Electrolytic Cell reactors Consists Three Stages
- Electrolyzer (Coagulation)
- Ionization (Oxidation )
- Flotation (Particles Floating & Skimmed)
Electro coagulation (Electrolyzer, Ionization, Flotation )
Electro coagulation is a technique involving the electrolytic addition of coagulating metal ions directly from sacrificial electrodes. These ions coagulate with turbidity agents in the water, in a similar manner to the addition of coagulating chemicals such as alum and ferric chloride, and allow the easier removal of the pollutants. In the EC process, the coagulant is generated in situ by electrolytic oxidation of an appropriate anode material. In this process, charged ionic species—metals or otherwise—are removed from wastewater by allowing it to react (i) with an ion having opposite charge, or (ii) with floc of metallic hydroxides generated within the effluent. The EC technology offers an alternative to the use of metal salts or polymers and polyelectrolyte addition for breaking stable emulsions and suspensions. The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species. These species neutralize the electrostatic charges on suspended solids and oil droplets to facilitate agglomeration or coagulation and resultant separation from the aqueous phase. The treatment prompts the precipitation of certain metals and salts.
The electrolytic dissolution of the aluminium anode produces the cationic monomeric species such as Al3+ and Al(OH)2+ at low pH, which at appropriate pH values are transformed initially into Al(OH)3 and finally polymerized to Aln(OH)3n according to the following reactions:
Al → Al3+ (aq) + 3e−
Al3+ (aq) + 3H2O → Al(OH)3 + 3H+ (aq)
n Al(OH)3 → Aln(OH)3n .
These gelatinous charged hydroxo cationic complexes can effectively remove pollutants by adsorption to produce charge neutralization, and by enmeshment in a precipitate. Defluorination of water can be achieved using aluminum electrodes.
Iron upon oxidation in an electrolytic system produces iron hydroxide, Fe (OH)n, where
n = 2 or 3.
4Fe(s) → 4Fe2+(aq) + 8e−
4Fe2+(aq) + 10 H2O(l) + O2(g) → 4Fe(OH)3(s) + 8H+(aq)
8H+(aq) + 8e− → 4H2(g)
4Fe(s) + 10 H2O(l) + O2(g) → 4Fe(OH)3(s) + 4H2(g)
The Fe(OH)n(s) formed remains in the aqueous stream as a gelatinous suspension, which can remove the pollutants from wastewater either by complexation or by electrostatic attraction, followed by coagulation. Wastewater containing chromium ions can be removed by the EC technique using iron as the sacrificial anode.
The H2 produced as a result of the redox reaction may remove dissolved organics or any suspended materials by flotation.
ADVANTAGES OF ELECTRO COAGULATION
The advantages of electro coagulation technology are given below:
- EC requires simple equipment and is easy to operate.
- Wastewater treated by EC gives clear, colourless and odourless water.
- Sludge formed by EC tends to be readily settable and easy to de-water, because it is composed of mainly metallic oxides/hydroxides. Above all, it is a low sludge producing technique.
- Flocs formed by EC are similar to chemical floc, except that EC floc tends to be much larger, contains less bound water, is acid-resistant and more stable, and therefore, can be separated faster by filtration.
- EC produces effluent with less total dissolved solids (TDS) content as compared with chemical treatments. If this water is reused, the low TDS level contributes to a lower water recovery cost.
- The EC process has the advantage of removing the smallest colloidal particles, because the applied electric field sets them in faster motion, thereby facilitating the coagulation.
- The EC process avoids uses of chemicals, and so there is no problem of neutralizing excess chemicals and no possibility of secondary pollution caused by chemical substances added at high concentration as when chemical coagulation of wastewater is used.
- The gas bubbles produced during electrolysis can carry the pollutant to the top of the solution where it can be more easily concentrated, collected and removed.