Extracellular Polymeric Substances Fractions Research Articles

Quantitative image analysis for assessing extracellular polymeric substances in activated sludge under atrazine exposure

Extracellular polymeric substances (EPS) play a vital role in biological wastewater treatment systems. This study investigates the impact of herbicide atrazine (ATZ) on the overall performance, EPS yield, composition, and sludge morphology in an activated sludge (AS) system operated in a sequencing batch reactor (SBR). Since conventional methods for analyzing EPS are time-consuming and releases residues, a new approach was developed in this work to evaluate the EPS fractions and components, based on the morphological characterization of the biomass using quantitative image analysis (QIA) technique coupled with multivariate statistics.Results showed that exposure to ATZ inhibit biomass activity in terms of organic matter (COD) and nitrogen removal. Moreover, both tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) increased under ATZ, indicating that microorganisms release EPS as a defense mechanism against environmental changes. The PN/PS ratio also increases, indicating likely increased hydrophobicity in ATZ phases. Furthermore, ATZ phases exhibit a predominance of large aggregates compared to intermediate and small ones, indicating a change in aggregate morphological structure associated with EPS production. The new approach using QIA coupled with partial least squares (PLS) modeling provides accurate predictions of EPS content. The increase in TB-EPS is closely related to the rise of large aggregates in phases exposed to higher ATZ concentrations. The PLS models demonstrate high accuracy for EPS prediction (coefficients of determination, R2 above 0.86), showcasing the feasibility of using QIA for EPS assessment in AS systems. This approach offers significant potential for regular process monitoring and management, providing a more environmentally friendly methodology by eliminating the need for chemical usage.

Molecular spectra and docking simulations investigated the binding mechanisms of tetracycline onto E. coli extracellular polymeric substances

Extracellular polymeric substances (EPS), which were an important fraction of natural organic matter (NOM), played an important role in various environmental processes. However, the heterogeneity, complexity, and dynamics of EPS make their interactions with antibiotics elusive. Using advanced multispectral technology, this study examined how EPS interacts with different concentrations of tetracycline (TC) in the soil system. Our results demonstrated that protein-like (C1), fulvic-like (C2), and humic-like (C3) fractions were identified from EPS. Two-dimensional synchronous correlation spectroscopy (2D-SF-COS) indicated that the protein-like fraction gave faster responses than the fulvic-like fraction during the TC binding process. The sequence of structural changes in EPS due to TC binding was revealed by two-dimensional Fourier Transformation Infrared correlation spectroscopy (2D-FTIR-COS) as follows: 1550 > 1660 > 1395 > 1240 > 1087 cm−1. It is noteworthy that the sensitivity of the amide group to TC has been preserved, with its intensity gradually increasing to become the primary binding site for TC. The integration of hetero-2DCOS maps with moving window 2D correlation spectroscopy (MW2DCOS) provided a unique insight into understanding the correlation between EPS fractions and functional groups during the TC binding process. Moreover, molecular docking (MD) discovered that the extracellular proteins would provide plenty of binding sites with TC through salt bridges, hydrogen bonds, and π-π base-stacking forces. With these results, systematic investigations of the dynamic changes in EPS components under different concentrations of antibiotic exposure demonstrated the advanced capabilities of multispectral technology in examining intricate interactions with EPS in the soil environment.

The water-soluble fraction of extracellular polymeric substances from a resource recovery demonstration plant: characterization and potential application as an adhesive.

Currently, there is a growing interest in transforming wastewater treatment plants (WWTPs) into resource recovery plants. Microorganisms in aerobic granular sludge produce extracellular polymeric substances (EPS), which are considered sustainable resources to be extracted and can be used in diverse applications. Exploring applications in other high-value materials, such as adhesives, will not only enhance the valorization potential of the EPS but also promote resource recovery. This study aimed to characterize a water-soluble fraction extracted from the EPS collected at the demonstration plant in the Netherlands based on its chemical composition (amino acids, sugar, and fatty acids) and propose a proof-of-concept for its use as an adhesive. This fraction comprises a mixture of biomolecules, such as proteins (26.6 ± 0.3%), sugars (21.8 ± 0.2%), and fatty acids (0.9%). The water-soluble fraction exhibited shear strength reaching 36-51 kPa across a pH range of 2-10 without additional chemical treatment, suggesting a potential application as an adhesive. The findings from this study provide insights into the concept of resource recovery and the valorization of excess sludge at WWTPs.

Aerobic granular sludge for complex heavy metal-containing wastewater treatment: characterization, performance, and mechanisms analysis.

Complex heavy metal (HM)-containing wastewater discharges pose substantial risks to global water ecosystems and human health. Aerobic granular sludge (AGS) has attracted increased attention as an efficient and low-cost adsorbent in HM-containing wastewater treatment. Therefore, this study systematically evaluates the effect of Cu(II), Ni(II), and Cr(III) addition on the characteristics, performance and mechanism of AGS in complex HM-containing wastewater treatment process by means of fourier transform infrared spectroscopy, inductively coupled plasma spectrocopcy, confocal laser scanning microscopy, extracellular polymeric substances (EPS) fractions detection and scanning electron microscope-energy dispersive X-ray. The results showed that AGS efficiently eliminated Cu(II), Ni(II), and Cr(III) by the orchestrated mechanisms of ion exchange, three-layer EPS adsorption [soluble microbial products EPS (SMP-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS)], and inner-sphere adsorption; notably, almost 100% of Ni(II) was removed. Three-layer EPS adsorption was the dominant mechanism through which the HM were removed, followed by ion exchange and inner-sphere adsorption. SMP-EPS and TB-EPS were identified as the key EPS fractions for adsorbing Cr(III) and Cu(II), respectively, while Ni(II) was adsorbed evenly on SMP-EPS, TB-EPS, and LB-EPS. Moreover, the rates at which the complex HM penetrated into the granule interior and their affinity for EPS followed the order Cu(II) > Ni(II) > Cr(III). Ultimately, addition of complex HM stimulated microorganisms to excrete massive phosphodiesterases (PDEs), leading to a pronounced decrease in cyclic diguanylate (c-di-GMP) levels, which subsequently suppressed EPS secretion due to the direct linkage between c-di-GMP and EPS. This study unveils the adaptability and removal mechanism of AGS in the treatment of complex HM-containing wastewater, which is expected to provide novel insights for addressing the challenges posed by intricate real wastewater scenarios.

Anionic extracellular polymeric substances extracted from seawater-adapted aerobic granular sludge.

Anionic polymers, such as heparin, have been widely applied in the chemical and medical fields, particularly for binding proteins (e.g., fibroblast growth factor 2 (FGF-2) and histones). However, the current animal-based production of heparin brings great risks, including resource shortages and product contamination. Recently, anionic compounds, nonulosonic acids (NulOs), and sulfated glycoconjugates were discovered in the extracellular polymeric substances (EPS) of aerobic granular sludge (AGS). Given the prevalence of anionic polymers, in marine biofilms, it was hypothesized that the EPS from AGS grown under seawater condition could serve as a raw material for producing the alternatives to heparin. This study aimed to isolate and enrich the anionic fractions of EPS and evaluate their potential application in the chemical and medical fields. The AGS was grown in a lab-scale reactor fed with acetate, under the seawater condition (35 g/L sea salt). The EPS was extracted with an alkaline solution at 80 °C and fractionated by size exclusion chromatography. Its protein binding capacity was evaluated by native gel electrophoresis. It was found that the two highest molecular weight fractions (438- > 14,320 kDa) were enriched with NulO and sulfate-containing glycoconjugates. The enriched fractions can strongly bind the two histones involved in sepsis and a model protein used for purification by heparin-column. These findings demonstrated possibilities for the application of the extracted EPS and open up a novel strategy for resource recovery. KEY POINTS: • High MW EPS from seawater-adapted AGS are dominant with sulfated groups and NulOs • Fifty-eight percent of the EPS is high MW of 68-14,320 kDa • EPS and its fractions can bind histones and fibroblast growth factor 2.

Galactosamine and mannosamine are integral parts of bacterial and fungal extracellular polymeric substances.

Extracellular polymeric substances (EPS) are produced by microorganisms and interact to form a complex matrix called biofilm. In soils, EPS are important contributors to the microbial necromass and, thus, to soil organic carbon (SOC). Amino sugars (AS) are used as indicators for microbial necromass in soil, although the origin of galactosamine and mannosamine is largely unknown. However, indications exist that they are part of EPS. In this study, two bacteria and two fungi were grown in starch medium either with or without a quartz matrix to induce EPS production. Each culture was separated in two fractions: one that directly underwent AS extraction (containing AS from both biomass and EPS), and another that first had EPS extracted, followed then by AS determination (exclusively containing AS from EPS). We did not observe a general effect of the quartz matrix neither of microbial type on AS production. The quantified amounts of galactosamine and mannosamine in the EPS fraction represented on average 100% of the total amounts of these two AS quantified in cell cultures, revealing they are integral parts of the biofilm. In contrast, muramic acid and glucosamine were also quantified in the EPS, but with much lower contribution rates to total AS production, of 18% and 33%, respectively, indicating they are not necessarily part of EPS. Our results allow a meaningful ecological interpretation of mannosamine and galactosamine data in the future as indicators of microbial EPS, and also attract interest of future studies to investigate the role of EPS to SOC and its dynamics.

Analysis of the Effects of Surfactants on Extracellular Polymeric Substances

Reservoirs after chemical flooding usually have residual chemicals, which can affect the driving effect of subsequent microbial drives. Among them, the effect of surfactants on the metabolites of oil-recovering bacteria is the most obvious. Therefore, this paper investigates the influence mechanism of sodium dodecyl sulfate (SDS) on the nature and structure of Extracellular Polymeric Substances (EPS) produced by metabolism of Enterobacter cloacae, through a variety of characterization to analysis the components and structure of EPS under SDS stress. The results showed that Enterobacter cloacae was identified as a glycolipid-producing strain, the main components of EPS were polysaccharides and proteins. The polysaccharide composition (%: w/w) was glucosamine, 37.2; glucose, 31.5; rhamnose, 26.3; xylose, 1.7; and unidentified sugar, 3.3; and the main component of proteins was polyglutamic acid. EPS under the stress of SDS showed an increase in the content of functional groups such as -C=O and -COOH and an increase in the cellular particle size, and production of EPS increased by 10.69 × 103 mg/L when the SDS concentration was 2.5 × 102 mg/L; 3D-EEM results showed that the components of all three types of EPS The 3D-EEM results showed that all three types of EPS fractions contained tryptophan and protein-like substances, humic acid-like substances were only distributed in the solubilized extracellular polymers (SL-EPS), and aromatic proteins were only present in the loosely bound type (LB-EPS) and tightly bound type (TB-EPS). In addition, the peaks representing humic-like substances showed a blue shift, indicating that SDS had the greatest effect on SL-EPS. This study provides a guidance for refining the mechanism of strain EPS response to reservoir residual surfactant SDS, and provides a more comprehensive and in-depth understanding of surfactant-protein interactions.

Fabrication of environmentally safe antifouling coatings using nano-MnO2/cellulose nanofiber composite with BED/GMA irradiated by electron beam

Marine biofouling, undesirable growth of organisms on submerged surfaces, poses significant challenges in various industries and marine applications. The development of environmentally safe antifouling coatings employing nano-MnO2/cellulose nanofiber (CNF) composite with bisphenol A epoxy diacrylate/glycidyl methacrylate (BED/GMA) irradiated by electron beam (T1) has been achieved in the current work. The physico-chemical characteristics of the fabricated coatings have been studied using Fourier transforms infrared spectroscopy, scanning electron microscope, water contact angle, and X-ray diffraction. The efficacy of T1 formulation and pure BED/GMA polymer (T2) in inhibiting biofouling formation was investigated in seawater of Alexandria Eastern Harbour by examining biofilm development morphologically and biochemically. In addition, regular analyses of seawater physicochemical parameters were conducted monthly throughout study. Results provide valuable information on coating performance as well as the complex interactions between coatings, biofilms, and environmental factors. The T1 formulation exhibited strong anti-fouling and anticorrosion properties over 2 months. However, after four months of immersion, all coated steel surfaces, including T1, T2, and T0, were heavily covered with macro-fouling, including tubeworms, barnacles, and algae. Biochemical analysis of extracellular polymeric substances (EPS) showed statistically significant variations in carbohydrates content between the coated surfaces. The T1 formulation showed decreased protein and carbohydrate content in EPS fractions after 14 days of immersion indicating less biofouling. Moreover, elemental analysis showed that carbon, oxygen, and iron were the predominant elements in the biofilm. Other elements such as sodium, silicon, chloride, and calcium were in lower concentrations. T2 and T0 surfaces revealed higher calcium levels and the appearance of sulphur peaks if compared with T1 surface. Diatoms and bacteria were detected on T1, T2, and T0 surfaces. The observed warming of seawater and nutrient-rich conditions were found to promote the growth of fouling organisms, emphasizing the importance of considering environmental factors in biofouling management strategies.

Production and composition of extracellular polymeric substances by a unicellular strain and natural colonies of Microcystis: Impact of salinity and nutrient stress.

The transfer of toxic cyanobacterial Microcystis blooms from freshwater to estuaries constitutes a serious environmental problem worldwide that is expected to expand in scale and intensity with anthropogenic and climate change. The formation and maintenance of Microcystis in colonial form is conditioned to the presence of extracellular polymeric substances (EPS). In this study, we attempted to better understand how the mucilaginous colonial form of Microcystis evolves under environmental stress conditions. In particular, we studied and compared the production and the composition of EPS fractions (attached and free) from natural colonies of a Microcystis bloom and from a unicellular M. aeruginosa strain under salinity and nutrient stress (representing a land-sea continuum). Our results highlighted a greater production of EPS from the natural colonies of Microcystis than the unicellular one under nutrient and combined stress conditions dominated by the attached form. In comparison to the unicellular Microcystis, EPS produced by the colonial form were characterized by high molecular weight polysaccharides which were enriched in uronic acids and hexosamines, notably for the free fraction in response to increased salinities. This complex extracellular matrix gives the cells the ability to aggregate and allows the colonial cyanobacterial population to cope with osmotic shock.

Extracellular polymeric substances sustain photoreduction of Cr(VI) by Shewanella oneidensis-CdS biohybrid system.

Photosensitized biohybrid system (PBS) enables bacteria to exploit light energy harvested by semiconductors for rapid pollutants transformation, possessing a promising future for water reclamation. Maintaining a biocompatible environment under photocatalytic conditions is the key to developing PBS-based treatment technologies. Natural microbial cells are surrounded by extracellular polymeric substances (EPS) that either be tightly bound to the cell wall (i.e., tightly bound EPS, tbEPS) or loosely associated with cell surface (i.e., loosely bound EPS, lbEPS), which provide protection from unfavorable environment. We hypothesized that providing EPS fractions can enhance bacterial viability under adverse environment created by photocatalytic reactions. We constructed a model PBS consisting of Shewanella oneidensis and CdS using Cr(VI) as the target pollutant. Results showed complete removal of 25mg/L Cr(VI) within 90min without an electron donor, which may mainly rely on the synergistic effect of CdS and bacteria on photoelectron transfer. Long-term cycling experiment of pristine PBS and PBS with extra EPS fractions (including lbEPS and tbEPS) for Cr(VI) treatment showed that PBS with extra lbEPS achieved efficient Cr(VI) removal within five consecutive batch treatment cycles, compared to the three cycles both in pristine PBS and PBS with tbEPS. After addition of lbEPS, the accumulation of reactive oxygen species (ROS) was greatly reduced via the EPS-capping effect and quenching effect, and the toxic metal internalization potential was lowered by complexation with Cd and Cr, resulting in enhanced bacterial viability during photocatalysis. This facile and efficient cytoprotective method helps the rational design of PBS for environmental remediation.

Sialylation and Sulfation of Anionic Glycoconjugates Are Common in the Extracellular Polymeric Substances of Both Aerobic and Anaerobic Granular Sludges.

Anaerobic and aerobic granular sludge processes are widely applied in wastewater treatment. In these systems, microorganisms grow in dense aggregates due to the production of extracellular polymeric substances (EPS). This study investigates the sialylation and sulfation of anionic glyconconjugates in anaerobic and aerobic granular sludges collected from full-scale wastewater treatment processes. Size exclusion chromatography revealed a wide molecular weight distribution (3.5 to >5500 kDa) of the alkaline-extracted EPS. The high-molecular weight fraction (>5500 kDa), comprising 16.9-27.4% of EPS, was dominant with glycoconjugates. Mass spectrometry analysis and quantification assays identified nonulosonic acids (NulOs, e.g., bacterial sialic acids) and sulfated groups contributing to the negative charge in all EPS fractions. NulOs were predominantly present in the high-molecular weight fraction (47.2-84.3% of all detected NulOs), while sulfated glycoconjugates were distributed across the molecular weight fractions. Microorganisms, closely related to genera found in the granular sludge communities, contained genes responsible for NulO and sulfate group synthesis or transfer. The similar distribution patterns of sialylation and sulfation of the anionic glycoconjugates in the EPS samples indicate that these two glycoconjugate modifications commonly occur in the EPS of aerobic and anaerobic granular sludges.

The mechanism of extracellular polymeric substances in the formation of activated sludge flocs

In this study, activated sludge (AS) presented high aggregation ability of 56.9% to form flocs. To elucidate the effects of extracellular polymeric substances (EPS) on the AS flocs formation, four EPS fractions, including soluble EPS (S-EPS), loosely bound EPS (LB-EPS), ionic tightly bound EPS (ionic TB-EPS) and hydrophobic tightly bound EPS (hydrophobic TB-EPS), were extracted and characterized. The ionic TB-EPS were the largest fraction, accounting for 51.3% of the total EPS. By extracting EPS fractions, it was shown that ionic TB-EPS followed by hydrophobic TB-EPS played positive contribution to the formation of AS flocs, while both S-EPS and LB-EPS had negative effects. Furthermore, chemical reagents (Urea, SDS and EDTA) assays, zeta potential and spectroscopic assays were conducted to explore the role of hydrogen bonds, electrostatic interaction and hydrophobic interaction in the formation of AS flocs. The result showed that ionic TB-EPS contained sufficient cation-binding sites, such as -OH and CO-O- groups, and promoted AS aggregation through ion bridging. Hydrophobic TB-EPS contained hydrophobic groups and promoted AS aggregation through hydrophobic action. A high proportion of uronic acids resulted in high surface negative charge, which might be the reason that LB-EPS and S-EPS inhibited AS aggregation through electrostatic repulsion. From the perspective of molecule structure, the proteins in ionic TB-EPS had a loose structure, which fully exposed the inner cation-binding sites. This might be the critical reason why ion bridging acted as the main force for the formation of AS flocs. This study provided a new sight for the extraction of EPS fractions and expanded the understanding of EPS in the formation of AS flocs.

Characterization of benthic biofilms in mangrove sediments and their variation in response to nutrients and contaminants.

Diatom-dominated biofilms and associated extracellular polymeric substances (EPS) may adapt to the stress of long-term exposure to nutrients and anthropogenic contaminants. However, such interactions in contaminated mangrove sediments have rarely been reported. Based on the in situ characterization of biofilm components and environmental factors, the present study aimed to explore the key factors involved in shaping sediment biofilms through correlational and multivariate analyses. The pennate diatom Navicula is the core taxon that plays a crucial role in balancing the abundance of Nitzschia and Cyclotella, and is the main producer of bound-polysaccharides. The taxa composition shifts in a high N/P matrix, with the populations of pennate diatoms increasing but that of centric diatoms decreasing. High nutrient concentrations yield more number of diatoms and elevated levels of EPS. Bacteria are the main consumers of EPS and tend to be more symbiotic with Nitzschia than the other two diatom taxa. Some bound-polysaccharides dominated by arabinose and glucose units are transformed into the colloidal fraction, whereas other conservative ones serve as structural materials in concert with the bound-proteins. The planktonic phase of Cyclotella breaks down the structural EPS secreted by pennate diatoms in a process that directly affects the dynamic renewal of benthic biofilms. Most heavy metals as well as bisphenol A inhibit the abundance of bacteria and diatoms but enhance most EPS fractions except bound-polysaccharides. The response of structural EPS to specific contaminants varies, exhibiting increases in Co and Ni levels but decreases in nonylphenol and methylparaben levels. The present study improves our understanding of the microbial carbon loop of benthic biofilms in mangrove ecosystems under stress by nutrients and mixed contaminants.

Effect of biomass retention time on performance and fouling of a stirred membrane photobioreactor

Co-culture of microalgae-activated sludge has the potential to purify wastewater while reduce energy demand from aeration. In this work, a mechanically stirred membrane photobioreactor (stirred-MPBR) was used to evaluate the impact of the biomass retention time (BRT) on the treatment performance and membrane fouling. Results showed that stirred-MPBR was affected by BRT during treating domestic wastewater at a flux of 16.5 L m−2 h−1. The highest productivity was attained at BRT 7d (102 mg L−1 d−1), followed by BRT 10d (86 mg L−1 d−1), BRT 5d (85 mg L−1 d−1), and BRT 3d (83 mg L−1 d−1). Statistical analysis results showed that BRT 7d had a higher COD removal rate than BRT 10d, however, there is no difference in total nitrogen removal rate. The highest TP removal occurred when the biomass operated at BRT as short as 3d. Reduced BRTs caused a change in the microalgae-activated sludge biomass fraction that encouraged nitrification activity while simultaneously contributing to a higher fouling rate. The bound protein concentrations dropped from 31.35 mg L−1 (BRT 10d) to 10.67 mg L−1 (BRT 3d), while soluble polysaccharides increased from 0.99 to 1.82 mg L−1, respectively. The concentrations of extracellular polymeric substance fractions were significantly altered, which decreased the mean floc size and contributed to the escalating fouling propensity. At the optimum BRT of 7d, the stirred-MPBR showed sufficient access to light and nutrients exchange for mutualistic interactions between the microalgae and activated sludge.

Enrichment and application of extracellular nonulosonic acids containing polymers of Accumulibacter.

Pseudaminic and legionaminic acids are a subgroup of nonulosonic acids (NulOs) unique to bacterial species. There is a lack of advances in the study of these NulOs due to their complex synthesis and production. Recently, it was seen that "Candidatus Accumulibacter" can produce Pse or Leg analogues as part of its extracellular polymeric substances (EPS). In order to employ a "Ca. Accumulibacter" enrichment as production platform for bacterial sialic acids, it is necessary to determine which fractions of the EPS of "Ca. Accumulibacter" contain NulOs and how to enrich and/or isolate them. We extracted the EPS from granules enriched with "Ca. Accumulibcater" and used size-exclusion chromatography (SEC) to separate them into different molecular weight (MW) fractions. This separation resulted in two high molecular weight (> 5500kDa) fractions dominated by polysaccharides, with a NulO content up to 4 times higher than the extracted EPS. This suggests that NulOs in "Ca. Accumulibacter" are likely located in high molecular weight polysaccharides. Additionally, it was seen that the extracted EPS and the NulO-rich fractions can bind and neutralize histones. This opens the possibility of EPS and NulO-rich fractions as potential source for sepsis treatment drugs. KEY POINTS: • NulOs in "Ca. Accumulibacter" are likely located in high MW polysaccharides • SEC allows to obtain high MW polysaccharide-rich fractions enriched with NulOs • EPS and the NulOs-rich fractions are a potential source for sepsis treatment drugs.

Potential causes of partial-denitrification (PD) granular sludge breakdown under high nitrate loading rates

The granule instability has been frequently reported during the operation of high loading rates. While, there no research was performed on the recently developed anoxic partial-denitrification (PD) granules, a novel pathway in producing nitrite from nitrate for anammox process. Herein, this work, for the first time, investigated the influence of nitrate loading rates on the instability of PD granules and identified the key causes. Two lab-scale sequencing batch reactors (SBRs) were operated with nitrate loading rates (NLR) increased from 0.48 to 3.84 kg N/m3/d (R1, 8 cycles/d), and 0.96 to 7.68 kg N/m3/d (R2, 16 cycles/d) by gradually elevating the influent nitrate concentration. Results showed that nitrite production rates increased with the NLRs, with a maximal value of 5.26 kg N/m3/d obtained. However, the compact regular PD granules were not stable and broke down when NLR was above 3.84 kg N/m3/d, which resulted in serious sludge washing out from SBR. The high NLRs led to the extracellular polymeric substances (EPS) transformation in terms of its composition and structure, which the protein content in the EPS and the tightly bound EPS (T-EPS) fraction was significantly decreased, this was supposed to be the major reason causing the breakdown of PD granules. Besides, it was found the PD granule in R2 was more deteriorated than that in R1 under the same high NLR, suggesting the short starvation (idle) times in SBR cycle was likely another reason impairing the stability of PD granules. Overall, this research provides useful information in development of granule-based PD systems and sheds light on achieving high-rate nitrite production in SBR with great stability.

Enhanced paper sludge dewatering and in-depth mechanism by oxalic acid/Fe2+/persulfate process

As a typical advanced oxidation process, Fe2+-persulfate (PDS) oxidation technology has been widely and efficiently reported for enhancing sludge dewaterability. However, higher dosage of Fe2+ must be added, which will restrain the oxidation efficiency of Fe2+-PDS process. In this work, the oxalic acid (OA)/Fe2+-PDS process was studied to improve paper sludge dewatering. With the OA dosage of 6 μmol (g total solid (TS))−1, Fe2+ dosage of 0.3 mmol (g TS)−1, and PDS dosage of 0.6 mmol (g TS)−1, sludge dewaterability was improved more efficiently. The specific resistance to filtration and water content of sludge cake were decreased by 70.7% and 8.0%, respectively. In comparison with Fe2+-PDS process, the viscosities of sludge suspension and supernatant were further reduced by 3.73% and 51.77%, respectively, and the contents of extracellular polymeric substances fractions were increased. The improved sludge dewaterability in OA/Fe2+-PDS process was mainly contributed by the synergistic effect of oxidative disintegration by free radicals and flocs re-flocculation, the contributions of which were the orders: metal cations > sulfate radical > hydroxyl radical. OA enhanced the efficient disintegration of sludge flocs, released more bound water, generated more Fe3+-oxalate complexes, and finally increased the sludge particle size significantly, forming a larger aggregation and obvious cracks. Additionally, the stabilization of several heavy metals was improved due to the chelating capacity of OA. These works will provide a novel approach for sludge dewatering in the PDS oxidation process.

The Roles of Different Fractions in Freshwater Biofilms in the Photodegradation of Methyl Orange and Bisphenol A in Aqueous Solutions.

Freshwater biofilms play an important role in the migration and transformation of organic pollutants, especially under illumination conditions. Nonetheless, the roles of variable fractions in freshwater biofilms, e.g., extracellular polymeric substances (EPS), microbial cells and original biofilms, in promoting the photodegradation of trace organic pollutants remain largely unclear. In this study, two contaminants, i.e., methyl orange (MO) and bisphenol A (BPA), were selected, and the roles of different fractions in freshwater biofilms in their photodegradation performances were investigated. After dosing 696 mg/L SS biofilm harvested from an effluent-receiving river, the direct photodegradation rate of MO and BPA was increased 8.7 times and 5.6 times, respectively. River biofilm EPS contained more aromatic fractions, chromogenic groups and conjugated structures than biofilm harvested from a less eutrophic pond, which might be responsible for the enhanced photodegradation process. The quenching experiments suggested that when EPS fractions derived from river biofilm were dosed, 3EPS* was the major reactive oxygen species during the photodegradation of MO and BPA. Meanwhile, for EPS derived from the pond biofilm, ·OH/1O2 was predominantly responsible for the enhanced photodegradation. Batch experimental results suggested that the cells and EPS in river biofilms could collaboratively interact with each other to enhance the preservation of reactive species and protection of microbes, thus facilitating the photoactivity of biofilms. Our results might suggest that biofilms generated from eutrophic waterbodies, such as effluent-receiving rivers, could play a more important role in the photodegradation processes of contaminants.

Changes of the physicochemical properties of extracellular polymeric substances (EPS) from Microcystis aeruginosa in response to microplastics

Microplastics (MPs) are ubiquitous in aquatic ecosystems and can significantly influence the growth, aggregation and functions of phytoplankton biomass. However, variations in the extracellular polymeric substances (EPS) of phytoplankton in terms of compositions and structures in response to MPs were still not reported. In this study, EPS matrix of Microsystis aeruginosa was applied and fractionated into loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) fractions, with the time-dependent changes in response to different concentrations (10, 100 and 500 mg/L) of MPs being explored via using the fluorescence excitation emission matrix coupled with parallel factor (EEM-PARAFAC) and two-dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR-COS) analysis. Results showed that 500 mg/L of MP concentration significantly inhibited Microcystis growth by 30.5% but enhanced EPS secretion. In addition, organic composition in LB-EPS and TB-EPS varied differently in response to increased MP exposure, as the ratio of polysaccharide/protein increased in the TB-EPS but decreased in LB-EPS. Further analysis revealed obvious heterogeneities in organic component variations in response to MPs, as the C–O functional groups and glycosidic bonds in the TB-EPS preferentially responded, which lead to the domination of polysaccharides and humus substances; while the carbonyl, carboxyl and amino functional groups in the LB-EPS exhibited a preferential response, which caused the enhanced percentage of the tryptophan-like proteins. In addition to organic compositions, the aromaticity, hydrophobicity and humification in the LB-EPS fraction increased with enhanced MP exposure, which, as a result, may influence the ecotoxicological risk of MPs. Therefore, Microcystis can dynamically adjust not only the EPS contents but also the compositions in response to MPs exposure. The results can improve our understanding on the eco-physiological impact of phytoplankton-MP interaction in aquatic environment, and indicate that the dose-dependent and long-term effects of MPs on phytoplankton should be considered in future study.

Biofouling of hollow fiber ultrafiltration membranes: A novel multiphase CFD – Porous - CES model and experimental study

The present study focuses on developing a multiphase CFD – porous- CES model to investigate the effect of biofouling in a membrane reactor. An experimental setup with an ultrafiltration (UF) hollow fiber (HF) membrane was constructed to understand the deposition and development of the cake layer due to biofouling. The CFD – porous sub-models were used to study the effect of hydrodynamics on fouling. While the CES (combined extracellular polymeric substances (EPS) and soluble microbial product (SMP)) sub-model incorporated the effect of EPS and SMP on the cake layer formation. The EPS and SMP fractions constitute a significant portion of the microbial mass and are critical in analyzing the biofouling in UF and microfiltration (MF) membranes. The developed membrane fouling model was validated with both literature experimental results and experimental observations from the laboratory-scale UF-HF membrane setup. It was observed that the effect of cake deposition on transmembrane pressure (TMP) and permeate flux was 1.5% higher for experimental set 2 (synthetic wastewater with sludge seeding) as compared to experimental set 1 (synthetic wastewater with yeast sludge). Also, the maximum percentage error between the experimental and simulation values was ±6.2%, thus validating the model. The validated model was then used to investigate the sensitivity of the CES sub-model by comparing it with the sectional resistance model (a commonly used model in literature for predicting membrane fouling). It was observed that the sectional resistance model underpredicted the mass of cake deposited by 13% and overpredicted the limiting flux by 4%. The limiting flux has a significant effect while designing a membrane system, and its accurate prediction helps prevent premature fouling in UF membranes. Hence, the preceding results suggest the importance of accounting for the influence of EPS and SMP on the cake layer formation and biofouling and the relevance of the current study.