decrease in acetaminophen removal (from 78.8 % to 60.1 %) and ammonia oxidation, ascribed to the inhibitory effect of FNA on AOB activity. Nitro substitution occurred under AOB-induced cometabolism, while hydroxylation was conducted by heterotrophs. N-deacetylation, ring cleavage, hydroxylation, nitro-reduction, and deamination at lower FNA levels (0.03 mg N L-1) contributed to the formation of small molecular products, supporting the feasibility of sidestream partial nitritation in the effective elimination of acetaminophen. This work provides strategies for optimizing anti-inflammatory drugs removal via the regulation of FNA in the sidestream wastewater treatment process.

Metagenomic insights into the influence of pH on antibiotic removal and antibiotic resistance during nitritation: Regulations on functional genus and genes

The changes in pH and the resulting presence of free nitrous acid (FNA) or free ammonia (FA) often inhibit antibiotic biodegradation during nitritation. However, the specific mechanisms through which pH, FNA and FA influence antibiotic removal and the fate of antibiotic resistance genes (ARGs) are not yet fully understood. In this study, the effects of pH, FNA, and FA on the removal of cefalexin and amoxicillin during nitritation were investigated. The results revealed that the decreased antibiotic removal under both acidic condition (pH 4.5) and alkaline condition (pH 9.5) was due to the inhibition of the expression of amoA in ammonia-oxidizing bacteria and functional genes (hydrolase-encoding genes, transferase-encoding genes, lyase-encoding genes, and oxidoreductase-encoding genes) in heterotrophs. Furthermore, acidity was the primary inhibitor of antibiotic removal at pH 4.5, followed by FNA. Antibiotic removal was primarily inhibited by alkalinity at pH 9.5, followed by FA. The proliferation of ARGs mediated by mobile genetic element was promoted under both acidic and alkaline conditions, attributed to the promotion of FNA and FA, respectively. Overall, this study highlights the inhibitory effects of acidity and alkalinity on antibiotic removal during nitritation.

Pharmaceutical metabolite identification in lettuce (Lactuca sativa) and earthworms (Eisenia fetida) using liquid chromatography coupled to high-resolution mass spectrometry and in silico spectral library

Pharmaceuticals released into the aquatic and soil environments can be absorbed by plants and soil organisms, potentially leading to the formation of unknown metabolites that may negatively affect these organisms or contaminate the food chain. The aim of this study was to identify pharmaceutical metabolites through a triplet approach for metabolite structure prediction (software-based predictions, literature review, and known common metabolic pathways), followed by generating in silico mass spectral libraries and applying various mass spectrometry modes for untargeted LC-qTOF analysis. Therefore, Eisenia fetida and Lactuca sativa were exposed to a pharmaceutical mixture (atenolol, enrofloxacin, erythromycin, ketoprofen, sulfametoxazole, tetracycline) under hydroponic and soil conditions at environmentally relevant concentrations. Samples collected at different time points were extracted using QuEChERS and analyzed with LC-qTOF in data-dependent (DDA) and data-independent (DIA) acquisition modes, applying both positive and negative electrospray ionization. The triplet approach for metabolite structure prediction yielded a total of 3762 pharmaceutical metabolites, and an in silico mass spectral library was created based on these predicted metabolites. This approach resulted in the identification of 26 statistically significant metabolites (p < 0.05), with DDA + and DDA - outperforming DIA modes by successfully detecting 56/67 sample type:metabolite combinations. Lettuce roots had the highest metabolite count (26), followed by leaves (6) and earthworms (2). Despite the lower metabolite count, earthworms showed the highest peak intensities, closely followed by roots, with leaves displaying the lowest intensities. Common metabolic reactions observed included hydroxylation, decarboxylation, acetylation, and glucosidation, with ketoprofen-related metabolites being the most prevalent, totaling 12 distinct metabolites. In conclusion, we developed a high-throughput workflow combining open-source software with LC-HRMS for identifying unknown metabolites across various sample types.

Ammonia monooxygenase-mediated cometabolic biotransformation of volatile 4-chlorophenol in nitrifying counter-diffused biofilms: A combined molecular dynamics simulation, DFT calculation and experimental study

Ammonia monooxygenase (AMO)-mediated cometabolism of organic pollutants has been widely observed in biological nitrogen removal process. However, its molecular mechanism remains unclear, hindering its practical application. Furthermore, conventional nitrification systems encounter significant challenges such as air pollution and the loss of ammonia-oxidizing bacteria, when dealing with wastewater containing volatile organic pollutants. This study developed a nitrifying membrane-aerated biofilm reactor (MABR) to enhance the biodegradation of volatile 4-chlorophenol (4-CP). Results showed that 4-CP was primarily removed via Nitrosomonas nitrosa-mediated cometabolism in the presence of NH4+-N, supported by the increased nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) content, AMO activity and the related genes abundance. Hydroquinone, detected for the first time and produced via oxidative dechlorination, as well as 4-chlorocatechol was primary transformation products of 4-CP. Nitrosomonas nitrosa AMO structural model was constructed for the first time using homology modeling. Molecular dynamics simulation suggested that the ortho-carbon in the benzene ring of 4-CP was more prone to metabolismcompared to the ipso-carbon. Density functional theory calculation revealed that 4-CP was metabolized by AMO via H-abstraction-OH-rebound reaction, with a significantly higher rebound barrier at the ipso-carbon (16.37 kcal·mol-1) as compared to the ortho-carbon (6.7 kcal·mol-1). This study fills the knowledge gap on the molecular mechanism of AMO-mediated cometabolism of organic pollutants, providing practical and theoretical foundations for improving volatile organic pollutants removal through nitrifying MABR.

An artificially evolved gene for herbicide-resistant rice breeding

Discovering and engineering herbicide-resistant genes is a crucial challenge in crop breeding. This study focuses on the 4-hydroxyphenylpyruvate dioxygenase Inhibitor Sensitive 1-Like (HSL) protein, prevalent in higher plants and exhibiting weak catalytic activity against many β-triketone herbicides (β-THs). The crystal structures of maize HSL1A complexed with β-THs were elucidated, identifying four essential herbicide-binding residues and explaining the weak activity of HSL1A against the herbicides. Utilizing an artificial evolution approach, we developed a series of rice HSL1 mutants targeting the four residues. Then, these mutants were systematically evaluated, identifying the M10 variant as the most effective in modifying β-THs. The initial active conformation of substrate binding in HSL1 was also revealed from these mutants. Furthermore, overexpression of M10 in rice significantly enhanced resistance to β-THs, resulting in a notable 32-fold increase in resistance to methyl-benquitrione. In conclusion, the artificially evolved M10 gene shows great potential for the development of herbicide-resistant crops.

Favipiravir biotransformation by a side-stream partial nitritation sludge: Transformation mechanisms, pathways and toxicity evaluation

Information on biotransformation of antivirals in the side-stream partial nitritation (PN) process was limited. In this study, a side-stream PN sludge was adopted to investigate favipiravir biotransformation under controlled ammonium and pH levels. Results showed that free nitrous acid (FNA) was an important factor that inhibited ammonia oxidation and the cometabolic biodegradation of favipiravir induced by ammonia oxidizing bacteria (AOB). The removal efficiency of favipiravir reached 12.6% and 35.0% within 6 days at the average FNA concentrations of 0.07 and 0.02 mg-N L-1, respectively. AOB-induced cometabolism was the sole contributing mechanism to favipiravir removal, excluding AOB-induced metabolism and heterotrophic bacteria-induced biodegradation. The growth of Escherichia coli was inhibited by favipiravir, while the AOB-induced cometabolism facilitated the alleviation of the antimicrobial activities with the formed transformation products. The biotransformation pathways were proposed based on the roughly identified structures of transformation products, which mainly involved hydroxylation, nitration, dehydrogenation and covalent bond breaking under enzymatic conditions. The findings would provide insights on enriching AOB abundance and enhancing AOB-induced cometabolism under FNA stress when targeting higher removal of antivirals during the side-stream wastewater treatment processes.

Modeling Free Nitrous Acid Inhibition on the Removal of Nitrogen and Atenolol during Sidestream Partial Nitritation Processes

Sidestream serves as an important reservoir collecting pharmaceuticals from sludge. However, the knowledge on sidestream pharmaceutical removal is still insufficient. In this work, atenolol biodegradation during sidestream partial nitritation (PN) processes characterized by high free nitrous acid (FNA) accumulation was modeled. To describe the FNA inhibition on ammonia oxidation and atenolol removal, Vadivelu-type and Hellinga-type inhibition kinetics were introduced into the model framework. Four inhibitory parameters along with four biodegradation kinetic parameters were calibrated and validated separately with eight sets of batch experimental data and 60 days' PN reactor operational data. The developed model could accurately reproduce the dynamics of nitrogen and atenolol. The model prediction further revealed that atenolol biodegradation efficiencies by ammonia-oxidizing bacteria (AOB)-induced cometabolism, AOB-induced metabolism, and heterotrophic bacteria-induced biodegradation were 0, ∼ 60, and ∼35% in the absence of ammonium and FNA; ∼ 14, ∼ 29, and ∼28% at 0.03 mg-N L-1 FNA; and 7, 15, and 5% at 0.19 mg-N L-1 FNA. Model simulation showed that the nitritation efficiency of ∼99% and atenolol removal efficiency of 57.5% in the PN process could be achieved simultaneously by controlling pH at 8.5, while 89.2% total nitrogen and 57.1% atenolol were removed to the maximum at pH of 7.0 in PN coupling with the anammox process. The pH-based operational strategy to regulate FNA levels was mathematically demonstrated to be effective for achieving the simultaneous removal of nitrogen and atenolol in PN-based sidestream processes.

Degradation of Chloroquine by Ammonia-Oxidizing Bacteria: Performance, Mechanisms, and Associated Impact on N2O Production

Since the mass production and extensive use of chloroquine (CLQ) would lead to its inevitable discharge, wastewater treatment plants (WWTPs) might play a key role in the management of CLQ. Despite the reported functional versatility of ammonia-oxidizing bacteria (AOB) that mediate the first step for biological nitrogen removal at WWTP (i.e., partial nitrification), their potential capability to degrade CLQ remains to be discovered. Therefore, with the enriched partial nitrification sludge, a series of dedicated batch tests were performed in this study to verify the performance and mechanisms of CLQ biodegradation under the ammonium conditions of mainstream wastewater. The results showed that AOB could degrade CLQ in the presence of ammonium oxidation activity, but the capability was limited by the amount of partial nitrification sludge (∼1.1 mg/L at a mixed liquor volatile suspended solids concentration of 200 mg/L). CLQ and its biodegradation products were found to have no significant effect on the ammonium oxidation activity of AOB while the latter would promote N2O production through the AOB denitrification pathway, especially at relatively low DO levels (≤0.5 mg-O2/L). This study provided valuable insights into a more comprehensive assessment of the fate of CLQ in the context of wastewater treatment.

Optimizing ciprofloxacin removal through regulations of trophic modes and FNA levels in a moving bed biofilm reactor performing sidestream partial nitritation

The performance of partial nitritation (PN)-moving bed biofilm reactor (MBBR) in removal of antibiotics in the sidestream wastewater has not been investigated so far. In this work, the removal of ciprofloxacin was assessed under varying free nitrous acid (FNA) levels and different trophic modes. For the first time, a positive correlation was observed between ciprofloxacin removal and FNA levels, either in the autotrophic PN-MBBR or in the mixotrophic PN-MBBR, mainly ascribed to the FNA-stimulating effect on heterotrophic bacteria (HB)-induced biodegradation. The maximum ciprofloxacin removal efficiency (∼98 %) and removal rate constant (0.021 L g-1 SS h-1) were obtained in the mixotrophic PN-MBBR at an average FNA level of 0.056 mg-N L-1, which were 5.8 and 51.2 times higher than the corresponding values in the autotrophic PN-MBBR at 0 mg FNA-N L-1. Increasing FNA from 0.006 to 0.056 mg-N L-1 would inhibit ammonia oxidizing bacteria (AOB)-induced cometabolism and metabolism from 10.2 % and 6.9 % to 6.2 % and 6.4 %, respectively, while HB-induced cometabolism and metabolism increased from 31.2 % and 22.7 % to 41.9 % and 34.5 %, respectively. HB-induced cometabolism became the predominant biodegradation pathway (75.9 %-85.8 %) in the mixotrophic mode. Less antimicrobial biotransformation products without the piperazine or fluorine were newly identified to propose potential degradation pathways, corresponding to microbial-induced metabolic types and FNA levels. This work shed light on enhancing antibiotic removal via regulating both FNA accumulation and organic carbon addition in the PN-MBBR process treating sidestream wastewater.

The successful application of light to the system of simultaneous nitrification/endogenous denitrification and phosphorus removal: Promotion of partial nitrification and glycogen accumulation metabolism

Partial nitrification (PN) and high glycogen accumulating metabolism (GAM) activity are the basis for efficient nitrogen (N) and phosphorus (P) removal in simultaneous nitrification endogenous denitrification and phosphorus removal (SNDPR) systems. However, achieving these processes in practical operations is challenging. This study proposes that light irradiation is a novel strategy to enhance the nutrient removal performance of the SNDPR system with low carbon to nitrogen ratios (C/N of 3.3-4.1) domestic wastewater. Light energy densities (Es) of 55-135 J/g VSS were found to promote the activity of ammonia-oxidizing bacteria (AOB) and GAM, while inhibiting the activity of nitrite-oxidizing bacteria (NOB) and polyphosphate accumulating metabolism (PAM). Long-term exposure to different light patterns at Es of 55-135 J/g VSS revealed that continuous light rapidly achieved PN by inhibiting NOB activity and promoted the growth of glycogen accumulating organisms (GAOs), allowing the removal of above 82 % N and below 80 % P. Intermittent light maintained stable PN by inhibiting the activity and growth of NOB and promoted the growth of polyphosphate accumulating organisms (PAOs) with high GAM activity (Accmulibacer IIC-ii and IIC-iii), allowing the removal of above 82 % N and 95 % P. Flow cytometry and enzyme activity assays showed that light promoted GAM-related enzyme activity and the metabolic activity of partial Accmulibacer II over other endogenous denitrifying bacteria, while inhibiting NOB translation activity. These findings provide a new approach for enhancing nutrient removal, especially for achieving PN and promoting GAM activity, in SNDPR systems treating low C/N ratio domestic wastewater using light irradiation.

The mitigation effect of free ammonia and free nitrous acid on nitrous oxide production from the full-nitrification and partial-nitritation systems

The potentials of using endogenous free ammonia (FA) and free nitrous acid (FNA) as nitrous oxide (N₂O) mitigators were investigated in treatment of both mainstream and sidestream wastewater. Although the N₂O emission factor of a sidestream partial-nitritation (PN) reactor (averaged 1.70 % ± 0.39 %, n = 30) was about 2.4 times higher than a mainstream full-nitrification (FN) reactor (averaged 0.72 % ± 0.24 %, n = 30) (P < 0.01), one-hour exposure of PN sludge to 1.5 mg HNO₂-N/L FNA could virtually abolish N₂O emission. As for FN sludge, both 45 mg NH₃-N/L FA and 0.015 mg HNO₂-N/L FNA successfully mitigated N₂O production at varying dissolved oxygen (DO) levels (50 % vs 61 %), while 1.5 mg HNO₂-N/L FNA not only reduced more N₂O (92 %) but also altered the N₂O dependency on DO. Both FNA and FA sludge treatment were effective N₂O mitigation strategies with FNA toward the end of carbon neutrality and FA being more economically appealing (2 % cost saving).