Oily Fire-Fighting Wastewater Disposal Solution

1. Sources and characteristics of oily fire-fighting wastewater

When a fire breaks out at a substation, the foam extinguishing agent and fire water used for firefighting mix with the transformer oil on site, forming complex oily wastewater. Although most of the oil and other pollutants enter the emergency pool, a small amount flows with the subsequent cooling water into the accident pool and must be treated promptly.

Such oily fire-fighting wastewater has the following characteristics:

• High oil content, strongly affecting the sludge activity at wastewater treatment plants;

• Foam extinguishing agents contain toxic substances harmful to sludge activity, such as PFOA;

• The wastewater contains oil and the organic components of extinguishing agents, so TOC and COD are high while BOD is low, indicating poor biodegradability;

• Surfactants in the wastewater alter the physical properties of the oil and reduce flotation performance;

• When adsorption treatment is used, the adsorbent media are easily clogged by oil;

• Because it is a sudden event causing an instantaneous surge in wastewater volume with large quality fluctuations, biological treatment cannot be used for continuous processing.

  
  

2. Conventional disposal of oily fire-fighting wastewater

At present, common disposal routes for this kind of wastewater mainly include the following three:

2.1 Discharge directly into the municipal pipe network or nearby water bodies. This approach not only severely damages the surrounding aquatic ecology but also shocks the biochemical systems of downstream wastewater treatment plants.

2.2 Build large buffer tanks for centralized storage and hand the wastewater over to third-party specialized units. However, buffer tanks occupy considerable land, consume much land resource, and treatment costs are high.

2.3 Build biological treatment ponds and discharge after biochemical treatment. But because of the strong shock load of the wastewater, the biochemical ponds require continuous maintenance, operating costs remain high, effluent quality is unstable, and the compliance discharge rate is low.

3. Innovative treatment process for oily fire-fighting wastewater

Oily fire-fighting wastewater treatment process flow diagram

3.1 Compact cyclonic flotation separator (CDFU), this device draws on advanced international technology and merges two techniques — cyclonic centrifugal separation and flotation separation — with its structure optimized through computational fluid dynamics (CFD), yielding a high-efficiency oil-water separation system at the internationally leading level. The cyclonic action markedly improves bubble flotation efficiency and shortens the time required for flotation, thereby achieving rapid and efficient oil removal; it is widely applicable to many kinds of oily wastewater and suspended-solids-laden wastewater.

Compact cyclonic flotation separator(CDFU)

The technology has the following technical features:

• Oil removal efficiency no lower than 90%, far higher than conventional IGF.

• Low energy consumption (10% of IGF energy consumption), low gas consumption (1%-3% of the treatment volume)

• Low chemical dosing, little sludge produced, low operating and maintenance costs.

• Stable performance, capable of accommodating flow variations from 10% to 120%.

CDFUTechnology advantages comparison

3.2 Modified activated carbon adsorption with high-efficiency regeneration (MACT) — this technology is a patented improved process over conventional activated carbon adsorption and regeneration methods. Through surface modification treatment, the physical and chemical properties of activated carbon are adjusted, enhancing its adsorption capacity for perfluorinated compounds (PFCs) and similar pollutants, thereby markedly raising adsorption efficiency and rate and achieving rapid, highly effective removal of PFC-type substances. Paired with the patented microwave regeneration process, the modified activated carbon is recycled, lowering operating costs. The technology also applies to many advanced wastewater treatment scenarios.

MACT

Compared with conventional methods, MACT technology offers the following advantages:

MACT technology advantages

• Better removal of COD and PFOA; after advanced treatment the wastewater can be discharged directly.

• Fast removal rate, large unit treatment capacity, higher adsorption capacity, more economical use of adsorbent, and longer replacement cycles.

• Modified activated carbon is stronger and does not easily crumble or shed.

• Activated carbon undergoes highly efficient regeneration: short regeneration cycle, high regeneration rate, and lower cyclic-use cost.

• Physical-method regeneration requires no backwashing and generates no additional wastewater.

• Stable performance, capable of accommodating flow variations from 10% to 120%.

Oily fire-fighting wastewater treatment results