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[Display omitted] • Variable load and intermittent facilitate low maintenance operation of the GDM. • c-TEP in raw water closely relates to biofouling layer formation. • Key genera in Patescibacteria are closely related to EPS degradation. • Comammox Nitrospira is a key species for achieving efficient nitrification. • Variable load GDM allows for high turbidity impacts with only sludge discharge. The gravity-driven membrane (GDM) systems offer a promising solution for decentralized drinking water supply due to its low maintenance and energy consumption. However, research on the practical application of GDM under variable hydrostatic pressure (variable load) and intermittent operation conditions, particularly in response to high-turbidity water, remains limited. This study investigates the long-term performance and characteristics of the biofouling layer of GDM under ultra-low variable hydrostatic pressure (20–60 mbar) and intermittent operation (8–12 h) conditions in practical decentralized water supply. The results indicate that the membrane flux (1.9–6.0 L∙m−2∙h−1, LMH) remained relatively stable despite variations in gravity-driven pressure (ΔP). Long-term operation of GDM can stably remove turbidity and potential pathogens from raw water. The total protein/polysaccharide ratios of extracellular polymeric substances (EPS) in the biofouling layer were below 0.50, reducing contaminant adhesion on the membrane surface. The 0.2–0.4 μm transparent exopolymer particles (TEP) fraction might be crucial for biofouling layer formation. The key species, belong to Proteobacteria and Patescibacteria , significantly alleviated membrane fouling by degrading polysaccharide and proteins in biofouling layer. Comammox Nitrospira were significantly enriched, contributing to efficient nitrification. GDM with variable load maintained a stable flux of 2.2–5.2 LMH under high-turbidity water conditions (300–1200 NTU), and simple forward flushing combined with sludge discharge can quickly restore ΔP. Overall, the variable load GDM system effectively manages membrane fouling and maintains stable filtration performance through the combined effects of variable load and intermittent operation, ensuring long-term and low-maintenance operation for decentralized water supply. [ABSTRACT FROM AUTHOR]

Pollution of the marine environment is an emerging threat. Nowadays, engineered nanoparticles (

Particle size distribution (PSD) in the ocean is a fundamental property that influences carbon export and food webs; however, PSD variation and its causes in oligotrophic oceans are not entirely clear. Here, we used Laser In-Situ Scattering and Transmissometry to investigate PSD (size range 5.2–119 μm) and related variables at 11 stations in the surface layer (0–20 m) of the Kuroshio region of the western North Pacific, where strong current causes dynamic hydrographic and ecological conditions. PSD slopes (range –3.2 to –4.2), derived from the power law model, were steeper at onshore stations and flatter at oligotrophic stations located offshore and at lower latitudes. Notably, slopes tended to become steeper with increasing chlorophyll a concentration, opposing the generally observed relationship between the two variables, whereas they became flatter with increasing transparent exopolymer particle (TEP) concentration. Possible explanations of the above results are localized occurrence of nanophytoplankton and TEP facilitation of particle aggregation. The results support the hypothesis that PSD slopes are controlled by a multitude of factors, including phytoplankton community dynamics and aggregation processes. To determine whether TEP-induced particle aggregation enhances or suppresses carbon export, we need a better understanding of the nature (porosity, density, and sinking velocity) of aggregates in oligotrophic oceans.

Microgels are plankton-derived transparent exopolymer particles (TEP) and have a significant impact on global marine carbon cycle. We investigated the influence of biogeochemical variables on the pattern of TEP abundance and its associated carbon (TEP C) distribution through a vertical transect of the northern South China Sea (nSCS) during summer, 2014. The average TEP concentration was 58.32±30.56 μg Xeq./L. Vertically, it was higher in the subsurface water column and lower at 200-m water depths. As chlorophyll a (chl a), TEP, and TEPC were highly concentrated at the bottom of the study transect, mainly on the continental shelf bottom and slope regions. Among biotic factors, cyanobacteria, especially Trichodesmium thiebautii showed significant positive correspondences with TEP through studied water columns in nSCS. In addition, TEP showed a positive correlation with chl-a distribution and clustered closely with diatom as well. It indicates a combined contribution of them on TEP sourcing accordingly. Nutrient concentrations were also high due to estuarine diluted water from Zhujiang (Pearl) River in the season that may intrigue those scenarios. Significant positive correlation (P<0.05) among biotic and abiotic parameters also supported the statement. Furthermore, mentionable contribution of TEP-derived TEPC was found after comparing the particulate organic carbon data, which may signify the importance of TEP in local carbon cycle in the nSCS. [ABSTRACT FROM AUTHOR]

The ability to produce fresh potable water is an ever-growing challenge, especially with an increase in drought conditions worldwide. Due to its capacity to treat different types of water, reverse osmosis (RO) technology is an increasingly popular solution to the water shortage problem. The major restriction associated with the treatment of water by RO technology is the fouling of the RO membrane, in particular through biofouling. Membrane fouling is a multifaceted problem that causes an increase in operating pressure, frequent cleaning and limited membrane lifespan. The current paper summarizes the impact of biofouling of RO membranes used in seawater desalination plants. Following a brief introduction, the elements that contribute to biofouling are discussed: biofilm formation, role of extracellular polymeric substances (EPS), marine environment, developmental phases of biofouling. Following this, is a section on the implications of membrane biofouling especially permeate flux and salt rejection. The final section focuses on the new phenomenon of compression and hydraulic resistance of biofilms. Lastly, considerations on future research requirements on biofouling and its control in seawater reverse osmosis (SWRO) membrane systems are presented at the end of the article. [ABSTRACT FROM AUTHOR]

Three-dimensional hydrogels of organic polymers have been suggested to affect a variety of processes in the ocean, including element cycling, microbial ecology, food-web dynamics, and air-sea exchange. However, their abundance and distribution in the ocean are hardly known, strongly limiting an assessment of their global significance. As a consequence, marine gels are often disregarded in biogeochemical or ecosystem models. Here, we demonstrate the widespread abundance of microgels in the ocean, from the surface to the deep sea. We exhibit size spectra of two major classes of marine gels, transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) for three different ocean regimes: (a) Polar Seas, (b) Eastern Boundary Upwelling Systems, and (c) the oligotrophic open ocean. We show the variations of TEP and CSP over the water-column, and compare them to dissolved organic carbon (DOC). We also discuss how the observed distributional patterns inform about productivity and particle dynamics of these distinct oceanic regimes. Finally, we exploit current research topics, where consideration of microgels may give new insight into the role of organic matter for marine biogeochemical processes.

[Display omitted] • Cations can regulate the aggregation of polysaccharide chains to affect fouling. • The gel layer homogeneity and permeability are mainly related to the TEP type. • Amorphous-TEP form a compact fouling layer with high filtration resistance. • Particulate-TEP form a porous gel layer, pre-filtrate foulants and alleviate fouling. • The resistance of fouling layer to cleaning is also subject to the Ca2+/Mg2+ ratio. Divalent cations and organics are two main types of foulants in feed water to the membrane processes and cations often bind to organic foulants which significantly affects fouling. Extensive efforts have been devoted to exploring the influence of single cation on organic fouling while there are diverse cations in the feed. Thus, it is essential to understand the coupling influence of different divalent cations on fouling development. In this study, sodium alginate was chosen as a model foulant to investigate the effect of different Ca2+/Mg2+ ratios on its fouling behavior. Filtration performances, the quantity and morphology of transparent exopolymer particles (TEP) derived from alginate were analyzed along with the morphology and structure of corresponding fouling layers. TEP measurements reveal that the Ca2+/Mg2+ ratio is crucial in the characteristics of TEP, which further determines the structure of the fouling layer. At a low Ca2+/Mg2+ ratio, the TEP are amorphous-TEP (a-TEP) with small and unconsolidated structure which forms a fouling layer under pressure with high hydraulic resistance. In contrast, interactions between polysaccharides at high Ca2+/Mg2+ ratio are much stronger and result in large and tight particulate-TEP (p-TEP). Such p-TEP lead to a fouling layer with high porosity and low hydraulic resistance. The role of Mg2+ in polysaccharide fouling is more important than expected because it promotes the formation of a-TEP, which show a high fouling potential at high levels because more dense gel layer forms. This study suggests that the morphology and structure of TEP play crucial roles in polysaccharide fouling propensities. A-TEP at high levels needs more attention to ensure the successful operation of membrane systems in future work. [ABSTRACT FROM AUTHOR]

Transparent exopolymer particles (TEP) and their precursors are gel-like acidic polysaccharide particles. Both TEP precursors and TEP have been identified as causal factors in fouling of desalination and water treatment systems. For comparison between studies, it is important to accurately measure the amount and fouling capacity of both components. However, the accuracy and recovery of the currently used Alcian blue based TEP measurement of different surrogates and different size fractions are not well understood. In this study, we compared Alcian blue based TEP measurements with a total carbohydrate assay method. Three surrogates; xanthan gum, pectin and alginic acid; were evaluated at different salinities. Total carbohydrate concentrations of particulates (>0.4 μm) and their precursors (<0.4 μm, >10 kDa) varied depending on water salinity and method of recovery. As xanthan gum is the most frequently used surrogate in fouling studies, TEP concentration is expressed as xanthan gum equivalents (mg XG eq /L) in this study. At a salinity of 35 mg/L sea salt, total carbohydrate assays showed a much higher particulate TEP fraction for alginic acid (38%) compared to xanthan gum (9%) and pectin (12%). The concentrations of particulate TEP therefore may only represent ∼10% of the total mass; while precursor TEP represents ∼80% of the total TEP. This highlights the importance of reporting both particulate and precursor TEP for membrane biofouling studies. The calculated concentrations of TEP and their precursors in seawater samples are also highly dependent on type of surrogate and resulting calibration factor. A linear correlation between TEP recovery and calibration factor was demonstrated in this study for all three surrogates. The relative importance and accuracy of measurement method, particulate size, surrogate type, and recovery are described in detail in this study. [ABSTRACT FROM AUTHOR]

Vast biofilm-like habitats at air⁻water interfaces of marine and freshwater ecosystems harbor surface-dwelling microorganisms, which are commonly referred to as neuston. Viruses in the microlayer, i.e., the virioneuston, remain the most enigmatic biological entities in boundary surface layers due to their potential ecological impact on the microbial loop and major air⁻water exchange processes. To provide a broad picture of the viral⁻bacterial dynamics in surface microlayers, this review compiles insights on the challenges that viruses likely encounter at air⁻water interfaces. By considering viral abundance and morphology in surface microlayers, as well as dispersal and infection mechanisms as inferred from the relevant literature, this work highlights why studying the virioneuston in addition to the bacterioneuston is a worthwhile task. In this regard, major knowledge gaps and possible future research directions are discussed.

Algal-derived organic matter (AOM), particularly transparent exopolymer particles, has been suspected to facilitate biofilm development in membrane systems (e.g., seawater reverse osmosis). This study demonstrates the possible role of AOM on biofouling in membrane systems affected by marine algal blooms. The tendency of AOM from bloom-forming marine algae to adhere to membranes and its ability to enhance biofilm growth were measured using atomic force microscopy, flow cytometry, liquid chromatography and accelerated membrane biofouling experiments. Adhesion force measurements indicate that AOM tends to adhere to clean membranes and even more strongly to AOM-fouled membranes. Batch growth tests illustrate that the capacity of seawater to support bacterial growth can significantly increase with AOM concentration. Biofouling experiments with spiral wound and capillary membranes illustrate that when nutrients availability are not limited in the feed water, a high concentration of AOM – whether in suspension or attached to the membrane – can substantially accelerates biofouling. A significantly lower biofouling rate was observed on membranes exposed to feed water spiked only with AOM or easily biodegradable nutrients. The abovementioned findings indicate that AOM facilitates the onset of membrane biofouling primarily as a conditioning platform and to some extent as a nutrient source for biofilm-forming bacteria. [ABSTRACT FROM AUTHOR]

Exchanges of matter and energy between ocean and atmosphere occur through the sea surface microlayer (SML). The SML is the thin surface layer of the ocean at the ocean-atmosphere interface that has distinctive physical, chemical and biological properties compared with the underlying water. We measured the concentration of two types of exopolymer particles in the SML and underlying water in the Pacific Ocean off the coast of Oregon (United States) during July 2011. Transparent exopolymer particles (TEP) are defined by their acidic polysaccharide content, whereas Coomassie staining particles (CSP) are composed of protein. TEP and CSP were ubiquitous in the SML. TEP were not significantly enriched in the SML compared with the underlying water. CSP were significantly enriched in the SML, with an enrichment factor (EF) of 1.4 to 2.4. The distribution of exopolymer particles in the water and microscopic imaging indicated that TEP and CSP are distinct populations of particles rather than different chemical components of the same particles. Dissolved polysaccharides were not enriched in the SML, whereas monosaccharides had an EF of 1.2 to 1.8. Sampling occurred during the collapse of a diatom bloom, and diatoms were found both in the water column and SML. While there were living diatoms in the samples, most of the diatoms were dead and there were abundant empty frustules covered in layer of TEP. The collapsing diatom bloom was probably the source of exopolymer particles to both the SML and underlying water. Exopolymer particles are a component of the SML that may play a significant role in the marine carbon and nitrogen cycles, and the exchange of material between ocean and atmosphere.

The aim of the study was to measure the transparent exopolymerparticles (TEP) concentration in cultures of Anabaena flos-aquae OL-K10and to determine the relationship between the quantity of particlesproduced and the light intensity, the age of the culture andthe presence of nitrogen in the culture medium. This is the firsttime TEP production has been investigated in the Nostocales,an order of nitrogen-fixing phytoplankton species. The resultsshowed that TEP production depends on the presence of nitrogenin the culture medium. The longer the culture is grown, the higherthe correlation between its TEP content and its chlorophyll aconcentration.

In this study, we investigated the organic matter responsible for reverse osmosis (RO) membrane fouling in seawater desalination. In addition, pretreatments by which fouling organic fractions causing severe membrane fouling can be removed effectively were investigated. The results from continuous operation of a pilot-scale sand filter indicated that the changes in the concentrations of specific organic fractions, such as transparent exopolymer particles (TEP) and biopolymers determined by liquid chromatography with organic carbon detection (LC-OCD), cannot be evaluated by comprehensive water quality indices (e.g., total organic carbon (TOC) or dissolved organic carbon (DOC) concentrations). In addition, the changes in the degree of membrane fouling cannot be explained by the comprehensive TOC and DOC concentrations. Among the water quality indices examined in this study, the concentration of TEP with relatively large particle size (i.e., > 1.0 μm) and content of protein-like organic matter that can be detected by fluorescence excitation-emission matrix (EEM) spectral analysis were well correlated to RO membrane fouling levels. The results obtained in this study strongly suggest that developing a pretreatment method that can effectively eliminate TEP and proteinaceous compounds contained in seawater is important for the stable operation of a seawater desalination plant utilizing an RO membrane. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al3+ and Fe3+ change the fouling mechanism via regulating the foulants. • Al3+ controls the formation of TEP from polysaccharide foulants. • The characteristics of TEP determines the permeability of the fouling layer. • An optimal level of coagulant alleviates membrane fouling can be obtained. Membrane fouling caused by organics in feedwater is a bottleneck factor limiting the development of membrane technology, which is often alleviated by addition of coagulants. However, the effect mechanism of coagulant components on organic foulants are lack of in-depth analysis. In this study, sodium alginate is selected as the surrogate of organic foulants to study the influence mechanism of typical coagulants Al3+ and Fe3+ on fouling control, especially the impact on the morphological characteristics of foulants at the micro level and the related fouling mitigation mechanism. The results show that the addition of different concentrations of coagulants will deeply affect the process of polysaccharide aggregation to form transparent exopolymer particles (TEP). Combination of filtration tests and analysis of fouling mechanism reveal that the small and amorphous TEP developed at low concentration of coagulant is intercepted by the membrane and forms a dense fouling layer resulting in the decreasing of membrane flux, while larger granular TEP developed from alginate accumulates on the membrane surface to form a porous fouling layer which in turn acts as a pre-filtering layer mitigating fouling. This study indicates that the addition of coagulants significantly changes the microscopic properties of foulants and thus the fouling problems. With the qualitative and quantitative analysis of TEP formed by foulant, the theoretical basis and data support are provided for the addition of coagulation to construct an effective pre-filtering layer for membrane fouling control. This work therefore, provides an effective way in application of coagulants for more accurate fouling control. [ABSTRACT FROM AUTHOR]

Extracellular Polymeric Substances (EPS), 1 1 EPS = exopolymers, extracellular polymeric substances; TEPs = transparent exopolymeric substances; DOM = dissolved organic matter; POM = particulate organic matter; DOC = dissolved organic carbon; QS = quorum sensing; TDA = tropodithietic acid; UV = ultraviolet light; RAS = recirculation aquaculture systems; MW = molecular weight. or exopolymers, play vital roles in the productivity of commercial hatcheries, yet have received little attention in aquaculture outside of their role in the biofilters of recirculating systems. Hatcheries have long dealt with EPS in microalgal cultures or larval rearing systems when quantities manifest themselves visually as biofilms or mucilaginous aggregates. The same polymers in lesser, visually undetectable quantities have the ability to attract commensal bacteria and sequester micronutrients, which can be essential in hatcheries for hygiene, stability of rearing environments, and the production of microalgae for live feeds. EPS may also serve an important role in nutrition both directly in the particle selection of filter feeders, and indirectly through their contribution to microflora in the larval gut of both fish and invertebrates. EPS have been well-studied in marine ecosystems, but their presence in hatcheries has until recently been largely overlooked, perhaps on account of their invisibility using normal microscopy and their extremely small size, both factors which may explain why they are sometimes also referred to as transparent exopolymeric substances (TEPs). This review examines recent literature for ways in which EPS affect hatchery processes, with suggestions as to how further research and development of biosensor technologies for EPS have the potential to improve production processes. [ABSTRACT FROM AUTHOR]

Transparent exopolymer particles (TEP) and their precursors produced by phyto-/bacterio-planktons in fresh and marine aquatic environments are increasingly considered as a major contributor to organic/particulate and biological fouling in micro-/ultra-filtration and reverse osmosis membrane (RO) systems. However, currently established methods which are based on Alcian blue (AB) staining and spectrophotometric techniques do not measure TEP-precursors and have the tendency to overestimate concentration in brackish/saline water samples due to interference of salinity on AB staining. Here we propose a new semi-quantitative method which allows measurement of both TEP and their colloidal precursors without the interference of salinity. TEP and their precursors are first retained on 10 kDa membrane, rinsed with ultra-pure water, and re-suspended in ultra-pure water by sonication and stained with AB, followed by exclusion of TEP-AB precipitates by filtration and absorbance measurement of residual AB. The concentration is then determined based on the reduction of AB absorbance due to reaction with acidic polysaccharides, blank correction and calibration with Xanthan gum standard. The extraction procedure allows concentration of TEP and their pre-cursors which makes it possible to analyse samples with a wide range of concentrations (down to <0.1 mg X eq /L). This was demonstrated through application of the method for monitoring these compounds in algal cultures and a full-scale RO plant. The monitoring also revealed that concentrations of the colloidal precursors were substantially higher than the concentration of TEP themselves. In the RO plant, complete TEP removal was observed over the pre-treatment processes (coagulation-sedimentation-filtration and ultrafiltration) but the TEP precursors were not completely removed, emphasising the importance of measuring this colloidal component to better understand the role of TEP and acidic polysaccharides in RO membrane fouling. [ABSTRACT FROM AUTHOR]

Abstract: The taxonomic composition and types of particles comprising the downward particle flux were examined during the mesoscale artificial iron fertilisation experiment LOHAFEX. The experiment was conducted in low-silicate waters of the Atlantic Sector of the Southern Ocean during austral summer (January–March 2009), and induced a bloom dominated by small flagellates. Downward particle flux was low throughout the experiment, and not enhanced by addition of iron; neutrally buoyant sediment traps contained mostly faecal pellets and faecal material apparently reprocessed by mesozooplankton. TEP fluxes were low, ≤5mgGXeq.m−2 d−1, and a few phytodetrital aggregates were found in the sediment traps. Only a few per cent of the POC flux was found in the traps consisting of intact protist plankton, although remains of taxa with hard body parts (diatoms, tintinnids, thecate dinoflagellates and foraminifera) were numerous, far more so than intact specimens of these taxa. Nevertheless, many small flagellates and coccoid cells, belonging to the pico- and nanoplankton, were found in the traps, and these small, soft-bodied cells probably contributed the majority of downward POC flux via mesozooplankton grazing and faecal pellet export. TEP likely played an important role by aggregating these small cells, and making them more readily available to mesozooplankton grazers. [Copyright &y& Elsevier]

Abstract: The demise phase of diatom blooms following nutrient exhaustion is characterised by the formation of aggregates with high sinking rates that facilitate carbon export to the seafloor. However, the nature of the binding substances involved and the physiological status of the phytoplankton during aggregation are not well established. Transparent Exopolymer Particles (TEP), exudated by living cells, have been proposed as a binding agent of aggregates but autolysed cytoplasm released after cell death might also play such a role. To differentiate these processes we studied the response of cultures of the mucilage and TEP-producing giant diatom Coscinodiscus wailesii to nutrient, in particular silicic acid, limitation. Two staining methods were applied: SYTOX® Green to follow cell viability and cell death and Alcian Blue (AB) to quantify the production of TEP. Large aggregates formed exclusively in cultures with high cell densities in which the SYTOX® Green signal increased during the senescence phase. TEP-production under nutrient replete (f/2 treatment) and nitrate reduced growth conditions (f/2-N treatment) with high cell densities was comparatively low, indicating reduced photosynthetic activity in the stationary and senescent phases. In contrast, TEP-production was enhanced in low-density Si-limited cultures (f/2-Si treatment), probably as a means to discharge excess photosynthate, as the cells were densely packed with chloroplasts. The C/N ratios of aggregated and solitary cells did not differ significantly indicating that the binding agent was not mainly polysaccharidic. We propose that aggregate formation in C. wailesii is a consequence of cell lysis after cell death and that autolysed cytoplasm is the binding agent rather than TEP. This would imply that cell lysis plays a substantial role in bloom termination and mucilage formation in C. wailesii, which would in turn influence biogeochemical cycling in regions where this diatom thrives. [Copyright &y& Elsevier]

Highlights: [•] The biological activity in contact flocculation filtration (CFF) was investigated. [•] Sand and anthracite filter media were evaluated in terms of biological activity. [•] Significant removal of LMW organics with an active microbial population was achieved. [•] Biofouling potential was reduced by CFF through biological activity and bio-stabilization. [Copyright &y& Elsevier]

This paper investigated the effect of food to microorganisms (F/M) ratios in the MBRs on membrane fouling propensities at fluxes of 10, 20, and 30 L/m2 hr (LMH). The high F/M-MBR had different biomass properties, more soluble extracellular polymeric substances (EPS), and faster fouling rate compared to the low F/M-MBR. However, the fouling mechanisms at the three fluxes were dissimilar. At a low flux, the microbial flocs dominant cake layers facilitated catching the soluble EPS to increase resistance. At a high flux, the great accumulation of soluble EPS (especially soluble polysaccharides) to form gel-like cake layers predominantly induced membrane fouling.Supplemental materials are available for this article. Go to the publisher's online edition ofSeparation Science and Technologyto view the free supplemental file. [ABSTRACT FROM AUTHOR]

Algal blooms are currently a major concern of the membrane industry as it generates massive concentrations of organic matter (e.g. transparent exopolymer particles [TEP]), which can adversely affect the operation of membrane filtration systems. The goal of this study is to understand the production, composition and membrane rejection of these organic materials using different characterisation techniques. Two common species of bloom-forming freshwater and marine algae were cultivated in batch cultures for 30 days and the productions of TEP and other organic matter were monitored at different growth phases. TEP production of the marine diatom, Chaetoceros affinis, produced 6-9 times more TEP than the freshwater bluegreen algae, Microcystis. The organic substances produced by both algal species were dominated by biopolymeric substances such as polysaccharides (45-64%) and proteins (2-17%) while the remaining fraction comprises of low molecular weight refractory (humic-like) and/ or biogenic organic substances. MF/UF membranes mainly rejected the biopolymers but not the low molecular weight organic materials. MF membranes (0.1-0.4 lm) rejected 42-56% of biopolymers, while UF membranes (10-100 kDa) rejected 65-95% of these materials. Further analysis of rejected organic materials on the surface of the membranes revealed that polysaccharides and proteins are likely responsible for the fouling of MF/UF systems during an algal bloom situation. [ABSTRACT FROM AUTHOR]

In the autumn of 2007, marine mucilage caused by the diatom Coscinodiscus granii occurred in the central area of Ariake Sound, Japan, and resulted in damage to fishery. To elucidate the mechanism underlying the outbreak of marine mucilage, we examined the effect of temperature on cell growth and production of transparent exopolymer particles (TEPs) in a culture of this species. Growth and TEP production of C. granii are influenced by temperature. The maximum growth rate (1.63 divisions day) and cell yield (1,280 cells mL) at all temperatures were obtained at 30°C. Optimal growth rates (>1.15 divisions day: ca. 70% of maximum) and cell yield (>900 cells mL: ca. 70% of maximum) were observed at temperatures of 25-30°C. TEP production by C. granii depended on whether volume- or cell-related values were considered. The maximum volume-normalized increase rates and concentrations of TEP at all temperatures were observed at 25°C. However, when production rates and concentrations of TEP were normalized to cell numbers, optimal values were measured at 10-15°C. In Ariake Sound, when marine mucilage caused by C. granii occurred, the temperature ranged from 25.0 to 25.4°C. This suggests that growth conditions of C. granii are important factors for production of marine mucilage. [ABSTRACT FROM AUTHOR]

In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean (36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems and ranged from 66 to 9,038 μg GX eq L. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes, the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column. [ABSTRACT FROM AUTHOR]

Transparent exopolymer particles (TEP) compose an important pool of particulate organic matter (POM) in aquatic systems. However, no studies of TEP contribution to C export to sediment exist for freshwaters. We quantify the contribution of TEP to C sinking fluxes in an oligotrophic reservoir (Quéntar, Southern Spain) by monitoring TEP in the water column and TEP, particulate organic carbon (POC) and dry weight in sedimentation traps. TEP sinking fluxes ranged from 0.73 to 183.23 mg C m−2 day−1 and from 0.51 to 177.04 mg C m−2 day−1 at the surface and at the bottom layer, respectively. These values represent that, over an annual basis, 5.59 Ton TEP-C (over 61.32 Ton POC) are exported, on an average, from the water column to the sediment of Quentar reservoir. TEP concentrations (average = 48.0 μg XG eq l−1) were lower than the scarce data reported for freshwaters. No significant relationships between TEP and Chl a concentrations or BA were observed. Average value for daily sedimentation flux (6.63 g Dry Weight m−2 day−1) in the study reservoir was higher than that documented for low productive natural aquatic ecosystems as a consequence of the high amount of allochthonous material input characterizing reservoirs. TEP contributed to C export to sediment with a value that range from 0.02 to 31%. Our results show that even in man-made systems, which are predominantly controlled by allochthonous inputs, TEP may be relevant for explaining POM settling fluxes. [ABSTRACT FROM AUTHOR]

The occurrence of Transparent Exopolymer Particles (TEP), an acidic fraction of polysaccharides, was monitored for more than six months in the activated sludge of three MBR units, and the relationship between TEP and other fouling indicators was studied. These compounds consist mainly of exopolysaccharides of a sticky nature, a characteristic which makes them a group of interesting substances in processes like sedimentation, flocculation and membrane fouling. The relationship between capillary suction time (CST) and polysaccharides (PS) was linear for the three tested sludges, although the correlation with TEP concentrations was stronger. A slight linear correlation of both TEP and PS was found with the critical flux (CF) measured with a small filtration test cell, which was submerged in the membrane tank to assess the filterability performance of the sludge in situ. However, the correlation CF-PS was clearer. The relationship between TEP, polysaccharides and sludge filterability highlights the potential of this parameter for the monitoring of membrane systems. [ABSTRACT FROM AUTHOR]

Abstract: In the marine environment, transparent exopolymer particles (TEP) are ubiquitous and abundant, playing a significant role in carbon cycling and the structuring of food webs. Previous studies have shown that phytoplankton, bacteria, and oysters contribute to the production of TEP through the release of exopolymers. However, little is known about other potential sources of TEP and TEP precursors, especially in coastal systems. It was hypothesized that suspension feeders contribute to the TEP pool in near-shore environments through the release of exopolymers in both the dissolved and particulate form, and tested these hypotheses in both laboratory and field experiments. In the laboratory, the production of TEP by several species of benthic suspension feeders (the blue mussel, Mytilus edulis; the bay scallop, Argopecten irradians; the slipper snail, Crepidula fornicata; and the solitary ascidians, Ciona intestinalis and Styela clava) was investigated from October to November 2002 and June 2003. Concentrations of TEP and DOC were determined by spectrophotometry after alcian blue staining and high-temperature, catalytic oxidation, respectively. Similar analyses were conducted on water samples from the field in July 2003, collected in close proximity to dense beds of mussels in the Poquonnock River, Connecticut, USA (41°19′ N, −72°02′ W). Laboratory results indicated that actively-pumping blue mussels, bay scallops, slipper snails, and both species of solitary ascidians significantly enhanced TEP concentrations above background levels over a five-hour period. However, only the solitary tunicate S. clava significantly enhanced DOC concentrations above background levels over the same period of time. Field samples indicated that TEP and DOC concentrations were high in close proximity to dense beds of mussels. These results imply that a variety of benthic suspension feeders produce TEP during feeding activities which could lead to enhanced flocculation of organic matter and carbon deposition in near-shore waters. [Copyright &y& Elsevier]

Polysaccharide is an important foulant in membrane filtration. Nevertheless, the "bridging effect" of divalent cations on polysaccharide fouling is still not completely understood and thus is the main objective of this study. To reveal the basic underlying mechanism, a wide range of concentrations of Ca2+ and Mg2+ were analysed and alginate sodium was employed as model foulant to generate results. Results showed that the fouling propensities of alginate first increased and then decreased along with the increasing of the concentration of Ca2+. Ca2+ at high concentration acted like coagulant in alleviating alginate fouling. While the membrane fouling caused by alginate continuously aggravated with increasing Mg2+ level in feed water and surprisingly the specific filtration resistances caused by Mg2+ were much higher than those of Ca2+ at all ion concentrations. Transparent exopolymer particles (TEP) measurements revealed that both Ca2+ and Mg2+ increased the molecular interactions of alginate via "bridging effect", while the binding of Ca2+ to alginate was much greater than that of Mg2+ which resulted with aforementioned fouling phenomenon. This study suggests that the roles of Ca2+ and Mg2+ in polysaccharide fouling are dramatically different and Mg2+ is more important than we thought. [Display omitted] • The roles of Ca2+ and Mg2+ in polysaccharide fouling are dramatically different. • Ca2+ at high concentration works like coagulant in alleviating alginate fouling. • Mg2+ caused higher specific filtration resistance than Ca2+ at all ion levels. • TEP measurements reveal the crosslinking of polysaccharide controlled by cations. [ABSTRACT FROM AUTHOR]

Membrane-based treatment of municipal wastewater plays a crucial role in wastewater recycling. Recently, transparent exopolymer particles (TEP) are reported to cause severe membrane fouling, but their fate in municipal wastewater remains largely unknown. Moreover, considering the inevitable interactions between TEP and other components in wastewater, how such interactions affect TEP-associated fouling also deserves in-depth studies. In this work the distribution of TEP in three different municipal wastewater treatment plants was investigated, and TEP were found to commonly exist in the influents (4.8–10.8 mg/L) and could not be completely removed by activated sludge process. Compared to typical organic foulants (e.g., proteins, polysaccharides (TEP-free), and humic acids), TEP at even a low concentration of 0.2 mg/L could cause significant fouling by depressing the flux by 54%. However, an unexpected alleviation of fouling was observed by mixing TEP with these foulants. The interactions between TEP and typical foulants were found to reduce the adhesion energy of TEP, leading to a lower specific filtration resistance of the mixed foulants. This work underscores that the coexistence of multiple foulants does not necessarily induce more severe fouling, and a better understanding of interactions among foulants will facilitate the development of efficient anti-fouling strategies. [Display omitted] • TEP widely present in municipal wastewater can't be completely removed in WWTP. • TEP lead to more severe fouling compared to other typical organics. • Interaction with other organics induces the alleviation of TEP-associated fouling. • Alleviation is caused by the reduced adhesion energy and specific filtration resistance. [ABSTRACT FROM AUTHOR]

Marine benthic microalgae always have their own ubiquitous nature to adhere to diverse submerged substrates. Immobilized submerged biofilm system offers huge reduction of liquid culture volume, high biomass production and ease of harvesting of biomass. The studies on the biofilm formation and properties towards membrane surfaces are rare therefore the objectives of this paper were to investigate the relationships between the algal attachment rate onto membranes via biofilm and the compositional changes of the extracellular polymeric substances in the biofilm. To delve further into the biofilm-forming capacity of three benthic diatoms (Amphora coffeaeformis , Cylindrotheca fusiformis and Navicula incerta) onto polyvinylidene fluoride membrane (PVDF), a simple adhesion test was run for 96 h under controlled temperature and light conditions. Attached biomass was carefully scraped for cell count and extracellular polymeric substances (EPS) were extracted for characterization in terms of its biochemical compositions. As a result, A. coffeaeformis and N. incerta were found to adhere well with membrane substrate with equal cell attachment (3 × 108 cells/m2) at the end of the experiment while the lowest was observed for C. fusiformis (1.33 × 108 cells/m2). Biofilm of three diatoms was observed to form as soon as 2 h after inoculation and its development was aided by the high accumulation of TEP amount at 96th hour ranging from 91 mg X eq/m2to 170.61 mg X eq/m2. EPS excreted was found to re-accumulate after 48 h with polysaccharides as major component (>59.87%) for N. incerta and C. fusiformis except A. coffeaeformis which was mainly composed of proteins (>50%). The biofilm formed by A. coffeaeformis was considered the most robust because of its hydrophobic-hydrophobic interaction between the cells and the membrane. Understanding of biofilm physiology will pave the way for describing biofilm systems and membrane-based wastewater treatment systems. Graphical abstract [Display omitted] • Diatoms form biofilm onto polyvinylidene fluoride membrane in gyration test. • Biochemical composition in biofilm was extracted and studied. • A. coffeaeformis was having the most robust biofilm formation and adhesion. • Polysaccharides and proteins in biofilm contributed the most to biofilm adhesion. [ABSTRACT FROM AUTHOR]

The Tampa Bay Water seawater reverse osmosis (SWRO) facility is the first large-capacity seawater desalination plant in the United States. The feedwater source for the facility is an estuarine system that is biologically very productive and contains naturally-occurring high concentrations of algae, marine bacteria, total organic carbon (mostly dissolved), transparent exopolymer particles (TEP), the biopolymer fraction of natural organic matter, and phosphate. The high-organic composition of the feedwater places stress on the conventional sand pretreatment system utilized at the facility resulting in high organic passage into the membrane process and flow through into the permeate. In particular, the direct passage of particulate TEP (p-TEP) into the membranes has a major impact on the biofouling rate. Based on the data collected, the pretreatment is ineffective at removing key organic components that impact the rate of membrane biofouling, particularly bacteria and p-TEP. Perhaps the pretreatment could be re-designed to use a dissolved air floatation system (DAF) followed by ultrafiltration as a remedy that would likely move the biofouling problem to the ultrafiltration process, which has an easier cleaning process. Consideration could be given to using a groundwater source of feedwater as a permanent remedy to the operational issues. • Measurement of organic carbon passage through all processes in an SWRO facility • Tampa Bay Water SWRO facility has very high organic carbon in feedwater (>5 mg/L). • Pretreatment processes inadequate to remove DOC and TEP • TEP and the biopolymer fraction of NOM are entering the membrane process. • DAF followed by ultrafiltration could be a more suitable pretreatment process. [ABSTRACT FROM AUTHOR]

• Gel layer formation was the dominant fouling mechanism of alginate with Mg2+. • TEP formed from alginate enhanced the gel layer formation during filtration. • TEP measurement provided a direct evaluation of the crosslinking extent of alginate. Polysaccharides have been recognized as a significant type of foulant due to their gelling property which is deeply affected by the existence of divalent cations. However, the effect of magnesium ion on polysaccharides fouling remains largely unknown and results reported by the limited studies are even controversial. In this study, alginate samples were employed to systematically study the effect of Mg2+ on polysaccharides fouling. Four levels of alginates were studied and results led to the same conclusion that the presence of Mg2+ aggravated fouling problems during membrane filtration. Cross-validation of filtration resistances, modelling of filtration data and autopsy of fouled membrane revealed that gel layer formation was the dominant fouling mechanism at the presence of Mg2+. Further analysis showed that the gel layer development strongly depended on the crosslinking of alginate. Moreover, crosslinking of alginate was enhanced by the Mg2+-alginate interaction including Mg2+⋯O(COO−) bonds, Mg2+⋯O(OH) bonds and sharing water molecules from the first coordination shell of Mg2+ with the carboxylate groups of alginate. Increased crosslinking of alginates resulted with the formation of networks with larger effective dimension and more complex three dimension structure, i.e. the transparent exopolymer particles (TEP). TEP promoted the gel layer formation on membrane. Emphasis is given to the link between the Mg2+-polysaccharide interaction and the fouling propensity of polysaccharides. Consequently, understanding the interaction between cations and organic foulants is important, which would provide an insightful guidance for fouling control. [ABSTRACT FROM AUTHOR]

Membrane technology has been one of the most promising techniques to solve the water problem in future. Unfortunately, it suffers from the fouling problem which is ubiquitous in membrane systems. The origin of the bewilderments of the fouling problem lies in the lack of deep understanding. Recent studies have pointed out that the molecular structure of foulant affects its fouling propensity which has been ignored in the past. In this study, the filtration behaviors of alginate blocks derived from the same source were comprehensively explored. Alginate blocks share the same chemical composition but differ from each other in molecular structure. The alginate was first extracted from natural seaweed using calcium precipitation and ion-exchange methods. Extracted alginate was further fractionized into MG-, MM- and GG-blocks and the characteristics of the three blocks were examined by Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) observations, and transparent exopolymer particles' (TEPs) measurements. Results showed that MG-, MM- and GG-blocks had the same functional groups, but they showed different intermolecular interactions. TEP formation from MG-, MM- and GG-blocks revealed that the molecule crosslinking of them decreased in the order of MM-blocks > GG-blocks > MG-blocks. It was further found from microfiltration tests that these alginate blocks had completely different fouling propensities which can be explained by the TEP formation. TEPs would accumulate on membrane surfaces and worked as a pre-filter to avoid serious pore blocking of membrane. That all suggested that the membrane fouling was closely related to the molecular structure of foulant. It is expected that this study can provide useful insights into the fouling propensities of different types of polysaccharides during filtration processes. [ABSTRACT FROM AUTHOR]