Composition and functional group characterization of extracellular polymeric substances (EPS) in activated sludge: the impacts of polymerization degree of proteinaceous substrates

Inhibition of zinc ions in sulfur-driven autotrophic denitrification process: What is the behavior of extracellular polymeric substances?

Sulfur-driven autotrophic denitrification (SAD) process is a cost-effective and sustainable method for nitrogen removal from wastewater. However, a higher concentration of zinc ions (Zn(II)) flowing into wastewater treatment plants poses a potential threat to the SAD process. This study examined that a half maximal inhibitory concentration (IC50) of Zn(II) was 7 mg·L-1 in the SAD process. Additionally, the addition of 20 mg·L-1 Zn(II) resulted in a severe accumulation of nitrite to 150.20 ± 6.00 mg·L-1 when the initial concentration of nitrate was 500 mg·L-1. Moreover, the activities of nitrate reductase, nitrite reductase, dehydrogenase and electron transport system were significantly inhibited under Zn(II) stress. The addition of Zn(II) inhibited EPS secretion and worsened electrochemical properties. The result was attributed to the spontaneous binding between EPS and Zn(II), with a ΔG of -17.50 KJ·mol-1 and a binding constant of 1.77 × 104 M-1, respectively. Meanwhile, the protein, fulvic acid, and humic-like substances occurred static quenching after Zn(II) addition, with -OH and -C=O groups providing binding sites. The binding sequence was fulvic acid→protein→humic acid and -OH → -C=O. Zn(II) also reduced the content of α-helix, which was unfavorable for electron transfer. Additionally, the Zn(II) loosened protein structure, resulting in a 50 % decrease in α-helix/(β-sheet+random coil). This study reveals the effect of Zn(II) on the SAD process and enhances our understanding of EPS behavior under metal ions stress.

Investigating the role of extracellular polymeric substances produced by Parachlorella kessleri in Zn(II) bioremediation using atomic force microscopy

Microalgae, such as Parachlorella kessleri, have significant potential for environmental remediation, especially in removing heavy metals like zinc from water. This study investigates how P. kessleri, isolated from a polluted river in Argentina, can remediate zinc. Using atomic force microscopy (AFM), the research examined the interactions between Zn particles and cells grown with different nitrogen sources-nitrate or ammonium. The results showed that cells grown with nitrate produced extracellular polymeric substances (EPS), while those grown with ammonium did not. Raman spectroscopy revealed distinct metabolic responses based on the nitrogen source, with nitrate-grown cells showing altered profiles after zinc exposure. Zinc exposure also changed the surface roughness and nanomechanical properties of the cells, particularly in those producing EPS. AFM force spectroscopy experiments then confirmed strong Zn binding to EPS in nitrate-grown cells, while interactions were weaker in ammonium-grown cells that lacked EPS. Overall, our results elucidate the critical role of EPS in Zn removal by P. kessleri cells and show that Zn remediation is mediated by EPS adsorption. This study underscores the significance of regulating nitrogen sources to stimulate EPS production, offering insights that are essential for subsequent bioremediation applications.

Nanoscale exopolymer reassembly-trap mechanism determines contrasting PFOS exposure patterns in aquatic animals with different feeding habitats: A nano-visualization study

The behavior and fate of PFOS (perfluorooctanesulfonate) in the aquatic environment have received great attention due to its high toxicity and persistence. The nanoscale supramolecular mechanisms of interaction between PFOS and ubiquitous EPS (exopolymers) remain unclear though EPS have been widely-known to influence the bioavailability of PFOS. Typically, the exposure patterns of PFOS in aquatic animals changed with the EPS-PFOS interaction are not fully understood. This study hypothesized that PFOS exposure and accumulation pathways depended on the PFOS-EPS interactive assembly behavior and animal species. Two model animals, zebrafish and chironomid larvae, with different feeding habitats were chosen for the exposure and accumulation tests at the environmental concentrations of PFOS in the absence and presence of EPS. It was found that PFOS triggered the self-assembly of EPS to form large aggregates which significantly trapped PFOS. PFOS accumulation was significantly promoted in zebrafish but drastically reduced in chironomid larvae because of the nanoscale interactive assembly between EPS and PFOS. The decreased dermal uptake but increased oral uptake of PFOS by zebrafish with large mouthpart size could be ascribed to the increased ingestion of PFOS-enriched EPS aggregates as food. For the chironomid larvae with small mouthpart size, the PFOS-EPS assemblies reduced the dermal, oral and intestinal uptake of PFOS. The nano-visualization evidences confirmed that the PFOS-enriched EPS-PFOS assemblies blocked PFOS penetration through skin of both animals. These findings provide novel knowledge about the ecological risk of PFOS in aquatic environments.

Interference-resistant gold nanoparticle assay for detecting Enterococcus in fresh and marine waters

Enterococci are common indicators of fecal contamination and are used to assess the quality of fresh and marine water, sand, soil, and sediment. However, samples collected from these environments contain various cells and other factors that can interfere with the assays used to detect enterococci. We developed a novel assay for the sensitive and specific detection of enterococci that is resistant to interference from other cells and environmental factors. Our interference-resistant assay used 30-nm gold nanoparticles (AuNPs), streptavidin, and a biotinylated Enterococcus antibody. Enterococci inhibited the interaction between streptavidin and biotin and led to the disaggregation of AuNPs. The absence of enterococci led to the aggregation of AuNPs, and this difference was easily detected by spectrophotometry. This interference-resistant AuNP assay was able to detect whole cells of Enterococcus in the range of 10 to 107 CFU/mL within 3 h, had high specificity for enterococci, and was unaffected by the presence of other intestinal bacteria, such as Escherichia coli. Our examination of fresh and marine water samples demonstrated no interference from other cells or environmental factors. The interference-resistant AuNP assay described here has the potential to be used as a rapid, simple, and effective method for monitoring enterococci in diverse environmental samples.

The biodegradation of polylactic acid microplastic and their toxic effect after biofouling in activate sludge

Biodegradable microplastics (MPs) can form biofilms through interactions with various microorganisms in aquatic system and can be exposed to organisms. This study first investigated biodegradability of polylactic acid (PLA) MPs and the characterization of PLA MPs before/after biofouling (4 weeks) and their toxic effects on the freshwater invertebrate Daphnia magna. The biodegradability rate of PLA MPs was up to 50% over 28 days, suggesting that even biodegradable MPs do not easily decompose under environmental conditions. Furthermore, biofouling of MPs led to an increase in size and, in the process, induced an additional functional peak in the PLA MPs. The exposure of biofouled MPs did not lead to a reduction in survival, reproduction, or growth during chronic exposure, nor did it cause feeding inhibition in juvenile (<4 days old) D. magna. However, pristine MPs significantly reduced survival, reproduction, and growth at concentrations of 5.0 mg L-1. Overall, pristine MPs caused inhibition of reproduction and growth and high mortality in D. magna, while the biofouling process did not induce these effects. Our findings highlight the complex interactions between MPs and biological components in aquatic environments, emphasizing the importance of considering biofouling dynamics when assessing the ecological impacts of biodegradable MPs.

Membrane fouling mechanisms in the presence of microplastics and organic matter: The unexpected mitigating role of Ca2

Ultrafiltration (UF) is demonstrated to be highly effective in the removal of microplastics (MPs), but the presence of coexisting foulants introduces significant uncertainties into the associated membrane fouling behaviors. In this study, membrane fouling mechanisms were investigated when MPs, represented by polystyrene (PS), coexisted with typical organic foulants (sodium alginate, SA) and inorganic ions (Ca2+). Fouling tests revealed that the order of Ca2+ addition significantly impacted the fouling behavior of the SA-PS combined foulants. Specifically, the specific filtration resistance (SFR) was reduced by 40.82 % in the SA-PS-Ca2+ foulants and by 90.92 % in the SA-Ca2+-PS foulants, compared to the SA-PS foulants. X-ray photoelectron spectroscopy and density functional theory calculations indicated that sufficient cross-linking of Ca2+ with SA molecular chains in the SA-Ca2+-PS foulants, forming a large-scale 3D network that encapsulated more PS particles and resulted in larger flocs than those found in the SA-PS-Ca2+ foulants. According to extended Flory-Huggins theory, the improved filtration performance of the SA-PS combined foulants was due to substantial changes in chemical potential during their transition from gel to flocs upon Ca2+ addition. Furthermore, interfacial thermodynamic analyses suggested that increased repulsion between SA-Ca2+-PS foulants and between them and the membrane led to a looser fouling layer, significantly mitigating membrane fouling. This study elucidates the fouling mechanisms in the presence of MPs and other foulants from the perspectives of energy changes and molecular structures, providing novel insights for developing strategies to mitigate membrane fouling.

Biological self-protection inspired engineering of nanomaterials to construct a robust bio-nano system for environmental applications

Nanomaterials can empower microbial-based chemical production or pollutant removal, e.g., nano zero-valent iron (nZVI) as an electron source to enhance microbial reducing pollutants. Constructing bio-nano interfaces is critical for bio-nano system operation, but low interfacial compatibility due to nanotoxicity challenges the system performance. Inspired by microorganisms' resistance to nanotoxicity by secreting extracellular polymeric substances (EPS), which can act as electron shuttling media, we design a highly compatible bio-nano interface by modifying nZVI with EPS, markedly improving the performance of a bio-nano system consisting of nZVI and bacteria. EPS modification reduced membrane damage and oxidative stress induced by nZVI. Moreover, EPS alleviated nZVI agglomeration and probably reduced bacterial rejection of nZVI by wrapping camouflage, contributing to the bio-nano interface formation, thereby facilitating nZVI to provide electrons for bacterial reducing pollutant via membrane-anchoring cytochrome c. This work provides a strategy for designing a highly biocompatible interface to construct robust and efficient bio-nano systems for environmental implication.

Interplay of humic acid and Cr(VI) on green microalgae: Metabolic responses and chromium enrichment

Dissolved organic matter (DOM) present in aquatic environments can significantly influence microalgal metabolism and the enrichment of heavy metals. However, the specific mechanism through which typical DOM affects the enrichment of the heavy metal chromium (Cr) in green algae remains unclear. This study investigates the impacts of varying concentrations of humic acid (HA), selected as a representative DOM in water, on the growth, metabolism, and Cr enrichment in Chlorella vulgaris, a typical green alga. The results indicated that low concentrations of HA were capable of enhancing Cr enrichment in C. vulgaris, with the highest Cr enrichment rate recorded at 41.50 % at TOC = 10 mg/L. The enrichment of Cr in algal cells primarily occurred through cell proliferation and complexation reduction of extracellular polymeric substances (EPS). In the presence of HA, C. vulgaris predominantly removed Cr through extracellular adsorption, accounting for 79.76-85.88 % of the total Cr removal. Furthermore, carboxyl complexation and hydroxyl reduction within EPS facilitated both the enrichment of Cr (18.72-21.49 %) and the reduction of Cr(VI) (63.93-74.10 %). These findings provide valuable insights into strategies for mitigating heavy metal pollution and managing associated risks in aquatic environments.

Simultaneous efficient removal of tetracycline and mitigation of antibiotic resistance genes enrichment by a modified activated sludge process with static magnetic field

To address the increasing issue of antibiotic wastewater, this study applied a static magnetic field (SMF) to the activated sludge process to increase the efficiency of tetracycline (TC) removal from swine wastewater and to reveal its enhanced mechanisms. The results demonstrated that the SMF-modified activated sludge process could achieve almost complete TC removal at sludge loading rates of 0.3 mg TC/g MLSS/d. Analysis of zeta potential and extracellular polymeric substances composition of the activated sludge revealed that SMF increased electrostatic interactions between TC and activated sludge and made activated sludge has much more binding sites, finally resulting in the increased TC biosorption. Metagenomic analysis showed that SMF promoted the enrichment of ammonia-oxidizing bacteria, TC-degrading bacteria, and aromatic compounds-degrading bacteria; it also enhanced ammonia monooxygenase- and cytochrome P450-mediated TC metabolism while upregulating functional genes associated with oxidase, reductase, and dehydrogenase - all contributing to increased TC biodegradation. Additionally, SMF mitigated the enrichment and spread of antibiotic resistance genes (ARGs) by decreasing the abundance of potential hosts of ARGs and inhibiting the upregulation of genes encoding ABC transporters and putative transposase. Based on these findings, this study demonstrates that magnetic field is an enhancement strategy with great potential to relieve the harmful impacts of the growing antibiotic wastewater problem on human health and the ecosystem.

Deciphering the molecular interaction of extracellular polymeric substances of a marine bacterium Pseudomonas furukawaii PPS-19 with petroleum hydrocarbons and development of bioadsorbent

Petroleum hydrocarbon contamination is a serious hazard to marine environments, affecting ecosystems and marine life. However, extracellular polymeric substances (EPS) of marine bacteria constituting various hydrophilic and hydrophobic functional groups sequester petroleum hydrocarbons (PHs). In this study, interaction of EPS of Pseudomonas furukawaii PPS-19 with PHs such as crude oil, n-dodecane, and pyrene and its impact on PHs adsorption was investigated. Protein component of EPS was increased after treatment with PHs. Red shift of UV-Vis spectra implied change in molecular structure of EPS. Functional groups of proteins (CO, NH2) and polysaccharides (C-C, C-OH, C-O-C) predominantly interacted with PHs. Interaction with PHs affected secondary structure of EPS. Change in binding energies of corresponding functionalities of C 1s, O 1s, and N 1s confirmed the interaction. Disruption of crystalline peaks led to increased pore size in EPS primarily due to the increase in surface electronegativity. Static quenching mechanism unveils formation of complex between fulvic acid of EPS and PHs. Relative expression of alg8 gene was significantly increased in the presence of n-dodecane (6.31 fold) (P < 0.05; One way ANOVA). n-dodecane and pyrene adsorption capacity of Immobilized EPS was significantly higher (356.5 and 338.2 mg g-1, respectively) (P < 0.001; One way ANOVA) than control. Adsorption rate fits into the pseudo-second-order kinetic model. This study establishes that interaction of PHs causes structural and physical changes in EPS and EPS could be used as an adsorbent material for the sequestration of PHs pollution.

Characterizing algal-bacterial symbiotic biofilms: Insights into coexistence of algae and anaerobic microorganisms

This study constructed an integrated algae/partial nitrification/anammox biofilm system and operated it for 240 days. The total nitrogen removal efficiency exceeded 90 %. The structure, compositions, and function of this symbiotic biofilm, which played a pivotal role in the system, were analyzed in detail. Microscope photos and fluorescence in situ hybridization both showed that bacteria and algae were well integrated. The dissolved oxygen gradient further confirmed that different functional microorganisms grew at varying depths within biofilm. Algae formed an oxygen-producing zone (0-0.48 mm), followed by ammonia oxidizing bacteria (AOB) consuming oxygen to form an oxygen-consuming zone (0.48-0.86 mm), and anaerobic ammonia oxidizing bacteria (AnAOB) removed nitrogen in anaerobic zone (>0.86 mm). Chlorella, Nitrosomonas and Candidatus_Kuenenia were identified as the dominant algae, AOB and AnAOB, with relative abundances of 11.80 %, 19.77 % and 3.07 %, respectively. This layered biofilm benefitted providing a suitable environment for various microorganisms to survive within a complex biofilm.

Characterization of the redox-active extracellular polymeric substances in an anaerobic methanotrophic consortium

Anaerobic oxidation of methane (AOM) is a microbial process of importance in the global carbon cycle. AOM is predominantly mediated by anaerobic methanotrophic archaea (ANME), the physiology of which is still poorly understood. Here we present a new addition to the current physiological understanding of ANME by examining, for the first time, the biochemical and redox-active properties of the extracellular polymeric substances (EPS) of an ANME enrichment culture. Using a 'Candidatus Methanoperedens nitroreducens'-dominated methanotrophic consortium as the representative, we found it can produce an EPS matrix featuring a high protein-to-polysaccharide ratio of ∼8. Characterization of EPS using FTIR revealed the dominance of protein-associated amide I and amide II bands in the EPS. XPS characterization revealed the functional group of C-(O/N) from proteins accounted for 63.7% of total carbon. Heme-reactive staining and spectroscopic characterization confirmed the distribution of c-type cytochromes in this protein-dominated EPS, which potentially enabled its electroactive characteristic. Redox-active c-type cytochromes in EPS mediated the EET of 'Ca. M. nitroreducens' for the reduction of Ag+ to metallic Ag, which was confirmed by both ex-situ experiments with extracted soluble EPS and in-situ experiments with pristine EPS matrix surrounding cells. The formation of nanoparticles in the EPS matrix during in-situ extracellular Ag + reduction resulted in a relatively lower intracellular Ag distribution fraction, beneficial for alleviating the Ag toxicity to cells. The results of this study provide the first biochemical information on EPS of anaerobic methanotrophic consortia and a new insight into its physiological role in AOM process.

Culturing partial-denitrification (PD) granules in continuous flow reactor with waste sludge as inoculum: performance, granular sludge characteristics and microbial community

Partial denitrification granular sludge (PDGS) can provide long-term stable nitrite for anaerobic ammonia oxidation (anammox). The cultivation of ordinary activated sludge from wastewater treatment plants into PDGS can further promote the application of PD in practical engineering. In this study, the feasibility of fast start-up of PDGS was explored by inoculating waste sludge in up-flow anaerobic sludge blanket (UASB) reactor with synergistic control of nitrogen load rate (NLR, 0.05-0.65 kg N/m3/d) and electron donor starvation (EDS) (240-168 mg L-1), and system performance, particle characteristics and microbial structure were studied. The results showed that PD-UASB started successfully within 48 days, the average nitrite accumulation rate (NTR) and nitrate removal ratio (NRR) reached 79.6% and 82.5% after successful initiation, accompanied by high abundance of PD bacteria (Thauera, Pseudomonas, unclassflied commamonadaceae and Limnobacter) (25.3%). The increase of PD activity, and the difference between nitrate reductase (NAR) and nitrite reductase (NIR) contributed to nitrite production. Besides, the sludge shifted from flocculated (≤0.5 mm, 95.37%) to granulated state (0.5-2 mm, 64.74%), which could be due to the increase of extracellular polymers (EPS) (especially T-EPS) and metabolism of specific microorganisms (Bacteroidota and Chloroflexi, 19.92%). Good sludge granulation promoted the settleability of PD (the SVI5 was 47.248 mL/ g. ss after successful start-up). In summary, good PD sludge granulation process could be achieved in a short time by synergistically controlling NLR and EDS.

Evaluating the effect of antibiotics on aerobic granular sludge treatment of pharmaceutical wastewater

Aerobic granular sludge (AGS) has been widely applied in pharmaceutical wastewater treatment due to its advantages such as high biomass and excellent settling performance. However, the influence of commonly found antibiotics in pharmaceutical wastewater on the operational efficiency of AGS has been poorly explored. This study investigated the effects of tetracycline (TE) on AGS treating pharmaceutical wastewater at room temperature and analyzed the related mechanisms. The results demonstrate a dose-dependent relationship between TE's effects on AGS. At concentrations below the threshold of 0.1 mg/L, the effects are considered trivial. In contrast, TE with more than 2.0 mg/L reduces the performance of AGS. In the 6.0 mg/L TE group, COD, TN, and TP removal efficiencies decreased to 72.6-75.5, 54.6-58.9, and 71.6-75.8%, respectively. High concentrations of TE reduced sludge concentration and the proportion of organic matter in AGS, leading to a decline in sludge settling performance. Elevated TE concentrations stimulated extracellular polymeric substance secretion, increasing polymeric nitrogen and polymeric phosphorus content. Intracellular polymer analysis revealed that high TE concentrations reduced polyhydroxyalkanoates but enhanced glycogen metabolism. Enzyme activity analysis disclosed that high TE concentrations decreased the activity of key enzymes associated with nutrient removal.

Effects of sludge retention time on sludge reduction by ultrasound treatment: Sludge characteristics, microbial community, and metabolism

Both ultrasound and sludge retention time (SRT) enable the in-situ sludge reduction during wastewater treatment, but the influence of SRT on ultrasonic lysis - cryptic growth is unclear. This paper researched the influence of different SRTs on sludge lysis - cryptic growth using a sequential bio-reactor (SBR), then explained in details the changes of microorganisms in the SBR. The best SRT for sludge reduction was 30 d, and 47.29% reduction in sludge was achieved. The different SRTs changed the organic matter removal in the wastewater, and the removal rate decreased when SRT exceeded 60 d. The size of the sludge particles varied depending on the SRT, with the smallest size at SRT of 10d being 45.6 μm and the largest size at SRT of 90d being 110.0 μm. SEM showed that the sludge surface changed rough at longer SRT. FTIR and XPS showed notable effect in sludge functional group strength at SRT of 30 d. Extracellular polymeric substance (EPS) reduced the most at SRT of 30 d. The microbial communities of sludge varied with the SRT, and the unique main genus at SRT of 5, 15, 30 and 90 d were C10-SB1A, Lactococcus, Propioniciclava, Lactococcus, respectively. Furthermore, the SRT changed relative abundance of enzymes concerned with metabolism of carbon, nitrogen, and phosphorus. Similarly, SRT changed the metabolic rate, and the metabolic rate of carbon, nitrogen and phosphorus was best at SRT of 30 d.

Insights into the effect of nitrate photolysis on short-chain fatty acids production from waste activated sludge in anaerobic fermentation system: Performance and mechanisms

Nitrate photolysis has become an efficient, low-cost and promising technology for emerging contaminants removal, while its performance and mechanism for waste activated sludge (WAS) treatment is still unknown. This study innovatively introduced nitrate photolysis for WAS disintegration, and investigated the effect of nitrate addition (150-375 mg N/L) for short-chain fatty acids (SCFAs) production during anaerobic fermentation (AF). The results showed that nitrate photolysis significantly promoted the SCFAs production from WAS, and peaked at 280.7 mg/g VSS with 7-d fermentation with 150 mg N/L addition (150N-UV), which increased by 8.8-35.0 % and 10.7-23.3 % compared with other photolysis groups and sole nitrate groups. Effective release of the soluble organics was observed in the nitrate photolysis groups during AF, especially soluble proteins, reaching 1505.4 mg COD/L at 9 d in 150N-UV group, promoted by 7.0∼15.7 % than nitrate/nitrate photolysis groups. The model compounds simulation experiment further demonstrated the positive effect of nitrate photolysis on organics hydrolysis and SCFAs accumulation. The result of the radical capture and quenching verified the reactive oxygen species contributed more compared with reactive nitrogen species. Functional group analysis confirmed the effective bioconversion of the macromolecular organics during the fermentation. Moreover, the nitrate photolysis enhanced the enrichment of the functional consortia, including anaerobic fermentation bacteria (AFB), e.g., Fnoticella, Romboutsia, Gracilibacter and Sedimentibacter, and nitrate reducing bacteria (NRB), e.g., Acinerobacter and Ahniella. The macrogenetic analysis further revealed that glycolysis, amino acid metabolism, acetate metabolism and nitrogen metabolism were the dominating metabolic pathways during fermentation, and the abundance of the relevant genes were enhanced in 150N-UV group.

Sulfate-reducing bacteria decreases fractional pressure of H2 to accelerate short-chain fatty acids production from waste activated sludge fermentation assisted with zero-valent iron activated sulfite pretreatment

The production of short-chain fatty acids (SCFAs) is constrained by substrate availability and the increased fractional pressure of H2 emitted by acidogenic/fermentative bacteria during anaerobic fermentation of waste activated sludge (WAS). This study introduced a novel approach employing zero-valent iron (ZVI)-activated sulfite pretreatment combined with H2-consuming sulfate-reducing bacteria (SRB) mediation to improve SCFAs, especially acetate production from WAS fermentation. Experimental results showed that the combined ZVI-activated sulfite and incomplete-oxidative SRB (io-SRB) process achieved a peak SCFAs production of 868.11 mg COD/L, with acetate accounting for 80.55 %, which was 7.90- and 2.18-fold higher than that obtained from raw WAS fermentation, respectively. This could be firstly attributed to the SO4- and OH generated by ZVI-activated sulfite, which significantly promoted WAS decomposition, e.g., soluble proteins and carbohydrates increased 14.3- and 10.8-fold, respectively, over those in raw WAS. The biodegradation of dissolved organic matter was subsequently enhanced by the synergistic interaction and H2 transfer between anaerobic fermentation bacteria (AFB) and io-SRB. The positive and negative correlations among AFB, nitrate-reducing bacteria (NRB) and the io-SRB consortia were revealed by molecular ecological network (MEN) and Mantel test. Moreover, the expression of functional genes was also improved, for instance, in relation to acetate formation, the relative abundances of phosphate acetyltransferase and acetate kinase was 0.002 % and 0.005 % higher than that in the control test, respectively. These findings emphasized the importance of sulfate radicals-based oxidation pretreatment and the collaborative relationships of multifunctional microbes on the value-added chemicals and energy recovery from sludge fermentation.

The effect of extracellular polymeric substances on MICP solidifying rare earth slags and stabilizing Th and U

Microbially induced carbonate precipitation (MICP) has been used to cure rare earth slags (RES) containing radionuclides (e.g. Th and U) and heavy metals with favorable results. However, the role of microbial extracellular polymeric substances (EPS) in MICP curing RES remains unclear. In this study, the EPS of Lysinibacillus sphaericus K-1 was extracted for the experiments of adsorption, inducing calcium carbonate (CaCO3) precipitation and curing of RES. The role of EPS in in MICP curing RES and stabilizing radionuclides and heavy metals was analyzed by evaluating the concentration and morphological distribution of radionuclides and heavy metals, and the compressive strength of the cured body. The results indicate that the adsorption efficiencies of EPS for Th (IV), U (VI), Cu2+, Pb2+, Zn2+, and Cd2+ were 44.83%, 45.83%, 53.7%, 61.3%, 42.1%, and 77.85%, respectively. The addition of EPS solution resulted in the formation of nanoscale spherical particles on the microorganism surface, which could act as an accumulating skeleton to facilitate the formation of CaCO3. After adding 20 mL of EPS solution during the curing process (Treat group), the maximum unconfined compressive strength (UCS) of the cured body reached 1.922 MPa, which was 12.13% higher than the CK group. The contents of exchangeable Th (IV) and U (VI) in the cured bodies of the Treat group decreased by 3.35% and 4.93%, respectively, compared with the CK group. Therefore, EPS enhances the effect of MICP curing RES and reduces the potential environmental problems that may be caused by radionuclides and heavy metals during the long-term sequestration of RES.

Novel insights into intrinsic mechanisms of magnetic field on long-term performance of anaerobic ammonium oxidation process

The performance of an anaerobic ammonium oxidation (anammox) reactor with the magnetic field of 40 mT was systematically investigated. The total nitrogen removal rate was enhanced by 16% compared with that of the control group. The enhancing mechanism was elucidated from the improved mass transfer efficiency, the complicated symbiotic interspecific relationship and the improved levels of functional genes. The magnetic field promoted formation of the loose anammox granular sludge and the homogeneous and well-connected porous structure to enhance the mass transfer. Consequently, Candidatus Brocadia predominated in the sludge with an increase in abundance of 13%. Network analysis showed that the positive interactions between Candidatus Brocadia and heterotrophic bacteria were strengthened, which established a more complicated stable microbial community. Moreover, the magnetic field increased the levels of hdh by 26% and hzs by 35% to promote the nitrogen metabolic process. These results provided novel insights into the magnetic field-enhanced anammox process.

Concentration properties of biopolymers via dead-end forward osmosis

Extracellular polymeric substances (EPSs) in excess sludge of wastewater treatment plants are valuable biopolymers that can act as recovery materials. However, effectively concentrating EPSs consumes a significant amount of energy. This study employed novel energy-saving pressure-free dead-end forward osmosis (DEFO) technology to concentrate various biopolymers, including EPSs and model biopolymers [sodium alginate (SA), bovine serum albumin (BSA), and a mixture of both (denoted as BSA-SA)]. The feasibility of the DEFO technology was proven and the largest concentration ratios for these biopolymers were 94.8 % for EPSs, 97.1 % for SA, 97.8 % for BSA, and 98.4 % for BSA-SA solutions. An evaluation model was proposed, incorporating the FO membrane's water permeability coefficient and the concentrated substances' osmotic resistance, to describe biopolymers' concentration properties. Irrespective of biopolymer type, the water permeability coefficient decreased with increasing osmotic pressure, remained constant with increasing feed solution (FS) concentration, increased with increasing crossing velocity in the draw side, and showed little dependence on draw salt type. In the EPS DEFO concentration process, osmotic resistance was minimally impacted by osmotic pressure, FS concentration, and crossing velocity, and monovalent metal salts were proposed as draw solutes. The interaction between reverse diffusion metal cations and EPSs affected the structure of the concentrated substances on the FO membrane, thus changing the osmotic resistance in the DEFO process. These findings offer insights into the efficient concentration of biopolymers using DEFO.

Exploring nature's filters: Peat-mineral mix for low and high-strength oilfield produced water reclamation

Nature-based solutions are encouraged for treating oilfield produced water from oil and gas extraction, a crucial undertaking that aligns with the Canadian oil sands industry's ambitious goal of zero waste, and the globally recognized Sustainable Development Goals (SDGs) pertaining to water conservation and ecosystem preservation. This study explored the use of peat-mineral mix (PMM), a leftover of inevitable oil sands mining, for treating low and high-strength wastewaters during biofiltration, which contained large molecular weight (44.3 kDa), which include alcohols, aliphatics, aromatics, and ketones, and can impart high toxicity to both fauna and flora (MicroTox: 99 %). The breakthrough curve indicated an effective initial adsorption phase driven by advection within the column dynamics. For complete organics removal and mechanistic insights, the wastewater was re-circulated in a continuous mode for up to 42 days. Here, we found that chemical oxygen demand was reduced from ∼85,000 mg/L to ∼965 mg/L). Kinetics investigations along with physicochemical characterization of PMM and wastewater suggested that chemisorption and anaerobic digestion contributed to the overall removal of contaminants. Chemisorption, led by hydrogen bonding and hydrophobic interactions, was the dominant mechanism, with a limited contribution from physical adsorption (surface area: 2.85 m2/g). The microbial community within the PMM bed was rich/diverse (Shannon > 6.0; Chao1 > 600), with ∼ 50 % unclassified phylotypes representing 'microbial dark matter'. High electric conductivity (332.1 μS cm-1) of PMM and the presence of Geobacter, syntrophs, and Methanosaeta suggest that direct interspecies electron transfer was likely occurring during anaerobic digestion. Both low and high-strength wastewaters showed effective removal of dissolved organics (e.g., naphthenic acids, acid extractable fraction, oil and grease content), nutrients, and potentially toxic metals. The successful use of PMM in treating oilfield produced water offers promising avenues for embracing nature-based remediation solutions at oil refining sites.

Formation of Sb2O3 microcrystals by Rhodotorula mucilaginosa

Antimony (Sb) pollution seriously endangers ecological environment and human health. Microbial induced mineralization can effectively convert metal ions into more stable and less soluble crystalline minerals by extracellular polymeric substance (EPS). In this study, an efficient Sb-resistant Rhodotorula mucilaginosa (R. mucilaginosa) was screened, which can resist 41 mM Sb(III) and directly transform Sb(III) into Sb2O3 microcrystals by EPS. The removal efficiency of R. mucilaginosa for 22 mM Sb(III) reached 70% by converting Sb(III) to Sb2O3. The components of supernatants as well as the effects of supernatants and pH on Sb(III) mineralization verified that inducible and non-inducible extracellular protein/polysaccharide biomacromolecules play important roles in the morphologies and sizes control of Sb2O3 formed by R. mucilaginosa respectively. Sb2O3 microcrystals with different morphologies and sizes can be prepared by the regulation of inducible and non-inducible extracellular biomacromolecules secreted by R. mucilaginosa. This is the first time to identify that R. mucilaginosa can remove Sb(III) by transforming Sb(III) into Sb2O3 microcrystals under the control of EPS. This study contributes to our understanding for Sb(III) biomineralization mechanisms and provides strategies for the remediation of Sb-contaminated environment.

Effects of cations on biofilms in gravity-driven membrane system: Filtration performance and mechanism investigation

The gravity-driven membrane (GDM) system is desirable for energy-efficient water treatment. However, little is known about the influence of cations on biofilm properties and GDM performance. In this study, typical cations (Ca2+ and Na+) were used to reveal the combined fouling behavior and mechanisms. Results showed that Ca2+ improved the stable flux and pollutant removal efficiency, while Na+ adversely affected the flux. Compared with GDM control, the concentration of pollutants was lower in Ca-GDM, as indicated by the low biomass, proteins, and polysaccharides. A heterogeneous and loose biofilm was observed in the Ca-GDM system, with roughness and porosity increasing by 43.06 % and 32.60 %, respectively. However, Na+ induced a homogeneous and dense biofilm, with porosity and roughness respectively reduced by 17.48 % and 22.04 %. The richness of bacterial communities increased in Ca-GDM systems, while it decreased in Na-GDM systems. High adenosine triphosphate (ATP) concentration in Ca-GDM system was consistent with the abundant bacteria and their high biological activity, which was helpful for the efficient removal of pollutants. The abundance of Apicomplexa, Platyhelminthes, Annelida and Nematoda increased after adding Ca2+, which was related to the formation of loose biofilms. Computational simulations indicated that the free volumes of the biofilms in Ca-GDM and Na-GDM were 13.7 and 13.2 nm3, respectively. The addition of cations changed intermolecular forces, Ca2+ induced bridging effects led to large and loose floc particles, while the significant dehydration of hydrated molecules in the Na-GDM caused obvious aggregation. Overall, microbiological characteristics and contaminant molecular interactions were the main reasons for differences in GDM systems.

New insights into nitrogen removal by divalent iron-enhanced moving bed biofilm reactor: Performance, interfacial interaction and co-occurrence network

A divalent iron-mediated moving bed biofilm reactor with intermittent aeration was developed to enhance the nitrogen removal at low carbon-to-nitrogen ratios. The study demonstrated thatammonia removal increased from 51 ± 4 % to 79 ± 4 % and nitrate removal increased from 72 ± 5 % to 98 ± 4 % in phases I-IV, and 2-5 mg·L-1 of divalent iron significantly increased the anoxic denitrification process. Divalent iron stimulated the secretion of extracellular polymeric substances, which facilitated the formation of cross-linked network between microbial cells. Furthermore, the cycle between divalent and trivalent iron decreased the energy barrier between the biofilm and the pollutant. The microbial community further revealed that Proteobacteria (relative abundance: 40-48 %) andBacteroidota(relative abundance: 31-37 %) were the dominant phyla, supporting the synchronous nitrification and denitrification processes as well as the lower accumulation of nitrite. In conclusion, iron redox cycling significantly enhanced the nitrogen removal. This study proposes a viable strategy for the efficient treatment of nutrient wastewater.

Mechanistic insight into the aggregation ability of anammox microorganisms: Roles of polarity, composition and molecular structure of extracellular polymeric substances

The chemical characteristics of extracellular polymeric substances (EPS) of anammox bacteria (AnAOB) play a crucial role in the rapid enrichment of AnAOB and the stable operation of wastewater anammox processes. To clarify the influential mechanisms of sludge EPS on AnAOB aggregation, multiple parameters, including the polarity distribution, composition, and molecular structure of EPS, were selected, and their quantitative relationship with AnAOB aggregation was analyzed. Compared to typical anaerobic sludge (anaerobic floc and granular sludge), the anammox sludge EPS exhibited higher levels of tryptophan-like substances (44.82-56.52 % vs. 2.57-39.81 %), polysaccharides (40.02-53.49 mg/g VSS vs. 30.22-41.69 mg/g VSS), and protein structural units including α-helices (20.70-23.98 % vs. 16.48-19.32 %), β-sheets (37.43-42.98 % vs. 25.78-36.72 %), and protonated nitrogen (Npr) (0.065-0.122 vs. 0.017-0.061). In contrast, it had lower contents of β-turns (20.95-27.39 % vs. 28.17-39.04 %). These biopolymers were found to originate from different genera of AnAOB. Specifically, the α-helix-rich proteins were mainly derived from Candidatus Kuenenia, whereas the extracellular proteins related to tryptophan and Npr were closely associated with Candidatus Brocadia. Critically, these EPS components could drive anammox aggregation through interactions. Substantial amounts of tryptophan-like substances facilitated the formation of β-sheet structures and the exposure of internal hydrophobic clusters, which benefited the anammox aggregation. Meanwhile, extracellular proteins with high Npr content played a pivotal role in the formation of mixed protein-polysaccharide gel networks with the electronegative regions of polysaccharides, which could be regarded as the key component in the maintenance of anammox sludge stability. These findings provide a comprehensive understanding of the multifaceted roles of EPS in driving anammox aggregation and offer valuable insights into the development of EPS regulation strategies aimed at optimizing the anammox process.

Iron-mediated DAMO-anammox process: Revealing the mechanism of electron transfer

The nitrate denitrifying anaerobic methane oxidation-anaerobic ammonia oxidation (DAMO-anammox) can accomplish nitrogen removal and methane (CH4) reduction. This process greatly contributes to carbon emission mitigation and carbon neutrality. In this study, we investigated the electron transfer process of functional microorganisms in the iron-mediated DAMO-anammox system. Fe3+ could be bound to several functional groups (-CH3, COO-, -CH) in extracellular polymeric substance (EPS), and the functional groups bound were different at different iron concentration. Fe3+ underwent reduction reactions to produce Fe2+. Most Fe3+ and Fe2+ react with microorganisms and formed chelates with EPS. Three-dimensional fluorescence spectra showed that Fe3+ affected the secretion of tyrosine and tryptophan, which were essential for cytochrome synthesis. The presence of Fe3+ accelerated c-type cytochrome-mediated extracellular electron transfer (EET), and when more Fe3+ existed, the more cytochrome C expressed. DAMO archaea (M. nitroreducens) in the system exhibited a high positive correlation with the functional genes (resa and ccda) for cytochrome c synthesis. Some denitrifying microorganisms showed positive correlations with the abundance of riboflavin. This finding showed that riboflavin secreted by functional microorganisms acted as an electron shuttle. In addition, DAMO archaea were positively correlated with the hair synthesis gene pily1, which indicated that direct interspecies electron transfer (DIET) may exist in the iron-mediated DAMO-anammox system.

Cadmium-Induced Physiological Responses, Biosorption and Bioaccumulation in Scenedesmus obliquus

Cadmium ion (Cd2+) is a highly toxic metal in water, even at low concentrations. Microalgae are a promising material for heavy metal remediation. The present study investigated the effects of Cd2+ on growth, photosynthesis, antioxidant enzyme activities, cell morphology, and Cd2+ adsorption and accumulation capacity of the freshwater green alga Scenedesmus obliquus. Experiments were conducted by exposing S. obliquus to varying concentrations of Cd2+ for 96 h, assessing its tolerance and removal capacity towards Cd2+. The results showed that higher concentrations of Cd2+ (>0.5 mg L-1) reduced pigment content, inhibited algal growth and electron transfer in photosynthesis, and led to morphological changes such as mitochondrial disappearance and chloroplast deformation. In this process, S. obliquus counteracted Cd2+ toxicity by enhancing antioxidant enzyme activities, accumulating starch and high-density granules, and secreting extracellular polymeric substances. When the initial Cd2+ concentration was less than or equal to 0.5 mg L-1, S. obliquus was able to efficiently remove over 95% of Cd2+ from the environment through biosorption and bioaccumulation. However, when the initial Cd2+ concentration exceeded 0.5 mg L-1, the removal efficiency decreased slightly to about 70%, with biosorption accounting for more than 60% of this process, emerging as the predominant mechanism for Cd2+ removal. Fourier transform infrared correlation spectroscopy analysis indicated that the carboxyl and amino groups of the cell wall were the key factors in removing Cd2+. In conclusion, S. obliquus has considerable potential for the remediation of aquatic environments with Cd2+, providing algal resources for developing new microalgae-based bioremediation techniques for heavy metals.

Roles of entrapped bubbles in methanogenic granules under oscillating pressure: Respiration and embolization for intra-granular transport

Anaerobic granular sludge plays a pivotal role in the treatment of concentrated organic wastewater. However, previous studies on intra- granular transport have generally overlooked lung-like respiration that expedites transport in response to fluctuating pressure. This study explored the activities of calcified and normal granules under simulated hydrostatic pressure oscillations. The results revealed a significant enhancement in the bioactivity of calcified granules under oscillating pressure, contrasting with the comparatively lower bioactivity observed in normal granules. The hypothesis posited that the gas pockets in calcified granules facilitated respiration as the functional structure. The presence of tiny bubbles exhibited a propensity for inducing clogging, thereby diminishing the capillary connectivity essential for substrate diffusion. The proposed respiration and embolization concepts decipher the distinct roles of entrapped bubbles in the granular bioactivity across diverse fluid states. This study offers valuable insights into the impact of fluidization on microscopic transport within granule-based bed reactors.

Targeted regulation of digestate dewaterability by the ozone/persulfate oxidation process

Dewatering is the first step in the subsequent treatment and disposal of food waste digestate (FWD). However, FWD is difficult to dewatering. In this study, persulfate was synergistic oxidized by ozone to improve digestate dewaterability. The optimal conditions was at pH = 3, O3＝40 mg/g TS and PDS＝0.1 g/g TS, under which the reductions in the normalized capillary suction time (NCST) and bound moisture (BM) of the FWD were 89.97% and 65.79%, respectively. Hydrophilic functional groups (oxygen- and nitrogen-containing groups) and hydrophilic protein molecular structures were decomposed by the reactive species of sulfate radical (SO4·-) and hydroxyl radicals (·OH) generated in the ozone-persulfate oxidation process, disrupting the binding between EPS and water molecules. The contributions of SO4·- and ·OH to digestate dewaterability were 42.51% and 28.55%. In addition, the introduction of H+ reduced electrostatic repulsion and contributed to the condensation of digestate flocs. The environmental implication assessment and economic analysis suggested that the O3/PDS oxidation process was cost-effective and has a low environmental implication when applied to the FWD dewaterability improvement process. These results can serve as a reference for the management of FWD and further improvement of FWD treatment and disposal efficiency.

The role of microstructure of extracellular proteins in dewaterability of alkaline pretreatment sludge during bioleaching

Alkaline pre-treatment is known to enhance the acid production efficiency of sludge but adversely affects its dewatering performance. In this study, the improvement of sludge dewaterability by a novel bioleaching system with inoculating domesticated acidified sludge (AS) and its underlying mechanism were investigated. The results showed that although the addition of Fe2+ and the reduction of pH improved the dewatering performance of sludge, their effects were inferior to that of AS + Fe. The addition of AS and Fe2+ significantly reduced the specific resistance to filtration and capillary suction time of the sludge by 98.6 % and 95.5 %, respectively. This improvement in dewatering performance was achieved through the combined actions of bio-acidification, bio-oxidation, and bio-flocculation. Remarkably, under alkaline pH, microorganisms in AS remained active, leading to the formation of iron-based bioflocculants, along with a rapid pH decrease. These bioflocculants, in combination with protein (PN) in tightly bound extracellular polymeric substances (TB-EPS) through amide bonding, transformed TB-EPS from extractable to non-extractable form, reducing PN content from 12.1 mg g-1DS to 5.09 mg g-1DS and altering the protein's secondary structure. Consequently, the gel-like TB-EPS matrix effectively broke down, releasing cellular water and significantly enhancing sludge dewaterability.

A novel co-metabolic mode with Spirulina powder in enhancing the anaerobic degradation of typical nitrogen heterocyclic compounds

Spirulina powder emerged as a novel and suitable co-metabolism substance significantly enhancing the anaerobic degradation of specific nitrogen heterocyclic compounds. On the addition of 1.0 mg/L of Spirulina powder, the reactor demonstrated optimal degradation efficiency for quinoline and indole, achieving ratios of 99.77 ± 1.83% and 99.57 ± 1.98%, respectively. Moreover, the incorporation of Spirulina powder resulted in increased concentrations of mixed liquor suspended solids, mixed liquor volatile suspended solids, proteins, and polysaccharides in anaerobic sludge. In addition, Spirulina powder led to reduced levels of Acinetobacter and enriched Aminicenantes genera incertae sedis, Levilinea, and Longilinea. The analysis of the archaeal community structure confirmed that the addition of Spirulina powder increased archaeal sequences, fostering greater richness and diversity in the archaeal community.

Larger hydroxyapatite aggregation from Ca2+ adhesion in ANAMMOX granular sludge caused by high dissolved oxygen

Anaerobic ammonia oxidation (ANAMMOX), a sustainable biological process, is promising to remove NH4+-N from municipal sewage. In this study, results showed that the anammox granular sludge morphology changes with the alternation of dissolved oxygen (DO), mainly attributing to the adhesion of calcium ions (Ca2+) to the surface of sludge particles. Diverse characterization methods revealed that gray adhesions in the form of hydroxyapatite covered the original holes on the anammox granular sludge surface, including scanning Electron Microscopy (SEM), digital camera images, Energy Dispersive Spectrometer (EDS), and X-ray diffraction (XRD). Ex-situ degradation of NH4+-N and NO2--N yielded diverse outcomes. The protein to polysaccharide ratio (PN/PS) in the total extracellular polymeric substances (EPS) across 4 size groups demonstrated a decrease under O2 exposure. Microbial community analysis indicated norank_f_A4b and Nitrolancea being the most abundant genus under O2 exposure at day 1 and day 100, respectively. These findings offer an effective strategy to prevent size-larger granular sludge from deteriorating through changing DO and Ca2+ in municipal wastewater in ANAMMOX.

Enhanced membrane fouling by microplastics during nanofiltration of secondary effluent considering secretion, interaction and deposition of extracellular polymeric substances

Microplastic (MP) has been found to influence membrane fouling during microfiltration/ultrafiltration processes in direct and indirect ways by acting as fouling components and changing microbial activities, respectively. However, there is no relevant research about the contribution of MPs to nanofiltration membrane fouling. In this study, for the first time, the impacts of MPs on membrane fouling during the nanofiltration of secondary effluent (SE) were systematically investigated from the perspective of bacterial extracellular polymeric substances (EPS) secretion, their interaction with coexisting pollutants and also deposition. Membrane flux behaviors indicate that MPs simultaneously aggravated the short-term and long-term membrane fouling resistance of nanofiltration by 46 % and 27 %, respectively. ATR-FTIR, XPS and spectrophotometry spectra demonstrate that the deteriorated membrane fouling by MPs directly resulted from the increased accumulation of protein-like, polysaccharides-like and humic-like substances on membranes. EEM spectra further confirmed that MPs preferred to induce serious cake layers, which dominated membrane flux decline but hindered pore fouling. According to CLSM and SEM-EDS mappings, MPs in SE could stimulate microbial activities and then aggravate EPS secretion, after which their interaction with Ca2+ was also enhanced in bulk solution. The cross-linker nets could promote the deposition of other unlinked pollutants on membranes. Besides, MPs could weaken the rejection of certain dissolved organic matters (from 57 % to 52 % on the 50th day of filtration) by aggravating cake-enhanced concentration polarization (CECP), but improved the average removal of inorganic salts from 58 % to 63 % by improving their back diffusion through cake layers. Based on these analyses, the mechanisms of MP-enhanced membrane fouling during the nanofiltration of SE can be thoroughly revealed.

Deterioration of sludge characteristics and promotion of antibiotic resistance genes spread with the co-existing of polyvinylchloride microplastics and tetracycline in the sequencing batch reactor

With the continuous increase in microplastics (MPs) and tetracycline (TC) entering wastewater treatment plants (WWTPs) along with sewage, the co-existence of MPs and TC in the biological treatment of wastewater has attracted extensive attention. This study investigated the effect of 1 mg/L polyvinyl chloride (PVC) MPs and 100 ng/L TC co-existing on sequencing batch reactors (SBRs) (S2) treating phenol wastewater in contrast to the control with TC alone (S1). The phenol removal efficiency was significantly inhibited by the co-existence of PVC MPs and TC. Sludge characteristics were also distinctively influenced. The decreased zone sludge velocity (ZSV) and increased sludge volume index (SVI) indicated that the combined effect of PVC MPs and TC deteriorated sludge settleability, which had positive and negative linear correlations with extracellular polymeric substances (EPS) content and the protein (PN)/polysaccharide (PS) ratio, respectively. Moreover, the decreased and increased relative abundances of potential phenol-degraders and antibiotic resistance gene (ARG) carriers may elucidate the inhibition of phenol removal and promotion of ARGs propagation with the co-occurrence of PVC MPs and TC. In addition, the enhanced potential ARGs hosts, loss of the EPS protective effect, and increased membrane permeability induced by reactive oxygen species (ROS) jointly promoted ARGs dissemination in the co-existence of PVC MPs and TC. Notably, the co-occurrence of ARGs and mobile genetic element (MGEs) indicated that the co-existence of PVC MPs and TC promoted the spread of some transposase-associated ARGs mediated by horizontal gene transfer (HGT).

Performance and mechanism of chromium reduction in denitrification biofilm system with different carbon sources

In the process of biological reduction of Cr(VI), the type of carbon sources affects the rate and effect of Cr(VI) reduction, but its specific performance and influencing mechanism have not yet been explored. In this study, four denitrification biofilm reactors were operated under four common carbon sources (C6H12O6, CH3COONa, CH3OH, CH3COONa:C6H12O6 1:1) to reveal the impact of carbon sources on Cr(VI) reduction. Through preliminary experimental concentration research, 75 mg/L Cr(VI) was selected as the dosing concentration. In long-term operation, the composite carbon sources of CH3COONa and C6H12O6 demonstrated excellent stability and achieved an impressive Cr(VI) removal efficiency of 99.5 %. The following sequence was C6H12O6, CH3COONa, and CH3OH. Among them, CH3OH was less competitive and the system was severely unbalanced with lowest Cr(VI) reduction efficiency. The toxicity reactions, changes in EPS and its functional groups, and electron transfer revealed the reduction and fixation mechanism of chromium on denitrification biofilm. The changes in microbial communities indicated that microbial communities in composite carbon sources can quickly adapt to the high toxic environment. The proportion of Trichococcus reached 43.6 %, which played an important role in denitrification and Cr(VI) reduction. Meanwhile, the prediction of microbial COG function reflected its excellent metabolic ability and defense mechanism.

Effects of lysed sludge reflux point on ultrasound lysis-cryptic growth in anaerobic/aerobic (A/O) wastewater treatment: Sludge reduction, microbial community, and metabolism

Ultrasonication allows sludge reduction to be performed in situ during wastewater treatment, and the reflux point of the lysed sludge affects this performance. This study investigated the effects of reflux point (anaerobic stage, carbon/nitrogen (C/N) lowest stage, and aerobic stage) on sludge lysis-cryptic growth in an anaerobic/aerobic reactor and variations in the sludge and microbial community. The best reflux point occurred at the lowest C/N ratio stage, and a 50.96% reduction in excess sludge was achieved. The reflux of the lysed sludge to the aerobic stage reduced nitrogen and phosphorus removal. The reflux of the lysed sludge decreased the average sludge size, reaching 29.2 μm when reflux to the aerobic stage. Scanning electron microscopy showed that the sludge surface was unaffected by the reflux point. The Fourier-transform infrared spectrometry and X-ray photoelectron spectroscopy results showed that the most prominent variation in the intensity of the sludge functional groups occurred when the reflux was at the lowest C/N stage. The amount of extracellular polymeric substances decreased the most during reflux to the anaerobic stage. The sludge microbial communities varied with the reflux point, and the dominant phyla during reflux to the anaerobic, lowest C/N, and aerobic stages were Bacteroidetes, Firmicutes, and Bacteroidetes, respectively. Furthermore, the reflux point did not alter the metabolic pathway of sludge microorganisms but increased the number of enzymes in metabolic pathways.

Novel thermodynamic mechanisms of co-conditioning with polymeric aluminum chloride and polyacrylamide for improved sludge dewatering: A paradigm shift in the field

This study investigated the combined effects of polymeric aluminum chloride (PAC) and polyacrylamide (PAM) on sludge dewatering, aiming to unveil underlying mechanisms. Co-conditioning with 15 mg g-1 PAC and 1 mg g-1 PAM achieved optimal dewatering, reducing specific filtration resistance (SFR) of co-conditioned sludge to 4.38 × 1012 m-1kg-1, a mere 48.1% of raw sludge's SFR. Compared with the CST of raw sludge (36.45 s), sludge sample can be significantly reduced to 17.7 s. Characterization tests showed enhanced neutralization and agglomeration in co-conditioned sludge. Theoretical calculations revealed elimination of interaction energy barriers between sludge particles post co-conditioning, converting sludge surface from hydrophilic (3.03 mJ m-2) to hydrophobic (-46.20 mJ m-2), facilitating spontaneous agglomeration. Findings explain improved dewatering performance. Based on Flory-Huggins lattice theory, connection between polymer structure and SFR was established. Raw sludge formation triggered significant change in chemical potential, increasing bound water retention capacity and SFR. In contrast, co-conditioned sludge exhibited thinnest gel layer, reducing SFR and significantly improving dewatering. These findings represent a paradigm shift, shedding new light on fundamental thermodynamic mechanisms of sludge dewatering with different chemical conditioning.

Role of Nano-Fe3O4 for enhancing nitrate removal in microbial electrolytic cells: Characterizations and microbial patterns of cathodic biofilm

Conductive magnetite nanoparticle (Nano-Fe3O4) can facilitate numerous biological reduction reactions as an outstanding electron mediator for electron transfer. The positive role of Nano-Fe3O4 for nitrate removal has gradually gained attention recent years, however, it has not been clarified for the persistence of the promoting effect under different concentrations addition. Performance of nitrogen removal and characteristics of cathodic biofilm were evaluated in this study after Nano-Fe3O4 addition with gradient concentration of 100∼500 mg L-1 in microbial electrolytic cells (MEC). Our study illustrated that the optimal concentration was 200 mg L-1 as the removal rate of nitrate increased by 24.76% and the removal rate of total dissolved nitrogen by 29.72%. At the optimal concentration, Nano-Fe3O4 increased cathodic biofilm DNA concentration by 61.04%, enhanced electron transport system activity, enriched iron redox bacteria, denitrifying bacteria and genes, as well as increased extracellular polymeric substances (EPS) amount, especially the protein content of soluble-EPS. However, promoting effect on nitrate removal was not visible in high concentration (500 mg L-1) addition, its electron transport system activity and EPS content were even declined. XPS results indicated that high concentration of Nano-Fe3O4 may reduce the availability of electrons to cathodic biofilm by competing for electrons, which inhibit nitrate removal.

Acclimation of electroactive biofilms under different operating conditions: comprehensive analysis from architecture, composition, and metabolic activity

Electroactive biofilms (EABs) have aroused wide concern in waste treatment due to their unique capability of extracellular electron transfer with solid materials. The combined effect of different operating conditions on the formation, microbial architecture, composition, and metabolic activity of EABs is still unknown. In this study, the impact of three different factors (anode electrode, substrate concentration, and resistance) on the acclimation and performance of EABs was investigated. The results showed that the shortest start-up time of 127.3 h and highest power density of 0.84 W m-2 were obtained with carbon brush as electrode, low concentration of substrate (1.0 g L-1), and 1000 Ω external resistance (denoted as N1). The EABs under N1 condition also represented strongest redox capacity, lowest internal resistance, and close arrangement of bacteria. Moreover, the EABs cultured under different conditions both showed similar results, with direct electron transfer (DET) dominated from EABs to anode. Microbial community compositions indicated that EABs under N1 condition have lowest diversity and highest abundance of electroactive bacteria (46.68%). Higher substrate concentration (3.0 g L-1) promoted the proliferation of some other bacteria without electroactivity, which was adverse to EABs. The metabolic analysis showed the difference of genes related to electron transfer (cytochrome C and pili) and biofilm formation (xap) of EABs under different conditions, which further demonstrated the higher electroactivity of EABs under N1. These results provided a comprehensive understanding of the effect of different operating conditions on EABs including biofilm formation and electrochemical activity.

A comprehensive assessment on sludge conditioning by pyrite acid eluent-activated peroxymonosulfate based on dewaterability, heavy metals risk and ore recovery

Wastewater activated sludge (WAS) has poor dewaterability and contains heavy metals (HMs), limiting its land application. Therefore, in this study, a novel pyrite acid eluent-activated peroxymonosulfate (Fe2+pyrite/PMS) conditioning approach that can completely recover the residual pyrite and greatly reduce acid use was developed to improve WAS dewaterability, and the HMs chemical speciation and risks of conditioned WAS were assessed. Our results showed that under the optimized operational parameters, the capillary suction time (CST) and water content (Wc) of WAS decreased by 46.03% and 7.75%, respectively. Furthermore, during Fe2+pyrite/PMS conditioning processing, sulfate radical (SO4-) destroyed the extracellular polymeric substances (EPS) matrix, causing bound water release and the decrease of proteins/polysaccharides in outer layered EPS, even the decomposition of some protein-N in tightly bound EPS (TB-EPS) into inorganic-N. In addition, although the total concentration of HMs in the conditioned WAS matrix increased, the Ni concentration decreased in the solid fraction. Further, the risk assessment code (RAC) levels did not increase, and the eco-toxicity of Cr became weakened after Fe2+pyrite/PMS conditioning. However, after acid extraction, the pyrite residue had worsened recycle performance because the passivation layer contained S0/Sn2- on its surface, and no additional elements were detected in the pyrite residue, which had almost no effect on its further usage.

Enhanced permeation performance of biofiltration-facilitated gravity-driven membrane (GDM) systems by in-situ application of UV and VUV: Comprehensive insights from thermodynamic and multi-omics perspectives

Biofouling is a major challenge limiting the practical application of biofiltration-facilitated gravity-driven membrane (GDM) systems in drinking water treatment. In this study, ultraviolet irradiation, including ultraviolet (UV) and vacuum ultraviolet (VUV) irradiation, was used for in-situ purification of membrane tanks to control membrane biofouling. After using UV and VUV, the permeate flux increased significantly by 26.1% and 78.3%, respectively, which was mainly due to the decreased cake layer resistance (Rc). The permeability of the biofouling layer improved after UV and VUV application, as evidenced by the increased surface porosity and decreased thickness. The contents of loosely bound extracellular proteins (LB-PN) and tightly bound extracellular proteins (TB-PN) in the biofouling layer were reduced after UV and VUV irradiation. The decreased LB-PN and TB-PN improved the interfacial free energy between the fouling itself and between the fouling and the membrane, which contributed to the reduction of interfacial cohesion and adhesion, resulting in a looser and thinner biofouling layer and a cleaner membrane. The concentration of protein-like material in the membrane tank decreased after UV and VUV irradiation, significantly altering the bacterial community structure on the membrane surface (Mantel's r > 0.7, p < 0.05). The changes in the metabolic state were responsible for the differences in the LB-PN and TB-PN contents. The inhibition of "Alanine, aspartate and glutamate metabolism" and "Glycine, serine and threonine metabolism" reduced amino acid biosynthesis, which restricted the secretion of LB-PN and TB-PN. Critical genera in the Proteobacteria phylum, such as Hirschia, Rhodobacter, Nordella, Candidatus_Berkiella, and Limnohabitans, were involved in metabolite transformation. Overall, the in-situ application of UV and VUV can be an effective alternative strategy to mitigate membrane biofouling, which would facilitate the practical application of biofiltration-facilitated GDM systems in drinking water treatment.

Nitrogen removal from mature landfill leachate through enhanced Partial Nitrification-Anammox process in an innovative multi-stage fixed biofilm reactor

In the current integrated PN/A method/process for mature landfill leachate treatment, microbial inhibition and low nitrogen removal capacity are the big barriers due to high ammonia concentration and low C/N. This study aimed to evaluate the performance of a high-rate nitrogen removal lab-scale reactor, which combines pre-denitrification and Partial Nitrification-Anammox (PN/A) in a multi-stage fixed biofilm reactor (MFBR), for mature landfill leachate treatment. A nitrogen removal efficiency (NRE) of 90.43 % and an average nitrogen removal rate (NRR) of 0.94 kg/m³·d were observed at an influent NH+ 4-N concentration of 2274.39 mg/L during the last operational phase. The nitrogen mass balance showed that the nitrogen concentration gradually decreases along the course, and nitrogen was mainly removed in the aerobic chambers, in which Anammox contributed to 86.4 % of the removed nitrogen, while the front anoxic chamber is mainly used to remove NO- 3-N from the recirculation. Redundancy analysis showed that the variation in NH+ 4-N concentration along the course was the main factor affecting microbial community succession, which shows that the reactor configuration enables efficient cooperation and distribution of different microorganisms. Moreover, economic analysis of MFBR process showed that the energy consumption and carbon addition were reduced by 58.9 % and 100 %, respectively. Therefore, the MFBR established in this study, with its new configuration, achieves efficient treatment of landfill leachate in a single reactor and is environmentally friendly, and could be considered as a reference for full-scale landfill leachate treatment.

Deciphering the contribution of microbial biomass to the properties of dissolved and particulate organic matter in anaerobic digestates

The recalcitrant structures either from substrate or microbial biomass contained in digestates after anaerobic digestion (AD) highly influence digestate valorization. To properly assess the microbial biomass contribution to the digested organic matter (OM), a combination of characterization methods and the use of various substrate types in anaerobic continuous reactors was required. The use of totally biodegradable substrates allowed detecting soluble microbial products via fluorescence spectroscopy at emission wavelengths of 420 and 460 nm while the protein-like signature was enhanced by the whey protein. During reactors' operation, a transfer of complex compounds to the dissolved OM from the particulate OM was observed through fluorescence applied on biochemical fractionation. Consequently, the fluorescence complexity index of the dissolved OM increased from 0.59-0.60 to 1.06-1.07, whereas it decreased inversely for the extractable soluble from the particulate OM from 1.16-1.19 to 0.42-0.54. Accordingly, fluorescence regional integration showed differences among reactors based on visual inspection and orthogonal partial latent structures (OPLS) analysis. Similarly, the impact of the substrate type and operation time on the particulate OM was revealed by ¹³C nuclear magnetic resonance using OPLS, providing a good model (R²X = 0.93 and Q² = 0.8) with a clear time-trend. A high signal resonated at ∼30 ppm attributed to CH₂-groups in the aliphatic chain of lipid-like structure besides carbohydrates intensities at 60-110 ppm distinguished the reactor fed with whey protein from the other, which was mostly biomass related. Indeed, this latter displayed a higher presence of peptidoglycan (δH/C: 1.6-2.0/20-25 ppm) derived from microbial biomass by ¹H-¹³C heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance. Interestingly, the sample distribution obtained by non-metric multidimensional scaling of bacterial communities resembled the attained using ¹³C NMR properties, opening new research perspectives. Overall, this study discloses the microbial biomass contribution to digestates composition to improve the OM transformation mechanism knowledge.

Biosorption of sub-micron-sized polystyrene microplastics using bacterial biofilms

Microplastics are becoming a global concern because they pose potential ecological and toxicological risks to organisms. Thus, removing microplastics from aquatic environments is important. In this study, we evaluated the capability of bacterial biofilms as a biological source for the biosorptive removal of sub-micron-sized polystyrene (PS) microplastics. Three bacterial strains-specifically, Pseudomonas aeruginosa, Bacillus subtilis, and Acinetobacter sp.-were used to form biofilms, and each biofilm was tested in batch experiments for the removal of sub-micron-sized PS microplastics. The Acinetobacter sp. biofilm demonstrated excellent removal performance against 430 nm-PS microplastics than other bacterial biofilms and showed a removal capacity of 715.5 mg/g upon treatment with the PS microplastics for 20 min, thus it employed further adsorption experiments. The biosorption of 430 nm-PS microplastics onto the Acinetobacter sp. biofilm was well explained by the pseudo-second-order kinetics and Freundlich isotherm models. Fourier transform infrared analysis indicated that biosorption of 430 nm-PS microplastics onto the Acinetobacter sp. biofilm involved chemisorption. Three environmental parameters-temperature, pH, and coexisting ions-marginally affected the biosorption of 430 nm-PS microplastics onto Acinetobacter sp. biofilm. However, the biosorption capability of Acinetobacter sp. biofilm was diminished when the 430 nm-PS microplastics were incubated in environmental freshwaters for 7 d.

Insight into the roles of soluble, loosely bound and tightly bound extracellular polymeric substances produced by Enterobacter sp. in the Cd2+ and Pb2+ biosorption process: Characterization and mechanism

Extracellular polymeric substances (EPSs) are macromolecular polymers formed by metabolic secretion, and they have great potential for removing heavy metal (HM) ions from the aquatic phase. In this study, the contributions of soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs) and tightly bound EPSs (TB-EPSs) secreted by Enterobacter sp. to Cd²⁺ and Pb²⁺ adsorption were analyzed. The results indicated that in a solution containing both Cd²⁺ and Pb²⁺, pH= 6.0 was best suited for the adsorption process, and adsorption equilibrium was reached in approximately 120 min. Moreover, the mechanism for adsorption of Cd²⁺ and Pb²⁺ by the different layers of EPSs involved spontaneous chemical processes. However, Cd²⁺ adsorption by the three layers of the EPSs was an exothermic process (∆H⁰ <0), but Pb²⁺ adsorption by the three layers of the EPSs was an endothermic process (∆H⁰ >0). The variations in zeta potentials indicated that ion exchange occurred during Cd²⁺ and Pb²⁺ adsorption. FT-IR, XPS and 3D-EEM analyses indicated that the functional groups of the EPSs involved in adsorption were mainly the CO, C-O and C-O-C groups of the polysaccharides; furthermore, fulvic acid-like substances, humic-like substances and tyrosine-like proteins played important roles in the adsorption of Cd²⁺ and Pb²⁺ by the different EPS layers.

Accumulating ammoniacal nitrogen instead of melanoidins determines the anaerobic digestibility of thermally hydrolyzed waste activated sludge

Full-scale thermal hydrolysis processes (THP) showed an increase in nutrients release and formation of melanoidins, which are considered to negatively impact methanogenesis during mesophilic anaerobic digestion (AD). In this research, fractionation of THP-sludge was performed to elucidate the distribution of nutrients and the formed melanoidins over the liquid and solid sludge matrix. Degradation of the different fractions in subsequent AD was assessed, and the results were compared with non-pre-treated waste activated sludge (WAS). Results showed that the THP-formed soluble melanoidins were partially biodegradable under AD, especially the fraction with molecular weight under 1.1 kDa, which was related to protein-like substances. The use of THP in WAS increased the non-biodegradable soluble chemical oxygen demand (sCOD) after AD, from 1.1% to 4.9% of the total COD. The total ammoniacal nitrogen (TAN) concentration only slightly increased during THP without AD. However, after AD, TAN released was 34% higher in the THP-treated WAS compared to non-treated WAS, i.e., 36.7 ± 0.7 compared to 27.4 ± 0.4 mgTANreleased/gCODsubstrate, respectively. Results from modified specific methanogenic activities (mSMAs) tests showed that the organics solubilised during THP, were not inhibitory for acetotrophic methanogens. However, after AD of THP-treated sludge and WAS, the mSMA showed that all analysed samples presented strong inhibition on methanogenesis due to the presence of TAN and associated free ammonia nitrogen (FAN). In specific methanogenic activities (SMAs) tests with incremental concentration of TAN/FAN and melanoidins, TAN/FAN induced strong inhibition on methanogens, halving the SMA at around 2.5 gTAN/L and 100 mgFAN/L. Conversely, melanoidins did not show inhibition on the methanogens. Our present results revealed that when applying THP-AD in full-scale, the increase in TAN/FAN remarkably had a greater impact on AD than the formation of melanoidins.

Aggregation and construction mechanisms of microbial extracellular polymeric substances with the presence of different multivalent cations: Molecular dynamic simulation and experimental verification

Interactions between cations and extracellular polymeric substances (EPS) play an important role in the formation of microbial aggregates and have key effects on the physical properties of activated sludge across wastewater and sludge treatment process. Here, a molecular model of EPS cluster in activated sludge was constructed and simulated by molecular dynamics (MD) to probe the structural properties of EPS and the interaction between EPS and prevalent multivalent cations (Ca²⁺, Mg²⁺, Al³⁺). Then the predicted changes in physical properties were validated against the dynamic light scattering, XAD resin fractionation and rheology test. The binding dynamics and interactions mechanisms between multivalent cations and EPS functional groups were further investigated using MD in combination with spectroscopic analysis. Results suggest that biopolymers are originally aggregated by electrostatic and intermolecular interactions forming dynamic clusters with negatively charged surface functional groups, which induced electrostatic repulsion preventing further agglomeration of biopolymer clusters. In the presence of multivalent cations, surface polar functional groups in biopolymers are connected, causing the rearrangement of EPS molecular conformation that forms larger and denser agglomerates. Reduced solvent accessible surface area, enhanced hydrophobicity, and increased binding free energy lead to a strong gel-like network of EPS. Ca²⁺ and Al³⁺ predominantly interact with functional groups in polysaccharides, promoting agglomeration of macromolecules. In contrast, Mg²⁺ and Al³⁺ disrupted the secondary structure of proteins, exposing hydrophobic interaction sites. Al³⁺ can better agglomerate biopolymers with its higher positive charge and shorter coordination distance as compared to Ca²⁺ and Mg²⁺, but compromised by the effect of hydration. This work offers a novel approach to explore the construction and molecular aggregation of EPS, enriching the theoretical basis for optimization of wastewater and sludge treatment.

Biotransformation of sulfamonomethoxine in a granular sludge system: Pathways and mechanisms

The biotransformation of sulfamonomethoxine (SMM) was studied in an aerobic granular sludge (AGS) system to understand the role of sorption by microbial cells and extracellular polymeric substances (EPS) and the role of functional microbe/enzyme biodegradation. Biodegradation played a more important role than adsorption, while microbial cells covered with tightly bound EPS (TB-EPS) showed higher adsorption capacity than microbial cells themselves or microbial cells covered with both loosely bound EPS (LB-EPS) and TB-EPS. The binding tests between EPS and SMM and the spectroscopic analyses (3D-EEM, UV-Vis, and FTIR) were performed to obtain more information about the adsorption process. The data showed that SMM could interact with EPS by combining with aromatic protein compounds, fulvic acid-like substances, protein amide II, and nucleic acids. Batch tests with various substances showed that SMM removal rates were in an order of NH₂OH (60.43 ± 2.21 μg/g SS) > NH₄Cl (52.96 ± 0.30 μg/g SS) > NaNO₃ (31.88 ± 1.20 μg/g SS) > NaNO₂ (21.80 ± 0.42 μg/g SS). Hydroxylamine and hydroxylamine oxidoreductase (HAO) favored SMM biotransformation and the hydroxylamine-mediated biotransformation of SMM was more effective than others. In addition, both ammonia monooxygenase (AMO) and CYP450 were able to co-metabolize SMM. Analysis of UPLC-QTOF-MS indicated the biotransformation mechanisms, revealing that acetylation of arylamine, glucuronidation of sulfonamide, deamination, SO₂ extrusion, and δ cleavage were the five major transformation pathways. The detection of TP202 in the hydroxylamine-fed Group C indicated a new biotransformation pathway through HAO. This study contributes to a better understanding of the biotransformation of SMM.

High propensity of membrane fouling and the underlying mechanisms in a membrane bioreactor during occurrence of sludge bulking

While sludge bulking often occurring in activated sludge processes generally leads to serious membrane fouling in membrane bioreactors (MBR), the underlying causes are still unclear. In this study, fouling behaviors of a MBR operated at stages of normal and sludge bulking were compared, and the fouling mechanisms of the different behaviors were explored. It was found that, the MBR could be stably operated in normal stage without membrane cleaning for about 60 days, whereas, daily membrane cleaning had to be carried out when operated in sludge bulking stage. The bulking sludge possessed a rather high specific filtration resistance (SFR) of about 1.36×10¹⁴ m·kg^-1, which is over 5.33 times than that of the normal sludge. A series of characterizations demonstrated that the bulking sludge had rather lower dewaterability, smaller particle size, higher fractal dimension, higher viscosity, abundant filamentous bacteria and different functional groups of extracellular polymer sustains (EPS). It was suggested that microbial community transition was responsible for the occurrence of sludge bulking, further affecting membrane fouling. Based on these characterizations, it was reported that adhesion propensity (indicated by the thermodynamic interaction) of the bulking sludge to the membrane surface is about 3.6 times than that of the normal sludge. It was proposed that, extra force should be provided to offset a chemical potential gap caused by foulant layer structure transition during sludge bulking in order to sustain filtration of the bulking sludge, resulting in extremely high SFR. This study offered deep thermodynamic mechanisms of MBR fouling during occurrence of sludge bulking.

Impact of hydrophilic functional groups of macromolecular organic fractions on food waste digestate dewaterability

：Deterioration of dewaterability is one of challenges faced by anaerobic digestion (AD) of food waste (FW). The underlying mechanism of the effect of AD on digestate dewaterability remains unclear. Thus, the effect of hydrophilic functional groups of macromolecular organic on FW digestate dewaterability in different stages during AD was studied. Results showed that the dewaterability first improved at the acidification stage, and then worsened at the gasification and stabilization stages. The correlations between normalized capillary suction time (NCST), bound moisture (BM) and extracellular protein (extra-PN) were significant (R = 0.736, p < 0.05, R = 0.637, p < 0.05). Macromolecular extra-PN that enhance the bonding between organic fractions and moisture via peptide bonds. In addition, carbonyl, phenolic and amide groups increased after AD, resulting in the enhancement of the digestate hydrophilicity. Furthermore, the evolution of microbial community during AD resulting in the wrapping of BM by increased organic fractions. Therefore, higher organic fractions with hydrophilic functional groups in digestate strongly hinder moisture removal. The findings obtained deepen our understanding of hydrophilic functional groups of macromolecular organic affecting FW digestate dewaterability and provide strong supports to treatment and disposal of FW digestate.