Slime Extracellular Polymeric Substances Research Articles

Deep dewatering of municipal sludge by combining alternating electric field electro-osmosis and nano-CaO2 oxidation

To improve the effect of traditional electroosmotic sludge dewatering, combining alternating electric field electro-osmosis and nano-calcium peroxide (CaO2) oxidation, a homemade vertical electro-osmosis dewatering device was employed in this work to study the effects of different parameter on the dewatering of primary dewatered sludge from municipal sewage treatment facilities with a moisture content of around 85%. The sludge water content (Wr) was used as an indicator, and concentration of extracellular polymeric substances (EPS) in the dewatered sludge was measured, and its structure was analyzed to investigate the effect of EPS changes on sludge dewatering.The response surface method was used to optimize the parameters. Wr decreased to 36.23 % at a CaO2 amount of 14.79 mg·g−1 dry sludge, a time ratio of 7.98:1, and a voltage gradient of 19.71 V·cm−1. Analysis of zeta potential and infrared characterization indicates that under acidic circumstances, CaO2 reacts more positively with water to produce hydrogen peroxide, and EPS is more easily destabilized and degraded, due to this, the problem of unequal water content in the cathode and anode sludge cakes is also solved. During the sludge dewatering process, the synergistic effect of alternating electric field and calcium peroxide together destroys the cell structure and EPS of sludge, especially the tightly bound EPS (TB-EPS), enabling the migration of substances and the formation of loosely bound EPS (LB-EPS), slime EPS (S-EPS), or filtrate, which can improve the sludge dewaterability.

Treatment of laundry wastewater using extracellular polymeric substances (EPS)

The problem of management and treatment of wastewater from commercial laundries is a matter of concern. The present study provides an effective and eco-friendly solution to the treatment of wastewater from commercial laundries in Quebec (Canada) by using the extracellular polymeric substance (EPS) as a bio-flocculant. EPS was produced from the valorization of crude glycerol and paper mill sludge by a bacterial strain (BS-04). Two different types of EPS: Slime EPS (S-EPS) and Broth EPS (B-EPS) were used for the treatment of commercial laundry wastewater (CLWW). This is the first study for the treatment of CLWW using bio-flocculant EPS. A comparison between the conventional treatment of laundry wastewater (LWW) by chemical coagulants (FeSO4, CaCl2, Alum) and enhanced treatment by bio-flocculant EPS has been drawn in the study. Moreover, LWW treatment by a combination of EPS and chemical coagulants was also investigated. It was observed that S-EPS (0.6 g/L) gave better flocculation activity (FA) than B-EPS. S-EPS alone can remove 83.20% of turbidity, 77.69% of suspended solids (SS), and 76.37% of chemical oxygen demand (COD). The best results were obtained by combining S-EPS (0.6 g/L) with alum (300 mg/L) at pH 7 for a treatment time of 30 min. This combination was able to remove 98% of turbidity, 95.42% of SS, and 83.08% of COD from LWW. When treatment time has been increased to 4 h at pH 7, it resulted in more than 88% COD removal from CLWW.Graphical

Structural insights into mechanisms of rapid harvesting of microalgae with pH regulation by magnetic chitosan composites: A study based on E-DLVO model and component fluorescence analysis

Magnetic harvesting of microalgae depends on the interface interactions between microalgal cells and flocculants, and thus it is important to find a reasonable evaluation method understand these interface interactions. In this effort, we discussed the formation mechanism and pH regulation of microalgae magnetic harvesting via magnetic chitosan (Fe3O4@SiO2-CS) synthesized by a micro-emulsion method. The flocculation performances and mechanisms during the harvesting of microalgae by the novel flocculant were evaluated. The synthesis process and structure were determined by XRD, FT-IR, SEM and XPS, and the results indicated that Fe3O4@SiO2-CS was successfully prepared. The collection efficiency of 96.52 % was achieved for Chlorella vulgaris within 3 min using Fe3O4@SiO2-CS with the Fe3O4@SiO2 and CS mass ratio of 1:3 under pH 1.0. Moreover, this study introduced the two-dimension fractal dimension and extended Derjaguin-Landau-Verwey-Overbeek (E-DLVO) model to evaluate the harvesting performances and mechanisms of Fe3O4@SiO2-CS. Experimental results showed that a strong electrostatic interaction was formed under acidic conditions between Fe3O4@SiO2-CS and microalgae cells with D2 = 1.82 (fractal dimension value). The hydrophobic tryptophan-like amino acid was observed in the slime-extracellular polymeric substances (S-EPS) secreted by microalgae. S-EPS was found to be a significant substance to promote harvesting performance when the system was neutral or alkaline. This work provides deeper insights into microalgae harvesting by Fe3O4@SiO2-CS as well as reasonable mechanisms to illustrate the interaction of Fe3O4@SiO2-CS and microalgae under different pH values.

Understanding the mechanism of denitrifying phosphorus removal from the perspective of intracellular carbon source and extracellular polymeric substances characteristics

Denitrifying phosphorus removal (DPR) is a novel approach for denitrification and phosphorus (P) adsorption simultaneously under an anoxic condition. A well-running DPR system was used in this study to investigate the DPR mechanism based on the changes in intracellular carbon sources and extracellular polymeric substances (EPS) characteristics. In the anaerobic stage, the intracellular carbon source and EPS characteristics test results showed that Poly-β-hydroxyalkanoates (PHA) increased by 1.75 ± 0.58 mmol C/L, which was related to the utilization of proteins slime EPS (S-EPS). Moreover, tyrosine-like substances in S-EPS were mainly used for the PHA synthesis by parallel factor analysis (PARAFAC) and correlation analysis. In addition, concentrations of K+, Mg2+ and Ca2+ in EPS were changed in different stratified EPS. EPS was an extracellular phosphorus reservoir for DPR activated sludge. In the anoxic stage, K+ and Mg2+ in the matrix had a linear relationship with P, but Ca2+ accumulated in TB-EPS. Further, the inorganic phosphorus absorbed by the activated sludge reacts with Ca2+ as P–Ca precipitation. Above the results are helping to preliminarily understand the mechanism of DPR from the perspective of intracellular carbon sources and EPS characteristics.

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.

Enhancement of sewage sludge dewaterability by fungal conditioning with Penicillium simplicissimum NJ12: from bench- to pilot-scale consecutive multi-batch investigations.

Bench- and pilot-scale successive multi-batch trials were conducted to investigate the performance and sustainability of fungal conditioning with Penicillium simplicissimum NJ12 for improving sludge dewatering. The dominant factors affecting the sludge dewaterability improvement by P. simplicissimum NJ12 were also identified. Fungal treatment with P. simplicissimum NJ12 at a volume fraction of 5% of the inoculum greatly improved the sludge dewaterability. This improvement was characterized by sharp decreases in the specific resistance to filtration from 1.97 × 1013 to 3.52 × 1011 m/kg and capillary suction time from 32 to 12 s within 3 days. Stepwise multiple linear regression analysis showed that a marked decrease (58.8%) in the protein content in slime extracellular polymeric substances and an increase in the zeta potential of the sludge (from -35 to -10 mV) were the most important factors that improved the dewaterability of sludge after fungal treatment. Consecutive processes of fungal treatment could be realized by recirculating the fungal-treated sludge with a recycling rate of 1:2 (Vbiotreated sludge/Vtotal sludge). The treatment effectiveness was maintained only over three successive cycles, but replenishment with fresh P. simplicissimum NJ12 would be provided periodically at set batch intervals. These findings demonstrate the possibility of P. simplicissimum NJ12-assisted fungal treatment for enhancing sludge dewatering.

Comparative study on production and characterisation of extracellular polymeric substances (EPS) using activated sludge fortified with crude glycerol from different biodiesel companies

Extracellular polymeric substances (EPS) are eco-friendly and economical biopolymers with a significant role in pollutant removal, bio-flocculation, settling and dewatering of activated sludge. In this study, growth profile and EPS production by an EPS-producing microbial strain (isolated from wastewater sludge or WWS) was studied using activated sludge fortified with glycerol. The study compared three crude glycerol samples as carbon sources from different biodiesel companies (BIO-LIQ, BIOCARDEL, ROTHSAY) and their effect on EPS production and characterisation was observed. The maximum slime EPS (S-EPS) concentration (12.34 g/L) was produced when sludge fortified with BIO-LIQ crude glycerol was used, higher than pure glycerol (10 g/L) at 72 h. The S-EPS was enhanced (16 g/L) when purified BIO-LIQ glycerol (by acid treatment) was used. It was also observed that S-EPS concentration increased 1.6–2.6 times by using sludge fortified with glycerol as compared to only glycerol (no sludge) as EPS production medium. In addition, the S-EPS produced from different glycerol samples yielded different characteristics in terms of protein-carbohydrate content, flocculation activity and dewaterability. The S-EPS from purified BIO-LIQ glycerol (with sludge) gave maximum flocculation activity and dewaterability i.e. 93.71% and 60.2% respectively. The comparison between Ca(OH)2 and NaOH used as alkaline sludge pre-treatment methods revealed that the EPS produced from Ca(OH)2-treated sludge fortified with glycerol solutions to be better in terms of protein content, flocculation activity and dewaterability. Structural composition analysis using Fourier Transform Infrared Spectroscopy (FT-IR) revealed the presence of distinct functional groups (carboxyl, hydroxyl, amine groups) in the produced S-EPS.

The influence of different sludge concentrations on its dewaterability during bioleaching.

Bioleaching, a technologically and economically feasible technology, is considered as the high efficiency method to improve dewaterability in sewage sludge. The objective of this study was to investigate the effect of different sludge concentrations on bioleaching dewaterability and understand the mechanism of the effect of bioleaching on sludge dewaterability. Variation in pH, oxidation-reduction potential (ORP), capillary suction time (CST), specific resistance to filtration (SRF) and different fractions of extracellular polymeric substances (EPS) including slime EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) were determined. Different sludge concentrations (5, 10, 15, 20 and 30 g·L-1) were selected to investigate during bioleaching. Results indicated that sludge buffering capacity significantly inhibited bioleaching efficiency as sludge concentrations increased. Optimum enhancements in sludge dewaterability were observed during the 10 g·L-1 sludge concentration treatment, and reached a maximum when the pH was 2.11. The variation of different fractions of EPS revealed that the ratio of S-EPS/TB-EPS significantly affected sludge dewaterability. Principal component analysis and Pearson's correlation analysis both provided evidence that the higher TB-EPS followed by a very large reduction was positively correlated with sludge dewaterability. However, the increase of protein and DNA in S-EPS content was negatively correlated with sludge dewaterability.

Effect of citric acid on extracellular polymeric substances disruption and cell lysis in the waste activated sludge by pH regulation

This paper investigated the effects of citric acid (CA) on extracellular polymer destruction and cell lysis in sludge at different initial pH by measuring capillary suction time (CST), extracellular polymeric substances (EPS) and intracellular bound water. The results indicated that under CA concentration at 0.05 g/g suspended solids (SS) and initial pH 4, the CST value decreased from 175.5 s to 112.3 s, slime extracellular polymeric substances (S-EPS) and loosely bound EPS (LB-EPS) content respectively to increase from 4.92 to 41.43, 2.27 to 5.49 mg/g volatile suspended solids (Vss), while tightly bound EPS (TB-EPS) content to decrease from 12.35 to 5.01 mg/g (Vss), which suggested CA could disrupt outer EPS effectively. Intracellular bound water content decreased from 1.23 g/g to 0.41 g/g dry solid (DS). As a result, CA could release intracellular bound water effectively, thereby improving sludge dewatering degree.

Synergy between denitrification and calcium bridging improves dewaterability of waste activated sludge

Abstract Dewaterability of waste activated sludge was significantly improved through a mild conditioning process without energy-intensive treatment. Calcium nitrate (Ca(NO3)2) addition enhanced sludge dewatering performance, with a reduction in capillary suction time (CST) and cake moisture content by 58.7% and 8.5%, respectively. Ca(NO3)2 treatment outperformed KNO3 and CaCl2 treatment by 59.1% and 6.5% regarding reduction in cake moisture content. Characterization of the sludge extracellular polymeric substances (EPS) revealed that proteins in the slime EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were decomposed by 97.7%, 89.6% and 60.9%, respectively, during the 5-day denitrification process triggered by nitrate supply, thus releasing bound water. Ca2+ addition induced charge neutralization of negatively-charged EPS functional groups and also facilitated flocculation, further enhancing the sludge filterability. This study also showed a proof-of-concept that nitrate brine (i.e. concentrated nitrification effluent) could be used to enhance sludge dewatering, which might provide a new paradigm of efficient sludge reduction for local municipal wastewater treatment facilities.

Improved sludge dewaterability by tannic acid conditioning: Temperature, thermodynamics and mechanism studies

Waste activated sludge (WAS), containing biological pathogens, chemical elements and high moisture (>99%), was generated continually from municipal sewage treatment plants. Sludge dewatering could diminish the volume of WAS and control the diffusion of environmental pollution efficiently. In this study, tannic acid (TA), as a plant-derived phenolic compound, was investigated for improving WAS dewaterability at different temperatures. Apparently, the WAS dewaterability was enhanced by TA conditioning in the range of 25–55 °C, but further increase in temperature did not significantly affect the dewatering. With the TA addition of 0.15 mmol/gTS (total solid) at 55 °C, the WAS dewaterability was improved by 84.5% decrease in capillary suction time (CST), 96.5% decrease in specific resistance of filtration (SRF), and 19.9% decrease in water content (Wc) of dewatered sludge cake. TA facilitated removing supernatant viscosity and protein of sludge EPS (extracellular polymeric substances), specifically with 88.9% and 75.0% protein removal of slime EPS (S-EPS) and loosely bound EPS (LB-EPS). Thermodynamics modeling revealed that the improved dewaterability was dominantly attributed to the hydrophobic bonding between TA and EPS proteins, which was strengthened with the increase in temperature. However, when the conditioning temperature exceeded 55 °C, thermal effect took place and accelerated the release of biopolymers into EPS and hence, counteracted the beneficial effect of TA conditioning to further improve WAS dewatering. The results offered not only the dewatering effectiveness and mechanism of TA conditioning, but also a potential approach of applying plant waste to treat WAS for the high dewaterability.

Insight into the enhanced sludge dewaterability by tannic acid conditioning and pH regulation

Tannic acid (TA), a phenolic compound, may be considered as a sludge conditioning agent on account of its ability to precipitate protein. In this study, the effectiveness of TA conditioning on enhancing waste activated sludge (WAS) dewatering was investigated at various pH values. The results indicated that with the conditioning of 0.15 mmol TA per gram of total solid (TS), the WAS dewaterability was affected distinctly by the pH regulation. The reductions of 86.8% capillary suction time (CST), 96.3% specific resistance of filtration (SRF), and 23.6% water content (Wc) of dewatered sludge cake were achieved at an optimal pH value of 4.0. Meanwhile, obvious alterations were observed in some aspects like supernatant viscosity, zeta potential, particle size and extracellular polymeric substances (EPS) polymers. Correlation analysis indicated that the proteins in slime EPS and loosely bound EPS dominantly governed sludge dewaterability. Fluorescence quenching analysis indicated that in the range of acidity, the increase of pH value afforded more binding sites of sludge EPS for TA. However, the removal of EPS protein depended on the combined effect of TA conditioning and pH regulation. The findings provided a novel approach and explanation of WAS dewaterability enhancement using organic additive conditioning and pH regulation.

Enhancement of biological fermented sludge dewaterability by inoculation of filamentous fungi Mucor circinelloides XY-Z and Penicillium oxalicum LY-1

The two filamentous fungi of Mucor circinelloides XY-Z and Penicillium oxalicum LY-1 isolated from citric acid wastewater sludge collectively enhanced sludge dewaterability by 85.83% to achieve the lowest value of normalized sludge specific resistance (SRF) to 6.8 × 1011 m·L/kg·g-TSS. The results showed that 75.77% of slime extracellular polymeric substances (EPS), 42.99% of protein in slime EPS and 60.27% of polysaccharide in LB-EPS were degraded during activated sludge treatment by the two mixed fungi of Mucor circinelloides XY-Z and Penicillium oxalicum LY-1, contributing to the conversion of 64.61% of bound water wrapped in EPS into free water, thereby improving activated sludge dewaterability.

Effective gel-like floc matrix destruction and water seepage for enhancing waste activated sludge dewaterability under hybrid microwave-initiated Fe(II)-persulfate oxidation process

Chemical conditioning before mechanical dewatering is an indispensable step to enhance the waste activated sludge (WAS) dewaterability and solid-liquid separation. Feasibility of utilizing Fe(II)/S2O82− oxidation integrated with microwave irradiation (MW) in improving gel-like floc destruction, water seepage and WAS dewaterability was investigated. Comprehensive characterization of the treated WAS was conducted to explore the effects of MW on the catalyzing kinetics of Fe(II)/S2O82− oxidation and reveal the underlying dewatering principle. The results demonstrated that MW-Fe(II)/S2O82–process was more cost-efficient, reagent-saving than single Fe(II)/S2O82− oxidation or MW irradiation in stimulating WAS dewaterability and the optimal conditions were 0.4/0.5 mmol-Fe(II)/S2O82− g−1-TS (total solids) and 500 W with 94.6% capillary suction time (CST) reduction within 120 s of conditioning. Thermal effect of MW reduced the activation energy of S2O82− decomposition and stimulated the generation of more SO4−· while athermal effect could create additional gel-network destruction and cell lysis, which reduced the water-binding energy and induced the seepage of more extracellular polymeric substances (EPS)-bound and cell water. Further analysis via fluorescence excitation-emission matrix combined with parallel factor analysis demonstrated that protein-like, humic- and fulvic-like substances in slime EPS (S-EPS) and loosely bound EPS (LB-EPS) together affected sludge dewaterability. Additionally, the hybrid process could further remove the released COD and ammonia, facilitating the subsequent advanced treatment.

Effect of using different proportions of inoculum during bioleaching on sludge dewaterability.

Bioleaching, the addition of bacteria to geological materials, has been applied to sludge to remove metals and improve upon sludge dewaterability. This paper investigates the effect of using different quantities of inoculum (bacteria) during bioleaching on sludge dewaterability. The analysis was based on bioleaching experiments conducted in a 20 L bio-reactor using different quantities of inoculum (20%, 10%, 5%, 2%, 0%). Changes in pH, oxidation reduction potential (ORP), capillary suction time (CST), specific resistance to filtration (SRF) and extracellular polymeric substances (EPS) were determined to gauge sludge dewatering. Results indicate that sludge dewaterability during the 2%, 10%, and 20% inoculum experiments declined through time. Decreased dewaterability is attributed to increases in the quantity of proteins and polysaccharides in slime EPS. Dewaterability improved during the 5% inoculum experiment, and reached a maximum when pH was 2.3. During this latter experiment, CST and SRF were reduced by 74% and 62%, respectively, in comparison to control conditions, while total EPS content decreased by 71%. The decrease in total EPS was primarily due to a decrease in proteins associated with tightly bound EPS (TB-EPS). Thus, changes in the amount of proteins in TB-EPS and sludge pH played a crucial role in sludge dewaterability.

Degradation of slime extracellular polymeric substances and inhibited sludge flocs destruction contribute to sludge dewaterability enhancement during fungal treatment of sludge using filamentous fungus Mucor sp. GY-1

Mechanisms responsible for the sludge dewaterability enhanced by filamentous fungi during fungal treatment of sludge were investigated in the present study. The filamentous fungus Mucor sp. GY-1, isolated from waste activated sludge, enhanced sludge dewaterability by 82.1% to achieve the lowest value of normalized sludge specific resistance to filtration (SRF), 8.18×1010m·L/kg·g-TSS. During the fungal treatment of sludge, 57.8% of slime extracellular polymeric substances (EPS) and 51.1% of polysaccharide in slime EPS were degraded, respectively, by Mucor sp. GY-1, contributing to the improvement of sludge dewaterability. Slime EPS is much more available for Mucor sp. GY-1 than either LB-EPS or TB-EPS that bound with microbial cells. In addition, filamentous fungus Mucor sp. GY-1 entrapped small sludge particles and inhibited the destruction of sludge flocs larger than 100μm, thus enhancing sludge dewaterability, during fungal treatment of sludge using Mucor sp. GY-1.

Disintegration of excess activated sludge with potassium permanganate: Feasibility, mechanisms and parameter optimization

Sludge disintegration destroys the sludge floc structure and releases the extracellular polymeric substances (EPS) and cell contents into the liquid phase, to enhance the sludge anaerobic digestion. Potential benefits of potassium permanganate (KMnO4) disintegrating excess sludge were investigated in this paper. Sludge disintegration feasibility was analyzed with soluble chemical oxygen demand (SCOD) increase in supernatant. Sludge disintegration mechanisms were explored with analyzing the change of particle size, EPS, oxidation reduction potential (ORP) and Mn state. Sludge disintegration process was optimized through analyzing disintegration degree (DDCOD). Results showed that KMnO4 effectively disintegrated the excess sludge with a SCOD increase of 3473% and more than 97% of Mn transferred into the solid phase. A slow decrease in particle size was observed. EPS was efficiently released into supernatant, and supernatant proteins and polysaccharides increased by 490% and 141%, respectively. Loosely bound EPS increased by 498%, which was much higher than slime EPS and tightly bound EPS. The main mechanism of sludge disintegration was KMnO4 oxidation. After sludge oxidation, KMnO4 mainly transferred to the sludge solids with the states of MnO2 and Mn3O4, and a state of KxMnO4 also existed in the solids. Optimization experiments showed that suitable reaction time was 30min, and KMnO4/sludge solid mass ratio was the most important factor and its optimal value was 0.1 with a stable DDCOD of about 34%.

Bacterial polymer production using pre-treated sludge as raw material and its flocculation and dewatering potential

Sterilization, alkaline-thermal and acid-thermal treatments were applied to different sludge solids concentrations (17.0; 22.4; 29.8; 37.3; 44.8g/L, respectively) and the pre-treated sludge was used as raw material for Serratia sp.1 to produce extracellular polymeric substances (EPS). After 72h of fermentation, total EPS of 2.3 and 3.4g/L were produced in sterilized and alkaline-thermal treated sludge as compared to that of 1.5g/L in acid-thermal treated sludge. Lower EPS were produced at relatively higher solids concentrations (37.3; 44.8g/L). Broth, crude forms of capsular and slime EPS were extracted from fermented broths and used as conditioning agents by combining with 150mg of Ca2+/L of kaolin suspensions. Maximum flocculation activity of 79.1% and increased dewatering by 52.2% was achieved using broth and crude capsular EPS, respectively. The results demonstrated that EPS having high flocculating capability could be produced using wastewater sludge as sole raw material.