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APPENDIX
1
ABBREVIATIONS
AND GLOSSARY OF TERMS
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| 1.
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Activated
sludge
A secondary (biological) treatment process in which sewage
is aerated with a biologically active sludge causing the
microorganisms to remove pollutants from the sewage. A
further settlement stage is required to separate the sludge. |
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| 2. |
Baffle
A device used in a tank to promote a more uniform flow
through the tank and to avoid short-circuiting. |
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| 3. |
Biochemical oxygen demand (BOD)
The amount of dissolved oxygen consumed by microbiological
action when a sample is incubated, usually for 5 days
at 20oC. It is a measure of the concentration
of biologically degradable pollutants in the sample. |
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| 4. |
Biological filter (Biofilter)
A type of secondary treatment process which consists of
a bed of inert material (moulded plastics, clinker, stones
etc.) on to which microorganisms will grow so as to promote
aerobic degradation of sewage. |
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| 5. |
Comminutor
A grinder or shredder that converts bulky solid wastes
into small particles. |
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| 6.
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Dry
weather flow (DWF)
The average daily flow to the treatment plant without
the influence of stormwater infiltration due to rainstorms. |
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| 7. |
Extended aeration
The extended aeration process is a type of secondary (biological)
treatment. It is a modification of the conventional activated
sludge process and operates in the endogenous phase of
growth, in which there is not enough food remaining in
the system to support all of the microorganisms present.
The microorganisms are aerated and suspended within the
sewage, where aerobic degradation of the pollutants takes
place. Residence time is of the order of 24 hours compared
to around 6 hours in conventional activated sludge tanks. |
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| 8. |
Mixed liquor suspended solids (MLSS)
The concentration of dry solids (in milligrams per litre)
of mixed liquor in the aeration tank of an extended aeration/activated
sludge plant. |
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| 9. |
Primary treatment
The treatment of sewage to a stage where the settleable
pollutants are removed by physical means (usually gravity
sedimentation). |
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| 10. |
Primary sedimentation tank
A primary treatment process. It is a gravity sedimentation
tank in which the majority of settlable solids are removed
from the crude sewage flowing through it. It is placed
before the secondary (biological) treatment processes. |
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| 11. |
Rotating biological contactor (RBC)
A type of secondary treatment process. It is a unit consisting
of a series of closely spaced, parallel discs, mounted
on a rotating shaft which is supported just above the
surface of the waste water to be treated. Microorganisms
grow on the disc surface where aerobic degradation of
the pollutants takes place. |
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| 12. |
Secondary sedimentation tank
Part of the secondary treatment process (e.g. biological
filters or an activated sludge plant) in which settleable
solids or humus resulting from the degradation of pollutants
are separated from the effluent. |
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| 13. |
Secondary treatment
Also called biological treatment, referring to the treatment
of sewage to a stage where the pollutants (settleable,
colloidal and dissolved) are removed biologically by the
action of microorganisms. |
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| 14. |
Septic tank
A primitive type of primary treatment process. It takes
the form of a settlement tank in which the sludge is retained
for sufficient time for the organic matter to undergo
anaerobic decomposition. |
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| 15. |
Sewage
The water-borne wastes of a community. |
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| 16. |
Sludge
A mixture of solids and water produced during the treatment
of sewage. |
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| 17. |
Sludge yield
The quantity of solids left over at the end of the secondary
treatment processes, consisting of dead cells, surplus
microorganisms, non-biodegradable matters. |
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| 18. |
Suspended solids (SS)
Solids in suspension in sewage liquors as measured by
filtration through a glass fibre filter paper followed
by washing and drying at 105oC. Expressed in
milligrams per litre (mg/L). |
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| 19. |
Tertiary treatment
A further stage of treating sewage following secondary
(biological) treatment processes, usually by filtering
the secondary effluent to remove suspended solids. Consequential
removal of residual BOD may also occur. |
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