Sludge Extracellular Polymeric Substances Research Articles

Response of extracellular polymeric substances to thermal treatment in sludge dewatering process

Sludge dewatering is an important process in municipal wastewater treatment and critically influences the subsequent transportation and disposal. Thermal treatment coupled with other chemical processes has been widely used to improve sludge dewaterability. However, information about the response of sludge extracellular polymeric substances (EPS) to thermal treatment and its role in sludge dewatering is still limited. In this work, the effects of thermal treatment on anaerobic and aerobic sludges were investigated with an emphasis on the colloid properties of released EPS in sludge dewatering process. The results indicate that sludge dewaterability became deteriorated with the increased temperature in the range of 30–170 °C, which was ascribed to the disintegration of sludge flocs and change of EPS characteristics. Disintegrated sludge induced the release of the negatively charged EPS, resulting in the weakened bridging interaction and lower compactness. After thermal treatment, the EPS with a higher average molecular weight and stretched coil configuration retained more water. In addition, difference in dewaterability between anaerobic and aerobic sludges was found to be attributed to their different contents and structures of EPS components. These results provide an insight into thermal-dependent sludge dewatering process and are useful to facilitate water-sludge separation.

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation (IC) reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste (MSW) incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates (OLR) of 21.06–25.16kg chemical oxygen demand (COD)/(m3∙day). The COD removal efficiency and biogas yield respectively reached 89.4%–93.4% and 0.42–0.50m3/kgCOD. The formation of extracellular polymeric substances (EPS) was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7mg/g Volatile Suspended Solid (VSS) during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from −26.2mV and 30.35% to −10.6mV and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FT-IR) analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

Transfer behavior of odorous pollutants in wastewater sludge system under typical chemical conditioning processes for dewaterability enhancement

Chemical conditioning has been used for enhancing wastewater sludge dewaterability for many years, but the characteristics of odorous pollutants emission in sludge conditioning were still unclear. In this work, the transfer behavior of different odorous pollutants between air, liquid and solid phases under typical chemical conditioning processes for high-pressure dewatering was systematically investigated. The results indicated that that besides hydrogen sulfide (H2S) and ammonia (NH3), 21 kinds of volatile organic contaminants (VOCs) were identified and quantified by gas chromatography-mass spectrometry (GC-MS), while the concentrations and composition of odorous pollutants varied greatly for different conditioning processes. VOCs were composed by three main constituents including benzenes, halogeno benzene and hydrocarbons. According to mass balance analysis, about 50% of VOCs adsorbed within sludge extracellular polymeric substances (EPS) fraction. Since EPS was damaged and/or flocculation in different chemical conditioning processes, VOCs distributed in solid phase transformed into liquid phase and then released into air. The discrepancies in mass of odorous pollutants before and after chemical conditioning were likely to be related to chemical conversion under acidification, oxidation and precipitation in the presence of ferric ions.

Effect of stirring rates in anodic area of sediment microbial fuel cell on its power generation

ABSTRACTThe effect of stirring rates in anodic area of sediment microbial fuel cell on its operating performance, in terms of variations in power generation and sludge properties, was investigated in this work. The power density under 100 r/min stirring rate amounted to the highest peak value (98.8 mW/m2 for the 9th cycle). The volume average sizes of sludge flocs decreased with increasing the stirring rates, but the content of extracellular polymeric substances of sludge increased. According to cyclic voltammetry examination, significant improvement in electrochemical activity with microorganism growth was due to some kinds of mediating compounds produced in cell-associated form.

Mechanisms of microbial community structure and biofouling shifts under multivalent cations stress in membrane bioreactors

Five lab-scale membrane bioreactors (MBRs) were continuously operated to investigate the mechanisms and linkages of the microbial community and membrane fouling with trivalent metal cations (Fe(III) and Al(III)) and bivalent metal cations (Ca(II) and Mg(II)) shock loads. COD and NH4+-N removals showed recovery trends along with treatment process in the presence of metals. Trivalent metal cations reduced trans-membrane pressure (TMP) as well as fouling rate (dTMP/dt) and extended membrane module replacement period by binding activated sludge extracellular polymeric substance (EPS) and effluent soluble microbial product (SMP) productions. Illunima sequencing of 16S rRNA gene showed that metal stress stimulated specific metal-tolerance bacteria in the MBRs. Canonical correspondence analysis indicated that EPS and SMP made different contributions to the distribution of microbial community structure in Fe(III) and Al (III) systems, respectively. Under bivalent metal conditions, microbial community shifts and Ca(II) binding bridge worked together to inhibit EPS and SMP, while filamentous bacteria stimulated by Mg(II) that mainly controlled membrane fouling. This study has shown that the comparison of tri- and bivalent metals for membrane fouling control with binding bridge and functional microorganisms can provide a strategy for practical membrane bioreactor applications.

Significances of deflocculated sludge flocs as well as extracellular polymeric substances in influencing the compression dewatering of chemically acidified sludge

Abstract Sludge extracellular polymeric substances (EPS) are frequently reported as a main factor determining sludge dewatering, but the role of sludge floc structure in influencing sludge dewatering has not been fully understood. The dewatering of chemically acidified sludge was investigated to reveal the respective role of sludge floc structure and sludge extracellular polymeric substances (EPS) in influencing the removal rate of moisture (i.e., dewatering rate) and the removal amount of moisture (i.e., dewatering extent) of acidified sludge. During the chemical acidification of sludge, serious lysis of microbial cells in sludge was induced to result in a decrease of moisture content in dewatered sludge cake, from 81.8% to only 66.7%, but both the significant increase of sludge outer layer EPS content and the deflocculated sludge flocs led to a serious deterioration of dewatering rate of acidified sludge. Further studies revealed that either decreasing sludge outer layer EPS content or modifying the deflocculated sludge flocs could improve both filtration and expression stages of compression dewatering of acidified sludge to enhance the dewatering rate of acidified sludge. Especially, only 5 mg/g dry solid of anionic synthetic organic polyelectrolyte polyacrylic acid (PAA) could condition acidified sludge to improve its dewatering rate at both filtration and expression dewatering stages through re-flocculating the deflocculated flocs in acidified sludge. Therefore, the deflocculated sludge floc structure is as significant as extracellular polymeric substances in influencing the compression dewatering of acidified sludge, and the treatment of sewage sludge through chemical acidification and followed conditioning using synthetic organic polyelectrolyte PAA can enhance the dewatering extent as well as dewatering rate.

Rapid start-up of the anammox process: Effects of five different sludge extracellular polymeric substances on the activity of anammox bacteria

This study investigated the rapid start-up of the anaerobic ammonium oxidation (anammox) strategy by inoculating different biomass ratios of denitrifying granular sludge and anammox bacteria. The results demonstrated that two reactors (R1 and R2) were rapidly and successfully started-up on days 25 and 28, respectively, with nitrogen removal rates (NRRs) of 0.70kg/(m3·d) and 0.72kg/(m3·d) at biomass ratios of 10:1 (R1) and 50:1 (R2). The explanation for rapid start-up was found by examining the effect of five different sludge extracellular polymeric substances (EPS) on the activity of anammox bacteria in the batch experiments. Batch experiments results first demonstrated that the denitrification sludge EPS (DS-EPS) enhanced the anammox bacteria activity the most, and NO2−-N, NH4+-N removal rates were 1.88- and 1.53-fold higher than the control with optimal DS-EPS volume of 10mL. The rapid start-up strategy makes possible the application of anammox to practical engineering.

Enhanced dewatering of excess activated sludge through decomposing its extracellular polymeric substances by a Fe@Fe2O3-based composite conditioner

Efficient sludge dewatering methods are highly desired by municipal wastewater treatment plants. In this study, Fe@Fe2O3 nanomaterial, combined with polydiallyldimethylammonium chloride (PDMDAAC) and H2SO4, was used for sludge dewatering. This composite conditioner exhibited an excellent dewatering capability. By using uniform design, the optimized dosages of Fe@Fe2O3, H2SO4 and PDMDAAC were determined to be 40, 136 and 4.8mg/gDS (dry solids), respectively. The moisture content of sludge cake decreased from 78.1% to 64.8%, and the capillary suction time from 56 to 21s. The sludge extracellular polymeric substances (EPS) were decomposed, resulting in greater conversion of the bound water into free water and the release of free water. The electron spin resonance results show that the molecular oxygen activation process induced by Fe@Fe2O3 produced hydroxyl radicals, which were mainly responsible for the EPS decomposition. In this way, an efficient composite conditioner for enhancing sludge dewatering was developed.

Influencing Mechanism of Titanium Salt Coagulant Chemical Conditioning on the Physical and Chemical Properties of Activated Sludge Flocs

The effect of the different forms of titanium salt coagulant conditioning on sludge dewatering performance was studied. The result showed that the sludge dewaterability was the best and the specific resistance to filtration (SRF), the compressibility and the content of organic content in EPS were the lowest when <i>B</i>=0.5 compared with others. The optimal dosage of polymeric titanium chloride (PTC) was 0.005 g·g^-1, which was far less than those of the traditional iron salts and aluminum coagulants. When the dosage of PTC with different <i>B</i> values was 0.005 g·g^-1, the order of dewaterability was:PTC 0.5> PTC1.5> TiCl4> PTC2.5. In addition, the variations of characteristics such as particle size (<i>d</i>0.5) and fractal dimension(<i>D</i>F) of sludge during conditioning were analyzed. The effect of titanium salt coagulant conditioning on the distribution and composition of the sludge extracellular polymeric substance(EPS) was characterized by Three-dimensional Excitation Emission Matrix Fluorescence (3DEEM) and High Performance Size Exclusion Chromatography(HPSEC).The decrease of fluorescent intensity and molecular weight of peak distribution and intensity of organics in EPS was highly correlated to the improvement of the dewatering performance and change of sludge properties.

Biological stability and dewaterability of CAS and MBR sludge

This paper investigates and compares the characteristics of sludges produced by membrane bio-reactor (MBR) and conventional activated sludge (CAS) systems. Stability and dewaterability of full-scale MBR and CAS treatment plants are measured and compared. Obtained results show that specific methane production is higher in CAS sludge compared to MBR sludge, although one of the CAS sludges investigated had a sludge retention time (SRT) higher than the two MBR sludges investigated. Nonetheless, MBR sludge results to be characterized by a non-negligible biometanation potential (BMP). Methane production measured during BMP tests is around 200 NmL/gVS for MBR sludge, equaling 2/3 of methane production obtained, in similar condition, for CAS sludge. Dewaterability of the sludge resulted to be linearly correlated with the SRT and the sludge extracellular polymeric substances (EPS) concentration. The higher the SRT and the lower the sludge EPS concentration, the lower the specific resistance to filtration.

Characterization of Extracellular Polymeric Substances (Eps) Produced by Cloacibacterium normanense Isolated from Wastewater Sludge for Sludge Settling and Dewatering

In this study, extracellular polymeric substances (EPSs) producing strain was isolated from municipal wastewater sludge (MWWS). Growth profile and the EPS production by Cloacibacterium normanense using wastewater sludge as raw material in shake flask fermentation for 96 h were investigated. The highest concentration of S-EPS (13.0 ± 0.8 g/L) and C-EPS (0.3 ± 0.1 g/L) were attained at 48 h of fermentation. S-EPS revealed higher flocculation activity (94.2%) and dewaterability (59.9%) than other types of EPS in kaolin suspension. The dewaterability of MWWS with 2 g suspended solids (SS)/L was improved by 37.6% using 0.02 ± 0.01 g/L of S-EPS and 600 mg/L of Al2(SO4)3. The study showed a promising approach of new isolated strain to produce high concentration EPS in sludge with high flocculation activity as well as good settling.

High-Rate Anaerobic Side-Stream Reactor (ASSR) Processes to Minimize the Production of Excess Sludge.

High-rate anaerobic side-stream reactor (ASSR) processes were developed to minimize excess sludge production during wastewater treatment. New ASSRs were operated in 2.5-day solids retention time (SRT), much shorter than 10-day SRT used by the commercial sludge reduction process. The 2.5-day was selected based on literature review and preliminary studies, showing that maximum solublization of key floc components, such as divalent cations, extracellular polymeric substances (EPS), and protease, occur within 2 to 3 days of anaerobic digestion. The laboratory reactor study showed that 2.5-day ASSR systems produced approximately 60 and 20% less sludge than the control (no ASSR) and the 10-day ASSR, respectively. The experimental systems showed acceptable effluent quality, despite minimal sludge wastage. This was possible because sludge EPS were continuously released/degraded and regenerated as sludge underwent recirculation between ASSR and the aerobic basin. The results supported that the activated sludge process incorporating small ASSRs significantly decrease the production of excess sludge during wastewater treatment.

Characterization of exopolysaccharides from floccular and aerobic granular activated sludge as alginate-like-exoPS

As a component of activated sludge (AS) extracellular polymeric substances, exopolysaccharides (exoPS) have been associated with contributing physically and chemically to the structural strength and coherence of both conventional (floccular) (CAS) and aerobic granular activated sludge (GAS). The study aims at characterization of exoPS extracted from CAS fed first with synthetic wastewater, then with brewery effluent and from GAS treating the latter. CAS and GAS exoPS were analyzed for their gel-forming capacity, morphology, and moisture content of the formed hydrogels, and chemical properties of the extracted exoPS by Fourier transform infrared (FTIR) spectroscopy. Commercially available sodium alginate was used as the reference polysaccharide for comparison. The extracted exoPS from both CAS and GAS formed hydrogels or gel-like structures in CaCl2 solution, similar to CaCl2 reactions of alginate. Environmental scanning electron microscopy images displayed similarities in the morphologies of hydrogels formed by the AS exoPS and alginate. The similarity between the two was further strengthened by FTIR spectroscopy which indicated similar functional groups in the chemical structure of both exoPS extracts and alginate. Moreover, characteristic peaks of the uronic acid residues, namely guluronic and mannuronic acids, were detected at 948 and 882 cm−1, 964 and 879 cm−1, 902 and 879 cm−1 for alginate, CAS-exoPS and GAS-exoPS, respectively. Results indicated that the exoPS extracted from the AS samples resembled alginate and likewise the functions of alginate; they seemingly contribute to the physical and chemical properties and structural strength and coherence of AS, especially to the compact and durable nature of excellently settling aerobic GAS.

Study on Characteristics of Activated Sludge at Low Temperature

The change rule of characteristics of activated sludge in urban sewage treatment by activated sludge process were investigated at low temperature of 15°C~3°C.The results showed that with the temperature decreased, average particle size and dehydrogenase activity showed a trend of decrease; sludge settlement ratio and sludge volume index and sludge extracellular polymeric substance showed a trend of increase.

Chronic Response of Waste Activated Sludge Fermentation to Titanium Dioxide Nanoparticles

Due to the large-scale production and wide applications, many nanoparticles (NPs) enter wastewater treatment plants and accumulate in activated sludge. It is reported that titanium dioxide (TiO2) NPs show severe damage to many model microbes. However, it is still unknown whether the long-term (e.g., 100d) presence of TiO2 NPs would affect the performance of sludge fermentation. In this study, long-term exposure experiments (105d) were conducted to investigate the potential risk of TiO2 NPs to sludge fermentation system. It is found that the presence of environmentally relevant [6mg·(gTSS)−1] and higher [150mg·(gTSS)−1] concentrations of TiO2 NPs does not affect methane production from sludge fermentation. The analysis of fluorescence in situ hybridization indicates that these concentrations of TiO2 NPs present marginal influences on abundances of bacteria and methanogenic archaea in sludge fermentation system. The viability of sludge microorganisms and activities of key enzymes related to methane production such as protease, acetate kinase, and coenzyme F420 are unchanged by the long-term presence of 6 and 150mg·(gTSS)−1 of TiO2 NPs. Further investigations reveal that the insolubility of NPs and the protection role of sludge extracellular polymeric substances are the main reasons for the marginal influence of TiO2 NPs on sludge fermentation.

Preparation of activated carbon from wet sludge by electrochemical-NaClO activation

Activated carbon (AC) from sludge is one potential solution for sewage sludge disposal, while the drying sludge is cost and time consuming for preparation. AC preparation from the wet sludge with electrochemical-NaClO activation was studied in this work. Three pretreatment processes, i.e. chemical activation, electrolysis and electrochemical-reagent reaction, were introduced to improve the sludge-derived AC properties, and the optimum dosage of reagent was tested from the 0.1:1 to 1:1 (mass rate, reagent:dried sludge). It was shown that the electrochemical-NaClO preparation is the best method under the test conditions, in which AC has the maximum Brunauer, Emmett and Teller area of 436 m2/g at a mass ratio of 0.7. Extracellular polymeric substances in sludge can be disintegrated by electrochemical-NaClO pretreatment, with a disintegration degree of more than 45%. The percentage of carbon decreased from 34.16 to 8.81 after treated by electrochemical-NaClO activation. Fourier transform infrared spectra showed that a strong C–Cl stretching was formed in electrochemical-NaClO prepared AC. The maximum adsorption capacity of AC reaches 109 mg/g on MB adsorption experiment at pH 10 and can be repeated for three times with high removal efficiency after regeneration.

Impact of certain household micropollutants on bacterial behavior. Toxicity tests/study of extracellular polymeric substances in sludge

The impact of eight household micropollutants (erythromycin, ofloxacin, ibuprofen, 4-nonylphenol, triclosan, sucralose, PFOA and PFOS (PFAAs)) on the laboratory bacterial strain Escherichia coli MG1655 and on activated sludge from an urban wastewater treatment plant was studied.Growth-based toxicity tests on E. coli were performed for each micropollutants. The effect of micropollutants on activated sludge (at concentrations usually measured in wastewater up to concentrations disturbing the bacterial growth of E. coli) was examined in batch reactors and by comparison to a control reactor (without micropollutants). The bound extracellular polymeric substances (EPS) secreted by the sludge were measured by size exclusion chromatography and their overexpression was considered as an indicator of bacteria sensitivity to environmental changes. The chemical oxygen demand (COD) and the ammonium concentration were monitored to evaluate the biomass ability to remove the macropollution.Some micropollutants induced an increase of bound EPS in activated sludge flocs at concentrations depending on the micropollutant: erythromycin from 100μg/L, ofloxacin from 10μg/L, triclosan from 0.5μg/L, 4-nonylphenol from 5000μg/L and PFAAs from 0.1μg/L. This suggests that the biomass had to cope with new conditions. Moreover, at high concentrations of erythromycin (10mg/L) and ibuprofen (5mg/L) bacterial populations were no longer able to carry out the removal of macropollution.Ibuprofen induced a decrease of bound EPS at all the studied concentrations, probably reflecting a decrease of general bacterial activity. The biomass was not sensitive to sucralose in terms of EPS production, however at very high concentration (1g/L) it inhibited the COD decrease.Micropollution removal was also assessed. Ibuprofen, erythromycin, ofloxacin, 4-nonylphenol and triclosan were removed from wastewater, mainly by biodegradation. Sucralose and PFOA were not removed from wastewater at all, and PFOS was slightly eliminated by adsorption on sludge.

Long-term performance of enhanced biological phosphorus removal with increasing concentrations of silver nanoparticles and ions

The wide use of silver nanoparticles (AgNPs) and silver ions (Ag+) as antimicrobial agents have caused concerns about their potential effects on the environment, such as wastewater treatment plants. This paper reports the effects of increasing the influent AgNPs and Ag+ from 1 to 5 mg L−1 on the performance of enhanced biological phosphorus removal (EBPR). The increase of AgNPs showed no significant influence on EBPR in both short-term and long-term experiments. Phosphorus removal, however, was decreased by a sudden increase in Ag+ concentration and it was gradually recovered after long-term culture. The mechanism studies showed that the transformation of polyhydroxyalkanoates and glycogen and the activity of exopolyphosphatase declined when Ag+ was increased suddenly, but they were recovered after long-term culture. The denatured gradient gel electrophoresis and fluorescence in situ hybridization analyses indicated that the bacterial community structure and the abundance of polyphosphate accumulation organisms were not changed by AgNPs or Ag+. Further investigations revealed that the long-term exposure of Ag+ increased the amount of sludge extracellular polymeric substances, which accounted for the mitigation of Ag+ toxicity to the EBPR key enzyme and microbes.

Effects of extracellular polymeric substances on granulation of anoxic sludge in sequencing batch reactor

Variations of extracellular polymeric substances (EPS) and its components with sludge granulation were examined in a lab-scale sequencing batch reactor (SBR) which was fed with sodium nitrate and sodium acetate. Ultrasonication plus cation exchange resin (CER) were used as the EPS extraction method. Results showed that after approximately 90 d cultivation, the sludge in the reactor was almost granulated. The content of extracellular polysaccharides increased from 10.36 mg/g-VSS (volatile suspended solids) at start-up with flocculent sludge to 23.18 mg/g-VSS at 91 d with matured granular sludge, while the content of extracellular proteins were almost unchanged. Polysaccharides were the major components of EPS in anoxic granular sludge, accounting for about 70.6-79.0%, while proteins and DNA accounted for about 16.5-18.9% and 4.6-9.9%, respectively. It is proposed that EPS play a positive role in anoxic sludge granulation and polysaccharides might be strongly involved in aggregation of flocs into granules.

Fractional, biodegradable and spectral characteristics of extracted and fractionated sludge extracellular polymeric substances

Correlation between fractional, biodegradable and spectral characteristics of sludge extracellular polymeric substances (EPS) by different protocols has not been well established. This work extracted sludge EPS using alkaline extractants (NH4OH and formaldehyde + NaOH) and physical protocols (ultrasonication, heating at 80 °C or cation exchange resin (CER)) and then fractionated the extracts using XAD-8/XAD-4 resins. The alkaline extractants yielded more sludge EPS than the physical protocols. However, the physical protocols extracted principally the hydrophilic components which were readily biodegradable by microorganisms. The alkaline extractants dissolved additional humic-like substances from sludge solids which were refractory in nature. Different extraction protocols preferably extracted EPS with distinct fractional, biodegradable and spectral characteristics which could be applied in specific usages.