Ion exchange membrane cathodes for scalable microbial fuel cells

One of the main challenges for using microbial fuel cells (MFCs) is developing materials and architectures that are economical and generate high power densities. The performance of two cathodes constructed from two low-cost anion (AEM) and cation (CEM) exchange membranes was compared to that achieved using an ultrafiltration (UF) cathode, when the membranes were made electrically conductive using graphite paint and a nonprecious metal catalyst (CoTMPP). The best performance in single-chamber MFCs using graphite fiber brush anodes was achieved using an AEM cathode with the conductive coating facing the solution, at a catalyst loading of 0.5 mg/cm2 CoTMPP. The maximum power densitywas 449 mW/ m2 (normalized to the projected cathode surface area) or 13.1 W/m3 (total reactor volume), with a Coulombic efficiency up to 70% in a 50 mM phosphate buffer solution (PBS) using acetate. Decreasing the CoTMPP loading by 40-80% reduced power by 28-56%, with only 16% of the power (72 mW/m2) generated using an AEM cathode lacking a catalyst. Using a current collector (a stainless steel mesh) pressed against the inside surface of the AEM cathode and 200 mM PBS, the maximum power produced was further increased to 728 mW/m2 (21.2 W/m3). The use of AEM cathodes and brush anodes provides comparable performance to similar systems that use materials costing nearly an order of magnitude more (carbon paper electrodes) and thus represent more useful materials for reducing the costs of MFCs for wastewater treatment applications.     

Electricity generation using an air-cathode single chamber microbial fuel cell in the presence and absence of a proton exchange membrane

Microbial fuel cells (MFCs) are typically designed as a two-chamber system with the bacteria in the anode chamber separated from the cathode chamber by a polymeric proton exchange membrane (PEM). Most MFCs use aqueous cathodes where water is bubbled with air to provide dissolved oxygen to electrode. To increase energy output and reduce the cost of MFCs, we examined power generation in an air-cathode MFC containing carbon electrodes in the presence and absence of a polymeric proton exchange membrane (PEM). Bacteria present in domestic wastewater were used as the biocatalyst, and glucose and wastewater were tested as substrates. Power density was found to be much greater than typically reported for aqueous-cathode MFCs, reaching a maximum of 262 +/- 10 mW/m2 (6.6 +/- 0.3 mW/L; liquid volume) using glucose. Removing the PEM increased the maximum power density to 494 +/- 21 mW/m2 (12.5 +/- 0.5 mW/L). Coulombic efficiency was 40-55% with the PEM and 9-12% with the PEM removed, indicating substantial oxygen diffusion into the anode chamber in the absence of the PEM. Power output increased with glucose concentration according to saturation-type kinetics, with a half saturation constant of 79 mg/L with the PEM-MFC and 103 mg/L in the MFC without a PEM (1000 omega resistor). Similar results on the effect of the PEM on power density were found using wastewater, where 28 +/- 3 mW/m2 (0.7 +/- 0.1 mW/L) (28% Coulombic efficiency) was produced with the PEM, and 146 +/- 8 mW/m2 (3.7 +/- 0.2 mW/L) (20% Coulombic efficiency) was produced when the PEM was removed. The increase in power output when a PEM was removed was attributed to a higher cathode potential as shown by an increase in the open circuit potential. An analysis based on available anode surface area and maximum bacterial growth rates suggests that mediatorless MFCs may have an upper order-of-magnitude limit in power density of 10(3) mW/m2. A cost-effective approach to achieving power densities in this range will likely require systems that do not contain a polymeric PEM in the MFC and systems based on direct oxygen transfer to a carbon cathode.     

Effects of membrane cation transport on pH and microbial fuel cell performance

Due to the excellent proton conductivity of Nafion membranes in polymer electrolyte membrane fuel cells (PEMFCs), Nafion has been applied also in microbial fuel cells (MFCs). In literature, however, application of Nafion in MFCs has been associated with operational problems. Nafion transports cation species other than protons as well, and in MFCs concentrations of other cation species (Na+, K+, NH4+, Ca2+, and Mg2+) are typically 10(5) times higher than the proton concentration. The objective of this study, therefore, was to quantify membrane cation transport in an operating MFC and to evaluate the consequences of this transport for MFC application on wastewaters. We observed that during operation of an MFC mainly cation species other than protons were responsible for the transport of positive charge through the membrane, which resulted in accumulation of these cations and in increased conductivity in the cathode chamber. Furthermore, protons are consumed in the cathode reaction and, consequently, transport of cation species other than protons resulted in an increased pH in the cathode chamber and a decreased MFC performance. Membrane cation transport, therefore, needs to be considered in the development of future MFC systems.     

Power densities using different cathode catalysts (Pt and CoTMPP) and polymer binders (nafion and PTFE) in single chamber microbial fuel cells

Cathode catalysts and binders were examined for their effect on power densities in single chamber, air-cathode, microbial fuel cells (MFCs). Chronopotentiometry tests indicated thatthe cathode potential was only slightly reduced (20-40 mV) when Pt loadings were decreased from 2 to 0.1 mg cm(-2), and that Nafion performed better as a Pt binder than poly(tetrafluoroethylene) (PTFE). Replacing the precious-metal Pt catalyst (0.5 mg cm(-2); Nafion binder) with a cobalt material (cobalt tetramethylphenylporphyrin, CoTMPP) produced slightly improved cathode performance above 0.6 mA cm(-2), but reduced performance (<40 mV) at lower current densities. MFC fed batch tests conducted for 35 cycles (31 days) using glucose showed that replacement of the Nafion binder used for the cathode catalyst (0.5 mg of Pt cm(-2)) with PTFE reduced the maximum power densities (from 400 +/- 10 to 480 +/- 20 mW m(-2) to 331 +/- 3 to 360 +/- 10 mW m(-2)). When the Pt loading on cathode was reduced to 0.1 mg cm(-2), the maximum power density of MFC was reduced on average by 19% (379 +/- 5 to 301 +/- 15 mW m(-2); Nafion binder). Power densities with CoTMPP were only 12% (369 +/- 8 mW m(-2)) lower over 25 cycles than those obtained with Pt (0.5 mg cm(-2); Nafion binder). Power densities obtained using with catalysts on the cathodes were approximately 4 times more than those obtained using a plain carbon electrode. These results demonstrate that cathodes used in MFCs can contain very little Pt, and that the Pt can even be replaced with a non-precious metal catalyst such as a CoTMPP with only slightly reduced performance.     

Electrical power from sea and river water by reverse electrodialysis: a first step from the laboratory to a real power plant

Electricity can be produced directly with reverse electrodialysis (RED) from the reversible mixing of two solutions of different salinity, for example, sea and river water. The literature published so far on RED was based on experiments with relatively small stacks with cell dimensions less than 10 × 10 cm(2). For the implementation of the RED technique, it is necessary to know the challenges associated with a larger system. In the present study we show the performance of a scaled-up RED stack, equipped with 50 cells, each measuring 25 × 75 cm(2). A single cell consists of an AEM (anion exchange membrane) and a CEM (cation exchange membrane) and therefore, the total active membrane area in the stack is 18.75 m(2). This is the largest dimension of a reverse electrodialysis stack published so far. By comparing the performance of this stack with a small stack (10 × 10 cm(2), 50 cells) it was found that the key performance parameter to maximal power density is the hydrodynamic design of the stack. The power densities of the different stacks depend on the residence time of the fluids in the stack. For the large stack this was negatively affected by the increased hydrodynamic losses due to the longer flow path. It was also found that the large stack generated more power when the sea and river water were flowing in co-current operation. Co-current flow has other advantages, the local pressure differences between sea and river water compartments are low, hence preventing leakage around the internal manifolds and through pinholes in the membranes. Low pressure differences also enable the use of very thin membranes (with low electrical resistance) as well as very open spacers (with low hydrodynamic losses) in the future. Moreover, we showed that the use of segmented electrodes increase the power output by 11%.     

磺化聚醚砜纳米纤维复合质子交换膜的制备及其性能

为开发燃料电池用高性能全氟磺酸(Nafion)质子交换膜,采用静电纺丝技术制备不同磺化度的磺化聚醚砜(SPES)纳米纤维,将其作为添加剂引入Nafion基体中,制备SPES纳米纤维/Nafion复合质子交换膜。探讨纺丝液浓度、纺丝电压、接收距离对SPES纳米纤维纺丝过程及纤维形貌的影响。在最优纺丝工艺下,着重研究不同磺化度SPES纳米纤维对复合膜微观结构、吸水率、溶胀率、质子传导率及甲醇渗透率等性能的影响。结果表明:在SPES质量分数为30%,纺丝电压为30 kV,接收距离为20 cm条件下制得磺化度为64%的SPES纳米纤维,将其作为添加剂构筑得到复合Nafion质子交换膜,该膜具有平衡的质子传导(0.144 S/cm)与甲醇渗透性(7.58×10^-7 cm²/s),综合性能最佳,满足高性能甲醇燃料电池的应用需求。     

A bipolar membrane combined with ferric iron reduction as an efficient cathode system in microbial fuel cells

There is a need for alternative catalysts for oxygen reduction in the cathodic compartment of a microbial fuel cell (MFC). In this study, we show that a bipolar membrane combined with ferric iron reduction on a graphite electrode is an efficient cathode system in MFCs. A flat plate MFC with graphite felt electrodes, a volume of 1.2 L and a projected surface area of 290 cm2 was operated in continuous mode. Ferric iron was reduced to ferrous iron in the cathodic compartment according to Fe(3+) + e(-) --> Fe2+ (E0 = +0.77 V vs NHE, normal hydrogen electrode). This reversible electron transfer reaction considerably reduced the cathode overpotential. The low catholyte pH required to keep ferric iron soluble was maintained by using a bipolar membrane instead of the commonly used cation exchange membrane. For the MFC with cathodic ferric iron reduction, the maximum power density was 0.86 W/m2 at a current density of 4.5 A/m2. The Coulombic efficiency and energy recovery were 80-95% and 18-29% respectively.     

Atmospheric HFEs degradation in the gas phase: reactions of HFE-7100 and HFE-7200 with Cl atoms at low temperatures

Kinetic rate coefficients for the reactions of HFE-7100 (1) (C4F9OCH3) and HFE-7200 (2) (C4F9OC2H5) with Cl atoms have been measured using a discharge flow mass spectrometric technique (DFMS) at 1 Torr total pressure. The reactions have been studied under pseudo-first-order kinetic conditions in excess of HFEs over Cl atoms and the study has been extended from 333 down to 234 K to approach the tropospheric temperature profile. At room temperature the measured rate constants are k (1) = (1.43 +/- 0.28) x 10(-13) cm3molecule(-1)s(-1) and k (2) = (2.1 +/- 0.1) x 10(-12) cm3molecule(-1)s(-1). The Arrhenius expressions from our results are (units in cm3molecule(-1)s(-1)): k (1) = (2.3 +/- 1.4) x 10(-10) exp - (2254 +/- 177)/T(234-315 K) and k (2) = (3.7 +/- 0.5) x 10(-11) exp - (852 +/- 38)/T(234-333 K) (errors are sigma). The reactions proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.88 +/- 0.09 and 0.95 +/- 0.10 (errors are 2sigma) were obtained for HFE-7100 and HFE-7200 reactions, respectively.     

Study of the OH and Cl-initiated oxidation, IR absorption cross-section, radiative forcing, and global warming potential of four C4-hydrofluoroethers

Infrared absorption cross-sections and OH and Cl reaction rate coefficients for four C4-hydrofluoroethers (CF3)2CHOCH3, CF3CH2OCH2CF3, CF3CF2CH2OCH3, and CHF2CF2CH2OCH3 are reported. Relative rate measurements at 298 K and 1013 hPa of OH and Cl reaction rate coefficients give k(OH+(CF3)2CHOCH3) = (1.27+/-0.13) x 10(-13), k(OH+CF3CH2OCH2CF3) = (1.51+/-0.24) x 10(-13), k(OH+CF3CF2CH2OCH3) = (6.42+/-0.33) x 10(-13), k(OH+CHF2CF2CH2OCH3) = (8.7 +/-0.5) x 10(-13), k(Cl+(CF3)2CHOCH3) = (8.4+/-1.3) x 10(-12), k(Cl+CF3CH2OCH2CF3) = (6.5+/-1.7) x 10(-13), k(Cl+CF3CF2CH2OCH3) = (4.0+/-0.8) x 10(-11), and k(Cl+CHF2CF2CH2OCH3) = (2.65+/-0.17) x 10(-11) cm3 molecule(-1) s(-1). The primary products of the OH and Cl reactions with the fluorinated ethers have been identified as esters, and OH and Cl reaction rate coefficients for one of these, CF3CH2OCHO, are reported: k(OH+CF3CH2OCHO) = (7.7+/-0.9) x 10(-14) and kCl+CF3CH2OCHO) = (6.3+/-1.9) x 10(-14) cm3 molecule(-1) s(-1) The rate coefficient for the Cl-atom reaction with CHF2CH2F is derived as k(Cl+CHF2CH2F) = (3.0+/-0.9) x 10(-14) cm3 molecule(-1) s(-1) at 298 K. The error limits include 3sigma from the statistical data analyses as well as the errors in the rate coefficients of the reference compounds employed. The tropospheric lifetimes of the hydrofluoroethers are estimated to be short tauOH((CF3)2CHOCH3) approximately 100 days, tauOH(CF3CH2OCH2CF3) approximately 80 days, tauOH(CF3CF2CH2OCH3) approximately 20 days, and tauOH(CHF2CF2CH2OCH3) approximately 14 days, and their global warming potentials are small compared to CFC-11.     

氧化石墨烯量子点/聚丙烯腈纳米纤维复合质子交换膜的制备及其性能

为提高全氟磺酸(Nafion)膜的质子传导率和尺寸稳定性,利用静电纺丝技术制备了氧化石墨烯量子点(GOQDs)/聚丙烯腈(PAN)纳米纤维膜,并通过Nafion溶液浸渍法制备了纳米纤维复合质子交换膜。借助扫描电子显微镜、共聚焦显微镜、热重分析仪和X射线衍射仪等对纳米纤维及复合膜的结构和性能进行表征。结果表明:GOQDs在PAN纳米纤维中均匀分布,GOQDs的加入减小了纳米纤维的直径;纳米纤维形成三维网络结构,对复合膜起到了骨架支撑作用,提高了复合膜的尺寸稳定性,同时提高了复合膜的热稳定性和吸水性;GOQDs质量分数的增加提高了复合膜的质子传导率,80 ℃时复合膜的质子传导率最高可达0.182 S/cm。     

Selective coagulant recovery from water treatment plant residuals using Donnan membrane process

Fouling of membrane surfaces by particulate matter and large organic molecules is relatively common for pressure-driven membrane processes, namely, reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF). Donnan membrane process (DMP) or Donnan Dialysis is driven by electrochemical potential gradient across a semipermeable ion exchange membrane. Theoretically, DMP is not susceptible to fouling by fine particulates and/or large organic molecules. According to information available in the open literature, however, DMP has not been tried to treat slurry or sludge with relatively high concentration of suspended solids or large organic molecules. This study presents the salient results of an extensive investigation pertaining to selective alum recovery from water treatment residuals (WTR) using DMP. Water treatment plants use alum, Al2(SO4)3 x 14H2O, as a coagulant, alum being finally converted and discharged as insoluble aluminum hydroxide along with natural organic matters (NOM), suspended solids, and other trace impurities. One commercial cation exchange membrane, namely Nafion 117 from DuPont Chemical Co., was used in the study for treating WTR obtained from two different water treatment plants in Pennsylvania. A series of laboratory tests confirmed that over 70% of alum is easily recoverable, and recovered alum is essentially free of particulate matter, NOM, and other trace metals. Most importantly, after repeated usage in the presence of high concentration of NOM and suspended solids, there was no noticeable decline in aluminum flux through the membrane, i.e., membrane surface fouling was practically absent. The DMP process involves coupled transport of Al3+ and H+ across the cation exchange membrane, and intramembrane transport was the rate-limiting step. Experimentally determined aluminum-hydrogen interdiffusion coefficient (D(Al-H)) values within the membrane were quite high (approximately 10(-6) cm2/s) under representative conditions, thus confirming high alum recovery rate. DMP was also found equally effective in recovering Fe(III) based coagulants from WTR.     

Cathode performance as a factor in electricity generation in microbial fuel cells

Although microbial fuel cells (MFCs) generate much lower power densities than hydrogen fuel cells, the characteristics of the cathode can also substantially affect electricity generation. Cathodes used for MFCs are often either Pt-coated carbon electrodes immersed in water that use dissolved oxygen as the electron acceptor or they are plain carbon electrodes in a ferricyanide solution. The characteristics and performance of these two cathodes were compared using a two-chambered MFC. Power generation using the Pt-carbon cathode and dissolved oxygen (saturated) reached a maximum of 0.097 mW within 120 h after inoculation (wastewater sludge and 20 mM acetate) when the cathode was equal size to the anode (2.5 x 4.5 cm). Once stable power was generated after replacing the MFC with fresh medium (no sludge), the Coulombic efficiency ranged from 63 to 78%. Power was proportional to the dissolved oxygen concentration in a manner consistent with Monod-type kinetics, with a half saturation constant of K(DO) = 1.74 mg of O2/L. Power increased by 24% when the cathode surface areas were increased from 22.5 to 67.5 cm2 and decreased by 56% when the cathode surface area was reduced to 5.8 cm2. Power was also substantially reduced (by 78% to 0.02 mW) if Pt was not used on the cathode. By using ferricyanide instead of dissolved oxygen, the maximum power increased by 50-80% versus that obtained with dissolved oxygen. This result was primarily due to increased mass transfer efficiencies and the larger cathode potential (332 mV) of ferricyanide than that obtained with dissolved oxygen (268 mV). A cathode potential of 804 mV (NHE basis) is theoretically possible using dissolved oxygen, indicating that further improvements in cathode performance with oxygen as the electron acceptor are possible that could lead to increased power densities in this type of MFC.     

Continuous electricity generation at high voltages and currents using stacked microbial fuel cells

Connecting several microbial fuel cell (MFC) units in series or parallel can increase voltage and current; the effect on the microbial electricity generation was as yet unknown. Six individual continuous MFC units in a stacked configuration produced a maximum hourly averaged power output of 258 W m(-3) using a hexacyanoferrate cathode. The connection of the 6 MFC units in series and parallel enabled an increase of the voltages (2.02 V at 228 W m(-3)) and the currents (255 mA at 248 W m(-3)), while retaining high power outputs. During the connection in series, the individual MFC voltages diverged due to microbial limitations at increasing currents. With time, the initial microbial community decreased in diversity and Gram-positive species became dominant. The shift of the microbial community accompanied a tripling of the short time power output of the individual MFCs from 73 W m(-3) to 275 W m(-3), a decrease of the mass transfer limitations and a lowering of the MFC internal resistance from 6.5 +/- 1.0 to 3.9 +/- 0.5 omega. This study demonstrates a clear relation between the electrochemical performance and the microbial composition of MFCs and further substantiates the potential to generate useful energy by means of MFCs.     

Challenges and constraints of using oxygen cathodes in microbial fuel cells

The performance of oxygen reduction catalysts (platinum, pyrolyzed iron(ll) phthalocyanine (pyr-FePc) and cobalt tetramethoxyphenylporphyrin (pyr-CoTMPP)) is discussed in light of their application in microbial fuel cells. It is demonstrated that the physical and chemical environment in microbial fuel cells severely affects the thermodynamics and the kinetics of the electrocatalytic oxygen reduction. The neutral pH in combination with low buffer capacities and low ionic concentrations strongly affect the cathode performance and limit the fuel cell power output. Thus, the limiting current density in galvanodyanamic polarization experiments decreases from 1.5 mA cm(-2) to 0.6 mA cm(-2) (pH 3.3, E(cathode) = 0 V) when the buffer concentration is decreased from 500 to 50 mM. The cathode limitations are superposed by the increasing internal resistance of the MFC that substantially contributes to the decrease of power output. For example, the maximum power output of a model MFC decreased by 35%, from 2.3 to 1.5 mW, whereas the difference between the electrode potentials (deltaE = E(anode) - E(cathode)) decreased only by 10%. The increase of the catalyst load of pyr-FePc from 0.25 to 2 mg cm(-2) increased the cathodic current density from 0.4 to 0.97 mA cm(-2) (pH 7, 50 mM phosphate buffer). The increase of the load of such inexpensive catalyst thus represents a suitable means to improve the cathode performance in microbial fuel cells. Due to the low concentration of protons in MFCs in comparison to relatively high alkali cation levels (ratio C(Na+,K+)/C(H+) = 5 x E5 in pH 7, 50 mM phosphate buffer) the transfer of alkali ions through the proton exchange membrane plays a major role in the charge-balancing ion flux from the anodic into the cathodic compartment. This leads to the formation of pH gradients between the anode and the cathode compartment.     

Atmospheric chemistry of 2-ethoxy-3,3,4,4,5-pentafluorotetrahydro-2,5-bis[1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl]-furan: kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of the title compound which we refer to as RfOC2H5. Rate constants of k(Cl + RfOC2H5) = (2.70 +/- 0.36) x 10(-12), k(OH + RfOC2H5) = (5.93 +/- 0.85) x 10(-14), and k(Cl + RfOCHO) = (1.34 +/- 0.20) x 10(-14) cm3 molecule(-1') s(-1) were measured in 700 Torr of N2, or air, diluent at 294 +/- 1 K. From the value of k(OH + RfOC2H5) the atmospheric lifetime of RfOC2H5 was estimated to be 1 year. Two competing loss mechanisms for RfOCH(O*)CH3 radicals were identified in 700 Torr of N2/O2 diluent at 294 +/- 1 K; decomposition via C-C bond scission giving a formate (RfOCHO), or reaction with 02 giving an acetate (RfOC(O)CH3). In 700 Torr of N2/O2 diluent at 294 +/- 1 K the rate constant ratio k(O2)/k(diss) = (1.26 +/- 0.74) x 10(-19) cm3 molecule(-1). The OH radical initiated atmospheric oxidation of RfOC2H5 gives Rf0CHO and RfOC(O)CH3 as major products. RfOC2H5 has a global warming potential of approximately 55 for a 100 year horizon. The results are discussed with respect to the atmospheric chemistry and environmental impact of RfOC2H5.     

Membrane technology in degumming, dewaxing, deacidifying, and decolorizing edible oils

A membrane process offers several advantages over the conventional method of oil refining. Conceptually, membranes could be used in almost all stages of processing. In the present review, various attempts made by the researchers towards degumming, dewaxing, deacidifying, and decolorizing edible oils using membrane technology with and without using solvents have been discussed. Attempts made with UF and nonporous membranes have demonstrated the ability of these membranes to separate phospholipids from undiluted and hexane-diluted oils and a high oil flux was obtained with UF membranes in hexane-diluted oils. MF membranes were very effective for dewaxing undiluted oils while UF membranes were effective in dewaxing hexane-diluted oils without a precooling step. Deacidification was successful only with either addition of an alkali followed by membrane filtration or by following an indirect route of selective solvent extraction of FFA followed by membrane separation. Consistent color reduction in terms of pigments (chlorophyll and xanthophylls) and other instrumental measurements (Lovibond and visible spectra) could be achieved only with nonporous membranes. Interestingly, these membranes did not have selectivity for alpha-and beta-carotenes. UF membranes are best suited for degumming and dewaxing applications, while nonporous membranes appear to be a better choice for achieving simultaneous degumming, dewaxing, and decolorization of oils. Hexane-dilution improved the oil flux of nonporous membranes by one order of magnitude, but further improvement is desirable for industrial adoption.     

Improvement of a sustainable hybrid technology for caseins isoelectric precipitation (electrodialysis with bipolar membrane/ultrafiltration) by mitigation of scaling on cation-exchange membrane

Electroacidification of milk by electrodialysis with bipolar membranes (EDBM) can be performed to produce isoelectric precipitated casein. In spite of advantages of EDBM, a problem of fouling hampers the industrial application of this technology. There are two types of fouling occurring during milk electroacidification such as protein fouling inside the EDBM stack and scaling on cation-exchange membrane (CEM). Recent studies demonstrated that protein fouling can be avoided by coupling an EDBM module with an ultrafiltration (UF) module. The present study aims the mitigation of scaling on the CEM. In order to attain this goal, two approaches were tested: 1) addition of KCl in the milk reservoir and 2) use of a UF membrane allowing higher permeate flux and consequently higher flow rates of solutions in the EDBM stack. Results of this study demonstrate the reasonableness of both approaches resulting in the significant decrease of CEM scaling (more than 30%).Industrial RelevanceCaseins are the major milk proteins largely produced in the world (around 330 000 t per year) and widely applied in the food and pharmaceuticals industries. There are several relevant features of proposed method (electrodialysis with bipolar membranes coupled with ultrafiltration (EDBM-UF)) for the casein production such as

• 1)absence of the hazardous reagents;
• 2)high purity of caseins due to the demineralization during EDBM;
• 3)no waste generation;
• 4)the base stream from EDBM module (co-product) can be used for the formation of caseinates.

The present work demonstrates the significant decrease of scaling on the cation-exchange membrane (more than 30%), which is the major problem of the EDBM-UF process. Indeed, during milk acidification, there is a liberation of minerals (Ca^2 + and Mg^2 +), which form the membrane deposit. This deposit negatively affects the process performance and leads to the membrane replacement. The cost of ion-exchange membranes in ED module comprises a major part of the total cost of EDBM-UF process. Thus, control and prevention of the membrane deposit will allow to increase a lifetime of ion-exchange membranes and to decrease a price of EDBM-UF treatment.     

Changes in functional properties of common carp (Cyprinus carpio) myofibrillar protein as affected by ultrasound-assisted freezing

Ultrasound-assisted freezing (UF) has proven to be a method that can effectively increase the freezing rate of frozen food and improve its quality. The functional properties of myofibrillar proteins (MP) are important factors that affect the further processing quality of meat products. At present, the effect of UF on the functional properties of frozen MP is not yet clear. Therefore, in the present study, changes in the functional properties (emulsifying and gel properties) of MP in common carps (Cyprinus carpio) frozen with UF at different power levels were investigated. The results revealed that, compared with immersion freezing (IF), UF at 175 W (UF-175) effectively inhibited the decrease in protein solubility, absolute Zeta potential, emulsion activity index, storage modulus (G'), and loss modulus (G'') caused by freezing. UF-175 sample had lower protein turbidity, and smaller protein particle size than any other frozen samples (P < 0.05), which suggested that UF-175 inhibited protein aggregation induced by freezing. In addition, shorter T₂₁ and T₂₂ relaxation times were obtained in UF-175 sample than other frozen samples, indicating that UF-175 reduced the mobility of immobilized and free water. Accordingly, UF-175 sample had higher gel strength and water holding capacity than other frozen samples (P < 0.05). A denser and more uniform gel network structure was also found in UF-175 sample than other frozen samples. In general, improved functional properties of common carp MP can be achieved by optimal UF.     

Membrane Clarification of Black Tea Extracts

Microfiltration (MF; 200 and 450 nm) and ultrafiltration (UF; 25, 50, 100 and 500 kDa) membranes were assessed for the clarification of black tea extracts. Rejection of tea components including cream components increased with decrease in membrane pore size. Clarity of membrane processed extracts was excellent (～4 Nephelometric Turbidity Units) even after 30 days of refrigerated storage. UF-500 and MF membranes resulted in greater retention of original colour, besides greater recovery of tea solids including polyphenols in the clarified extract. Increase in feed concentration affected the recovery while diafiltration improved the solids recovery including polyphenols and theaflavins. Highest productivity was achieved at 2 % feed concentration followed by 0.6 %. Solids and polyphenols recoveries obtained with 0.6 % feed concentration and MF-450 membrane combination were unmatched with any other combination. The results favoured employing MF as a means of clarification of tea extracts, preferably at low feed concentration which provided greater recovery and productivity, adequately meeting the quality requirements of ready-to-drink tea beverages.     

Recovery and purification of potato proteins from potato starch wastewater by hollow fiber separation membrane integrated process

Potato starch wastewater contains high-concentration potato proteins which have great potential in the fields of food and health care. Most researches on potato protein recovery by membrane separation technique are focused on flat sheet or tubular ultrafiltration (UF) and reverse osmosis (RO) membranes and lack the further protein purification and the in-depth discussions on the fouling behavior. In this laboratory-scale study, potato proteins were recovered and purified from the simulated potato starch wastewater by the self-made hollow fiber (HF) UF and nanofiltration (NF) separation membrane integrated process. 85.62% potato proteins with high molecular weight in the potato starch wastewater could be retained by UF membrane and 92.1% potato proteins with low molecular weight were rejected by NF membrane. The concentrated solution after UF and NF filtration was desalinated and purified by diluting the solution eight times and filtering the diluted solution with UF membrane. Both types of HF membranes, UF and NF, suffered the inevitable membrane fouling. After the traditional physical washing and chemical cleaning, water flux of UF and NF membranes can be effectively recovered. The corresponding recovery rates of UF and NF membranes can reach 93.5% and 84.7%, respectively. The hollow fiber UF-NF separation membrane integrated process was proved to be a promising technique of high-purity potato protein recovery from potato starch wastewater.