Microbial Extracellular Polymers Research Articles

Effectiveness of biological drying for citric acid dewatered sludge: Evaluating the impact of energy-efficient ventilation strategies

The effectiveness of dehydration and utilization processes for citric acid dewatered sludge is hampered by its high concentrations of polysaccharides, proteins, and water-binding properties of microbial extracellular polymers (EPS). This research explores the efficacy and mechanisms involved in extracting water from this type of sludge using biological drying technology, with varying rates of ventilation. Especially pertinent was the use of low ventilation rates as control variables. Our results suggest that a scheduled intermittent ventilation at lower rates allows for the most efficient removal of water, achieving a rate of 41.71 % within eight days, according to the zero-order kinetic model. Remarkably, the peak temperature registered was 60 °C, reaching this threshold in just 0.1 days and maintaining high temperatures for approximately 5.9 days. Component analysis of organic matter illustrated a preferential degradation process for lipids under these ventilation conditions which is pivotal for releasing and transforming bound water for efficient extraction, as well as facilitating the breakdown of easily hydrolysable materials. Further, polysaccharide/protein (EPS) decomposition contributed to water removal, though less significantly. The periodic ventilation strategy allowed for the maximum cumulative temperature to be sustained, demonstrating superior efficiency in harnessing bio-generated heat (82.77 % for water evaporation), resulting in dry sludge suitable for self-sustained combustion at relatively low cost ($26.61/t). Highlighted by this study is the considerable potential of energy-efficient ventilation methods in the biological drying treatment of citric acid fermented sludge and similar industrial waste materials.

Production of polymeric silver nanocomposites using microbial extracellular polymers for the effective removal of chromium (VI) from water

Production of polymeric silver nanocomposites using microbial extracellular polymers for the effective removal of chromium (VI) from water

Effect of Aeration on Blockage Regularity and Microbial Diversity of Blockage Substance in Drip Irrigation Emitter

Aerated drip irrigation is rendered as a new water-saving irrigation method based on drip irrigation technology, which is endowed with the function of effectively alleviating the problem of rhizosphere hypoxia in crop soil, enhancing the utilization rate of water and fertilizer; as a result, it improves the harvest and quality of crops. However, clogged emitters are important indexes, among others, that pose an influence to the service effect and life duration of drip irrigation systems. At present, the working principle and mechanism of the influence of air feeding on the blockage of drip irrigation emitters remain unclear. Therefore, based on the two gas filling methods of the micro/nano bubble generator and Venturi injector, the dynamic change process for the average flow ratio of an air-filled drip irrigation emitter was studied by the method of emitter plugging test. 16S rRNA sequencing was used to analyze the microbial diversity of the emitter plugs. The results show that the air injection can pose influence on the clogging procedure of drip irrigation emitters, and more importantly, it makes the distribution of blocked emitters more uniform, thus improving the uniformity of the system. Different filling methods have different effects on the blockage of the emitter. Among them, the blockage time of drip irrigation system under the micro/nano aerated drip irrigation (MAI) mode is 5.73 times longer than that under unaerated drip irrigation (UVI), and similarly, Venturi gas drip irrigation (VAI) is close to that under UVI. The filling method changed the microbial diversity of the blockage in the emitter. Among them, the number of operational taxonomic unit (OTU) unique to MAI was 2.1 times that of UVI, and the number of OTU unique to VAI was 1.3 times that of UVI. Meanwhile, gas addition will inhibit the growth of Nitrospirae and Proteobacteria microbial communities and promote the growth of Firmicutes and Actinobacteria microbial communities. Furthermore, the increase in microbial extracellular polymer in the plugging material of the emitter was inhibited and the plugging process of the emitter was slowed down. The research results are of great significance in the disclosure of the clogging mechanism of drip irrigation emitter and constructing the green, anti-blockage technology of aerated drip irrigation.

Insight into biosorption of heavy metals by extracellular polymer substances and the improvement of the efficacy: a review.

Heavy metals are continuously released into aquatic environments in which they accumulate. This phenomenon endangers public health because heavy metals accumulate along the food chain. However, conventional remediation methods are inefficient, expensive and yield toxic intermediate products, which adversely affect the environment. The discovery of green bio-adsorbents such as microbial extracellular polymer substance (EPS) has quickly attracted considerable worldwide attention because of their low cost, high removal efficiency of heavy metals and industrial availability. Hence, this review considers the sources, hazards and treatment methods of heavy metals pollution, particularly the biosorption mechanism of EPS to heavy metals and the influencing factors of the bio-adsorption process, which are significant in the efficient removal of heavy metals-containing wastewater treatment. This review also focuses on strengthening the process of EPS adsorption of heavy metals, which can further contribute to heavy metals removal. Finally, it has been proposed that improving the yield, stability, selectivity and recoverability of EPS is the key direction of further research.

Catalytic reduction of 4-nitrophenol by green silver nanocomposites assembled using microbial extracellular polymer substances

Silver (Ag) nanocomposites were prepared via a facile and eco-friendly route using microbial extracellular polymer substances (EPSs) as green substrates for the catalytic reduction of 4-nitrophenol. Batch adsorption experiments demonstrated the binding of microbial EPSs to silver ions (Ag+), which was promoted by UV light, as was evident in the kinetics and thermodynamics analyses. The assembly mechanism of Ag nanocomposites prepared using microbial EPSs in the presence of UV light was investigated using the spectral analysis. The results showed that Ag+ was reduced and transformed into Ag0 by the hemiacetal groups in the microbial EPSs, and that UV light accelerated the nucleation and growth of Ag0 to form Ag nanoparticles (diameter about 12 nm), followed by loading on the surface of microbial EPSs. Catalytic reduction of 4-nitrophenol over Ag nanocomposites was almost completed within 60 s without stirring, and the kinetic rate constant (k) was 49.9 × 10−3 s−1. The recyclability test showed that Ag nanocomposites stably maintained the efficiency of catalytic reduction through five repeated reaction cycles. This work proved that Ag nanocomposites assembled using microbial EPSs have great catalytic activity in the reduction of 4-nitrophenol, providing the green and efficient catalyst for the reduction of organic pollutants in the environment.

Influence of water availability and temperature on estimates of microbial extracellular enzyme activity.

Soils are highly heterogeneous and support highly diverse microbial communities. Microbial extracellular enzymes breakdown complex polymers into small assimilable molecules representing the limiting step of soil organic matter mineralization. This process occurs on to soil particles although currently it is typically estimated in laboratory aqueous solutions. Herein, estimates of microbial extracellular enzyme activity were obtained over a broad range of temperatures and water availabilities frequently observed at soil upper layers. A Pseudomonas strain presented optimum extracellular enzyme activities at high water activity whereas a desiccation resistant bacterium (Deinococcus) and a soil thermophilic isolate (Parageobacillus) showed optimum extracellular enzyme activity under dried (i.e., water activities ranging 0.5–0.8) rather that wet conditions. Different unamended soils presented a distinctive response of extracellular enzyme activity as a function of temperature and water availability. This study presents a procedure to obtain realistic estimates of microbial extracellular enzyme activity under natural soil conditions of extreme water availability and temperature. Improving estimates of microbial extracellular enzyme activity contribute to better understand the role of microorganisms in soils.

Regeneration and reuse of microbial extracellular polymers immobilised on a bed column for heavy metal recovery

Regeneration and reuse of microbial extracellular polymers immobilised on a bed column for heavy metal recovery

Regeneration and reuse of microbial extracellular polymers immobilised on a bed column for heavy metal recovery

Microbial extracellular polymeric substances (EPS) have gained increasing attention for various water treatment applications. In this study, EPS produced from nitrogen-limited glycerol/ethanol-rich wastewater were used to recover Cu2+ and Pb2+ from aqueous solutions. Continuous flow-through tests were conducted on a column packed with silica gel coated with polyethyleneimine, to which EPS were irreversibly attached as shown by optical reflectometry. These immobilised EPS excellently adsorbed Cu2+ and Pb2+, with 99.9% of influent metal adsorbed before the breakthrough points. Metal desorption was achieved with 0.1M HCl, with an average recovery of 86% for Cu2+ and 90% recovery for Pb2+. For the first time, we successfully showed the possibility to regenerate and reuse the immobilised EPS for five adsorption-desorption cycles (using Cu2+ as an example) with no reduction in the adsorbed amount at the breakthrough point (qbp). Based on the mass balance of the associated metal ions participating in the adsorption process, ion exchange was identified as the major mechanism responsible for Cu2+ and Pb2+ adsorption by EPS. The results demonstrate the potential of wastewater-produced EPS as an attractive and perhaps, cost-effective biosorbent for heavy metal removal (to trace effluent concentrations) and recovery (86–99%).

Role of Cationization in Bioflocculant Efficiency: a Review

Organic and synthetic flocculants are conventional flocculants used in wastewater treatment and tap water purification. The challenges of toxic residue and the resultant secondary pollutants generated from organic and synthetic flocculants have attracted research efforts towards microbial extracellular polymers as nontoxic and biodegradable substitutes. However, the bioflocculants themselves have been associated with high production costs and low efficiency. To address these challenges, tremendous efforts have been made to hybridise cations with the bioflocculants. The contradictory reports on the role of cations in bioflocculation have necessitated this review. This paper reviews the relevant and recent literature on EPS-cation structuring, cationization of bioflocculants, the efficiency of the cationization of bioflocculants, the factors affecting cation induced bioflocculation, and the mechanisms of cation induced bioflocculation. Variations in experimental procedures microbial species and growth medium composition yield bioflocculants with positive or negative functional sites and may be responsible for the contradictory effect of the cations. Establishment of a standard fermentation system that could elucidate the mechanism of cation induced bioflocculation and of the standard techniques for evaluation of the cationic content of wastewater treated with cationized bioflocculants is needded for better understanding of the cation stimulated bioflocculation.

Effects of pH and Salinity on Adsorption of Hypersaline Photosynthetic Microbial Mat Exopolymers to Goethite: A Study Using a Quartz Crystal Microbalance and Fluorescence Spectroscopy

ABSTRACTSalinity and pH are two water chemical factors that vary drastically—seasonally or daily—in a variety of aquatic environments. Drastic change of salinity and pH may have a significant impact on adsorption of microbial extracellular polymers (EPS) to sediment minerals and thus influence many other important elemental geochemical processes. However, how salinity and pH changes affect EPS adsorption to minerals is poorly known. In the present study, adsorption of EPS from a hypersaline microbial mat to goethite at different pH values (4, 7 and 10) and salinity (0.15‰, 35‰ and 70‰) was monitored online using a quartz crystal microbalance (QCM) with EEM fluorescence spectroscopy as a complementary method. The adsorption kinetics were well described by an exponential function. The adsorption capacity of EPS to goethite significantly increased as the pH and salinity increased. The pH and salinity dependence of EPS adsorption to goethite is of great importance for understanding the environmental geochemistry of heavy metals in aquatic environments. In inland lakes and estuary zones, the seasonal or daily pulse of hydrological events will drastically alter water salinity and pH and consequently exert significant influences on the mobility, chemical species and ecotoxicity of heavy metals through the EPS pathway. It is necessary to systematically investigate the geochemical behavior of EPS in such dynamic aquatic environments and their potential effects on other geochemical processes.

Insight into the roles of microbial extracellular polymer substances in metal biosorption

Biosorption presents a potent technology to remediate metal-contaminated aqueous environment or even to recover precious metals. Extracellular polymeric substances (EPS) are believed to play an important role in metal biosorption by microorganisms, but the reported results have been rather contradictory and the underlying mechanisms remain largely unclear so far. This review aims to clarify why large discrepancies existed for different EPS-metal systems through systematically exploring into the adsorption mechanisms and influential factors, and to offer some implications for advancing the implementation of metal biosorption technologies. The state-of-the-art methodologies for characterizing metal-EPS binding are summarized; several interaction mechanisms, including ion exchange, complexation and surface precipitation, are analyzed; the major influential factors such as EPS composition, metal species, solution chemistry and operating conditions are discussed; and lastly future research needs to advance the investigations and implementations of such biosorption processes are proposed.

Crystal ball – 2013

Crystal ball – 2013

Imaging Hydrated Microbial Extracellular Polymers: Comparative Analysis by Electron Microscopy

Microbe-mineral and -metal interactions represent a major intersection between the biosphere and geosphere but require high-resolution imaging and analytical tools for investigation of microscale associations. Electron microscopy has been used extensively for geomicrobial investigations, and although used bona fide, the traditional methods of sample preparation do not preserve the native morphology of microbiological components, especially extracellular polymers. Herein, we present a direct comparative analysis of microbial interactions by conventional electron microscopy approaches with imaging at room temperature and a suite of cryogenic electron microscopy methods providing imaging in the close-to-natural hydrated state. In situ, we observed an irreversible transformation of the hydrated bacterial extracellular polymers during the traditional dehydration-based sample preparation that resulted in their collapse into filamentous structures. Dehydration-induced polymer collapse can lead to inaccurate spatial relationships and hence could subsequently affect conclusions regarding the nature of interactions between microbial extracellular polymers and their environment.

Effect of carbon to nitrogen ratio on the physical and chemical properties of activated sludge

The effect of carbon to nitrogen ratio (C/N) of the feed on the physical and surface chemical properties of activated sludge is investigated. Semi‐continuous reactors with 2 liters volume were operated at a mean cell residence time of 8 days. These mixed culture reactors were operated at 3 different carbon to nitrogen ratio. The operation of conventional activated sludge plants treating municipal wastewater is represented with reactors having a C/N ratio of 21 (in terms of the ratio of COD to TKN). Carbon and nitrogen limited activated sludge systems are represented by reactors with a C/N ratio of 9 and 43, respectively. The results show that C/N ratio has a profound effect on the ultimate physical and surface chemical properties of activated sludge. Both the steady state microorganism concentration and the amount of microbial extracellular polymers produced increase with increasing C/N ratio. The sludge becomes much harder to dewater and settle and it becomes more viscous as the C/N ratio increases. A decrease in surface hydrophobicity and an increase in surface charge of the sludge accompany these physical changes.

Relationship Between Plant Phenolic Acids Released during Soil Mineralization and Aggregate Stabilization

Phenolic acids (PAs) from plant and microbial sources have been implicated as important components in a variety of soil processes, but little information is available on the decomposition rates of plant‐derived PAs, synthesis of soil microbial PAs, incorporation of PAs into humic substances and stabilization of soil aggregate fractions. To obtain this information, a Webster soil (fine‐loamy, mixed, superactive, mesic Typic Endoaquoll) was amended with seven plant residues (2% w/w) and incubated at 22 ± 2°C. Duplicate samples were extracted after incubation for 9, 29, and 84 d and analyzed for PA composition. The plant residues contained large amounts of ferulic [3‐(4‐hydroxy‐3‐methoxyphenyl)‐2‐propenoic acid] and coumaric acids [3‐(4‐hydroxyphenyl)‐2‐propenoic acid] (both C6–C3, phenylpropyl type), which decomposed according to pseudo first‐order kinetics. Most of the remaining PAs showed little change in concentration after 9 d and only microbial synthesis of 4‐hydroxybenzoic acid was noted during the study. Analysis of six purified soil microbial polymers isolated from pure culture confirmed that the tested microbial extracellular polymers contained benzoic and benzaldehyde PAs (C6–C1, phenylmethyl type). Evaluation of humic acids isolated from different residue‐amended soil showed the majority of humic‐PAs were C6–C3 PAs of plant origin. Increased mean weight diameter of soil aggregates was closely related to the increase in soil PA concentration and organic C content in the amended soil during incubation. The results suggest that plant PAs are extremely important in the soil C cycle, soil aggregation and in the formation of stable C, and measurement of soil ester‐linked PA composition can provide an index of plant‐derived C in soil.

Effect of influent organic content on digested sludge extracellular polymer content and dewaterability

The organic composition of the feed sludge to six laboratory-scale anaerobic digesters was adjusted by substituting a proportion of the primary sludge for glucose or propionic acid solution. Substitution with glucose caused an increase in the microbial extracellular polymer (ECP) content of the digested sludge, which altered the particle size distribution of the sludge and made the sludge more difficult to dewater. Substitution with propionic acid gave similar results to the control. The relationship between the digested sludge extracted ECP yield and sludge filtrability determined using the capillary suction time test was significant at the P=0.01 level. The level of ECP for optimum sludge dewaterability was calculated as 17.2 mg g −1 SS. The protein and carbohydrate composition of the extracted polymer did not appear to affect the sludge dewaterability. Results present will allow predictions to be made into the effect that changes in the influent sewage composition has on essential downstream processes.

Effect of carbon to nitrogen ratio on the composition of microbial extracellular polymers in activated sludge

Effect of carbon to nitrogen ratio (C/N) on the sludge extracellular polymer composition is studied in synthetically fed semi-continuous reactors with 8 days of sludge age. Results show that C/N ratio influences the relative distribution of polymer carbohydrate and protein. At low C/N ratio of 5, polymer extracts have high protein and low carbohydrate content. As the C/N ratio is increased to 17.5 and then to 40, carbohydrate concentration increases sharply and protein concentration decreases.

Municipal wastewater sludge dewaterability and the presence of microbial extracellular polymer

Dewatering of sewage sludge is an essential and costly part of the wastewater treatment process. The presence of microbial extracellular polymer (ECP) is important for sludge flocculation, but ECP has also been shown to have a detrimental effect on the dewaterability of certain sludge types. This paper investigates the relationship between sludge dewaterability and the level of ECP present in a range of sludges obtained from 8 full-scale municipal treatment works in the UK. Sludge dewaterability was determined using the capillary suction time (CST) test, and a thermal extraction process followed by solvent precipitation was used for ECP extraction. The results indicate that for each type of sludge examined there appears to be an optimum level of ECP (raw sludge 20 mg ECP/g SS; activated sludge 35 mg ECP/g SS; digested sludge 10 mg ECP/g SS) at which the sludge should exhibit maximum dewaterability. The establishment of a trend between sludge dewaterability and the quantity of ECP present opens up the possibility of manipulating the level of microbial polymer present to aid sludge dewatering, and hence reduce plant operating costs.

Bioflocculation of Activated Sludge: The Role of Calcium Ions and Extracellular Polymers

In an attempt to identify the bioflocculation mechanisms, this study examines the role of calcium ions in flocculation of activated sludge. Two calcium specific chelants, ethylenebis (oxyethylenenitrilo) tetraacetic acid (EGTA) and sodium hexametaphosphate (HMP) are used to extract calcium ions. Both chemicals successfully extract the calcium ions from sludge structure, which is confirmed either by an increase in solution calcium concentration or by a decrease in calcium concentration in the sludge solid matrix. When calcium ions are removed from sludge, the physical properties of sludge change significantly. Filterability decreases, while both the turbidity of the supernatant and the solution carbohydrate concentration increase. The decrease in filterability and increase in turbidity indicate a floc breakup, and the increase in solution carbohydrate concentration gives evidence of the release of extracellular polymeric materials from the sludge floc structure. Application of both complexing agents (EGTA and HMP) creates similar changes in sludge properties. A sludge floc model is proposed which suggests that calcium ions help form colonies from individual microorganisms interacting with microbial extracellular polymers; following this they can further take part in bridging the microbial colonies together to form flocs. These interactions are believed to be among important biofloc formation mechanisms.

The Impact of Digester Retention Time on Microbial Extracellular Polymer Production and Sludge Dewaterability

Anaerobic digestion of wastewater sludge has found widespread use as a method of sludge stabilisation, but the waste sludge remaining can be more difficult to dewater. One factor thought to influence sludge dewaterability is the level of microbial extracellular polymer present in the sludge. Utilising laboratory scale anaerobic digesters, this study aimed to assess the effect that digester retention time has on extracellular polymer production and its associated impact on sludge dewaterability. Six digesters were constructed and operated, as matched pairs, over a range of retention times (10, 15, and 30 days) for 4 full retention periods. The end point extracted extracellular polymer yield was related to the sludge dewaterability, as measured using the capillary suction time test. There was a strong, positive correlation (r2=0.999) between the extracellular polymer yield and sludge dewaterability, but no relationship was found between extracellular polymer yield and digester retention time. Further analysis of the extracted polymer organic and inorganic content demonstrated that the digester retention time had no effect on polymer composition, but polymer composition did appear to have an impact on the sludge dewaterability.