Electrochemical Technologies for Removing Petroleum Hydrocarbons from Produced Water
a report by
Jessica Horacina Bezerra Rocha and Carlos Alberto Martínez-Huitle Chemistry Department, Federal University of Rio Grande do Norte, Lagoa Nova, Brazil
Produced water is the largest waste stream generated in the oil and gas industries. It is a mixture of different organic and inorganic compounds. Due to the increasing volumes of waste worldwide, the outcomes and effects on the environment of discharging produced water have become a significant issue of concern. Produced water is conventionally treated through different physical, chemical and biological methods. On offshore platforms, because of space constraints, compact physical and chemical systems are used. However, current technologies cannot remove small suspended oil particles and dissolved elements. Future major research efforts need to focus on optimising the current technologies for treating produced water, in order to comply with re- use regulations and discharge limits. Recent electrochemical technologies are a promising alternative for treating these kinds of wastewaters containing organic and/or inorganic pollutants. This paper presents a review of efficient electrochemical technologies developed to remove petroleum hydrocarbons from produced water generated by the petrochemical industry.
Produced Water
The significance of oil and natural gas in modern civilisation is well known. However, like most production activities, oil and gas production generates large volumes of liquid waste. Oilfield wastewater – or produced water – contains various organic and inorganic components. Discharging produced water can pollute surface and underground water and soil.1
In some countries, the permitted oil and grease limits for treated produced water discharge offshore are around 30 mg/l daily average and 50 mg/l instantaneous.2
Many countries have implemented more
Jessica Horacina Bezerra Rocha is working on her master degree in chemistry at the Federal University of Rio Grande do Nort in Lagoa Norte, north-eastern Brazil. Her research interests include electrochemical oxidation and electrocatalysis. She has a degree in chemistry from the Federal University of Rio Grande do Norte.
E:
jhoracina@yahoo.com.br
Carlos Alberto Martínez-Huitle is Associate Professor at the Federal University of Rio Grande do Norte, Lagoa Norte, Brazil. He has studied and worked in Mexico, taught and researched in Italy and Brazil, and conducted research in Switzerland. The focus of his scientific work is electrochemical environmental processes, such as electrochemical water treatment and electrochemical soil remediation. His collaboration with the Brazilian petroleum industry has led to the development of electrochemical oxidation processes in which the oxidants are generated using a flow electrochemical reactor to remove organic pollutants.
E:
carlosmh@quimica.ufrn.br
stringent regulatory standards for discharging produced water. Because large volumes of produced water are being generated, many countries with oilfields, which are also generally water-stressed countries, are increasingly focusing their efforts on finding efficient and cost-effective treatment methods to remove pollutants from produced water as a way to supplement their limited fresh water resources.
Characteristics of Produced Water
Naturally occurring rocks in subsurface formations are generally permeated by different underground fluids such as oil, gas and saline water. Before trapping hydrocarbon compounds, they were saturated with saline water. Hydrocarbons with lower density migrated to trap locations and displaced some of the saline water from the formation. Finally, reservoir rocks absorbed saline water and hydrocarbons (oil and gas). There are three sources of saline water:
• • •
flow from above or below the hydrocarbon zone; flow from within the hydrocarbon zone; and
flow from injected fluids and additives resulting from production activities.1
The last category is called ‘connote water’ or ‘formation water’, and becomes ‘produced water’ when saline water mixed with hydrocarbons comes to the surface.3
In oil and gas production
activities, additional water is injected into the reservoir to sustain the pressure and achieve greater recovery levels. Both formation water and injected water are produced along with the hydrocarbon mixture. At the surface, different processes are used to separate hydrocarbons from the produced fluid or water.4
Produced water is considered to be one of the largest waste streams in the petroleum, oil and gas industry.
Produced water’s characteristics depend on the nature of the producing/storage formation from which they are withdrawn, the operational conditions and the chemicals used in the processing facilities. The composition of produced water from different sources can vary by order of magnitude. However, produced water composition is qualitatively similar to oil and/or gas production.5
The
major compounds of produced water include: •
dissolved and dispersed oil compounds (a mixture of hydrocarbons including benzene, toluene, ethylbenzene and xylenes [BTEX]; naphthalene, phenantherene and dibenzothiophene [NPD]; polycyclic aromatic hydrocarbons [PAHs]; and phenols);
• dissolved formation minerals; •
production chemical compounds, including chemicals that are added to treat or prevent operational problems; treatment
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Factors such as geological location of the field, its geological formation, the lifetime of its reservoirs and the type of hydrocarbon product being produced affect the physical and chemical properties of produced water.1,3
HSE – Produced Water
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