Removal Of Extracellular Polymeric Substances Research Articles

The effect of extracellular polymeric substances on the adhesion of bacteria to clay minerals and goethite

The functions of extracellular polymeric substances (EPS) during the adhesion of Bacillus subtilis to kaolinite, montmorillonite, and goethite were examined by a direct comparison of the adhesion behaviors of native and EPS-free cells via cation exchange resin (CER) treatment using batch experiments, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, and potentiometric titration. The EPS removal had no apparent influence on bacterial adhesion when the wet bacteria/mineral mass ratio was low (<0.4 for the clay mineral systems and <1.8 for the goethite system). With higher mass ratios, the absence of EPS reduced adhesion to clay minerals but enhanced adhesion to goethite. The ATR-FTIR spectra suggested that protein conformational changes were involved in the adhesion of bacteria to clay minerals, whereas additional chemical interactions such as POFe bonds were important for adhesion to goethite. In addition to electrostatic forces (repulsion for clays and attraction for goethite), absence of chemical interactions may also cause the relatively much weaker bacterial adhesion to clay minerals than to goethite. The absence of EPS did not change the interaction mode of the adhesion to clay minerals but enhanced the chemical interactions via carboxyl groups for bacteria–goethite adhesion. The potentiometric titration results coupled with the ATR-FTIR spectra showed a significant increase in site concentrations of the CER-treated bacteria as compared to the native cells. Changes in surface site concentrations and chemical interactions that were accompanied by the EPS removal may reasonably explain the influences of EPS on bacterial adhesion to different minerals.

Enhancing aerobic digestion potential of municipal waste-activated sludge through removal of extracellular polymeric substance

A protease-secreting bacteria was used to pretreat municipal sewage sludge to enhance aerobic digestion. To enhance the accessibility of the sludge to the enzyme, extracellular polymeric substances were removed using citric acid thereby removing the flocs in the sludge. The conditions for the bacterial pretreatment were optimized using response surface methodology. The results of the bacterial pretreatment indicated that the suspended solids reduction was 18% in sludge treated with citric acid and 10% in sludge not treated with citric acid whereas in raw sludge, suspended solids reduction was 5.3%. Solubilization was 10.9% in the sludge with extracellular polymeric substances removed in contrast to that of the sludge with extracellular polymeric substances, which was 7.2%, and that of the raw sludge, which was just 4.8%. The suspended solids reduction in the aerobic reactor containing pretreated sludge was 52.4% whereas that in the control reactor was 15.3%. Thus, pretreatment with the protease-secreting bacteria after the removal of extracellular polymeric substances is a cost-effective and environmentally friendly method.

Effect of extra polymeric substance removal on sludge reduction potential of Bacillus licheniformis at its optimised pH condition

AbstractThe effect of extracellular polymeric substances (EPSs) on the solubilisation of municipal wastewater sludge by protease‐secreting bacteria was investigated. The untreated sludge is an environmental menace, so sludge management techniques are introduced to treat and dispose sludge in a proper way. Sludge pretreatment is needed to increase the solubilisation and the efficiency of treatment methods. The present study deals with sludge solubilisation by bacterial enzymatic pretreatment. The EPS present in the sludge was removed by sodium hydroxide and formaldehyde to enhance solubilisation and increase the bacterial enzymatic activity. After the removal of EPS with different normalities of NaOH, there was about 11–18% sludge solubilisation and about 8–16% sludge reduction during bacterial pretreatment. Bacterial enzymatic pretreated sludge was further treated using aerobic digesters. From the results obtained in aerobic digestion, 0.06 N NaOH was chosen as the optimal concentration to remove EPSs.

Effect of temperature on intracellular phosphorus absorption and extra-cellular phosphorus removal in EBPR process

This study investigated the temperature influence on intracellular absorption and extra-cellular phosphorus removal by extra-cellular polymeric substance (EPS) in enhanced biological phosphorus removal (EBPR) process. Three sequencing batch reactors (SBRs) were operated in anaerobic/aerobic sequence at 5.0, 15.0 and 25.0°C. Phosphorus removed by intracellular absorption was demonstrated as the dominant part (>80%) in total phosphorus removal operated under different temperatures and the highest total phosphorus removal rate of 95% was obtained due to the highest intracellular phosphorus absorption of 18.2mg P in a typical cycle at 15.0°C. Phosphorus removed by EPS removal achieved the highest value at 5.0°C (2.4mg P/cycle), which resulted in a higher total phosphorus removal rate at 5.0°C (90%) than that at 25.0°C (83%). Low temperature was propitious to EPS phosphorus removal, accounting for 13% of total phosphorus removal at 5.0°C, which could be mainly due to magnesium phosphate precipitation.

Breakage and Regrowth of Sludge Flocs by Removal and Readdition of Extracellular Polymeric Substances Fractions

Different extracellular polymeric substances (EPS) fractions, including supernatant, slime, loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), have different binding characteristics to sludge flocs and thus different influences on sludge dewaterability and effluent quality. In this study, EPS removal and readdition tests as well as a flocculating test of kaolin clay solution were conducted to explore their binding characteristics. Results showed that removal of different EPS fractions from sludge flocs resulted in a decrease of particle size and an increase in zeta potential; readdition of supernatant and slime fractions to sludge flocs restored the particle size and zeta potential to their initial status, however, readdition of LB-EPS and TB-EPS fractions to sludge flocs did not allow particle size and zeta potential to return to the initial level. Similarly, variations of sludge dewaterability also followed similar trends. Extracellular polymers in the supernatant and slime fractions were likely bound to sludge flocs by physical adsorption, whereas their distributions in the TB-EPS fraction were probably bound to sludge flocs by chemical bonds. Based on the binding characteristics, good effluent quality can be achieved by the control of operating conditions.

Influence of Extracellular Polymeric Substances (EPS) on Deposition Kinetics of Bacteria

The significance of extracellular polymer substances (EPS) on cell deposition on silica surfaces was examined by direct comparison of the deposition kinetics of untreated "intact" bacteria versus those from the same strain but with EPS removal via cation exchange resin (CER) treatment using a quartz crystal microbalance with dissipation (QCM-D). Four bacterial strains, mutant Escherichia coli BL21 (gram-negative, nonmotile), Pseudomonas sp QG6 (gram-negative, motile), Rhodococcus sp QL2 (gram-positive, nonmotile), and Bacillus subtilis (gram-positive, motile), were employed to determine the influence of EPS on cell deposition. Experiments were conducted in both monovalent (NaCl) and divalent (CaCl2) solutions under a variety of environmentally relevant ionic strength ranging from 1 to 100 mM at pH 6.0. The effectiveness of EPS removal via CER method was ensured by biochemical composition analysis of EPS solutions and further confirmed by FTIR analysis. Comparable zeta potentials were observed for untreated and CER treated bacterial cells in both NaCl and CaCl2 solutions, indicating that removal of EPS from cell surfaces via CER treatment did not affect the electrokinetic properties of the cell surfaces for all four strains. However, observed deposition efficiencies (alpha) were greater for untreated cells relative to those with CER treated cells across the entire ionic strength range examined in both NaCI and CaCl2 solutions for all four bacterial strains. These results strongly demonstrated that the removal of EPS from cell surfaces for all four strains decreased the deposition of bacteria on silica surfaces. This study clearly showed that the enhancement of cell deposition on silica surfaces due to the presence of EPS on cell surfaces was relevant to all bacterial strains examined regardless of cell types and motility.

Cd adsorption onto Pseudomonas putida in the presence and absence of extracellular polymeric substances

The role of bacterial extracellular polymeric substances (EPS) in metal adsorption was determined by studying Cd adsorption onto the gram-negative bacterial species Pseudomonas putida with and without enzymatic removal of EPS from the biomass material. A range of experimental approaches were used to characterize the Cd adsorption reactions, including bulk proton and Cd adsorption measurements, FTIR spectroscopy, and fluorescence microscopy. The proton-reactivities of the biomass samples with EPS are not significantly different from those obtained for EPS-free biomass. Similarly, the presence of EPS does not significantly affect the extent of Cd removal from solution by the biomass on a mass-normalized basis, based on bulk Cd adsorption measurements conducted as a function of pH, nor does it appear to strongly affect the Cd-binding groups as observed by FTIR. However, fluorescence microscopy indicates that Cd, although concentrated on cell walls, is also bound to some extent to EPS. Together, the results from this study suggest that the P. putida EPS can bind significant concentrations of Cd from solution, and that the nature and mass-normalized extent of the binding is similar to that of the cell wall. Therefore, the EPS-bearing systems do not exhibit enhanced mass-normalized removal of Cd from solution relative to the EPS-free systems. The presence of the EPS effectively increases the viability of cells exposed to aqueous Cd, likely due to sequestration of the Cd away from the cells due to Cd-EPS binding.

Removal of Pseudomonas putida Biofilm and Associated Extracellular Polymeric Substances from Stainless Steel by Alkali Cleaning

Alkali (NaOH)-based compounds are commonly used in the food industry to clean food contact surfaces. However, little information is available on the ability of alkali and alkali-based cleaning compounds to remove extracellular polymeric substances (EPS) produced by biofilm bacteria. The objectives of this study were to determine the temperature and NaOH concentration necessary to remove biofilm EPS from stainless steel under turbulent flow conditions (clean-in-place simulation) and to determine the ability of a commercial alkaline cleaner to remove biofilm EPS from stainless steel when applied under static conditions without heat. Biofilms were produced by growing Pseudomonas putida on stainless steel for 72 h at 25°C in a 1:10 dilution of Trypticase soy broth. The biofilms were treated using NaOH at concentrations of 1.28 to 6.0% and temperatures ranging from 66 to 70°C. Other biofilms were treated with commercial alkaline cleaner at 25 or 4°C for 1 to 30 min. Removal of EPS was determined by direct microscopic observation of samples stained with fluorescent-labeled peanut agglutinin lectin. Treatment with 1.2% NaOH at 66°C for 3 min was insufficient to remove biofilm EPS. A minimum of 2.5% NaOH at 66°C and 2.0% NaOH at 68°C for 3 min were both effective for EPS removal. Commercial alkaline cleaner removed over 99% of biofilm EPS within 1 min at 4 and 25°C under static conditions. Selection of appropriated cleaning agent formulation and use at recommended concentrations and temperatures is critical for removal of biofilm EPS from stainless steel.