Rapid Fluid Flow Research Articles

Coupled finite element analysis of the dynamics of poroelastic media considering the relative fluid acceleration

AbstractThis paper mainly discusses the dynamics of poroelastic media using the finite element analysis based on the u‐v‐p full formulation, where , , and p denote the solid displacement, relative fluid velocity with respect to solid velocity, and pore fluid pressure. It incorporates the effect of relative fluid acceleration with respect to solid acceleration on soil dynamic response. The ‐‐p formulation is first verified through the comparison with the analytical solution. After that, the response of one‐dimensional saturated soil column and two‐dimensional partially saturated soil layer subjected to vertical loading with different combinations of soil permeability and loading frequency are investigated using the analyses with the ‐‐p and ‐p formulations, based on which the effect of relative pore fluid motion is discussed and the differences in the soil response between two kinds of analysis approaches are examined. Results reveal that the rapid fluid flow has a pronounced effect on soil dynamics and the soil with a greater degree of saturation is more sensitive to the increase of loading frequency and soil permeability. The soil dynamic response can basically be divided into two main categories that represent insignificant and significant flow motion depending on loading frequency and soil permeability. Furthermore, despite vertical loading, horizontal soil response can also be affected by the large relative pore fluid flow when loading frequency and soil permeability are large. In addition, the simplified formulation can still be applicable to predict dynamics of poroelastic media in cases with high loading frequency and low soil permeability.

Visualizing the velocity fields and fluid behavior of a solution using artificial intelligence during EndoActivator activation

Background: Electrical devices driven sonically have been found in several studies to be effective to clean root canals but the effect of the EndoActivator irrigant activation flow behavior on cleaning efficacy is not completely understood. Purpose: The study aimed to provide an initial understanding of flow behavior and velocity field generation during the irrigant activation process by EndoActivator using artificial intelligence (AI). Methods: A straight glass model was filled with a solution containing 17% EDTA. Meanwhile, a medium activator tip with 22-mm polymer noncutting #25, 0.04 file driven by an electrical sonic hand-piece at 190 Hz (highest level) was used to induce velocity field to produce micro-bubbles. The physical mechanisms involved were recorded using a Miro 320S highspeed imaging system, the hydrodynamic responses were recorded, and analyzed using a motion estimation program supported by LiteFlowNet (AI). Results: The rapid fluid flow was visualized clearly in the model when it was activated by an EndoActivator tip. It was also observed that the distal end of the EndoActivator tip generated a near-wall high gradient velocity apically in all directions of the oscillation. Conclusion: The analysis showed that the proposed motion estimation program, supported by LiteFlowNet (AI), was able to capture velocity magnitude estimation of a non-PIV experiment and visualize the bubbles generated in the solution.

Fruitful femtofluidics using fast (acousto)fluidics

Acoustic streaming relies upon viscous attenuation of a propagating acoustic wave in a fluid to generate momentum flux and fluid flow. It is a nonlinear second-order phenomenon that generally produces rapid (∼10 cm/s) fluid flow but only against weak (∼10 kPa) pressure gradients. Here we describe a new form of acoustic streaming—acoustogeometric streaming—that is still nonlinear but relies on the interaction between the acoustic wave and the bounds of the fluid passage. If the boundaries oscillate with an amplitude that is significant in comparison to the width of the fluid passage, similarly rapid fluid flows may be generated even against very large (>1MPa) pressure gradients. This is used to propel fluids at 6 mm/s in 20–150 μm wide, 100 nm tall nanoslit geometries and to transport, split, combine, and mix ∼100 fl droplets of fluid. In this presentation, we will also show what happens when the nanoslit height is reduced below 10 nm, and demonstrate specific examples with some simple analysis that explains the various phenomena, closed by some explanation of the broader potential benefit of this approach.

A Simple Technique to Facilitate Sheath Irrigation of Septic Flexor Tenosynovitis

Septic flexor tenosynovitis is an aggressive hand infection that requires expedient attention. We describe the use of readily available red rubber catheters and arthroscopy tubing in operative irrigation of septic flexor tenosynovitis. The advantage of this technique over more open or invasive techniques is its simplicity, minimally invasive and tissue sparing nature, and rapid flow of fluid within the tight flexor sheath.

A digital PCR system based on the thermal cycled chip with multi helix winding capillary

This paper presents a digital PCR system based on a novel thermal cycled chip, which wraps microchannels on a trapezoidal structure made of polydimethylsiloxane (PDMS) in a multi-helix manner for the first time. It is found that compared to the single helix chip commonly used in previous reports, this kind of novel multi-helix chip can make the surface temperature in the renaturation zone more uniform, and even in the case of rapid fluid flow, it can improve the efficiency of the polymerase chain reaction. What’s more, the winding method of multi helix (such as double helix, six helix and eight helix) can obtain better temperature uniformity than the winding of odd helix (such as single helix and three helix). As a proof of concept, the temperature-optimized double-helical chip structure is applied to continuous-flow digital PCR and there is no need to add any surfactant to both the oil phase and reagent. In addition, we successfully analyzed the fluorescence signal of continuous-flow digital PCR by using CMOS camera. Finally, this method is applied for the absolute quantification of the clinical serum sample infected by HBV. The accuracy of the test results has been confirmed by commercial instruments.

Ultrafast microliter centrifuge platform for size‐based separation using novel omnidirectional spiral surface acoustic wave for point‐of‐care diagnostics

Lab‐on‐a‐chip diagnostic devices have long promised the future ability to provide point‐of‐care information on a patient’s medical conditions from a small blood sample. Within the blood, there are numerous functional entities, including exosomes, microRNA, large functional proteins within the plasma and indeed platelets and white blood cells that altogether can provide a great deal of details regarding a patient’s burden of disease and disorders.Despite years of investment and research, none have found a method to perform rapid and effective centrifugation and separation of cells from whole blood. Still today a key reason that diagnostics remains a laboratory‐based activity is the need for centrifugation and fractionation of whole blood with sample sizes of at least 10 mL (about the volume of a large lipstick case). With humans, this requires drawing blood from the arm, uncomfortable and not possible to be repeated numerous times. With small animals used in research, such separations are tedious and certainly require less than 10 mL of blood to avoid killing the animal.Here, we have devised a solution to the true problem of lab‐on‐a‐chip, point‐of‐care diagnostic devices—fluid handling at chip (micro to nano) scales—by using a carefully designed, sterilizable ~40 MHz surface acoustic wave microfluidics handling device that can centrifuge and fractionate whole blood using samples as small as 2 μL. This is a mere pinprick of blood from a human or animal.Acoustic waves transmitted into fluids at frequencies above 5 MHz can generate rapid fluid flows via a combination of compressibility and local fluid motion from the passage of the acoustic wave, but avoid damaging the cells and molecules in the sample as determined via proliferation, QPCR, and mass spectroscopy techniques among other methods. Placing a droplet of whole blood on our device allows it to be spun at over 3000 RPM to cause separation of the particulate components of the blood due to centrifugation and direct interaction of the acoustic wave with those particulates (i.e., the cells). With our unique device, we can furthermore rapidly reverse the rotation of the blood in a few milliseconds, producing an additional means to induce mixing and more finely controlled separation of objects in the blood. The centrifugation completes in ~1 s, about two orders of magnitude quicker than in an ultracentrifuge. After centrifugation, we extract the various components of the blood through microchannels strategically placed to deliver red blood cells, platelets, and other cells separated from each other. These advancements potentially provide an effective platform for whole blood separation and point‐of‐care diagnostics without need for micro or nanoscale fluidic enclosure.Image of 40MHz Omnidirectional spiral surface acoustic wave device with microliter sessile drop on inner circular region. Scale bar: 0.5mm.Figure 1(a) 1.5 μl drop with 3.3μm (red), 5.73μm (green), 43.2μm (green) polystyrene (PS) particles randomly distributed inside. (b) After surface acoustic wave induced separation, showing 3.3μm, 5.73μm, 43.2μm PS particles separated from periphery to center of the droplet. (c) 1.5 μl diluted mouse blood before separation. (d) After surface acoustic wave induced separation, obtaining red blood cells at center and other components of blood at periphery of the drop. Scale bar: 0.5mm.Figure 2

Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece

The Maronia Cu-Mo ± Re ± Au deposit is spatially related to a microgranite porphyry that intruded an Oligocene monzonite along the Mesozoic Circum-Rhodope belt in Thrace, NE Greece. The magmatic rocks and associated metallic mineralization show plastic and cataclastic features at the south-eastern margin of the deposit that implies emplacement at the ductile-brittle transition, adjacent to a shear zone at the footwall of the Maronia detachment fault. The conversion from ductile to brittle deformation caused a rapid upward magmatic fluid flow and increased the volume of water that interacted with the host rocks through high permeable zones, which produced extensive zones of potassic and sodic-calcic alteration. Potassic alteration is characterized by secondary biotite + K-feldspar (orthoclase) + magnetite + rutile + quartz ± apatite and commonly contains sulfides (pyrite, chalcopyrite, pyrrhotite). Sodic-calcic alteration consists of actinolite + sodic-calcic plagioclase (albite/oligoclase/andesine) + titanite + magnetite + chlorite + quartz ± calcite ± epidote-allanite. The high-oxidation state of the magmas and the hydrothermal fluid circulation were responsible for the metal and sulfur enrichments of the aqueous fluid phase, an increase in O2 gas content, the breakdown of the magmatic silicates and the production of the extensive potassic and sodic-calcic alterations. Brittle deformation also promoted the rapid upward fluid flow and caused interactions with the surrounding host rocks along the high temperature M-, EB-, A- and B-type veins.

Active peristaltic movements and fluid production of the mouse oviduct: their roles in fluid and sperm transport and fertilization†.

To study how the oviduct behaves in relation to fluid secretion and sperm transport, ovary-oviduct-uterus complexes of the mouse were installed in a fluid-circulating chamber without disturbing the blood circulation or parasympathetic innervation. Injection of a bolus of Indian ink into the lower isthmus revealed very active adovarian peristalsis of the isthmus, which was most prominent during the periovulatory period. Oviduct fluid, secreted by the entire length of the isthmus, was rapidly transported to the ampulla and ovarian bursa before draining into the peritoneal cavity. The upper isthmus, in particular the isthmic-ampullary junction, was responsible for this adovarian fluid flow. Peristalsis of the oviduct, undisturbed flow of oviduct fluid from the isthmus to the peritoneal cavity, and the spermatozoon's own motility all contribute to efficient sperm ascent and to fertilization within the oviduct. Therefore, chemotaxis, rheotaxis, and thermotaxis of spermatozoa toward oocyte-cumulus complexes in the ampulla are all unlikely mechanisms for explaining sperm-oocyte contact and successful fertilization, given the rapid adovarian flow of oviduct fluid in this species.

Clumped isotope evidence for episodic, rapid flow of fluids in a mineralized fault system in the Peak District, UK

We have used clumped isotope thermometry to study a fault-hosted hydrothermal calcite vein associated with the Mississippi Valley Type (MVT) mineralization on the Derbyshire Platform in the southern Pennines, UK. This is the first published dataset obtained using a new mass spectrometer, MIRA, optimized for clumped isotope analysis and an associated clumped isotope–temperature calibration. We analysed multiple generations of vein growth at high spatial resolution in two transects across the vein. The vein grew episodically at temperatures between 40 and 100°C. We interpret each episode of growth as being associated with an increasing flux of formation waters from deep sedimentary basins next to the mineralized platform and an accompanying increase in the precipitation temperatures. Heat is conserved in the fluid as it ascends along the fault surface and, thus, flow must have been fast and restricted to short-lived pulses. The flux could have been driven by high pore pressures associated with rapid sedimentation, hydrocarbon generation and diagenesis in the basinal facies of the Visean Bowland–Hodder group. Natural hydraulic fracturing of shale units and failure of capillary seals, possibly triggered by uplift, allowed the release of fluids into aquifers within the sediment pile. The transmission of high pore fluid pressures from the shales to the fault zone, aided by the compressibility of the gas phase in two-phase pore fluids, may have resulted in fault rupture, accompanied by enhanced fracture permeability and rapid fluid flow. Vein growth ceased as pore pressures dissipated. Such behaviour is closely related to a seismic valve type model for mineralization. Supplementary material: Details of the methods and equipment are available at https://dx.doi.org/10.6084/m9.figshare.3808329.v9

Management of chronic osteomylitis by wide debridement and closed suction: Drainage technique

Background: Chronic osteomyelitis remains one of the most challenging problems in orthopaedic surgery [1-6]. It commonly occurs after sequele of acute osteomylitis in children and teenagers, secondary osteomylitis due to trauma involving either an open fracture or internal fixation [1]. Materials & Methods: This is prospective longitudinal study. We have prospectively studied 98 patients with chronic osteomyelitis treated by the technique of wide debridement and closed suction and drainage and describe the results at a mean follow-up of 21.96 months (min-max 20 to 24; median 22). The procedure involved radical debridement and excision of all avascular scarred and infected granulation tissue, followed by debridement of the infected endosteum, reaming and the insertion of closed suction drainage system. The system rely on rapid fluid flow of 5 ml 10% povidon iodine in 500 ml normal saline and mechanical washing in association with appropriate intravenous antibiotic. The fluid used for drainage is normal saline and mixture of 5 ml 10% povidon iodine in 500 ml normal saline. Results: Healing was achieved in all patient with fractures which had not previously united. There were three cases with recurrent infection with this procedure. Three patients required below-knee amputation due to eradication of the infection. These three patient had post traumatic osteomylitis. The mean follow-up was for 21.96 months (min-max 20to24; Conclusions: The procedure of wide debridement and closed suction drainage is indicated for complex cases of osteomyelitis in which conventional surgical debridement have failed.

Effective and energy-preserving time discretization for a general nonlinear poromechanical formulation

We consider a general nonlinear poromechanical model, formulated based on fundamental thermodynamics principle, suitable for representing the coupling of rapid internal fluid flows with large deformations of the solid, and compatible with a wide class of constitutive behavior. The objective of the present work is to propose for this model a time discretization scheme of the partitioned type, to allow the use of existing time schemes – and possibly separate solvers – for each component of the model, i.e. for the fluid and the solid. To that purpose, we adapt and extend an earlier proposed approach devised for fluid-structure interaction in an Arbitrary Lagrangian-Eulerian framework. We then establish an energy estimate for the resulting time scheme, in a form that is consistent with the underlying energy principle in the poromechanical formulation, up to some numerical dissipation effects and some perturbations that we have carefully identified and assessed. In addition, we provide some numerical illustrations of our numerical strategy with test problems that present typical features of large strains and rapid fluid flows, and also a case of singular transition related to total drainage. An example of challenging application envisioned for this model and associated numerical coupling scheme concerns the perfusion of the heart.

Cross-hole tracer experiment reveals rapid fluid flow and low effective porosity in the upper oceanic crust

Numerous field, laboratory, and modeling studies have explored the flows of fluid, heat, and solutes during seafloor hydrothermal circulation, but it has been challenging to determine transport rates and flow directions within natural systems. Here we present results from the first cross-hole tracer experiment in the upper oceanic crust, using four subseafloor borehole observatories equipped with autonomous samplers to track the transport of a dissolved tracer (sulfur hexafluoride, SF6) injected into a ridge-flank hydrothermal system. During the first three years after tracer injection, SF6 was transported both north and south through the basaltic aquifer. The observed tracer transport rate of ∼2–3 m/day is orders of magnitude greater than bulk rates of flow inferred from thermal and chemical observations and calculated with coupled fluid-heat flow simulations. Taken together, these results suggest that the effective porosity of the upper volcanic crust through which much tracer was transported is <1%, with fluid flowing rapidly along a few well-connected channels. This is consistent with the heterogeneous (layered, faulted, and/or fractured) nature of the volcanic upper oceanic crust.

Rapid fluid flow along fractures at greenschist facies conditions on Syros, Greece

This thesis aims to provide a better understanding of the role of mountain building in the carbon cycle. The amount of CO2 released into the atmosphere due to metamorphic processes is largely unknown. To constrain the quantity of CO2 released, fluid-driven reactions in metamorphic rocks can be studied by tracking fluid-rock interactions along ancient fluid flow pathways. The thesis is divided into two parts: 1) modeling of fluid flow rates and durations within shear zones and fractures during greenschist- and blueschist-facies metamorphism and 2) the assessment of possible mechanisms of fluid infiltration into rocks during greenschist- to epidote-amphibolite-facies metamorphism and controlling chemical and mineralogical factors of reaction front propagation.On the island Syros, Greece, fluid-rock interaction was examined along a shear zone and within brittle fractures to calculate fluid flux rates, flow velocities and durations. Petrological, geochemical and thermodynamic evidence show that the flux of CO2-bearing fluids along the shear zone was 100-2000 times larger than the fluid flux in the surrounding rocks. The time-averaged fluid flow velocity and flow duration along brittle fractures was calculated by using a governing equation for one-dimensional transport (advection and diffusion) and field-based parameterization. This study shows that fluid flow along fractures on Syros was rapid and short lived.Mechanisms and controlling factors of fluid infiltration were studied in greenschist- to epidote-amphibolite-facies metabasalts in SW Scotland. Fluid infiltration into metabasaltic sills was unassisted by deformation and occurred along grain boundaries of hydrous minerals (e.g. amphibole) while other minerals (e.g. quartz) prevent fluid infiltration. Petrological, mineralogical and chemical studies of the sills show that the availability of reactant minerals and mechanical factors, e.g. volume change in epidote, are primary controls of reaction front propagation.

Palagonitization of Basalt Glass in the Flanks of Mid-Ocean Ridges: Implications for the Bioenergetics of Oceanic Intracrustal Ecosystems.

When basalt is exposed to oxygenated aqueous solutions, rims of palagonite form along fractures at the expense of glass. We employed electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fresh glass and adjacent palagonite crusts to determine the geochemical changes involved in palagonite formation. Samples were retrieved from drill cores taken in the North Pond Area, located on the western flank of the Mid-Atlantic Ridge at 22°45'N and 46°05'W. We also analyzed whole rock powders to determine the overall crust-seawater exchange in a young ridge flank. Radioactive elements are enriched in palagonite relative to fresh glass, reaching concentrations where radiolytic production of molecular hydrogen (H2) may be a significant energy source. Based on these results, we hypothesize that microbial ecosystems in ridge flank habitats undergo a transition in the principal energy carrier, fueling carbon fixation from Fe oxidation in very young crust to H2 consumption in older crust. Unless the H2 is swept away by rapid fluid flow (i.e., in young flanks), it may easily accumulate to levels high enough to support chemolithoautotrophic life. In older flanks, crustal sealing and sediment accumulation have slowed down seawater circulation, and the significance of radiolytically produced H2 for catalytic energy supply is expected to increase greatly. Similar habitats on other planetary surfaces are theoretically possible, as accumulation of radiolytically produced hydrogen merely requires the presence of H2O molecules and a porous medium, from which the hydrogen is not lost.

Design and parallelisation of a miniature photobioreactor platform for microalgal culture evaluation and optimisation

Miniature photobioreactors (mPBr) represent a potential platform technology for the high-throughput, phototrophic cultivation of microalgae. This work describes the development and characterisation of a novel orbitally shaken twin-well mPBr, and its scale-out to a 24-well microplate format, suitable for optimisation of microalgae culture conditions. Fluid hydrodynamics, oxygen mass transfer coefficient (kLa) and light intensity distribution in the mPBr were first investigated as a function of orbital shaking frequency. High speed video analysis of the shaken wells indicated rapid fluid flow and good mixing while measured kLa values varied between 20 and 80h−1. Light intensity variation across the scaled-out platform was in the range ±20μmolm−2s−1. The use of the mPBr platform was demonstrated for optimisation of conditions for the batch cultivation of Chlorella sorokiniana. Using a modified tris-base phosphate (TBP) medium, the highest biomass concentration and productivity achieved were 9.2gL−1 and 2.5±0.2gL−1d−1 respectively at 5% CO2 with a light intensity of 380μmolm−2s−1. In general, cell growth rate and yield increased with increasing shaking frequency (up to 300rpm) while culture conditions had limited impact on pigment production. Overall, these results demonstrate the application of the mPBr for rapid optimisation of phototrophic culture conditions and establishment of high cell density cultures.

Ca, Sr, O and D isotope approach to defining the chemical evolution of hydrothermal fluids: Example from Long Valley, CA, USA

We present chemical and isotopic data for fluids, minerals and rocks from the Long Valley meteoric-hydrothermal system. The samples encompass the presumed hydrothermal upwelling zone in the west moat of the caldera, the Casa Diablo geothermal field, and a series of wells defining a nearly linear, ∼16km long, west-to-east trend along the likely fluid flow path. Fluid samples were analyzed for the isotopes of water, Sr, and Ca, the concentrations of major cations and anions, alkalinity, and total CO2. Water isotope data conform to trends documented in earlier studies, interpreted as indicating a single hydrothermal fluid mixing with local groundwater. Sr isotopes show subtle changes along the flow path, which requires rapid fluid flow and minimal reaction between the channelized fluids and the wallrocks. Sr and O isotopes are used to calculate fracture spacing using a dual porosity model. Calculated fracture spacing and temperature data for hydrothermal fluids indicate the system is (approximately) at steady-state. Correlated variations among total CO2, and the concentration and isotopic composition of Ca suggest progressive fluid degassing (loss of CO2), which drives calcite precipitation as the fluid flows west-to-east and cools. The shifts in Ca isotopes require that calcite precipitated at temperatures of 150–180°C is fractionated by ca. −0.3‰ to −0.5‰ relative to aqueous species. Our data are the first evidence that Ca isotopes undergo kinetic fractionation at high temperatures (>100°C) and can be used to trace calcite precipitation along hydrothermal fluid flow paths.

Non-aqueous microchip electrophoresis for characterization of lipid biomarkers

In vivo measurements of lipid biomarkers are hampered by their low solubility in aqueous solution, which limits the choices for molecular separations. Here, we introduce non-aqueous microchip electrophoretic separations of lipid mixtures performed in three-dimensional hybrid nanofluidic/microfluidic polymeric devices. Electrokinetic injection is used to reproducibly introduce discrete femtolitre to picolitre volumes of charged lipids into a separation microchannel containing low (100 μM-10 mM) concentration tetraalkylammonium tetraphenylborate background electrolyte (BGE) in N-methylformamide, supporting rapid electro-osmotic fluid flow in polydimethylsiloxane microchannels. The quality of the resulting electrophoretic separations depends on the voltage and timing of the injection pulse, the BGE concentration and the electric field strength. Injected volumes increase with longer injection pulse widths and higher injection pulse amplitudes. Separation efficiency, as measured by total plate number, N, increases with increasing electric field and with decreasing BGE concentration. Electrophoretic separations of binary and ternary lipid mixtures were achieved with high resolution (R s ∼ 5) and quality (N > 7.7 × 10(6) plates m(-1)). Rapid in vivo monitoring of lipid biomarkers requires high-quality separation and detection of lipids downstream of microdialysis sample collection, and the multilayered non-aqueous microfluidic devices studied here offer one possible avenue to swiftly process complex lipid samples. The resulting capability may make it possible to correlate oxidative stress with in vivo lipid biomarker levels.

Combining biomimetic principles from the lotus leaf and mussel adhesive: polystyrene films with superhydrophobic and adhesive layers

Lotus leaves are well known for their extremely water repellent surfaces. Marine mussels are also a popular research topic when considering biological adhesives. Both organisms have inspired the development of several biomimetic materials. Herein we describe a two-sided film made almost entirely from polystyrene onto which the properties of both lotus leaves and mussel adhesive are incorporated. On one side of the film, imparting micrometer and nanometer scale hierarchical roughness yields superhydrophobicity and water repellency, which facilitates rapid fluid flow. The other side of the film is modified with a copolymer mimic of 3,4-dihydroxyphenylalanine (DOPA)-containing mussel adhesive proteins. This copolymer incorporates 3,4-dihydroxystyrene, to represent DOPA, randomly into a polystyrene host polymer. The flexibility of the polystyrene backing film enabled rolling of the assembly into a tubular shape. Inside the polystyrene tube was the superhydrophobic lotus mimic. The mussel adhesive mimic, on the outer layer, was used to glue the tube to itself, thus maintaining the tubular shape. The film was also successfully glued to a variety of flat substrates. These two-dimensional and three-dimensional assemblies can be used to direct and localize the flow of fluids, with partitioning between superhydrophobic and relatively hydrophilic regions. Such assemblies may facilitate the design of liquid transport for industrial and biomedical devices.

Wastewater filtration and re-use: An alternative water source for London

The rapid growth and climate of the Greater London region have contributed towards large deficits in water supply. Inexpensive, energy-efficient and sustainable water resource schemes are increasingly sought as a means to boost supply. Here, we propose a small-scale recycling scheme whereby tertiary-treated wastewater is pumped to the Cretaceous chalk of the London Basin. By taking advantage of the natural filtration properties of the underlying chalk, contaminants can be effectively attenuated over relatively short length scales to result in pure water. The problem is approached from four different scales. First, we define two localities in London where such a pumping scheme might operate; regions which combine a thick unsaturated zone and high chalk transmissivity, both essential to ensure maximum contaminant removal and minimum environmental impact. Secondly, the effects of pumping fluid into the Chalk at the two localities are quantified using a finite-difference groundwater flow model. We show that rivers impose a regular groundwater flow regime, whereas pre-existing abstraction wells will lead to less predictable results. Thirdly, we consider the effect of fractures on channelling rapid fluid flow within the rock mass. By digitising a fracture map based upon outcrop measurements from chalk exposed on the Kent coast similar to that beneath London, we quantify transport patterns of wastewater after injection. Imbibition to the chalk matrix (and therefore filtration) will occur where fluid pressure gradients are highest, for instance around disconnected fracture tips. Finally we demonstrate the efficacy of chalk in contaminant removal by injecting an analogue ‘effluent’ through a chalk core. ICP-AES analysis on the recovered solution shows the contaminants (viz. a suite of heavy metals) are arrested or removed over relatively small time- and length-scales. Numerical and analytical solutions fit the data poorly, shedding some light on the importance of hydrodynamic dispersion of aqueous contaminants within the chalk.

Volcanic arcs fed by rapid pulsed fluid flow through subducting slabs

During subduction, the seawater-altered lithosphere becomes dehydrated and expels fluids. Isotopic analysis of an exhumed oceanic slab in the Tianshan Mountain Range shows that although subduction can continue for many millions of years, fluids are expelled in short-lived channels over periods of just a few hundred years. At subduction zones, oceanic lithosphere that has interacted with sea water is returned to the mantle, heats up during descent and releases fluids by devolatilization of hydrous minerals. Models for the formation of magmas feeding volcanoes above subduction zones require largescale transport of these fluids into overlying mantle wedges1,2,3. Fluid flow also seems to be linked to seismicity in subducting slabs. However, the spatial and temporal scales of this fluid flow remain largely unknown, with suggested timescales ranging from tens to tens of thousands of years3,4,5. Here we use the Li–Ca–Sr isotope systems to consider fluid sources and quantitatively constrain the duration of subduction-zone fluid release at ∼ 70 km depth within subducting oceanic lithosphere, now exhumed in the Chinese Tianshan Mountains. Using lithium-diffusion modelling, we find that the wall-rock porosity adjacent to the flowpath of the fluids increased ten times above the background level. We show that fluids released by devolatilization travelled through the slab along major conduits in pulses with durations of about ∼ 200 years. Thus, although the overall slab dehydration process is continuous over millions of years and over a wide range of pressures and temperatures, we conclude that the fluids produced by dehydration in subducting slabs are mobilized in short-lived, channelized fluid-flow events.