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In this study, a large-area N-doped graphene film (NG/NF) was fabricated on a nickel foam (NF) substrate viathermal chemical vapor deposition along with the flow of gaseous C2H4/NH3mixtures. It was demonstrated to enable the sequential process of anodic organic oxidation followed by non-electrochemical activation of anodically formed persulfate. NG-20/NF exhibited the highest electrical conductivity owing to the presence of a pyridinic-N dopant. It thus substantially outperformed the undoped graphene film (G/NF) and NF in initiating anodic oxidation reactions, that is, oxidative organic degradation and conversion of SO42−into persulfate. NG-20/NF performed non-radical persulfate activation, achieving constant treatment efficiency, regardless of whether electric current was applied. A marginal reduction in treatment performance occurred in the electrochemical system using NG/NF during recurring cycles of separate switch-on and -off periods. Accordingly, the dual role of NG/NF as the cathode in paired redox reactions and as the carbocatalyst in persulfate activation was shown.

This study is the first to demonstrate the capability of Cl–to markedly accelerate organic oxidation using thermally activated peroxymonosulfate (PMS) under acidic conditions. The treatment efficiency gain allowed heat-activated PMS to surpass heat-activated peroxydisulfate (PDS). During thermal PMS activation at excess Cl–, accelerated oxidation of 4-chlorophenol (susceptible to oxidation by hypochlorous acid (HOCl)) was observed along with significant degradation of benzoic acid and ClO3–occurrence, which involved oxidants with low substrate specificity. This indicated that heat facilitated HOCl formation via nucleophilic Cl–addition to PMS and enabled free chlorine conversion into less selective oxidizing radicals. HOCl acted as a key intermediate in the major oxidant transition based on temperature-dependent variation in HOCl concentration profiles, kinetically retarded organic oxidation upon NH4+addition, and enabled rapid organic oxidation in heated PMS/HOCl mixtures. Chlorine atom that formed via the one-electron oxidation of Cl–by the sulfate radical served as the primary oxidant and was involved in hydroxyl radical production. This was corroborated by the quenching effects of alcohols and bicarbonates, reactivity toward multiple organics, and electron paramagnetic resonance spectral features. PMS outperformed PDS in degrading benzoic acid during thermal activation operated in reverse osmosis concentrate, which was in conflict with the well-established superiority of heat-activated PDS.

Flow-electrode capacitive deionization (FCDI) is a promising technology for sustainable water treatment. However, studies on the process have thus far been limited to lab-scale conditions and select fields of application. Such limitation is induced by several shortcomings, one of which is the absence of a comprehensive process model that accurately predicts the operational performance and the energy consumption of FCDI. In this study, a simulation model is newly proposed with initial validation based on experimental data and is then utilized to elucidate the performance and the specific energy consumption (SEC) of FCDI under multiple source water conditions ranging from near-groundwater to high salinity brine. Further, simulated pilot-scale FCDI system was compared with actual brackish water reverse osmosis (BWRO) and seawater reverse osmosis (SWRO) plant data with regard to SEC to determine the feasibility of FCDI as an alternative to the conventional membrane processes. Analysis showed that FCDI is competent for operation against brackish water solutions under all possible operational conditions with respect to the BWRO. Moreover, its distinction can be extended to the SWRO for seawater conditions through optimization of its total effective membrane area via scale-up. Accordingly, future directions for the advancement of FCDI was suggested to ultimately prompt the commercialization of the FCDI process.

This study reports distillation-based salt removal by Ohmic heating in a hybrid process, in which electrochemical oxidation (EO) and direct contact membrane distillation (DCMD) are performed sequentially. In addition to anodically destructing the organics, the hybrid process also separated the sulfate-based electrolytes from treated water through distillation, without consuming external energy, owing to the temperature of the aqueous sulfate solution being elevated to 70 °C via resistive heating. The hybrid process treated organic compounds in a nonselective fashion, whereas DCMD alone did not completely reject (semi)volatile organics. Integrating EO with DCMD made the hybrid process resistant toward the wetting phenomenon; the process exhibited a steady distillate flux and salt rejection as the initial loading of amphiphilic sodium dodecyl sulfate was increased to 0.3 mM. Anodic persulfate formation from the sulfate and Ohmic heating caused an in situ yield of the sulfate radical in the feed solution; this eliminated membrane fouling, according to the observation that the water flux, which was drastically reduced upon adding alginate, was recovered immediately after an electric current was applied. The hybrid process concurrently decomposed spiked organics and removed naturally present inorganic ions in actual flue gas desulfurization wastewater, without an external supply of electrolyte and heat energy.

The imperative to establish environmentally friendly and sustainable food processing techniques has compelled the food industry to explore alternative approaches that uphold food quality, ensure nutritional integrity, and minimize energy consumption. Extensive research conducted in the past decade has substantiated the superiority of membrane-based dewatering technology over conventional methods, owing to its ability to retain nutrients effectively while minimizing energy requirements. Notably, forward osmosis (FO) and membrane distillation (MD) have emerged as viable membrane technologies for food processing in the industry. However, recent reviews have underscored the prominence of FO in the enrichment of liquid food, positioning it as a preferred choice among other membrane-based processes. This review paper aims to elucidate the advancements and contributions of FO and MD in the realm of food processing while evaluating their maturity and technology readiness level for food concentration. Moreover, it endeavors to delineate specific parameters, including pretreatment techniques, membrane cleaning strategies, and membrane configurations/modules tailored to liquid food sources' distinct dewatering requirements. Although most FO and MD studies have focused on lab-scale fruit juice and whey concentration, future investigations should encompass pilot-scale process development alongside comprehensive techno-economic analyses to facilitate the smooth transition of these technologies to an industrial scale.

This study investigates the fouling mechanisms in membrane distillation, focusing on the impact of foulant type and membrane surface chemistry. Interaction forces between a surface-functionalized particle probe simulating a range of organic foulants and model surfaces, modified with different surface energy materials, were measured by atomic force microscopy. The measured interaction forces were compared to those calculated based on the experimentally determined surface energy components of the particle probe, model surface, and medium (i.e., water). Surfaces with low interfacial energy exhibited high attractive interaction forces with organic foulants, implying a higher fouling potential. In contrast, hydrophilic surfaces (i.e., surfaces with high interfacial energy) showed the lowest attractive forces with all types of foulants. We further performed fouling experiments with alginate, humic acid, and mineral oil in direct contact membrane distillation using polyvinylidene fluoride membranes modified with various materials to control membrane surface energy. The observed fouling behavior was compared to the interaction force data to better understand the underlying fouling mechanisms. A remarkable correlation was obtained between the evaluated interaction force data and the fouling behavior of the membranes with different surface energy. Membranes with low surface energy were fouled by hydrophobic, low surface tension foulants via “attractive” and subsequent “adsorptive” interaction mechanisms. Furthermore, such membranes have a higher fouling potential than membranes with high or ultralow surface energy.

PVDF (poly vinylidene fluoride) membrane was modified with glycidyl methacrylate (GMA) and sodium sulfite using a radiation-induced graft polymerization technique for unique ammonia removal process. Ion exchange capacities (IECs) of unmodified PVDF membrane, modified PVDF membrane and commercial cation exchange membrane (CEM) were investigated. The IEC value increased as the concentration of GMA increased. Batch experiments were carried out to evaluate the ion transport via the modified membrane. The mass flux of ammonia via the CEM and modified membrane at the initial ammonia concentration of 2000 mg/L were 1.16 mg-NH 4 + /m 2 s and 2.89 mg-NH 4 + /m 2 s, respectively. [ABSTRACT FROM AUTHOR]

In the membrane-applied water treatment process, residual manganese often generates a significant problem because scaling of oxidized manganese can lead to irreversible membrane fouling. For the membrane process to operate effectively, advanced treatment process should be considered for manganese removal. In this study, an adsorption process utilizing a newly developed magnetite-coated adsorbent was adopted to overcome manganese fouling in ultrafiltration (UF) applications, particularly during chemically enhanced backwashing. Typical manganese-coated sand (i.e., Ferox) was also evaluated simultaneously for comparison. These adsorbents were assessed for basic performance in a fixed bed adsorption column test under various operating conditions. With the addition of chlorine dosing, the efficiency of manganese removal was improved dramatically. Specifically, magnetite column was effective to prevent flux decline in typical UF applications even with an empty bed contact times of 1 min, while severe fouling was observed with no such pretreatment, suggesting it as a promising technology for the control of fouling caused by manganese.

We present a nonconventional membrane surface modification approach that utilizes surface topography to manipulate the tribology of foulant accumulation on water desalination membranes via imprinting of submicron titanium dioxide (TiO2) pillar patterns onto the molecularly structured, flat membrane surface. This versatile approach overcomes the constraint of the conventional approach relying on interfacial polymerization that inevitably leads to the formation of ill-defined surface topography. Compared to the nonpatterned membranes, the patterned membranes showed significantly improved fouling resistance for both organic protein and bacterial foulants. The use of hydrophilic TiO2as a pattern material increases the membrane hydrophilicity, imparting improved chemical antifouling resistance to the membrane. Fouling behavior was also interpreted in terms of the topographical effect depending on the relative size of foulants to the pattern dimension. In addition, computational fluid dynamics simulation suggests that the enhanced antifouling of the patterned membrane is attributed to the enhancement in overall and local shear stress at the fluid–TiO2pattern interface.

Membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20–30°C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50–70°C) is available.

AbstractMembrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20–30°C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50–70°C) is available.

AbstractThis study investigated pressure-assisted osmosis (PAFO), which uses the external pressure together with osmotic gradient across a membrane, to improve flux through forward osmosis (FO) membranes. Experiments were performed in a laboratory-scale PAFO system, which allows the application of external pressure up to 13 bar on the feed solution side. Deionized water (D.I. water) and synthetic seawater (35,000 mg/L NaCl) were used as feed solutions, and MgCl2was used as a draw solution. Humic acid was used as a model foulant to examine the characteristics of membrane fouling. A theoretical model based on osmotic transport theory incorporating internal/external concentration polarization, and mass balance equations were used to analyze the performance of FO and PAFO system. Results indicated that the addition of external pressure to the osmotic pressure allowed higher flux in PAFO than FO. Nevertheless, the flux in PAFO was less than the sum of the flux in RO and that in FO, which attributed to the increase in the internal concentration polarization by the external pressure. Under the test conditions in this study, fouling by sodium alginate and humic acid was negligible in FO, RO, and PAFO.

This study investigated pressure-assisted osmosis (PAFO), which uses the external pressure together with osmotic gradient across a membrane, to improve flux through forward osmosis (FO) membranes. Experiments were performed in a laboratory-scale PAFO system, which allows the application of external pressure up to 13 bar on the feed solution side. Deionized water (D.I. water) and synthetic seawater (35,000 mg/L NaCl) were used as feed solutions, and MgCl2was used as a draw solution. Humic acid was used as a model foulant to examine the characteristics of membrane fouling. A theoretical model based on osmotic transport theory incorporating internal/external concentration polarization, and mass balance equations were used to analyze the performance of FO and PAFO system. Results indicated that the addition of external pressure to the osmotic pressure allowed higher flux in PAFO than FO. Nevertheless, the flux in PAFO was less than the sum of the flux in RO and that in FO, which attributed to the increase in the internal concentration polarization by the external pressure. Under the test conditions in this study, fouling by sodium alginate and humic acid was negligible in FO, RO, and PAFO.

The ability to prepare solid surfaces with well-controlled superhydrophobic and superoleophilic properties is of paramount importance to water–oil separation technology. Herein, we successfully prepared superhydrophobic-superoleophilic membranes by single-step deposition of polystyrene (PS) nanofibers onto a stainless steel mesh via electrospinning. The contact angles of diesel and water on the prepared PS nanofiber membrane were 0° and 155° ± 3°, respectively. Applications of the PS nanofiber membrane toward separating liquids with low surface tension, such as oil, from water were investigated in detail. Gasoline, diesel, and mineral oil were tested as representative low-viscosity oils. The PS nanofiber membranes efficiently separated several liters of oil from water in a single step, of only a few minutes’ duration. The superhydrophobic PS nanofiber membrane selectively absorbs oil, and is highly efficient at oil–water separation, making it a very promising material for oil spill remediation.

ABSTRACTTransport and deposition characteristics of natural organic matter (NOM) are systematically investigated using flow field-flow fractionation (Fl-FFF) at various chemical and physical conditions. Humic acid (HA) was chosen as model organic foulants. Prior to Fl-FFF analysis, HA was fractionated by membranes with different molecular weight cut-offs. To elucidate physicochemical factors affecting the deposition and transport characteristics of organic foulants, various concentrations of NaCl (i.e. up to seawater level) and CaCl2were employed as carrier solutions in Fl-FFF. Each fractionated NOM showed different transport and deposition characteristics with respect to the chemical and physical conditions employed during Fl-FFF analysis. When the total dissolved solids (TDS) concentration increased, there was more significant variation in the retention time for large NOM fractions compared with small NOM fractions. This means that the transport and deposition tendency of the larger NOM fractions varied more significantly with the alteration of ionic strength in Fl-FFF channel than the smaller ones. However, the smaller NOM fractions showed more considerable variation in retention time with increasing cross-flow intensity (i.e. flow perpendicular to channel flow in Fl-FFF) in Fl-FFF channel. This also means that the variation of physical factor could affect the transport and deposition tendency of the smaller ones more influentially. Results also elucidated that the retention time and area of elution peak of fractionated NOM were directly related to the amount of organic foulants attached to the membrane in Fl-FFF channel. It has been demonstrated that the deposition tendency of organic foulants increased at the higher TDS concentration, calcium concentration, and cross-flow intensity. This has been quantitatively determined using fouling index, Qf, derived from the data obtained from Fl-FFF. Based on this study, it is implied that Fl-FFF can be a useful tool to characterize the transport and deposition behavior of organic foulants in the solid–water interface and optimize pretreatment options for reducing membrane fouling.

Transport and deposition characteristics of natural organic matter (NOM) are systematically investigated using flow field-flow fractionation (Fl-FFF) at various chemical and physical conditions. Humic acid (HA) was chosen as model organic foulants. Prior to Fl-FFF analysis, HA was fractionated by membranes with different molecular weight cut-offs. To elucidate physicochemical factors affecting the deposition and transport characteristics of organic foulants, various concentrations of NaCl (i.e. up to seawater level) and CaCl2were employed as carrier solutions in Fl-FFF. Each fractionated NOM showed different transport and deposition characteristics with respect to the chemical and physical conditions employed during Fl-FFF analysis. When the total dissolved solids (TDS) concentration increased, there was more significant variation in the retention time for large NOM fractions compared with small NOM fractions. This means that the transport and deposition tendency of the larger NOM fractions varied more significantly with the alteration of ionic strength in Fl-FFF channel than the smaller ones. However, the smaller NOM fractions showed more considerable variation in retention time with increasing cross-flow intensity (i.e. flow perpendicular to channel flow in Fl-FFF) in Fl-FFF channel. This also means that the variation of physical factor could affect the transport and deposition tendency of the smaller ones more influentially. Results also elucidated that the retention time and area of elution peak of fractionated NOM were directly related to the amount of organic foulants attached to the membrane in Fl-FFF channel. It has been demonstrated that the deposition tendency of organic foulants increased at the higher TDS concentration, calcium concentration, and cross-flow intensity. This has been quantitatively determined using fouling index, Qf, derived from the data obtained from Fl-FFF. Based on this study, it is implied that Fl-FFF can be a useful tool to characterize the transport and deposition behavior of organic foulants in the solid–water interface and optimize pretreatment options for reducing membrane fouling.

Feasibility of osmotic backwashing for cleaning fouled membranes during forward osmosis (FO) process was investigated focusing on the mechanisms and factors involved. Alginate and humic acids were used as model organic foulants; and colloidal silica particles with different sizes were used as model inorganic particulate foulants. Results showed that noticeable flux recovery was achieved by osmotic backwashing through the instantaneous replacement of the draw solution with the dilute solution that has much less osmotic pressure than that of the feed solution. The switch of water flow direction through the membrane from feed-to-draw to draw-to-feed allows the effective detachment of foulants from the membrane surface. It was found that the efficiency of osmotic backwashing was affected by several factors including foulant type, membrane orientation and backwashing conditions (i.e. initial flux and duration). In addition, concentration polarization was found to play an important role in determining fouling behaviour, and thus, the osmotic backwashing efficiency.

The chemical heterogeneity of reverse osmosis membrane surface and its impacts on membrane fouling were investigated using dynamic hysteresis, which is a newly developed surface analytical technique. Based on dynamic hysteresis measurements, it has been demonstrated that the chemical heterogeneity of membrane surface was greatly influenced by solution—pH and ionic strength. Significant variation of dynamic hysteresis was observed as solution pH changed, implying the alteration of membrane surface heterogeneity. Interestingly, there existed the interplay between chemical and physical surface heterogeneity with respect to solution ionic strength. At low ionic strength, dynamic hysteresis mostly reflected chemical surface heterogeneity, while physical surface heterogeneity played more dominant role in the change of dynamic hysteresis with increasing ionic strength. This implies that membrane fouling due to chemical surface heterogeneity of the membrane is less remarkable in seawater desalination compared to wastewater and brackish water treatments. In addition, mechanisms and factors affecting chemical and physical surface heterogeneity and their interplay with respect to solution chemistry including pH, ionic strength and divalent cation concentration are discussed and elucidated.

AbstractThe chemical heterogeneity of reverse osmosis membrane surface and its impacts on membrane fouling were investigated using dynamic hysteresis, which is a newly developed surface analytical technique. Based on dynamic hysteresis measurements, it has been demonstrated that the chemical heterogeneity of membrane surface was greatly influenced by solution—pH and ionic strength. Significant variation of dynamic hysteresis was observed as solution pH changed, implying the alteration of membrane surface heterogeneity. Interestingly, there existed the interplay between chemical and physical surface heterogeneity with respect to solution ionic strength. At low ionic strength, dynamic hysteresis mostly reflected chemical surface heterogeneity, while physical surface heterogeneity played more dominant role in the change of dynamic hysteresis with increasing ionic strength. This implies that membrane fouling due to chemical surface heterogeneity of the membrane is less remarkable in seawater desalination compared to wastewater and brackish water treatments. In addition, mechanisms and factors affecting chemical and physical surface heterogeneity and their interplay with respect to solution chemistry including pH, ionic strength and divalent cation concentration are discussed and elucidated.

AbstractFeasibility of osmotic backwashing for cleaning fouled membranes during forward osmosis (FO) process was investigated focusing on the mechanisms and factors involved. Alginate and humic acids were used as model organic foulants; and colloidal silica particles with different sizes were used as model inorganic particulate foulants. Results showed that noticeable flux recovery was achieved by osmotic backwashing through the instantaneous replacement of the draw solution with the dilute solution that has much less osmotic pressure than that of the feed solution. The switch of water flow direction through the membrane from feed-to-draw to draw-to-feed allows the effective detachment of foulants from the membrane surface. It was found that the efficiency of osmotic backwashing was affected by several factors including foulant type, membrane orientation and backwashing conditions (i.e. initial flux and duration). In addition, concentration polarization was found to play an important role in determining fouling behaviour, and thus, the osmotic backwashing efficiency.

In Republic of Korea, seawater engineering and architecture of high efficiency reverse osmosis (SEAHERO) research and development (R&D) program started from 2007 to lead the top seawater reverse osmosis (SWRO) plant technologies for desalination with the fund of US $165 million for 6 years including test-bed plant construction. There are three technical strategies for SEAHERO R&D program called 3L, which represents large scale, low fouling, and low energy, respectively. Large scale means design, construction, and operation of the largest unit SWRO train [daily water production rate = 8 MIGD (36,000 m3/day)] in the world. Low-fouling strategy targets the decrease of RO membrane fouling by 50%. The specific target for low energy is total energy consumption of whole SWRO plant (including intake, pretreatment, SWRO systems, and so on) less than 4 kWh/m3. The core parts for SWRO plant, such as 16 in. diameter RO membrane and energy recovery device, were developed and will soon be introduced to a test-bed including the largest unit SWRO train. The next step of SEAHERO is real field scale test-bed application of the unit technologies developed for the past 4 years (2007–2010) such as strategic pretreatment, energy-saving technology, and reliable system monitoring.

Physical aspects of dynamic hysteresis for characterizing reverse osmosis (RO) membranes have been investigated. Dynamic hysteresis was used as a parameter of showing physical surface characteristics of RO membranes. Automated microbalance was utilized to determine dynamic hysteresis based on the Wilhelmy plate method. Dynamic hysteresis determined with non-polar liquid was related to physical surface characteristics including surface roughness and heterogeneity determined by atomic force microscopy imaging and analysis. A remarkable correlation between dynamic hysteresis and surface heterogeneity was obtained when nonpolar liquid was used during the measurements. Dynamic hysteresis increased as the surface heterogeneity of RO membrane increased.

Physical aspects of dynamic hysteresis for characterizing reverse osmosis (RO) membranes have been investigated. Dynamic hysteresis was used as a parameter of showing physical surface characteristics of RO membranes. Automated microbalance was utilized to determine dynamic hysteresis based on the Wilhelmy plate method. Dynamic hysteresis determined with non-polar liquid was related to physical surface characteristics including surface roughness and heterogeneity determined by atomic force microscopy imaging and analysis. A remarkable correlation between dynamic hysteresis and surface heterogeneity was obtained when nonpolar liquid was used during the measurements. Dynamic hysteresis increased as the surface heterogeneity of RO membrane increased.

The effects of water quality on total copper release in drinking water distribution systems were investigated in a field study using pilot distribution systems (PDSs) that distributed different finished waters produced from groundwater, surface water, and saline sources. Finished groundwater was produced by conventional treatment (i.e., aeration, disinfection, and stabilization), softening, and nanofiltration. Finished surface water was produced by enhanced coagulation–ozone–biological granular activated carbon and nanofiltration. Finished desalinated water was simulated by reverse osmosis filtration of groundwater and sea salt addition. PDS water quality was varied quarterly over one year by blending different finished waters. Total copper release was found to be dependent on blended water quality, increasing as alkalinity, sulfate levels, and temperature increased and decreasing as pH and silica increased. Calcium, chloride, dissolved oxygen, total dissolved solids, and ultraviolet absorbance at 254 nm did not affect total copper release in these investigations. Total copper release was accurately described by nonlinear regression models as a function of water quality.

The objective of this study was to quantify the assimilable organic carbon (AOC) in processing water at several stages of a full‐scale nanofiltration (NF) water treatment plant. The NF membrane plant investigated was a 45,400‐m3/d (12‐mgd) water‐softening facility in Plantation, Fla. The average AOC concentration of raw feedwater was estimated at 158 μg/L acetate‐C. After pretreatment (acid and antiscalant addition), AOC levels increased by 12.7% (p‐value = 0.055), suggesting that pretreatment chemicals used to control scaling may enhance bacterial growth potential on the membrane surface. The results also demonstrated that the membrane system was capable of effectively removing 63.4% of AOC and showed a decrease in membrane productivity over time (declined linearly at a rate of approximately 1.2 times 10‐4L/m2/h ÷ kPa [4.9 times 10‐4gfd ÷ psi] per d). This decrease could be attributed to biofouling, as observed by a steady increase in differential pressure during operation, and to natural organic matter fouling, as shown by the composition of the organic matter in the feedwater (54.9% hydrophobic and 18.1% hydrophilic neutral compounds).

A series of well-controlled membrane filtration experiments are performed to systematically investigate the dynamic behavior of permeate flux in crossflow membrane filtration of colloidal suspensions. Results are analyzed by a transient permeate flux model which includes an approximate closed-form analytical expression for the change of permeate flux with time. The model is based on a simplified particle mass balance for the early stages of crossflow filtration before a steady-state flux is attained, and Happel's cell model for the hydraulic resistance of the formed particle cake layer. The filtration experiments demonstrate that permeate flux declines faster with increasing feed particle concentration and transmembrane pressure and with a decrease in the particle size of the suspension. It is also shown that crossflow velocity (shear rate) has no effect on permeate flux at the transient stages of crossflow filtration. Pressure relaxation experiments indicate that the particle cake layer is reversible, implying no irreversible deposition (attachment) of particles onto the membrane surface or the accumulated (retained) particles. The experimental results are shown to be in very good agreement with the theoretical predictions, thus verifying the validity of the model for the transient permeate flux in crossflow filtration and the underlying assumptions in the derivation of the model.

Chloroform was treated with ultrasound at 35 and 283 kHz in a compound parabolic concentrators (CPCs) system to assess the applicability of ultrasound as a supporting process of solar-photocatalysis and verify the enhancement of ultrasound combined solar-photocatalysis. Chloroform was degraded by 22.5% in the Solar/TiO2process over a 200 min period. At an ultrasound frequency of 283 kHz, chloroform was degraded by 52.6% (Sono), 47.0% (Sono/TiO2) and 64.4% (Sono/Solar/TiO2). On the other hand, at 35 kHz, chloroform was degraded by 49.0% (Sono), 46.1% (Sono/TiO2) and 80.0% (Sono/Solar/TiO2). Ultrasound at 35 kHz was more effective for degrading chloroform in the Sono/Solar/TiO2process than 283 kHz. The rate of hydrogen peroxide formation, particle size and specific surface area of TiO2were measured to determine why 35 kHz is more effective than 283 kHz.