Optimal design of an electrodialysis brackish water desalination plant

This paper considers the optimal design and operation of electrodialysis (ED) desalination plants. In general an ED plant aims to produce potable water from a high salinity source, like brackish water or high salinity water. The system is modelled mathematically as mixed-integer non-linear programming (MINLP) optimization problem, determining the number of desalination stages, the membrane area, the total required energy so as to minimise the total annualised cost of the investment accounting for both infrastructure and operating costs. Two examples from the literature illustrate the applicability of the proposed approach and evaluate the quality of the results obtained.     

Designing of an electrodialysis desalination plant

The design and operation of an electrodialysis desalination process are based on a set of fixed and variable parameters such as stack construction, feed and product concentration, membrane properties, flow velocities, current density, recovery rates, etc. These parameters are interrelated and may be rather different for different applications. For an efficient operation of an electrodialysis desalination plant, the process has to be optimized in terms of overall costs considering component properties and operating parameters. In this study the design and optimization of an electrodialysis plant to be used for brackish water desalination has been treated. The required equations were derived or, as in the case of the limiting current density, were experimentally determined. As an example, an electrodialysis plant with a sheet-flow stack construction and given feed solution composition was designed and optimized in terms of overall costs and the sensitivities of the different parameters are analyzed.     

Performance evaluation and process design of an electrodialysis plant by overpotential measurements

In this paper an investigation of Ionics Mark III ED stack is reported. The experimental techniques used allowed ED plant performance to be evaluated as a series of elementary subsystems; concentration boundary layer overpotentials were measured at different locations along the membrane flow path. The current interruption technique was used in order to calculate interfacial concentrations and diffusion boundary layer thickness.The results obtained established the dependence of concentration polarization on membrane path length; the last membrane sections were found to be strongly polarized even at relatively low operating current densities. Hence a better ED plant design should make use of a sequence of stack sections at different applied voltages.     

Performance analysis of photovoltaic electrodialysis desalination plant at Tanote in Thar desert

The 450 peak watts photovoltaic panel coupled electrodialysis(PV-ED) plant of size 30 × 60 cms with 42 cell pairs operating at about 80 volts gives about 1000 litres per day of product water with salinity less than 1000 ppm from feed water having total dissolved solids(tds) of about 5000 ppm. The flow is fixed at 120 litres per hour for 8 hours operation per day between 8.30 a.m. to 4.30 pm.     

Seawater desalination and reverse osmosis plant design

Plant site, water intake, pretreatment, choice of materials of construction, design alternatives and energy recovery are important variables to be considered in the design of seawater desalination plants employing “permasep” B-10 reverse osmosis modules. Techniques are outlined to permit custom design of seawater desalination plants which offer reliable long term performance as well as competitive economics.     

An integral design for desalination plant using the secondary refrigerant freeze process

A review of an earlier SRF design revealed the need for reappraisal, and has led to the identification of an integral design in which the four main process stages of the primary cycle are contained within separate compartments of a single vessel capable of producing up to 2$\text{1}\text{2}$mgd (11,250 m³/day). A commercial design using two integral vessels has been formulated and costed. Its capital cost is around 20% below the up-dated costs of the previous design and it shows the prospect of producing water at a level below those of competing systems.     

The Sydney University solar desalination pilot plant design

Following an extensive feasibility study, a solar distillation pilot plant using Sydney University evacuated tubular collectors was designed. In this paper, the major design decisions regarding plant and fluid circulation are discussed.     

Neural network modeling of Pb removal from wastewater using electrodialysis

Artificial neural network (ANN) was applied to predict separation percent (SP) of lead ions from wastewater using electrodialysis (ED). The aim was to predict SP of Pb²⁺ as a function of concentration, temperature, flow rate and voltage. Optimum numbers of hidden layers and nodes in each layer were determined. The selected structure (4:6:2:1) was used for prediction of SP of lead ions as well as current efficiency (CE) of ED cell for different inputs in the domain of training data. The modeling results showed that there is an excellent agreement between the experimental data and the predicted values.     

Treatment of sea water using electrodialysis: Current efficiency evaluation

In this paper, desalination of seawater using a laboratory scale electrodialysis (ED) cell was investigated. At steady state operation of ED, the outlet concentration of dilute stream was measured at different voltages (2−6 V), flow rates (0.1−5.0 mL/s) and feed concentrations (5000−30,000 ppm). The electrical resistance of sea water solution in the dilute compartment was initially calculated using basic electrochemistry rules and average concentration of feed and dilute streams. Then, current intensity in each run was evaluated using Ohm's law. Finally, current efficiency (CE) which is an important parameter in determining the optimum range of applicability of an ED cell was calculated. It was found out that, at flow rates larger than 1.5 mL/s, higher feed concentrations lead to larger values of CE. However, exactly opposite behavior was observed at lower flow rates. Increasing the feed flow rate increases CE to a maximum value then decreases it down to zero for all cell voltages and feed concentrations. In the case of higher feed concentrations, maximum values of CE are obtained at higher flow rates. As expected, in almost all experiments, CE increases by intensifying cell voltage. CE values of up to 48 indicate effective ion transfer across the ion exchange membranes in spite of low separation performance of the ED cell.     

Performance evaluation of BWRO desalination plant — A case study

Fouling and scaling are the most serious problems in membrane processes. In sea/brackish water applications, pretreatment of RO feed water is the key step in designing the plants to avoid membrane fouling and scaling. Recent developments in pretreatment processes are more adapted to raw water quality. But, in some cases, raw water quantity/quality varies during seasons and is also influenced by the environment. Thus, pretreatment design becomes complicated and should cope with the raw water quality changes. The success of such operation requires qualified operators who will be able to adapt with different situations. Surface and brackish water sources are mostly facing these problems. In this paper, performance evaluation carried out for a brackish water reverse osmosis (BWRO) plant located in the west of Algeria is presented. This plant showed poor performance after a few months of operation. The operating pressure and pressure drop increased significantly without an increase in the production capacity and the permeate conductivity decreased surprisingly. Frequent shutdowns of the plant were observed due to severe membrane fouling. To identify the causes for the poor performance, different investigations were carried out. Membrane autopsy was performed and chemical analyses of foulants on the membrane surface by scanning electron microscopy were carried out to identify the matters responsible for fouling. The results showed that the quality of raw water changed widely due to drying of some wells and decrease of the water level in other wells. RO membranes were fouled by inorganic matters mainly colloidal/particulate silica and fine particles of clay present in raw water. Thus, the pretreatment scheme was thoroughly reviewed to find out why suspended solids were not removed by the sand and cartridge filters even though SDI was always less than 1. The problem was resolved by injecting a coagulant before the sand filters.     

Separation of copper ions by electrodialysis using Taguchi experimental design

With the aid of atomic absorption, a systematical and analytical evaluation method called Taguchi's quality engineering has been applied for the separation of copper ions from a solution using a laboratory electrodialysis set-up to evaluate the optimal experimental conditions and hence to achieve the highest removal percentage and the best robustness of the quantitation from the least number ofexperimental runs. Fourparameters at three levels were studied: concentration (100, 500, 1000 ppm), temperature (25, 40, 60°C), flow rate (0.07, 0.7, 1.2 mL/s) and voltage (10, 20, 30 V). Two types of different membranes with different ion-exchange capacities were used. The optimal levels thus determined for the four influential factors were: concentration 1000 ppm, temperature 60°C, flow rate 0.07 mL/s and voltage 30 V. It has also been found that using a membrane pair with higher ion-exchange capacity improves performance. The highest removal percentage was found to be 94.94% and 97.33% for the two types of membranes.     

Industrial wastewater collection using a separation technique

Water is an essential element within normal functioning throughout the chemical industry. The reuse of water, or more precisely water condensate collection, is very important during real chemical processes because it can reduce raw materials, energy losses, and costs, and can improve the operations of energy and process systems.The effect of industrial activity on the environment has attracted considerable attention over the past few decades. Industry, therefore, has started looking at methods of reducing the volumes of produced wastewater. This paper presents the industrial separation of lower and higher temperature condensates’ collection using the heating utility of steam production, by separation techniques. The existing condensate collection regarding utilities’ preparation for steam-generation may no longer be optimal; the basic intention is that minimal changes in the system can produce an efficient improvement by using separate collections of low and high-temperature condensates, and the use of available heat with little heat flow rate loss. This separated water condensate collection preparation for the utility of steam production by using a separation technique and MINLP (mixed-integer nonlinear programming) was tested on an existing methanol process, which allowed for an efficient and additional 7% water condensate collection system for steam-generation.     

电渗析脱盐过程中胺液损失的因素分析及改进措施

在实验室装置中研究分析了电渗析法脱除胺液热稳盐过程中影响胺液损耗的因素,结果表明:胺液通过浓差扩散进入废液的量较少,影响胺液损耗的主要因素是胺液中的热稳盐质量分数与电渗析电压;随着胺液中热稳盐质量分数的降低,胺液损耗量逐步升高;随着电压的提高,胺液热稳盐脱除速率加快,胺液损耗量增加;当热稳盐质量分数降至1.5%以下时,电压的影响变得明显。将研究结果应用于脱硫胺液电渗析脱盐工业装置,对工艺参数进行优化,通过调整自动控制程序,由程序自动调节循环时间及不同热稳盐质量分数下的膜堆电压数值,可确保废液中MDEA质量分数小于1 000×10~(-6),达到减少胺液损耗、有效降低脱盐污水中胺液浓度的目的。     

Synthesis of a polyaminophosphonate and its evaluation as an antiscalant in desalination plant

The cationic monomer, N,N‐diallyl‐3‐(diethylphosphonato)propylammonium chloride, was cyclopolymerized in aqueous solutions using t‐butylhydroperoxide (TBHP) or ammonium persulfate (APS) as initiators to afford a cationic polyelectrolyte (CPE) having a (diethylphosphonato)propyl pendent. The CPE on acidic hydrolysis of the diester groups gave pH‐responsive polyzwitterionic acid (PZA) which on treatment with one and two equivalents NaOH gave zwitterionic/anionic polyelectrolyte (ZAPE) and dianionic polyelectrolyte (DAPE), respectively. The solution properties of the CPE, PZA, ZAPE, and DAPE were investigated in detail by viscometric technique. For the purpose of comparison, the solution properties of the polymers were correlated to a structurally similar polyzwitterion (PZ) having monoethylphosphonate and NH⁺ groups. When performance evaluation was carried out for application in reverse osmosis (RO) plants, DAPE at a concentration of 10 ppm in brackish water feed proved very effective as an inhibitor against calcium sulfate scale. POLYM. ENG. SCI., 54:166–174, 2014. © 2013 Society of Plastics Engineers     

Reverse electrodialysis: evaluation of suitable electrode systems

Reverse electrodialysis (RED) is a method for directly extracting electrical energy from salinity gradients, especially from sea and river water. For the commercial implementation of RED, the electrode system is a key component. In this paper, novel electrode systems for RED were compared with existing systems on safety, health, environment, technical feasibility and economics. Systems with inert DSA-type electrodes and a NaCl–HCl supporting electrolyte with the reversible Fe²⁺/Fe³⁺ redox couple or the [Fe(CN)₆]^4–/Fe(CN)₆]^3– couple achieved the highest ranking. Improvements of the electrode system are also discussed like the use of special stable metal electrodes, graphite electrodes, other reversible redox couples, capacitive electrodes and electrolytes with carbon particles.     

Development of a four-grade and four-segment electrodialysis setup for desalination of polymer-flooding produced water

An electrodialysis (ED) setup with an 11 m³/h water treatment scale was designed based on a small experimental device. The setup adopts four-grade and four-segment (four-GS) reversal electrodialysis (EDR) technology to desalinate polymer-flooding produced water (PFPW). The removal rate of total dissolved solids (TDS) with different flow rates was measured with different grades and segments. The operating performance of this setup was determined to meet design standards. The maximum treatment capacity and the optimal operation conditions of the tested setup were studied. The design standards were met only by adopting a four-GS ED setup. The maximal capacity of the four-GS ED setup for treating PFPW was 5 m³/h. The optimal operating condition and results were at an operating electric current of 86 A, 62.5% production rate of diluted treated PFPW, 0.89 kW?h/m³ energy consumption, and 78.7% TDS removal rate. Under optimal conditions, the treated PFPW has two beneficial uses. First, the diluted treated PFPW is feasible for preparing polymer solutions. Second, the concentrated treated PFPW is feasible for replacing the original PFPW as the injecting water in the water-flooding process for high permeability layers.     

抚顺洗涤剂化工厂废水处理工程设计

洗涤剂化工厂废水中含有大量的石油类、固体悬浮物(SS)、硫化物、酚及BOD、COD等有机污染物．采用隔油、涡凹气浮(CAF)、接触氧化、混凝沉淀、过滤、活性炭吸附等工艺处理后,出水达到循环水回用及生活杂用水水质标准。     

Ammonium nitrate wastewater treatment by coupled membrane electrolysis and electrodialysis

A process coupling membrane electrolysis and electrodialysis is implemented to treat ammonium nitrate wastewater. Membrane electrolysis produces ammonia and nitric acid while electrodialysis reconcentrates the depleted salt solution. Ammonia is removed continuously by in situ stripping; thus allowing gas production with a constant current efficiency (about 70%). Nitric acid up to 8 mol L^–1 is obtained. The current efficiency of acid production depends on nitric acid concentration. When this concentration varies from 1 to 8 mol L^–1 the average current efficiency is about 58%. Electrodialysis produces a rejected stream containing less than 3 × 10^–3 mol L^–1 of ammonium nitrate.     

Optimization of solar-powered reverse osmosis desalination pilot plant using response surface methodology

A solar thermal and photovoltaic-powered reverse osmosis (RO) desalination plant has been constructed and optimized for brackish water desalination. The central composite experimental design of orthogonal type and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of different responses such as the salt rejection coefficient, the specific permeate flux and the RO specific performance index that takes into consideration the salt rejection coefficient, the permeate flux, the energy consumption and the conversion factor. The considered input variables were the feed temperature, the feed flow-rate and the feed pressure. Analysis of variance (ANOVA) has been employed to test the significance of the RSM polynomial models. The optimum operating conditions have been determined using the step adjusting gradient method. An optimum RO specific performance index has been achieved experimentally under the obtained optimal conditions. The RO optimized plant guarantees a potable water production of 0.2 m³/day with energy consumption lower than 1.3 kWh/m³.