Advantages , features and application of electro dialysis

in water processing

ELECTRODIALYSIS•ED is an electrochemical separation process in which ions are transferred through ion exchange membranes by means of a direct current (DC) voltage. The process uses a driving force to transfer ionic species from the source water through cathode (positively charged ions) and anode (negatively charged ions) to a concentrate wastewater stream, creating a more dilute stream .

General principles in electrodialysisMost salts dissolved in water are ionic, being positively (cationic) or

negatively (anionic) charged.Membranes can be constructed to permit selective passage of either

anions or cations.The dissolved ionic constituents in saline solution are Na+ , Ca2+ , and

Co32+ are dispersed in water, effectively neutralizing their individual

charges. When electrodes connected to an outside source of direct current like a battery are placed in a container of saline water, electrical current is carried through the solution, with the ions tending to migrate to the electrode with the opposite charge.

INTRODUCTIONFirst commercial equipment based on electrodialysis (ED) technology was developed in

1950’s to demineralize brackish water. ED has advanced rapidly because of improved ion exchange membrane properties,

better materials of construction and advances of technology. Applications of ED : 1. To reduce inorganics like radium, perchlorate, bromide, fluoride, iron and manganese

and nitrate in drinking water2. To recycle municipal and industrial waste water3. Recovering reverse osmosis reject4. Desalting wells, surface waters5. final effluent treatment for reuse in cooling towers6. whey and soy purification7. Table salt production etc…

ELECTRODIALYSISAdvantages

• ED system separates without phase change, which results in relatively low energy consumption.

• When brackish water is desalted by ED system, the product water needs only limited pre-treatment. Typically only chlorination for disinfection is required.

DISADVANTAGES

• Organic matter, colloids and SiO2 are not removed by ED system.

• Feedwater pre-treatment is necessary to prevent ED stacks fouling

ELECTRODIALYSISADVANTAGES

• Because ED system removes only ionised species, it is particularly suitable for separating non-ionised from ionised components.

• Osmotic pressure is not a factor in ED system, so the pressure can be used for concentrating salt solutions to 20% or higher.

DISADVANTAGES

• Elaborate controls are required, and keeping them at optimum condition ca be difficult.

• Selection of materials of construction for membranes and stack is important to ensure compatibility with the feed stream.

ELECTRODIALYSIS

ADVANTAGES

• Low cost for capital equipment

• Self- regulating, responsive to water condition and flow demands

• Recover higher concentration of ion than reverse osmosis

DISADVANTAGES

• Adequate electrical safety measures should be taken• It may cause local air pollution.

Because H2 and Cl2 may be generated at the electrode surface

• Uncertainty in membrane life and integrity

ELECTRODIALYSISAdvantages

• Low chemical usage for chemical pretreatment

• Construction is almost entirely of plastic materials with minimum metal components, eliminating the problems of corrosion

• No mechanical moving parts, silent and vibration free operation

disadvantages

• Efficiency drops as purity of the product water increases

Application of electrodialysis in water treatment

• Potable water from brackish water• Production of high purity water for pharmaceutical

industries• Production of demineralised water for food

industries• Treatment of rinse water for electronic industries• Industrial water purification for removal of ionic

components• Cooling tower water treatment

APPLICATION ELECTRODIALYSIS IN INDUSTRIAL PROCESS

• Concentration of rejected salt in RO brine• Table salt manufacturing process• Reclaiming and recovering and recovering nickel and gold from

electroplating rinse water• Reclaiming and recovering silver from photographic rinse water• Reclaiming and recovering zinc from galvanizing rinse water• Remove of citric acid from fruit juice• Removal of tannic acid from wine• Recover amino acids from proteins

• Electrodialysis uses an electric current in the water to remove contaminants. The electric current pulls impurities through a membrane that filters out these impurities from water. The result is purified water.• Electrodialysis requires a large amount of electricity to

produce a current in the water strong enough to manipulate the impure ions.• Electrodialysis also has a limited range of contaminants

with which it can filter. It cannot remove organics, pyrogens and elemental metals

DESALINATION BY ELECTRODIALYSIS• The production of potable water from brackish water sources is

certainly the most important application of electrodialysis• The brackish water treated by ED has generally a relatively low salt

concentration in the range of 2000 to 5000 mg/l TDS Features of electrodialysis which makes suitable for desalination of

brackish water 1. ED is less sensitive to membrane fouling and scaling 2. higher recovery rates and minimum brine disposal problems 3. ion exchange membranes can be operated at elevated temperatures 4. membrane is stable at high and low p H values 5. less sensitive to oxidizing agents

Configuration of desalting process1.Cation exchange membrane2.Anion exchange membrane3.Cathode4.anode

REDUCTION OF TOTAL DISSOLVED SOLIDS

• The most common application of ED is reduction of TDS to meet drinking water standards•Plants treating brackish sources contain 10,000mg/l TDS

can reliably and economically yield product water containing less than 500mg/l of TDS.

Control of inorganics and ionized contaminants

• ED control specific inorganic constituents or ionized contaminants in water• ED used to remove or reduce some of the following

common ionized constituents: TDS, chromium, sodium, mercury, chloride, copper,

sulfate, uranium, fluoride, nitrate and nitrite, iron, selenium, hardness, barium, bicarbonate, cadmium, strontium