Removal Of Extracellular Polymeric Substances Research Articles

Roles of extracellular polymeric substances in arsenic accumulation and detoxification by cell wall intact and mutant strains of Chlamydomonas reinhardtii

Arsenic (As) pollution seriously threatens human and ecological health. Microalgal cell wall and extracellular polymeric substances (EPS) are known to interact with As, but their roles in the As resistance, accumulation and speciation in microalgae remain unclear. Here, we used two strains of Chlamydomonas reinhardtii, namely CC-125 (wild type) and CC-503 (cell wall-deficient mutant), to examine the algal growth, EPS synthesis, As adsorption, absorption and transformation under 10–1000 µg/L As(III) and As(V) treatments for 96 h. In both strains, the As absorption increased after the EPS removal, but the growth, As adsorption, and transformation of C. reinhardtii declined. The CC-125 strain was more tolerant to As stress and more efficient in EPS production, As accumulation, and redox transformation than CC-503, irrespective of EPS presence or absence. Three-dimension excitation-emission matrix (3D-EEM) and attenuated total reflectance infrared spectroscopy (ATR-IR) analyses showed that As was bound with functional groups in the EPS and cell wall, such as -COOH, -NH and -OH in proteins, polysaccharides and amino acids. Together, this study demonstrated that EPS and cell wall acted as barriers to lower the As uptake by C. reinhardtii. However, the cell wall mutant strain was more susceptible to As toxicity due to lower EPS induction and higher As absorption.

Aluminum chloride enhances the production of short-chain fatty acids from waste activated sludge: Insights to performance, mechanism, and implications

Waste activated sludge (WAS), the major by-products during wastewater treatment, is hugely produced, which poses great environment and operation pressures. This work investigated feasibility, mechanism, and implications of aluminum chloride for carbon recovery enhancement from WAS. Results showed that aluminum chloride enhanced short-chain fatty acids (SCFAs) production potential, and the enhancement potentials were dosage dependent. The optimal dosage was 10 mg Al/g total suspended solids (TSS), with the maximum SCFAs production potential of 140 mg chemical oxygen demand/g volatile suspended solids, which was 52.2 % higher compared to that of control. Meanwhile, the compositions of SCFAs were regulated, suggesting that the recovered SCFAs were potential carbon source. Mechanism analysis showed that aluminum chloride increased the release of polysaccharides and proteins by 23.6 % and 71.7 %, respectively, compared to that in control, as well as the removal of extracellular polymeric substances to 27.5 % and the contribution of intracellular release to 38.0 %. This situation facilitated the solubilization of WAS and improved the biochemical degradability of organic matters. In addition, aluminum chloride promoted hydrolysis and acidification stages through affecting the activities of hydrolase, enriching acid-producing microorganisms, and inhibiting the activities of methanogens. This work provided some novel solutions for sludge treatment and carbon recovery, driving wastewater treatment plants to achieve carbon-neutral operation.

Effect of extracellular polymeric substances removal and re-addition on anaerobic digestion of waste activated sludge

Extracellular polymeric substances (EPS) play a key role in anaerobic digestion of excess sludge. The influence of EPS removal and re-addition on sludge anaerobic digestion were investigated by batch experiment. The results showed that both EPS removal and re-addition improved sludge anaerobic digestion, the cumulative methane production increased by 14.9 % and 50.4 %. EPS removal promoted sludge hydrolysis and acidification, the soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) concentration increased by 31 % and 29 %. The re-addition of EPS increased the substrate of sludge fermentation, resulting in 1.64 and 1.77 times higher SCOD and VFAs concentration than that of control group. In addition, EPS contained lots of electrochemically active substances, and re-adding EPS increased the electron transfer system activity in anaerobic digestion by 164 %, which enhanced significantly methane production. Both removal and re-addition of EPS altered the microbial community structure in anaerobic digestion, the bacteria with hydrolysis and acidification functions were enriched, such as Chloroflexi and Desulfobacterota. Methanobacterium and Methanosaeta were the dominant methanogens in anaerobic digestion systems, and their relative abundance were increased by removing and re-adding EPS.

Effect of NaOCl and ClO2 on seawater desalination using reverse osmosis with cartridge filtration as the pretreatment during the algal bloom

Increased seawater temperature leads to harmful algal blooms (HABs), which releases toxic materials and extracellular polymeric substances (EPS) that are harmful to both humans and the environment. Reverse osmosis (RO) with cartridge filter (CF) as the pretreatment process is often used for desalination process. However, the EPS causes severe fouling on the CF, and RO membrane. Disinfectants, such as NaOCl and ClO2, are commonly used to remove biofouling, because they can oxidize and kill microorganisms. Therefore, our study aims to utilize NaOCl and ClO2 during the CF-RO process to minimize the algal growth within the system and minimize the fouling induced by EPS. Results from this study show that CF can remove more than 50% of protein and 14% of polysaccharides but is not effective in removing toxins. However, with disinfectants, toxic materials were completely oxidized. Improved removal of EPS with CF improved overall performance. The flux reduction in RO process without disinfection was over 60%, however, the flux decline was about 44% and 10% with NaOCl and ClO2, respectively. Both disinfectants were found to be effective, however use of ClO2 is recommended because it is less damaging the membrane, yet more effective in enhancing the performance.

Upgrade of the biggest catalytic ozonation wastewater treatment plant in China: From pollution control to carbon reduction

Catalytic ozonation is a widely used effective technology in advanced treatment for the removal of refractory organics from wastewater. However, it is also a highly energy-consuming technology, usually accounting for 30%∼40% of the total electricity consumption of a wastewater treatment plant (WWTP). The O3 consumption per unit of COD removed (g-O3/g-COD) is usually higher than 1.5 g-O3/g-COD, and the total carbon emission from catalytic ozonation is usually higher than 393.12 kgCO2 e/m3 of wastewater. In this study, we investigated an energy reduction strategy for the biggest catalytic ozonation WWTP, from laboratory-scale experimentation to corresponding engineering application. Laboratory-scale experiments showed that the mass transfer rate of dissolved O3 to the catalyst surface is crucial for COD removal efficiency. To improve the efficiency of catalytic ozonation, adding effluent backflow is a simple method that can enhance the removal of extracellular polymeric substances (EPS) from the catalyst surface and promote surface exposure. In the pilot-scale experiment (48 m3/d), when the backflow ratio increased from 0% to 100% (the optimal value), the proteins in EPS on the catalyst surface decreased significantly by 66.7%. The corresponding O3 consumption per unit of COD removed was reduced from 2.0 to 1.0 g-O3/g-COD. Furthermore, in the engineering application (52,000 m3/d) with a backflow ratio of 100%, the average effluent COD reduced from 52.0 to 43.3 mg/L, and the O3 consumption per unit of COD removed decreased from 0.98 to 0.69 g-O3/g-COD. In terms of carbon reduction, the indirect carbon emission reduction was approximately 3.0 × 103 t CO2 e/a. This study demonstrates the advantages of catalytic ozonation improvement and provides an engineering model of energy conversation and carbon emission reduction for over 35 similar WWTPs in China.

Unveiling the Biochar-Respiratory Growth of Methanosarcina acetivorans Involving Extracellular Polymeric Substances.

Biochar can be applied to diverse natural and engineered anaerobic systems. Biochar plays biogeochemical roles during its production, storage, and environmental dynamics, one of which is related to the global methane flux governed by methanotrophs and methanogens. Our understanding of relevant mechanisms is currently limited to the roles of biochar in methanotrophic growth, but less is known about the roles of biochar in methanogenic growth. Here, we demonstrated that biochar enhanced the methanogenic growth of a model methanogen, Methanosarcina acetivorans, and the role of biochar as an electron acceptor during methanogenic growth was confirmed, which is referred to as biochar-respiratory growth. The biochar-respiratory growth of M. acetivorans promoted the secretion of extracellular polymeric substances (EPS) with augmented electron transfer capabilities, and the removal of EPS significantly attenuated extracellular electron transfer. Identification and quantification of prosthetic cofactors for EPS suggest an important role of flavin and F420 in extracellular electron transfer. Transcriptomic analysis provided additional insights into the biochar-respiratory growth of M. acetivorans, showing that there was a positive response in transcriptional regulation to the favorable growth environment provided by biochar, which stimulated global methanogenesis. Our results shed more light on the in situ roles of biochar in the ecophysiology of methanogens in diverse anaerobic environments.

Effect of thermal-calcium peroxide mediated exopolymer release on disperser pre-treatment for efficient anaerobic digestion

The present study aimed to improve the hydrolysis potential of paper mill sludge through a two-phase disintegration process. In Particular, attention was focused on removal of extracellular polymeric substance (EPS) i.e. deflocculation of sludge in order to improve the efficiency of subsequent disperser disintegration. During deflocculation, carbohydrate, protein and deoxyribonucleic acids (DNA) were used as assessment parameters. During disintegration, soluble chemical oxygen demand (SCOD) and suspended solids (SS) reduction were used as assessment index to evaluate the efficiency of disintegration. A greater EPS removal was attained while deflocculating the sludge at calcium peroxide dosage of 0.05 g/g suspended solids (SS) and at a temperature of 70 °C. When comparing the disintegrated samples, a clear variation was noted in deflocculated and disintegrated sludge (19.2%) than the disintegrated sludge alone (13.5%). This clearly shows the need for deflocculation prior to disintegration. Likewise, a higher biomethane production of 0.214 L/g COD was achieved in deflocculated and disintegrated sludge than the pretreated sludge alone. Deflocculation reduces sludge management cost from 170 USD (Disperser alone (D alone disintegration)) to 51 USD (Thermal calcium peroxide mediated-Disperser (TCaO2-D disintegration), indicating the efficiency of the proposed disintegration.

Promoting performance of Anammox by iron loaded sludge biochar with hydrothermal carbonization (HTC-Fe-BC) addition

Anaerobic ammonia oxidation (Anammox) treatment cannot always achieve optimal efficiency due to its sensitivity to environmental conditions. The nitrogen removal efficiency of Anammox reactors with different iron loaded sludge biochar modified by hydrothermal carbonization (HTC-Fe-BC) addition dose of 0, 2.5 and 5.0 g/L (named BC0, BC1 and BC2) were analyzed. The effects of adding HTC-Fe-BC on the performance of Anammox reactor, extracellular polymeric substances (EPS), microbial community and functional genes were investigated. The results showed that the addition of HTC-Fe-BC could reduce the environmental sensitivity of Anammox reactor, the removal efficiency of total nitrogen increased from 51.20 (BC0) to 70.83 % (BC2), and the activity of Anammox sludge improved by 49.58 %. HTC-Fe-BC increased the activity of Anammox sludge by promoting the secretion of protein, humic acids and cytochrome c in EPS and alleviated the inhibitory effect by mediating the Anammox electron transfer process. After EPS removal and enzymatic hydrolysis, the activity of Anammox sludge in BC2 decreased by 61.38% and 79.80 %, respectively, significantly higher than the reduced values of BC0. Further, the relative abundance of Candidatus_Brocadia in Anammox reactors supplemented with HTC-Fe-BC was increased by 35.56–55.56 % compared to the control group, as were the relative abundances of the key functional genes connected to N transformation. These results deepened the understanding of the potential mechanism by which HTC-Fe-BC improved the efficiency of Anammox system.

Enhanced biohydrogen generation through calcium peroxide engendered efficient ultrasonic disintegration of waste activated sludge in low temperature environment

Waste activated sludge is a renewable source for biohydrogen production, whereas the presence of complex biopolymers limits the hydrolysis step during this process, and thus pretreatment is required to disintegrate the sludge biomass. In this study, the feasibility of utilizing waste activated sludge to produce biohydrogen by improving the solubilization by means of thermo CaO2 engendered sonication disintegration (TCP-US) was studied. The optimized condition for extracellular polymeric substance (EPS) dissociation was obtained at the CaO2 dosage of 0.05 g/g SS at 70 °C. The maximum disintegration after EPS removal was achieved at the sonic specific energy input of 1612.8 kJ/kg TS with the maximum solubilization and SS reduction of 23.7% and 18.14%, respectively, which was higher than the US alone pretreatment. Thus, this solubilization yields higher biohydrogen production of 114.3 mLH2/gCOD in TCP-US sample.

Effect of extracellular polymeric substances removal and re-addition on the denitrification performance of activated sludge: Carbon source metabolism, electron transfer and enzyme activity

Extracellular polymeric substances (EPS) play an important role in the metabolic activities of activated sludge. The effect of EPS removal (pellet group) and re-addition (pellet + EPS group) on the denitrification of activated sludge were analyzed in this study. The results indicated that EPS removal deteriorated the denitrification performance of the activated sludge. The denitrification rates in the pellet group with EPS extraction degrees of 7.77%, 12.37%, 35.89%, and 100% were only 82.6%, 75.7%, 64.1%, and 26.9%, respectively, of the control group. However, the denitrification rate of the pellet increased by 19–34% by re-adding the extracted EPS. Moreover, when the EPS extraction degree was 7.77%, the denitrification rate of the pellet + EPS group was 10.4% higher than that of the control group. The EPS contain many redox mediators. The electron transport system activity (ETSA) and key enzymes in biological denitrification were improved by re-adding EPS. The ETSA in the pellet + EPS group were 1.66-fold that in control group. The pellet + EPS group had a lower reaction activation energy, which was 42.9% lower with that of the control group. In addition, EPS re-addition promoted the activities of enzymes related to glycolysis by 9.60–18.08%, and nicotinamide adenine dinucleotide yield increased by 6.5%, which enhanced the denitrification rate of activated sludge. This study provides a novel method to enhance the denitrification performance of activated sludge by in situ appropriate desorption of EPS as endogenous redox mediator.

Ultrasound-Assisted Extracellular Polymeric Substance Removal from the Diatom Navicula sp.: A Route to Functional Polysaccharides and More Efficient Algal Biorefineries

Ultrasound-Assisted Extracellular Polymeric Substance Removal from the Diatom <i>Navicula</i> sp.: A Route to Functional Polysaccharides and More Efficient Algal Biorefineries

The role of extracellular polymeric substances (EPS) in the reduction of Cr(VI) by Pannonibacter phragmitetus BB

Cr(VI) contamination is a worldwide environmental problem, and bacterial reduction is considered a promising method for Cr(VI) remediation. In the present study, the role of extracellular polymeric substances (EPS) in the remediation of Cr(VI) by Pannonibacter phragmitetus BB was thoroughly studied. The results showed that the secretion of protein-fraction EPS by P. phragmitetus BB was significantly induced by Cr(VI), which increased from 382.70 to 1483.29 μg/mL with the increase of the initial Cr(VI) concentration (48–60 h). The polysaccharide content in slime EPS (SL-EPS) and loosely bound EPS (LB-EPS) increased gradually with time when the Cr(VI) concentration increased from 0 to 200 mg/L, with the highest polysaccharide content being higher than 2500 μg/mL. In contrast, the change in polysaccharides in tightly bound EPS (TB-EPS) was insignificant (p < 0.05). When the Cr(VI) concentration was higher than 200 mg/L, the secretion of polysaccharide-fraction EPS was inhibited (lower than 1000 μg/mL). Moreover, EPS removal inhibited the growth of P. phragmitetus BB and decreased Cr(VI) reduction efficiency. The adsorption capacity of intact cells to chromium was higher than that of EPS-free cells, which was fit with the Freundlich adsorption model with an R2 value of 0.96. FTIR and XPS analyses demonstrated that intact cells had a higher adsorption capacity for Cr(VI) than EPS-free cells and that Cr(III) mainly existed as Cr2O3, Cr(OH)3, CrCl3 or organic-Cr(III). In addition, the protein-fraction EPS had a critical role in Cr(VI) remediation, and the main functional groups were amine, carboxyl, hydroxyl and phosphate groups.

A novel Fe2+/persulfate/tannic acid process with strengthened efficacy on enhancing waste activated sludge dewaterability and mechanism insight

As an essential section before final sludge disposal, sludge dewatering has currently been one of the focus issues. In this study, an innovative Fe2+/persulfate/tannic acid (TA) process was verified to further strengthen systemic efficacy on enhancing sludge dewaterability, compared with the conventional Fe2+/persulfate process. With the efficient TA/Fe2+ (molar ratio) of 0.25 added in Fe2+ (0.3 mmol/gTS (total solid))/persulfate (0.6 mmol/gTS) process, sludge dewaterability was enhanced remarkably. Capillary suction time, specific resistance to filtration, and water content of dewatered sludge cake were further reduced by 61.5%, 35.3%, and 6.4% than these in Fe2+/persulfate. Sludge supernatant viscosity was further reduced by 86.7% due to the more removal of extracellular polymeric substances (EPS). The secondary structure of EPS protein changed apparently and fluorescent components of EPS decreased distinctly. Sludge functional group contents were observed to be lower. TA effectually increased sludge particle size and heightened sludge flocculability, rendering the large and compact aggregations. Moreover, TA accelerated the recovery of Fe2+, facilitating persulfate activation to generate more SO4·− and ·OH for EPS disruption and cell lysis in the conditioning system. These findings provided a novel approach based on the Fe2+/persulfate process in sludge treatment for desirable dewaterability.

The influence of extracellular polymeric substances on the coagulation process of cyanobacteria

The hydrophobicity and flocculation properties of cyanobacterial cells are closely related to their extracellular polymeric substances (EPS). During the treatment of drinking water, the coagulation and removal of EPS-wrapped cyanobacterial particles from natural water sources is very difficult. In this work, a series of surface characteristics of cyanobacterial cells with different EPS fractions were analyzed to evaluate their influences on the coagulation process. With the removal of EPS, the coagulation efficiency of cyanobacteria was gradually improved. The intracellular microcystin release showed that the cyanobacterial cells in each EPS removal phase were almost intact with few broken cells. The surface of cyanobacterial cells had higher hydrophobicity and lower zeta potentials with each step of the EPS extraction, which improved the ratio of particles that were in an unstable state. Furthermore, the deeper the EPS extraction phase, the larger the decreased in size of cyanobacterial particles, thus increasing their specific surface area for adsorption with coagulant. It was concluded that the coagulation mechanism of EPS-wrapped cyanobacterial particles was: the cyanobacterial cells were first peeled off through attraction by opposite charges from the coagulant, and then they were adsorbed before settling down. This study provides a scientific basis for the removal of cyanobacteria by enhancing coagulation.

Extracellular polymeric substances alter cell surface properties, toxicity, and accumulation of arsenic in Synechocystis PCC6803

Arsenic (As) contamination of water poses severe threats to human health and thus requires effective remediation methods. In this study, Synechocystis PCC6803, a model cyanobacterium common in aquatic environments, was used to investigate the role of extracellular polymeric substances (EPS) in As toxicity, accumulation, and transformation processes. We monitored the growth of Synechocystis with As exposure, measured the zeta potential and binding sites on the cell surface, and analysed As accumulation and speciation in Synechocystis cells with and without EPS. After EPS removal, the binding sites and zeta potential of the cell surface decreased by 44.43% and 31.9%, respectively. The growth of Synechocystis decreased 49.4% and 43.7% with As(III) and As(V) exposure, and As accumulation in the cells decreased by 12.8–44.5% and 14–42.7%, respectively. As absorption was enhanced in cells with EPS removed. The oxidation of As(III) and reduction of As(V) were significantly greater in cells with intact EPS compared to those with EPS removed. Fourier transform infrared spectroscopy (FTIR) showed that functional groups of EPS and Synechocystis cells, including –NH, –OH, CO, and CC, interacted with As species. Together the results of this work demonstrate that EPS have significant impacts on cell surface properties, thereby affecting As accumulation and transformation in Synechocystis PCC6803. This work provides a basis for using EPS to remedy As pollution in aquatic environments.

The role of extracellular polymeric substances in bacterial adhesion onto variable charge soils

ABSTRACT We investigated the role of extracellular polymeric substances (EPS) in the adhesion of Pseudomonas fluorescens, Bacillus subtilis, and Escherichia coli on four variable charge soils. Cation exchange resin was used to remove surface-bound EPS. It was observed that soil cation exchange capacity (CEC) and Fe2O3 contents greatly influenced their adhesion ability for the bacteria. The maximum adhesion capacity of Ultisol from Guangzhou for E. coli, P. fluorescens, and B. subtilis were 609.3, 1113.9, and 2169.2 mg g−1, respectively. The values were 434.7, 837.5, and 2067.9 mg g−1 for Oxisol and 134, 632.3, and 408.5 mg g−1 for Alfisol. EPS removal decreased the adhesion of the bacteria in variable charge soils and thus increased their mobility in the soils. However, EPS removal did not greatly alter the electrokinetic properties of bacterial cells. There was significant (p ˃ 0.05) difference in the rates of deprotonation between the different bacteria species. The deprotonation rates were 53.8, 71.7, and 5.6% for native P. fluorescens, B. subtilis, and E. coli, and 22.4, 63.9, and 6.5% for the EPS-free bacteria, respectively. Therefore, bacterial mobility in variable charge soils is greatly influenced by the concentration of EPS and CEC as well as Fe2O3 contents of the soils.

Extracellular Polymeric Substances Acting as a Permeable Barrier Hinder the Lateral Transfer of Antibiotic Resistance Genes.

Antibiotic resistance genes (ARGs) in bacteria are emerging contaminants as their proliferation in the environment poses significant threats to human health. It is well recognized that extracellular polymeric substances (EPS) can protect microorganisms against stress or damage from exogenous contaminants. However, it is not clear whether EPS could affect the lateral transfer of ARGs into bacteria, which is one of the major processes for the dissemination of ARGs. This study investigated the lateral transfer of ARGs carried by plasmids (pUC19, pHSG298, and pHSG396) into competent Escherichia coli cells with and without EPS. Transformant numbers and transformation efficiency for E. coli without EPS were up to 29 times of those with EPS at pH 7.0 in an aqueous system. The EPS removal further increased cell permeability in addition to the enhanced cell permeability by Ca2+, which could be responsible for the enhanced lateral transfer of ARGs. The fluorescence quenching experiments showed that EPS could strongly bind to plasmid DNA in the presence of Ca2+ and the binding strength (LogKA = 10.65–15.80 L mol-1) between EPS and plasmids was positively correlated with the enhancement percentage of transformation efficiency resulting from the EPS removal. X-ray photoelectron spectroscopy (XPS) analyses and model computation further showed that Ca2+ could electrostatically bind with EPS mainly through the carboxyl group, hydroxyl group, and RC-O-CR in glucoside, thus bridging the plasmid and EPS. As a result, the binding of plasmids with EPS hindered the lateral transfer of plasmid-borne ARGs. This study improved our understanding on the function of EPS in controlling the fate and transport of ARGs on the molecular and cellular scales.

Role of extracellular polymeric substances on the behavior and toxicity of silver nanoparticles and ions to green algae Chlorella vulgaris

The effect of extracellular polymeric substances (EPS), vital organic matters and nutrient elements in the natural environment, on the behavior and toxicology of silver nanoparticles (AgNPs) and ions remains ambiguous. In this study, the role of EPS on the toxicity of AgNPs and dissolved silver ions (from AgNO3) to a green algae Chlorella vulgaris was investigated. After the removal of EPS, algae accumulated more silver, about 7.41- and 1.25-fold of those in the algae with EPS for AgNPs and AgNO3 treatments, respectively. The large amount of accumulated silver was bound to the algal cell surface for AgNPs treatment and was internalized in the algae for AgNO3 treatment, irrespective of the presence of EPS in algae. After exposure to AgNPs, the ruffles in the surfaces of algal cells were filled by AgNPs, and almost invisible. FTIR showed that for both AgNPs and AgNO3, the aldehyde groups on the cell surface were oxidized to carboxyl groups by silver ions, irrespective of the presence of EPS in algal cells, indicating that silver ions were released from the oxidization of AgNPs and reacted with algal cells. The content of chlorophyll showed that AgNPs depressed algal growth more remarkably than did AgNO3, independent of the presence of EPS in algae, suggesting that AgNPs had greater toxic effects on algae than did silver ions. The findings suggest that the barrier effect of EPS gave nanoparticles an extraordinary edge over ions, but EPS had no discerning effect on the interaction of algal cells with the silver ions released from AgNPs and AgNO3, and also on the effect of AgNPs and AgNO3 on algal growth.

Comparison of different chemical cleaning reagents on fouling recovery in a Self-Forming dynamic membrane bioreactor (SFDMBR)

Abstract Self-forming dynamic membrane bioreactor (SFDMBR) using large pore size (>5 μm) membrane material is regarded as a cost-effective technology with less fouling and high permeate flux. However, no successful long-term operation without chemical cleaning is achieved. Therefore, an optimum chemical cleaning reagent needs to be explored with the understanding of foulants structure. This study compared the cleaning effects of three typical chemical cleaning reagents, i.e. sodium hydroxide (NaOH), sodium hypochlorite (NaClO), and sodium dodecyl sulfate (SDS), using a lab-scale SFDMBR. NaClO is identified as the most effective cleaning reagent in view of its trans-membrane pressure (TMP) reduction and permeability recovery efficiency. NaClO could achieve 99.0% of permeability recovery and full TMP reduction, while NaOH and SDS could only recover 87.7% and 76.5% of initial permeability and showed limited efficiency in TMP reduction, although all three reagents can achieve over 70% of extracellular polymeric substances (EPSs). The major foulant of the SFDMBR was a complex mixture of sludge flocs with EPS. NaClO cleaning can largely remove the flocs and EPS by oxidization effects while NaOH and SDS were only effective in EPS removal, which explained why NaClO cleaning showed the best performance. β-polysaccharide attached on the mesh fibers and acted as the binding substance between the foulants and mesh fibers is the main reason for irremovable inner pore fouling, which only could be significantly removed with NaClO cleaning. These results well explain the difference of filtration performance after three types of chemical cleaning.

Role of extracellular polymeric substances in biosorption of Pb2+ by a high metal ion tolerant fungal strain Aspergillus niger PTN31

It is widely reported that fungal strains show good heavy metal ions tolerance, but the role of fungal extracellular polymeric substances (EPS) in heavy metal ion biosorption and tolerance is still not clear. In this study, a high metal ion tolerant fungal strain PTN31, identified as Aspergillus niger, was isolated, which could grow in the medium with coexistence of various metal ions. The minimum inhibitory concentration (MIC) for Pb was up to 72 mM. Moreover, biosorption behaviors and mechanisms of Pb2+ by PTN31 and extracted EPS were fully tested. Higher pH promoted biosorption of Pb2+ by the both biosorbents due to deprotonation of the functional groups in microorganisms and EPS. High and low temperature affected the physiological and metabolic activity of the biosorbents, leading to low Pb2+ adsorption. The adsorption kinetic process was well described by pseudo-second order model (R2 > 0.98) and the adsorption isotherm fit well with Freundlich model (R2 > 0.95). The maximum monolayer Pb2+ biosorption capacity of extracted EPS form PTN31 was as high as 713.6 mg/g, whereas Pb2+ biosorption capacity of PTN31 was decreased by 40.9%–66.8% after removal of EPS. Therefore, large Pb2+ biosorption capability of EPS is primarily responsible for the high lead tolerance of strain PTN31. EDS and FTIR indicated that EPS with abundant functional groups was highly related to the formation of cell aggregates, which could build a protective barrier for protecting cells from hostile environments.