Impact Of Extracellular Polymeric Substances Research Articles

Transport and interaction of cadmium and active sludge extracellular polymeric substances in saturated sand influenced by ionic strength and composition.

Artificial groundwater recharge with reclaimed water (secondary effluent from wastewater treatment plants) has become an important approach to solving water scarcity worldwide. Microorganisms in activated sludge can secrete many extracellular polymeric substances (EPS). However, information on the impact of EPS on the movement of heavy metals in porous media and their environmental effects on underground networks is limited. To assess this risk, we extracted EPS from the aerobic section of a wastewater treatment plant using hot sodium hydroxide and conducted experiments using one-dimensional sand columns to investigate how ion composition and strength affect the movement and interaction of cadmium (Cd) and EPS in porous media. The results showed that EPS facilitated Cd migration in porous media. Sodium (Na) and calcium (Ca) ions promoted the migration of Cd in porous media and EPS-Cd complexation. The effect of Ca was more significant than that of Na. As the Na adsorption ratio increased, the migration ability of Cd in porous media and the complexation ability of EPS with Cd decreased. Therefore, when estimating the migration of EPS and Cd in subsurface environments, careful consideration should be given to prevent the risk of groundwater pollution.

Biosorption of lanthanum by acidophile Euglena mutabilis biofilms and the role of extracellular polymeric substances

Enhancing the recovery of rare earth elements from wastewaters is of increasing interest given their growing economic and strategic importance as critical materials for a range of technologies including those required for renewable energy. We are particularly interested in the potential for using microalgal biofilms as sorbents given that they can grow as concentrated structures in the absence of organic carbon. In this study we assess and contrast biofilm and suspensions of Euglena mutabilis with respect to the kinetics and isotherms for the biosorption of lanthanum. The impact of extracellular polymeric substances (EPS) on biofilm biosorption was also examined. Suspension and biofilm adsorption kinetics were found to be similar with equilibrium being after approximately 2 to 3 h. Biofilms adsorbed significantly greater amounts of lanthanum compared to the suspension with a maximum adsorption capacity of 65 mg/g and 25 mg/g respectively for an increase of approximately 160 %. This difference in maximum adsorption capacities was attributed to the biofilm's increased EPS content which had an estimated adsorption capacity of 360 mg/g EPS. The proposed mechanism for EPS adsorption of lanthanum is via an ion exchange mechanism where calcium and magnesium were released into solution after lanthanum uptake. FTIR results also showed no change between the suspended Euglena and biofilm in terms of the available functional groups for adsorption.

Surface characterisation of pyrite exposed to A. brierleyi

The surface of pyrite exposed to the thermophilic archaeon Acidianus brierleyi was investigated to elucidate the impact of extracellular polymeric substances (EPS) and/or cells on mineral surface hydrophobicity. The interaction of cells with the surface of pyrite and the physicochemical properties of the mineral surface were studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), captive bubble contact angle measurements and time of flight – secondary ion mass spectrometry (ToF-SIMS). The ToF-SIMS results show no clear evidence of EPS on the pyrite surface after exposure to A. brierleyi and further suggests significant contamination of the surface by the yeast extract included in the recommended A. brierleyi growth medium. It was found that the presence of yeast extract made it impossible to accurately determine the action of EPS on the surface, and potentially impeded chemical and biological reactions and interactions on the surface. Investigation of the impact of A. brierleyi on pyrite in the absence of yeast extract found up to 24° decrease in contact angle compared to the control after 2 h. It was found that A. brierleyi produced very little EPS and as such is unlikely to alter the surface through a contact mechanism, with little to no cell attachment observed on the pyrite surface. Thus removal of yeast extract may improve the application of this archaea to biomining applications.

Effect of extracellular polymeric substances on the phosphorus adsorption characteristics of sediment particles

Extracellular polymeric substances (EPS) have a great impact on the characteristics of sediment particles and their environmental effects in hydro-environmental systems, yet little effort has been made to study the considerable variability in the element adsorption process of sediment particles caused by EPS. Understanding the variability of the adsorption characteristics of sediment particles associated with EPS and quantifying the scale of the adsorption isotherm parameters are important for understanding how EPS mediate sediment properties and environmental factors. In this paper, isothermal equilibrium adsorption experiments are done on phosphorus to study the influence of EPS on the adsorption characteristics of sediment particles, and the Langmuir adsorption isotherm is applied to analyze the adsorption rule of sediment particles under the impact of EPS. The current research demonstrates that significant differences will take place in the adsorption characteristics of sediments coated with EPS at different development phases and the phosphorus adsorption capacity of sediment particles increases with the growth of EPS. The difference in the adsorption percentage between sediment particles coated with EPS of 0 and 6 weeks growth time is about 42%–60% for different initial aqueous phosphorus concentration. A formula describing the adsorption isotherm parameter of the maximum material (element) adsorption capacity of sediment particles change over time is further proposed based on the experimental data. The current study provides some evidence for the interaction of sediment particles, EPS, and adsorbed elements in the water environment.

Roles of carbon source-derived extracellular polymeric substances in solids accumulation and nutrient removal in horizontal subsurface flow constructed wetlands

The sustainable operation of horizontal subsurface flow constructed wetlands (HSSF CWs) is challenging due to the accumulation of organic and inorganic solids in substrate interspaces. In this study, wetland microcosms with (EC-CWs) and without (C-CWs) external carbon source were monitored for 120 days to investigate the impact of extracellular polymeric substances (EPS) on inorganic particle settlement and nutrient removal of HSSF CWs. EPS flocculation aggravated the solids accumulation in the inlet zone of the EC-CWs, and ion bridging through EPS and sweep flocculation were the main flocculation mechanisms. EPS increased the hydraulic resistance of the accumulated solids, which almost halved the hydraulic retention time (HRT) of the EC-CWs. Compared with the C-CWs, the media storage of total phosphorus (TP) in the EC-CWs was improved by 70.18 ± 2.74%, which was mainly due to the increased adsorption sites introduced by EPS. RDA analysis showed that solids accumulation in the HSSF CWs was positively correlated with the TP removal, but the process had a minor influence on organic matter and nitrogen removal. Combined analyses revealed that the accumulation of EPS and inorganic particle not only caused HRT reduction but also introduced abundant adsorption sites. The present results would promote the understanding on role of EPS in sustainable operation of HSSF CWs, and further maintain the stable nutrient removal performance.

Understanding the Impact of Extracellular Polymeric Substances on Lead Release in Drinking Water Systems.

Lead release in a lead (Pb, anode)–iron oxide (α-Fe2O3, cathode) galvanic system was studied under the influence of synthetic extracellular polymeric substances (sEPS). Sodium alginate, bovine serum albumin (BSA), and cytochrome c represented extracellular polysaccharides, proteins, and electrochemically active components, respectively. Microbiologically influenced corrosion was investigated using sEPS and pelleted and resuspended Pseudomonas aeruginosa cells. Relative to the anaerobic inorganic control, Pb release increased by 156, 202, and 198 μg/L when sEPS was present on the cathode side at 200 mg/L (100 mg/L alginate + 100 mg/L BSA), 400 mg/L (200 mg/L alginate + 200 mg/L BSA), and 200 mg/L with 123.84 mg/L cytochrome c, respectively, under anaerobic conditions. When the cathode was aerated, Pb release increased by 75, 260, and −71 μg/L under the aforementioned conditions, all relative to the aerated inorganic control. When sEPS was instead present on the anode side, sEPS caused localized corrosion on Pb and resulted in higher Pb release than predicted by electric current. P. aeruginosa generally enhanced corrosion; when cells were dosed in the anode side, part of the oxidized Pb was immobilized by cells or organic compounds adhered to the electrodes.

The mutual co-regulation of extracellular polymeric substances and iron ions in biocorrosion of cast iron pipes

New insights into the biocorrosion process may be gained through understanding of the interaction between extracellular polymeric substances (EPS) and iron. Herein, the effect of iron ions on the formation of biofilms and production of EPS was investigated. Additionally, the impact of EPS on the corrosion of cast iron coupons was explored. The results showed that a moderate concentration of iron ions (0.06mg/L) promoted both biofilm formation and EPS production. The presence of EPS accelerated corrosion during the initial stage, while inhibited corrosion at the later stage. The functional groups of EPS acted as electron shuttles to enable the binding of iron ions. Binding of iron ions with EPS led to anodic dissolution and promoted corrosion, while corrosion was later inhibited through oxygen reduction and availability of phosphorus from EPS. The presence of EPS also led to changes in crystalline phases of corrosion products.

Impact of extracellular polymeric substances on the settlement ability of aerobic granular sludge

Instability of aerobic granular sludge (AGS), which is mainly caused by filamentous outgrowth, is a bottleneck in applying this technology to treat wastewater. In order to reduce the effect of filamentous outgrowth on settlement ability of AGS, the role of the distribution of extracellular polymeric substances (EPS) in settlement ability was investigated in this study. Chemical oxygen demand (COD) of influent increased gradually from 1000 mg L−1 to 2000 mg L−1 to 4000 mg L−1 as organic loading rate (OLR) changed from 2 to 4 to 8 kg COD m−3 d−1 in the synthetic influent. The relationship between settlement ability and EPS was investigated. The sharp increase in loosely bound EPS (LB‐EPS) content reduced the settlement ability, whereas the highest content of tightly bound EPS (TB‐EPS) was observed in the sludge with best settlement ability. The TB‐EPS plays an important role in maintaining the matrix structure of AGS. Abundance of LB‐EPS did not favour the settlement ability of AGS. These results would provide useful information for improvement of stability of AGS.

Impact of extra-cellular polymeric substances on the filterability of activated sludge in membrane bioreactors for landfill leachate treatment

The impact of extra-cellular polymeric substances (EPS), especially dissolved polysaccharides, on the filterability of activated sludge, was investigated. Samples were taken from full-scale membrane bioreactors of landfill leachate treatment plants and two municipal treatment plants (full scale and pilot) for comparison. The activated sludge samples were characterised by means of determination of total solids (TS), mixed liquor volatile suspended solids (MLVSS), chemical oxygen demand (COD), biochemical oxygen demand after 5 days (BOD 5) and concentration of dissolved polysaccharides (PS diss) according to an analytical method of Dubois. To compare the filterability of the different sludge samples, filtration tests were carried out in a filtration test cell under constant conditions, and the filterability was described by means of a dimensionless filtration index. The results show the impact of high concentrations of PS diss on filtration index, dewaterability and permeability. The higher the polysaccharide concentration was in the activated sludge, the more the permeate flux and correspondingly the filtration index as well as the dewaterability tended to decrease. The concentration of dissolved polysaccharides fluctuated strongly depending on the origin of the activated sludge. The conditions for the development of polysaccharides in activated sludge systems are still not completely understood and should be investigated in further studies. The retention of the PS diss with ultrafiltration membranes was determined on average to be 80%.