Entsalzung von Umkehrosmosekonzentraten mittels elektrisch getriebenen Membranverfahren zur Maximierung der Permeatausbeute einer Prozesswasseraufbereitungsanlage

Worldwide present water stress situations lead to the necessity to use alternative water sources like brackish water or wastewater. To enable this, new desalination technologies like electrically driven membrane processes have to be implemented. These technologies were used to desalinate the reverse osmosis concentrate of a process water treatment plant up to a certain point, at which the resulting diluate could be used as feed water for the reverse osmosis. As a result, the concentrate volume to be discharged was halved and the permeate yield of the overall plant was increased. A focus was set on the required energy consumption for the additional treatment step.     

Separation of mixed salts(Cl~-/SO_4~(2-)) by ED based on monovalent anion selective membranes

The industrial products or wastewater rich in the mixed salts(Cl~-/SO_4~(2-)) not only causes the environmental damage, but also induces waste of resource. In this study, an ED stack with monovalent selective AEMs and conventional CEMs was employed to separate the Cl~-and SO_4~(2-)from simulated wastewater. The effect of current density and mass fraction percentage was investigated in order to optimize the experimental conditions during ED process. It was found that at a concentration ratio between NaCl and Na_2SO_4 of 95/5(wt%/wt%) and a current density of40 m A·cm~(-2), a current efficiency of 72%, an energy consumption of 1.6 k W·h·kg~(-1) Na Cl and a Cl~-/SO_4~(2-)concentration(67.5/3.5 g·L~(-1)) were obtained. Hence, it is appropriate and effective to separate Cl~-and SO_4~(2-)by ED using the monovalent selective AEMs.     

Investigation of the adsorption and transport of natural organic matter (NOM) in ion-exchange membranes

The adsorption and transport characteristics of natural organic matter (NOM) in an ion-exchange (IX) membrane were investigated and the various methods to characterize the properties of NOM and the IX membrane were collectively evaluated in this study. NOM adsorption by an IX membrane is affected by both pH and ion strength. Under alkaline pH and low ionic strength, greater NOM adsorption can be expected. A good relationship was obtained between the amount of adsorbed NOM and the zeta potential. The NOM acids constituents are expected to be transported preferentially through an IX membrane during the electrodialysis (ED) process because of their negative charge density. However, the molecular mass of the NOM acids was too high to allow them to pass through the IX membrane pores, and this caused an accumulation or adsorption of the solutes on the membrane surface. A fractional-rejection method was applied to determine the apparent pore size distribution of IX membranes and the selectivity coefficient was used to calculate apparent charges of NOM. The major apparent pore size distribution (PDS) of the IX membrane used in this study lay in the range 100-200 mass units. The apparent charge of the NOM used was 5.5 (dimensionless).     

The effect of temperature on limiting current density and mass transfer in electrodialysis

This study focuses on a high-temperature operation in electrodialysis of salt solutions and studies the effect of temperature on limiting current density and mass transfer. Experiments were conducted under various conditions of temperature (T), varying from 15 to 90°C; of dialysate concentration (C_d), varying from 5 × 10^?3 to 3 × 10^?2M ; and of dialysate velocity (u_d), varying from 0.206 to 2.44 cm s^?1. A least squares fitting of the experimental data on limiting current density (I_lim) yields an Arrhenius equation as follows: The molar flux N? (mol cm^?2 s^?1), initial concentration (C₀; M ) and temperature (T; °C) were found to have the following relationship: N?/C₀ is slightly increased with increasing temperature ranging from 25 to 70°C.     

Improved antifouling of anion-exchange membrane by polydopamine coating in electrodialysis process

The fouling, in particular the organic fouling of anion exchange membranes (AEMs), is a serious problem in electrodialysis (ED). In this paper, we attempted to improve the antifouling potential of AEM by surface modification with polydopamine (PDA). The antifouling potential was evaluated by the transition time, i.e. the time elapsed before fouling took place, using sodium dodecyl benzene sulfonate (SDBS) as a model foulant. The negative surface charge density, hydrophilicity and roughness of the membrane surface were increased with increasing dopamine concentration in the modification solution. The increases in negative surface charge density and hydrophilicity increased the antifouling potential, while the increase in surface roughness decreased the antifouling potential. Consequently, the optimum modification condition was the immersion into a 0.1 kg/m³ dopamine aqueous solution at pH 8.8 for 24 h. Under this condition, the antifouling potential of AEM was sufficiently improved. It was shown by theoretical analysis of the fouling data that the surface modification with PDA prevented the adsorption of SDBS micelles and improved the antifouling potential. Furthermore, it was experimentally confirmed that the modified membrane was highly stable.     

Desalination of underground brackish waters using an electrodialysis system powered directly by photovoltaic energy

The aims of this paper are: to demonstrate the feasibility of the desalination of brackish water from aquifers (total dissolved solids=2300-5100 g m⁻³) by means of an electrodialysis system powered directly by photovoltaic solar panels, and improve the mathematical model developed in a previous work in order to apply it to real brackish waters. The application of this model allows to predict the behaviour of the electrodialysis-photovoltaic system under different operational and meteorological conditions, and the time required to reach a given final concentration. Finally, the cost of electrodialysis-photovoltaic systems for small applications in isolated locations with lack of electric grid has been estimated.     

电渗析在化工行业中应用展望

简要介绍近几年电渗析技术在化工领域中浓缩海水制盐，纯水技术，化工过程等方面的研究和应用情况。     

Early days in electrodialysis

The author reflects on the development of the electrodialysis process for desalination from its early days in the 1950s.     

Electrodialysis desalination designed for off-grid wind energy

An electrodialysis desalination plant has been set up and tested to treat brackish water while driven from an off grid wind energy system. The tests were carried out in the framework of a wider scope project, located on Gran Canaria Island (Spain). The main goal of this project was to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off grid wind farm. After having previously analysed the behaviour of the system on-grid, the following stage was to develop an operational envelope for the electrodialysis reversal (EDR) unit while operating off grid, i.e., only coupled to the wind farm. The unit included power converters for the membrane stacks (DC-drivers) and variable frequency drivers (VFD) for the feed pumps. The tests were carried out to establish the power intervals for the EDR unit depending on the product flow rate specified as well as water quality. Product flow rate between 3 and 8.5 m³/h, power requirements between 4 and 19 kW, while product water conductivity ranged between 200 and 500 μS/cm were recorded. The desalination unit showed good flexibility, adapting smoothly to variations in wind power, even when sudden drops or rises occurred. The control system, slightly modified from a standard design, can cope with such sudden variations. Good agreement between performance predicted with software and the actual operating performance was observed. The presence of harmonics in the electric system due to DC drivers and VFD became harmful for the control and electric system, and care must be taken through appropriate mitigating measures.     

超滤和电渗析联合处理含聚废水的试验研究

较高的矿化度(TDS)是制约聚合物驱采出水做为配制聚合物用水的主要因素,进行了利用超滤膜和电渗析联合处理含聚废水的试验。通过现场试验,表明管式超滤膜能有效地去除水中的原油、悬浮物和聚合物等杂质,保证了电渗析的平稳运行;控制电导率为950μS/cm时,电渗析的脱盐率为80%,淡水产率为80%。处理后的低矿化度含聚废水能够达到和清水一样的配聚效果,从而可以代替清水用于现场配制聚合物溶液驱油。