Analysis and Treatment Challenges of Oil-Containing Wastewater in Light Oil Storage Tanks
1. Sources of Oil-Containing Wastewater in Light Oil Storage Tanks
The oil-containing wastewater in light oil storage tanks mainly comes from the following processes:
· Water Draining in Oil Tanks: During the oil storage process, water, due to its density difference, settles at the bottom of the tank. The oil content in manually separated water often exceeds 500 mg/L, while automatic dehydrators can reduce the oil content to below 300 mg/L. For example, the oil content in manually separated water from a gasoline storage tank can reach up to 14,828 mg/L, highlighting the necessity of control.
· Tank Cleaning Water: Cleaning operations, especially water washing, generate high-concentration oil-containing wastewater, with instantaneous discharge levels exceeding 3,000 mg/L. The wastewater contains emulsified oil and suspended solids, and is chemically complex.
· Pipeline Leaks: Oil leakage due to pipeline aging, corrosion, or interface defects leads to contamination of soil or groundwater, forming a long-term pollution source.
· Other Sources: These include wash water from loading and unloading areas, pump seal leaks, and initial rainwater runoff from tank areas (which may contain condensed oil droplets from the tank roof), all of which have a dispersed and sudden pollution characteristic.
2. Characteristics and Treatment Challenges of Light Oil Tank Wastewater
Wastewater Characteristics
Indicator | Typical Value | Treatment Challenge |
Oil Content | 500-150,000 mg/L | High percentage of emulsified oil, low efficiency of traditional gravity separation |
Suspended Solids | 100-600 mg/L | Clogs traditional filter elements, increasing maintenance costs |
Form of Oil | Floating oil, emulsified oil, dissolved oil coexist | Requires multi-stage process combination for treatment |
BOD/COD Value | Low (150-670 mg/L) | Difficulty in biochemical treatment, requiring more physical-chemical methods |
Treatment Challenges
· Emulsified Oil Demulsification: Oil droplets smaller than 10 μm require special coalescing materials for separation.
· Significant Composition Fluctuations: Wastewater from different sources has significant variations in oil content and suspended solids, requiring flexibility in the treatment process.
· Strict Environmental Standards: Must meet the "Comprehensive Wastewater Discharge Standards" or industry-specific indicators (e.g., petroleum ≤10 mg/L).
· Operational Cost Constraints: Traditional processes (e.g., flotation + membrane filtration) face issues such as clogging, high energy consumption, and frequent material replacements.
