Recirculation Regime Research Articles

An Integrated Approach to Identify the Total Recirculation Regime for a Gas–Liquid System in an Agitated and Sparged Tank Contactor

An Integrated Approach to Identify the Total Recirculation Regime for a Gas–Liquid System in an Agitated and Sparged Tank Contactor

Start-up of non-bioaugmented pumice biofilters in flow-through and recirculating flow regime for Mn removal

Abstract Biofilters are effectively used for drinking water treatment. However, the long ripening time of virgin media for manganese (Mn) removal is a major concern. In this study, the influence of the flow regime on the ripening time of virgin pumice medium was investigated. For this purpose, pilot-scale experiments were performed to compare the start-up of flow-through and recirculating filter columns using inherent inoculation with the same groundwater source. The systems were operated at 2 m·h−1 with gradual flow increments up to 5 m·h−1 and avoiding Fe-loading. Effective Mn removal (>90%) in flow-through and recirculating columns was achieved after 8 and 23 days, respectively. Flow-through columns reached compliance with a local drinking water criterion (Mn < 0.1 mg·L−1) at 15 cm filter depth in 11 days. Recirculating filter columns required 32 days to reach compliance at 30 cm depth. The start-up in recirculation regime resulted in a water consumption reduction of about 50% compared with flow-through regime. The intermittent provision of the Mn-loading in recirculating regime impacted the Mn-oxidizing bacteria (MOB) concentration in the pumice stone medium. Both flow regimes required a similar total Mn-loading (0.16 and 0.11 kg·Mn·m−2, respectively), suggesting that Mn-loading was the limiting factor for the ripening of pumice.

Resolution of conflict of reduced sludge production with EBPR by coupling OSA to A2/O process in a pilot scale SBR

The pinnacle of all the efforts of nutrient removal is practically put-down the moment biological cells are lysed, hydrolyzed or digested causing subsequent reappearance of assimilated nitrogen and phosphorus in any biological process. While sludge reduction requires high SRT, the enhanced phosphorus assimilative uptake demands low SRT. A novel reactor configuration for enhanced sludge and phosphorus removal was put to test by incorporating a side stream anaerobic reactor to an Anaerobic-Anoxic-Aerobic (A2O) SBR with a pre-anoxic chamber and an influent receiving inlet anaerobic reactor. The reactor was operated at the average and lowest range of prevailing carbon/phosphorus (C/P) ratio of 50 and 15 in the sewage. The phosphorus enrichment was 0.0469–0.135 mgTP/mgVSS resulting in 1.76–5.05-fold increase from cellular content by virtue of maintaining sludge recycle from SBR aeration tank to side stream anaerobic reactor from 3.78 to 9.78 (average 4.4–8.2) gVSS/gVSS present in the reactor. However, the sludge was also reduced from 3% to 51% on an average basis during the same recirculation regime. This novel configuration consists of an inlet anaerobic reactor, one pre-anoxic chamber and one intermittent oxic anoxic reaction SBR and a side stream anaerobic reactor. The first anaerobic reactor at inlet followed by pre-anoxic chamber was provided for increased ortho-p released and nitrification respectively and a side stream anaerobic reactor for sludge reduction through sludge fasting mechanism. The EBPR and lesser sludge growth were two conflicting parameters reconciled to the extent that if sludge recycled up to 6.41 gVSS/gVSS the sludge growth would be reduced by 25% and phosphorus enrichment could be attained up to 3.46 times the stoichiometric value. Any further recirculation would reduce the sludge further but at the expense of enhanced phosphorus uptake as released phosphorus from side stream anaerobic reactor also recycled back to main SBR causing looping and at more than 6.41gVSSrecycled/gVSS it nullified the enhanced effect.

A high-throughput microfluidic device based on controlled incremental filtration to enable centrifugation-free, low extracorporeal volume leukapheresis

Leukapheresis, the extracorporeal separation of white blood cells (WBCs) from red blood cells (RBCs) and platelets (PLTs), is a life-saving procedure used for treating patients with cancer and other conditions, and as the initial step in the manufacturing of cellular and gene-based therapies. Well-tolerated by adults, leukapheresis poses a significant risk to neonates and low-weight infants because the extracorporeal volume (ECV) of standard centrifugation-based machines represents a particularly large fraction of these patients’ total blood volume. Here we describe a novel high-throughput microfluidic device (with a void volume of 0.4 mL) based on controlled incremental filtration (CIF) technology that could replace centrifugation for performing leukapheresis. The CIF device was tested extensively using whole blood from healthy volunteers at multiple hematocrits (5–30%) and flow rates (10–30 mL/min). In the flow-through regime, the CIF device separated WBCs with > 85% efficiency and 10–15% loss of RBCs and PLTs while processing whole blood diluted with saline to 10% hematocrit at a flow rate of 10 mL/min. In the recirculation regime, the CIF device demonstrated a similar level of separation performance, virtually depleting WBCs in the recirculating blood (~ 98% reduction) by the end of a 3.5-hour simulated leukapheresis procedure. Importantly, the device operated without clogging or decline in separation performance, with minimal activation of WBCs and PLTs and no measurable damage to RBCs. Compared to the typical parameters of centrifugation-based leukapheresis, the CIF device had a void volume at least 100-fold smaller, removed WBCs about twice as fast, and lost ~ 2–3-fold fewer PLTs, while operating at a flow rate compatible with the current practice. The hematocrit and flow rate at which the CIF device operated were significantly higher than previously published for other microfluidic cell separation methods. Finally, this study is the first to demonstrate a highly efficient separation of cells from recirculating blood using a microfluidic device. Overall, these findings suggest the feasibility of using high-throughput microfluidic cell separation technology to ultimately enable centrifugation-free, low-ECV leukapheresis. Such a capability would be particularly useful in young children, a vulnerable group of patients who are currently underserved.

CONCENTRATION OF SOLUBLE SALTS IN COOLING WATER OF POWER PLANTS WITH BLOW DOWN RECIRCULATION

The method for calculating the dynamics of concentration of soluble salts (tracers) using the assumption of their homogeneous distribution in the water volume of the circulated cooling system (CCS) under the conditions of recirculation of part of the purge water was proposed. The assumption of homogeneity of salt distribution is substantiated by the fact that the period of mixing of cold water (CW) in CCS is equal to several hours, and the period of setting the concentration limits is calculated in tens of days. In this approximation the law of change of concentration of tracers in time from the moment of their supply in CCS in modes without and with recirculation of a part of purge water and without any processing is received. It is shown that without recirculating treatment, recirculation of purge water increases the maximum salt concentration and the time to reach it. Attention is drawn to the fact that the flow rate consists of two parts: controlled and uncontrolled. When calculating the allowable amount of purge recirculation, it is necessary to use the value of the total purge flow. It is important to understand that the relative change in total purge is always less than the controlled one. To obtain the cost of full purge, it is necessary to calculate its uncontrolled part. The procedure for calculating the uncontrolled purge is given in the paper. Since there are restrictions for of maximum allowable concentration (MAC) on the concentrations of tracers in the CCS, the expressions obtained in this work are consistent with the requirements of the MAC and allow for a given degree of concentration of salts φ, to calculate the limit of recirculation flow. It is shown that the recirculation regime can be applied without additional measures for CCS with a low initial degree of salt concentration and low concentration in the feed water. The proposed algorithm is used to predict the results of recirculation in the case of a specific CСS for thermal power plants with an electrical capacity of 1200 MW and the ratio CMAC/C0 = 5. It is shown that in this case recirculation has significant economic and environmental effects. However, at high, concentrations of tracers C0, compared to MAC, feed water recirculation is meaningless. The calculation algorithm applies to tracers, i.e. salts that do not give deposits, but only limited by the MAC requirements and the risk of corrosion or environmental considerations. Therefore, the above technique cannot be directly used for sparingly soluble salts, such as calcium carbonate. In this case, it requires significant correction. Note the convenient use in calculations of the earlier introduced by us concept of regime (dynamic) factor φ, especially when comparing the real consumption of the main flows of ССS to calculated and in determining the evaporative capacity of cooling towers, or assessing the degree of salt concentration.

Impact of different ventilation strategies on aircraft cabin air quality and passengers’ comfort and well-being – the ComAir study

Indoor air quality can affect occupants in numerous ways. Especially carbon dioxide (CO2) and volatile organic compounds (VOCs) have been debated in their effects on health, well-being, and cognition of people. Aircraft cabins present indoor environments with distinctive features, where passengers are exposed to a mixture of outside and recirculated air. They include conditions such as high occupant density, inability to leave the environment, low relative humidity and need for pressurization. The ComAir study, funded by the Clean Sky 2 Initiative of the European Union, aims to investigate the impact of reducing outdoor air intake in the total volume of air supplied on cabin air quality and passengers’ wellbeing. The main experiment of the study uses a 2(‘occupancy’) X 4 (‘air ventilation regime’) factorial design with stratified randomization of participants. Occupancy denotes the number of people in the aircraft (half vs. full) and varies the psychological important wellbeing factor of proxemics. The four air ventilation regime levels are: Baseline with typical aircraft airflows regimes per person, ASHRAE 161 requirement (standard recommendation), ASHRAE 161 half (half of the recommended flow), and a recirculation regime with a target CO2 concentration close to regulatory limit. This paper presents the background and experimental procedure of ComAir and gives some preliminary results on environmental conditions and subjects’ wellbeing and health under the baseline air ventilation regime.

Influence of hydrotherapy pool water recirculation regime on Staphylococcus species concentration at subsurface: Preliminary experimental data from a pilot

Pools are prone to contamination from microbial pathogens from human external microbiota, including mainly Staphylococcus species. These bacteria originate mainly from the skin and rhinopharynx and tend to concentrate at the surface/subsurface. Being protected by films derived from mucus and sebum, they are markedly resistant to biocides. Our study aimed to evaluate the respective impact of mixed and reverse hydraulicity techniques on the concentration of Staphylococcus species at the subsurface following bathing by four individuals in an experimental pool. Disinfection, filtration and water renewal of the pool were stopped in order to study only the influence of the water recirculation regime. We found a significant reduction of 31.7% (Test 1), 50.9% (Test 2) and 41.9% (Test 3) in total Staphylococcus species counts at the subsurface when using reverse versus mixed hydraulicity. However, this reduction is not a pollution cut but a pollution shift, resulting from an increase in the outlet water flow rate by overflow channel from 49.3 to 100%. This experimental model was far removed from real life conditions and associated with a series of limitations. However, it seems that the type of water recirculation regime is a critical factor in the bacterial quality of pool water. These preliminary findings need to be confirmed in additional studies using more realistic conditions.

An improved hydrodynamic model for percolation and drainage dynamics for household and agricultural waste beds

This study focuses on the hydrodynamic modelling of percolation and drainage cycles in the context of solid-state anaerobic digestion and fermentation (VFA platform) of household solid wastes (HSW) in leach bed reactors. Attention was given to the characterization of the water distribution and hydrodynamic properties of the beds. The experimental procedure enabled the measurement of water content in waste beds at different states of compaction during injection and drainage, and this for two types of HSW and for two other type of wastes. A numerical model, set up with experimental data from water content measurements, highlighted that a capillary-free dual-porosity model was not able to correctly reproduce all the hydrodynamic features and particularly the drainage dynamics. The model was improved by adding a reservoir water fraction to macroporosity which allowed to correctly simulate dynamics. This model, validated with data obtained from agricultural wastes, enabled to explain more precisely the water behaviour during percolation processes and these results should be useful for driving either solid-state anaerobic digestion or fermentation reactors. Indeed, this implies that the recirculation regime will impact the renewal of the immobile water fraction in macroporosity, inducing different concentration levels of fermentation products in the leachate.

Influence of recirculation over COD and N-NH4 removals from landfill leachate by horizontal flow constructed treatment wetland

Treatment of landfill leachate is a challenge due to its complex chemical composition and high recalcitrance and because of high costs for conventional wastewater treatment. In our study, leachate from the Quitaúna Landfill, Sao Paulo Metropolitan Region, Brazil, was treated at a laboratory scale with a horizontal subsurface flow constructed treatment wetland (HF-CTW) operating under a recirculation regime. Two units planted with Heliconia psittacorum (HP) and Cyperus papyrus (CP), and one unplanted control unit were assessed. With a recirculation regime over 21 days, the planted units removed 40% of chemical oxygen demand (COD) while the control unit removed only 29%. True color removal efficiencies were 2, 22, and 23% for the control, HP, and CP HF-CTWs, respectively. The ammonium nitrogen removal efficiencies for a 21-day hydraulic retention time (HRT) were 63–81% for planted units and 72% for the control. The increase of the HRT from 7 to 21 days led to the enhancement of ammonium nitrogen removal but did not affect the COD and total nitrogen removals. This phenomenon is a consequence of leachate’s low biodegradability. The present study shows the importance of the HRT and plant presence for landfill leachate treatment using HF-CTWs.

Buoyant wind-driven pollutant dispersion and recirculation behaviour in wedge-shaped roof urban street canyons.

The present study investigated the buoyant wind-driven pollutant plume dispersion and recirculation behaviour inside urban street canyons formed by buildings with wedge-shaped roofs. Numerical modelling was performed using a computational fluid dynamics (CFD) large eddy simulation (LES). Street canyon models with a strongly buoyant fire source located on the street and environmental winds perpendicular to the canyon were developed using the fire dynamics simulator (FDS). The complex interaction of buoyancy and wind, as well as their combined effects on the pollutant plume dispersion, was simulated inside the urban street canyon. The results showed that the flow pattern of pollutant plume dispersion inside the street canyon with increasing wind speed for different roof inclination angles could be divided into three regimes, including a recirculation regime, a quasi-recirculation regime and a non-recirculation regime. The pollutant levels in the street canyon, as indexed by carbon monoxide (CO) concentration, increased under the recirculation regime. For the quasi-recirculation regime, however, the leeward buildings primarily suffered from the higher pollutant levels. The critical wind speed needed to trigger recirculation was analysed for various roof inclination angles. A correlation was proposed to predict the critical wind speed of various wedge-shaped roof angles for recirculation regime and quasi-recirculation regimes.

Reproducible, high-yielding, biological caproate production from food waste using a single-phase anaerobic reactor system

BackgroundNowadays, the vast majority of chemicals are either synthesised from fossil fuels or are extracted from agricultural commodities. However, these production approaches are not environmentally and economically sustainable, as they result in the emission of greenhouse gases and they may also compete with food production. Because of the global agreement to reduce greenhouse gas emissions, there is an urgent interest in developing alternative sustainable sources of chemicals. In recent years, organic waste streams have been investigated as attractive and sustainable feedstock alternatives. In particular, attention has recently focused on the production of caproate from mixed culture fermentation of low-grade organic residues. The current approaches for caproate synthesis from organic waste are not economically attractive, as they involve the use of two-stage anaerobic digestion systems and the supplementation of external electron donors, both of which increase its production costs. This study investigates the feasibility of producing caproate from food waste (FW) without the supplementation of external electron donors using a single-phase reactor system.ResultsReplicate leach-bed reactors were operated on a semi-continuous mode at organic loading of 80 g VS FW l−1 and at solid retention times of 14 and 7 days. Fermentation, rather than hydrolysis, was the limiting step for caproate production. A higher caproate production yield 21.86 ± 0.57 g COD l−1 was achieved by diluting the inoculating leachate at the beginning of each run and by applying a leachate recirculation regime. The mixed culture batch fermentation of the FW leachate was able to generate 23 g caproate COD l−1 (10 g caproate l−1), at a maximum rate of 3 g caproate l−1 day−1 under high H2 pressure. Lactate served as the electron donor and carbon source for the synthesis of caproate. Microbial community analysis suggested that neither Clostridium kluyveri nor Megasphaera elsdenii, which are well-characterised caproate producers in bioreactors systems, were strongly implicated in the synthesis of caproate, but that rather Clostridium sp. with 99% similarity to Ruminococcaceae bacterium CPB6 and Clostridium sp. MT1 likely played key roles in the synthesis of caproate. This finding indicates that the microbial community capable of caproate synthesis could be diverse and may therefore help in maintaining a stable and robust process.ConclusionsThese results indicate that future, full-scale, high-rate caproate production from carbohydrate-rich wastes, associated with biogas recovery, could be envisaged.

Airflow patterns in a 3D model of the human acinus

Based on the recent photographs of microstructures of anacinus a novel 3D computational model for airflow and particle transport and deposition was developed. To model the entireacinar region simultaneously, an approach was proposed to reduce the computational space. The airflow was solved using numerical simulations for the cases of expanding and contracting the asinus wall. The volume change of the lung was imposed based on the normal breathing condition with 15% volumetric expansion ratio. Since the entire acinar region was modeled, realistic pressure type boundary conditions were used and the use of earlier unrealistic boundary conditions was avoided. The simulation results showed that the flow patterns in an acinus with moving walls were significantly different from those for the rigid wall case. Furthermore, due to the asymmetric configuration, the flow patterns were not quite symmetric. It was shown that the ratio of alveolar flow to ductal flow rate controlled the dominant flow regime in each generation. Ratios below 0.005led to recirculation regime where flow separation occurred, while values above this threshold led to flows with radial streamlines. In summary, while the flow in the primary generations was characterized by the formation of recirculation regions in the alveoli, the terminal generations were characterized by radial streamlines which move towards the alveolar wall. Both flow regimes had substantial effects on particle deposition in the acinus.

Influence of Gaussian Hill on Concentration of Solid Particles in Suspension Inside Turbulent Boudary Layer

The soil erosion is a major problem that affects the agriculture, climate and health. It is therefore necessary to understand the phenomena that are its wheels in order to either predict or limit it. One of the main problem of this kind of study is the presence of high particle concentration that restricts measurements of either particle concentration or carrier flow rate. In so numerical simulations are essential for detailed studies. Nevertheless these numerical models have to be performant enough and validated with situations that if they are not realistic are representative of phenomena involved. So here we focused on the problem of the possibility of trapping the solid particles in the recirculation zones. We have reproduced in laboratory a configuration representative of sites with enough steep hills to generate recirculation zones during saltation regimes.Measurements have been made of the dispersion of solid particles released from a rectangular area flushed at the ground of a flat plate on which evolved a turbulent boundary layer. The originality here is that it is flushed at the ground and push up the particles to continuously feed the ground at the same mean rate as the mean local erosion rate. One or more Gaussian hills were disposed transversally to the flow downstream the solid particle injection. Various Reynolds number where chosen to caracterise take-off regimes and recirculation regime behind the Gaussian hill(s). One optical system combined with CMOS camera is used successively to measure the velocity of career fluid or solid particles by PIV. Digital Image treatment is used to separate fluid seeding from solid particle images. Supplementary comparison was done to compare velocity field of the career flow for smooth and rough floor only for kinematic around the hill(s).In this paper, in a first part we will present kinematic caracteristics of the flow whereas in a second part of this work, the data will provide some concentration profiles of solid particles. The results presented concerning the velocity and concentration field are related to streamwise vertical planes at the center of the wind tunnel at successive longitudinal positions. For velocity field we will report different regimes for smooth and rough plate. Only one regime will be presented for solid particles. We present in a first part the kinematic study and in the second part results on the concentrations of solid particles.

New type of pump for the heart-lung bypass system

Objective: Complications arising from roller pump usage in modern heart-lung bypass (HLB) systems are widely known. Alternative to roller pumps has existed as various devices. This work is dedicated to developing new, considerably simpler and less expensive pump device for HLB systems, which provides maximally physiological pulsating blood flow. Material and Method: We used pediatric cardiotomy reservoirs of HLB systems as blood chambers. Two such reservoirs were placed in front of the oxygenator, with their in-flow tubes connected to the venous blood tubes, and the outflow tubes – to the entry to the oxygenator. In each reservoir, 2 air outlets tubes were connected to pneumo-receivers of positive and negative pressure. We filled up one of the reservoirs whith closed of exit blood tube by creating negative pressure in it. Simultaneously, with closed entry blood tube of the second reservoir, we ejected blood from it by created positive pressure. Used external pulsator. Results: In stand testing under re-circulation regime, productivity of the device was 12,5 liters/minute. Pressure on exit blood pump was within 0 to 300mm.Hg. The pump operating system enabled laminar, as well as pulsating flow of liquid, with frequency of 0-200 pulses/minute. Research is based on experiments conducted on 14 mongrel dogs weighing 20 kg. Standard methodology was used to cannulate Venae cavae and aorta, and to connect perfusion system to body. Duration of complete HLB reached 2 hours. Systolic pressure was maintained within 120-130mm.Hg.; diastolic – 70-80 mmHg. Velocity of blood flow in the aorta arc fluctuated within 950-1100 ml/min; in the femoral artery – within 60-80 ml/min. Conclusion: Preliminary tests of the new pump indicate that its hemodynamic characteristics are maximally approximated to physiological ones. In comparison to modern machines, a perfusion system with new pump type has minimal volume of fill-up and does not damage formative elements of blood.

Effects of stenotic severity on the flow structure in a circular channel under a pulsatile flow

Stenosis is the drastic reduction in the cross-sectional area of blood vessel caused by accumulations of cholesterol. It affects the blood flow property and structure from the fluid dynamic point of view. To understand the flow phenomenon more clearly, a particle image velocimetry method is used and the fluid dynamic characteristics in a circular channel containing stenosis structure is investigated experimentally in this study. Different stenotic-structured models made of acrylic material are subjected to a pulsatile flow generated by an in-house designed pulsatile pump. The inner diameter of the tube inlet is 20 mm and the length of reduced area for stenosis ranges between 35mm and 40mm. It is circulated continuously through a circular channel by the pump system. Pressure is measured at four different sections during systolic and diastolic phase changes. The phase-averaged velocity field distribution shows a recirculation regime after the stenotic structure. The effects of the stenotic obstructions are found to be more severe when the aspect ratio is varied.

Measurement of Fluid Dynamic Characteristics around Stenotic Obstruction in a Circular Channel

We measured experimentally the properties of fluid dynamics, velocity fields, and the pressure, around stenotic obstruction located inside a circular channel structure. Particle image velocimetry system was employed to obtain velocity fields at the central section of the circular channel in the streamwise direction. The stenosis model used was made of acrylic material with different stenotic aspect ratios. The working fluid was water and it was returned by a centrifugal pump system. Pressure measurements were carried out to validate the effect of a narrow passageway. Results showed that the acceleration of gap flow through stenotic obstruction and the pressure drop in the recirculation regime behind the stenosis model can be observed.

Photocatalytic air purification: Comparative efficacy and pressure drop of a TiO 2-coated thin mesh and a honeycomb monolith at high air velocities using a 0.4 m 3 close-loop reactor

Photocatalytic purifiers, which are in development for treating gaseous effluents at flow rates generally higher than several tens of m 3 h −1, usually employ TiO 2-coated materials either as planar or folded fibrous filters, or as honeycomb monoliths. Our primary objective was to compare the photocatalytic efficacy of two types of these materials using a ca. 0.4 m 3 close-loop, air tight, photocatalytic reactor we built at EDF. This loop – through which air can be flowed at rates from 16 to 1800 m 3 h −1, i.e. 0.11–12.25 m s −1 – includes a paralleliped (560 mm × 295 mm × 200 mm) into which alternate banks of lamps and TiO 2 coated-materials (entrance area = 408 cm 2) can be accommodated. The materials tested were (i) an Ahlstrom-supplied, thin, non-woven tissue dried at room temperature after impregnation with both Degussa TiO 2 P-25 and colloidal SiO 2 used as a binder and (ii) an aluminum honeycomb-shaped material we coated with Degussa TiO 2 P-25 and dried at room temperature. U-shaped lamps emitting at 254 nm and having an electrical power of 18 or 35 W were employed. The geometries of the materials and the spatial arrangements of the lamps and materials provided an irradiance of the materials as high and homogeneous as possible according to our modeling [Catal. Today 122 (2007) 66–77]. Methanol was chosen as the test pollutant because it is easily mineralized, which minimized the inhibition of the photocatalytic activity by intermediate products. In the recirculation regime, the initial rates of methanol removal observed for the folded tissue were multiplied by at least four – depending on the numbers of materials and banks of three 35 W lamps – when the honeycomb material was utilized. Several factors can add to cause this high increase in efficacy: distinct shapes and TiO 2 supports, differences in photons scattering, and the reduced accessibility of reactants to TiO 2 because of SiO 2. Regarding energy consumption, the use of two photocatalytic materials sandwiching one bank of three 35 W lamps instead of one material in-between two banks of three lamps led to about the same efficacy. The honeycomb material was also tested with toluene at an initial concentration corresponding to the same amount of carbon as when methanol was the pollutant. The removal rate and CO 2 formation rate were lower for toluene than for methanol, which can be easily explained by a lower reactivity with respect to oxidation, a smaller adsorbed amount and a higher competition with the more numerous degradation intermediate products. That comparison illustrates the need of trials for every effluent to be treated. Considerable differences in pressure drop between the two materials clearly demonstrated another interest of using honeycomb shapes, at least for the materials and configurations investigated. Furthermore, a deactivation, together with a yellowing, was noticed at high irradiance for the Ahlstrom tissue, which included cellulose fibers. Folding the material enables one to employ lower irradiances for minimizing this effect, while maintaining the efficacy because of the increase in the material area in the reactor, as well as slightly lowering the pressure drop.

Comparison of different ED stack conceptions when applied for drinking water production from brackish waters

Three types of electrodialysis (ED) and electrodeionization (EDI) stacks are studied when treating NaCl solutions in the range of concentrations from 10 − 5 to 3 × 10 − 2 M: (1) with a non-conducting network spacer, (2) with a mixed ion-exchange monolayer bed, (3) with profiled membranes. The Sherwood number characterizing the desalination rate is measured in recirculation regime when the concentration of feed solution is slowly decreasing in time. The data obtained are compared with the results calculated and measured for “empty” desalination channels not containing any filling. It was established that the measured Sherwood numbers at overlimiting currents in stacks with filling are higher than that in “empty” channel under the same potential drop, while the latter, in turn, are higher than the Sherwood numbers calculated for limiting current density. The mass transfer rate in several cases (under 2.5 V par cell pair in diluted, < 10 − 4 M, solutions and high flow rates, > 7 dm 3 h − 1 dm − 1 , a stack with profiled membranes) may be 4 times higher than that in “empty” channel at limiting current density. The stacks with profiled membranes are shown to be effective in the overall range of concentrations. The stacks with non-conducting spacer can be used if the feed solution concentration is not too low, > 2 × 10 − 3 M in our experiments. The stacks with ion-exchange resins are more preferable in the case of treatment of strongly diluted solutions (e.g. at the second stage following an ED with profiled membranes), as well as in the cases where it is necessary to use a compact unit characterized by a low flow velocity, though the power consumption is slightly higher.

Heterogeneous photocatalytic degradation of pharmaceuticals in water by using polycrystalline TiO 2 and a nanofiltration membrane reactor

A study of the photodegradation of different pharmaceuticals [furosemide, ranitidine (hydrochloride), ofloxacine, phenazone, naproxen, carbamazepine and clofibric acid] in aqueous medium at various pHs by using a batch photoreactor and a photocatalytic membrane reactor working in recirculation regime was carried out. Polycrystalline TiO 2 was used as the photocatalyst, and different membranes (NTR 7410, PAN GKSS HV3/T, N 30 F, NF PES 10) were tested. A different adsorption of the substrates onto the catalyst surface was observed owing to the hydrophilic/hydrophobic character of the catalyst, depending on the pH. The photodegradation of the seven molecules in the batch reactor was successfully carried out and the behaviour was in accordance with pseudo-first order kinetics. Furosemide and ranitidine were selected to carry out the study of rejection and photodegradation in the hybrid membrane system. The permeate flux of the treated water was in the 31.5–60.0 L/(h m 2) range for NTR 7410 membrane, whereas rejection values in the range 10–60% for furosemide and 5–30% for ranitidine in the dark (without photoreaction) were found. The degradation in the hybrid membrane photoreactor showed that the photocatalyst was retained by the membrane in the reaction ambient, while the membrane rejection towards the pollutants was not very satisfactory. A net decrease of the rejection down to 0 was observed in the contemporary presence of light, photocatalyst and oxygen.

Path and variability of the Agulhas Return Current

The combined analysis of hydrographic, kinematic, and dynamic data collected during the 1997–1999 KAPEX (CAPe of Good Hope EXperiments) reveals a quasi-stationary meandering pattern of the Agulhas Retroflection Current east and upstream of the Southwest-Indian Ridge. The current meanders between 38°S and 40°S in a spatially and temporally continuous fashion and has a core width of approximately Full-size image (<1 K) with an associated transport of Full-size image (<1 K) in the upper Full-size image (<1 K). Peak surface velocities decrease from Full-size image (<1 K) near the Agulhas Retroflection to Full-size image (<1 K) around 32°E. Meander troughs (northward extremes) are found predominantly near 26.8°E, 32.6°E and 38.9°E, while crests (southward extremes) are located with high probability near 29.7°E, 35.5°E and 42.9°E, resulting in a typical wavelength of Full-size image (<1 K). Cold eddies are shed along the northern boundary of the current from meander troughs into the recirculation regime between the Agulhas Current proper and the Agulhas Return Current. Strongest cyclonic eddies are preferably shed in austral autumn. The cyclonic eddies so formed propagate westward at an average phase-speed of Full-size image (<1 K), with, however, a variability of at least the same magnitude. Subsequently, the cyclones are absorbed by the next meander trough located upstream and to the west of the shedding trough.