Effects of sliver nanoparticles on nitrogen removal by the heterotrophic nitrification-aerobic denitrification bacteria Zobellella sp. B307 and their toxicity mechanisms

Due to the widespread use of sliver nanoparticles (AgNPs), a large amount of AgNPs has inevitably been released into the environment, and there is growing concern about the toxicity of AgNPs to nitrogen-functional bacteria. In addition to traditional anaerobic denitrifying bacteria, heterotrophic nitrification-aerobic denitrification (HNAD) bacteria are also important participants in the nitrogen cycle. However, the mechanisms by which AgNPs influence HNAD bacteria have yet to be explicitly demonstrated. In this study, the inhibitory effects of different concentrations of AgNPs on a HNAD bacteria Zobellella sp. B307 were investigated, and the underlying mechanism was explored by analyzing the antioxidant system and the activities of key denitrifying enzymes. Results showed that AgNPs could inhibit the growth and the HNAD ability of Zobellella sp. B307. AgNPs could accumulate on the surface of bacterial cells and significantly destroyed the cell membrane integrity. Further studies demonstrated that the presence of high concentration of AgNPs could result in the overproduction of reactive oxygen species (ROS) and related oxidative stress in the cells. Furthermore, the catalytic activities of key denitrifying enzymes (nitrate reductase (NAR), nitrite reductase (NIR), and nitrous oxide reductase (N2OR)) were significantly suppressed under exposure to a high concentration of AgNPs (20 mg·L-1), which might be responsible for the inhibited nitrogen removal performance of strain B307. This work could improve our understanding of the inhibitory effect and underlying mechanism of AgNPs on HNAD bacteria.

Effect of CeO2 Nanoparticles on the Spread of Antibiotic Resistance in a Reclaimed Water-Soil-Radish System - Shenzhen City, Guangdong Province, China, April 2023

Introduction

The use of reclaimed water (RW) for irrigation in agricultural practices raises concerns regarding the dissemination of antibiotic resistance genes (ARGs) from soils to edible crops. The effectiveness of nanoparticles (NPs) in reducing antibiotic resistance in vegetables irrigated with RW remains largely unexplored.

Methods

To investigate the effects, we conducted pot experiments in which radishes were planted in soil amended with CeO2 NPs using various application techniques. The abundance of ARGs was characterized using high-throughput quantitative PCR (HT-qPCR). Concurrently, we utilized 16S ribosomal RNA (rRNA) gene sequencing to evaluate the microbial community structure of both the rhizosphere soil and the endophytic compartment within the radishes. Employing bioinformatics analysis, we probed the potential mechanisms by which NPs influence the resistome within the reclaimed water-soil-radish system.

Results

Following the application of CeO2 NPs, there was a noticeable reduction in both the number and concentration of ARG genotypes in the rhizosphere soil, as well as within the radish. Concurrently, CeO2 NPs appeared to mitigate the propagation of ARGs within the reclaimed water-soil-radish system. The ability of CeO2 NPs to modulate the resistome is linked to alterations in microbial community structure. Soil treatment with NPs emerged as the most effective strategy for curbing the spread of ARGs.

Discussion

This finding provides a theoretical foundation for the development of nano-agricultural technologies aimed at controlling the proliferation of ARGs.

Long-Term Exposure and Effects of rGO-nZVI Nanohybrids and Their Parent Nanomaterials on Wastewater-Nitrifying Microbial Communities

Single nanomaterials and nanohybrids (NHs) can inhibit microbial processes in wastewater treatment, especially nitrification. While existing studies focus on short-term and acute exposures of single nanomaterials on wastewater microbial community growth and function, long-term, low-exposure, and emerging NHs need to be examined. These NHs have distinctly different physicochemical properties than their parent nanomaterials and, therefore, may exert previously unknown effects onto wastewater microbial communities. This study systematically investigated long-term [∼6 solid residence time [(SRT)] exposure effects of a widely used carbon-metal NH (rGO-nZVI = 1:2 and 1:0.2, mass ratio) and compared these effects to their single-parent nanomaterials (i.e., rGO and nZVI) in nitrifying sequencing batch reactors. nZVI and NH-dosed reactors showed relatively unaffected microbial communities compared to control, whereas rGO showed a significantly different (p = 0.022) and less diverse community. nZVI promoted a diverse community and significantly higher (p < 0.05) biomass growth under steady-state conditions. While long-term chronic exposure (10 mg·L^-1) of single nanomaterials and NHs had limited impact on long-term nutrient recovery, functionally, the reactors dosed with higher iron content, that is, nZVI and rGO-nZVI (1:2), promoted faster NH₄⁺-N removal due to higher biomass growth and upregulation of amoA genes at the transcript level, respectively. The transmission electron microscopy images and scanning electron microscopy─energy-dispersive X-ray spectroscopy analysis revealed high incorporation of iron in nZVI-dosed biomass, which promoted higher cellular growth and a diverse community. Overall, this study shows that NHs have unique effects on microbial community growth and function that cannot be predicted from parent materials alone.

Effects of nano metal oxide particles on activated sludge system: Stress and performance recovery mechanism

Nano metal oxide particles (NMOPs) are widely used in daily life because of their superior performance, and inevitably enter the sewage treatment system. Pollutants in sewage are adsorbed and degraded in wastewater treatment plants (WWTPs) depending on the microbial aggregates of activated sludge system to achieve sewage purification. NMOPs may cause ecotoxicity to the microbial community and metabolism due to their complex chemical behavior, resulting in a potential threat to the safe and steady operation of activated sludge system. It is of great significance to clarify the influencing mechanism of NMOPs on activated sludge system and reduce the risk of WWTPs. Herein, we first introduce the physicochemical behavior of six typical engineering NMOPs including ZnO, TiO₂, CuO, CeO₂, MgO, and MnO₂ in water environment, then highlight the principal mechanisms of NMOPs for activated sludge system. In particular, the performance recovery mechanisms of activated sludge systems in the presence of NMOPs and their future development trends are well documented and discussed extensively. This review can provide a theoretical guidance and technical support for predicting and evaluating the potential threat of NMOPs on activated sludge systems, and promoting the establishment of effective control strategies and performance recovery measures of biological wastewater treatment process under the stress of NMOPs.

Short-term effects of Mn2O3 nanoparticles on physiological activities and gene expression of nitrifying bacteria under low and high dissolved oxygen conditions

The short-term effects of Mn₂O₃ nanoparticles (NPs) were examined for nitrifying bacterial enrichments exposed under low and high dissolved oxygen (DO) conditions using substrate (ammonia) specific oxygen uptake rates (sOUR), reverse transcriptase - quantitative polymerase chain reaction (RT-qPCR) assays, and by analysis of 16S rRNA sequences. Samples from nitrifying bioreactor were exposed in batch vessels to Mn₂O₃ NPs (1, 5 and 10 mg/L) for either 1 or 3 h under no additional aeration or 0.25 L/min aeration. There was increase in nitrification inhibition as determined by sOUR with increasing dosages of Mn₂O₃ NPs for both low and high DO. At 10 mg/L Mn₂O₃ NPs, the inhibition was about 7-10% for 1 and 3 h exposure in both cases. There was notable reduction in the transcript levels of amoA, hao and nirK for 10 mg/L of Mn₂O₃ NPs under 3 h, high DO exposure, which corresponded well with sOUR. The 16S rRNA sequencing showed that there was an inhibitory effect on ammonia oxidizers activity upon exposure to 10 mg/L of Mn₂O₃ NPs. Collectively, the findings in this study advanced understanding of the different effects of Mn₂O₃ NPs on nitrifying bacteria.

Size-dependent effects of ZnO nanoparticles on performance, microbial enzymatic activity and extracellular polymeric substances in sequencing batch reactor

ZnO nanoparticles (NPs) have been detected in various wastewater treatment plants. It is widely assumed that size has a crucial effect on the NPs toxicity. Concerns have been raised over probable size-dependent toxicity of ZnO NPs to activated sludge, which could eventually affect the treatment efficiencies of wastewater treatment facilities. The size-dependent influences of ZnO NPs on performance, microbial activities, and extracellular polymeric substances (EPS) from activated sludge were examined in sequencing batch reactor (SBR) in present study. Three different sizes (15, 50, and 90 nm) and five concentrations (2, 5, 10, 30, and 60 mg L^-1) were trialled. The inhibitions on COD and nitrogen removal were determined by the particle size, and smaller ZnO NPs (15 nm) showed higher inhibition effect than those of 50 and 90 nm, whereas the ZnO NPs with size of 50 nm showed maximum inhibition effect on phosphorus removal among three sizes of ZnO NPs. After exposure to different sized ZnO NPs, microbial enzymatic activities and removal rates of activated sludge represented the same trend, consistent with the nitrogen and phosphorus removal efficiency. In addition, apparent size- and concentration-dependent effects on EPS contents and components were also observed. Compared with the absence of ZnO NPs, 60 mg L^-1 ZnO NPs with sizes of 15, 50, and 90 nm increased the EPS contents from 92.5, 92.4, and 92.0 mg g^-1 VSS to 277.5, 196.8, and 178.2 mg g^-1 VSS (p < 0.05), respectively. The protein and polysaccharide contents increased with the decreasing particle sizes and increasing ZnO NPs concentrations, and the content of protein was always higher than that of polysaccharide.

Effects of Exogenous N-Acyl-Homoserine Lactone as Signal Molecule on Nitrosomonas Europaea under ZnO Nanoparticle Stress

Despite the adverse effects of emerging ZnO nanoparticles (nano-ZnO) on wastewater biological nitrogen removal (BNR) systems being widely documented, strategies for mitigating nanoparticle (NP) toxicity impacts on nitrogen removal have not been adequately addressed. Herein, N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) was investigated for its effects against nano-ZnO toxicity to a model nitrifier, Nitrosomonas europaea. The results indicated that AHL-attenuated nano-ZnO toxicity, which was inversely correlated with the increasing dosage of AHL from 0.01 to 1 µM. At 0.01 µM, AHL notably enhanced the tolerance of N. europaea cells to nano-ZnO stress, and the inhibited cell proliferation, membrane integrity, ammonia oxidation rate, ammonia monooxygenase activity and amoA gene expression significantly increased by 18.2 ± 2.1, 2.4 ± 0.9, 58.7 ± 7.1, 32.3 ± 1.7, and 7.3 ± 5.9%, respectively, after 6 h of incubation. However, increasing the AHL dosage compromised the QS-mediated effects and even aggravated the NPs’ toxicity effects. Moreover, AHLs, at all tested concentrations, significantly increased superoxide dismutase activity, indicating the potential of QS regulations to enhance cellular anti-oxidative stress capacities when facing NP invasion. These results provide novel insights into the development of QS regulation strategies to reduce the impact of nanotoxicity on BNR systems.

Impact of engineered nanoparticles on microbial transformations of carbon, nitrogen, and phosphorus in wastewater treatment processes - A review

Concern regarding the potential negative impacts of released engineered nanoparticles (ENPs) on pollutant removal performance of wastewater treatment systems has received booming attention in recent years. However, the conclusions drawn from different studies often lead to fragmented overall knowledge, some of which are even contradictory. This scenario shows the necessity for a comprehensive review of the interactions of ENPs in wastewater treatment systems, particularly on the impacts of ENPs on microbial processes of carbon (C), nitrogen (N), and phosphorus (P) removal in water treatment systems. This review introduced the impact of 6 often reported ENPs in 5 types of treatment systems. We found that exposure to most of the investigated ENPs at low concentrations doesn't adversely influence the growth of the heterotrophic microbes, which are responsible for organic matter removal. The impacts of ENPs on various microbial nitrogen transformation processes have been investigated. Dosing of ENPs often causes acute microbial nitrogen removal inhibition at various concentrations, but does not influence long-term operation due to microbial adaption. No significant negative effects on biological phosphorus removal in different wastewater treatment processes have been reported after both short-term and long-term exposure (except copper nanoparticles). Environmentally relevant concentrations of ENPs have been reported to enhance the photosynthetic capacity of wetland plants, whereas chronic inhibition to photosynthesis was found in exposure to high concentrations of ENPs. Inhibition effects are often overestimated in pure cultivated toxicity test assays compared to testing with artificially prepared wastewater containing various ingredients or with real wastewater. Potential ligands in real wastewater can bind with ENPs and lower their dissolution. Some challenges exist regarding detection and quantification techniques of ENPs at environmental concentrations, modeling of engineered nanomaterial release on a worldwide scale, and inhibitory mechanisms to microbial transformations.

Effects of metal oxide nanoparticles on nitrification in wastewater treatment systems: A systematic review

While the variety of engineered nanoparticles used in consumer products continues to grow, the use of metal oxide nanoparticles in electronics, textiles, cosmetics and food packaging industry has grown exponentially in recent years, which will inevitably result in their release into wastewater streams in turn impacting the important biological processes in wastewater treatment plants. Among these processes, nitrification play a critical role in nitrogen removal during wastewater treatment, however, it is sensitive to a wide range of inhibitory substances including metal oxide nanoparticles. Therefore, it is essential to systematically asses the effects of metal oxide nanoparticles on nitrification in biological wastewater treatment systems. In this review we discuss the present scenario of metal oxide nanoparticles and their impact on biological wastewater treatment processes, specifically nitrogen removal through nitrification. We also summarize the various methods used to measure nitrification inhibition by metal oxide nanoparticles and highlight corresponding results obtained using those methods. Finally, the key research gaps that need to be addressed in future are discussed.

Evaluation of performance and microbial community successional patterns in an integrated OCO reactor under ZnO nanoparticle stress

An integrated OCO reactor was used to investigate the performance and microbial community successional changes under long-term exposure to relatively low levels of ZnO nanoparticles (NPs). Relatively higher concentrations of ZnO NPs (1.5 mg L⁻¹) could adversely affect the nitrogen and phosphorus removal in the reactor. The diversity and richness of the microbial communities chronically declined with an increasing concentration of ZnO NPs higher than 1.5 mg L⁻¹. With the elevated ZnO NPs, the phyla abundances of Proteobacteria, Firmicutes and Actinobacteria decreased slightly, whereas those of Bacteroidetes and Acidobacteria increased. Bacteroidetes and Proteobacteria were the predominant phyla in each phase (with a variation in abundance), together with some common taxa responses to ZnO NP stress as revealed by Venn diagram analysis. Some genera associated with the removal of nitrogen and phosphorus, such as Acinetobacter, Stenotrophomonas and Pseudomonas, decreased significantly. The present results are significant for expanding our understanding of the functional performance and microbial community successions of activated sludge which has experienced long-term exposure to environmentally relevant concentrations of ZnO NPs.

An integrated OCO reactor was used to investigate the performance and microbial community successional changes under a long-term exposure to relatively low-level ZnO nanoparticles (NPs).

Effect of zinc oxide nanoparticles on nitrogen removal, microbial activity and microbial community of CANON process in a membrane bioreactor

In this study, a membrane bioreactor (MBR) was adopted for completely autotrophic nitrogen removal over nitrite (CANON) process. Zinc oxide nanoparticles (ZnO NPs) was step-wise increased to analyze the influence on nitrogen removal, microbial activity and microbial communities. Finally ZnO NPs was removed to study its recovery capability. The bioactivities of ammonia-oxidizing bacteria (AOB), anaerobic ammonia-oxidizing bacteria (AAOB) and nitrite-oxidizing bacteria (NOB) were detected by batch experiments. Results showed that the ZnO NPs with low concentration (≤5mgL^-1) was profitable for nitrogen removal while the high concentration performed inhibition, and it lowered the abundance of both AOB and NOB while enhanced that of AAOB. ZnO NPs with high concentration (≥10mgL^-1) suppressed both AOB and AAOB, and long-term exposure within ZnO NPs led to microbial diversity decrease. The inhibition threshold of ZnO NPs on CANON process was 10mgL^-1, and the profitable concentration was 1mgL^-1.

Application of magnetic OMS-2 in sequencing batch reactor for treating dye wastewater as a modulator of microbial community

The potential and mechanism of synthesized magnetic octahedral molecular sieve (Fe₃O₄@OMS-2) nanoparticles in enhancing the aerobic microbial ability of sequencing batch reactor (SBR) for treating dye wastewater have been revealed in this study. The addition of Fe₃O₄@OMS-2 of 0.25g/L enhanced the decolorization of SBRs with an operation cycle of 24h by more than 20%. The 16S rRNA gene high-throughput sequencing indicated Fe₃O₄@OMS-2 increased the microbial richness and diversity of SBRs, and more importantly, promoted the potential dye-degrading bacteria. After a series of enriching and screening, four bacterial strains with the considerable decolorizing ability were isolated from SBRs, designating Alcaligenes faecalis FP-G1, Bacillus aryabhattai FP-F1, Escherichia fergusonii FP-D1 and Rhodococcus ruber FP-E1, respectively. The growth and decolorization of these pure strains were promoted in the presence of Fe₃O₄@OMS-2, which agrees with the result of high-throughput sequencing. Monitoring dissolved Fe/Mn ions and investigating the change of oxidation states of Fe/Mn species discovered OMS-2 composition played the critical role in modulating the microbial community. The significant enhancement of Mn-oxidizing/-reducing bacteria suggested microbial Mn redox may be the key action mechanism of Fe₃O₄@OMS-2, which can provide numerous benefits for the microbial community and decolorization of SBRs.

Fate and transformation of nanoparticles (NPs) in municipal wastewater treatment systems and effects of NPs on the biological treatment of wastewater: a review

Fate, transformation of NPs in WWTP & effects on wastewater treatment.

Long-term effects of ZnO nanoparticles on nitrogen and phosphorus removal, microbial activity and microbial community of a sequencing batch reactor

The performance, microbial activity, and microbial community of a sequencing batch reactor (SBR) were investigated under the long-term exposure of ZnO nanoparticles (ZnO NPs). Low ZnO NPs concentration (less than 5mg/L) had no obvious effect on the SBR performance, whereas the removals of COD, NH4(+)-N, and phosphorus were affected at 10-60mg/L ZnO NPs. The variation trend of nitrogen and phosphorus removal rate was similar to that of microbial enzymatic activity with the increase of ZnO NPs concentrations. The richness and diversity of microbial community showed obvious variations at different ZnO NPs concentrations. ZnO NPs appeared on the surface and cell interior of activated sludge, and the Zn contents in the effluent and activated sludge increased with the increase of ZnO NPS concentration. The present results provide use information to understand the effect of ZnO NPS on the performance of wastewater biological treatment systems.

Retention of titanium dioxide nanoparticles in biological activated carbon filters for drinking water and the impact on ammonia reduction

Given the increasing discoveries related to the eco-toxicity of titanium dioxide (TiO2) nanoparticles (NPs) in different ecosystems and with respect to public health, it is important to understand their potential effects in drinking water treatment (DWT). The effects of TiO2 NPs on ammonia reduction, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in biological activated carbon (BAC) filters for drinking water were investigated in static and dynamic states. In the static state, both the nitrification potential and AOB were significantly inhibited by 100 μg L(-1) TiO2 NPs after 12 h (p < 0.05), and the threshold decreased to 10 μg L(-1) with prolonged exposure (36 h, p < 0.05). However, AOA were not considerably affected in any of the tested conditions (p > 0.05). In the dynamic state, different amounts of TiO2 NP pulses were injected into three pilot-scale BAC filters. The decay of TiO2 NPs in the BAC filters was very slow. Both titanium quantification and scanning electron microscope analysis confirmed the retention of TiO2 NPs in the BAC filters after 134 days of operation. Furthermore, the TiO2 NP pulses considerably reduced the performance of ammonia reduction. This study identified the retention of TiO2 NPs in BAC filters and the negative effect on the ammonia reduction, suggesting a potential threat to DWT by TiO2 NPs.

Microbiote shift in sequencing batch reactors in response to antimicrobial ZnO nanoparticles

Zinc oxide nanoparticles (ZnO NPs) have been monitored in wastewater treatment plants as their potential adverse effects on functional microorganisms have been causing increasing concern.

The impact of zinc oxide nanoparticles on phosphorus removal and the microbial community in activated sludge in an SBR

10 and 20 mg L⁻¹ ZnO NPs damaged the integrity of cell membranes and the microbial community and affected phosphorus removal.