Electrochemical Technologies for Removing Petroleum Hydrocarbons from Produced Water Figure 2: Direct (A) and Indirect (B) Electro-oxidation Treatment
AB Pollutants
e-
Destroyed pollutants
Anode surface
Electrolyte Direct oxidation Adapted from Martínez-Huitle and Ferro, 2006.20
Figure 3: Electrochemical Plants and Cells Used in Electro-oxidation in Batch Operation Mode
Multimeter
Bipolar trickle tower reactor
Thermjacket Anode
Power supply
Peristaltic pump
Cathode
Water bath
pH meter Tank Peristaltic pump
One-compartment cell
Magnetic bar Anode
Magnetic stirrer
Turbulence promoter
Flow inlet
FM01-LC reactor Spacer
Anode
Off gas
Water bath
Cathode Tank
Flow cell parallel plate electrodes
Electrochemistry can be considered a credible alternative for the prevention of pollution problems. Intensive research is ongoing, with the goal of discovering more efficient techniques, processes, materials, technologies and applications for removing organic pollutants from wasterwaters.
Back plate Outlet
Flat plate electrodes
Gasket Electroreduction (ER)
Bipolar trickle tower reactor with a jacket for external thermostatisation (top left); one-compartment cell with parallel plate electrodes (top right); stirred two-electrode one-compartment tank reactor (bottom left); and filterpress flow cell FM01-LC reactor (bottom right).
A limited number of papers have been published dealing with the direct ER of petroleum hydrocarbons in aqueous solution on suitable cathodes.14
However, as the financial cost of the physical methods and chemicals used to treat hazardous sludge is high, the application of these methods is limited. Current methods cannot remove minute suspended oil and/or hazardous dissolved organic and inorganic components. Biological treatment is a cost-effective alternative method for removing dissolved and suspended compounds from oilfield wastewater in onshore extraction facilities. A considerable number of studies have been conducted to investigate new treatment technologies to remove the pollutants from produced water. Figure 1 summarises the main technologies used for the removal of these pollutants. Extensive information regarding the characteristics and applications of the main conventional technologies – including physico-chemical and chemical methods, advanced oxidation processes, microbiological treatments and biological decomposition – has been collected in an authoritative review.1
In contrast, only a few scientific studies have been published in recent years about the emerging electrochemical technologies that can be used to remove petrochemical pollutants from produced water.7–14 Additionally, there has been very recent advances in these promising methods.15–18
The reason for this low interest in this conventional electrochemical technique is that it offers poor decontamination of wastewaters compared with the more potent direct and indirect EO methods. An example is the elimination of PAHs,13–15
where the
principal degradation mechanism occurs through EO; however, a certain amount of PAHs is degraded by ER at the cathode surface.
Electrochemistry offers promising approaches for the prevention of pollution problems in the processing industries.
The abatement of these organic compounds has high priority, because they cause serious disequilibrium in aquatic environments, even dissolved in lower concentrations.
Electrocoagulation (EC)
This article will therefore present a general overview of laboratory and pilot plant experiments relating to the most relevant applications of electrochemical methods for removing petroleum hydrocarbons from produced water.
112
A traditional physico-chemical treatment of phase separation for the decontamination of petroleum hydrocarbons in wastewaters before discharge to the environment is coagulation. It consists in the addition of coagulating agents such as Fe3+ or Al3+ ions, usually in the form of
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2
The main electrochemical methods for the removal of petroleum pollutants from wastewaters are electroreduction (ER), electroflotation, electrocoagulation (EC), electro-oxidation (or electrochemical oxidation [EO]) with different anodes and indirect electro-oxidation (IEO) with active chlorine. Emerging technologies, including electro-Fenton (EF) and photoassisted systems such as photoelectro-Fenton (PEF) and photoelectrocatalysis (PEC), have recently received great attention. The fundamentals of each of these technologies will be briefly outlined here to help better understand their advantages and limitations in the environmental prevention of pollution by petroleum hydrocarbons from produced water.
Anode surface
e- Oxidant Electrolyte Indirect oxidation Mediator
Oxidation in the bulk
Destroyed pollutants
Pollutants Electrochemical Methods
Other advantages are its versatility, energy efficiency, amenability to automation and cost-effectiveness. Electrochemistry has reached a promising stage of development and can now be effectively used for the destruction of toxic or biorefractory agents.20,21
Electrochemistry, as a branch of physical chemistry, plays an important role in most areas of science and technology. Electrochemistry offers promising approaches for the prevention of pollution problems in the processing industries. Its inherent advantage is its environmental compatibility, due to the fact that it uses a clean reagent, the electron.19,20
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