Bound EPS Research Articles

Sludge bound-EPS solubilization enhance CH4 bioconversion and membrane fouling mitigation in electrochemical anaerobic membrane bioreactor: Insights from continuous operation and interpretable machine learning algorithms

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days’ operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/Lreactor/d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/Lreactor/d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPSPS and S-EPSPN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR.

Comparative study of the quick action effect of multiple enzyme-based nano-emulsified oils in enhancing nitrate contamination remediation in groundwater

Emulsified vegetable oil (EVO), as a novel green slow-releasing substrate, has performed great potential in subsurface bioremediation due to its slow release and longevity. Nevertheless, the long time it takes to initiate this process still exposed some limitations. Herein, multiple enzyme-based EVOs (EN-EVOs) were developed to enhance the quick-acting effect in nitrate-contaminated bioremediation. This study demonstrated that EN-EVOs loaded with cellulose (c-EVO) and protein enzymes (p-EVO) performed best, not only did not change the advantages of traditional EVO, but also optimized the stability and particle size to the level of 0.8–0.9 and 247.95–252.25 nm, respectively. Nitrate (NO3–N) degradation further confirmed the superiority of c-EVO in rapidly initiating degradation and achieving stable denitrification. Compared with traditional EVO, the maximum start-up efficiency and the rapid achieving stable denitrification efficiency were improved by 37.6% and 1.71 times, respectively. In such situation, the corresponding NO3–N removal efficiency, kinetics rate constant (k1), and half-life period (t1/2) reached as high as 85.39%, as quick as 1.079 d−1, and as short as 0.64 d after 30-day cultivation. Meanwhile, the rapid conversion efficiency of NO2–N was observed (k2 = 0.083 d−1). High-throughput 16S rRNA gene sequencing indicated that the quick-acting process of NO3–N reduction coupled to c-EVO was mediated by microbial reducers (e.g., Ralstonia, Gulbenkiania, and Sphingobacterium) with regulations of narG, nirS and norB genes. Microorganisms with these genes could achieve quick-acting not only by enhancing microbial activity and the synthesis and metabolism of volatile fatty acids, but also by reducing the production and accumulation of loosely bound-extracellular polymeric substances (LB-EPS). These findings advance our understanding on fast-acting of NO3–N degradation supported by c-EVO and also offer a promising direction for groundwater remediation.

Salinity-mediated enhancement of quaternary ammonium compounds resistance and removal in endophytic bacteria LSE01

The widespread usage of quaternary ammonium compounds (QACs) as disinfectants during the COVID-19 pandemic poses significant environmental risks, such as toxicity to organisms and the emergence of superbugs. In this study, different inorganic salts (NaCl, KCl, CaCl2, MgCl2) were used to induce endophytes LSE01 isolated from hyperaccumulating plants. After five generations of cultivation under 80 g/L NaCl, the minimum inhibitory concentration (MIC) of LSE01 to QACs increased by about 3-fold, while its degradation extent increased from 8% to 84% for C12BDMA-Cl and 5%–89% for C14BDMA-Cl. Transmission electron microscopy (TEM) and three-dimensional fluorescence spectra indicated that the cells induced by high concentration of salt caused plasmolysis and secreted more bound extracellular polymeric substances (B-EPS); these changes are likely to be an important reason for the observed increased resistance and enhanced degradation extent of LSE01 to QACs. Our findings suggest that salt-induction could be an effective way to enhance the resistance and removal of toxic organic pollutants by functional microorganisms.

Effect of salinity on the operational efficiency, microbial community, and metabolism of a bioelectrochemical-granular sludge coupled system for treating sulfate wastewater

The effect of salinity on biological processes makes the removal of sulfate from saline wastewater challenging. The objectives of this study were to investigate the effect of salinity on the removal of sulfur-containing wastewater from a coupled anaerobic baffled reactor and microbial electrolysis cell (ABR-MEC). Results showed that at a NaCl concentration of 20 g/L, the anaerobic and aerobic systems were 78 % and 62 %, respectively, effective in removing SO42−. The polysaccharides and proteins of loosely bound-extracellular polymeric substances (LB-EPS) and tightly bound-extracellular polymeric substances (TB-EPS) decreased as the NaCl concentration increased. The dominant genera changed to Solidesulfovibrio, Desulfovibrio, and Klebsiella, with relative abundances of 10.40 %, 4.18 %, and 3.88 %, respectively. During sulfur metabolism, the abundance of AprAB functional genes was 0.021 %, 0.024 %, and 0.047 % at NaCl concentrations of 0 g/L, 10 g/L, and 20 g/L, respectively, with the relative abundance showing an increasing trend, and the pathway of anisotropic sulfur metabolism was strengthened.

Stress responses of partial denitrification system under long-term ciprofloxacin exposure in an anaerobic sequencing batch reactor

This study evaluated the stress response of partial denitrification (PD) sludge system under ciprofloxacin (CIP) exposure. The results showed that the nitrite accumulation rate (NAR) decreased from 77.41 % to 28.39 % under CIP stress of 200 µg/L, and after adapting to CIP stress, the NAR of PD system recovered to 61.56 % even the CIP increased to 1000 µg/L. The average COD removal efficiency increased from 69.08 ± 2.01 % to 73.33 ± 2.33 %, and the average removal efficiency of CIP increased from 9.83 % ± 0.71 % in phase II (CIP=50 µg /L) to 30.15 % ± 1.63 % in phase V (CIP=1000 µg /L). Under CIP stress, the protein (PN) in Tightly Bound-extracellular polymeric substances (TB-EPS) increased from 77.60 mg/(g-SS) in phase I to 135.58 mg/(g-SS) in phase Ⅲ (influent CIP=200 µg /L). FTIR revealed that functional groups (CO, C-H, C-O-C) in EPS of PD sludge could bind to CIP to protect microbial cells from damage. The results of principal co-ordinates analysis (PCoA) showed that the addition of CIP had a significant effect on the microbial community structure, CIP exposure led to an increase in biodiversity of PD system. At genus level, Thauera genus abundance decreased, while OLB12 and Denitratisoma genus abundances increased under CIP stress. This was consistent with the result that the conversion of NO3--N to NO2--N was inhibited while NO2--N reduction was promoted. The findings of this study provided insight into the stress-responses of PD system under long-term CIP exposure and provided useful guidance for the risk assessment and control strategy of wastewater treatment plants (WWTPs).

Obtaining mutant Chlorella vulgaris strains with excellent self-flocculation properties and high wastewater treatment efficiency via atmospheric and room temperature plasma technique

In this study, atmospheric and room temperature plasma technique (ARTP) was applied to generate mutants of Chlorella vulgaris to improve its self-flocculation. Four high self-flocculation mutant strains named SDJZM-1, SDJZM-2, SDJZM-3 and SDJZM-4 were obtained. Among them, SDJZM-1showed the highest self-flocculation efficiency of 92.34 %, and the lowest self-flocculation efficiency of SDJZM-2 was still increased by 78.85 % compared to the original type. In addition, four mutants showed high capability to uptake nutrients from wastewater. Especially, mutant SDJZM-4 increased the removal of total nitrogen, phosphorus and ammonia nitrogen by 29.39 %, 22.72 % and 14.82 %, respectively, in comparison with wild-type strain. Three-dimensional excitation and emission matrix fluorescence spectroscopy analysis showed that more protein was found in mutant strains, and a significant correlation between the protein content in bound extracellular polymeric substances (B-EPS) and flocculation efficiency was observed. The main self-flocculation mechanism of mutant strains was the bridging and sweeping made by B-EPS.

Stability and mobility of zinc oxide nanoparticles in aquatic environment: Influence of extracellular polymeric substances from cyanobacteria and microalgae

The stability and mobility of engineered nanoparticles in the natural water environment are influenced by various environmental factors, such as electrolyte conditions and the presence of natural organic matters. Cyanobacterial and microalgal extracellular polymeric substances (EPSs) are complex organic mixtures ubiquitous in eutrophic waters. In this study, bound EPSs (B-EPSs) and dissolved EPSs (D-EPSs) of Microcystis sp. and Chlorella vulgaris were extracted as the representative natural organic matters in the aquatic environment. Time-resolved dynamic light scattering and quartz crystal microbalance with dissipation monitoring were applied to investigate the influence of the extracted EPSs on zinc oxide nanoparticle (ZnO NP) aggregation and deposition behaviors. Data showed that EPSs with higher protein fractions were more efficient in hindering the aggregation of ZnO NPs in NaCl solutions and low CaCl2 concentration solutions. In higher CaCl2 concentration solutions (>50 mM), the presence of D-EPSs promoted aggregation by forming intermolecular bridging. By accelerating the Brownian movement of NPs and providing electrostatic and hydrophilic attraction between NPs and silica surfaces, B-EPSs facilitated ZnO NP deposition. On the contrary, D-EPSs hindered the deposition through steric repulsion. Moreover, B-EPS-coated ZnO NPs formed a more rigid layer, while the D-EPS-coated ZnO NPs formed a softer layer.

A novel pre-magnetized ZVI/PS pretreatment for improving sludge dewaterability: The role of EPS fractions.

The dewaterability of waste-activated sludge (WAS) has been extensively examined using zero-valent iron (ZVI)-based advanced oxidation processes (AOPs). However, the high dosage and low utilization efficiencies of ZVI cast doubt on the dependability and viability of ZVI-based AOPs. In this study, we successfully demonstrated pre-magnetization as an efficient, chemical-free, and ecological method for improving the efficiency of sludge dewatering by ZVI/persulfate (PS) process, in which the reduction ratios of capillary suction time (CST) and specific resistance to filtration (SRF) increased by 8.67% and 11.06% under optimal conditions, respectively. The highly active Fe2+ released during ZVI corrosion may be more essential than ZVI itself during PS activation, which could be strengthened by pre-magnetization. Both homogeneous and heterogeneous Fe2+ could react with PS to produce aqueous hydroxyl radicals (∙OH) and sulfate radicals (SO4-∙) as well as surface-bound ∙OH and SO4-∙, further decomposing bound-extracellular polymeric substances fractions, broking hydrophilic functional groups and compounds, altering protein secondary structure to expose more hydrophobic sites, and releasing abundant EPS-bound water. Due to the protection of tightly-bound extracellular polymeric substances (TB-EPS) and the competitive oxidation of organics released during the early disintegration stage, radical oxidation primarily occurs at extracellular levels, releasing a bit of intracellular water. Besides, polysaccharides in TB-EPS may function a more significant role in flocculation than proteins, and a porous structure favorable to drainage will be formed after the pre-magnetized ZVI/PS treatment. The cost-benefit analysis further reveals that the Pre-ZVI/PS process presents high reusability and utilization, making it potential for particle application in sludge dewatering.

Contribution of extracellular polymeric substances fractions to the adsorption of silver nanoparticles by activated sludge

The extracellular polymeric substances (EPS) from activated sludge played significant roles in the removal of nanoparticles from wastewater. A series of batch experiments were carried out to determine the adsorption mechanism of three nano-Ag by activated sludge, as well as the contributions of EPS fractions including dissolved EPS (DEPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS). The results demonstrated that the adsorption of nano-Ag by sludge biomass agreed with pseudo-second-order kinetic reaction model and Freundlich isotherm model. About 26.0–41.2% of nano-Ag was trapped by the bound EPS (BEPS) matrix of activated sludge (especially LB-EPS) and 42.5–52.6% of them was adsorbed onto the inner cells after the adsorption. Moreover, the interaction energy contributions of EPS fractions followed the order of EDE > 0 > ETB > ELB, suggesting DEPS in wastewater went against the removal of nano-Ag due to steric repulsion while LB-EPS and TB-EPS were positive to nano-Ag adsorption by modifying biomass surface and providing extensive binding sites. Besides, EPS fractions played significant roles in the adsorption of nano-Ag with low initial concentrations but had limited effect at high concentrations. Overall, this study investigated the effect of EPS fractions on the adsorption behaviors of nano-Ag by activated sludge biomass, which is meaningful to understand the removal mechanism of nanoparticles in sewage and the potential role of EPS fractions.

Enhanced nutrient removal from mixed black water by a microbial ultra-low weak electrical stimulated anaerobic-two stage anoxic/aerobic process

Efficient nutrient removal from mixed black water is under challenge in the context of global pollution control and circular economy. The anaerobic-anorexic-aerobic process is a widely used biological nutrient removal technology for wastewater treatment, yet its denitrification capacity is limited by the low biodegradable organics to nitrogen (C/N) ratio due to prior degradation of mixed black water. We have previously proved that weak electrical of 0.2 V could stimulate microbial denitrification of black water using an external electrical supply to ensure voltage stability. To reduce the dependence on additional electrical and to ensure a stable voltage output, we built a microbial fuel cell (MFC) and a microbial electrolytic cell (MEC) embedded in the anaerobic-two stage anoxic/aerobic (A-(A/O)2) system in this study, where the MFC degrades organic matter and generates electricity first. Then, the electroactive bacteria in the MEC catalyze denitrification at low carbon levels, which is affected by microbial ultra-low weak electrical stimulation (MUlWES) generated by MFC. Results showed that the removal rates of total nitrogen (TN) and total phosphorus (TP) were up to 91.3% and 98.3% respectively at a stimulation voltage of 0.1 V. Fluorescence spectroscopy revealed the formation of aromatic proteins and an increase in tightly bound-extracellular polymeric substances (TB-EPS), suggesting the involvement of these compounds in electron transfer. Community analysis disclosed the activation of autotrophic denitrifying bacteria and the inhibition of most heterotrophic denitrifying bacteria.

The effect of Bacillus cereus LV-1 on the crystallization and polymorphs of calcium carbonate.

The study of CaCO3 polymorphism is of great significance for understanding the mechanism of carbonate mineralization induced by bacteria and the genesis of carbonate rock throughout geological history. To investigate the effect of bacteria and shear force on CaCO3 precipitation and polymorphs, biomineralization experiments with Bacillus cereus strain LV-1 were conducted under the standing and shaking conditions. The results show that LV-1 induced the formation of calcite and vaterite under the standing and shaking conditions, respectively. However, the results of mineralization in the media and the CaCl2 solution under both kinetic conditions suggest the shear force does not affect the polymorphs of calcium carbonate in abiotic systems. Further, mineralization experiments with bacterial cells and extracellular polymeric substances (EPS) were performed under the standing conditions. The results reveal that bacterial cells, bound EPS (BEPS), and soluble EPS (SEPS) are favorable to the formation of spherical, imperfect rhombohedral, and perfect rhombohedral minerals, respectively. The increase in the pH value and saturation index (SI) caused by LV-1 metabolism under the shear force played key roles in controlling vaterite precipitation, whereas bacterial cells and EPS do not play roles in promoting vaterite formation. Furthermore, we suggest that vaterite formed if pH > 8.5 and SIACC > 0.8, while calcite formed if pH was between 8.0-9.0 and SIACC < 0.8. Bacterial cells and BEPS are the main factors affecting CaCO3 morphologies in the mineralization process of LV-1. This may provide a deeper insight into the regulation mechanism of the polymorphs and morphologies during bacterially induced carbonate mineralization.

Defense pathways of Chlamydomonas reinhardtii under silver nanoparticle stress: Extracellular biosorption, internalization and antioxidant genes

Numerous studies have been investigated the toxic effects of silver nanoparticle (Ag-NPs) on algae; however, little attention has been paid to the defense pathways of algae cells to Ag-NPs. In the study, Chlamydomonas reinhardtii (C. reinhardtii) was selected as a model organism to investigate the defense mechanisms to Ag-NPs exposure. The results showed that exopolysaccharide and protein in bound-extracellular polymeric substances significantly increased under Ag-NPs stress. These metal-binding groups including C–O–C (exopolysaccharide), CH3/CH2 (proteins), O–H/N–H (hydroxyl group) and C–H (alkyl groups) played a key role in extracellular biosorption. The internalized or strongly bound Ag (1.90%–17.45% of total contents) was higher than the loosely surface biosorption (0.31%–1.79%). The accumulation of glutathione disulfide (GSSG), together with the decline of reduced glutathione/GSSG (GSH/GSSG) ratio in C. reinhardtii cells, indicated a significant oxidative stress caused by exposure of Ag-NPs. The increasing phytochelatin accompanied with the decreasing GSH level indicated a critical role to intracellular detoxification of Ag. Furthermore, upregulation of antioxidant genes (MSOD, QTOX2, CAT1, GPX2, APX and VTE3) can cope with oxidative stress of Ag-NPs or Ag+. The up-regulation of ascorbate peroxidase (APX) and glutathione peroxidase (GPX2) genes and the reduction in GSH contents showed that the toxicity of Ag-NPs could be mediated by an intracellular ascorbate-GSH defense pathway. These findings can provide valuable information on ecotoxicity of Ag-NPs, potential bioremediation and adaptation capabilities of algal cells to Ag-NPs.

The promotion and inhibition effect of graphene oxide on the process of microbial denitrification at low temperature

This study found that graphene oxide (GO) improved microbial denitrification at low temperatures (~12 °C), and the optimal concentration was 10 mg/L as the removal rate of NO3-N increased by 17%. At the optimal concentration, GO improved the electron transport system activity of the microbes and enhanced the activity of nitrate reductase and nitrite reductase while exhibited low microbial toxicity. The addition of GO increased the content of tightly bound extracellular polymeric substances (EPS). The results of fluorescence spectrometer indicated that GO accelerated the renewal of bound EPS (B-EPS). Fourier Transform infrared spectroscopy (FTIR) results showed that GO affected the secondary structure of the protein in B-EPS, making B-EPS more hydrophobic and promoting microbial aggregation. B-EPS affected by GO can promote the electron transfer process of microorganisms. However, high concentration (>25 mg/L) of GO may inhibit denitrification by competing for electrons, which was not conducive to denitrification thermodynamically.

Quantitative assessment of extraction methods for bound extracellular polymeric substances (B-EPSs) produced by Microcystis sp. and Scenedesmus sp.

Extracellular polymeric substances (EPSs) play a significant role in the growth and survival of microorganisms. They have been applied in various fields, such as animal feed, pharmaceuticals and cosmetics, due to their physicochemical characteristics (e.g., high contents of polysaccharides and proteins, properties of antivirus, antitumor and antioxidant). However, lack of standard evaluation methods for efficient extraction restricts further investigation on the characteristics or functions of EPSs and their commercial applications. In this study, the Bound-EPS (B-EPS) Extraction Efficiency Evaluation Model (B-E4 Model) was developed to assess various extraction methods for two microalgae (i.e., the prokaryotic Microcystis sp. and the eukaryotic Scenedesmus sp.), including heating, centrifugation, ultrasound, ethylenediaminetetraacetic acid, cation-exchange resin or sodium hydroxide. The evaluation parameter k, was introduced to represent the extraction yields of B-EPSs, which was normalized to the per unit mass of released intracellular organics. This study revealed that heating at 70 °C for 10 min led to the highest extraction efficiency for both Microcystis sp. and Scenedesmus sp., with k values of 12.34 ± 1.48 and 6.02 ± 0.14, respectively. Moreover, model predictions for cell rupture were in close agreement with the results of flow cytometry analysis obtained in this study and the literature. Moreover, to test the applicability of B-E4 Model established in this study, it was utilized to evaluate the extraction efficiencies of various methods applied in a previous study on the microalgae Neocystis mucosa SX, and cation-exchange resin treating for 6 h was found to be the optimal method. The B-E4 model developed in this study was proven to be a powerful tool for optimizing the microalgal B-EPS extraction procedures.

Mechanism of Membrane Fouling Control by HMBR: Effect of Microbial Community on EPS.

A hybrid membrane bioreactor (HMBR) employing activated sludge and biofilm simultaneously is proved to represent a good performance on membrane fouling control compared to conventional membrane bioreactor (CMBR) by reducing extracellular polymeric substances (EPS), especially bound EPS (B-EPS). In order to better understand the mechanism of membrane fouling control by the HMBR in regard of microbial community composition, a pilot scale HMBR operated to treat domestic wastewater for six months, and a CMBR operated at the same time as control group. Results showed that HMBR can effectively control membrane fouling. When transmembrane pressure reached 0.1 MPa, the membrane module in the HMBR operated for about 26.7% longer than that in the CMBR. In the HMBR, the quantity of EPS was significantly lower than that in the CMBR. In this paper, soluble EPS was also found to have a close relationship with cake layer resistance. The species richness and diversity in the HMBR were higher than those in the CMBR, and a certain difference between the compositions of microbial communities in the two reactors was confirmed. Therefore, the difference in microbial community compositions may be the direct reason why EPS in the HMBR was lower than that in the CMBR.

Long-term effects of N-acyl-homoserine lactone-based quorum sensing on the characteristics of ANAMMOX granules in high-loaded reactors

Laboratory experiments were carried out to determine the long-term effects of N-acyl-homoserine lactone (AHL)-based quorum sensing on the characteristics of ANAMMOX granules in high-loaded reactors. Results clearly showed that adding 30 mg L−1 N-octanoyl-DL-homoserinelactone (C8-HSL) at the initial stage (1–40 d) of the experiment had long-term positive effects on the settleability of granules and controlled the sludge floatation effectively. C8-HSL decreased the content of bound extracellular polymeric substances (B-EPS) and the ratio of protein to carbohydrate (PN/PS) by 17% and 48%, respectively and increased the relative hydrophobicity (RH) of the granules by 28%. The results of batch tests indicated that C8-HSL significantly reduced the content of loosely-bound EPS (LB-EPS) in the B-EPS, which was responsible for variations in granule settleability and stability. Thus, the settleability of the granules was improved significantly due to addition of C8-HSL, contributing to operational stability and the high TN removal efficiency of the reactor. On day 150, when the nitrogen loading rates of all reactors were 13.4 kg TN m−3 d−1, the nitrogen removal rate and nitrogen removal efficiency of the reactor with C8-HSL (R3) were up to 11.2 kg TN m−3 d−1 and 88%, respectively. N-hexanoyl-DL-homoserine lactone (C6-HSL) improved activity of the granules, while N-dodecanoyl-DL-homoserine lactone (C12-HSL) had no effect on the characteristics of the granules. The long-term effects of C8-HSL on the settleability of granules may be attributed to sustainable release of endogenous signals induced by exogenous signal.

Influence of extracellular polymeric substances on cell-NPs heteroaggregation process and toxicity of cerium dioxide NPs to Microcystis aeruginosa

The presence of abundant extracellular polymeric substances (EPS) play a vital role in affecting heteroaggregation process and toxicity of nanoparticles (NPs) to Microcystis aeruginosa. Interactions between n-CeO2 and cyanobacteria with/without EPS and the toxicity of n-CeO2 to M. aeruginosa were investigated in this study. Aggregation kinetics of n-CeO2 under both soluble EPS (SEPS) and bound EPS (BEPS) indicated the presence of EPS could induced the formation of EPS-NPs aggregates. Heteroaggregation between cells and n-CeO2 was confirmed through co-settling experiment and SEM-EDS observation. SEPS contributed to the observable heteroaggregation using spectral measurement. Heteroaggregation between cells and n-CeO2 under no BEPS was hardly obtained through spectral measurement, but SEM-EDS observation convinced this process. And the DLVO theory explained this heteroaggregation process under various EPS conditions, where the energy barrier decreased with gradual EPS extraction. In addition, the order for 96 h half growth inhibition concentration (IC50) was Raw M9 > M9-SEPS > M9+BEPS > M9-BEPS. These results revealed that not all heteroaggregation between cell-NPs can lead to the NPs toxicity to cells. BEPS act more important role in buffering against the toxicity of NPs from ambient adverse factors, but SEPS increase the stability of NPs which could aggravate the adverse effects of NPs in the environment.

High-Rate Contact Stabilization Process-Coupled Membrane Bioreactor for Maximal Recovery of Organics from Municipal Wastewater

The high-rate activated sludge (HRAS) process is being studied for the removal and recovery of organics with short solids retention time (SRT) from wastewater, facilitating energy recovery by the subsequent anaerobic digestion process. In the present study, the feasibility of a novel high-rate contact stabilization (HRCS) process coupled with a membrane bioreactor (MBR) was investigated as a HRAS technique to harvest organics compared to a high-loaded MBR (HL-MBR) process treating the same sewage. Results showed that higher chemical oxygen demand (COD) removal efficiency and better bioflocculation performance were obtained using HRCS-MBR compared with HL-MBR with SRTs from 0.5 to 1.8 days. The increased bound extracellular polymeric substances content in the contactor was responsible for the improved biosorption and bioflocculation performance in the HRCS-MBR configuration. At an optimal SRT of 1.2 days, incoming organics of 47.5% and 40.5% were harvested in concentrate for HRCS-MBR and HL-MBR. These harvested organics from the concentrate per liter from HRCS-MBR and HL-MBR produced 4.28 × 10−3 and 3.72 × 10−3 kWh of electricity, respectively. The clear advantage of fouling control for HRCS-MBR was determined because of significantly lower concentrations of colloidal materials and soluble microbial products in the concentrate compared with HL-MBR. Therefore, HRCS-MBR holds promise for organics recovery and sustainable wastewater treatment.

Effect of chromium on granule-based anammox processes

In this study, the feasibility of application of anaerobic ammonium oxidation (anammox) to teat wastewater containing chromium was assessed. Anammox granule activity decreased with increasing Cr(VI) concentration and pre-exposure time in batch tests, and the 50% inhibition concentration of Cr(VI) on anammox biomass was 296.5 mg L−1. Approximately 93.9% chromium was absorbed by loosely bound-extracellular polymeric substances and tightly bound-extracellular polymeric substances when less than 60 mg L−1 Cr(VI) was added. During long-term operation in up-flow anaerobic sludge blanket reactor, significant inhibitory effects anammox performance were observed for Cr(VI) concentrations up to 2 mg L−1. The nitrogen removal rate (NRR) rapidly decreased to 1.49 ± 0.89 kg N m−3 d−1, whereas the NRR was 11.37 ± 1.30 kg N m−3 d−1 in a control reactor. Compared with initial levels, specific anammox granule activity was 22%. The tolerance of the anammox process to Cr(VI) can be enhanced after a long-term adaptive phase.

Antagonistic effect of nano-ZnO and cetyltrimethyl ammonium chloride on the growth of Chlorella vulgaris: Dissolution and accumulation of nano-ZnO

The interaction of nanoparticles with coexisting chemicals affects the fate and transport of nanoparticles, as well as their combined effects on aquatic organisms. Here, we evaluated the joint effect of ZnO nanoparticle (nano-ZnO) and cetyltrimethyl ammonium chloride (CTAC) on the growth of Chlorella vulgaris and explored the possible mechanism. Results showed that an antagonistic effect of nano-ZnO and CTAC (0.1, 0.2 and 0.3 mg L−1) was found because CTAC stop nano-ZnO being broken down into solution zinc ions (Zn2+). In the presence of CTAC, the zinc (including nano-ZnO and released Zn2+) showed a higher adsorption on bound extracellular polymeric substances (B-EPS) but lower accumulation in the algal cells. Moreover, we directly demonstrated that nano-ZnO was adsorbed on the algal B-EPS and entered into the algal cells by transmission electron microscope coupled with energy dispersive X-ray (TEM-EDX). Hence, these results suggested that the combined system of nano-ZnO and CTAC exhibited an antagonistic effect due to the inhibition of CTAC on dissolution of nano-ZnO and accumulation of the zinc in the algal cells.