Water and wastewater treatment sludges exhibit compressible behaviour due to flocculation and aggregation. At a critical solids concentration called the gel point, which is as low as 1–2 v/v%, a ...continuous interconnected network of particles is formed that can resist an applied load. The applied load (mechanical filtration pressure or buoyancy in settling for example) must exceed the network strength in order to consolidate the network. The network strength increases with solids concentration such that the equilibrium extent of consolidation is a function of the applied load. Improved understanding of the nature of compressible suspensions can have a significant impact through optimising design and operation of sludge handling and dewatering processes. This work gives an overview of compressional rheology, which has proven to be a useful tool for describing the solid–liquid separation of compressible systems. This is followed by three examples where compressibility effects must be taken into account, namely the extraction of material properties for extremely compressible materials, consolidation and crust formation during constant rate evaporation, and the effect of bed height in thickening.
•The importance of considering the compressibility of sludges.•An overview of compressional rheology theory for describing sludge dewatering.•The importance of using local properties in dewatering characterisation.•Incorporating compressibility effects in sludge drying.•Incorporating compressibility effects in sludge thickening.
Materials assembled by coordination interactions between naturally abundant polyphenols and metals are of interest for a wide range of applications, including crystallization, catalysis, and drug ...delivery. Such an interest has led to the development of thin films with tunable, dynamic properties, however, creating bulk materials remains a challenge. Reported here is a class of metallogels formed by direct gelation between inexpensive, naturally abundant tannic acid and group(IV) metal ions. The metallogels exhibit diverse properties, including self‐healing and transparency, and can be doped with various materials by in situ co‐gelation. The robustness and flexibility, combined with the ease, low cost, and scalability of the coordination‐driven assembly process make these metallogels potential candidates for chemical, biomedical, and environmental applications.
Ti‐tannic gels: The direct gelation of the natural polyphenol tannic acid, by coordination‐driven supramolecular assembly with titanium(IV), is reported. These metallogels exhibit a range of properties, including transparency, injectability, moldability, self‐healing, shape persistence, adhesiveness, and tunable mechanics.
Filamentous bacteria can impact on the physical properties of flocs in the activated sludge process assisting solid-liquid separation or inducing problems when bacteria are overabundant. While ...filamentous bacteria within the flocs are understood to increase floc tensile strength, the relationship between protruding external filaments, dewatering characteristics and floc stability is unclear. Here, a quantitative methodology was applied to determine the abundance of filamentous bacteria in activated sludge samples from four wastewater treatment plants. An automated image analysis procedure was applied to identify filaments and flocs and calculate the length of the protruding filamentous bacteria (PFB) relative to the floc size. The correlation between PFB and floc behavior was then assessed. Increased filament abundance was found to increase interphase drag on the settling flocs, as quantified by the hindered settling function. Additionally, increased filament abundance was correlated with a lower gel point concentration leading to poorer sludge compactability. The floc strength factor, defined as the relative change in floc size upon shearing, correlated positively with filament abundance. This influence of external protruding filamentous bacteria on floc stability is consistent with the filamentous backbone theory, where filamentous bacteria within flocs increase floc resistance to shear-induced breakup. A qualitative correlation was also observed between protruding and internal filamentous structure. This study confirms that filamentous bacteria are necessary to enhance floc stability but if excessively abundant will adversely affect solid-liquid separation. The tools developed here will allow quantitative analysis of filament abundance, which is an improvement on current qualitative methods and the improved method could be used to assist and optimize the operation of waste water treatment plants.
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•An image analysis method for quantifying filament length per unit area is presented.•Filaments increased interphase drag, as measured by the hindered settling function.•The gel point has a strong inverse correlation with filament abundance.•Protruding bacteria correlate with internal structure and enhance floc stability.
Quantification and comparison of the dewatering characteristics of fifteen sewage sludges from a range of digestion scenarios are described. The method proposed uses laboratory dewatering ...measurements and integrity analysis of the extracted material properties. These properties were used as inputs into a model of filtration, the output of which provides the dewatering comparison. This method is shown to be necessary for quantification and comparison of dewaterability as the permeability and compressibility of the sludges varies by up to ten orders of magnitude in the range of solids concentration of interest to industry. This causes a high sensitivity of the dewaterability comparison to the starting concentration of laboratory tests, thus simple dewaterability comparison based on parameters such as the specific resistance to filtration is difficult. The new approach is demonstrated to be robust relative to traditional methods such as specific resistance to filtration analysis and has an in-built integrity check. Comparison of the quantified dewaterability of the fifteen sludges to the relative volatile solids content showed a very strong correlation in the volatile solids range from 40 to 80%. The data indicate that the volatile solids parameter is a strong indicator of the dewatering behaviour of sewage sludges.
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•A new method of quantifying the dewaterability of sewage sludges is proposed.•Numerical analysis of filtration data shows excellent agreement with theory.•Dewaterability is shown to be strongly correlated with the volatile solids of the sludge.•The analysis is consistent against 15 sludges from Australia and the UK.
At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer (
vdM
) method are affected by the mutual electromagnetic interaction of the two beams. The colliding ...bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic-
β
effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the
vdM
regime, the beam–beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic-
β
corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam–beam effects on the
vdM
-based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam–beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute
pp
-luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam–beam-related systematic uncertainty on beam–beam corrections to absolute luminosity calibrations by the van der Meer method.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this work, a combined smoothed particle hydrodynamics and discrete element method (SPH-DEM) model was proposed to model particle agglomeration in a shear flow. The fluid was modeled with the SPH ...method and the solid particles with DEM. The system was governed by three fundamental dimensionless groups: the Reynolds number Re (1.5~150), which measured the effect of the hydrodynamics; the adhesion number Ad (6 × 10−5~6 × 10−3), which measured the inter-particle attraction; and the solid fraction α, which measured the concentration of particles. Based on these three dimensionless groups, several agglomeration regimes were found. Within these regimes, the aggregates could have different sizes and shapes that went from long thread-like structures to compact spheroids. The effect of the particle–particle interaction model was also investigated. The results were combined into ‘agglomeration maps’ that allowed for a quick determination of the agglomerate type once α, Re, Ad were known.
The prediction and optimisation of the performance of dewatering devices such as filters and thickeners requires the laboratory measurement of fundamental material characteristics. This work presents ...the application of recently developed methods for the extraction of meaningful phenomenological properties from filtration and sedimentation testing of wastewater sludges, which has previously been limited due to theoretical and experimental constraints. The results for a sample of digested wastewater treatment sludge described a material with weak network strength that was quite permeable at low solids concentrations and the gel point was about 1
v/v%. The sample compressed to high solids concentrations at moderate pressures (up to 40
v/v% at 400
kPa) but became extremely impermeable at these high concentrations. The solids concentration dependencies of the material characteristics had a form that was expected for highly compressible materials such as wastewater sludges, but had not been reported previously. The extracted material characteristics were then used to predict the test results to show that the characterisation was valid.
•Long-chain PFAS enrichment occurred in aerated bioreactors’ foams.•Low to marginal enrichment was observed for short-chain PFAS.•PFAS enrichment was observed in both aqueous and solid phases of ...foamates.•PFAS sorption to the solid phase of foamates should be accounted.•Further investigations for foam fractionation implementation at WWTPs are needed.
Foaming in aerated bioreactors at wastewater treatment plants (WWTPs) has been identified as an operational issue for decades. However, the affinity of per- and polyfluoroalkyl substances (PFAS) for air-liquid interfaces suggests that foam harvesting has the potential to become a sustainable method for PFAS removal from sewage. Aerated bioreactors’ foams are considered three-phase systems, comprising air, aqueous and solid components, the latter consisting of activated sludge biomass. To achieve a comprehensive understanding of the capability of aerated bioreactors’ foams to enrich PFAS, we analysed PFAS concentrations from WWTPs in both the solid and aqueous phases of the collapsed foams (foamate) and underlying bulk mixed liquors. Our findings show that PFAS enrichment occurs not only in the aqueous phase but also in the solid phase of the foamate. This suggests that previous field studies that only analysed the aqueous phase may have underestimated the capability of the aerated bioreactors’ foams to enrich PFAS. Fractions of PFOA and PFOS sorbed to the solid phase of the foamate can be as high as 60 % and 95 %, respectively. Our findings highlight the importance of implementing effective foamate management strategies that consider both the aqueous and solid phases.
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Measuring yielding in cohesive suspensions is often hampered by slip at measurement surfaces. This paper presents creep data for strongly flocculated suspensions obtained using vane-in-cup tools with ...differing cup-to-vane diameter ratios. The three suspensions were titania and alumina aggregated at their isoelectric points and polymer-flocculated alumina. The aim was to find the diameter ratio where slip or premature yielding at the cup wall had no effect on the transient behaviour. The large diameter ratio results showed readily understandable material behaviour comprising linear viscoelasticity at low stresses, strain-softening close to yielding, time-dependent yield across a range of stresses and then viscous flow. Tests in small ratio geometries however showed more complex responses. Effects attributed to the cup wall included delayed softening, slip, multiple yielding and stick–slip events, and unsteady flow. The conclusion was that cups have to be relatively large to eliminate wall artefacts. A diameter ratio of three was sufficient in practice, although the minimum ratio must be material dependent.
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