Refinery Wastewater Treatment for Contaminant Degradation and Removal
Crude oil development and 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 design and operation of modern refinery wastewater treatment plants are challenging and are essentially technology driven. In order to process this wastewater, the sources of wastewater pollutants need to be identified to specific sources and operations, and suitable treatment technologies selected.
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) and chemical oxygen demand (COD) levels of approximately 150–250 milligrams per liter (mg/l) and 300–600 mg/l, respectively; phenol levels of 20–200 mg/l; oil levels of 100–300 mg/l in desalter water and 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. Currently the most important pollutants in wastewater treated stream in refineries is the presence of polyaromatic compounds, phenols and cobalt that are diluted by sea water and discharged into the sea or at a collection pits. The dilution does not degrade or eliminate these specific pollutants, thus making a strong case for the design and implementation of further treatment processes that should include biological reactors.
Biological treatment has proven to be the most economical and reliable tool after preliminary oil/water separation. Among hydrocarbons present in refinery wastewater, phenol is one of the main dissolved components and it is also one of the toughest hydrocarbons to degrade biologically. Proprietary and specialized mix of bacterium can be fitted in the digesters to work simultaneously in combination with other bacteria cultures known for its capacity to degrade phenolic compounds and other aromatic substances.
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