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It needs to be improved the conversion efficiency and stable operation of conventional pyrolysis with high-temperature flue gas heating (HFH). Herein, a new radiative heating (RH) pyrolysis method is proposed. Experimental studies are carried out on a self-made radiation pyrolysis pilot plant to investigate the effects of different factors (pyrolysis final temperature, residence time, and carrier gas volume) on product distribution. The results show that with the increase of pyrolysis temperature, the yield of the gas phase consistently increases, and the proportion of CH4 and H2 in the pyrolysis gas reaches 62.31% at 700 °C. The yield of the liquid phase increases and then decreases. The recovery rate of pyrolysis oil achieves 68.07% when the pyrolysis temperature is 600 °C with main components of ketones and unsaturated hydrocarbon compounds. The yield of the solid phase consistently decreases. The RH in this work generates more pyrolysis gas in the pyrolysis process and alleviates the effects of fouling layers on the continuous operation of the equipment which has guiding significance for the efficient resource utilization of oil sludge. [ABSTRACT FROM AUTHOR]

The gravity-driven membrane bioreactor (MBR) system is promising for decentralized sewage treatment because of its low energy consumption and maintenance requirements. However, the growing sludge not only increases membrane fouling, but also augments operational complexities (sludge discharge). We added the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to the system to deal with the mentioned issues. Based on the results, TCS addition effectively decreased sludge ATP and sludge yield (reduced by 50%). Extracellular polymeric substances (EPS; proteins and polysaccharides) decreased with the addition of TCS and were transformed into dissolved soluble microbial products (SMPs) in the bulk solution, leading to the break of sludge flocs into small fragments. Permeability was increased by more than two times, reaching 60–70 L/m2/h bar when 10–30 mg/L TCS were added, because of the reduced suspended sludge and the formation of a thin cake layer with low EPS levels. Resistance analyses confirmed that appropriate dosages of TCS primarily decreased the cake layer and hydraulically reversible resistances. Permeability decreased at high dosage (50 mg/L) due to the release of excess sludge fragments and SMP into the supernatant, with a thin but more compact fouling layer with low bioactivity developing on the membrane surface, causing higher cake layer and pore blocking resistances. Our study provides a fundamental understanding of how a metabolic uncoupler affects the sludge and bio-fouling layers at different dosages, with practical relevance for in situ sludge reduction and membrane fouling alleviation in MBR systems. [ABSTRACT FROM AUTHOR]

Highlights • Dynamic formation of fouling layer in cross-flow NF was visualized by LIF technique. • Fouling layer was quantitatively analyzed in terms of its real-time concentration and thickness. • Effect of hydraulic conditions in NF on fouling development was evaluated. Abstract In-situ non-invasive observation of concentration polarization (CP) and fouling layer is of vital importance to understanding membrane filtration process and membrane permeability loss. This study developed a novel real-time technique, laser induced fluorescence (LIF) technique, to visualize CP development and fouling layer formation, and to measure solute concentration field on the membrane surface directly during cross-flow nanofiltration, which helped to quantitatively evaluate the effect of various operation conditions on membrane permeability. The solute concentration distribution on the membrane surface was successfully determined from the LIF images, and the fouling layer thickness was measured by series of processed images after binary subtraction. LIF results demonstrated that the fouling development experienced approximate two stages, i.e. rapid growth phase and consolidation phase, and visualized the transition from initial CP to the later fouling layer formation. Afterwards, the formed fouling layer tend to be steady with nearly unchanging concentration and thickness. Quantitative analysis proved that the operational hydraulic condition has a significant influence on the formation and stabilization of fouling layer. The developed method and obtained results were very useful to in-depth recognize the nanofiltration process and to understand the membrane fouling mechanism. [ABSTRACT FROM AUTHOR]

In this work, the dynamic changes in the composition of fouling layer as a function of operating time were systematically investigated and compared in forward osmosis (FO) based membrane processes for municipal wastewater treatment. Fouled membranes were collected from four different operational cycles (3, 8, 16 and 30 days) and prepared for quantitative analyses of organic and inorganic foulants and microscopic observation by confocal laser scanning microscopy (CLSM). Moreover, the dynamic changes of bacterial concentration and community structure were characterized by the plate count method and Illumina MiSeq sequencing, respectively. The results showed that with the extension of operation time, the amount of organic foulants, inorganic species and bacteria deposited on the membrane surface exhibited a gradual increase trend in direct FO, resulting in a corresponding increase of fouling resistance and decline of water flux. As for OMBR, apart from the organic foulants such as polysaccharides and proteins, both the inorganic species and membrane surface bacterial concentration reached to a plateau phase after 8 days of operation, leading to a much lower fouling resistance and flux reduction. The bacterial community analysis indicated that two dominant genus were detected in the biofilm of OMBR; however, the bacterial community on the membrane surface of direct FO exhibited a significantly higher diversity but with a lower abundance. [ABSTRACT FROM AUTHOR]

Using adsorbents/flocculants in anaerobic membrane bioreactors (AnMBRs) to reduce membrane fouling is comparatively rare. This study evaluated 8 additives: 3 powdered activated carbons, 2 granular activated carbons, 1 cationic polymer, and 2 metal salts to identify the best additive and dose to minimise membrane fouling. Small cross flow filtration tests showed 400 mg/L PAC SAE2, or 150 mg/L FeCl 3 , reduced the transmembrane pressure (TMP) rise from 0.94 to 0.06 kPa/h, indicating excellent fouling reduction. The best filtration performance correlated with a significant reduction in supernatant supracolloidal particles, colloids and SMPs. FESEM-EDX showed that PAC SAE 2 and FeCl 3 reduced the thickness of the fouling layer dramatically, while FeCl 3 increased sludge floc size and particle size of the colloids, while decreasing the negative charge of colloids, and SMP size. Furthermore, Fe was not found in the supernatant or effluent, but precipitated with the solids, which is beneficial for its long-term use. [ABSTRACT FROM AUTHOR]

To alleviate the fouling of a filter, simple substrates, dynamic filtration, and granular sludge were applied in an anaerobic membrane bioreactor (AnMBR). The results showed that under a transmembrane pressure < 20 kPa, the filter flux ranged between 15 and 20 l (m−2 h)−1for a period of 30 days. The flux was higher than the typical flux of AnMBRs with conventional membranes and most current dynamic filters. In addition, the low cost of the filter avoided the need for a higher flux. Moreover, a stable granular sludge bed, which consumed all volatile fatty acids, was maintained. A compact fouling/filtration layer formed on the filter, which contributed to low effluent chemical oxygen demand concentrations and turbidity. In addition, substrate scarcity in the filtration zone resulted in the evolution of diverse bacteria on the filter. [ABSTRACT FROM AUTHOR]

Coal seam gas-associated water (CSGAW), which is a by-product of coal seam gas (CSG) production typically contains significant amounts of salts and has potential environmental issues. In this study, we optimized a bench-scale vacuum membrane distillation (VMD) process with flat-sheet hydrophobic polytetrafluoroethylene (PTFE) membranes for the treatment of synthetic CSGAW (conductivity = 15 mS/cm). To study performance of the VMD process, we explored the effects of feed temperature (Tf = 60, 70, and 80 °C), feed flow rate (Vf = 60, 120, and 240 mL/min), and vacuum pressure (Pv = 3, 6, and 9 kPa) on water permeability through the PTFE membrane in the VMD process. Under the optimum conditions (i.e. Tf = 80 °C, Vf = 240 mL/min, Pv = 3 kPa), water permeability and rejection efficiency of salts by the VMD process were found to be 5.5 L/m2/h (LMH) and 99.9%, respectively, after 2 h filtration. However, after 8 h operation, the water permeability decreased by 70% compared with the initial flux due to the formation of fouling layer of calcium, chloride, sodium, magnesium, and potassium on the membrane surface. [ABSTRACT FROM AUTHOR]

Organic conditioning films have been shown to alter properties of surfaces, such as hydrophobicity and surface free energy. Furthermore, initial bacterial adhesion has been shown to depend on the conditioning film surface properties as opposed to the properties of the virgin surface. For the particular case of nanofiltration membranes under permeate flux conditions, however, the conditioning film thickens to form a thin fouling layer. This study hence sought to determine if a thin fouling layer deposited on a nanofiltration membrane under permeate flux conditions governed bacterial adhesion in the same manner as a conditioning film on a surface. Thin fouling layers (less than 50 μm thick) of humic acid or alginic acid were formed on Dow Filmtec NF90 membranes and analysed using Atomic Force Microscopy (AFM), confocal microscopy and surface energy techniques. Fluorescent microscopy was then used to quantify adhesion of Pseudomonas fluorescens bacterial cells onto virgin or fouled membranes under filtration conditions. It was found that instead of adhering on or into the organic fouling layer, the bacterial cells penetrated the thin fouling layer and adhered directly to the membrane surface underneath. Contrary to what surface energy measurements of the fouling layer would indicate, bacteria adhered to a greater extent onto clean membranes (24 ± 3% surface coverage) than onto those fouled with humic acid (9.8 ± 4%) or alginic acid (7.5 ± 4%). These results were confirmed by AFM measurements which indicated that a considerable amount of energy (10 −7 J/μm) was dissipated when attempting to penetrate the fouling layers compared to adhering onto clean NF90 membranes (10 −15 J/μm). The added resistance of this fouling layer was thusly seen to reduce the number of bacterial cells which could reach the membrane surface under permeate conditions. This research has highlighted an important difference between fouling layers for the particular case of nanofiltration membranes under permeate flux conditions and surface conditioning films which should be considered when conducting adhesion experiments under filtration conditions. It has also shown AFM to be an integral tool for such experiments. [ABSTRACT FROM AUTHOR]

Abstract: Effects of ultrasound (US) on the structural organization within concentrated particle layers during cross-flow ultrafiltration of Laponite dispersions have been characterized for the first time by in-situ time-resolved small-angle X-ray scattering (SAXS). A novel ‘SAXS Cross-Flow US-coupled Filtration Cell’ has been developed to, on one hand, apply ultrasonic waves close to the flat membrane by embedding in the feed compartment a thin titanium vibrating blade connected to a 20kHz ultrasonic generator and on the other hand, to monitor in-situ the colloidal organization of the concentrated layer by SAXS. Thanks to this cell, concentration profiles have been measured as a function of the distance z from the membrane surface with a 20µm accuracy and simultaneously linked to the permeate flux, cross-flux and transmembrane pressure. In-situ ultrasonication leads to a significant increase of permeate flux arising from the break-up of the concentrated layer. Results also suggest that ultrasonication could be considered as an additional force of an effective range on the order of micrometers or smaller. It is capable to completely remove the particles from the membrane surface when the feed dispersions are dense and aggregated, and is more efficient than classical procedures based on an increase of the cross-flow flux. [Copyright &y& Elsevier]

Abstract: The intact cross-section of two fouled reverse osmosis membranes was characterized using a scanning transmission electron microscope (STEM) equipped with an electron energy dispersive spectroscope (EDS). Focused ion beam (FIB) was used to prepare a thin lamella of each membrane. These lamellas were then attached to a TEM grid for further STEM/EDS analysis. The foulant in sample A was mainly inorganic in nature and predominantly composed of alumino-silicate particles. These particles were surrounded by carbon at high concentrations, indicating the presence of organic materials. Iron was diffusely present in the cake layer and this could have enhanced the fouling process. The cake layer of membrane B was mainly consisted of organic matter (C, O, and N representing 95% of the total elemental composition) and organized in thin parallel layers. Small concentrations of Si, F, Na, Mg, and Cl were detected inside the active layer and support layer of the membrane. Due to the high sensitivity of the cake layer of membrane A to the electron beam, STEM/EDS line analyses might have been performed on large areas. On the other hand, the cake layer of sample B was resistant to the electron beam and the resolution of STEM/EDS was gradually improved until obtaining a resolution of 25nm. [Copyright &y& Elsevier]

Abstract: Foulants with low concentration in effluent are generally considered minor for determining resistance to membrane filtration. This study probed spatial distribution of proteins, nucleic acids and α- and β-d-glucopyranose polysaccharides in fouling layer using multiple staining technique and confocal laser scanning microscope (CLSM) imaging and clarify their individual contributions to the overall permeate flow resistance. In the present case, the β-d-glucopyranose polysaccharides occupied over 80% of the volume of the fouling layer and were the major foulant. The other three components (proteins, nucleic acids and α-d-glucopyranose polysaccharides) were minor foulants. The computational fluid dynamics calculations revealed that the β-d-glucopyranose polysaccharides contributed much greater to cake resistance than did the other three foulants; however, its contribution could only count 12–15% of the overall resistance of filter cake. Marked reduction in cake permeability is yielded by blockage of large pore in fouling layer by minor pollutants. [Copyright &y& Elsevier]

Abstract: The technique that employs flash freezing and environmental scanning electron microscopy (ESEM) was utilised for detailed investigation of the fouling materials in a membrane bioreactor (MBR). The method involves the flash freezing of a wet sample in liquid nitrogen for 10s to preserve its structure for direct ESEM observation with a high image resolution. ESEM images show that the sludge cake formed by simple filtration of the MBR bulk sludge has a highly porous, sponge-like structure with a fairly low resistance. However, the fouling layer attached to the membrane surface contains a thin gel layer under the main body of the sponge-like sludge cake, which is similar to that formed by filtration of a dispersion of biopolymer clusters (BPCs). It is apparent that BPCs tend to accumulate on the membrane surface, and the gel layer is largely responsible for the high filtration resistance of the cake layer on the fouled membranes. [Copyright &y& Elsevier]

conjugate gradient method (CGM) based on the inverse algorithm is used to estimate the unknown fouling-layer profile on the inner wall of a pipe system using simulated temperature measurements taken within the pipe wall. It is assumed that no prior information is available about the functional form of the unknown profile. Therefore, the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The accuracy of the inverse analysis is examined using the simulated exact and inexact temperature measurements. The results show that the excellent estimation of the fouling-layer profile can be obtained for the test case considered in this study. The technique presented in this study can be used in a warning system to call for pipe maintenance when the thickness of fouling exceeds a predefined criterion. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a conjugate gradient method based inverse algorithm is applied to estimate the unknown fouling-layer profile on the inner wall of a duct system using simulated temperature measurements taken on the duct wall. The temperature data obtained from the direct problem are used to simulate the exact temperature measurements. Results show that an excellent estimation on the fouling-layer profile can be obtained for the case without separation bubble. The predictive accuracy, however, slightly deteriorates when there is a separation bubble in the duct flow. The technique presented in this study can be used in a warning system to call for maintenance when the thickness of fouling exceeds a pre-defined criterion. [Copyright &y& Elsevier]

Abstract: In this paper, a novel submerged ultrafiltration (UF) membrane coagulation bioreactor (MCBR) process was evaluated for drinking water treatment at a hydraulic retention time (HRT) as short as 0.5h. The MCBR performed well not only in the elimination of particulates and microorganisms, but also in almost complete nitrification and phosphate removal. As compared to membrane bioreactor (MBR), MCBR achieved much higher removal efficiencies of organic matter in terms of total organic carbon (TOC), permanganate index (CODMn), dissolved organic carbon (DOC) and UV absorbance at 254nm (UV254), as well as corresponding trihalomethanes formation potential (THMFP) and haloacetic acids formation potential (HAAFP), due to polyaluminium chloride (PACl) coagulation in the bioreactor. However, the reduction of biodegradable dissolved organic carbon (BDOC) and assimilable organic carbon (AOC) by MCBR was only 8.2% and 10.1% higher than that by MBR, indicating that biodegradable organic matter (BOM) was mainly removed through biodegradation. On the other hand, the trans-membrane pressure (TMP) of MCBR developed much lower than that of MBR, which implies that coagulation in the bioreactor could mitigate membrane fouling. It was also identified that the removal of organic matter was accomplished through the combination of three unit effects: rejection by UF, biodegradation by microorganism and coagulation by PACl. During filtration operation, a fouling layer was formed on the membranes surface of both MCBR and MBR, which functioned as a second membrane for further separating organic matter. [Copyright &y& Elsevier]

Abstract: The structure of fouling layer determines the pressure drop across the fouling layer. Three-dimensional distributions of nucleic acids, proteins, α-d-glucopyranose polysaccharides, β-d-glucopyranose polysaccharides and lipids in the biofouling layer that is formed on a mixed cellulose ester membrane were determined using a six-fold staining protocol combined with confocal laser scanning microscopy (CLSM). Based on the three-dimensional volumetric grid model of the fouling layer structure observed from the series of CLSM images, the intra-layer flow field during filtration was simulated using commercial software. The effective permeability of the fouling layer was estimated to be 2.65×10−12 m2, which determines the upper estimate on the permeability of the fouling layer. The pores were categorized according to their diameters, using the maximum convex perimeter approach, and then the effects of the blocking pores on the permeability of the fouling layer were investigated. Blocking the large pores that accounted for 15% of the porosity reduced the mean permeability by 58%. [Copyright &y& Elsevier]

Membrane biofouling via microbial products limits the feasibility of utilizing membrane bioreactor (MBR) for treating wastewater. Fouling layer would be built up when activated sludge was filtered with a mixed cellulose ester membrane. This study probed the three‐dimensional distributions of protein, α‐polysaccharide, and β‐polysaccharide in fouling layer using fluorescently labeled lectins and fluorescein isothiocyanate (FITC) as staining agents in combination with confocal laser scanning microscopy (CLSM). These extracellular polymeric substances (EPS) distributed heterogeneously in the fouling layer, with α‐polysaccharide being concentrated close to the membrane surface. The flow pattern yielded in the fouling layer determines the filtration resistance of biofouling. [ABSTRACT FROM AUTHOR]

• The oxidation ditch integrated with flat sheet membrane module was built-up. • The bioreactor could be operated under a continuous-flow mode. • The fouling characteristics of the bioreactor were revealed by multi-methods. • The factors causing the differences of foulants on membrane surface were analyzed. • Unique microbial species in a foulant layer determined the heterogeneity of foulants. This work investigated the operational and fouling characteristics of the combined oxidation ditch-membrane bioreactor under a continuous-flow mode. During the operating period (80 days), foulants gradually accumulated on the membrane surface and caused increasing in the filtration resistance, whose appearance showed obvious heterogeneity along with the variation of some influencing factors. Correlation analysis of all variable factors revealed the key factor that contributed to the difference in membrane fouling. Results indicated that the foulants with loose structure caused the largest ratio in membrane resistance among all the foulants on surface and they could be easily cleaned by a physical method. After totally physical and chemical cleaning, some residues still remained in the membrane module, which determined the lifespan of membrane modules. From the different operational stages, the foulants were sampled and characterized with multi-method to reveal their physic-chemical composition and microbial community, though, these properties and communities were very close to each other, the unique microbial species contained in the foulants might be an important factor leading to their different properties and actually determined their heterogeneity, which were also heavily affected by the temperature change. [ABSTRACT FROM AUTHOR]

• The fouling potential of two kind secondary effluents were compared in a long-term. • The secondary effluent from municipal sewage caused more serious membrane fouling. • More foulants deposited on the leading membranes in both two reclaimed water plants. • Several bacteria species which could cause serious membrane biofouling were verified. • Organics facilitated biofouling while high ion concentration restrained biofouling. In order to analyze and verify the association of the reverse osmosis (RO) membrane fouling with water quality in full-scale plants, two RO systems (40, 000 m3/d and 20, 000 m3/d) treating different secondary effluents were operated in parallel. The quality of secondary effluents and the performance of RO systems were monitored over 12 months. Difference in foulants distribution and fouling layer composition between the two systems were evaluated by membrane autopsy and foulants characterization. Results verified that: 1) the secondary effluent from municipal sewage caused more serious membrane fouling; 2) more foulants deposited on the surface of leading membrane both in two systems (3.11 ± 0.15 g/m2 and 2.93 ± 0.13 g/m2); 3) the microbial community on the RO membrane surface contained more colonizing bacteria in the system treating municipal sewage secondary effluent ; 4) organics in the secondary effluent facilitated biofouling while higher ion concentration restrained biofouling. [ABSTRACT FROM AUTHOR]

• Three typical fouling layers are proposed under (85/65/45 °C) heating temperatures. • Heat transfer performances of fouling layers are studied in two kinds of boilers. • Micro-topography and mineralogy of typical ash deposit samples are analyzed. • Acid-ash reaction mechanisms for three typical fouling layers are obtained. Comparative field experiments of typical low-temperature fouling layers are carried out in pulverized coal furnace (PCF) and circulating fluidized bed boiler (CFB). The reduction of heat transfer characteristics of test pipe is determined by the transformation of fouling layer, caused by the quantity of condensed acid solution exceeding the adsorption capacity of deposited ash particles. Based on the heat transfer performance of fouling layer covering the test pipe, as well as the appearance characteristics and degree of adhesion to the heating surface, three typical fouling layers are collected, i.e. dry loose ash deposits (85 °C), adhering ash deposits (65 °C) and viscous ash deposits (45 °C). Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) are used to analyze the formation mechanisms of three typical fouling layers. The characteristic fouling layer is determined by the reaction degree of condensed acid solution and ash particles deposited on the heating surface. Furthermore, the formation mechanisms of unsaturated acid-ash action fouling layer, supersaturated acid-ash action fouling layer and mixed acid-ash action fouling layer are proposed, providing useful guidance for the safe and efficient operation of heat exchange equipment in coal-fired boilers. [ABSTRACT FROM AUTHOR]