Response to shock load of engineered nanoparticles in an activated sludge treatment system: Insight into microbial community succession

Enhancing methane production and interspecies electron transfer of anaerobic granular sludge by the immobilization of magnetic biochar

Supplementation of conductive materials has been proved to be a promising approach for enhancing microbial interspecies electron transfer (IET) in anaerobic digestion systems. In this study, magnetic bamboo-based biochar was prepared at temperatures of 400-800 °C via a ball milling/carbonization method, and it immobilized in mature anaerobic granular sludge (AGS) aimed to enhance methane production by improving the IET process between syntrophic microbial communities in the AGS. Results showed that the AGS with magnetic biochar immobilization demonstrated increased glucotrophic and acetotrophic methane production by 69.54-77.56 % and 39.96-54.92 %, respectively. Magnetic biochar prepared at 800 °C with a relatively higher Fe content (0.37 g/g magnetic biochar) displayed a stronger electron charge/discharge capacity (36.66 F/g), and its immobilization into AGS promoted methane production most. The conductivity of AGS increased by 52.13-87.32 % after incorporating magnetic biochar. Furthermore, the extracellular polymeric substance (EPS) of AGS showed an increased capacitance and decreased electron transfer resistance possibly due to the binding of magnetic biochar and more riboflavin secretion in EPS, which could contribute to the accelerated IET process in the inner AGS. In addition, the immobilization of magnetic biochar could promote the production of volatile fatty acids by 15.36-22.50 %. All these improvements may jointly lead to the enhanced methane production capacity of AGS. This study provided a fundamental understanding of the role of incorporated magnetic biochar in AGS in promoting anaerobic digestion performance.

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.

Combined impact of TiO2 nanoparticles and antibiotics on the activity and bacterial community of partial nitrification system

The effects of TiO2 nanoparticles (nano-TiO2) together with antibiotics leaking into wastewater treatment plants (WWTPs), especially the partial nitrification (PN) process remain unclear. To evaluate the combined impact and mechanisms of nano-TiO2 and antibiotics on PN systems, batch experiments were carried out with six bench-scale sequencing batch reactors. Nano-TiO2 at a low level had minimal effects on the PN system. In combination with tetracycline and erythromycin, the acute impact of antibiotics was enhanced. Both steps of nitrification were retarded due to the decrease of bacterial activity and abundance, while nitrite-oxidizing bacteria were more sensitive to the inhibition than ammonia-oxidizing bacteria. Proteobacteria at the phylum level and Nitrosospira at the genus level remained predominant under single and combined impacts. The flow cytometry analysis showed that nano-TiO2 enhanced the toxicity of antibiotics through increasing cell permeability. Our results can help clarify the risks of nano-TiO2 combined with antibiotics to PN systems and explaining the behavior of nanoparticles in WWTPs.

Cytotoxicity of functionalized CeO2 nanoparticles towards Escherichia coli and adaptive response of membrane properties

The cytotoxicity and mechanisms of cerium oxide nanoparticles (CeO₂-NPs) on organisms have attracted great concerns recently, while that of CeO₂-NPs with functional groups remains unclear. This study investigated cytotoxic effects and mechanisms of CeO₂-NPs with hydroxyl, carboxyl, or amino functional groups towards a strain Escherichia coli (E. Coli). Results showed that CeO₂-NPs produced a stronger cytotoxicity in NaCl medium than in PBS medium at the concentrations of 10-400 mg/L. The toxicity followed the order of CeO₂-COOH > CeO₂-NH₂ > CeO₂-OH. Exposing to CeO₂-NPs increased cell membrane permeability and reduced membrane fluidity. The membrane phospholipid fatty acid compositions also varied greatly as a response to the stress of CeO₂-NPs, with the proportion of unsaturated fatty acids increased and saturated fatty acids decreased. Both intracellular reactive oxygen species (ROS) level and malonaldehyde (MDA) level declined, suggesting the oxidative stress from ROS may be not the primary reason for the membrane damage. Other mechanisms such as direct membrane oxidation by Ce⁴⁺ or physical penetration based on a close contact between nanoparticles and microbes might contribute to the membrane damages and cell viability loss. The present study provides a significant insight into the influence of functionalized CeO₂-NPs on a gram-negative bacterium.

Changes in bacterial diversity of activated sludge exposed to titanium dioxide nanoparticles

The rapid growth of the use of nanomaterials in different modern industrial branches makes the study of the impact of nanoparticles on the human health and environment an urgent matter. For instance, it has been reported that titanium dioxide nanoparticles (TiO₂ NPs) can be found in wastewater treatment plants. Previous studies have found contrasting effects of these nanoparticles over the activated sludge process, including negative effects on the oxygen uptake. The non-utilization of oxygen reflects that aerobic bacteria were inhibited or decayed. The aim of this work was to study how TiO₂ NPs affect the bacterial diversity and metabolic processes on an activated sludge. First, respirometry assays of 8 h were carried out at different concentrations of TiO₂ NPs (0.5-2.0 mg/mL) to measure the oxygen uptake by the activated sludge. The bacterial diversity of these assays was determined by sequencing the amplified V3-V4 region of the 16S rRNA gene using Illumina MiSeq. According to the respirometry assays, the aerobic processes were inhibited in a range from 18.5 ± 4.8% to 37.5 ± 2.0% for concentrations of 0.5-2.0 mg/mL TiO₂ NPs. The oxygen uptake rate was affected mainly after 4.5 h for concentrations higher than 1.0 mg/mL of these nanoparticles. Results indicated that, in the presence of TiO₂ NPs, the bacterial community of activated sludge was altered mainly in the genera related to nitrogen removal (nitrogen assimilation, nitrification and denitrification). The metabolic pathways prediction suggested that genes related to biofilm formation were more sensitive than genes directly related to nitrification-denitrification and N-assimilation processes. These results indicated that TiO₂ NPs might modify the bacteria diversity in the activated sludge according to their concentration and time of exposition, which in turn impact in the performance of the wastewater treatment processes.

Resistance of multidrug resistant Escherichia coli to environmental nanoscale TiO2 and ZnO

Excessive production and utilization of nanoparticles (NPs) at industrial and household levels releases substantial quantities of NPs into the environment. These can be harmful to different types of organisms and cause adverse effects on ecosystems. Purchased TiO₂ and ZnO NPs were characterized via XRD, XPS, FESEM, and Zeta potential. This study elucidates how multidrug resistant Escherichia coli LM13, which was recovered from livestock manure, counteracts the antibacterial activities of TiO₂ and ZnO NPs to survive in the environment. E. coli ATCC25922, which is susceptible to antibiotics, was used as control. A dose-response experiment showed that the antibacterial activity of TiO₂ was lower than that of ZnO NPs and, LM13 was more resistant to NPs than ATCC25922. An AcrAB-TolC efflux pump along with its regulation genes helped LM13 to minimize NP toxicity. Flow cytometry findings also indicated that the intensity of the side-scatter light parameter increased with TiO₂ and ZnO NPs in a dose dependent manner, suggesting NP uptake by the both strains. The generation of reactive oxygen species in LM13 was several-fold lower than in ATCC25922, suggesting that reactive oxygen species mainly contribute to the toxicity mechanism. These results illustrate the necessity to evaluate the impacts of NPs on the survival capacity of bacteria and on the resistance genes in bacteria with higher NP resistance than NP susceptible bacteria.

Effects of aging and transformation of anatase and rutile TiO2 nanoparticles on biological phosphorus removal in sequencing batch reactors and related toxic mechanisms

The effect of nanomaterials aging, namely the transformation of comprehensive characteristics after experiencing real or complex environmental behaviors, on their ecotoxicology is still lacking. Moreover, the mechanisms by which NPs influence biological phosphorus (P) removal during sewage treatment require further elucidation. Therefore, we used both pristine and aged anatase (TiO₂-A) and rutile (TiO₂-R) NPs to investigate the mechanisms by which NPs affect P removal in a SBR. At 0.1 mg/L, the four types of NPs (pristine and aged) had no significant effect on sludge purification after acute (72-h) exposure under simulated sunlight. However, at 50 mg/L-regardless of the crystalline phase of the NPs-SOP and COD removal efficiency dropped steeply to approximately 42.2-82.4 % (p < 0.05) and 69.8-83.3 % (p < 0.05), respectively, especially in the pristine TiO₂-NPs groups because of decrease of richness and diversity of genus level of PAOs and enzyme activity of both PPK and PPX, and the sluggish transformation of PHA and glycogen. Aging reduced the ability of NPs toxicity. The toxicity mechanisms of TiO₂-NPs included lipid peroxidation and contact damage, or leakage from bacterial cytoplasmic membrane, which are closely related to photooxidation capacity and aqueous solution stability-i.e., nanoscale effects-and the impacts of aging or inclusion.

Simultaneous evaluation of bioactivity and settleability of activated sludge using fractal dimension as an intermediate variable

Bioactivity and settleability of activated sludge are essential for the operation of activated sludge systems in wastewater treatment. In this work, the fractal dimension of sludge image is proposed as a tool to evaluate these two factors. The specific endogenous respiration rate (SOUR_e) and the specific quasi-endogenous respiration rate (SOUR_q) are found to be more dependent on the 3D structure of sludge than the specific total respiration rate (SOUR_t). The relationship between the fractal structure and bioactivity suggests that the bioactivity governs the acceptable upper bound of the fractal dimension (D_f), as at its theoretical maximum of 2.0, the non-porous compact flocs are predominant. The settleability or the biomass concentration determines the acceptable lower bound of D_f, as at its theoretical minimum of 1.0, the free-swimming microbes are predominant. Our data reveal that the activated sludge has an acceptable fractal dimension D_f in a range of 1.07-1.68. In practice, the fractal dimension should be controlled at a reasonable value as there is a trade-off between the bioactivity and physical structure to achieve better performance. A decrease or increase in the fractal dimension can serve as a signal for the change of the operational status, and this is further elucidated from the perspective of settling tanks using state point analysis. Compared with respirogram measurement, measuring fractal dimension is a complex process and its online implementation is challenging. Also, the measured value varies with the methods used. In addition, the difference in their theoretical values depends on the homogeneity of the sludge structure. Since the fractal dimension D_f reflects both bioactivity and settleability of the sludge but is difficult to measure, in this work a relationship between D_f and the easily measurable respirogram is established, and a method using the respirogram as a proxy of D_f is proposed to control the bioactivity and settleability simultaneously. This respiration-based method is able to simultaneously control aeration and settling tanks, and could serve as an efficient tool for the management of wastewater treatment plants.

Differential responses of encoding-amoA nitrifiers and nir denitrifiers in activated sludge to anatase and rutile TiO2 nanoparticles: What is active functional guild in rate limiting step of nitrogen cycle?

The long-terms effects of different crystal-composition TiO₂ nanoparticles (NPs) on nitrogen-cycle-related functional guilds in activated sludge remain unclear, especially under natural light irradiation. Accordingly, activated sludge was exposed to anatase TiO₂-NPs (TiO₂-A) and rutile TiO₂-NPs (TiO₂-R) for up to 45 days. With markedly (p < 0.05) reducing nitrification-/denitrification-enzymatic-activities and abundances of ammonia-oxidizing-microorganisms (AOMs) and nitrite-reducing-bacteria (NRB), TiO₂-NPs triggered bacteria and archaea UPGMA clustering and a deep modification of N-cycling functional diversity guided by crystal structure. in situ¹³C-DNA-SIP confirmed ammonia-oxidizing-bacteria (AOB) (Nitrosomonas and Nitrosospira) in original sludge as main active AOMs with 75.4 times more abundance than ammonia-oxidizing-archaea (AOA), while AOA within Nitrosopumilus and Nitrososphaera genera were the main active AOMs and tended to aggregate inside sludge after 10-mg/L TiO₂-NPs exposure. Encoding-nirK NRB were more sensitive, while encoding-nirS Zoogloea with a total share of 4.97% to 14.93%, etc. were the main active NRB. AOB was more sensitive to TiO₂-A, while TiO₂-R showed the stronger toxicity to AOA and NRB resulting from differences in water environmental behaviors and crystal characteristics of two TiO₂-NPs. This work expands understanding of the ecological risks of titanium-dioxide-crystal-NPs in aquatic environment and may help devise better methods to alleviate environmental stress caused by NPs at wastewater treatment plants.

The performance and microbial community in response to MnO2 nanoparticles in anammox granular sludge

The response of anaerobic ammonium oxidation (anammox) process and granular sludge in the upflow anaerobic sludge blanket reactor was analyzed under long-term exposure to MnO₂ nanoparticles (NPs) (1-200 mg L^-1). The addition of 200 mg L^-1 MnO₂ NPs had a significantly positive effect on nitrogen removal and this system exhibited excellent performance, with a total nitrogen removal efficiency of 93.1%. Moreover, the specific anammox activity enhanced with increasing concentrations of MnO₂ NPs up to the maximum value of 657.3 ± 9.3 mg TN g^-1 VSS d^-1 under MnO₂ NPs concentration of 200 mg L^-1. This value was approximately 1.6-fold higher than that of the reactor in the absence of MnO₂ NPs. The extracellular polymeric substances and settling velocity were both increased with MnO₂ NPs addition. Meanwhile, the high-throughput sequencing results revealed that MnO₂ NPs increased the relative abundance of dominant bacteria (Candidatus Kuenenia) from 17.3% at the absence of MnO₂ NPs to 23.9% at 200 mg L^-1 MnO₂ NPs, which resulted in a higher efficiency of biological nitrogen removal on the anammox system. These results indicated that MnO₂ NPs enhanced nitrogen removal performance of anammox process.

Effects of ZnO nanoparticles on the performance of anaerobic membrane bioreactor: An attention to the characteristics of supernatant, effluent and biomass community

Two laboratory-scale anaerobic membrane bioreactor (AnMBRs) were built to investigate the effect of zinc oxide nanoparticles (ZnO-NPs) on their performance, and the recovery phase was also examined. Results showed that the addition of ZnO-NPs with 0.4 mg/L caused significant deteriorations of AnMBR performance, including decrements of chemical oxygen demand (COD) removal efficiency from 96.4% to 81.5% and biogas production from 0.36 to 0 L/g COD removal within 40 days. A significant increment from 13.2 to 52.1 mg/L in soluble microbial products (SMP) was obtained, while no obvious effect on colloids was observed except an increased fluctuation of colloid concentration. Additionally, gas chromatography-mass spectrometry (GC-MS) analysis revealed remarkable changes of compounds in effluent with exposure to ZnO-NPs, and some new alkanes and esters were produced, such as Cyclobutane, 1,2-diethyl-, trans-, Tetradecane, Cyclopropane, octyl-, and Butanoic acid, methyl ester. The microbial community was compared using high-throughput sequencing, clearly showing the changes in both bacteria and archaea communities. Furthermore, results for recovery phase indicated that the AnMBR performance can be recovered within around 60 days after stopping ZnO-NPs addition, accompanied by the decrement of zinc concentration mainly adsorbed by sludge.

Iohexol Degradation by Biogenic Palladium Nanoparticles Hosted in Anaerobic Granular Sludge

To improve the degradation ability of anaerobic granular sludge (AGS) toward the iodinated contrast media (ICM) iohexol, biogenic nanoscale palladium (Pd) was formed in AGS via microbial reduction. The Pd hosted in AGS (Pd-AGS) was used for iohexol degradation. The effects of the electron donor, reaction medium, iodide ion fouling, and polymer embedding of the Pd-AGS on the reactivity were investigated. Our results showed the Pd-AGS increased the degradation rate of iohexol, with a conversion rate constant increased by 86.3-fold compared to the AGS control. Various organic compounds were investigated as electron donors to initiate the catalytic activity of Pd-AGS and the promotion achieved with the tested electron donors was in the following order: formate > lactate > ethanol > glucose > acetate. The Pd-AGS had high reactivity in deionized water at mild pH, and almost no reactivity under acidic (pH = 1.2) and alkaline (pH > 11) conditions. The presence of iodide ions in the medium inhibited the catalytic activity of Pd-AGS toward iohexol because of catalyst fouling. Embedding the Pd-AGS in alginate, chitosan, or polyvinyl alcohol (PVA) could prevent Pd loss but it also retarded the iohexol degradation rate. The Pd-AGS, as a combination of Pd catalyst and AGS, provides a novel strategy for iohexol degradation in polluted water and wastewater.

Evaluation of robustness of activated sludge using calcium-induced enhancement of respiration

Robustness of an activated sludge system, describing uncertainty and operational risk, was evaluated using the absence or presence of calcium-induced enhancement of respiration (CaER) effect. Generally, the fast-growing system was susceptible to external environmental variations, of which the sludge exhibited significant CaER effect under normal operational conditions, while the slow growing system showed less significant CaER effect. However, sludge in both systems exhibited CaER effect under stressed conditions of decreasing temperature or ammonia shocking. Therefore, the absence of CaER effect indicates a more robust system, while the presence of CaER effect indicates a susceptible system. Additionally, a method to identify safe and dangerous shocking was established by a hybrid usage of absence or presence of CaER effect and recovery index (RI) curve type. The evaluation of robustness could help determining when adjustment should be really taken to cope with the uncertainty, and thus holds a high promise for field application.

Aged-engineered nanoparticles effect on sludge anaerobic digestion performance and associated microbial communities

To investigate the potential effect of aged engineered nanoparticles (a-ENPs) on sludge digestion performance, 150L pilot anaerobic digesters (AD) were fed with a blend of primary and waste activated sludge spiked either with a mixture of silver oxide, titanium dioxide and zinc oxide or a mixture of their equivalent bulk metal salts to achieve a target concentration of 250, 2000, and 2800mgkg^-1 dry weight, respectively. Volatile fatty acids (VFA) were 1.2 times higher in the spiked digesters and significantly different (p=0.05) from the control conditions. Specifically, isovaleric acid concentration was 2 times lower in the control digester compared to the spiked digesters, whereas hydrogen sulfide was 2 times lower in the ENPs spiked digester indicating inhibitory effect on sulfate reducing microorganisms. Based on the ether-linked isoprenoids concentration, the total abundance of methanogens was 1.4 times lower in the ENPs spiked digester than in the control and metal salt spiked digesters. Pyrosequencing indicated 80% decrease in abundance and diversity of methanogens in ENPs spiked digester compared to the control digester. Methanosarcina acetivorans and Methanosarcina barkeri were identified as nano-tolerant as their relative abundance increased by a factor of 6 and 11, respectively, compared to the other digesters. The results further provide compelling evidence on the resilience of Fusobacteria, Actinobacteria and the Trojan horse-like effect of ENPs which offered a competitive advantage to some organisms while reducing microbial abundance and diversity.

Response of anaerobic membrane bioreactor to the presence of nano-Bi2WO6: reactor performance, supernatant characteristics, and microbial community

Considering the increasing incorporation of manufactured nano-material into consumer products, there is a concern about its potential impacts in biological wastewater treatment. In this study, the response of anaerobic sludge to the presence of Bi₂WO₆ nano-particles (NPs) was investigated in the anaerobic membrane bioreactor (AnMBR). As the concentration of Bi₂WO₆ in the reactor was controlled around 1 mg/L, there was no significant difference in effluent water quality or bacterial activities before and after NP exposure, partially due to the microbial-induced NP aggregation and stable complex formation. However, with the increasing dosage of Bi₂WO₆ from 5 to 40 mg/L, great influences on the AnMBR performance were observed, including the reduction of COD removal efficiency, inhibition of the mechanization step, increased production of soluble microbial products, and enhanced secretion of extracellular polymer substrates. Additional investigation with high-throughput sequencing was conducted, clearly demonstrating that Bi₂WO₆ NPs induced changes in the bacterial community.

Changes in nutrient removal and flocs characteristics generated by presence of ZnO nanoparticles in activated sludge process

The aim of this work was to evaluate the impact generated by ZnO NPs on the activated sludge process treating raw (RWW) and filtered wastewater (FWW). It was analyzed the oxygen uptake rate, nutrient removal, flocs characteristics and the morphological interactions between activated sludge and ZnO NPs, in presence of 450-2000 mg/L. The results showed that the presence of more than 450 mg/L of ZnO NPs in raw and filtered wastewater inhibited the oxygen uptake by activated sludge. The highest inhibition was 35% in presence of 1500 mg/L in RWW. The organic matter removal was only inhibited in the presence of 450 and 900 mg/L of ZnO NPs; while ammonia removal decreased for all concentrations of ZnO NPs in both types of wastewater, around 13% for RWW and up to 9% for FWW. The orthophosphate removal improved as the concentration of ZnO NPs increased for both wastewater types, enhancing up to 8% for RWW and 17% for FWW. The flocs size of activated sludge exposed to ZnO NPs in RWW decreased as the concentration of ZnO NPs increased; while for FWW, an opposite effect was observed. The elemental mapping allowed detect the Zn inside of microorganisms, which may correspond to a toxicity mechanism in RWW and FWW. These results indicated that the changes in nutrient removal and flocs characteristics caused by the presence of ZnO NPs on the activated sludge are related to wastewater characteristics, such as suspended solids, type of substrate and concentration of ZnO NPs.

Effects of graphite nanoparticles on nitrification in an activated sludge system

Graphite nanoparticles (GNPs) might result in unexpected effects during their transportation and transformation in wastewater treatment systems, including strong thermo-catalytic and catalytic effects and microbial cytotoxicity. In particular, the effects of GNPs on the nitrification process in activated sludge systems should be addressed. This study aimed to estimate the influence of GNPs on the nitrification process in a short-term nitrification reactor with exposure to different light sources. The results indicated that GNPs could only improve the efficiency of photothermal transformation slightly in the activated sludge system because of its photothermal effects under the standard illuminant (imitating 1 × sun). However, even with better photothermal effects, the nitrification efficiency still decreased significantly with GNP dosing under the standard illuminant, which might result from stronger cytotoxic effects of GNPs on the nitrifying bacteria. The disappearance of extracellular polymeric substances (EPS) around bacterial cells was observed, and the total quantity of viable bacteria decreased significantly after GNP exposuring. Variation in bacterial groups primarily occurred in nitrifying microbial communities, including Nitrosomonas sp., Nitrosospira sp., Comamonas sp. and Bradyrhizobiace sp. Nitrifiers significantly decreased, while the phyla Gammaproteobacteria, Deinocccus, and Bacteroidetes exhibited greater stability during GNP treatment.

Interactions and effects of metal oxide nanoparticles on microorganisms involved in biological wastewater treatment

To clarify the toxicological effects of metal oxide nanoparticles (NPs) on microorganisms with environmental relevance, it is necessary to understand their interactions. In this work, they were studied the effects and the morphological interactions of two metal oxide NPs (ZnO and TiO₂ ) with microorganisms, during aerobic treatment of wastewater. The effects were evaluated according to nutrient removal from wastewater, while morphological interactions were determined by three different techniques such as TEM, HAADF-STEM, as well as an elemental mapping. According to results about effects of both NPs, they inhibited the removal of organic matter and ammonia nitrogen, and enhanced the orthophosphate removal. Related to morphological interactions, the electron-dense material of both NPs was mainly observed bounded to cell membrane. In tests with ZnO NPs, it was also observed electron-dense material internalized in microorganisms without physical damage in cell membrane. The elemental mapping was useful to determine that the electron-dense material corresponded to Zn and Ti. Both interactions, internalization and attachment of NPs on cell membrane of microorganisms may trigger the negative effect in the removal of organic matter and nitrogen.

Novel bioflocculant produced by salt-tolerant, alkaliphilic strain Oceanobacillus polygoni HG6 and its application in tannery wastewater treatment

The optimized production of MBF-HG6, which is a novel salt-tolerant alkaliphilic bioflocculant produced by Oceanobacillus polygoni with its application in tannery wastewater treatment was investigated in this study. It was found the optimal carbon source, nitrogen source, cation, and initial pH of the medium for bioflocculant production were starch, urea, Fe2+, and pH 9.0, respectively. The best stability in the temperature range was from 0 to 80°C and the purified MBF-HG6 contained polysaccharides of 81.53% and proteins of 9.98%. The carboxyl, hydroxyl, and amino groups were determined in bioflocculants, while the optimized bioflocculating activity was observed as 90.25% for the dosages of 6.96mL MBF-HG6, 4.77mL CaCl2 (1%, m/v), and 19.24g/L NaCl using response surface methodology. In addition, SS and turbidity removal rates of the tannery wastewater (4g/L MBF-HG6) could, respectively, reach 46.49% and 91.08%, indicating that the great potential was emerged in enhancement of tannery wastewater treatment by MBF-HG6.

Long-term effect of metal oxide nanoparticles on activated sludge

This study evaluated the influence of metal oxide nanoparticles (NPs) (Ag₂O, TiO₂) and their mixture on activated sludge for 180 days. When tested, a mixture of NPs at 1 and 10 mg/L had greater impact than individual NPs, in which maximum reduction in chemical oxygen demand (COD) elimination (76.3%) was observed after 150 days for 1 mg/L (500 mg/L COD concentration) and after 180 days (70.2%) for 10 mg/L (250 mg/L COD concentration). TiO₂ had higher inhibition on COD reduction than Ag₂O NPs at 1 and 10 mg/L. An antagonistic effect was observed in which the combination of individual NPs had a greater effect than a mixture of NPs. Reduction in COD elimination was found to be dependent on NP type and concentration (p < 0.05). Further, metal ion concentration was higher in sludge than supernatant irrespective of NPs, while microscopic analysis showed the presence of NPs inside activated sludge. Among NPs tested, the concentration of Ti⁴⁺ ion was greater in sludge than in the Ag⁺ ion, thus indicating that TiO₂ has a greater affinity than Ag₂O NPs. All three factors (NP type, NP concentration, organic concentration) play a significant role in imparting COD removal (p < 0.05). Future studies are required to quantify NP concentration to minimize NP effect on plant performance.

Short-term performance of enhanced biological phosphorus removal (EBPR) system exposed to erythromycin (ERY) and oxytetracycline (OTC)

The effects of Erythromycin (ERY) and oxytetracycline (OTC), including individual and combinative effect, on enhanced biological phosphorus removal (EBPR) system within a short-term (24h) were evaluated in this study. Results showed that the P-removal efficiency decreased to 34.6% and 0.0% under the effect of ERY (10mg/L) and OTC (10mg/L) for 24h. OTC concentration higher than 5mg/L was sufficient to cause serious adverse impact on the EBPR performance. While the performance of EBPR system will be impacted by ERY above 10mg/L. OTC, due to its special antibacterial action to the gram-negative bacteria which most PAOs belong to, has more serious negative effect on the EBPR performance than ERY does. Moreover, in the combined antibiotics test, neither synergistic nor antagonistic effect was detected between ERY and OTC. Finally, ERY (10mg/L) and OTC (10mg/L) could inhibit the microorganisms' activity, while couldn't induce serious microorganisms death within 24h.

Insight into the short-term effect of titanium dioxide nanoparticles on active ammonia oxidizing microorganisms in a full-scale wastewater treatment plant: a DNA-stable isotope probing study

Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are two distinct ammonia-oxidizing microorganisms (AOMs) responsible for nitrification in wastewater treatment plants (WWTPs).