source:LASEN Environmental Protection release date:2025-02-26 Number of reads:4678
1.Problem Statement
In steel mills, concentrated and dilute oily wastewaters are generated during production processes such as cold rolling, hot rolling, and color coating. These wastewaters primarily contain emulsified oils, degreasers, lubricants, surfactants, sulfides, suspended solids (SS), iron (Fe), acids, alkalis, and other organic or inorganic contaminants. The composition of this oily wastewater is highly complex, exhibits poor biodegradability, and is extremely stable. Moreover, steel mill wastewaters typically contain large amounts of iron oxides and surfactants, along with high concentrations of oil and emulsified substances, substantial flow volumes, all of which result in very high treatment costs.
2.Client Requirements
The client hopes to effectively treat the emulsified wastewater so that the treated effluent meets national or local discharge standards, ensuring regulatory compliance. At the same time, they aim to minimize treatment costs and improve treatment efficiency as much as possible. The client also requires the treatment process to be stable and reliable, minimizing secondary environmental pollution. Additionally, they would like to recover certain resources from the wastewater—such as oil—to reduce overall production costs.
3.Treatment Challenges
Complex composition: The wastewater contains a variety of organic and inorganic contaminants that interact with each other, significantly increasing the difficulty of treatment.
Poor biodegradability: Conventional biological treatment methods struggle to effectively degrade the pollutants, making it difficult to achieve satisfactory treatment results.
High stability: The emulsified oil droplets carry surface charges, forming a stable emulsion system that is difficult to break and separate.
Large wastewater volume: The substantial quantity of wastewater requiring treatment places high demands on the capacity of treatment equipment and processes.
4. Treatment Processes and Water Treatment Chemicals(AI生成)
Treatment Process
A combination of process equipment and chemical agents is employed, with the main treatment sequence being mixing → flocculation → sedimentation.
Water treatment chemicals
Demulsifier: A demulsifier is a surfactant capable of breaking emulsions and exhibits strong reverse-phase demulsification capability. It functions by partially displacing the stabilizing film around emulsified droplets, thereby eliminating the repulsive and attractive forces that maintain the emulsion. This allows the oil in the emulsion to coagulate into floc-like particles ("alum flowers"), facilitating oil-water separation.
The demulsifier can be dosed directly or first dissolved in a preparation tank to form a 10–20% solution. After thorough mixing, the solution is pumped into the reaction tank for dosing.
This chemical performs best under acidic conditions (pH ≤ 7). The typical dosage ranges from 500 to 5,000 ppm (i.e., 0.5–5 kg per ton of wastewater). The exact dosage should be determined experimentally based on the concentration and type of emulsified substances present in the wastewater.
Coagulants: Examples include polyaluminum ferric chloride (PAFC), ferrous sulfate, and polyaluminum chloride (PAC). After adding the demulsifier and stirring for 2 minutes, the coagulant is introduced to further aggregate the fine flocs into larger, denser flocs, facilitating subsequent sedimentation and separation.
5.Treatment Performance
After treatment with the demulsifier and coagulant, the stability of the wastewater is disrupted, causing oil substances to flocculate into floc-like particles ("alum flowers") and enabling effective oil-water separation. The resulting supernatant is clear and can either be directly reused in subsequent biochemical processes or discharged in compliance with environmental regulations. This approach meets the client’s wastewater treatment requirements, significantly reduces environmental pollution, and partially recovers oil resources from the wastewater, thereby lowering overall production costs.
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