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The assessment of a pilot-scale hybrid system coupling powdered activated carbon (PAC) adsorption with membrane ultrafiltration (UF), in respect of activated carbon regeneration and organic micropollutant removal, was investigated in this study. Field tests with two adsorbents (i.e. a commercial PAC and a PAC-Fe(II) composite), conducted in the premises of Thessaloniki Water Treatment Plant, demonstrated the high efficiency of the combined PAC/UF process. Regeneration efficiencies varying between approximately 95% and 110%, complete diclofenac (DCF) degradation and rather moderate mineralization (TOC removal) rates of up to 47%, can be achieved by UVC/H2O2 or photo-Fenton oxidation after 4 hours of treatment; this performance is attributed to the in situ generation of reactive oxidant species by photolysis of H2O2, which seems to enhance the process effectiveness. Among the two adsorbent materials tested, composite PAC-Fe(II) exhibited a higher DCF adsorption capacity than the original PAC, probably due to the improved chemisorption and/or the electrostatic attractive interactions between the negatively charged DCF molecules and the positively charged iron species, at neutral pH. Furthermore, a rather insignificant effect of PAC-Fe(II) loading on the regeneration efficiency was observed. The advantages of totally controlled H2O2 dosages and short operating times render the hybrid PAC/UF system a promising alternative to conventional and advanced drinking water purification methods.

Diminishing clean water resources and their pollution (due to human activities and climatic change) are of great concern on a global basis. Under such conditions, the adequacy of drinking water (DW) standards and their meticulous implementation are issues of utmost importance in safeguarding human health. Unfortunately, the significant number of disease outbreaks (and of other suspected/potential health effects) related to DW, even in developed countries, attests to the fact that these issues require vigilance and continuous re-appraisal, particularly considering the assorted emerging contaminants and the ever-improving technological tools to cope with them. Therefore, the present comprehensive assessment addresses the main issues and concerns regarding DW standards and implementation thereof. Emphasis is placed on identifying the inherent deficiencies of standards (due to neglect of potential toxic contaminants and to debatable specifications/limit values) and regulations for their implementation and the monitoring of DW quality (due to weaknesses of available analytical/measurement techniques and inadequacies of tools and protocols). Rather serious deficiencies on these aspects are evident regarding the main categories of contaminants, i.e., synthetic chemicals and biological species. In regard to addressing these issues, progress made in recent years at the scientific/technical level and the main challenges are outlined toward the goal of an improvement in standards and their implementation.

The oxidation of pharmaceutical diclofenac (DCF) was investigated in a catalytic membrane reactor (CMR) comprising a tubular porous alumina (α-Al2O3) membrane, as support material, with embedded iron oxide nanoparticles (nFe) in situ generated in its pores. The performance of the heterogeneous Fenton-type oxidation reaction was examined in a laboratory-scale membrane pilot, with the addition of hydrogen peroxide. Aiming to optimize this CMR, Central Composite Design with Response Surface Methodology was employed to assess the effects of three key process parameters and their interaction on DCF degradation. Encouraging results were obtained, showing a significant DCF oxidation/mineralization by the α-Al2O3/nFe CMR. Feed solution pH was found to be the most significant variable, with acidic values leading to improved performance. Under near optimum operating conditions (pH 3 and 42.9 mg/L H2O2), the removal and mineralization of DCF was ∼65% and ∼48%, respectively. Negligible iron leaching was observed in the tests, which confirms the effective embedding and stability of catalytic nanoparticles in the ceramic porous matrix, thus allowing multiple membrane utilization. Future research directions are proposed towards method optimization, with emphasis given to membrane modification for improving the adsorption of organic pollutants and their oxidation within the catalytic membrane matrix.

Facile methods for accurate fluid-mechanical characterization of haemofilters (HF) are indispensable for haemofiltration process improvements, equipment design/optimization, and reliable module specifications. Currently employed methods, implemented through specific experimental in vitro protocols, are assessed herein in detail, considering the conditions prevailing during haemofiltration. Minimum number of key parameters required to fully describe the common countercurrent flow field, in the HF active section, include membrane permeance K and friction coefficients in lumen and shell side (ff and fs ). It is shown that the countercurrent flow mode itself is incapable of yielding these parameters, based on externally measured flow rates and pressures. Similarly, the relevant ISO protocol is deficient as it can only provide rough underpredictions of permeance K. The causes of such inherent deficiencies of current standards and practices are analyzed. In contrast, a recently developed methodology, accounting for the (heretofore ignored) pressure drop in module headers and combining a mechanistic theoretical model with experimental data from 2 special haemofilter operating modes, yields an accurate determination of the key parameters (K, ff , fs ). Additionally, it permits a full description of flow field for Newtonian liquids, for both constant and axially varying viscosity in fiber-lumen due to the transmembrane flux. Development of new reliable standards is suggested, facilitated by the insights gained in this work.

This paper aims to quantify the contribution of the various factors to energy consumption in reverse osmosis (RO) desalination processes and to identify those with the greatest potential for reduction. Specific energy consumption (SEC), in kWh per m3 of permeate production, is due to the retentate osmotic pressure, the resistance to fluid permeation through the membrane, the friction losses in the retentate and permeate channels of the spiral wound membrane (SWM) modules and the non-ideal operation of high pressure pumps and energy recovery devices (ERD). Taking advantage of a recently developed SWM-module performance simulator, the aforementioned individual contributions to SEC are determined for two case studies, typical of seawater and brackish water desalination processes, for steady state operation. Detailed results are obtained with SEC itemized per SWM element in a typical 7-element pressure vessel. Comparative assessment of the results is enlightening, showing that the greatest margin for the desirable SEC reduction is related to improvements of membrane permeability and efficiency of pumps and ERD. The indirect, yet significant, effect of other key design and operating process parameters is also discussed.

Net-type spacers are essential components of the spiral-wound membrane (SWM) modules employed in reverse osmosis (RO) desalination plants. Despite progress made in designing SWM modules in recent years, key issues related to feed-spacer characteristics (particularly spacer material properties in conjunction with their geometry), which affect module performance and membrane integrity, have been neglected by the research community. This paper focuses on the effect of compressive stresses, imposed on membrane spacers and envelopes during SWM-module fabrication to achieve module compactness and resistance to deformation during operation. A comprehensive method is presented (involving experimental and computational tools) which allows to quantify compressive stress effects, on the characteristics of spacer-filled membrane channels, and further to assess their impact on the key SWM-module operating parameters and on overall RO process performance. The method is demonstrated by assessing the performance of 26-mil commercial feed-spacer in an appropriate range of compressive stresses; it is interesting that modest nominal applied pressure, at the level of 1–2 bar, tends to cause significant feed-spacer compression, channel-gap reduction and membrane indentations impairing the active layer. The novel method is considered most helpful for selecting appropriate feed-spacer material and geometric characteristics, for a membrane of particular mechanical properties.

The topic of chemical-free spiral wound membrane (SWM) cleaning, dealt with in this paper, is certainly of great interest to both industry and academia. However, in this Letter, the reasons are outlined for the serious limitations, imposed on implementation of the proposed deformation-induced cleaning (DIC) method to SWM modules, which have been apparently disregarded in this paper. These limitations are due to the dominant structural characteristics of SWM module-design; in particular, to the imposed (during fabrication) interlayer pressure on the membrane leaves and to the overall rigidity of the currently employed modules. These issues/imitations, and the implications of neglecting them are outlined herein.

The reported pilot-scale development of hybrid process alternatives, combines in-situ regenerated powdered activated carbon (PAC), H 2 O 2 -based advanced oxidation techniques and membrane ultrafiltration (UF). Commercial PAC and special iron-impregnated PAC (PAC-Fe) were used as adsorbents, whereas diclofenac (DCF), a commonly detected pharmaceutical in water-sources, was employed as representative micro-pollutant. For PAC regeneration, modest on-line H 2 O 2 dosage was adopted, alone or in combination with UV-C irradiation. Large DCF uptake was measured for both PAC (154.5 mg/g) and PAC-Fe (116.7 mg/g), while the regeneration efficiencies achieved with the photo-assisted H 2 O 2 processes were much greater (122.2% and 131.6% for H 2 O 2 +UVC and photo-Fenton, respectively) than those obtained with H 2 O 2 alone (70% and 77.6% for H 2 O 2 and Fenton, respectively). For PAC-Fe, enhanced recovery of adsorption capacity suggests occurrence of heterogeneous Fenton-like reactions on iron-oxide particle surfaces leading to generation of OH and other reactive species by H 2 O 2 -decomposition. The catalytic adsorbent (PAC-Fe) retained its stability and activity after three operating cycles, which would significantly reduce operating cost in practical applications. Considering the rather short regeneration-time of present tests (180 min) and the nearly basic pH of feed solutions, the novel processes investigated herein, involving PAC regeneration in the same equipment employed for water purification, hold distinct advantages over conventional methods.

Experimental results are reported on the effect of polysaccharides in the early stage of membrane scaling. Sodium alginate at small concentration (2 and 10 mg/L) was employed as typical polysaccharide. Synthetic solutions, characterized by small bulk supersaturation ratio S in calcium sulfate (S ~ 1.4), were filtered through a desalination membrane in dead-end cells under agitation. Three types of tests were performed; i.e. membrane scaling in absence of alginates (as reference), combined fouling-scaling (i.e. scaling in presence of alginates) and scaling tests after a fouling layer was formed on the membrane. Examination of various deposits by Scanning Electron Microscopy (SEM) and determination of calcium on membrane deposits and in filtered solids (from retentate and feed-fluid samples) provide useful insights including clear evidence that alginates tend to inhibit CaSO4 crystallization, likely due to calcium binding with carboxylates of alginate macromolecules and formation of gel deposits. The inhibition effect, manifested in the reduced deposit-mass density on membranes and crystallization–rate, as well as in crystal-shape modification, is stronger at the higher alginate concentration. Similarly, incipient membrane scaling, pretreated with alginate foulant solution, appears to be significantly inhibited compared to clean membranes. Under the conditions tested, membrane salt rejection was unaffected.

BACKGROUND Wine waste lees are currently partly exploited for tartaric acid (TA) production, through an environment offensive process, while concurrently occurring bio-active polyphenolic compounds are wasted. This paper, deals with the development of an integrated, environment friendly process, using mild conditions, for recovering TA with simultaneous exploitation of total polyphenols (TPP) from wine lees. RESULTS A first process step, described in a previous publication, yields a liquid stream containing approx. 44.2 g/L TA and 323.3 mg GAE/L TPP. In the present study, various ultrafiltration and nanofiltration membranes, are assessed, in bench-scale filtration tests, for their efficiency in separating the two main products (i.e. TA and TPP) from this stream. The most promising process configurations are also tested in a laboratory scale cross-flow membrane filtration pilot plant and assessed concerning the separation efficiency and the membrane filtration performance, to determine process feasibility at industrial scale. CONCLUSIONS The results show that a nanofiltration membrane with typical pore size approx. 1 kDa exhibits satisfactory separation and low-fouling filtration performance. The permeate, containing the bulk of TA (approx. 42.6 g/L), could be used for TA recovery, whereas the concentrate, with antioxidant activity (EC50 = 10.0 mg sample/mg DPPH˙), could be further purified to obtain polyphenolic-rich formulations.

The synthesis, characterization, and performance of composite photocatalytic adsorbents are investigated in this work using the dip-coating and the electrophoretic coating methods for the deposition of titanium dioxide (TiO2) on porous activated carbon fiber (ACF) substrates. The adsorption and photocatalytic efficiency of the synthesized catalytic adsorbents were compared using phenol as the model pollutant. Both immobilization techniques resulted in composite ACF/TiO2 adsorbents characterized by large surface area (844.67 &plusmn, 45.58 m2 g&minus, 1), uniform distribution of TiO2 nanoparticles on the activated carbon fibers, and high phenol adsorption. The method and the treatment time affected the phenol adsorption, while the highest sorption was determined in the case of the ACF/TiO2 sample prepared by the electrophoretic coating method (at 20 V) for an electrolysis time of 120 s (7.93 mgphenol g&minus, 1ACF/TiO2). The UV-A irradiation of most ACF/TiO2 samples led to a faster removal of phenol from water as a result of the combined sorption and heterogeneous photocatalysis. The stability and the effective regeneration of the most promising composite photocatalytic adsorbent was proved by multiple filtration and UV-A irradiation cycles.

Enhanced mineralization of phenol in brines with high chloride content was investigated by employing an electrochemical advanced oxidation treatment that couples anodic oxidation, electrochlorination and electro-Fenton in a single process. Experimental work was carried out in a pilot scale unit with an undivided plate-and-frame cell equipped with a boron-doped diamond anode and a carbon-PTFE gas diffusion electrode as cathode, in batch recirculation mode. The effects of operating conditions on phenol degradation, including current density, air flow rate, water feed flow rate, Fe2+ dosage and pH as well as of the water matrix, were evaluated. Applied current exhibited the greatest effect on phenol degradation/mineralization efficiency. Complete degradation of phenol (of initial concentration 50 mg L−1) was achieved under the near-optimum operating conditions (40 mA cm−2, pH 7, 0.4 m3 h−1 water circulation rate) within 30 min. Both air flow rate and Fe2+ dosage did not show a measurable impact on phenol removal. However, increasing the chloride content of water significantly improved the efficiency of treatment due to the enhanced indirect oxidation by the electrogenerated chlorine. Several trihalomethane intermediates (chloroform, bromodichloromethane) and chlorinated/brominated phenol byproducts forming during treatment, were eliminated after 60 min of processing time.

Proper fluid-mechanical characterization of haemo-catharsis (HC) modules is indispensable for optimizing their design and operation. A recently developed methodology allows determination of (heretofore ignored) significant pressure losses in the headers of HC-modules, taking into account the main fluid-mechanical phenomena through appropriate/representative parameters. The latter comprise friction coefficients ff and fs (for fiber-lumen and shell-side flow), membrane permeance K and four parameters ζi1-ζi4 representative of pressure drop in the module-headers. A mechanistic model and pressure/flow-rate measurements, taken with two specially-selected operating modes, are used for such parameter estimation. Implementation of this methodology is reported herein, to the practically important case of counter-current flow, that involves theoretical-model extension/adaptation and experiments with liquids of viscosity 1 cp and 2 cp. These data are employed to investigate and optimize the data-fitting procedure (considering computational accuracy/stability and convenience) and to validate the counter-current flow model. Assessment of experimental and theoretical-model results suggests that the procedure involving data from the two special operating-modes is essential for facile implementation of the novel methodology, including the accurate determination of membrane permeance K. The methodology developed, allows reliable prediction of the key spatially-evolving process-variables, and is recommended for practical applications and advanced overall HC-module performance modeling. Suggested future work is outlined.

This study aims to shed light into the complicated phenomena occurring during the early stages of RO-membrane scaling when organic-foulants are present. Experiments were performed, using spacer-filled channel in once-through flow-mode, closely simulating conditions prevailing at tail elements of pressure-vessels. The effect was studied of a typical foulant (polysaccharide, sodium-alginate, SA), at small concentrations (~2 mg/L and ~10 mg/L), on incipient crystallization/deposition of calcium sulfate (CaSO4·2H2O, gypsum) during RO-desalination of synthetic brackish-water at small super-saturation ratio S (1.0 to 1.5). Scanning Electron Microscopy and membrane-scale/foulants dissolution techniques were employed. At small SA concentration (~2 mg/L) incipient-scaling inhibition is observed (likely due to crystallite-growth retardation by adsorbed organic molecules); however, at higher SA concentration (~10 mg/L), significant enhancement of incipient scaling occurs, attributed to formation of coherent organic-gel fouling-layer, favoring concentration increase of inorganic-scalants at the membrane-surface and consequent increase of supersaturation. Under such conditions, although the fouling-layer thickness remains roughly constant (due to constant deposited organic-matter), the specific fouling resistance α tends to significantly increase with increasing supersaturation, likely due to physico-chemical structural changes within the alginate gel-layer. The techniques employed allow determination and correlation of key fouling/scaling parameter-values (i.e. scale-mass deposition-rate and resistance α), that are necessary for developing reliable process modeling/simulation tools.

The development of reliable criteria for determining the onset of scaling of sparingly soluble salts on reverse osmosis desalination membranes is of great practical significance. Calcium carbonate, which is dealt with in this study, is a commonly encountered membrane scale compound. Reliable modeling and simulation tools of the reverse osmosis operation (accounting for onset and development of scaling) are very important for process optimization, aiming to reduce the effects of scaling and to minimize the use of antiscalants; such comprehensive modeling requires knowledge of key scaling parameters. In recent years a procedure has been developed to extract these parameters by employing a facile testing procedure, involving a small pressurized dead-end filtration cell. Using such a stirred test cell, the conditions are much closer to the actual reverse osmosis desalination process, compared to those in a non-agitated cell. Here, a detailed model of the testing process is developed and a procedure for estima...

A novel, fully automated photocatalytic membrane reactor (PMR) pilot unit is presented and evaluated (at different operating process parameters and real treatment conditions) for degradation of the pharmaceutical diclofenac (DCF), a typical recalcitrant micropollutant. The PMR-pilot has a maximum system capacity of 1.2 m 3 /d of treated water, 52 W of UV-C power, and combines two modern processes; i.e. heterogeneous photocatalysis and membrane separation, employing dispersed TiO 2 nanoparticles with UV-C irradiation, and submerged ultrafiltration hollow fibers, respectively. Pilot tests with two types of natural (tap and surface) water under stable, continuous operation, permitted the assessment of the PMR unit performance (for DCF degradation, TOC mineralization) in terms of hydraulic residence time (HRT), TiO 2 loading, UV-C irradiation dose, and DCF feed concentration. Under the specific conditions tested, the catalyst loading and UV-C radiant power significantly affected DCF removal; however, HRT had a rather insignificant effect. Additionally, several transformation products (TPs) were identified by means of liquid chromatography–mass spectrometry using electrospray interfacing technique, thus, shedding light into possible reaction pathways leading to DCF mineralization.

Reliable simulation of membrane-module dynamic operation is essential in optimizing its detailed geometric characteristics and operation, as well as that of membrane plants, for various types of fluid treatment applications. This paper is part of systematic efforts toward development of such a comprehensive model, considering temporal variability caused by organic membrane fouling. To render the mathematical problem tractable, justified simplifications (retaining the physical parameter interdependencies) lead to a system of basic equations in two spatial planar coordinates, enabling to obtain a realistic temporal evolution of all process parameters. The flexible model structure allows integration of sub-models, for phenomena occurring (and researched) at small spatial scales, which account for retentate spacer effects on friction losses and mass transfer, and constitutive expressions for fouling rates during desalination. The robust numerical algorithm developed to solve the system of differential and algebraic equations exhibits satisfactory convergence, appropriate for applications. The results presented herein demonstrate the versatility of the numerical code and its potential to analyze the interaction of mechanisms involved in fouling evolution, which is impossible by the much simpler one dimensional models. Directions for future developments are indicated.

A common type of ultrafiltration (UF) membrane fouling is due to organic gel, encountered in the treatment of various effluents and feed waters to desalination plants; polysaccharides are a major component of such fouling layers. In standard methods, dead-end UF tests under constant pressure are used to determine membrane-fouling propensity, but the results are applied with questionable success to the case of constant flux filtration, favored in practice. Observed differences between fouling resistances from the two modes of UF filtration have not been adequately explained yet. The temporal evolution of specific resistance α (considered as the most representative fouling parameter) is investigated herein, aiming to elucidate differences and possible similarities in the different filtration modes. During alginate-solution ultrafiltration, typical gel-type membrane fouling layers are formed with time-varying deposited mass density m (g/cm 2 ) depending on permeate flux; thus, the temporal variation of specific resistance α , of pressure difference across the fouling layer/cake ΔP c , and of pressure drop per unit depth of cake (the latter proportional to ΔP c /m ) are studied for both constant pressure P and constant flux J operation, within P and J ranges of practical interest. These detailed data suggest that permeation flux is the process variable controlling the development of resistance α . Specifically, for constant-flux filtration, the resistance α data are well correlated with flux J (as also shown recently), whereas in the constant-pressure mode the commonly observed constant resistance α , over a rather broad range of declining flux, is due to the high flux level prevailing in the early stage of filtration. A successful approach is demonstrated to compare and correlate the specific resistance α data obtained from the two different filtration modes. The usefulness of the new results in practice is also discussed.

Membrane desalination is associated with significantly increased ion concentration of rejected sparingly soluble salts (commonly of calcium, magnesium, barium, etc) right at the membrane surface, leading to undesirable membrane scaling. Optimization of desalination membrane-plant design and its operation strategy requires quantification of scaling evolution phenomena, through appropriate mathematical models involving experimentally determined system parameters. In recent years, a modeling approach based on heterogeneous nucleation-growth theory was developed for this purpose, and proven to be successful in the case of non-stirred dead-end desalination experiments but not in the case of cross-flow and stirred dead-end desalination. To resolve this inconsistency, new results from numerous sets of improved dead-end non-stirred experiments (some with controlled changes of imposed pressure difference during testing) are reported that provide useful quantitative information and insights regarding incipient scaling. The previous modeling approach is generalized considering non-classical nucleation. Moreover, the likely scatter of local membrane-surface properties is considered in a parameter estimation approach. The new modeling approach leads to estimation of a range of scaling-model parameters consistent with the experimental data. Such parameters can be employed in comprehensive modeling tools of membrane-modules, to simulate their operation for the particular type of membrane for which parameters are extracted.

A crucial first step in developing a novel cost-effective and environment-friendly process for recovering tartaric acid and bioactive polyphenolic compounds from wine lees involves tartrates dissolution by mild means, aiming to maximize tartaric acid recovery, while minimizing the concentration of undesirable potassium. Such a processing step, using cation exchange resin, has been systematically assessed to obtain a set of near-optimum values of the key variables (i.e. pH, water dosage and cation exchange resin dosage). An experimental design was carried out based on Central Composite Design (CCD) with Response Surface Methodology (RSM) to evaluate the effects of process parameters and their interaction towards the attainment of optimum conditions. All three variables considered were found to be significant; however, the most influential factor for maximum tartaric acid concentration was the volume of added water, whereas for potassium removal the cation exchange resin dosage. A quadratic model was developed that fitted well to the experimental data confirmed by the high R 2 values, greater than 0.98. A set of optimum values of the three main variables was determined to be pH = 3.0, water dosage 10 ml/g dry lees and resin dosage 3.5 g/g dry lees. Under these optimum conditions, the predicted tartaric acid and potassium concentration were 43,143 ppm and 178 ppm, respectively, which correspond to 74.9% tartaric acid recovery and 98.8% potassium removal. Furthermore, the corresponding experimental values, from the validation experiment, fitted well to these predictions. This work clearly shows that the recovery of tartaric acid from wine lees can be achieved using cation exchange resin, under mild conditions (ambient temperature) avoiding the waste calcium sulfate sludge of the conventional process.

To assess the performance of a novel ‘filter’-type electro-Fenton (EF) device, results are reported from pilot-scale studies of continuous water treatment, to degrade diclofenac (DCF), a typical organic micro-pollutant, with no addition of oxidants. The novel ‘filter’ consisted of three pairs of anode/cathode electrodes made of carbon felt, with cathodes impregnated with iron nanoparticles (γ-Fe 2 O 3 /F 3 O 4 oxides). The best ‘filter’ performance was obtained at applied potential of 2 V and low water superficial velocities (∼0.09 cm/s), i.e., the mineralization current efficiency (MCE) was >20%, during continuous steady state treatment of tap water with low DCF concentrations (16 μg/L). The EF ‘filter’ exhibited satisfactory stability regarding both electrode integrity (no iron leaching) and removal efficiency, even after multiple filtration/oxidation treatment cycles, achieving (under steady conditions) DCF and TOC removal 85% and 36%, respectively. This performance is considered satisfactory because the EF process took place under rather unfavorable conditions, such as neutral pH, low dissolved O 2 concentration, low electrical conductivity, and presence of natural organic matter and inorganic ions in tap water. Ongoing R&D is aimed at ‘filter’ development and optimization for practical applications.

Results are reported of a systematic study on the performance of an advanced oxidation treatment that couples anodic oxidation (AO) and in situ generation of strong oxidants (Cl2, S2O82−) in the electrolytic cell, for removing benzene, toluene, ethyl benzene, and xylenes (i.e. BTEX) from high salinity waters. A batch-mode pilot electrochemical unit equipped with a boron-doped diamond (BDD) anode and a carbon-PTFE electrode as cathode was employed. Contrary to most published work, special focus was placed on the treatment efficiency, individually for benzene, toluene, ethyl benzene and xylene compounds (m&p-xylene, o-xylene) in a real water matrix (seawater), aiming to evaluate the oxidation mechanisms and to optimize the experimental conditions (such as current density, feed water flow rate, concentration of BTEX) for electrochemical decomposition, using an experimental design based on Face Centered Composite design coupled with Response Surface Methodology. The response surface plots verify the results of the statistical analysis, since electric current is the most detrimental factor to benzene removal, whereas feed flow rate and BTEX initial concentration are the two most significant factors, affecting negatively the removal efficiency of the other four hydrocarbons. Under the optimum conditions (current density ∼74 mA/cm2, feed recirculation flow rate 0.2 m3/h and BTEX initial concentration 2.5 mg/L) xylenes and ethyl benzene were completely (100%) removed within 30 min of electrolysis, more than 90 % of toluene was removed within 60 min, while 70–80 % of benzene was eliminated within 120 min. The study demonstrated the efficiency of electrochemical process for treating recalcitrant organics in concentrated brines.

Haemo-catharsis (HC) modules comprise the cylindrical fiber-bundle section and two flow inlet/outlet headers. Available models ignore the substantial pressure-drop (varying non-linearly with flow-rate) in the headers, while employing linear pressure-drop expressions for the entire module, which lead to erroneous assessment of HC-module performance/characteristics. The novel method reported herein to address this issue, enables reliable determination of key HC-module fluid-mechanical parameters. In specially designed facility, accurate pressure measurements are made (for typical flow-rate ranges) under carefully selected inlet/outlet flow-modes. Fitting a mechanistic model to appropriate pressure-difference versus flow-rate data, allows determination of four parameters ζi associated with pressure-drop in headers (for inlet-/outlet-fluid flow), two friction-coefficients for laminar flow in fiber-lumen and shell-side, plus the hydraulic membrane-permeability. Applying this method to a typical commercial high-flux HC-module, realistic values are obtained of membrane-permeability and friction-coefficients, whereas the magnitude of coefficients ζi manifests the significance of pressure-drop in the headers. Friction-coefficient predictions by a theoretical model applicable to the main HC-section, compared to experimentally-determined values, show weaknesses of the former whereas the latter can reliably account for particular geometric/morphological features of real HC-modules. Further testing of the method is recommended, while its adaptation to a comprehensive model for HC-module performance simulation is in progress.

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This manuscript summarizes the successful start-up and operation of a hybrid eco-engineered water treatment system, at pilot scale. The pilot unit, with 100 L capacity, has been devised for the efficient electrocatalytic production of H2O2 at an air-diffusion cathode, triggering the formation of OH from Fenton’s reaction with added Fe2+ catalyst. These radicals, in combination with those formed at a powerful boron-doped diamond (BDD) anode in an undivided cell, are used to degrade a mixture of model pesticides. The capability of the plant to produce H2O2 on site was initially optimized using an experimental design based on central composite design (CCD) coupled with response surface methodology (RSM). This aimed to evaluate the effect of key process parameters like current density (j) and solution pH. The influence of electrolyte concentration as well as liquid and air flow rates on H2O2 electrogeneration and current efficiency at optimized j and pH was also assessed. The best operation conditions resulted in H2O2 mass production rate of 64.9 mg min−1, 89.3% of current efficiency and 0.4 kWh m-3 of energy consumption at short electrolysis time. Performance tests at optimum conditions were carried out with 75 L of a mixture of pesticides (pyrimethanil and methomyl) as a first step towards the elimination of organic contaminants by solar photoelectro-Fenton (SPEF) process. The combined action of homogeneous ( OH) and heterogeneous (BDD( OH)) catalysis along with photocatalysis (UV photons collected at a solar CPC photoreactor) allowed the removal of more than 50% of both pesticides in 5 min, confirming the fast regeneration of Fe2+ catalyst through cathodic reduction and photo-Fenton reaction.

Vacuum membrane distillation (VMD) is an attractive variant of the novel membrane distillation process, which is promising for various separations, including water desalination and bioethanol recovery through fermentation of agro-industrial by-products. This publication is part of an effort to develop a capillary membrane module for various applications, as well as a model that would facilitate VMD process design. Experiments were conducted in a laboratory pilot VMD unit, comprising polypropylene capillary-membrane modules. Performance data, collected at modest temperatures (37 °C to 65 °C) with deionized and brackish water, confirmed the improved system productivity with increasing feed-water temperature, excellent salt rejection was obtained. The recovery of ethanol from ethanol-water mixtures and from fermented winery by-products was also studied, in continuous, semi-continuous, and batch operating modes. At low-feed-solution temperature (27–47 °C), ethanol-solution was concentrated 4 to 6.5 times in continuous operation and 2 to 3 times in the semi-continuous mode. Taking advantage of the small property variation in the module axial-flow direction, a simple VMD process model was developed, satisfactorily describing the experimental data. This VMD model appears to be promising for practical applications, and warrants further R&amp, D work.

BACKGROUND: Table olive processing wastewater (TOPW) is a seriously polluting and difficult to treat effluent, characterized by widely fluctuating pH and salinity, as well as high concentrations of organic matter and polyphenols. This systematic long-term study in a laboratory-scale pilot demonstrates that membrane bioreactor (MBR) technology is effective in substantially bio-degrading TOPW. RESULTS: After implementation of an appropriate protocol of active biomass acclimatization/proliferation, the MBR pilot was operated for 6 months with real TOPW effluent, under various operating conditions. Total organic carbon (TOC) and total polyphenol (TPh) compounds removal efficiencies were very high with mean values 91.5 and 82.8%, respectively; nutrient (N and P) removal was also satisfactory. The membrane exhibited stable performance at moderate biomass concentration, with a tendency to deteriorate at higher biomass concentration. Fouled membrane permeability could be fully restored by implementing the usual chemical cleaning protocols. CONCLUSIONS: Despite the high percentage TOC and TPh removal, the MBR effluent requires final post-treatment to remove a yellowish tint and further reduce its organic content, depending on local discharge standards. The MBR can serve as the basic treatment process in an integrated scheme for TOPW management, which needs additional R&D to further develop and optimize.

The investigated novel retentate-spacer design comprises spherical nodes symmetrically connected with cylindrical filaments, thus forming a net-type structure with parallelogram unit-cells. Key feature of this configuration is the contact points (or small contact-regions) of nodes with bounding membranes, instead of filament-membrane contact lines characterizing the conventional unwoven-filament geometries; undesirable contact lines create “dead-flow” zones, that promote reduced mass-transfer (i.e. increased concentration polarization-CP) and fouling. Direct numerical simulations of the flow field and mass transfer, complemented by pressure drop and mass-transfer coefficient measurements, reveal the advantages of novel spacers. The flow field, and local shear-stress and mass-transfer-coefficient distributions on membranes, are rather uniform. The novel spacers, considering also the extensive flow constrictions between filaments and membranes, exhibit broader distributions of these time-averaged transport parameters, which extend to higher values (compared to conventional spacers), with insignificant percentage of zero values; a fairly uniform shear-stress distribution is also identified on spacer filaments. Thus, significant benefits are expected in mitigating CP and fouling phenomena in membrane operation. Friction losses show increased dependence on cross-flow velocity (compared to conventional designs), as they are affected more by flow-shearing at the membrane surfaces, than by form-drag. Useful pressure drop and mass-transfer correlations are obtained.

RO membrane fouling is unavoidable as no pretreatment method exists for perfect removal of foulants, which comprise various organic compounds including those from bio-activity. Improved understanding of fouling layer characteristics and correlations of permeation resistance with desalination process parameters (pursued herein) are essential for improving RO-membrane operations. Organic-gel formation is a major type of RO-membrane fouling, in the absence or presence of micro-organisms. Alginates, in dilute brackish-water solutions, are employed as representative gel-forming foulants. Recent experimental results are summarized regarding fouling-layer rheological properties and specific resistance α , focusing on ionic environment and permeation flux effects. Comparative assessment of these characteristics sheds light into the development and structure of gel layers during desalination; in particular, the nature of these layers (i.e. thixotropic material with yield stress ) explains their coherence and resistance to shear forces. The investigated relatively thin fouling layers (of practical significance) appear to develop uniformly, with resistance α strongly dependent on flux. Exploiting the rich literature on synthetic alginate hydrogels, a new modeling approach is presented for the resistance α , using measured fouling-gel structural parameters. The fair agreement of predictions with measurements, using no arbitrary constants, warrants further work on model development. Research priorities on membrane fouling are indicated.

The geometric design parameters of spiral-wound membrane (SWM) elements include retentate- and permeate-spacer characteristics and number of membrane envelopes (or sheet width) for constant total membrane area. A systematic assessment is made herein of the effect of these parameters (varying within realistic ranges) on the spatial distribution of all operating variables, including the permeate flux, trans-membrane pressure (TMP), retentate- and permeate-side local pressures, velocities and salt concentrations. The advanced software employed is capable of such detailed simulation of SWM module performance with no recourse to empirical parameters. The parametric study involves typical cases of desalinating (under constant recovery) brackish- and sea-water with 2000 mg/L and 40,000 mg/L TDS, respectively, in pressure vessels with seven 8-in. SWM-elements. The results confirm that membrane width is very important, with short sheets leading to best overall performance. The permeate-side fabric characteristics (neglected by researchers so far) significantly affect TMP and overall SWM performance, with more pronounced effect in the low-pressure modules. The effect of retentate-side spacer manifests itself mainly in the pressure drop across the module. Low-pressure module performance is comparatively more sensitive to variations of geometric parameters. The product quality (especially from high-pressure SWM modules) exhibits reduced sensitivity to significantly different design parameter-values.

The rheological properties of membrane biofouling layers developing in Membrane Bioreactors (MBR) have not been measured directly so far, although they are essential for understanding biofouling and for determining conditions to mitigate it. The development of a novel method is reported herein, which permits accurate rheological measurements on membrane biofouling layers, using specimens withdrawn from an operating laboratory-scale MBR. A specially designed test-section (with a pair of flat membrane specimens) allows implementation of realistic operating modes, including automatic periodic back-washing. The membrane specimens, with a biofouling layer representative of a well-controlled MBR operating history, are examined in an advanced parallel-plate rheometer, where special care is taken to prevent ex-situ biofouling layer changes. Measurements performed in oscillatory and steady shearing modes provide valuable information on biofouling layer rheological characteristics, confirming that these layers are typical viscoelastic materials with yield stress exhibiting thixotropic, shear-thinning behavior. Rheological properties of the activated sludge liquor are also assessed. The rheological properties of activated sludge and of biofouling layers display qualitative similarities, although the elastic character of the latter is much more pronounced. The new technique is most useful for studying biofouling layers as a function of the main MBR process parameters. Improvements of the technique for such applications are discussed.

This study is a step toward integrated modeling of the evolving (in space and time) flow and concentration fields during water desalination in membrane spacer-filled channels. Such detailed model predictions are of practical significance, leading to improved understanding of spiral wound membrane (SWM) module operation. Submerged and zigzag spacer filament 2-dimentional configurations are employed, as they create geometric flow-channel features (contact lines, flow constrictions, etc) encountered in SWM modules. The numerical study, performed in a Reynolds number range typical for desalination modules, is focused on the evolution of local mass transfer coefficient k and concentration polarization, which significantly affect SWM module performance. A detailed quantitative prediction is obtained of these parameters, which are linked to the variation of wall shear stress, static pressure and permeation flux. By focusing on a typical region of the membrane channel (adequately capturing the evolving flow characteristics), it is predicted that increasing average k values (with the concomitant reduction of concentration polarization) are associated with the undesirable increase of pressure drop; these conflicting requirements can be balanced through the selection of appropriate spacer geometry. The negative effect of membrane-filament contact lines on concentration polarization is well documented. An assessment is made of the two spacer filament configurations, from this perspective, and directions for future research are outlined.

Despite extensive research on several aspects of photocatalytic membrane reactors (PMRs) and their well-recognized attributes, no significant large-scale applications have been reported in the area of water treatment. A comprehensive assessment of the three components of this potential technology (i.e., photocatalysts, light source, and membranes) and their interaction suggests that the respective technology readiness level (TRL) is relatively low (at ∼4 to 5) at present; therefore, substantial development work is required to render PMR systems attractive and ready for commercialization (with TRL = 9). These efforts should be guided by the need to develop a modern sustainable technology, satisfying economic, environmental, and social criteria. In pursuing PMR process development toward commercialization, significant research and development (R&D) is required (with emphasis on pilot plant testing and demonstration in real environments) to optimize key design and operating parameters, including apparent quantum efficiency, photocatalyst concentration, and hydraulic residence time. Priorities of R&D on technical issues are recommended. After PMR pilot-scale testing/demonstration, it will be possible to determine process economic and environmental indicators (i.e., total processed water unit cost, CO 2 /environmental footprint) with good accuracy. In general, because of the modular-type PMR components, no significant scale-up issues are foreseen and the steps toward PMR full-scale development appear to be straightforward. However, the pilot PMR data have to be fairly accurate and the respective performance indicators have to be attractive because such a novel hybrid process would compete for a place in a market characterized by conservatism and well-entrenched conventional processes, operating with fair reliability for a long time. Nevertheless, some distinct advantages of the novel PMR systems, over conventional techniques, particularly in respect of overall environmental performance emphasized in recent year (e.g., elimination or minimization of sidestreams, no addition of oxidants), may prove decisive in favor of large-scale PMR applications.

Lycopene is an abundant natural carotenoid pigment with several biological functions (well-known for its antioxidant properties) which is under intensive investigation in recent years. Lycopene chemistry, its natural distribution, bioavailability, biological significance, and toxicological effects are briefly outlined in the first part of this review. The second, major part, deals with various modern downstream processing techniques, which are assessed in order to identify promising approaches for the recovery of lycopene and of similar lipophilic compounds. Natural lycopene is synthesized in plants and by microorganisms, with main representatives of these two categories (for industrial production) tomato and its by-products and the fungus Blakeslea trispora, respectively. Currently, there is a great deal of effort to develop efficient downstream processing for large scale production of natural-origin lycopene, with trends strongly indicating the necessity for "green" and mild extraction conditions. In this review, emphasis is placed on final product safety and ecofriendly processing, which are expected to totally dominate in the field of natural-origin lycopene extraction and purification.

New results are presented on the preparation and performance of iron-impregnated carbon electrodes for a novel electro-Fenton “filter”-type device, reported in a previous publication. Two composite Fe/carbon-felt electrodes were prepared via different procedures: one prepared under oxidizing conditions (i.e., dissolved oxygen) through immersion of carbon felt in an iron ethanolic solution (CFm-Fe), and another prepared under reduced oxidative conditions (nitrogen, ammonia, etc.) leading to in situ formation of iron nanoparticles on the carbon surface (CFm-nFe). The cathodes were characterized by X-ray diffraction (XRD), N2 adsorption–desorption (BET), scanning electron microscopy (SEM), Raman microspectroscopy, and linear sweep voltammetry (LSV). The stability and oxidation performance of these electrodes were evaluated by measuring the leaching of iron species and the degradation in aqueous medium of a common pharmaceutical compound (diclofenac), respectively. The results show that the flow-through opera...

Spiral Wound Membrane (SWM) modules are the basic components of modern desalination and water treatment technology. To advance this technology, a comprehensive SWM-element model and related performance simulator are indispensable tools. A flexible and efficient simulator is needed to optimize SWM modules, and to be integrated into general-purpose software for designing and monitoring/controlling entire desalination plants. Desirable features of SWM-model are outlined first, considering practical constraints. Reviewing related work, it is recognized that the complicated physico-chemical phenomena (and interactions) occurring in SWM-modules extend over several length- and time-scales, thus rendering impossible direct solution of the complete problem. Therefore, a tractable modeling-structure is needed, whereby properly correlated results of detailed studies (at small scale) on flow and mass transfer in spacer-filled channels, and sub-models representing the membrane function, are integrated into an appropriate modeling framework for a broad spatial domain, i.e. for performance simulation of entire SWM modules. Available steady-state models are reviewed and investigations toward development of dynamic simulators are outlined. Typical results are discussed of detailed two-dimensional distributions of process parameters, throughout the SWM-modules in a pressure vessel, for steady-state operation. An overall assessment of simulating SWM-module performance and of design-parameter effects, considering industry requirements, leads to suggestions on R&D priorities.