## 2 Sources and Impacts of Hydrocarbon-Containing Wastewater  
Potential sources of hydrocarbon-containing wastewater are petroleum, metallurgical and transportation industries, which are concerned about the separation and recovery of oil from water and the treatment of oily wastewater. Large volumes of wastewater having high concentrations of free and emulsified oil are generated from oil and gas fields, refineries and petrochemical plants, thus leading to severe contamination of soil and water bodies. Oilfield wastewater typically includes produced water, used drilling fluid and wastewater after washing the drilling/extraction equipment and storage tanks. The wastewater volume has increased worldwide with increasing oil and gas production despite the large proportion of produced water being reinjected into wells or pumped underground for disposal [8; 9; 10]. The amount of produced water depends on the extraction technology, the reservoir characteristics and the rate of oil extraction. In different sites, the amount of water may be 2-5 or up to 50 times more than the amount of oil produced [10]. Oilfield wastewater is a complex mixture of oil, water, suspended and dissolved solids. It may contain high mineral salt concentrations, heavy metals, naturally occurring radioactive elements and chemical additives used in drilling and operating the well (surfactants, biocides, pH controlling agents, etc.) [8; 10]. Of the oilfield wastewater constituents, polycyclic aromatic hydrocarbons (PAHs), phenols, heavy metals and radioactive elements are of environmental concern [8] (Table 1). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of the Effluent** & **Toxic Organic Components** & **Toxic Inorganic Components** & **References** \\ \hline \multirow{3}{*}{Oilfield produced water} & Benzene, toluene, ethylbenzene, xylene & Mineral salts (salinity up to & \\  & (BTEX), PAHs, phenols, surfactants, & 300\%\({}_{\infty}\)), heavy metals, & [8;10] \\  & biocides & radioactive elements & \\ \hline \multirow{3}{*}{Refinery wastewater} & BTEX, PAHs, phenols, MTBE, & Ammonia, cyanides, hydrogen & \\  & naphthentic acids, methanol, ketones, & sulphide, halides, sulphides, mercaptans, heavy metals, radioactive elements & [3;11] \\ \hline \multirow{3}{*}{Petrochemical wastewater} & Chlorinated and nitro-benzes, phenols, pesticides, brominated organic compounds, estrogens, PAHs, PCBs, phthalates, antilines, tenside, thioanisol, indole, dimethyl- and trimethylpyazines, dimethylyrimidine, dimethyl- and trimethylpyrolidines & \\  & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Toxic Organic and Inorganic Compounds Present in Major Hydrocarbon-Containing Wastewater Streams. Petroleum refinery effluents are generated in oil refinery processes that convert crude oil into numerous refined products, such as liquefied petroleum gas, fuels, lubricants and petrochemical intermediates. These processes consume a large volume of water ranged between 0.2 m\({}^{3}\)/t and 25 m\({}^{3}\)/t of feedstock refined for the European refineries [11] with 10% reduction due to efficient water reuse and recycling [1]. The amount and composition of the refinery wastewater vary considerably depending on crude oil characteristics, plant configuration and process designs. Regardless of configuration, the main wastewater stream is generated from cooling systems, distillation, hydrotreating and desalting [3]. In particular, the water used in crude oil processing (e.g., desalting, distillation and cracking) or washing and cleaning operations comes into direct contact with either crude oil or various hydrocarbon fractions, and thus representing the main organic load. On the other hand, the water used for cooling systems and boilers is usually less contaminated but quantitatively represents the largest part (more than 50% on average) of the wastewater effluent. Crude oil and hydrocarbons are the main pollutants found in wastewater generated by refineries.