Fundamental water and salt transport properties of polymeric materials

Fundamental water and salt transport properties of polymers are critical for applications such as reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), and membrane capacitive deionization (MCDI) that require controlled water and salt transport. Key developments in the field of water and salt transport in polymer membranes are reviewed, and a survey of polymers considered for such applications is provided. Many polymers considered for such applications contain charged functional groups, such as sulfonate groups, that can dissociate in the presence of water. Water and ion transport data from the literature are reviewed to highlight the similarities and differences between charged and uncharged polymers. Additionally, the influence of other polymer structure characteristics, such as cross-linking and morphology in phase separated systems, on water and salt transport properties is discussed. The role of free volume on water and salt transport properties is discussed. The solution–diffusion model, which describes the transport of water and ions in nonporous polymers, is used as a framework for discussing structure/property relations in polymers related to water and salt transport properties. Areas where current knowledge is limited and opportunities for further research are also noted.     

The significance of cooling rate on water dynamics in porcine muscle from heterozygote carriers and non-carriers of the halothane gene-a low-field NMR relaxation study

The post mortem changes in the chemical/physical state distribution of water were followed in pig muscle (M. longissimus dorsi) from heterozygote (n=12) and non-carriers (n=12) of the halothane gene exposed to two different cooling profiles using continuous low-field NMR relaxation measurements. T₂ relaxation data were analyzed using distributed exponential fitting analysis. Independent of genotype post mortem changes were observed in the two water populations characterizing water within the myofibrillar space (T₂₁) and the extra-myofibrillar space (T₂₂), respectively, as a function of chilling regime. The effect was most pronounced in samples from heterozygote carriers of the halothane gene. The obtained results strongly suggest that improved water-holding capacity of muscles upon fast chilling can be ascribed to a reduced accumulation of extra-myofibrillar water in the meat post mortem, and it is hypothesized that differences in the accumulation of extra-myofibrillar water post mortem can be ascribed largely to the time at which disruption of cell membrane integrity takes place.     

Ammonia removal by sweep gas membrane distillation

Wastewater containing low levels of ammonia (100 mg/L) has been simulated in experiments with sweep gas membrane distillation at pH 11.5. The effects of feed temperature, gas flow rate and feed flow rate on ammonia removal, permeate flux and selectivity were investigated. The feed temperature is a crucial operating factor, with increasing feed temperature increasing the permeate flux significantly, but reducing the selectivity. The best-performing conditions of highest temperature and fastest gas flow rate resulted in 97% removal of the ammonia, to give a treated water containing only 3.3 mg/L of ammonia.     

Role of the glass transition temperature of Nafion 117 membrane in the preparation of the membrane electrode assembly in a direct methanol fuel cell (DMFC)

The glass transition temperature (T_g) of the Nafion 117 membrane was traced by DSC step by step during the preparation of the membrane electrode assembly (MEA). Wide-angle x-ray diffraction and frequency response analysis were used for the determination of the crystallinity and proton conductivity of the membrane. As-received Nafion 117 membrane showed two glass transition temperatures in the DSC thermogram. The first T_g, caused by the mobility of the main chain in the polymer matrix, was 125 °C; the second T_g, derived from the side chain due to the strong interaction between the sulfonic acid functional groups, was 195 °C. During the pretreatment of the membrane, the T_g of the Nafion 117 membrane drastically decreased because of the plasticizer effect of water. In the hot-pressing process, the T_g of the Nafion 117 membrane gradually increased due to the loss of water. When the Nafion 117 was completely dried, the T_g of the membrane finally reached 132 °C. Thermal heat treatment was then applied to the MEA to obtain high interfacial stability; however, the membrane developed a crystalline morphology that led to reduced water uptake and proton conductivity. Therefore, the thermal heat treatment of the MEA should be carefully controlled in the region of the glass transition temperature (120–140 °C) of the Nafion 117 membrane to ensure the high performance of the MEA.     

THE FABRICATION AND PERFORMANCE OF CELLULOSE REVERSE OSMOSIS MEMBRANES

A method for the fabrication of reverse osmosis membranes made from cellulose material is reported along with their performance data with respect to the separation of single electrolyte solutes from their aqueous solutions. The separation depends on the charge and the valence of the ions involved as well as the porosity of the membrane. The larger rejection for electrolytes involving negative ions of higher valence is attributed to a net negative charge on the surface of the membrance. Further, it was found that the solute separation decreases with an increase of feed solute concentration, which is also attributable to the charge on the membrane surface.     

Effect of mechanical cleaning with granular material on the permeability of submerged membranes in the MBR process

The research on fouling reduction and permeability loss in membrane bioreactors (MBRs) was carried out at two MBR pilot plants with synthetic and real wastewater. On the one hand, the effect of mechanical cleaning with an abrasive granular material on the performance of a submerged MBR process was tested. Additionally, scanning electron microscopy (SEM) measurements and integrity tests were conducted to check whether the membrane material was damaged by the granulate.The results indicate that the fouling layer formation was significantly reduced by abrasion using the granular material. This technique allowed a long-term operation of more than 600 days at a flux up to 40 L/(m² h) without chemical cleaning of the membranes. Moreover, it was demonstrated that the membrane bioreactor (MBR) with granulate could be operated with more than 20% higher flux compared to a conventional MBR operation. SEM images and integrity tests showed that in consequence of abrasive cleaning, the granular material left brush marks on the membrane surface, however, the membrane function was not affected.In a parallel experimental set up, the impact of the operationally defined “truly soluble fraction” <0.04 μm from wastewater and activated sludge on the ultrafiltration membrane fouling characteristics was investigated. It was shown that the permeability loss was caused predominantly by the colloidal fraction >0.04 μm rather than by the dissolved fraction of wastewater and activated sludge.     

Performance of a PEM electrolyzer using RuIrCoOx electrocatalysts for the oxygen evolution electrode

The Proton Exchange Membrane Water Electrolyzer (PEMWE) can be coupled to renewable energy sources (solar radiation and wave energy), which produce the necessary electricity for splitting the water. In this work the performance of a PEMWE using RuIrCoO_x as anodic electrocatalyst had been examined. The oxide powder was synthesized using a chemical reduction method, followed by thermal oxidation. The electrochemical properties of the electrocatalysts were examined by cyclical and lineal voltammetry in 0.5 M H₂SO₄. It was found that RuIrCoO_x oxide electrodes present a stable performance for OER. The PEMWE was designed and in-home built. Chrono-potentiometric experiments were recorded in the current range of 0.25 mA cm⁻² to 75 mA cm⁻² at 300 s. The current pulses length is chosen to be sufficiently long so that the voltage remains constant. Their intrinsic electrocatalytic activity in combination with their large surface area and stability are quite promising for the development of economically feasible electrocatalysts for (PEMWE).     

贫营养条件下膜生物反应器污泥减量化研究

主要针对贫营养条件下膜生物反应器（membrane bioreactor,MBR）污泥减量化进行研究,在封闭条件下对MBR污泥进行为期16 d的监测。实验期间主要针对污泥浓度及污泥活性进行了定期取样分析,采用修正的污染指数（modified fouling index,MFI）对污泥混合液可滤性进行评价。实验结果表明,长时间的内源呼吸过程将加速降低污泥活性及强化污泥混合液可滤性的恶化;短时间内源呼吸过程将改善污泥混合液可滤性,有利于MBR工艺实现污泥减量化。     

一体式膜生物反应器中生活污水的处理

利用一体式膜生物反应器对生活污水的处理进行了研究。结果表明,出水COD稳定,平均COD去除率达96%以上;NH4+—N的去除率受pH影响较大,当硝化好氧段pH为6.5~7.0时,NH4+—N的平均去除率高达99%以上,当硝化好氧段pH为4.7~5.8时,NH4+—N的平均去除率降为85%左右;系统运行期间污泥的质量浓度先由启动时的6 g/L降低到5 g/L,而后随着系统的运行呈增长趋势,试验结束时增长到8.14 g/L;粘度不随系统运行而增大,而是呈下降趋势,最终稳定在2.1 mPa.s左右。     

无机膜回收硫酸法钛白生产中偏钛酸的研究

膜分离技术是近几十年迅速发展的新型分离技术.采用具有优异的化学稳定性、热稳定性及高机械强度等特点的无机膜进行溶液中微米及亚微粒子的分离,在化学工业、石油化工等高温、腐蚀性环境下,有其独特的优势.以无机盐生产过程中微米和亚微米粒子的液固分离为工业背景,对α-Al2O3陶瓷微滤膜回收硫酸法钛白生产酸性废水中的偏钛酸粒子进行了研究,考察了陶瓷微滤膜处理钛白废水过程的工艺参数对过程的影响,确定了合适的操作参数及有效的膜污染控制和清洗方法,为该技术的工业化应用奠定了基础,使无机膜回收偏钛酸技术的工业化进程又推进了一步,同时本研究为微米及微米粒子的液固分离特别是苛刻体系条件下的分离提供了一条新途径.