Refinery Wastewater: Oil & Grease Removal

Refinery wastewater oil and grease removal is a critical process in treating effluent from petroleum refineries. The treatment typically involves multiple stages to separate different forms of oil contamination:

1. API Separators: These are usually the first treatment step, using gravity separation to remove free-floating oil. The oil's lower specific gravity causes it to rise to the surface where it can be skimmed off. Heavier oils settle to the bottom.

2. Chemical Treatment: Emulsified oils, which are suspended oil droplets, require chemical addition to break the emulsion. This often involves lowering the pH.

3. Dissolved Air Flotation: After chemical treatment, the wastewater enters an air flotation unit where dissolved oxygen or nitrogen is used to remove newly separated emulsified oils.

4. Biological Treatment: The final stage uses bioreactors with activated sludge to remove dissolved oils that are in true molecular solution. This process requires careful monitoring and control of factors like temperature (10-40°C optimal), pH (6.5-8.5 ideal), nutrient levels, and dissolved oxygen (1-3 mg/L).

Throughout the process, pH measurement is crucial, particularly at the API separator outlet to indicate potential downstream issues. However, oil coating can cause sluggish pH readings. The biological treatment stage is especially sensitive, requiring precise balance of biomass, air, return activated sludge, waste activated sludge, and throughput to achieve optimal efficiency in removing remaining contaminants.

This multi-stage approach allows refineries to effectively treat their wastewater, removing various forms of oil contamination before discharge or reuse.