Electroflotation
Uploaded by
ScribdTranslationsElectroflotation
Uploaded by
ScribdTranslationsELECTROFLOTATION
Electroflotation (EF) is a simple process that allows for the flotation of contaminants (or others)
substances), through their adhesion to small bubbles of hydrogen and oxygen generated
from the electrolysis of aqueous solutions. The electrochemical reactions present
son
CATODE 2H2O + 2e- → H2+ 2OH-
ANODE 2H 2O → O2+ 4H+ + 4e-
The effectiveness in the separation of a flotation process largely depends on the size.
of the bubbles. This is because the smaller bubbles provide a greater
surface for contact with the particles.
Generally, the electroflotation stage is found complementing a previous stage.
electrocautery call
ELECTROCOAGULATION
It is a widely used technique for the removal of solid pollutants present in the
wastewater, in the form of colloids or suspensions. It consists of the destabilization of
colloid through the passage of electric current from an external source.
of two electrodes that are generally made of iron and aluminum. This current induces a voltage
able to render the negatively charged contaminant insoluble,
positive ions from the anode neutralize such charges, causing agglomeration of
these stabilized components of various sizes, the larger suspensions
precipitate and the smaller ones adhere to the hydrogen bubbles causing their
floating. These bubbles are generated at the cathode, while at the anode there is
release of metal ions (Fe)+2to Al+3, as the case may be) that allow coagulation of the
contaminant and provoke its precipitation.
Electrocoagulation applied to different industries, among which stand out:
Agroindustry.
Fishing.
Sawmill.
Food Industry.
Textile Industry.
Livestock Industry.
Among others.
Electrocoagulation process
The process can be defined as the destabilization of suspended chemical species or
dissolved present in a solution, resulting from the application of a potential difference
electric through a cathode-anode system immersed in the water to be treated solution.
consequence and in the course of said process, the cationic species produced in the
anodes enter the solution, react with other species, form metal oxides and
the respective hydroxides precipitate. Unlike chemical coagulation, in the
electrocoagulation, the cation comes from the dissolution of the metallic anode, whether it is iron or
aluminum.
In other words, electrocoagulation uses direct current to make the ions of
the sacrificial electrodes eliminate unwanted contaminants, either through reaction
chemistry and precipitation or causing colloidal materials to agglomerate and be
eliminated by electrolytic flotation. Figure 2 shows the electrocoagulation process in
a wastewater.
In this process, an electric current is induced in the water through metal plates.
parallels of various materials that optimize the removal process. Two of the metals
the most used are iron and aluminum. Metal ions are released and dispersed in the
liquid medium; these tend to form metal oxides that attract electromagnetically to
the pollutants that have been destabilized and these recently formed particles are
they are precipitated and mechanically removed.
Operating conditions
The operating conditions of an electrocoagulation system are highly
dependent on the chemical conditions, pH, particle size of the water to be treated and
especially of its conductivity. The general treatment of wastewater requires
low voltage applications, generally of <50 Volts, with variable amperage, according to
with the chemical characteristics of water.
In general, the results of the application of this electrochemical treatment for the
the most common contaminants found in wastewater are shown in the following
table
Parameters % removal
DBO greater than 90
DQO > 90
Oils and fats 95
Total nitrogen > 80
Total phosphorus > 70
Suspended solids 95
Fecal coliforms 99%
Factors that affect electrocoagulation
Current density: The current density to choose is important as it will determine the
amount of Fe ions+2to Al+3that will be released, but although it may be tempting to keep elevated
this current value is not advisable, as if it rises too much, it produces a
transformation of electrical energy into thermal energy which would cause the heating of water
decreasing the efficiency of electrolysis.
Temperature: Generally speaking, temperature increases the efficiency of the current, but
up to a value around 600C, because as the temperature increases, it increases the
destruction of aluminum oxide formed on the surface of the anode, beyond this value the
efficiency decreases.
Presence of NaCl: The Cl ions- the negative effects caused by the ions decrease
HCO3 and SO4-2, as these react with Ca ions.+2y Mg+2and precipitate forming a layer
insoluble on the electrodes, causing an increase in potential and decreasing the
current efficiency.
pH: The best removals have been observed for pH values close to 7, although for
a neutral pH, the energy consumption is high. The pH tends to increase for solutions.
acidic and to decrease for alkaline solutions.
Advantages of electrocoagulation
Advantages:
Lower operating costs compared to conventional methods that use
polymers.
The obtained water can be considered drinkable, colorless, and odorless.
Lower investment costs.
Lower energy consumption per cubic meter of treated water.
The flakes formed are larger than those produced by methods.
conventional ones, so there is more precipitation.
Does not use chemicals.
Less sludge is produced than in normal coagulation, which also contains
less water (lower transportation cost).
A wide variety of pollutants can be removed. The removal of matter
organic is very effective
Increases the pH of the solutions to be treated, which promotes the formation of
heavy metal hydroxides.
Bubbles can carry the smaller colloids to the surface for later.
extraction.
Disadvantages:
Additional cost for replacement of sacrificial anodes.
It is not effective in the removal of soluble BOD, coming from solvents and
de-icing agents.
A waterproof oxide film can form on the cathode, which decreases the
efficiency of the process.
Electrocoagulation in an oil-water emulsion
An oil-in-water emulsion (oil dispersed in water) is typically found stabilized.
Due to the presence of surfactants, these surfactants have anionic molecules that repel each other.
with the other oil molecules preventing their coagulation. Electrolysis releases
metal ions from the anode, and these react with the anionic molecules of the surfactant
destabilizing the oil.
Oil-water emulsion
Electrochemical reactions:
Cathodic reaction 2H2O + 2e- → H2+ 2OH-
Anodic reaction Iron Fe+2+2e- Fe+3+ 1e-
Destabilized oil-water emulsion
The oil molecules clump together and precipitate, and the smaller ones are carried away.
through the H bubbles2allowing its flotation and subsequent mechanical separation.
Applications in the industry
Dairy industry
The dairy industry generates a large quantity in volume and organic load of wastewater, which
By legal standards, it is required to decrease. A study was conducted for water treatment.
residual for which the electrocoagulation technique was used, and the results were analyzed
based on the removal of COD and oils and fats. To measure the effects of the
An experimental design was used with the following factors: current density
electric (J), initial pH of the wastewater and treatment time (min); maintaining as
sacrificial electrode to iron (anode) and aluminum as cathode.
The experimental design used in the research is a factorial design of three factors (pH,
current density and time), completely at random. The levels for each of these
factors are recorded in Table 1.
Table N01 Variables to study
FACTORS VALUES
pH 5, 7, 8
Current density (A/m)2) 32.43, 43.23
Time (min) 5, 10, 15
For each of the experiments, four repetitions were performed. The variables of
the response was the percentage of removal of COD and that of fats and oils. The COD was
corrected by the interference of iron. The results obtained were:
Table N02 Variations of the % removal of COD for different pH levels
pH Time (min) % removal of % removal of Percentage of removal
DQO at 32.43 DQO a 43.23 DQ
A/m2 A/m2
5 15 75.73 93.99 18.26
7 15 62.36 70.83 8.47
8 15 46.55 51.44 4.89
Table N0Removal of COD, fats and oils for pH of 5 and current density of 43.23
A/m2
Time (min) COD Removal Removal of oils and
fats
5 43.88 60.40
10 77.29 84.53
15 93.99 99.32
Analyzing the resulting tables, the effect of the three variables (pH,
current density and treatment time) on the performance of electrocoagulation.
For example from table N02, for a fixed treatment time and a fixed current density,
if the pH increases, the % of COD removal decreases, but if the current density increases,
a higher % of removal is obtained. This is explained by the precipitation properties.
Proteins and organic matter of dairy components are presented at acidic pH.
Similarly from table N0It is observed that as the treatment time increases the % of
removal also increases.
From this, it follows that electrocoagulation is an efficient technique in the treatment of
effluents in the dairy industry.
CONCLUSIONS
Electrocoagulation has high efficiency in the destruction of organic matter and
pathogenic microorganisms.
Allows the recovery and reuse of industrial water, and in case of disposing of it, this
waters are free of contaminants that can cause environmental impacts.
It can treat a wide variety of wastewater.
Its efficiency is strongly influenced by the parameters of pH, current density,
electrolysis time and temperature, mainly.
BIBLIOGRAPHY
hthttp://www.lasallista.edu.co/fxcul/media/pdf/RevistaLimpia/vol2n2/PL_V2N2_23-
No text provided for translation.