Identification of the function of extracellular polymeric substances (EPS) in denitrifying phosphorus removal sludge in the presence of copper ion

Impact of heavy metals on the formation and properties of solvable microbiological products released from activated sludge in biological wastewater treatment

This study investigated the acute impact of heavy metals on activated sludge with respect to the amount properties of biopolymers and other solvable microbiological products (SMPs) released from the sludge. Ten heavy metals were selected for the evaluation. Under the experimental conditions, exposing activated sludge to different metals led to an increase in SMPs, with a more significant increase in nitrogenous organics than in carbonaceous ones, where Hg²⁺, Ag⁺, Cu²⁺, and Cr⁶⁺ led to the highest increase in SMP species, while Cd²⁺, Ni²⁺, Mn²⁺, Pb²⁺, and Co²⁺ caused limited increase in the middle and small SMP molecules, and Zn²⁺ and Cr³⁺ resulted in a decrease in SMP content. To probe the molecular impact of heavy metals and the association between cellular stress and SMP formation, the toxicity of heavy metals was evaluated using a toxicogenomics assay. Based on a correlation analysis between the increase in SMP and the molecular toxicity index-transcriptional effect level index (TELI) of different genes under corresponding stress conditions, eight genes demonstrated a strong correlation with SMP properties and were pre-assumed to have the most significant influence on the increment in SMPs. We further validated the correlation equation established to predict SMP production based on the molecular disturbance of the eight key biomarkers, using arsenic As³⁺ and vanadium V⁵⁺ as tests, and by quantifying the amount of SMPs released from the activated sludge under the influence of these metals using a TELI-derived equation. In addition, the heavy metals that generated greater amounts of reactive oxygen species also caused larger increases in SMPs.

Response of Bacillus vallismortis sp. EPS to exogenous sulfur stress/ induction and its adsorption performance on Cu(II)

The chemical composition of EPS (Extracellular Polymeric Substances) produced by Bacillus vallismortis sp. and its adsorption performance on typical heavy metal were studied under Na₂S stress/induction at different concentrations. Its structure was characterized by three-dimensional fluorescence spectrogram (3D-EEM), infrared spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that, when the Na₂S stress/induction intensity was 20 mg/L, the protein concentration was nearly doubled compared with Control-EPS (EPS produced by Bacillus vallismortis sp. without exogenous sulfur stress); furthermore, the 3D-EEM results also demonstrated that there was an increase in the protein content, with the -SH content reaching 154.36 μmol/L, which was 48.2% higher than before stress (104.15 μmol/L). Under this condition, S-EPS (EPS produced by Bacillus vallismortis sp. stressed by exogenous sulfur) exhibited the best adsorption effect on Cu(II), with the theoretical maximum adsorption capacity reaching 1428.57 mg/g EPS. FTIR and XPS analyses revealed that the -SH, CO, N-H played a major role in the adsorption of Cu(II); among those, -SH played a key role. Moreover, the adsorption capacity of Cu(II) by S-EPS was correlated with the content of sulfhydryl protein; indeed, the exogenous sulfur stress/induction can effectively regulate the chemical composition of EPS and improve its adsorption performance, which can be crucial in the prevention and control of heavy metal pollution.

Influence of metals and metalloids on the composition and fluorescence quenching of the extracellular polymeric substances produced by the polymorphic fungus Aureobasidium pullulans

Abstract

Aureobasidium pullulans is a ubiquitous and widely distributed fungus in the environment, and exhibits substantial tolerance against toxic metals. However, the interactions between metals and metalloids with the copious extracellular polymeric substances (EPS) produced by A. pullulans and possible relationships to tolerance are not well understood. In this study, it was found that mercury (Hg) and selenium (Se), as selenite, not only significantly inhibited growth of A. pullulans but also affected the composition of produced EPS. Lead (Pb) showed little influence on EPS yield or composition. The interactions of EPS from A. pullulans with the tested metals and metalloids depended on the specific element and their concentration. Fluorescence intensity measurements of the EPS showed that the presence of metal(loid)s stimulated the production of extracellular tryptophan-like and aromatic protein-like substances. Examination of fluorescence quenching and calculation of binding constants revealed that the fluorescence quenching process for Hg; arsenic (As), as arsenite; and Pb to EPS were mainly governed by static quenching which resulted in the formation of a stable non-fluorescent complexes between the EPS and metal(loid)s. Se showed no significant interaction with the EPS according to fluorescence quenching. These results provide further understanding of the interactions between metals and metalloids and EPS produced by fungi and their contribution to metal(loid) tolerance.

Key points

• Metal(loid)s enhanced production of tryptophan- and aromatic protein-like substances.

• Non-fluorescent complexes formed between the EPS and tested metal(loid)s.

• EPS complexation and binding of metal(loid)s was dependent on the tested element.

• Metal(loid)-induced changes in EPS composition contributed to metal(loid) tolerance.

Enhanced treatment performance of phenol wastewater and membrane antifouling by biochar-assisted EMBR

Biochar-assisted EMBR (BC-assisted EMBR) was built to enhance treatment performance of phenol wastewater and membrane antifouling. BC-assisted EMBR significantly increased phenol degradation efficiency, owing to combined effects of biodegradation, adsorption and electro-catalytic degradation. Meanwhile, BC-assisted EMBR obviously mitigated membrane fouling. The coupling effect of BC and voltage led to the lower N-acyl-homoserine lactones (AHLs) and bound extracellular polymeric substances (bound EPS) contents around and on membrane surface. Protein (PN)/polysaccharide (PS) in bound EPS was decreased, led to the increase of negative charge and decrease of hydrophobicity of sludge, which abated bound EPS adsorption on membrane surface. Microbial community analyses revealed that the coupling effect of BC and voltage could enrich phenol-degraders (e.g., Comamonas), electron transfer genus (Phaselicystis), and biopolymer-degraders (Phaselicystis and Tepidisphaera) in BC-assisted EMBR and on its membrane surface, while decrease biofilm-former (e.g., Acinetobacter) and bound EPS-producer (Devosia), which was beneficial to promote phenol treatment and mitigate membrane fouling.

Quorum quenching bacteria bioaugmented GO/PPy modified membrane in EMBR for membrane antifouling

A novel integrated system with quorum quenching (QQ) bacterium Burkholderia sp. ssn-2 bioaugmented graphene oxide/polypyrrole (GO/PPy) conductive polymercomposite membrane (CPM) in MBR with electric field (EMBR) was established. The integrated system exhibited the highest degradation efficiency for phenol (100%) and COD (93.2%-99.9%) during the 120 days operation. Membrane fouling in the integrated system was notably mitigated by the coupling effect of CPM + voltage and QQ bacterium ssn-2. The hydrophilicity and antibacterial activity of CPM inhibited the hydrophobic protein foulants adsorption, bacteria colonization and attachment on the CPM surface. Extracellular polymeric substances (EPS) content was positively correlated with N-acyl-homoserine lactones (AHLs) concentration, and decreased with AHLs degradation by QQ bacterium ssn-2. The increased negative charge of EPS on the CPM surface augmented the electrostatic repulsion between the EPS and cathode CPM in the integrated system. Moreover, the coupling effect altered the microbial communities. A decreased AHLs concentration had a significantly negative correlation with QQ bacterium ssn-2 enrichment, which exhibited the dual effects of degrading phenol and AHLs, and enriching biopolymer-degrading genera Clostridium sensu strict and Acidovorax in the integrated system and on the CPM surface. This can lead to a decrease in the EPS content.

Fate and role of fluorescence moieties in extracellular polymeric substances during biological wastewater treatment: A review

In biological wastewater treatment systems, extracellular polymeric substances (EPS) are continuously excreted as a response to environmental changes and substrate conditions. It could severely affect the treatment efficacy such as membrane fouling, dewaterability and the formation of carcinogenic disinfection by-products (DBPs). The heterogeneous dissolved organic matter (DOM) with varying size and chemical nature constitute a primary proportion of EPS. In the last few decades, fluorescence spectroscopy has received increasing attention for characterizing these organic substances due to the attractive features of this low-cost spectroscopic approach, including easy sample handling, rapid, non-destructive and highly sensitive nature. In this review, we summarize the application of fluorescence spectroscopy for characterizing EPS and provide the potential implications for online monitoring of water quality along with its limitations. We also link the dynamics of fluorescent dissolved organic matter (FDOM) in EPS with operational and environmental changes in wastewater treatment systems as well as their associations with metal binding, membrane fouling, adsorption, toxicity, and dewaterability. The multiple modes of exploration of fluorescence spectra, such as synchronous spectra with or without coupling with two-dimensional correlation spectroscopy (2D-COS), excitation-emission matrix (EEM) deconvoluted fluorescence regional integration (FRI), and parallel factor analysis (PARAFAC) are also discussed. The potential fluorescence indicators to depict the composition and bulk characteristics of EPS are also of interest. Further studies are highly recommended to expand the application of fluorescence spectroscopy paired with appropriate supplementary techniques to fully unravel the underlying mechanisms associated with EPS.

Humification in extracellular polymeric substances (EPS) dominates methane release and EPS reconstruction during the sludge stabilization of high-solid anaerobic digestion

High-solid anaerobic digestion (HAD) can directly treat dewatered sewage sludge (total solid content ≥15%) with superior volume efficiency. Sludge stabilization during HAD is expected to achieve by throughout organic degradation and conversion towards methane-rich biogas release and humic formation. Sewage sludge is the combination of microbial zoogleas and theirs adsorption of organic and inorganic matter, in which the extracellular polymeric substances (EPS) account 60-80% of total sludge organic matter, inevitably participating most extracellular metabolic pathways. The interactions between EPS transformation and genetically annotated metabolic pathways were found in this research. In brief, noticing the highly cross-linked structures in EPS with major active components of humic substances (HS) and protein (PN), as PN hydrolysis and decomposition in EPS were enhanced in the high-solid anaerobic condition, the exposure of aromatic groups and sites in HS were considerable. HS release was the main factor shifting the electron exchange capacity and activity, which aided in energy metabolism of sludge microorganisms involved in redox reactions, especially the methanogenesis, thus in turn facilitating the PN degradation; Then, the screened humic groups and active protein derives might act as the beneficial precursors to regenerate neo-humic structures, whose significant bridging effect and signal role on stimulating amino acid biosynthesis, member transport and metallic complexation could further contribute to proteolytic condensation and EPS reconstruction. Hence, the in-depth sludge stabilization mechanism during HAD process was established for developing enlightening strategies.

Impacts of long-term electric field applied on the membrane fouling mitigation and shifts of microbial communities in EMBR for treating phenol wastewater

The membrane antifouling and shifts of microbial communities of long-term electric field applied in MBR (EMBR) for treating phenol wastewater was systematically investigated. The increased voltage increased the phenol degradation rate and slowed down the TMP increase rate in EMBR (G1-G4: 1.65 × 10^-3-8.40 × 10^-4 Mpa/d), indicated the enhancement of phenol treatment and mitigation of membrane fouling. Decrease of protein (PN)/polysaccharide (PS) in EPS increased the negative charge and decreased the hydrophobicity of sludge, thus abated its adsorption on membrane surface. The decrease of AHLs concentration attributed to the electrolysis of AHLs by the electro-generated H₂O₂. Besides, the AHLs had significantly negative correlation with QQ bacteria Rhodococcus and Stenotrophomonas enrichment and positive correlation with QS bacteria Aeromonas decrease in EMBRs, suggesting that coupling effects of voltage and QQ bacteria degraded AHLs, thus decreased EPS content which was positively correlated with AHLs concentration. Biopolymer-degrading genera (Clostridium sensu strict etc.) increased in EMBR and on membrane surface, while biofilm-forming genera (Pseudomonas etc.) decreased on membrane surface. These resulted in EPS content decrease and membrane antifouling.

Synergistic Partial-Denitrification, Anammox, and in-situ Fermentation (SPDAF) Process for Advanced Nitrogen Removal from Domestic and Nitrate-Containing Wastewater

This study presents a new method for energy-efficient wastewater treatment that synergizes the partial-denitrification, anammox, and in-situ fermentation (SPDAF) processes in an up-flow reactor. Nitrate-containing wastewater and actual domestic sewage were fed into this SPDAF system, which was operated for 180 days without the addition of external carbon sources and aeration. The total inorganic nitrogen (TIN) removal efficiency reached 93.1% with a low C/N ratio of 1.6, a NO₃^--N/NH₄⁺-N ratio of 1.13 and a TIN concentration of 92.5 mg N/L. The contribution of anammox to nitrogen removal accounted for 95.6%. Batch tests demonstrated that the partial-denitrification process was able to use organics from either the influent or those produced by fermentation, thus providing nitrite for anammox. Significantly, fermentation played a key role in using the slowly biodegradable organics and provided adequate electron donor for partial-denitrification. Metagenomic sequencing analysis showed that the genera related to partial-denitrification, anammox, and fermentation bacteria were coexisted in this SPDAF system. The key functional genes of anammox bacteria (Hzs, 3986 hits; Hdh, 2804 hits) were highly detected in this study. The abundances of cytoplasmic nitrate reductase (58 706 hits) and periplasmic nitrate reductase (70 540 hits) were much higher than copper nitrite reductase (16 436 hits) and cytochrome cd₁ nitrite reductase (14 264 hits), potentially contributing to the occurrence of partial-denitrification. Moreover, different abundances of genes involved in fermentation metabolism suggested that fermentation likely generated easily biodegradable organics for partial-denitrification.

A novel SNPR process for advanced nitrogen and phosphorus removal from mainstream wastewater based on anammox, endogenous partial-denitrification and denitrifying dephosphatation

For achieving energy-efficient wastewater treatment, a novel simultaneous nitrogen and phosphorus removal (SNPR) process, which integrated anammox, endogenous partial-denitrification and denitrifying dephosphatation in a sequencing batch reactor with granular sludge was developed to treat mainstream wastewater. After 200 days of operation, a simultaneous high-level nitrogen and phosphorus removal of 93.9% and 94.2%, respectively was achieved with an average influent C/N ratio of 2.9. Anammox pathway contributed 82.9% of the overall nitrogen removal because of the stable nitrite production from nitrate via endogenous partial-denitrification. In addition, phosphorus was mainly removed via denitrifying dephosphatation utilizing nitrate as the electron acceptor, resulting in a significant saving of carbon sources and oxygen demands. Further, adsorption/precipitation of phosphorus occurred in this novel SNPR process, which displaced the energy source to the metabolism of glycogen accumulating organisms (GAOs) for nitrite production and alleviated competition between phosphorus accumulating organisms (PAOs) and anammox for electron acceptor. Using 16S rRNA gene amplicon sequencing analysis, the study found that anammox bacteria (8.4%), GAOs (1.5%) and PAOs (1.1%) co-existed in this system, potentially resulting in simultaneous endogenous partial-denitrification, anammox and denitrifying dephosphatation. The above results demonstrated that the novel SNPR process is a promising technique for energy-efficient wastewater treatment.

Bioremediation of copper by active cells of Pseudomonas stutzeri LA3 isolated from an abandoned copper mine soil

Copper bioremoval efficiency and bioaccumulation capacity of Pseudomonas stutzeri LA3 isolated from copper contaminated soil were investigated. P. stutzeri LA3 removed about 50% of Cu (II) at 50 mg l^-1 of concentration and accumulated a maximum of 1.62 mg of Cu g^-1 biomass dry weight. Bioremediation by P. stutzeri LA3 partially depended on the production of extracellular polymeric substances, composed of proteins and carbohydrates. Cell surface alterations were observed on the Cu (II) treated biomass through a scanning electron microscope (SEM). Energy dispersive spectrometer (EDX) investigation of Cu (II) treated biomass showed clear signals of Cu, confirming the presence of copper ions on the cell surface. Fourier transform infrared spectroscopy (FTIR) showed the contribution of functional groups such as hydroxyl (-OH), carboxyl (-COOH), amide and amine (-NH₂) in the remediation process. Based on the results, the isolated strain P. stutzeri LA3 could serve as a potential candidate for copper due to its significant copper removal effeciency.

Hectogram-scale green synthesis of hierarchical 4A zeolite@CuOx(OH)(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures with Superb Congo red adsorption performance

Delicate design of hierarchical nanoarchitectures has become a highly effective strategy to develop novel adsorbents with improved adsorption capacity. Herein, hectogram-scale green fabrication of hierarchical 4A zeolite@CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures (4A-Cu-T, T was the calcination temperature) with terrific Congo red (CR) dye adsorption performance was achieved through a simple, template-free and surfactant-free hydrothermal approach. A series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction and photoelectron spectroscopy demonstrated that all resultant adsorbents featured a core–shell structure with 4A zeolite as core ingredients and CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies as shell components. The adsorption experimental results pointed out that 4A-Cu-300 with a maximum adsorption capacity of 512.987 mg g⁻¹ showed the best adsorption performance amongst all as-prepared adsorbents, and the adsorption capacity of shell component-CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies was calculated up to 3685.500 mg g⁻¹. The shell thickness and phase ratio of CuO and Cu(OH)₂ in CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies played key roles in improving the adsorption capacity. The successive tests suggested that the “carbon deposition” resulted in the decreased adsorption capacity of first-regenerated adsorbents, but little variance in adsorption performance among regenerated samples demonstrated the good stability of such adsorbents. This work unlocks a method for the rational design of high-performance adsorbents via delicate decoration of poor-performance materials with nanosheet assemblies, which will endow the non-active materials with enhanced adsorption properties.

The growth of CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies on the surface of 4A zeolite transforms poor-performance 4A zeolite adsorbents into high-performance 4A-Cu-300 adsorbents for Congo red study.

Composition change and adsorption performance of EPS from Bacillus vallismortis sp. induced by Na2S

Sodium sulfide (Na₂S) was used as an inducer to regulate the components of Bacillus vallismortis sp. EPS (Extracellular Polymeric Substances). The main objective of this study was to improve the content of sulfhydryl protein and the adsorption property of EPS to Zn (Ⅱ) that as an typical heavy metal. The results showed that the maximum EPS production of 105.58 mg/g VSS coupling with doubled increase in protein in which the contant of -SH increased by 48.2% from 104.15 to 154.36 μmol/L were recorded in the presence of 20 mg/L Na₂S. Under this condition, the adsorption capacity of S-EPS (EPS with added exogenous Na₂S) for Zn (Ⅱ) was highest. The kinetics of the adsorption process of Zn (Ⅱ) by the S-EPS can be well fitted by the Langmuir isotherm model and the theoretical maximum adsorption amount of 979.09 mg/g EPS could be obtained. The results of 3D-EEM and FTIR analyses, illustrated that -SH, CO, and N-H/C-N played major roles in the removal of Zn (Ⅱ) by S-EPS. The results obtained in this study demonstrated that the addition of sulfur source could increase the content of sulfhydryl protein, and effectively regulate the content of chemical composition, expecially for the sulfhydryl of EPS, and thereby greatly improving the removal efficiency of heavy metals, which showed a great application prospect in the prevention and control of heavy metal pollution.

Roles of extracellular polymeric substances in uranium immobilization by anaerobic sludge

The specific roles of extracellular polymeric substances (EPS) and how factors influenced EPS’s roles during U(VI) immobilization are still unclear. In this study, high content of U with the main form of nanoparticles was detected in EPS, accounting for 10–42% of total U(VI) removal. EPS might be utilized as energy source or even as electron donors when external carbon source was unavailable. The influencing degree of each experimental parameter to uranium (U) removal process was elucidated. The influential priority to U(IV)/U(VI) ratios in sludge was as follows: acetate, U(VI), and nitrate. The influential priority to total EPS contents was as follows: U(VI), nitrate and acetate. The complex interaction mechanism between U(VI) and EPS in the U immobilization process was proposed, which might involve three ways including biosorption, bioreduction and bioprecipitation. These results indicate important and various roles of EPS in U(VI) immobilization.

Biorecovery of cobalt and nickel using biomass-free culture supernatants from Aspergillus niger

In this research, the capabilities of culture supernatants generated by the oxalate-producing fungus Aspergillus niger for the bioprecipitation and biorecovery of cobalt and nickel were investigated, as was the influence of extracellular polymeric substances (EPS) on these processes. The removal of cobalt from solution was >90% for all tested Co concentrations: maximal nickel recovery was >80%. Energy-dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) confirmed the formation of cobalt and nickel oxalate. In a mixture of cobalt and nickel, cobalt oxalate appeared to predominate precipitation and was dependent on the mixture ratios of the two metals. The presence of EPS together with oxalate in solution decreased the recovery of nickel but did not influence the recovery of cobalt. Concentrations of extracellular protein showed a significant decrease after precipitation while no significant difference was found for extracellular polysaccharide concentrations before and after oxalate precipitation. These results showed that extracellular protein rather than extracellular polysaccharide played a more important role in influencing the biorecovery of metal oxalates from solution. Excitation–emission matrix (EEM) fluorescence spectroscopy showed that aromatic protein-like and hydrophobic acid-like substances from the EPS complexed with cobalt but did not for nickel. The humic acid-like substances from the EPS showed a higher affinity for cobalt than for nickel.

Stress-responses of activated sludge and anaerobic sulfate-reducing bacteria sludge under long-term ciprofloxacin exposure

The activated sludge (AS) and sulfate-reducing bacteria (SRB) sludge systems were continuously operated for 200 days in laboratory to investigate the stress-responses of these two sludge systems under ciprofloxacin (CIP) exposure. It was found that CIP was effectively removed by SRB sludge via adsorption and biodegradation, but little biodegradation in AS system. The CIP biodegradation by SRB sludge made the SRB sludge system more sustainable and tolerant to long-term CIP exposure than AS system with significant (p < 0.05) CIP desorption and decrease of CIP removal. CIP shaped the microbial communities in AS and SRB sludge, and significantly (p < 0.05) inhibited the family Nitrosomonadaceae (ammonia-oxidizing bacteria (AOB)) and genus Nitrospira (nitrite-oxidizing bacteria (NOB)/complete ammonia oxidizer(comammox)) and the nitrogen removal in AS system. Moreover, CIP posed the increase of genus Zoogloea-like organisms and the non-filamentous bulking of AS, e.g. 313 ± 12 mL/g of sludge volume index (SVI) at phase V (influent CIP = 5000 μg/L). The genus Desulfobacter was enriched in SRB sludge system under long-term CIP exposure, and stimulated chemical oxygen demand (COD) removal and sulfate reduction. The increase of genera Zoogloea, Acinetobacter and Flavobacterium in AS, and Zoogloea and Acinetobacter in SRB sludge systems under CIP exposure promoted extracellular polymeric substances (EPS) production and CIP adsorption for self-protection of microbes against CIP toxicity. The functional groups of N-H, O-H, C-O-C and C=O in EPS of AS and SRB sludge provided adsorption sites for CIP and impeded CIP impact on microbial cells. The findings of this study provide an insight into the stress-responses of AS and SRB sludge under long-term CIP exposure, and exhibit the great potential of treating CIP-laden wastewater by SRB sludge system.

Adsorption behaviors of Cu2+, Zn2+ and Cd2+ onto proteins, humic acid, and polysaccharides extracted from sludge EPS: Sorption properties and mechanisms

To clarify the adsorption behaviors of typical heavy metals onto sludge extracellular polymeric substances (EPS), the adsorption capacities and mechanisms, as well as the contributions of the different EPS components (proteins, humic acids and polysaccharides), to the adsorption of Zn²⁺, Cu²⁺ and Cd²⁺ were separately explored. Overall, proteins exhibited a relatively high adsorption capacity for the three metals ions, followed by humic acid, whereas least for polysaccharides. The adsorption of Cu²⁺ and Cd²⁺ onto proteins, humic acid and polysaccharides fit well to the Freundlich isotherm, whereas Langmuir model was the best fit for Zn²⁺ bindings onto polysaccharides/humic acid. The binding of Cu²⁺, Zn²⁺ and Cd²⁺ onto the three EPS components was exothermically favorable, and significant electrostatic interactions were observed for the heavy metals sorption onto humic acid and proteins. In addition, the effect of metal ions sorption on the spectrum of the proteins, polysaccharides and humic acid was also explored.

Mechanism of enhancing pyrene-degradation ability of bacteria by layer-by-layer assembly bio-microcapsules materials

The mechanism of improving pyrene (PYR)-degrading ability of bacteria CP13 in Layer-by-layer (LBL) assembly chitosan/alginate (CHI/ALG) bio-microcapsules was investigated. Flow cytometry analysis showed that LBL microcapsules could effectively slow down the increasing rate of bacterial cell membrane permeability and the decreasing rate of the membrane potential, so as to reduce the death rate and number of the cells, which could protect the degrading bacteria. The results of Fluorescence spectrum, circular dichroism (CD) spectrum and laser light scattering (LLS) analysis revealed that the other possible mechanism for LBL microcapsules to promote bacterial degradation were following: CHI could enter the secondary structure of the protein of the extracellular polymeric substances (EPS) from CP13 and combined with EPS to generate a stable ground material, which had larger molecular weight (3.76×10⁶ g mol^-1) than the original EPS (2.52×10⁶ g mol^-1). The combination of CHI and EPS resulted in the decrease of the density of EPS from 1.18 to 0.72 g L^-1, suggesting that CHI can loosen the EPS configurations, improving the capture ability of bacteria for PYR as well as the mass transfer of PYR from the extracellular to intracellular, thus eventually promoting the bacteria degrade performance.

Stable long-term operation and high nitrite accumulation of an endogenous partial-denitrification (EPD) granular sludge system under mainstream conditions at low temperature

In this study, the robustness of an endogenous partial-denitrification (EPD) system was demonstrated during a 105 days operation under mainstream conditions at low temperature. The results showed a high nitrate-to-nitrite transformation ratio (NTR) of 88.7%, a suitable NO₂^--N/NH₄⁺-N ratio of 1.09, and no residual NO₃^--N in the effluent, as reactor temperature was decreased from 25 °C to 13.5 °C. The stable morphology of the EPD granular sludge with high extracellular polymeric substance content (273.6-308.1 mg/g VSS) contributed to the steady performance of the EPD system. Bath tests revealed that the maximum NTRs (95.6% and 96.3%) were slightly higher at 10 °C and 15 °C than those (90.4% and 92.0%) at 20 °C and 30 °C, resulting from the lower poly-β-hydroxyvalerate degradation rate or the negligible denitrifying dephosphatation activity at low temperatures. Thus, the EPD system has the potential to provide stable nitrite for mainstream anammox at low temperature.

Enhanced denitrifying phosphorus removal and mass balance in a worm reactor

Phosphorus release is one of the disadvantages during worm predation, which has an adverse effect on wastewater treatment. In order to investigate and reveal the effects and mechanisms of worm predation on phosphorus transformation, batch experiments were conducted on a long-running worm reactor (WR). Denitrifying phosphorus removal (DPR) was observed in WR for the first time owing to the special reactor configuration and operating conditions. After DPR in WR, the concentration of supernatant phosphorus increased to 42.2 ± 1.1 mg L^-1 owing to bacterial phosphorus release and worm predation, which further promoted DPR in the subsequent cycle. DPR rate in the WR was 12.3 times higher than that in the blank reactor (BR). In addition, the synergistic effects of worm predation and bacterial metabolism on sludge reduction and nutrients transformation were analyzed. The sludge reduction of WR was 84.5% higher than that of BR. Bacterial metabolism played an important role in the removal of supernatant nutrients, which consumed 60.2% of total nitrogen and 55.5% of chemical oxygen demand derived from the reduced sludge. The study suggested that under certain conditions, WR could be functionalized as a bacteria selection tank to further improve the wastewater treatment efficiency. Bacterial metabolism was essential for supernatant nutrients removal during worm predation.

Cold anammox process and reduced graphene oxide - Varieties of effects during long-term interaction

Because of its energy efficiency, the anaerobic ammonium oxidation (anammox) process has been recognized as the most promising biological nitrogen removal process, but its implementation in mainstream wastewater treatment plants is limited by its relatively high optimal temperature (30 °C). Recently, it was shown that during short-term batch experiments, reduced graphene oxide (RGO) displayed accelerated reaction activity at low temperatures (10-15 °C). In this study, the long-term effects of RGO on the low-temperature anammox process in a sequencing batch reactor (SBR), are studied for the first time, including different methods of interaction. The results presented here show that RGO can stimulate anammox activity up to 17% through two factors: bacterial growth stimulation, which was especially significant at higher temperatures (>15 °C), and an increase of the anammox reaction rate, which occurred only below 15 °C. The bacterial community structure was not influenced by addition of RGO. Moreover, after incubation in an anammox bioreactor, RGO showed signs of degradation and chemical changes as evidenced by the presence of oxygen and calcium on its surface. According to the literature and the obtained results, it is proposed that RGO is oxidized and oxygen is reduced by the organic mediator that is involved in the enzymatic reactions. However, activated sludge is a very complex structure created by numerous, undefined microorganisms, which makes it difficult to determine the exact oxidation mechanism.

Impacts of applied voltage on EMBR treating phenol wastewater: Performance and membrane antifouling mechanism

The impacts of electric field applied in MBR (EMBR) for treating phenol wastewater and membrane antifouling mechanism were systematically investigated. Phenol degradation rate increased from 0 to 0.8 V/cm, while decreased from 0.8 to 1.75 V/cm, which significantly positively correlated with key enzymes. The membrane fouling rate of EMBR gradually slowed down with voltage increasing. The applied voltage significantly reduced EPS contents, and altered its compositions probably due to H₂O₂ oxidation, which were the major reasons for membrane antifouling. Red shift in UV-Vis spectrum at 210-220 nm and reduction of fluorescence emission intensity from tryptophan protein-like substances in EPS reduced the energy requirement for electrons transition of electron-donating groups with voltage increasing. Positively charged bond NH₂ decreased and negatively charged bond COO increased in EPS with voltage increasing, which led to the increase of absolute value of zeta potential and then remarkable augmented of electrostatic repulsion between sludge and membrane.

Performance of microaeration hydrolytic acidification process in the pretreatment of 2-butenal manufacture wastewater

The performance of the microaeration hydrolytic acidification (MAHA) process and microbial community were investigated under different organic loading rates (OLRs) for the pretreatment of 2-butenal manufacture wastewater (2-BMW). Results indicated that OLRs had different impact on the performance of MAHA process. More than 23.7 ± 2.3% of the chemical oxygen demand (COD) removal and the highest acidification degree (20.9 ± 3.1%) were obtained when OLRs were less than 4.0 ± 0.1 kgCOD/m³ d. However, further increasing OLRs to 6.1 ± 0.1 kgCOD/m³ d subsequently led to the significant reductions of COD removal and acidification degree. In addition, it could be preliminarily inferred that 2H-pyran-2-one tetrahydro-4-(2-methyl-1-propen-3-yl), 5-formyl-6-methyl-4,5-dihydropyran and ethyl sorbate were the main refractory and toxic organics for microorganisms in the wastewater. The soluble microbial product (SMP) and extracellular polymeric substance (EPS) contents (protein, polysaccharide, nucleic acid) had obvious changes under different OLRs. With parallel factor (PARAFAC) model, four fluorescent components were identified. The F_max of protein-like substances in SMP significantly decreased with increasing OLRs to 6.1 ± 0.1 kgCOD/m³ d, which might attribute to fluorescence quenching. Illumina MiSeq sequencing revealed that Pseudomonas, Longilinea, T78, Clostridium, WCHB1-05, Acinetobacter, SHD-231 and Oscillospira were dominant genera at different OLRs.

Accelerated productions and physicochemical characterizations of different extracellular polymeric substances from Chlorella vulgaris with nano-ZnO

Extracellular polymeric substances (EPS) play significant roles in protecting cells against environmental stresses. However, little information is known about the roles of different EPS in these processes. In this study, the productions and physicochemical characterizations of soluble-EPS (S-EPS) and bound-EPS (B-EPS), the two different fractions of EPS from a green alga Chlorella vulgaris under the stress of ZnO nanoparticle (nano-ZnO) were investigated. The contents of S-EPS and B-EPS which described as dissolved organic carbon, polysaccharides and proteins, both increased with the addition of tested nano-ZnO (0.01 and 0.04 mM) in a 72 h cultivation. EPS-Free (EPS-F) cells produced more S-EPS and B-EPS than the EPS-Cover (EPS-C) cells did with the tested nano-ZnO, especially the contents of protein in the S-EPS of EPS-F cells increased by 45.5% with 0.04 mM nano-ZnO compared to the control at 72 h. Tryptophan-like substances of the protein in S-EPS exhibited a stronger chemical static quenching than tyrosine-like substances with nano-ZnO. In addition, the hydroxyl (OH) as well as carboxyl (CO) group, and CO of amide I, NH/CN of amide II groups in proteins were confirmed that involved in the reaction of S-EPS and B-EPS with nano-ZnO, meanwhile hemiacetal groups in saccharides were oxidized to carboxyl groups. This study could provide a better understanding of EPS in protecting against cells damage with nanoparticles.

Bioimmobilization of lead by Bacillus subtilis X3 biomass isolated from lead mine soil under promotion of multiple adsorption mechanisms

In this study, a lead-resistant bacterium, Bacillus subtilis X3, was used to prepare a lead bioadsorbent for immobilization and removal of lead in lead solution. The lead shot precipitate was analysed by scanning electron microscopy combined with energy dispersive X-ray fluorescence microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The adsorbed lead was mainly mineralized to form Pb₅(PO₄)₃OH, Pb₁₀(PO₄)₆(OH)₂ and Pb₅(PO₄)₃Cl; however, other mechanisms that can also promote the mineralization of lead should not be ignored. For example, Na⁺ and Ca²⁺ on the cell wall surface were exchanged with Pb²⁺ in solution, which confirmed that the ion-exchange process occurred before mineralization. Moreover, adsorption bridging caused by extracellular polymeric substances also accelerated the further aggregation of lead, and the biomass was encapsulated by lead gradually. Hydroxyl, carbonyl, carboxyl and amine groups were not observed in lead mineral crystals, but the complexation between lead and these groups still benefited the mineralization of lead. The valence of Pb(II) was not changed after mineralization, which indicated that the biosorption process was not a redox reaction. Finally, biosorption occurred on the outer surface of the cell, but its specific surface area was relatively small, limiting the amount and efficiency of biosorption.

Impacts of the heavy metals Cu (II), Zn (II) and Fe (II) on an Anammox system treating synthetic wastewater in low ammonia nitrogen and low temperature: Fe (II) makes a difference

In this study, the impacts of heavy metals (1 mg L^-1) on the nitrogen removal, bioactivity of anaerobic ammonia-oxidizing bacteria (AAOB) and the microbial community of anaerobic ammonium oxidation (Anammox) process were investigated. It was observed that short-term exposure in Cu (II) and Zn (II) both improved AAOB bioactivity, while long-term exposure significantly lowered the nitrogen removal to 0.218 and 0.302 kg m^-3 d^-1, when treated the wastewater with 100 mg L^-1 nitrogen under 14-16 °C. Fe(II) had slight impact on Anammox in short-term experiment but deeply enhanced nitrogen removal during the long-term contact, and finally increased the that to 0.58 kg m^-3 d^-1. The impact on Anammox was Cu(II) > Zn(II) > Fe(II). Cu(II) and Zn(II) lowered the share of Candidatus Kuenenia to 3.32% and 3.80%, while Fe(II) improved that to 11.30% from 7.99%. Extracellular polymeric substance in biofilm had prominent iron adsorption capacity, which was the key factor that help AAOB resist Fe(II).

Enhancement of the adaptability of anammox granules to zinc shock by appropriate organic carbon treatment

Heavy metals, which are commonly present in high ammonia-containing wastewater, can cause inhibitory effects to anammox reaction. This study proposes a novel approach to enhance the adaptability of anammox granules to heavy metal [Zn(II)] shock by organic carbon (sodium acetate, NaAc) treatment, paying special attention to optimization of the treatment dosage and duration. For granules treated with 200 mg chemical oxygen demand (COD)/L NaAc for 2 d, the activity recovery (six cycles) efficiency after Zn(II) (40 mg/L) shock reached 127.4%. The extracellular polymeric substance (EPS) production increased by 168% and heterotrophic bacteria mildly proliferated (increased by 14%) in such granules compared with the control. The dramatic recovery capacity was likely due to the entrapment and barrier function of EPS and the outer-layer proliferated heterotrophic bacteria. This finding offers a useful process to enable maximum adaptability of anammox granules from heavy metals shocks, allowing anammox technology to be more widely applied.

Effects of salinity build-up on the performance and microbial community of partial-denitrification granular sludge with high nitrite accumulation

High inorganic salts inevitably impose a toxic impact on biological treatment processes. In this study, the effect of salinity on the performance and microbial community structures of partial-denitrification (PD) was firstly investigated. Results showed the denitrifying activities of non-domesticated PD sludge were completely inhibited under a temporary high salinity (≥1.5 wt%). However, after domestication, denitrifying activities maintained above 50% of the maximum with salinity build-up step-by-step from 0.0 wt% to 3.0 wt%. High nitrite production was stably achieved during 120 days with nitrate-to-nitrite transformation ratio around 90%. Further investigation showed extracellular polymeric substances content of PD sludge increased from 184.59 mg gVSS^-1 to 560.64 mg gVSS^-1, accompanied by the elevation of average particle size. This occurred against high salinity as a protective response of PD bacteria. Moreover, Thauera, the functional bacteria of PD system, was still dominant with the relative abundance increasing to 83.36% (3.0 wt%) from 51.33% (0.0 wt%).

Simultaneous nitrification, denitrification and phosphorus removal in aerobic granular sequencing batch reactors with high aeration intensity: Impact of aeration time

A new operating approach by reducing the aeration time while keeping high intensity was evaluated for enhanced nutrients removal and maintenance of granular stability. Three aerobic granular sequencing batch reactors (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) were run at different aeration time (120, 90, and 60 min). Aerobic granules could remain their integrity and stability over long-term operation under high aeration intensity and different time, and shorter aeration time favored the retention of biomass, better settleability, and more production of extracellular polymeric substances (EPS). Besides, efficient and stable reactor performance for carbon and phosphorus were achieved, especially, enhanced nitrogen removal was obtained due to reduction of aeration time. Further exploration revealed that the aeration time shaped the bacterial community in terms of diversity, composition, as well as the distribution of functional groups involving carbon, nitrogen and phosphorus removal.

Nutrients removal and recovery from saline wastewater by Spirulina platensis

As an important alternative to alleviate the pressure of fresh water shortage, seawater application is facing a great challenge on the wastewater treatment due to the salinity brought from seawater. Spirulina platensis originated from salty lake was used to treat mixed synthetic toilet flushing wastewater of seawater with washing wastewater of freshwater. It was showed that 79.96% of TN (to 15.69mg/L), 93.35% of TP (to 1.03mg/L) and 90.02% of COD_Cr (to 90.24mg/L) were removed with 0.76g/L of biomass production in the optimal ratio 7:3 of the above mixed synthetic wastewater. The performance was better than that of current strategy of seawater toilet flushing treatment. With the evaluation of nutrients uptake, biomass composition and microalgal aggregation, a model of nutrients recovery and metabolism of Spirulina platensis in saline wastewater treatment was proposed. It is provided a promising strategy for saline wastewater treatment with valuable biomass yield.

Characterization of extracellular polymeric substances in biofilms under long-term exposure to ciprofloxacin antibiotic using fluorescence excitation-emission matrix and parallel factor analysis

The presence of antibiotic residues in the environment has been regarded as an emerging concern due to their potential adverse environmental consequences such as antibiotic resistance. However, the interaction between antibiotics and extracellular polymeric substances (EPSs) of biofilms in wastewater treatment systems is not entirely clear. In this study, the effect of ciprofloxacin (CIP) antibiotic on biofilm EPS matrix was investigated and characterized using fluorescence excitation-emission matrix (EEM) and parallel factor (PARAFAC) analysis. Physicochemical analysis showed that the proteins were the major EPS fraction, and their contents increased gradually with an increase in CIP concentration (0-300 μg/L). Based on the characterization of biofilm tightly bound EPS (TB-EPS) by EEM, three fluorescent components were identified by PARAFAC analysis. Component C1 was associated with protein-like substances, and components C2 and C3 belonged to humic-like substances. Component C1 exhibited an increasing trend as the CIP addition increased. Pearson's correlation results showed that CIP correlated significantly with the protein contents and component C1, while strong correlations were also found among UV₂₅₄, dissolved organic carbon, humic acids, and component C3. A combined use of EEM-PARAFAC analysis and chemical measurements was demonstrated as a favorable approach for the characterization of variations in biofilm EPS in the presence of CIP antibiotic.

Continuous removal and recovery of tellurium in an upflow anaerobic granular sludge bed reactor

Continuous removal of tellurite (TeO₃^2-) from synthetic wastewater and subsequent recovery in the form of elemental tellurium was studied in an upflow anaerobic granular sludge bed (UASB) reactor operated at 30°C. The UASB reactor was inoculated with anaerobic granular sludge and fed with lactate as carbon source and electron donor at an organic loading rate of 0.6g CODL^-1d^-1. After establishing efficient and stable COD removal, the reactor was fed with 10mg TeO₃^2-L^-1 for 42 d before increasing the influent concentration to 20mg TeO₃^2-L^-1. Tellurite removal (98 and 92%, respectively, from 10 and 20mg TeL^-1) was primarily mediated through bioreduction and most of the removed Te was retained in the bioreactor. Characterization using XRD, Raman spectroscopy, SEM-EDX and TEM confirmed association of tellurium with the granular sludge, typically in the form of elemental Te(0) deposits. Furthermore, application of an extracellular polymeric substances (EPS) extraction method to the tellurite reducing sludge recovered up to 78% of the tellurium retained in the granular sludge. This study demonstrates for the first time the application of a UASB reactor for continuous tellurite removal from tellurite-containing wastewater coupled to elemental Te(0) recovery.

Multi-spectral and thermodynamic analysis of the interaction mechanism between Cu2+ and α-amylase and impact on sludge hydrolysis

An increasing amount of heavy metals (e.g., Cu²⁺) is being discharged into sewage treatment plants and is accumulating in sludge, which is toxic to the enzyme in sludge or soil when the sludge is used as fertilizer, resulting in unfavorable effect on the biological treatment of sludge and the circulation and conversion of materials in soil. In this research, effect of Cu²⁺ on sludge hydrolysis by α-amylase is studied from the respect of concentration and components of soluble organic matter in sludge, using three-dimensional fluorescence spectra. Results show that Cu²⁺ exposure not only inhibits the hydrolysis of sludge due to the denaturation of α-amylase but also affects the components of soluble organic matter in sludge. In order to illuminate the interaction mechanism between Cu²⁺ and α-amylase (a model of hydrolase in sludge), multi-spectra and isothermal titration microcalorimetry techniques are applied. Results show that the secondary structure of α-amylase is changed as that the α-helical content increases and the structure loosens. The microenvironment of amino acid residue in α-amylase is changed that the hydrophobicity decreases and the polarity increases with Cu²⁺ exposure. Isothermal titration calorimetry results show that Van der Waals force and hydrogen bond exist in the interaction between Cu²⁺ and α-amylase. Results from this research would favor the development of advanced process for the biological treatment of sludge containing heavy metals.

Response of wastewater biofilm to CuO nanoparticle exposure in terms of extracellular polymeric substances and microbial community structure

The growing production and application of CuO nanoparticles increase the chance that these particles will be released into wastewater treatment plants (WWTPs) and interact with microorganisms. However, the toxicity response mechanism of biofilm to NP exposure may be different from that of activated sludge due to the denser and stronger microbial aggregate structure of biofilm. Thus, in this study, the response to CuO NPs of wastewater biofilm collected from a rotating biological contactor was investigated. Short-term exposure (24h) to CuO NPs led to a great loss in cell viability, and SEM-EDS images revealed that the nano-CuO aggregates were not transformed to Cu-S species in the biofilm samples. In response, more extracellular polymeric substance (EPS) (especially loosely bound-EPS) was produced in wastewater biofilm exposed to CuO NPs, with a higher content of protein compared to polysaccharides. The shifts of fluorescence intensity and peak locations in 3D-EEM fluorescence spectra indicated chemical changes of the EPS components. FT-IR analysis revealed that exposure to nano-CuO had more distinct effects on the functional groups of proteins and polysaccharides in LB-EPS. Illumina sequencing of 16S rRNA gene amplicons revealed that CuO NPs enhanced bacterial diversity. The bacterial community structure significantly shifted, with a significantly increased abundance of Comamonas, a slight increase in Zoogloea, and a notable decrease in Flavobacterium. The shifts of these dominant genera may be associated with altered EPS production, which might result in microbial community function fluctuations. In conclusion, exposure to high concentrations of CuO NPs has the potential to shape wastewater biofilm bacterial community structure.

Characterization of extracellular polymeric substances produced during nitrate removal by a thermophilic bacterium Chelatococcus daeguensis TAD1 in batch cultures

Positive correlation was observed between EPS production and nitrate removal efficiency during aerobic denitrification byChelatococcus daeguensisTAD1.

Interaction between common antibiotics and a Shewanella strain isolated from an enhanced biological phosphorus removal activated sludge system

With increasing production and consumption, more antibiotics are discharged into wastewater treatment plants and generally cannot be sufficiently removed. Because of the complexities of biological treatment processes, the fates of antibiotics and their effects on microorganisms, particularly those involved in the phosphorus removal system, are still unclear. Here, a Shewanella strain was isolated from an enhanced biological phosphorus removal (EBPR) system and was found to have the ability to remove phosphorus (P) and chemical oxygen demand (CODcr). Antibiotics affected the Shewanella strain through metabolism of the three main intracellular polymers, altering the ability of the strain to remove P and CODcr. These effects varied with the structure and concentration of the antibiotics. The Shewanella strain removed cefalexin and amoxicillin by degradation or adsorption, producing 2-hydroxy-3-phenyl pyrazine from cefalexin. This study enabled the recognition of the effect and removal of antibiotics during wastewater treatment.

Differential ultraviolet-visible absorbance spectra for characterizing metal ions binding onto extracellular polymeric substances in different mixed microbial cultures

Ultraviolet-visible (UV-vis) absorbance spectra was adopted to quantify the binding of major metal ions (e.g., Na(I), Ca((II)), Fe(III), Cu(II), and Pb(II)) on extracellular polymeric substances (EPSs) extracted from different mixed cultures. The results showed that the differential absorbance spectra (DAS) provided discernible features for revealing the changes in optical properties of EPSs induced by metals, i.e., the intensity of DAS increased largely with incrementally increased metal concentrations (Fe(III), Cu(II), and Pb(II)). It can be assumed attributable to the changes in the conformations and inter-chromophores of the EPS biomolecules. In addition, the changes in spectral parameters of DSlope325-375 (spectral slope in the range of wavelengths 325-375 nm) and DA300 (differential absorbance at 300 nm) were found to be closely related to the amounts of metals bound onto all extracted EPSs, particularly for Fe(III) and Cu(II). The decreased SR (the ratio of slope275-295 to slope350-400) of the EPS solutions after dosage of metals suggested increased molecular weight or size of the EPS biomolecules. Deconvolution of the DAS yielded six Gaussian bands, which were present in all of the EPS samples with various metals. Moreover, the relative contributions of different Gaussian bands in the DAS were determined by the nature of EPS-metal ions interactions good correlated with the covalent-bonding index. This study concluded that DAS and selected spectral parameters (DA300, DSlope325-375 and SR) can be used to successfully characterize the binding of metals onto EPS at environmentally relevant concentrations.

Insight into the short- and long-term effects of Cu(II) on denitrifying biogranules

This study aimed to investigate the short- and long-term effects of Cu(2+) on the activity and performance of denitrifying bacteria. The short-term effects of various concentrations of Cu(2+) on the denitrifying bacteria were evaluated using batch assays. The specific denitrifying activity (SDA) decreased from 14.3 ± 2.2 (without Cu(2+)) to 6.1 ± 0.1 mg N h(-1)g(-1) VSS (100 mg Cu(2+)L(-1)) when Cu(2+) increased from 0 to 100 mg L(-1) with an increment of 10 mg Cu(2+)L(-1). A non-competitive inhibition model was used to calculate the 50% inhibition concentration (IC50) of Cu(2+) on denitrifying sludge (30.6 ± 2.5 mg L(-1)). Monod and Luong models were applied to investigate the influence of the initial substrate concentration, and the results suggested that the maximum substrate removal rate would be reduced with Cu(2+) supplementation. Pre-exposure to Cu(2+) could lead to an 18.2-46.2% decrease in the SDA and decreasing percentage of the SDA increased with both exposure time and concentration. In the continuous-flow test, Cu(2+) concentration varied from 1 to 75 mg L(-1); however, no clear deterioration was observed in the reactor, and the reactor was kept stable, with the total nitrogen removal efficiency and total organic carbon efficiency greater than 89.0 and 85.0%, respectively. The results demonstrated the short-term inhibition of Cu(2+) upon denitrification, and no notable adversity was observed during the continuous-flow test after long-term acclimation.

Simultaneous nitrification and denitrification by EPSs in aerobic granular sludge enhanced nitrogen removal of ammonium-nitrogen-rich wastewater

In this study, role of extracellular polymeric substances (EPSs) in enhancing nitrogen-removal from ammonium-nitrogen-rich wastewater using aerobic granular sludge (AGS) technology were analyzed. AGS enabled ammonium oxidation and denitrification to occur simultaneously. Air stripping and simultaneous nitrification-denitrification contributed to total-nitrogen removal. Clone-library analysis revealed that close relatives of Nitrosomonas eutropha and heterotrophic denitrifiers were dominant in the AGS, whereas anammox bacteria were not detected. EPSs adsorption of ammonium, nitrite, and nitrate nitrogen results in improved removal of nitrogen in batch experiments.

Roles of extracellular polymeric substances in enhanced biological phosphorus removal process

Enhanced biological phosphorus removal (EBPR) process is known to mainly rely on the ability of phosphorus-accumulating organisms to take up, transform and store excess amount of phosphorus (P) inside the cells. However, recent studies have revealed considerable accumulation of P also in the extracellular polymeric substances (EPS) of sludge, implying a non-negligible role of EPS in P removal by EBPR sludge. However, the contribution of EPS to P uptake and the forms of accumulated extracellular P vary substantially in different studies, and the underlying mechanism of P transformation and transportation in EPS remains poorly understood. This review provides a new recognition into the P removal process in EBPR system by incorporating the role of EPS. It overviews on the characteristics of P accumulation in EPS, explores the mechanism of P transformation and transportation in EBPR sludge and EPS, summarizes the main influential factors for the P-accumulation properties of EPS, and discusses the remaining knowledge gaps and needed future efforts that may lead to better understanding and use of such an EPS role for maximizing P recovery from wastewater.

Nitrification recovery behavior by bio-accelerators in copper-inhibited activated sludge system

Copper (Cu) is a toxic heavy metal which can cause inhibitory effects on nitrification process in biological wastewater treatment systems. However, few studies have done to dose accelerators into Cu-inhibited activated sludge system to promote bioactivity recovery of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). In this study, four ingredients of bio-accelerators were developed and dosed in five parallel SBRs. The effluent NH4(+)-N, NO2(-)-N and NO3(-)-N concentrations, specific oxygen uptake rate (SOUR), and Cu distribution were investigated to assess the bioactivity recovery effects. Results showed that, among biotin, L-aspartic acid and cytokinin, L-aspartic acid was the most effective for the fast bioactivity recovery of nitrifying bacteria. The combination of these three substances was optimum and Cu-inhibited activated sludge system could be 100% recovered in 8 days. The bio-accelerators proposed in this study can be potentially applied in the emergency treatment in biological wastewater treatment systems.