All waste water effluents from the industries which are discharged to public and/or natural water sources or directed to recycling purpose inside the industry and may contain a wide variety of matters in solution or suspension should be controlled according to the requirements imposed by the final destination.
In any case elimination of the waste or the hazard potential of the waste shall be ultimate goal in the management of hazardous wastes. Under no circumstances shall the effluent water cause oil traces on the surface or embankments of the receiving water, or affect the natural self-purification capacity of the receiving water to such an extent that it would cause hindrance to others.
Under no conditions shall polluted streams be combined with unpolluted streams if the resultant stream would then require purification.
In general main sewer systems in the industry shall be segregated according to the following categories:
- Storm Water Sewer System.
- Oily Water Sewer System.
- Non Oily Water Sewer System.
- Chemical Sewer System.
- Sanitary Sewer System
- Special Sewer Systems
In all areas including process, offsite and utility Units, provisions shall be made to foresee any of the above mentioned sewer systems as required.
Also Drain systems are separated in to two sections “Closed drain system” and “Open drain system”. Process fluids contained in equipment must be collected when equipment are emptied for their maintenance.
KASRAVANAD’s drain system process description is:
The volume can be significant hence must be recovered.
The inventory is collected from the bottom of the vessels to a recovery vessel in the Closed Drain piping system where it flows by gravity.
The word "Closed" refers to the fact that the drainage system is not open to atmosphere.
The fluid is hazardous/ flammable so that it must be piped in a closed piping system, not in contact with atmosphere, to the recovery vessel.
On the other hand, numerous operations, such as bleeding the small process fluid inventory between two isolation valves to dismantle a filter or for inserting an isolating spade etc. will require small amounts of process fluids to be disposed off.
A plant will have numerous such small bleed-off points.
Due to the small inventory of process fluids contained, the drain valves will be open directly to atmosphere.
These drains are, for this reason, called "Open Drain".
They will be collected either by mobile equipment or dumped in the area water drainage.
INDUSTRIAL MAIN SEWER SYSTEMS shall consist of pipes and open ditches collecting clean and/or oily storm waters, fire and washing waters from the non-polluted areas.
The storm water shall be disposed to the oily storm water basin located in the waste water treatment area through the storm water network. It shall mainly collect the following non-polluted areas clean waters:
- Diked and undiked tank areas
- Unpaved areas
- Process and utilities non-polluted paved areas (excluding concrete paved areas)
- Roads, yards and roofs
The collected storm water after oil removal in the oily storm water basin shall be stored in the clean storm water basin.
The final disposal of such clean waters will be to:
- Waste water treating Unit at API separator(s) effluent for further oil removing.
- Evaporation pond(s)
- Ocean/river if complies with the local conditions of effluent waste streams
Oily Water Sewer System shall collect:
- Process spillages and drainages
- Drains of all hydrocarbon equipment
- Pumps and compressors cooling water
- Oily condensate
- Cooling water drains which have a chance of becoming polluted with oil
- Waters coming from all hydrocarbons pollutable paved areas mainly including the following:
- Process Units
- Non-volatile products truck loading stations
- Transport & mobile plant garage
- Pump stations
- Pipe trench drains
- Sample point drains
- Drainage from level gages, cocks and similar equipment
Drains of the following fluids are excluded because of flowing in pit for truck disposal:
- Heavy viscous fluids such as asphalt
- Motor gasoline contaminated with TEL
- Any fluid containing hazardous materials with concentrations more than allowable figures set out by the environmental and/or biological treatment restrictions
The system shall consist of drains, funnels, underground piping, clean-outs, catch basins, manholes, sealed manholes and vent pipes. The final main of the oily water sewer shall flow into API separator(s) in Waste Water Treating Area through a dedicated underground gravity flow network. Open ditches shall be avoided. Leakages of manifolds can be collected in a suitable collecting basin, located underneath the manifold. The basin shall drain into a sump located outside the manifold/piping area. The sump can be emptied intermittently (e.g., by vacuum truck) or it can be connected to the continuously oil contaminated drain system.
Non-Oily Water Sewer System shall collect special oil free waters containing high total dissolved solids such as:
- Boiler blow-down
- Desalination Unit blow-down
- Brine drainage
- Neutralized effluents from all neutralization sumps through the plant
- Storm, fire and washing run-off waters from sulphur solidification and crushing area after removal of sulphur particles through a sedimentation sump
- Tempered water system drains
- Cooling water (circulated) blow-down and drains, provided that there is no possibility of oil contamination