## 2 Sources and Impacts of Hydrocarbon-Containing Wastewater
Inputs of organic contaminants and metals to the urban wastewater system occur from three generic sources: domestic, commercial and urban runoffs. Typical domestic wastewater contains 10-50 mg/L of oil and grease (O&G). Over 6000 organic compounds have been detected in raw water sources within European urban areas, most of which are due to human activities [14]. While some of these are highly persistent, others are easily biodegradable. These organic compounds include aliphatic and aromatic hydrocarbons, PAHs, fatty acids, ketones, phthalate esters, plasticizers and other polar compounds. Solvent extractable organics are dominated by petroleum hydrocarbons, which arise from motor oil leaks, degraded asphalt and worn tires from the roads. Most toxic and recalcitrant organic pollutants found in urban wastewaters include PAHs, polychlorinated biphenyls (PCBs), di-(2-ethylhexyl)phthalate (DEHP), linear alkyl benzene sulphonates (LAS), nonylphenol ethoxylates (NPE), dioxins (PCDD) and furans (PCDF). Also, emerging micropollutants (e.g., pharmaceuticals, personal care compounds, flame-retardants, biocides and pesticides) are increasingly detected in urban wastewaters [2]. While starting in the 1990s, the strict control of organic pollutants from small industrial, domestic and transport sources in Europe allowed the reduction of the levels of urban contamination; the concentrations of petroleum hydrocarbons in sewage treatment influents remain quite high. Moreover, some organic substances, with the potential to exert a health or environmental hazard, were identified in sludges and sewage treatment effluents [14; 16], thus requiring more regulatory, economic and educational instruments to mitigate the problem of wastewater pollution. According to the Rules of Cold Water Supply and Sanitation approved by the Russian Federation Government Decree No. 644 (new edition from 26 July 2018), new standards for the concentrations of pollutants in wastewater allowed to discharge to a centralized sewage system were established. In particular, the maximum allowable concentration (mg/L) of petroleum products is 10, fats--50, volatile organic compounds (toluene, benzene, acetone, methanol, butanol, propanol, their isomers and alkyl derivatives)--20, suspended solids--300, synthetic surfactants--10, phenols 5, and polychlorinated biphenyls--0.001. These new regulations have prompted dozens of local treatment facilities to be established by transport, small industrial and road construction companies, in which the advanced and cost-efficient technologies of wastewater purification are applied [17]. It is worth noting that the environmental and human health risks of hydrocarbon pollutants are determined by their toxicity, how they spread if released into the environment, how long they stay in the environment, and whether they bioaccumulate in the food chain. Therefore, understanding the fate and transport of contaminants is crucial for risk assessment, while this analysis can be very complicated because it requires the best approximation of the environmental chemistry of hydrocarbon contaminants (e.g., biodegradability, hydrophobicity) and the environment at the site (e.g., geology, geochemistry). At the heart of this problem is the concept of bioavailability [18]. If a pollutant is present in soil or water but is not available to the biota, then it presents minimal risk (unless chemical conditions change that can subsequently increase the bioavailability). However, measuring bioavailability is often a difficult task and cannot be estimated directly from the total pollutant concentration since the bioavailability level can vary significantly. Bioavailability is indirectly related to partitioning phenomena, biodegradability and toxicity [19] and it is also dependent on the organism exposed.