Immersed membrane bioreactors for produced water treatment

The performance of a submerged membrane bioreactor for the duty of gas field produced water treatment was appraised. The system was operated under steady state conditions at a range of mixed liquor suspended solids (MLSS) concentrations and treatment and membrane performance examined. Organics removal (COD and TOC) display removal rates between 90 and 97%. Removal of specific target compounds Benzene, Toulene, Ethylbenzene and Xylene were removed to above 99% in liquid phase with loss to atmosphere between 0.3 and 1%. Comparison of fouling rates at a number of imposed fluxes has been made between long term filtration trials and short term tests using the flux step method. Produced water fed biomass displays a greater fouling propensity than municipal wastewater fed biomass from previous studies. Results indicate an exponential relationship between fouling rate and flux for both long and short term trials, although the value was an order of magnitude lower during long term tests. Moreover, operation during long term trials is characterised by a period of pseudo stable operation followed by a catastrophic rise in TMP at a given critical filtration time (tfi, ) during trials at 6 g. L"1. This time of stable operation, tfit, is characterised by a linear relationship between fouling rate and flux. Results have been compared with the literature. Data for membrane fouling prior to the end of t fit yielded a poor fit with a recently proposed model. Trends recorded at t> trlt revealed the fouling rate to follow no definable trend with flux. The system showed resilience to free oil shocking up to an oil concentration of 200ppmv. Following an increase in oil concentration to 500 ppmv, rapid and exponential fouling ensued.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The effect of physical fatigue on oscillatory dynamics of the sensorimotor cortex

AIM: While physical fatigue is known to arise in part from supraspinal mechanisms within the brain exactly how brain activity is modulated during fatigue is not well understood. Therefore, this study examined how typical neural oscillatory responses to voluntary muscle contractions were affected by fatigue. METHODS: Eleven healthy adults (age 27±4 years) completed two experimental sessions in a randomised crossover design. Both sessions first assessed baseline maximal voluntary isometric wrist-flexion force (MVFb ). Participants then performed an identical series of fourteen test contractions (2 × 100%MVFb , 10 × 40%MVFb , 2 × 100%MVFb ) both before and after one of two interventions: forty 12-s contractions at 55%MVFb (fatigue intervention) or 5%MVFb (control intervention). Magnetoencephalography (MEG) was used to characterise both the movement-related mu and beta decrease (MRMD and MRBD) and the post-movement beta rebound (PMBR) within the contralateral sensorimotor cortex during the 40%MVFb test contractions, while the 100%MVFb test contractions were used to monitor physical fatigue. RESULTS: The fatigue intervention induced a substantial physical fatigue that endured throughout the post-intervention measurements (28.9-29.5% decrease in MVF, P<0.001). Fatigue had a significant effect on both PMBR (ANOVA, session × time-point interaction: P=0.018) and MRBD (P=0.021): the magnitude of PMBR increased following the fatigue but not the control interventions, whereas MRBD was decreased post-control but not post-fatigue. Mu oscillations were unchanged throughout both sessions. CONCLUSION: Physical fatigue resulted in an increased PMBR, and offset attenuations in MRBD associated with task habituation. This article is protected by copyright. All rights reserved

Microbubbles and their application to ozonation in water treatment: A critical review exploring their benefit and future application

Ozonation is a widely applied water treatment process, used for oxidation of contaminants, as well as for the disinfection of water. However, the conventional ozonation process demands a high energy requirement and deep tanks to ensure effective mass transfer and oxidation. Microbubble technologies have emerged which have the potential to improve gas-liquid contacting. Microbubbles have diameters of 1–100 µm, while conventional bubbles used in ozonation are between 2 and 6 mm. Microbubbles have many favorable characteristics that make them suitable for ozonation. In this review, the attributes of microbubbles for ozonation have been compared with those of conventional bubbles. The higher interfacial area and lower rise velocity of microbubbles compared with conventional bubbles means that ozone in the gas phase can be more efficiently transferred into the liquid phase. This is due to a higher contact time and increased contact area of the bubble with the bulk liquid. The analysis reveals that the volumetric mass transfer coefficient can be significantly enhanced through the use of microbubbles. In addition, the steady state dissolved ozone concentration was positively impacted by the use of microbubbles. Microbubbles were shown to be able to oxidize a broader range of organic compounds more quickly than for conventional bubbles. However, the review highlighted that comparison of microbubbles with conventional bubbles is not always carried out in a fair and consistent way with respect to reactor configuration. Requirements for future research, more consistent experimental comparisons and the steps needed to enable implementation of microbubbles have been discussed

Chemically reactive membrane crystallisation reactor for CO2–NH3 absorption and ammonium bicarbonate crystallisation: Kinetics of heterogeneous crystal growth

The feasibility of gas-liquid hollow fibre membrane contactors for the chemical absorption of carbon dioxide (CO2) into ammonia (NH3), coupled with the crystallisation of ammonium bicarbonate has been demonstrated. In this study, the mechanism of chemically facilitated heterogeneous membrane crystallisation is described, and the solution chemistry required to initiate nucleation elucidated. Induction time for nucleation was dependent on the rate of CO2 absorption, as this governed solution bicarbonate concentration. However, for low NH3 solution concentrations, a reduction in pH was observed with progressive CO2 absorption which shifted equilibria toward ammonium and carbonic acid, inhibiting both absorption and nucleation. An excess of free NH3 buffered pH suitably to balance equilibria to the onset of supersaturation, which ensured sufficient bicarbonate availability to initiate nucleation. Following induction at a supersaturation level of 1.7 (3.3 M NH3), an increase in crystal population density and crystal size was observed at progressive levels of supersaturation which contradicts the trend ordinarily observed for homogeneous nucleation in classical crystallisation technology, and demonstrates the role of the membrane as a physical substrate for heterogeneous nucleation during chemically reactive crystallisation. Both nucleation rate and crystal growth rate increased with increasing levels of supersaturation. This can be ascribed to the relatively low chemical driving force imposed by the shift in equilibrium toward ammonium which suppressed solution reactivity, together with the role of the membrane in promoting counter-current diffusion of CO2 and NH3 into the concentration boundary layer developed at the membrane wall, which permitted replenishment of reactants at the site of nucleation, and is a unique facet specific to this method of membrane facilitated crystallisation. Free ammonia concentration was shown to govern nucleation rate where a limiting NH3 concentration was identified above which crystallisation induced membrane scaling was observed. Provided the chemically reactive membrane crystallisation reactor was operated below this threshold, a consistent (size and number) and reproducible crystallised reaction product was collected downstream of the membrane, which evidenced that sustained membrane operation should be achievable with minimum reactive maintenance intervention

Measuring temporal, spectral and spatial changes in electrophysiological brain network connectivity

The topic of functional connectivity in neuroimaging is expanding rapidly and many studies now focus on coupling between spatially separate brain regions. These studies show that a relatively small number of large scale networks exist within the brain, and that healthy function of these networks is disrupted in many clinical populations. To date, the vast majority of studies probing connectivity employ techniques that compute time averaged correlation over several minutes, and between specific pre-defined brain locations. However, increasing evidence suggests that functional connectivity is non-stationary in time. Further, electrophysiological measurements show that connectivity is dependent on the frequency band of neural oscillations. It is also conceivable that networks exhibit a degree of spatial inhomogeneity, i.e. the large scale networks that we observe may result from the time average of multiple transiently synchronised sub-networks, each with their own spatial signature. This means that the next generation of neuroimaging tools to compute functional connectivity must account for spatial inhomogeneity, spectral non-uniformity and temporal non-stationarity. Here, we present a means to achieve this via application of windowed canonical correlation analysis (CCA) to source space projected MEG data. We describe the generation of time–frequency connectivity plots, showing the temporal and spectral distribution of coupling between brain regions. Moreover, CCA over voxels provides a means to assess spatial non-uniformity within short time–frequency windows. The feasibility of this technique is demonstrated in simulation and in a resting state MEG experiment where we elucidate multiple distinct spatio-temporal-spectral modes of covariation between the left and right sensorimotor areas

Feasibility study of suspended ion exchange for organic matter removal and disinfection by-product minimisation in UK lowland waters

This investigation compared the performance of suspended ion exchange (SIX) and granular activated carbon (GAC) filtration for organic matter removal and reduction of trihalomethane (THM) and haloacetic acid (HAA) formation potential. SIX treatment resulted in increased organic matter removal (60%) when compared with GAC (45%). SIX treatment produced a stable treated water Dissolved Organic Carbon (DOC), while changes in brine concentration had no effect on the removal of organic disinfection by-product (DBP) precursors. Liquid chromatography organic carbon detection analysis (LC-OCD) showed that the differences in the organic matter removal by SIX in comparison to GAC were caused by the increased affinity of the SIX process towards the 1 kDa and 0.5-0.35 kDa organic matter size bands. These were the molecular weight fractions comprising most of the overall DOC. Organic matter removal was consistent with the minimisation of THM and HAA formation. THM formation was reduced by 50% and 65%, whereas HAA formation was lowered by 60% and 70% in comparison to the untreated water, after GAC and SIX treatment, respectively. A linear correlation between the Br:DOC ratio and the bromine substitution factor was found for THMs and HAAs, suggesting that the formation of Br-DBPs was not selective to the treatment but attributed to bulk organic matter removal and bromide content at source. The use of resin in chloride form increased the chloride to sulphate mass ratio and Larson Index suggesting a risk for increased corrosivity of SIX treated water in the distribution network

Enhancement of ozonation using microbubbles – Micropollutant removal, mass transfer and bromate formation

Microbubble technology is a promising development in the optimisation of gas–liquid contacting processes. When applied to ozonation, microbubbles have demonstrated significant enhancements to mass transfer, dissolved ozone residual and the speed and extent of compound removal. However, the mechanism by which microbubbles enhance performance over conventional bubbles is not well understood and numerous explanations exist within the literature. To elucidate the critical components that drive such enhancements the performance of microbubbles (Sauter mean diameter 37 µm) and conventional bubbles (5.4 mm) were compared under identical conditions in terms volumetric mass transfer coefficient, steady state dissolved ozone concentration, rate constant for ozone self-decomposition and the rate constant for degradation of two pesticides: mecoprop and metaldehyde. Overall, the improvement observed in performance can be attributed to the increase in the volumetric mass transfer coefficient through the combination of an increase in specific interfacial area and a decrease in the mass transfer coefficient. The increase in area outweighed the decrease in mass transfer coefficient such that an overall improvement factor of 1.6 was observed for microbubbles over conventional bubbles. All other differences were an artefact of the enhanced mass transfer leading to higher dissolved ozone concentrations when operating at a fixed input dose. For the first time it has been shown that when normalised to the amount of ozone transferred to the water, no enhancement in hydroxyl radical production, bromate formation or impact from the background constituents could be observed

The effect of physical fatigue on oscillatory dynamics of the sensorimotor cortex

Aim: While physical fatigue is known to arise in part from supraspinal mechanisms within the brain exactly how brain activity is modulated during fatigue is not well understood. Therefore, this study examined how typical neural oscillatory responses to voluntary muscle contractions were affected by fatigue. Methods: Eleven healthy adults (age 27±4 years) completed two experimental sessions in a randomised crossover design. Both sessions first assessed baseline maximal voluntary isometric wrist-flexion force (MVFb). Participants then performed an identical series of fourteen test contractions (2 × 100%MVFb, 10 × 40%MVFb, 2 × 100%MVFb) both before and after one of two interventions: forty 12-s contractions at 55%MVFb (fatigue intervention) or 5%MVFb (control intervention). Magnetoencephalography (MEG) was used to characterise both the movement-related mu and beta decrease (MRMD and MRBD) and the post-movement beta rebound (PMBR) within the contralateral sensorimotor cortex during the 40%MVFb test contractions, while the 100%MVFb test contractions were used to monitor physical fatigue. Results: The fatigue intervention induced a substantial physical fatigue that endured throughout the post-intervention measurements (28.9-29.5% decrease in MVF, P<0.001). Fatigue had a significant effect on both PMBR (ANOVA, session × time-point interaction: P=0.018) and MRBD (P=0.021): the magnitude of PMBR increased following the fatigue but not the control interventions, whereas MRBD was decreased post-control but not post-fatigue. Mu oscillations were unchanged throughout both sessions. Conclusion: Physical fatigue resulted in an increased PMBR, and offset attenuations in MRBD associated with task habituation

Recovery and concentration of ammonia from return liquor to promote enhanced CO2 absorption and simultaneous ammonium bicarbonate crystallisation during biogas upgrading in a hollow fibre membrane contactor

In this study, thermal desorption was developed to separate and concentrate ammonia from return liquor, for use as a chemical absorbent in biogas upgrading, providing process intensification and the production of crystalline ammonium bicarbonate as the final reaction product. Applying modest temperature (50°C) in thermal desorption suppressed water vapour pressure and increased selective transport for ammonia from return liquor (0.11MNH3) yielding a concentrated condensate (up to 1.7MNH3). Rectification was modelled through second-stage thermal processing, where higher initial ammonia concentration from the first stage increased mass transfer and delivered a saturated ammonia solution (6.4MNH3), which was sufficient to provide chemically enhanced CO2 separation and the simultaneous initiation of ammonium bicarbonate crystallisation, in a hollow fibre membrane contactor. Condensate recovered from return liquor exhibited a reduction in surface tension. We propose this is due to the stratification of surface active agents at the air-liquid interface during primary-stage thermal desorption which carried over into the condensate, ‘salting’ out CO2 and lowering the kinetic trajectory of absorption. However, crystal induction (the onset of nucleation) was comparable in both synthetic and thermally recovered condensates, indicating the thermodynamics of crystallisation to be unaffected by the recovered condensate. The membrane was evidenced to promote heterogeneous primary nucleation, and the reduction in the recovered condensate surface tension was shown to exacerbate nucleation rate, due to the reduction in activation energy. X-ray diffraction of the crystals formed, showed the product to be ammonium bicarbonate, demonstrating that thermal desorption eliminates cation competition (e.g. Ca2+) to guarantee the formation of the preferred crystalline reaction product. This study identifies an important synergy between thermal desorption and membrane contactor technology that delivers biogas upgrading, ammonia removal from wastewater and resource recovery in a complimentary process

CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration

Solids formation can substanitally reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Under conditions comparable to existing literature, NH4HCO3 was evidenced to primarily crystallise in the gas-phase (lumen-side of the membrane) due to the high vapour pressure of ammonia, which promotes gaseous transmission from the solvent. Investigation of solvent reactivity demonstrated how equilibria dependent reactions controlled the onset of NH4HCO3 nucleation in the solvent, and limited ‘slip’ through transfomation of ammonia into its protonated form which occurs prior to the phase change. Crystallisation in the solvent was also dependent upon ammonia concentration, where sufficient supersaturation must develop to overcome the activation energy for nucleation. However, this has to be complemented with a reduction in solvent temperature to offset vapour pressure and limit the risk of gas-phase crystallisation. While changes to the solvent chemistry were sufficient to shift from gas-phase to liquid phase crystallisation, wetting was observed immediately after nucleation in the solvent. This was explained by a local region of supersaturation within the coarse membrane pores that promoted a high nucleation rate, altering the material contact angle of the membrane sufficient for solvent to breakthrough into the gas phase. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS