Wastewater Treatment In Oil Refineries
Refineries are among the major consumers of water that has both process and non-process origins. The average refinery requires 2.5 gallons of water for every gallon of crude oil processed. Depending on the type of crude oil, composition of condensate and treatment processes, the characteristics of refinery wastewater varies widely. The design and operation of modern refinery wastewater treatment plants are challenging and are driven by technology. This article will highlight the most common types of waste streams in a refinery and suitable wastewater treatment strategies.
Types of wastewater streams in refineries and treatment technologies
A large volume of water is used in refining processes, especially for cooling systems, stripping, fractionation, and desalting. Additionally, tank drains, equipment flushing, surface water runoff and sanitary wastewaters are also generated. Refinery water sources can include surface water, purchased municipal water, or groundwater wells. The goal of the treatment process is typically a combination of removal of suspended solids, organic material, dissolved solids, and oil & grease. Typical refinery wastewater treatment includes primary treatment such as oil/water separation, and a clarifier to remove solids; secondary treatment to remove organics, metals, and other contaminants; and tertiary treatment for polishing before discharge into the environment.
Surface water/Raw influent - Screening equipment is used to remove large pieces of solid matter that would interfere with subsequent processing operations or would cause damage to equipment such as pumps. Coarse screening devices may consist of parallel bars, perforated plates, wedge wire or wire mesh. Parkson’s Aqua Guard® In-Channel Self-Moving Media Screen and Rotoshear® Internally-Fed Rotating Drum Screen are cost-effective options for removing debris from surface water. Screens may be followed by DAF, clarifier or filter for further treatment.
Oil/Water separation - This is normally the first, and arguably the most important, wastewater treatment step in most petroleum refineries. Removing the bulk of free oils and greases from the plant wastewater stream reduces overloading and other problems in downstream treatment processes. Parkson Oil/Water Separators can be used for tank wash, ballast water, desalter waste, and storm wastewater run-off. Oil/Water separation is typically followed by processes for additional removal of O&G and suspended solids.
Solid/Liquid separation - The three most widely used processes for solid/liquid separation are gravity sedimentation, flotation and filtration. Chemical pre-treatment is typically required prior to separation to increase the solids removal efficiency. Parkson’s Lamella EcoFlow® and DynaSand® ENR Filtration System are proven technologies of suspended solids removal from a variety of refinery wastewater streams.
Biological treatment - Biological wastewater treatment is the most widely used technology for removing organic compounds in refining and petrochemical industries. Biological treatment can be aerobic or anaerobic. Aerobic treatment includes trickling filters or activated sludge process in aerated lagoons, oxidation ditches, or packaged tanks. VariOx™ jet aeration offers high oxygen transfer efficiencies and excellent mixing characteristics in a variety of refinery wastewaters. EcoCycle SBR™ (sequencing batch reactor) and Biolac® Long Sludge Age Process offer a simple, reliable, and cost-effective solution for many treatment applications.
Effluent guidelines
The effluent guidelines and standards are established for direct discharge and pretreatment for indirect discharge. The Clean Water Act prohibits anybody from discharging "pollutants" through a "point source" into a "water of the United States" unless they have an NPDES permit. The permit contains limits on what you can discharge, monitoring and reporting requirements, and other provisions tailored to the operations of the polluting facility. The permittee may choose which technologies to use to achieve the effluent permit levels. The national pretreatment program identifies specific discharge standards and requirements that apply to sources of nondomestic wastewater discharged to a publicly owned treatment works (POTW).
EPA is conducting a detailed study of the petroleum refining category to consider revisions to the regulations. They are additionally collecting various data about wastewater characteristics from petroleum refining companies to re-evaluate effluent standards and guidelines.
For additional information on any of the Parkson technologies mentioned, please visit https://www.parkson.com/