Oily waste water is treated using a combination of conventional and advanced methods, including gravity separation, flotation, chemical treatment, and biological processes. Advanced options like membrane separation (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis) are also used for highly emulsified oils, though they can face challenges like membrane fouling. Often, multiple methods are combined to achieve the desired water quality.

Conventional methods.

Gravity separation: Uses gravity to separate oil from water, which is effective for free-floating oil.

Flotation: Introduces fine bubbles that attach to oil particles, causing them to float to the surface where they can be skimmed off. Dissolved Air Flotation (DAF) is a common type that uses pressurized air to create microbubbles.

Coagulation: Uses chemicals to destabilize and aggregate small oil particles, allowing them to clump together and settle out or be removed by flotation.

Biological treatment: Uses microorganisms that produce enzymes like lipase to break down biodegradable organic substances in the waste water.

Advanced and other methods.

Membrane separation: Employs semi-permeable membranes to physically separate contaminants based on pore size.This includes:.

Microfiltration (MF): Removes suspended solids and oil droplets.

Ultrafiltration (UF): Can remove smaller oil particles, suspended solids, and some dissolved components.

Nanofiltration (NF): Filters out ions and smaller molecules.

Reverse Osmosis (RO): A final treatment step that removes most dissolved salts and molecules, but is very susceptible to fouling from oil.

Adsorption: Uses materials like activated carbon to physically remove oil from the water.

Electrocoagulation: Uses an electric current to cause the aggregation of oil particles.

Chemical precipitation: A process that uses chemicals to convert dissolved pollutants into solid particles that can be easily removed.

Key considerations.

Waste water characteristics: The type and concentration of oil, as well as the presence of emulsified or dissolved oil, determine the best treatment combination.

Membrane fouling: A major challenge for membrane-based systems, where contaminants build up on the membrane surface, reducing its efficiency and requiring cleaning or replacement.

Combination of methods: Oily wastewater treatment often requires a multi-stage approach, using a combination of methods to remove different types of contaminants effectively.