Chemical cleaning is vital for the optimal operation of membrane systems. Membrane chemical cleaning protocols are often developed in the laboratory flow cells (e.g., Membrane Fouling Simulator ...(MFS)) using synthetic feed water (nutrient excess) and short experimental time of typically days. However, full-scale Reverse Osmosis (RO) membranes are usually fed with nutrient limited feed water (due to extensive pre-treatment) and operated for a long-time of typically years. These operational differences lead to significant differences in the efficiency of chemical Cleaning-In-Place (CIP) carried out on laboratory-scale and on full-scale RO systems. Therefore, we investigated the suitability of lab-scale CIP results for full-scale applications. A lab-scale flow cell (i.e., MFSs) and two full-scale RO modules were analysed to compare CIP efficiency in terms of water flux recovery and biofouling properties (biomass content, Extracellular Polymeric Substances (EPS) composition and EPS adherence) under typical lab-scale and full-scale conditions. We observed a significant difference between the CIP efficiency in lab-scale (~50%) and full-scale (9–20%) RO membranes. Typical biomass analysis such as Total Organic Carbon (TOC) and Adenosine triphosphate (ATP) measurements did not indicate any correlation to the observed trend in the CIP efficiency in the lab-scale and full-scale RO membranes. However, the biofilms formed in the lab-scale contains different EPS than the biofilms in the full-scale RO modules. The biofilms in the lab-scale MFS have polysaccharide-rich EPS (Protein/Polysaccharide ratio = 0.5) as opposed to biofilm developed in full-scale modules which contain protein-rich EPS (Protein/Polysaccharide ratio = 2.2). Moreover, EPS analysis indicates the EPS extracted from full-scale biofilms have a higher affinity and rigidity to the membrane surface compared to EPS from lab-scale biofilm. Thus, we propose that CIP protocols should be optimized in long-term experiments using the realistic feed water.
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•CIP efficiency in full-scale RO is lower than “typical” lab-scale MFS.•CIP efficiency are not correlated to biomass removal indicators (ATP and TOC).•Full-scale RO biofilms have protein-rich EPS while lab-scale EPS has sugar-rich EPS.•Biofilm from full-scale EPS has higher affinity to membrane than lab-scale EPS.•CIP protocols should be developed using real feed water and for longer experiment.
Chemical cleaning is routinely performed in reverse osmosis (RO) plants for the regeneration of RO membranes that suffer from biofouling problems. The potential of urea as a chaotropic agent to ...enhance the solubilization of biofilm proteins has been reported briefly in the literature. In this paper the efficiency of urea cleaning for RO membrane systems has been compared to conventionally applied acid/alkali treatment. Preliminary assessment confirmed that urea did not damage the RO polyamide membranes and that the membrane cleaning efficiency increased with increasing concentrations of urea and temperature. Accelerated biofilm formation was carried out in membrane fouling simulators which were subsequently cleaned with (i) 0.01M sodium hydroxide (NaOH) and 0.1M hydrochloric acid (HCl) (typically applied in industry), (ii) urea (CO(NH
)
) and hydrochloric acid, or (iii) urea only (1340 g/L
). The pressure drop over the flow channel was used to evaluate the efficiency of the applied chemical cleanings. Biomass removal was evaluated by measuring chemical oxygen demand (COD), adenosine triphosphate (ATP), protein, and carbohydrate content from the membrane and spacer surfaces after cleaning. In addition to protein and carbohydrate quantification of the extracellular polymeric substances (EPS), fluorescence excitation-emission matrix (FEEM) spectroscopy was used to distinguish the difference in organic matter of the remaining biomass to assess biofilm solubilization efficacy of the different cleaning agents. Results indicated that two-stage CO(NH
)
/HCl cleaning was as effective as cleaning with NaOH/HCl in terms of restoring the feed channel pressure drop (>70% pressure drop decrease). One-stage cleaning with urea only was not as effective indicating the importance of the second-stage low pH acid cleaning in weakening the biofilm matrix. All three chemical cleaning protocols were equally effective in reducing the concentration of predominant EPS components protein and carbohydrate (>50% reduction in concentrations). However, urea-based cleaning strategies were more effective in solubilizing protein-like matter and tyrosine-containing proteins. Furthermore, ATP measurements showed that biomass inactivation was up to two-fold greater after treatment with urea-based chemical cleanings compared to the conventional acid/alkali treatment. The applicability of urea as an alternative, economical, eco-friendly and effective chemical cleaning agent for the control of biological fouling was successfully demonstrated.
Expanded graphite has been applied widely in thermal insulation, adsorption, vibration damping, gasketing, electromagnetic interference shielding etc. It is made by intercalation of natural flake ...graphite followed by thermal expansion. Intercalation is a process whereby an intercalant material is inserted between the graphene layers of a graphite crystal. Exfoliation, a huge unidirectional expansion of the starting intercalated flakes, occurs when the graphene layers are forced apart by the sudden decomposition and vaporization of the intercalated species by thermal shock. Along with production methodologies, such as the intercalation process and heat treatment, the raw material characteristics, especially particle size, strongly influence the properties of the final product.This report evaluates the influence of the particle size of the raw material on the intercalation and expansion processes and consequently the properties of the exfoliated graphite. Natural crystalline flake graphite with wide particle diameter distribution (between dp = 80 and 425 µm) was divided into four size-range portions by sieving. Graphite was intercalated via perchloric acid, glacial acetic acid and potassium dichromate oxidation and intercalation procedure. 5.0 g of graphite, 7.0 g of perchloric acid, 4.0 g of glacial acetic acid and 2.0 g of potassium dichromate were placed in glass reactor. The mixture was stirred with n = 200 min–1 at temperature of 45 °C during 60 min. Then it was filtered and washed with distilled water until pH~6 and dried at 60 °C during 24 h. Expansion was accomplished by thermal shock at 1000 °C for 1 min. The prepared samples were characterized by means of exfoliation volume measurements, simultaneous differential thermal analysis and thermo-gravimetry (DTA/TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET measurements and scanning electron microscopy (SEM).X-ray diffraction indicated a change of distance between the graphene layers due to oxidation and repulsion of positively charged layers. The increased width and reduced height of diffraction peaks were a consequence of small-sized ordered domains. The intercalation is partial, intercalated layers are divided by a considerable number of non-intercalated layers. FTIR spectra revealed that dominant intercalating species is perchloric acid.Thermo-gravimetric analysis revealed that deintercalation occurs in the temperature interval between 150 and 300 °C and that a mass loss in this temperature interval is dependent on particle diameter, i. e. the intercalation is more intensive for greater particles. The fact that deintercalation proceeds as a one-stage process indicates the existence of only one intercalating specie. Additional mass loss at higher temperatures is a consequence of graphite oxidation.The particles with a higher amount of interlcalant showed greater expansion volumes as well as specific surface area. The fraction with greatest particle diameter (315–425 µm) showed expansion specific volume of v=86 cm3g–1. Weaker expansion of smaller particles is a consequence of intercalant thermal degradation gaseous products loss at the layer edges, as well as of lesser amount of intercalants due to their removal during washing.Adsorption-desorption isotherms of expanded graphite could be classified as type III, according to BDDT/IUPAC classification, characteristic for macro porous materials. Small variations in adsorption and desorption pressure for the same amount of adsorbed gas indicate that the macro pores are open. Specific surface area was calculated using BET equation and for sample 315–425 yields s = 36 m2 g–1.SEM micrographs revealed typical worm-like microstructure generated by exfoliation of graphene sheets. The areas of intense exfoliation forming typical pores, as well as less exfoliated sheets canbe observed.
High-performance bioinspired materials have shown rapid development over the last decade. Examples are brick-and-mortar hierarchical structures, which are often achieved via solvent evaporation. ...Although good properties are claimed, most systems are composed of stacked or intercalated platelets. Exfoliation is a crucial step to give ultimate anisotropic properties, e.g., thermal, mechanical, and barrier properties. We propose a general framework for all the various types of micro-scale structures that should be distinguished for 2D filler nanocomposites. In particular, the exfoliated state is systematically explored by the immobilization of montmorillonite platelets via (gelatin) hydrogelation. Scattering techniques were used to evaluate this strategy at the level of the particle dispersion and the regularity of spatial arrangement. The gelatin/montmorillonite exfoliated nanostructures are fully controlled by the filler volume fraction since the observed gallery d-spacings perfectly fall onto the predicted values. Surprisingly, X-ray analysis also revealed short- and quasi long-range arrangement of the montmorillonite clay at high loading.
Wastewater solids could be an attractive source of secondary raw cellulose, mainly originating from toilet paper. Cellulose can be recovered through sieving of raw wastewater, return sludge, or ...excess sludge. In particular, a large fraction of cellulose (13–15%) can be found in the excess sludge of the aerobic granular sludge produced by the Nereda® wastewater technology. A cellulose extraction method was developed during this study, allowing the recovery of a pulp with over 86 wt% purity. The wastewater derived cellulose fibres could be an excellent source for production of recovered cellulose nanocrystals (rCNC). Several pre-treatment steps needed in cellulose nanocrystals (CNC) production from wood pulp are already performed in the production of toilet paper. Here, the technical feasibility of such rCNC is studied. As reference materials, microcrystalline cellulose and toilet paper were also used. The rCNC were obtained by acid hydrolysis, with yields of ∼30 wt% (pulp basis). The wastewater-based material was rod-like, with high aspect ratio (10–14), crystallinity (62–68%), and chemical structure similar to commercial CNC. The yield of rCNC per gram of cellulose recovered from the influent was 22%, while for excess sludge cellulose it was less (4%). Bio-nanocomposites of rCNC and alginate were also investigated. At 50 vol% loading of rCNC, there was a 50% relative increase in stiffness (18 GPa) compared to matrix (12 GPa). The characterization of rCNC and positive impact in composite materials confirms a suitable quality of wastewater derived CNC. Ultimately, the nanocellulose is a tangible example that recovery of high-end products from wastewater is possible, in line with a circular economy.
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•A facile method for cellulose recovery and estimation in wastewater was proposed.•Nanocellulose (CNC) was obtained from toilet paper and wastewater cellulose.•Recovered CNC is similar to commercial CNC (shape, crystallinity, stiffness).•Recovered CNC results in high stiffness bio-nanocomposites with alginate.
Tailoring the order in hierarchical structures is a key goal of bioinspired nanocomposite design. Recently, nacre-like materials have been developed by solvent evaporation methods that are scalable ...and attain advanced functionalities. However, understanding the alignment mechanisms of 2D fillers, nanosheets, or platelets remains challenging. This work explores possible pathways for nanocomposite ordering via orientation distribution functions. We demonstrate how the immobilization of 2D materials via (pseudo)network formation is crucial to alignment based on evaporation. We show a modified affine deformation model that describes such evaporative methods. In this, a gel network develops enough yield stress and uniformly deforms as drying proceeds, along with the immobilized particles, causing an in-plane orientation. Herein, we tested the dominance of this approach by using a thermo-reversible gel for rapid montmorillonite (MMT) particle fixation. We researched gelatin/MMT as a model system to investigate the effects of high loadings, orientational order, and aspect ratio. The nacre-like nanocomposites showed a semiconstant order parameter (⟨P 2⟩ ∼ 0.7) over increasing nanofiller content up to 64 vol % filler. This remarkable alignment resulted in continuously improved mechanical and water vapor barrier properties over unusually large filler fractions. Some variations in stiffness and diffusion properties were observed, possibly correlated to the applied drying conditions of the hybrid hydrogels. The affine deformation strategy holds promise for developing next-generation advanced materials with tailored properties even at (very) high filler loadings. Furthermore, a gelling approach offers the advantages of simplicity and versatility in the formulation of the components, which is useful for large-scale fabrication methods.
The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. ...Here, we demonstrate that anisotropic agarose gel networks can mechanically “mold” calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically “molding” biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties.
Istražen je utjecaj veličine čestica prirodnog grafita na procese interkaliranja i ekspanzije te svojstva ekspandiranog grafita. Prirodni grafit s vrlo širokom raspodjelom veličina čestica (između dp ...= 80 i 425 µm) prosijavanjem je podijeljen na četiri veličinske klase. Uzorci su podvrgnuti procesu oksidacije i interkaliranja s kalijevim dikromatom, perklornom kiselinom i ledenom octenom kiselinom. Ekspanzija je provedena termošokiranjem pri 1000 °C u trajanju od jedne minute. Pripravljeni uzorci karakterizirani su mjerenjem ekspandiranog obujma, termogravimetrijskom analizom (TGA), rendgenskom difrakcijskom analizom (XRD), Fourier-transformiranom infracrvenom spektroskopijom (FTIR), BET apsorpcijsko-desorpcijskim izotermama i pretražnom elektronskom mikroskopijom (SEM).
Rendgenska difrakcija i Fourier transformirana infracrvena spektroskopija ukazale su na to da dolazi do interkalacije te da je dominantna interkalirajuća vrsta perklorna kiselina. Termogravimetrijskom analizom utvrđeno je da do deinterkalacije dolazi u temperaturnom intervalu od 150-300 °C te da je gubitak mase u ovom temperaturnom intervalu ovisan o veličini čestica, odnosno da je interkalacija intenzivnija što su čestice grafita veće. Utvrđeno je i da čestice s više interkalanta više i ekspandiraju te imaju veću specifičnu površinu. Uzorak s najvećim promjerom čestica (dp = 315-425 µm) imao je nakon ekspanzije specifični obujam od v=86 cm3 g-1 i specifičnu površinu od s=36m2 g-1. Pretražna elektronska mikroskopija pokazala je da se ekspandirani grafit sastoji od makroporoznih crvolikih čestica.
A highly ordered alginate/montmorillonite bionanocomposite structure is presented. The alignment of the bionanocomposites has been determined by environmental scanning electron microscopy (ESEM) and ...wide-angle X-ray scattering (WAXS). The ESEM micrographs show a high in-plane orientation of the bionanocomposite, while 2D X-ray scattering images show a clear angle dependency that confirms preferential orientation of montmorillonite (MMT) platelets. The order parameter (⟨P 2⟩) was calculated from azimuthal intensity profiles derived from WAXS measured over the MMT 001 reflection, using the Maier–Saupe and the affine deformation model. We observe that the ⟨P 2⟩ values depend on the MMT concentration, which is explained by the MMT–alginate interaction. We propose an affine deformation model based on gel formation achieved by alginate adsorption on the edges of MMT, which develops yield stress and deforms the MMT platelets during drying resulting in high range ⟨P 2⟩ values.
•Alginate and montmorillonite form a dynamic physical gel with a randomly dispersed montmorillonite platelets interacting with the polymer.•The associative network starts to be formed at 20wt.% ...montmorillonite with a peak level of association at a concentration of around 80wt.%.•The gel formation is a crucial factor to explain the observed highly organised structure during film formation.
Here we report on a study of a rheological behavior of sodium alginate and montmorillonite suspension. We find that viscoelastic behavior of this suspension is dramatically affected with increasing volume fraction of montmorillonite platelets. Addition of montmorillonite generally leads to gel formation, which is attributed to interactions of montmorillonite and alginate via H-bonding and attraction between the positive edges of the platelets and the anionic backbone of the biopolymer. A critical concentration for the measured system was observed at 20wt.% montmorillonite, where a crossover to a gel-like structure was detected. The observed gel has a rubber plateau, which develops further with higher montmorillonite concentration. In this physical gel the relaxation maximum was detected, which is associated with the breaking and reformation of the bonds between the platelets and the biopolymer. For this transient behavior, we find that a Maxwell type viscoelasticity quite well describes the relaxation time and the observed G’-G” crossover. We believe that this gel-like behavior plays an important role in formation of highly ordered nanostructures that develop during the drying of these bio-nanocomposite suspensions.
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