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4.1.1. Sour waters stripping 
This operation is a pre-treatment operation before release to the principal wastewater 
treatment. It is necessary due to high content of NH
4
+
and H
2
S. It consists firstly in an 
acidification with a strong acid to dissociate HSNH
4
into H
2
S and (NH
4
)
2
SO
4
and then in a 
vapor stripping of H
2
S and NH
3
. This operation results in sulfur elimination of about 90 to 
98% and ammonium elimination of about 92 to 97%. Phenols are however not well-stripped 
and only 30% of linked ammonia is stripped. 

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Sour waters
Desulfured waters
Vapor
Incineration or 
Claus unit
Figure A-4-1: Sour waters stripping system 
4.1.2. Oil water separation 
Oil water separation is the first step of general treatment of residuals refinery waters. Its 
purpose is to eliminate insoluble hydrocarbons and suspended matters. It is classically carried 
out by gravity. Several separators are available which can be longitudinal (API separators), 
circular, or lamellar.
4.1.3. Physical and chemical purification 
This step is necessary before biological treatment. This technique associates one chemical 
reaction with a physical separation. Most used techniques are coagulation, flocculation, air 
flotation and filtration. It allows elimination of colloidal suspended matters and insoluble 
hydrocarbons. 
4.1.4. Biological treatment 
After physical and chemical treatment, dissolved pollutants are still to be removed. These 
pollutants include soluble hydrocarbons, soluble CODs and BODs, phenols and nitrogen 
compounds. They are biodegradable and can be removed with biological treatment techniques 
such as activated sludge or trickling filters.
4.2. Best management practices 
Treatment techniques are quite well-known and widely used in refineries to treat wastewater. 
However liquid effluents may also result from accidental releases or leaks. In order to prevent 
prevention from these events, management practices can be applied: 
- Regularly inspect and perform maintenance of storages and equipment for prevention and 
control of accidental releases. 
- Maximize recovery into the process and avoid massive discharge of process liquids into the 
oily water drainage system. 
- Construct storage containment basins with impervious surfaces to prevent contamination of 
soil and groundwater. 
- Segregate process water from other wastewaters. 
- Direct spent caustic soda to caustic oxidation before wastewater treatment system.
- Install a closed process drain system to collect and recover spills of MTBE, ETBE and 
TAME. 

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4.3. Pollution prevention 
In addition to these management practices, some pollution prevention solutions can be 
noticed: 
- Control solids entering sewers, which produced more oily sludges. 
- Improve recovery of oils from oily sludges. 
- Identify benzene sources and install upstream water treatment. 
- Recycle and regenerate spent caustics. 
- Use oily sludges as feedstock for coking or crude distillation units. 
- Recycle lab samples. 

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