Electrochemical Technologies for Removing Petroleum Hydrocarbons from Produced Water
chlorides, for the precipitation of organic pollutants. Similar effects can be obtained by means of the electrochemical version of this method. This technique uses a current to dissolve Fe (or steel) or Al sacrificial anodes immersed in the polluted water, giving rise to the corresponding metal ions that yield different Fe(II) – and/or Fe(III) – or Al(III) species with
electroflotation with evolved H2; and
• other electrochemical and chemical reactions involving reduction of organic impurities and metal ions at the cathode and coagulation of colloidal particles.
Many advantages of EC have been reported:21 •
In indirect electro-oxidation with active chlorine, the type of anode material chosen merits special attention.
hydroxide ion depending on the medium’s pH. These species act as coagulants or destabilising agents that bring about charge neutralisation for separating organic pollutants from wastewater. When the
coagulated particles are attached to the bubbles of H2 gas evolved at the cathode and transported to the top of the solution, they can also be separated by electroflotation. In general, the following main processes take place during an EC treatment:21
• electrode reactions to produce metal ions from Fe or Al anodes and H2 gas at the cathode;
• •
formation of coagulants in the wastewater; removal of pollutants with coagulants by sedimentation or by
• • •
more effective and rapid organic matter separation than with physico-chemical coagulation;
pH control not necessary, except for extreme values; small amount of chemicals required;
smaller amount of sludge produced than with coagulation; for example, the sludge produced by EC through the action of Fe has a higher content of dry and hydrophobic solids than that produced
by coagulation through the action of FeCl3 followed by the addition of NaOH or lime; and
•
much lower operating costs than most conventional technologies. However, EC also presents major disadvantages: •
•
anode passivation and sludge deposition on the electrodes, which can inhibit the electrolytic process in continuous operation mode; and
high concentrations of iron and aluminium ions in the effluent, which have to be removed.
Apart from the electrolytic system and anode material used, the removal of petrochemical hydrocarbons by EC mainly depends on
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