Sewage treatment

Primary &
secondary
processes remove
90% of all solids &
organic wastes

Solid
objects
(rags,
disposable
diapers,
etc)

Sand,
grit,
coffee
grounds
settle to
bottom

Primary
Clarifier

Suspended
particles
settle to
bottom
(sludge) &
Grease floats
to top
(skimmed
off)

Microorganisms
decompose organic
materials – Air/O2
bubbled into H2O –
swirling increases
biological activity

Secondary
clarifier-
sludge settles
to bottom

Protozoa &
some viruses –
Uses:
Chlorination,
UV,
ozone

Discharge
(effluent)
released
into
waterway

* Tertiary
treatment
(see below)

Microorganisms
decompose organic
materials – Air/O2
bubbled into H2O –
swirling increases
biological activity

Secondary
clarifier-sludge
settles to bottom

* Tertiary
treatment
(see below)

Discharge
(effluent) released
into waterway

Protozoa &
some viruses –
Uses:
Chlorination,
UV,
ozone

Suspended
particles settle to
bottom (sludge) &
Grease floats to top
(skimmed off)

* Tertiary Treatment
•-- to remove phosphates, nitrates, salts,
radioactive materials, pesticides

•-- chemical or physical processes to
remove specific pollutants (absorption,
oxidation, reverse osmosis)

•-- mostly done by industries & some
municipalities

Solid objects (rags,
disposable diapers,
etc)

Sand, grit,
coffee grounds
settle to
bottom

Primary &
secondary processes
remove 90% of all
solids & organic
wastes

Primary
Clarifier