Heavily polluted wastewater streams come in direct contact with petroleum fractions and require serious treatment processes for purification. Hydrocarbons such as aromatic compounds and heteroatoms can be found in wastewater streams from distillation and different forms of cracking. There is a set of quality parameters to measure the treatment required for the wastewater processes including amount of suspended solids, hydrocarbon content, nitrogen content, phenols content, and acidity. Municipal wastewater treatment cannot handle treating the pollutants because the different streams need to be kept separate to reduce the load on the treatment units. The wastewater treatment constitutes a very significant supporting process for safe operation. Most municipal wastewater treatment facilities can only handle cooling water and sanitary sewage water after it has had minor treatments. The amount of refinery equipment and treatment processes require expensive machinery as well as many units for the processes that municipals may not be able to afford. Primary treatments are physical whereas secondary treatments are biological processes. Primary treatment of sour water contaminated with oils and solid particles involve the stripped of dissolved H2S using steam, separators, and settling tanks. After primary treatments are conducted typically water can be sent to municipalities for further treatment processes because they are at a acceptable level for municipalities to handle. Secondary treatments utilize microorganisms to further remove organic contaminants.

The wastewater from refineries can not be treated in regular municipal wastewater treatment plants for a variety of reasons. Municipal wastewater treatment plants are designed to treat wastewater from residential houses. There can also be some rainwater runoff going it to these plants as well. These plants are not equipped to clean the wastewater that would be coming from a refinery. The waste water coming from a refinery is divided into four different types. The types of wastewater are Storm water, sanitary sewer water, cooling water, and the most polluted process water and steam. The process water and steam contains many forms of pollutants that include liquid hydrocarbons, suspended solids, dissolved solids, mercaptans, phenols, amines, and cyanides. These chemicals would not be able to be processed by a municipal wastewater treatment because of the toxicity of some of these compounds. These compounds have to be stripped from the sour water using steam to remove H2S, float/sink density separators, as well as settling tanks to separate heavier oils. After these processes are completed the water can be directed to a wastewater treatment plant where the water can be completely processed. There is also a secondary treatment process that uses microorganism to remove organic compounds from the waste water. This process produces a substance called biocoke.

Wastewater treatment is considered an important supporting process in petroleum refining. The four types of refinery wastewater include cooling water, process water and steam, storm water, and sanitary sewage water. The refinery stages that produce the most wastewater are desalting, distillation, thermal and catalytic cracking, and coking. The most polluted wastewater is the process water that comes into direct contact with petroleum fractions; thus it cannot be simply treated in municipal wastewater treatment plants. Storm water is considered contaminated as a result of incidental exposure to pollutant sources and accidental spills during refinery reactions. The refinery’s cooling water and sanitary sewage water will probably not require much treatment before sending it to public water facilities where municipal wastewater is treated. Different wastewater streams are usually not mixed even if it reduces the load on treatment units. This is because different wastewater streams have different components and toxicities. The wastewater’s contamination level depends on its usage in the petroleum refinery. Generally, the pollutants in the streams include hydrocarbons, particularly toxic aromatic compounds such as benzene. Also, the wastewater streams include other heteroatom compounds mercaptans, amines, phenols, and cyanides, dissolved gases (H₂S and NH₃), and acids (H₂SO₄ and HF). Such components require much more treatment than municipal wastewater. In addition, environmental policies such as the Clean Water Act and Safe Drinking Water Act require refineries to effectively treat their wastewater.

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Wastewater that comes into contact petroleum fractions cannot be treated at municipal water treatment facilities. This is because municipal water treatment does not have the equipment to clean the pollutants that are added to the water during petroleum processing. It is also not the job of the municipal water treatment to clean the many poisons that were added to the water during petroleum processing. Municipal water treatment facilities clean the water of sewage and storm run off. The kind of toxic chemicals found in the petroleum refining waste water contain poisonous compounds which under normal circumstances would never come into contact with any water stream. For instance, a multitude of hydrocarbons, aromatic compounds, such as benzene and heteroatom compounds like mercaptans, amines, phenols, cyanide’s. These polluted streams of water also contain dissolved gases like H2S and NH3, acids such as H2SO4 and HF. All of which a municipal waste water facilities is not capable of removing to a safe level for release back into the environment.

While similar in nature, a municipal wastewater treatment facility and an industrial wastewater treatment facility such as one located onsite in petroleum processing plants may not be able to handle mixing input streams. This would especially be the case for adding industrial wastewater to a municipal treatment outfit because they are designed for specific types of pollutants. These pollutants include food wastes, microorganisms, viruses, bacteria, certain nutrients such as Nitrogen and Phosphorous, and household organic products such as pharmaceuticals and soaps.¹ Beyond these contaminants, municipal treatment also controls levels of suspended solids and biochemical oxygen demand (BOD) among other things which do exist in industrial wastewater, however the problems is there are more than just these pollutants coming from refineries. For example, BOD, Nitrogen, Phosphorous, and suspended solids are accompanied by contaminants like oils, hydrocarbons, mercaptans, phenols, toxic compounds such as cyanides and H₂S or even strong acids such as sulfuric acid and hydrofluoric acid. Municipal installations are simply not built to handle these types of pollutants and would therefore either slowly destroy the municipal plant or allow the toxins to flow directly into the clean water supply. A report by the EPA said that refineries may use one to two and a half gallons of water for every gallon of product they produce³ which would lead to an enormous amount of pollutants entering our water supply.

1. Velegol, Stephanie . “CE 370 – Module #7a: Wastewater Components.” Penn State College of Engineering . N.p., n.d. Web. 23 July 2014. http://www.engr.psu.edu/mediaportal/flvplayer.aspx?FileID=4b42d423-1a7d-4e05-accd-9
2. Eser, Semih. “Wastewater Treatment.” F SC 432: Petroleum Processing. N.p., n.d. Web. 23 July 2014. <https://cms.psu.edu/section/content/default.asp?WCI=pgDisplay&WCU=CRSCNT&ENTRY_ID=F20C6357261A4AE2A750C141B721E8C1>
3. “Water & Energy Efficiency by Sectors, Oil refineries.” EPA. Environmental Protection Agency, n.d. Web. 23 July 2014. <http://www.epa.gov/region9/waterinfrastructure/oilrefineries.html#water>.