We refer to this industry as the industry that manufactures petrochemicals, which are chemicals derived from petroleum and natural gas. Key products include ethylene, propylene, butylene, benzene, toluene, styrene, xylene, ethyl benzene and cumene. These products are basic building blocks used in the production of consumer products, automotive components and various durable and non-durable goods. Organic compounds like ethyl alcohol and inorganic chemicals like carbon black are not included in this industry.

Crude oil and condensate refineries generate a large amount of wastewater that has both process and non-process origins. Depending on the type of crude oil, composition of condensate and treatment processes, the characteristics of refinery wastewater vary according to a complex pattern.

The petroleum refining industry converts crude oil into more than 2500 refined products, including liquefied petroleum gas, gasoline, kerosene, aviation fuel, diesel fuel, fuel oils, lubricating oils, and feedstocks for the petrochemical industry. Typically, petroleum refining activities start with receipt of crude oil for storage at the refinery, include all petroleum handling and refining operations, and they terminate with storage prior to shipping the refined products from the refinery.

The petroleum refining industry employs a wide variety of physical and chemical treatment processes. A refinery processing flow scheme is largely determined by the composition of the crude oil feedstock and the chosen final petroleum products. Typical processing and auxiliary units in refineries are presented below:


Separation processes

  • Atmospheric distillation
  • Vacuum distillation
  • Light ends recovery (gas processing)

Petroleum conversion processes

  • Cracking (thermal and catalytic)
  • Reforming
  • Alkylation
  • Polymerization
  • Isomerization
  • Coking
  • Visbreaking

Petroleum treating processes

  • Hydrodesulfurization
  • Hydrotreating
  • Chemical sweetening
  • Acid gas removal
  • Deasphalting

Auxiliary facilities

  • Boilers
  • Wastewater treatment
  • Hydrogen production
  • Sulfur recovery plant

Large volumes of water are employed in refining processes, especially for cooling systems, distillation,hydrotreating, and desalting. Tank drains, equipment flushing, surface water runoff and sanitary wastewaters are also generated. It is therefore clear that refinery wastewater can be broadly categorized as process or nonprocess wastewater.

The quantity of wastewaters generated and their characteristics depend on the process configuration. As a general guide, approximately 3.5–5 cubic meters (m3) of wastewater per ton of crude are generated when cooling water is recycled.

Refineries generate polluted wastewaters, containing:

  • biochemical oxygen demand (BOD) of 150–250 milligrams per liter (mg/l)
  • chemical oxygen demand (COD) levels of approximately 300–600 mg/l
  • phenol levels of 20–200 mg/l
  • oil levels of 100–300 mg/l in desalter water
  • oil levels up to 5,000 mg/l in tank bottoms
  • benzene levels of 1–100 mg/l;
  • benzo(a)pyrene levels of less than 1 to 100 mg/l;

Heavy metals levels of:

  • 0.1–100 mg/l for chrome and
  • 0.2–10 mg/l for lead; and other pollutants.

Refineries also generate solid wastes and sludges (ranging from 3 to 5 kg per ton of crude processed), 80% of which may be considered hazardous because of the presence of toxic organics and heavy metals

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