A comparison of alginate fouling in forward osmosis (FO) with that in reverse osmosis (RO) was made. A key experimental finding, corroborated by membrane autopsies, was that FO is essentially more ...prone to fouling than RO, which is opposite to a common claim in the literature where deductions on fouling are often based solely on the water flux profiles. Our theoretical analysis shows that, due to a decrease in the intensity of internal concentration polarization (ICP), and thus an increase in the effective osmotic driving force during FO fouling tests, the similarity of experimental water flux profiles for FO and RO is in accordance with there being greater fouling in FO than RO. The specific foulant resistance for FO was also found to be greater than that for RO. Possible explanations are discussed and these include the influence of reverse solute diffusion from draw solution. Whilst this explanation regarding specific foulant resistance is dependent on the draw solution properties, the finding of greater overall foulant accumulation in FO is considered to be a general finding. Additionally, the present study did not find evidence that hydraulic pressure in RO plays a critical role in foulant layer compaction. Overall this study demonstrated that although FO has higher fouling propensity, it offers superior water flux stability against fouling. For certain practical applications this resilience may be important.
Display omitted
•FO has higher fouling propensity but greater flux stability against fouling than RO.•No evidence is found that hydraulic pressure in RO plays a critical role in foulant layer compaction.•ICP self-compensation in FO is the major reason for the different fouling behaviour between FO and RO.•Cake-enhanced concentration polarization plays a less important role in flux decline in FO than RO.•High water flux recovery after membrane cleaning in FO is due to the change in ICP and Δπeff.
The goal of therapy for bradycardia or tachycardia is to rapidly identify and treat patients who are hemodynamically unstable or symptomatic due to the arrhythmia. Drugs or, when appropriate, pacing ...may be used to control unstable or symptomatic bradycardia. Cardioversion or drugs or both may be used to control unstable or symptomatic tachycardia. ACLS providers should closely monitor stable patients pending expert consultation and should be prepared to aggressively treat those with evidence of decompensation.
Intense single-cycle THz pulses resonantly interacting with molecular rotations are shown to induce field-free orientation and alignment under ambient conditions. We calculate and measure the degree ...of both orientation and alignment induced by the THz field in an OCS gas sample, and correlate between the two observables. The data presents the first observation of THz-induced molecular alignment in the gas phase.
Since its invention in 2006, the broadband chirped pulse Fourier transform spectrometer has transformed the field of microwave spectroscopy. The technique enables the collection of a ≥10 GHz ...bandwidth spectrum in a single shot of the spectrometer, which allows broadband, high-resolution microwave spectra to be acquired several orders of magnitude faster than what was previously possible. We discuss the advantages and challenges associated with the technique and look back on the first ten years of chirped pulse Fourier transform spectroscopy. In addition to enabling faster-than-ever structure determination of increasingly complex species, the technique has given rise to an assortment of entirely new classes of experiments, ranging from chiral sensing by three-wave mixing to microwave detection of multichannel reaction kinetics. However, this is only the beginning. Future generations of microwave experiments will make increasingly creative use of frequency-agile pulse sequences for the coherent manipulation and interrogation of molecular dynamics.
The interaction of carbonyl sulfide dipolar gas molecules with two time-delayed, single-cycle THz pulses is shown both experimentally and theoretically to induce two-quantum rotational coherences ...that are significantly enhanced with respect to those induced by one THz pulse, depending on the relative delay of the pulses. The underlying phenomenon is quite general in that it can occur even after a single THz pulse if more than one molecular species is present, since the free induction decay emitted by one species (demonstrated here by atmospheric water vapor) can provide the second field interaction for the other.
It has been established that slug bubbling is an effective strategy to control fouling in flat sheet MBRs (FSMBR). Following prior work that ascertained optimal values of plate thickness and channel ...gaps, the focus here is on optimizing aerator spacing for operation under a range of aeration rates. The overall objective is to enhance fouling control of commercial-scale FSMBRs through optimization of the bubble distribution and the intensity of the induced shear stress. Three-dimensional Computational Fluid Dynamics (CFD) simulation was used to predict the aeration process of bubble coalescence, development, split and distribution into channels between every membrane pair. The bubble features and behavior were analyzed and compared with experimental measurements and substantial agreement was obtained. The aeration inlet conditions, including aerator spacing, were varied to control the slug bubbling process. The combination of aeration inlet velocity at 11 m/s and aerator spacing of 156 mm was verified to be an optimal condition, which would give a combination of uniform distribution of slug bubbles between the plates, high induced shear stress at the membrane surface and an economic air consumption. The aeration consumption for 100 sheets of membranes would be reduced by 47% compared to the conventional industrial norm.
Display omitted
•Optimizing aerator spacing for operation over a range of aeration rates.•Intermittent slug bubbling induces high shear stress and maintains economic air consumption.•Optimal nozzle velocity established.
Critical flux theory evolved as a description of the upper bound in the operating envelope for controlled steady state environments such as cross-flow systems. However, in the application of UF ...membranes in the water industry, dead-end (direct-flow) designs are used. Direct-flow is a pseudo steady state operation with different fouling characteristics to cross-flow, and thus the critical flux concept has limited applicability. After a review of recent usage of the critical flux theory, an alternative concept for providing design guidelines for direct-flow systems namely that of the threshold flux is introduced. The concept of threshold flux can also be applicable to cross-flow systems. In more general terms the threshold flux can be taken to be the flux that divides a low fouling region from a high fouling region. This may be linked both to the critical flux concept and to the concept of a sustainable flux. The sustainable flux is the one at which a modest degree of fouling occurs, providing a compromise between capital expenditure (which is reduced by using high flux) and operating costs (which are reduced by restricting the fouling rate). Whilst the threshold flux can potentially be linked to physical phenomena alone, the sustainable flux also depends upon economic factors and is thus of a different nature to the critical and threshold fluxes. This distinction will be illustrated using some MBR data. Additionally the utility of the concept of a threshold flux will be illustrated using pilot plant data obtained for UF treatment of four sources of water.
►Reviewed briefly the recent usage of the critical flux theory. ►Threshold flux concept introduced. ►Threshold flux illustrated using pilot plant data for four different waters. ►Nature of sustainable flux analysed.
Slug bubbling in flat sheet MBRs (FSMBR) is of interest in water treatment industry to effectively control fouling. In this work, a novel bubbling method is used to produce slug bubbles into all ...channels between every pair of membranes for a large-scale 100-sheets commercial FSMBR. Below the membrane plates, coalescent bubbles formed and these developed into large-sized bubbles, which eventually distributed between channels as a set of slug bubbles. Computational Fluid Dynamics (CFD) was used to predict the bubble size and distribution among different channels, and associated hydrodynamic features. Substantial agreement was observed with the experiment results. The configuration of membrane plate centrally located above the aeration nozzles was determined to have superior hydrodynamic performance of high shear stress on the membrane surfaces. The effect of membrane plate and channel dimensions were studied to identify the optimized design for hydrodynamics enhancement on fouling control. The combination of membrane thickness at 5mm and channel gap at 6mm was verified to be the optimal configuration, which would give uniform distribution of slug bubbles and provide high shear stress in the channels. The optimized air flow rate was successfully reduced to 4.7L/minm2, which corresponds to a 53% reduction compared with traditional usage (10L/minm2) in industry.
Display omitted
•A Novel Aeration Process for slug bubbling in large-scale commercial Flat Sheet MBR is proposed.•In this process, hydrodynamic effect is enhanced by various configuration of aerator and membrane plate.•Energy cost from this bubbling process is optimized and successfully reduced by 53% compared with traditional usage in industry.
PDF
