Free Extracellular Polymeric Substances Research Articles

Predictive performance of auto-aerated immobilized biomass reactor treating anaerobic effluent of cardboard wastewater enriched with bronopol (2-bromo-2-nitropropan-1,3-diol) via artificial neural network

Anaerobically-pretreated cardboard wastewater (APCW) contains significant residuals of organics, nitrogen species and coarse suspended solids, making the effluent quality not complying for disposal. This is the 1st investigation for treating APCW by an auto-aerated immobilized biomass (AIB) reactor packed with sponge media and ventilated naturally. The optimum hydraulic retention time (HRT) was 4.3 h, achieving CODtotal, CODsoluble, TSS, VSS, TKN, carbohydratetotal, and carbohydratesoluble removal efficiencies of 63.0, 58.8, 71.6, 66.0, 25.5, 38.0, and 33.5%, respectively. The bronopol (2-bromo-2-nitropropan-1,3-diol) supplementation to the APCW feed reduced those removal efficiencies by 20%–40%. The mitigation of bronopol toxicity was illustrated regarding the secretion of extracellular polymeric substances (EPS) to protect the bacterial biomass against the severe environment. The FTIR bands revealed the presence of bound EPS at 1633 and 1403 cm−1 and free EPS at 1035 and 862 cm−1. The alkanes (CH) peaks could be an indicator for the biodegradation of bronopol into formaldehyde by the sponge-retained biomass. An artificial neural network (ANN) model was developed and optimized to predict the COD removal efficiency based on the reactor’s operational conditions, attaining high accuracy (R2: 0.90). The model findings verify the applicability of ANN to simulate the performance of sponge-packing systems, retaining various aerobic, anoxic, and anaerobic species.

Fouling of enhanced biological phosphorus removal–membrane bioreactors by humic-like substances

Fouling by free extracellular polymeric substances was studied in an enhanced biological phosphorus removal–membrane bioreactor. It was demonstrated that the free extracellular polymeric substances, primarily consisting of humic-like substances, were adsorbed to the membrane used in the enhanced biological phosphorus removal–membrane bioreactor plant. Infrared analyses indicated the presence of the humic-like substances on the membrane’s active surface after filtration of the free extracellular polymeric substances suspension. Scanning electron microscopy showed the presence of a gel layer on the membrane surface after filtration of the free extracellular polymeric substances suspension. The gel layer caused a significant decline in water flux. This layer was not entirely removed by a backwashing, and the membrane’s water flux could not be re-established. The membrane used in the enhanced biological phosphorus removal–membrane bioreactor plant showed infrared spectra similar to that fouled by the free extracellular polymeric substances suspension in the laboratory. Thus, the results of this study show the importance of humic-like substances in irreversible fouling of enhanced biological phosphorus removal–membrane bioreactor systems.

Irreversible fouling of membrane bioreactors due to formation of a non-biofilm gel layer.

Extra-cellular polymeric substances (EPS), known to contribute to fouling in membrane bio-reactors (MBRs), are generally divided into bound and free EPS. The free EPS are able to form a gel layer on the membrane active surface. The mechanisms involved in formation of such layer and its effects on performance of the MBR membranes were studied. The free EPS, extracted by centrifugation and microfiltration, contained a significant amount of humic-like substances. Under static contact to the membrane, adsorption of humic-like substances to the membrane occurred and could be explained by conventional adsorption kinetics. Due to static adsorption, surface roughness of the membrane declined significantly, indicating that adsorbed matters to the membrane filled the cavities of the membrane surface. Filtration of the free EPS caused 50% water flux decline. The fouling resistance linearly increased with the amount of the humic-like substances retained during filtration as predicted by gel growth theory. A low pressure backwash could re-establish the water flux only up to 70%.

Enhanced nitrobenzene biotransformation by graphene‐anaerobic sludge composite

AbstractBACKGROUNDTraditional anaerobic bioprocesses have failed to achieve the efficient biotransformation of nitrobenzene. Thus, graphene‐anaerobic sludge composite as a novel biocatalyst was proposed for the enhancement of nitrobenzene biotransformation.RESULTSReduced graphene oxide/anaerobic sludge (RGO/AS) composite presented good settling performance when graphene oxide (GO) was added into an AS system for 24 h cultivation. The presence of RGO resulted in enhanced nitrobenzene biotransformation by AS, and the highest removal efficiency of nitrobenzene was observed with initial GO (3–5 µm) vs sludge ratio of 0.075 (w/w). Dehydrogenase activity in the RGO/AS system increased approximately 2‐fold over that in the AS system and redox active species appeared in supernatant from the RGO/AS system. The ratio of acetate to propionate increased in the RGO/AS system during glucose fermentation, and nitrobenzene biotransformation by both AS and RGO/AS systems was independent of methanogenesis, but dependent on acetogenesis. Moreover, bound and free extracellular polymeric substances (EPS) from RGO/AS composite were involved in direct biotransformation of nitrobenzene, and bound EPS might interact with secreted redox active species to accelerate nitrobenzene biotransformation by extracellular electron transfer.CONCLUSIONRGO/AS composite was efficient for the treatment of nitrobenzene wastewater. © 2013 Society of Chemical Industry

EPS (Extracellular Polymeric Substances), silk, and chitin: vitally important exudates in aquatic ecosystems

AbstractExudates are ubiquitous in marine and fresh waters. They include Extracellular Polymeric Substances (EPS; including mucus, slimes, and biofilm matrices), silk, and chitin. EPS have many uses for the organisms that produce them—attachment, locomotion, feeding, and protection. They also act as glues to bind other materials, including the egesta within fecal pellets. Silk, an exudate produced only in fresh waters, is used in tube construction, to make nets used in feeding, and as a means of attachment. Chitin is the basis of the peritrophic matrix that surrounds the gut contents of some invertebrates and may act as a binding surrounding their fecal pellets. EPS are found free in the water column and in and on the substratum, as well as in close contact with the organisms that exude them. Free EPS have an essential role in particle formation and aggregation, processes that have been studied primarily in marine systems. Like EPS, silk is highly adsorptive and is found free within substrata, but rarely ...

Sequestration of Reactive Blue 4 by free and immobilized Bacillus subtilis cells and its extracellular polysaccharides

Bacillus subtilis a gram positive bacteria and its extracellular polysaccharide were used in free form as well as immobilized form as biosorbent for sequestration of an anionic dye, Reactive Blue 4 (RB) in aqueous phase. The dye uptake enhanced with decrease in pH. Extracellular polymeric substances (EPS) and free cells were found to be better adsorbents when compared to alginate immobilized cells (IC) and EPS (IEPS). The presence of functional groups in free cells and EPS was confirmed by FT-IR analysis. Immobilization resulted in poor adsorption performance due to increase in mass transfer resistance by the polymeric matrix. High Q max and b values were noted in the case of free cells and free EPS in contrast to IC and IEPS. From the kinetic experiments, the adsorption system was found to be a pseudo-first-order reaction at low dye concentration. Desorption of RB was found to be 100% in 1N NaOH. However, the alginate beads were found to be unstable under high alkaline conditions of NaOH.

Characterization of the Extracellular Polymeric Substances Produced by Escherichia coli Using Infrared Spectroscopic, Proteomic, and Aggregation Studies

The aim of this study was twofold: first, to characterize the free extracellular polymeric substances (EPS) and bound EPS produced by Escherichia coli during different growth phases in different media, and then to investigate the role of the free EPS in promoting aggregation. EPS was extracted from a population of E. coli MG1655 cells grown in different media composition (Luria-Bertani (LB) and Luria-Bertani with the addition of 0.5 w/v% glucose at the beginning of the growth phase (LBG)) and at different growth phases (6 and 24 h). The extracted EPS was characterized using Fourier transform infrared spectroscopy and further identified using one-dimensional gel-based electrophoresis and tandem mass spectrometry. E. coli MG1655 was found to produce significantly lower amounts of bound EPS compared to free EPS under all conditions. The protein content of free EPS increased as the cells progressed from the exponential to stationary phase when grown in LB or LBG, while the carbohydrate content only increased across the growth phases for cells grown in LBG. FTIR revealed a variation in the different functional groups such as amines, carboxyl, and phosphoryl groups for free EPS extracted at the different growth conditions. Over 500 proteins were identified in the free EPS, with 40 proteins common in all growth conditions. Proteins with functionality related to amino acid and carbohydrate metabolism, as well as cell wall and membrane biogenesis were among the highest proteins identified in the free EPS extracted from E. coli MG1655 under all growth and media conditions. The role of bound and free EPS was investigated using a standardized aggregation assay. Bound EPS did not contribute to aggregation of E. coli MG1655. The readdition of free EPS to E. coli MG1655 resulted in aggregation of the cells in all growth conditions. Free EPS extracted from the 24 h E. coli MG1655 cultures grown in LB had the greatest effect on aggregation of cells grow in LBG, with a 30% increase in aggregation observed.

Membrane fouling in a submerged membrane bioreactor (SMBR): Characterisation of the sludge cake and its high filtration resistance

The attachment of sludge cake to the membrane surface is the main cause of the fouling problem in the submerged membrane bioreactors (SMBR) used in biological wastewater treatment. In this laboratory study, the sludge cake deposited on the membrane was found to have a specific filtration resistance of the order of 10 14 m/kg, which is much greater than expected for sludge cake formed during the dewatering of activated sludge. The filterability tests showed that the cake sludge removed from the fouled membrane of the SMBR had an average specific filtration resistance of 4.9 × 10 13 m/kg, whereas the sludge cake of the SMBR bulk sludge had an average filtration resistance of only 1.9 × 10 11 m/kg. Detailed chemical analysis showed there was a pool of biopolymer clusters (BPC) that was trapped within the sludge cake on the membrane. These clusters could be readily separated from the cake sludge by stirring it into a suspension. The abundance of non-filterable BPC as measured by the total organic carbon (TOC) in the suspended solids (SS) was about 10.3 mg/g SS for the cake sludge, in comparison to 0.4 mg/g SS for the bulk sludge. When the BPC were removed from the cake sludge, the filtration resistance of the cake sludge could be reduced considerably from 4.9 × 10 13 to 8.4 × 10 12 m/kg. It is argued that the BPC are a special form of organic matter formed by affinity clustering of the free extracellular polymeric substances (EPS) and soluble microbial products (SMP) in the sludge cake deposited on the membrane surface. The accumulation of BPC within the pores of the sludge cake is mostly responsible for the unusually high filtration resistance of the cake sludge during the SMBR operation.