Electrocoagulation-new technology for the wastewater treatment

One of the basic requirements of a human being is Water. Globalization, un-controlled population and other factors are creating shortage of pure water and the issue is a concern for many countries. Thus, it becomes imperative to think about water purification using effective and inexpensive techniques and its reusability. A wide range of wastewater treatments are currently known to people. With the recent technology development in electrochemical field, a new technique has been introduced in the industry, named as electrocoagulation. The main objective of this article is focusing on electrocoagulation process methodology and its applications.

Introduction

The classical physico-chemical treatment processes that are used for the wastewater treatment is filtration, air stripping, ion-exchange, chemical precipitation, chemical oxidation, carbon adsorption, ultrafiltration, reverse osmosis, electrodialysis, volatilization and gas stripping.  One of the advanced electrochemical technology based technique is the electrocoagulation process.

Electrocoagulation (EC), the passing of electric current through water, has proven very effective in the removal of contaminants from water. Electrocoagulation systems have been in existence for many years (Dietrich, patented, 1906) using a variety of anode and cathode geometries, including plates, balls, fluidized bed spheres, wire mesh, rods and tubes. 

In the past few decades it has been used for the treatment for the water containing foodstuff wastes, oil wastes, dyes, suspended particles, chemical and mechanical polishing waste, organic matter from landfill leachates, defluorination of water, synthetic detergent effluents, mine wastes and heavy metal-containing solution.

EC has become one of the affordable wastewater treatment processes around the world by reducing electricity consumption and miniaturization of the needed power supplies. 

Methodology

EC offers an alternative to the use of metal salts or polymers and polyelectrolyte addition for breaking stable emulsions and suspensions. EC removes metals, colloidal solids and particles and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species. 

EC uses a proprietary treatment chamber and electricity to treat a wide range of differing waste streams containing heavy metals, virus, bacteria, pesticides, arsenic, MTBE, cyanide, Biochemical oxygen demand (BOD), Total dissolved solids (TDS), and Total suspended solids (TSS). It is used to treat municipal, industrial and commercial wastewater. 

EC reactor is made up of an electrolytic cell with one anode and one cathode. EC system essentially consists of pairs of conductive metal plates in parallel, which act as monopolar electrodes. The requirements to operate EC are

Direct current power source

Resistance Box

Multimeter

The conductive metal plates are commonly known as “sacrificial electrodes.” The sacrificial anode lowers the dissolution potential of the anode and minimizes the passivation of the cathode. The sacrificial anodes and cathodes can be of the same or of different materials.

The monopolar electrodes with cells are arranged in series. In series cell arrangement, a higher potential difference is required for a given current to flow because the cells connected in series have higher resistance. During electrolysis, the positive side undergoes anodic reactions, while on the negative side, cathodic reactions are encountered.  Coagulation process will initiated by neutralizing the charges of the particles by released ions. The released ions remove undesirable contaminants either by chemical reaction and precipitation, or by causing the colloidal materials to coalesce, which can then be removed by flotation. Water containing colloidal particulates, oils, or other contaminants move through the applied electric field, there may be ionization, electrolysis, hydrolysis, and free-radical formation which can alter the physical and chemical properties of water and contaminants. The reactive and excited state causes contaminants to be released from the water and destroyed or made less soluble.

Within the electrocoagulation reactor, several distinct electrochemical reactions are produced independently

Seeding - It is resulting from the anode reduction of metal ions that become new centers for larger, stable, insoluble complexes that precipitate as complex metal ions.

Emulsion Breaking – It is resulting from the oxygen and hydrogen ions that bond into the water receptor sites of oil molecules creating a water-insoluble complex separating water from oil, driller's mud, dyes, inks, etc.

Halogen Complexing - as the metal ions bind themselves to chlorines in a chlorinated hydrocarbon molecule resulting in a large insoluble complex separating water from pesticides, herbicides, chlorinated PCBs, etc.

Bleaching by the oxygen ions produced in the reaction chamber oxidizes dyes, cyanides, bacteria, viruses, biohazards, etc. Electron Flooding of the water eliminates the polar effect of the water complex, allowing colloidal materials to precipitate and the increase of electrons creates an osmotic pressure that ruptures bacteria, cysts, and viruses.

Oxidation Reduction reactions are forced to their natural end point within the reaction tank which speeds up the natural process of nature that occurs in wet chemistry.

Advantages of EC

Removes heavy metals as oxides that pass Toxicity characteristic leaching procedure (TCLP)

Removes suspended and colloidal solids

Breaks oil emulsions in water

Removes fats, oil, and grease

Removes complex organics

Destroys and removes bacteria, viruses and cysts

Benefits of electro-coagulation

Supplied as a skid mounted unit, fully assembled for inlet/outlet and backwash connections

Low operating costs

Low power requirements

Minimal chemical additions

Low maintenance

Sludge minimization

Disadvantages of EC

1. The ‘sacrificial electrodes’ are dissolved into wastewater streams as a result of oxidation, and need to be     regularly replaced.
2. The use of electricity may be expensive in many places.
3. An impermeable oxide film may be formed on the cathode leading to loss of efficiency of the EC unit.
4. High conductivity of the wastewater suspension is required.
5. Gelatinous hydroxide may tend to solubilize in some cases.

Applications

• Ground Water Cleanup
• Surface Water Cleanup
• Process Rinse Water and Wash Water
• Sewage Treatment
• Cooling Towers
• Water Pretreatment

Ground Water Cleanup

EC is extremely effective in the removal of naturally occurring salts in well water, as well as the separation of iron, magnesium, calcium, metals, nitrates and sulfur. EC is also well suited for the reclamation of ground water that has been contaminated with heavy metals, high molecular weight hydrocarbons and Halogenated hydrocarbons.

Surface Water Cleanup

EC is used to remove bacteria, viruses and cysts from surface water, thereby rendering contaminated waste streams into potable water. EC is particularly effective in the removal of life threatening contaminants such as giardia and cryptosporidium.

Process Rinse Water and Wash Water

EC routinely treats process and rinse water from the electroplating, computer board manufactures, textile industry, paint rinse water, steel production, mining industry, automotive industry, equipment repair industry, stack wash water, and pulp and paper. In most cases, the treated water can be recycled and reused.

Sewage Treatment

EC has proven effective in treating sewage water, sewage sludge concentrations, and sewage sludge metal fixation sufficiently to enable land application.

Cooling Towers

EC is used to pre-treat water entering towers as well as blow down water to remove algae, suspended solids, calcium, and magnesium buildup, thereby eliminating costly replacement water.

Water Pretreatment

Water pretreatment with EC has proven effective in removing bacteria, silica and TSS prior to subsequent polishing with reverse osmosis, ultra filtration, nanofiltration, and photocatalytics.

Conclusion

Electrocoagulation has a wide variety of wastewater treatment capabilities. It is the process of destabilizing suspended, emulsified or dissolved contaminants in aqueous medium by introducing a minimal amount of electrical current. It thereby reduces additional costs involved for the process. It even replaces traditional treatment process such as filtration, chemical treatment, which have proved to be less effective and expensive processes. Considering the benefits, EC process helps removal of TSS by 95-99 per cent; BOD by 50-98 per cent and Bacteria by 95-99 per cent. This suggests that the technique is effective and reliable for a wide variety of future applications, which in turn will give hope for purified water for all.

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