1. Sources of Oil Contamination in Water
Global oil pollution enters aquatic systems through multiple pathways:
•Industrial Processes: Petroleum refining, metalworking coolants (e.g., rolling mill emulsions)
•Transportation: Rail tank cleaning, ship bilge water, vehicle wash runoff
•Commercial Operations: Food processing, textile manufacturing, restaurant grease
•Environmental Impact: 5-10 million tons annual contamination worldwide, causing:
• Elevated COD/BOD levels
• Flammability hazards
• Persistent odors/discoloration
2. Classification of Oil Forms in Water
| Form | Particle Size | Properties | Separation Difficulty |
|---|
| Free Oil | >100 μm | Rapidly surfaces as continuous film | Low (Physical skimming) |
| Dispersed Oil | 10-100 μm | Unstable suspension, aggregates over time | Moderate |
| Emulsified Oil | 0.1-10 μm | Stable dispersion, resists gravity separation | High |
| Dissolved Oil | <0.1 μm | Molecular-level homogeneity with water | Very High |
| Oil-Solid Complex | Variable | Adsorbed onto suspended solids | Medium-High |
3. Advanced Removal Technologies
► Primary Separation Methods
•Air Flotation: Introduces micro-bubbles to attach oil droplets → 1000x faster ascent
•Membrane Filtration: Hydrophobic membranes block oil/surfactants (0.01-1μm pore size)
•Electrochemical: Aluminum/iron anodes destabilize emulsions via electrolysis
► Chemical & Biological Solutions
•Coagulation-Flocculation: Polymer-based agents (e.g., polyaluminum chloride) aggregate droplets
•Activated Sludge: Microbial consortia metabolize dissolved oils (COD reduction >90%)
•Biofiltration: Fixed-film bioreactors degrade organic fractions
4. Treatment System Selection Guide
| Influent Oil Conc. | Recommended Technology | Output Range | Key Equipment |
|---|
| >1000 ppm | Physical Skimming | 30-200 ppm | Belt/disk skimmers |
| 300-600 ppm | Coalescing Separators | 10-15 ppm | Corrugated plate interceptors |
| 100-150 ppm | Integrated Solid-Liquid Separation | 5-10 ppm | Multi-stage filtration trains |
| <5 ppm Target | Advanced Membrane Systems | <1 ppm | Nanofiltration/RO units |
5. Technical Considerations
•Emulsion Breaking: Critical pretreatment for chemical/biological systems (pH control + demulsifiers)
•Footprint Optimization: Compact systems (e.g., dissolved air flotation + membrane bioreactors) for space-limited sites
•Cost Drivers:
• Energy consumption: Electrochemical > Biological > Physical
• Maintenance: Membrane replacement vs. adsorbent regeneration
