Oil-Depot Oily Wastewater Treatment Process: Unlocking the Environmental Code of Oil-Water Separation
Throughout the entire process of finished-oil storage, transfer, and loading/unloading, oil depots continuously generate oily wastewater. This wastewater is not ordinary sewage; it carries floating oil, emulsified oil, suspended solids, and trace organic pollutants. If discharged directly, it blocks the aeration channels of water bodies, inhibits the growth of aquatic organisms, and causes long-term pollution of soil and water sources, while also wasting recoverable oil resources. Oil-depot oily-wastewater treatment is a core link in the environmental management of the oil and gas industry. A scientific and complete treatment process can achieve compliant discharge while also recovering oil and saving O&M costs. Today we comprehensively break down the mainstream treatment processes for oil-depot oily wastewater and understand the “oil-water purification logic” of industrial wastewater treatment.
I. First Understand: Characteristics and Treatment Difficulties of Oil-Depot Oily Wastewater
Oil-depot oily wastewater mainly comes from tank-cleaning water, ground-flushing water, rainwater from loading/unloading zones, and equipment condensate. Its water-quality characteristics differ from those of refining and oilfield wastewater, featuringlarge oil-load fluctuation, complex pollutant morphology, and unstable water quality—three core characteristics that are also the key basis for treatment-process design.
From the perspective of existence form, the oil in the wastewater is divided into three types, with treatment difficulty increasing step by step: first,floating oil, with oil-droplet size greater than 50 µm, which rapidly floats and stratifies after standing, accounts for over 70% of the oil content in the wastewater, and is the easiest to remove; second,dispersed oil, with oil-droplet size 20–50 µm, suspended in water, which can slowly stratify after prolonged standing; third,emulsified oil, with oil-droplet size less than 20 µm, stably suspended in water due to surface tension, with oil and water completely blended. It cannot be separated by conventional standing and is the core difficulty of wastewater treatment. In addition, the wastewater is mixed with sand, rust, and colloidal suspended matter; the COD value fluctuates greatly, imposing very high requirements on the adaptability and stability of the process.
II. Core Treatment Logic: Pure-Physical Graded Oil Removal for Streamlined and Efficient Purification
Aviation-fuel oil-depot oily wastewater has clean water quality, stable water volume, and single pollutants, differing from ordinary finished-oil depots and refining wastewater, and does not require complex biochemical degradation processes. The overall treatment follows“multi-stage physical oil removal + auxiliary demulsification + deep filtration purification” as its core principle, relying on pure-physical processes with a small amount of auxiliary chemicals to achieve compliance. By progressively removing floating oil, dispersed oil, trace emulsified oil, and fine suspended matter, the process is streamlined; while ensuring stable and compliant effluent quality, it further reduces equipment investment and O&M costs, fully adapting to the low-pollution, stable-water-quality treatment scenario of aviation-fuel depots.
III. Detailed Explanation of the Full-Process Mainstream Treatment Process
Combining the characteristics of good water quality and small fluctuation of aviation-fuel depots, the industry's common mature process is apretreatment + core precision oil removal + deep purification pure-physical integrated flow that requires no biochemical treatment unit. The whole process is streamlined, efficient, stable in operation, and has a low failure rate, fully meeting the compliant discharge and recycling reuse requirements of aviation-fuel depots. Each stage filters layer by layer and purifies progressively, adapting to the low-impurity, light-pollution water-quality characteristics of aviation-fuel wastewater.
1. Pretreatment Stage: Intercept Impurities and Coarsely Separate Floating Oil
Pretreatment is the first checkpoint of wastewater treatment; its core role is to remove large-particle impurities and the vast majority of floating oil, stabilize influent water quality, and protect subsequent equipment from clogging and wear. It mainly includes two steps.
First isbar screen and sedimentation tank treatment: wastewater first passes through a mechanical bar screen to intercept floating debris such as leaves, packaging bags, and large pieces of sand; then it enters a sedimentation tank, where gravity settling removes suspended solids, rust, and other heavy impurities, preliminarily purifying the water quality.
Next isoil-separator coarse oil removal, which is the core equipment for oil-depot wastewater pretreatment. The mainstream uses an inclined-plate oil separator (CPI), which, based on the shallow-settling principle, greatly shortens the oil-water stratification time. Large floating-oil droplets in the water quickly float to the surface and are collected and recovered by oil-scraping equipment, while sludge and impurities settled at the bottom are regularly discharged. This stage can remove more than 90% of the floating oil in the water; the effluent retains only a small amount of dispersed oil and emulsified oil, reducing the burden on subsequent fine treatment. It has the advantages of low cost, simple O&M, and no chemicals, and is standard pretreatment equipment for all oil depots.
2. Core Oil-Removal Stage: Break Emulsified Oil and Achieve Deep Oil-Water Separation
After pretreatment, the residual emulsified oil cannot be separated by gravity and is the main cause of water-quality non-compliance; it must be deeply removed through a combined coalescing separation + dissolved-air flotation process, which is also the core of the whole treatment system.
Coalescing oil removal: wastewater flows through specialized coalescing media; tiny emulsified and dispersed oil droplets are adsorbed and aggregated on the surface of the media, gradually coalescing into large oil beads that quickly float for oil-water separation. This process requires no chemical addition and is a pure-physical separation, specifically targeting the fine oil droplets remaining after pretreatment, suitable for high-oil-concentration wastewater scenarios, with stable and efficient oil removal.
CDFUDissolved-air flotation (DAF): as the core equipment for fine oil removal, it integrates cyclone separation and dissolved-air flotation dual technologies, generating 5–30 µm ultra-fine bubbles through nitrogen to precisely capture residual emulsified oil and fine suspended matter in the water. After bubbles adsorb oil droplets, they float to the surface to form scum, which is automatically scraped off and separated; the oil-removal efficiency can reach over 90%. The whole process uses nitrogen flotation, which avoids oil oxidation caused by oxygen ingress, ensuring oil-removal effect while recovering high-quality oil and eliminating secondary pollution. Compared with traditional flotation, it has a smaller footprint, higher efficiency, and no chemical consumption.
For a very small number of severely emulsified wastewaters, auxiliarycoagulation demulsification process can be adopted: add efficient coagulants such as PAC and PAM to destroy the stable structure of emulsified oil, allowing fine oil droplets to coagulate into masses and rapidly settle or float, completely solving the difficult separation of emulsified oil.
3. Deep Purification and Compliant Reuse Stage
After pretreatment and core oil removal, the aviation-fuel wastewater's oil content and suspended-solids indicators are basically compliant, with no large amounts of dissolved organic pollutants, so no biochemical degradation step is needed. Only a multi-stage deep-purification process is required to remove trace residual oil stains and fine colloidal impurities in the water, ensuring long-term stable effluent quality and meeting high-standard discharge and depot reuse requirements.
4. Deep Purification and Compliant Discharge Stage
The core deep purification uses aquartz-sand filtration + fine activated-carbon adsorption combined process. Wastewater first enters a quartz-sand filter, which precisely intercepts residual fine sand, colloids, and suspended impurities, further clarifying the water quality; it then flows into an activated-carbon adsorption unit, where the abundant microporous structure of activated carbon strongly adsorbs trace emulsified oil, residual hydrocarbons, and a small amount of off-color and off-odor impurities, completely making up for water-quality shortfalls and preventing fluctuation-induced non-compliance.
The treated clean water can fully meet the discharge standard of the “Technical Code for Wastewater Treatment Engineering of the Petroleum Refining Industry,” and can be either directly discharged in compliance or reused for oil-depot ground flushing, equipment cooling, and green-space irrigation, realizing water-resource recycling. The floating oil, oil sludge, and sludge generated during treatment are uniformly collected, dewatered, and then compliantly disposed of, eliminating secondary pollution.
IV. Core Advantages of the Mainstream Process Combination
The pure-physical process system of “oil-separator pretreatment + coalescing oil removal +CDFU dissolved-air flotation + multi-stage deep filtration,” adapted for aviation-fuel depots, is optimized for the characteristics of good water quality and small water-volume fluctuation of aviation-fuel wastewater, and is more suitable for the scenario than traditional oily-wastewater treatment processes, with four core advantages. First,Streamlined and Efficient Process: it cancels the biochemical treatment unit, with a short flow and fast startup, and no need for strain cultivation or sludge acclimation, adapting to the depot's normalized stable water-supply treatment needs; second,Stable Effluent Quality: multi-stage physical graded oil removal targets various forms of oil pollution in aviation-fuel wastewater, with strong resistance to small water-quality fluctuations and constant compliant effluent indicators; third,Extremely Low O&M Cost: the whole process is mainly pure-physical treatment, with only a small amount of chemicals added in extreme emulsification conditions, no biochemical sludge generation, simple equipment maintenance, and lower energy consumption; fourth,Strong Safety and Environmental Performance: no odor from biochemical systems, no risk of strain failure, high purity of recovered oil, and no secondary pollution, meeting the high-standard safety-control requirements of aviation-fuel depots.
V. Process Application Summary
The core key of aviation-fuel oil-depot oily-wastewater treatment is torely on a streamlined physical process to precisely remove oil, strictly control impurities, and avoid redundant steps. Different from the treatment mode of ordinary oil depots that must be equipped with a biochemical system, aviation-fuel wastewater has clean water quality and single pollutants; through an integrated process of multi-stage physical oil removal + deep filtration, it can fully achieve efficient oil-water separation and compliant water-quality purification, without the need for a complex biochemical degradation flow.
This customized pure-physical treatment process is highly adaptable to the wastewater-treatment needs of various aviation-kerosene depots and aviation-fuel storage depots, fitting the environmental and safety-control standards of the aviation-fuel industry. It not only simplifies the O&M flow and reduces project investment and operating costs, but also stably achieves compliant wastewater discharge and depot recycling reuse, balancing environmental compliance, energy conservation, consumption reduction, and safe production, and is currently the optimal mainstream solution for aviation-fuel oil-depot oily-wastewater treatment.
