Historically unit operations have been
grouped together to provide various levels of treatment. Preliminary
and/or Primary Treatment refers to physical unit operations
and is the first stage of treatment applied to any sewage.
Secondary Treatment refers to biological and chemical unit
processes, while Tertiary refers to combinations of all three.
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| Preliminary Sewage
Treatment |
Preliminary sewage treatment
is defined as the removal of sewage constituents that may cause
maintenance or operational problems with the treatment operations.
This includes screening and comminution (grinding) for the removal
of debris and rags, grit removal by sedimentation and flotation
for the removal of excess oil and grease. |
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| Primary Sewage Treatment |
In primary treatment
screening and sedimentation remove some of the suspended solids
and organic matter. The effluent from primary treatment will
contain high amounts or organic matter. |
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| Secondary Sewage
Treatment |
Secondary sewage treatment
is directed at the removal of biodegradable organic and suspended
solids, mainly using biological unit processes. Disinfection
may be included in secondary sewage treatment. |
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| Tertiary Sewage
Treatment |
Tertiary sewage treatment includes the
removal of nutrients, toxic substances including heavy metals
and further removal of suspended solids and organic. Effluent
from tertiary treatment is of a high standard and suitable
for reuse.
There is no plan to build tertiary treatment
systems in Malaysia. The focus has been providing a basic
standard of preliminary, primary and secondary treatment.
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