FAQ > Sewerage > Glossary-Sewerage
Glossary (Sewerage)
1. Biochemical Oxygen Demand (BOD)
The amount of oxygen consumed by micro-organism to break down organic matter.
2. Bypass
When untreated, or not fully treated, sewage bypasses the sewage treatment facilities, usually caused by plant failures or flows exceeding plant capacity.
3. Chlorination
The application of chlorine to potable water or sewage to remove disease-carrying microorganisms.
4. Dechlorination

A process that neutralizes the toxicity of chlorine and chloramines (a by-product of chlorine).

5. Sewage Outfall
A submarine tunnel or pipeline which carries treated effluent away from the shoreline into deep waters where the treated effluent can be diluted and dispersed.
6. Disinfection
Removal of disease-causing micro-organism such as bacteria and parasites in wastewater by chemical or physical processes.


7. E. coli (Escherichia coli)
Faecal bacteria found in the digestive tract of mammals, which are used to indicate presence of wastewater contamination within an environment.
8. Effluent reuse
A process which recycles treated sewage for useful purposes e.g. flushing, watering plants, etc. instead of discharging it to sea or waterway. 
9. Flocculation
Agglomeration of suspended particles in the sewage to form larger settleable flocs by aid of addition of chemicals in the treatment process.
10. Grit
Hard and heavier solid matters in wastewater, usually inorganic such as sand, gravel, ash, glass, metal fragments, etc.
11. Infiltration
Water entering the sewerage system through cracked pipes or faulty joints.
12. Nutrients
Compounds required for growth by plants and other organisms.  Phosphorus and nitrogen are major plant nutrients.
13. Odour scrubber
A device for removing odours released during sewage treatment process.

14. Screenings
Materials removed from wastewater by screening processes during the preliminary treatment. 
15. Scum
Materials that float to the surface of wastewater during sedimentation in the treatment process.
16. Sedimentation
A treatment process which allows particles to settle out of the sewage.
17. Septic tank
Underground tank used for treatment of wastewater through chemical process. 
18. Sewage
All the used water that goes down the drain from the bath, shower, laundry, sink, drain and toilet and the waste from commercial and industrial establishments.
19. Sewage Pumping stations
Buildings that house mechanical pumping equipment used to lift sewage from lower ground to higher ground.
20. Sewage treatment: Preliminary Treatment
The initial stage of wastewater treatment process through screening and de-gritting to remove large solid matters such as paper, cotton tips, plastic, as well as heavy particles, like sand, gravels, ash, glass, etc. from wastewater.
21. Sewage treatment: Primary Treatment
Removal of solid waste and suspended solids from the sewage by screening and sedimentation processes.  Typically 30% to 40% of BOD, and 55% to 65% of suspended solids are removed in a primary treatment process. 
22. Sewage treatment: Chemically Enhanced Primary Treatment (CEPT)
A sewage treatment process that involves adding chemicals like ferric chloride to increase the removal of suspended solids and other pollutants through sedimentation. The CEPT process at the Stonecutters Island Sewage Treatment Plant is removing some 70% of BOD and 80% of suspended solids from the sewage.
23. Sewage treatment: Secondary Treatme
Purification of sewage by means of biological treatment processes after the sewage has undergone primary treatment to capture the dissolved organic matters in the sewage and remove further the suspended solids in the sewage.  Typically this process can remove between 80% of BOD and 90% of suspended solids.
24. Sewage treatment: Tertiary Treatment
Highest level of treatment consisting of a combination of physical, chemical and biological processes with the objective of removing nutrients and any remaining suspended solids in the sewage. 
25. Sewage treatment plant
A facility that treats sewage collected from the sewerage system before discharging it to sea or watercourse.
26. Sludge
Solid matter removed from the sedimentation and biological treatment processes.
27. Suspended solids
Particles in sewage that can be removed by sedimentation process.
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