WASTE WATER TREATMENT
PRIMARY TREATMENT
SECONDARY TREATMENT
TERTIARY TREATMENT
the physical settling of solid matter
the biological degradation of organic wastes
the removal of special contaminants such as organic chemicals, nutrients & pathogens
Pre-treatment/screening
traps things like vegetable matter, paper, cloth & plastics
solid waste is washed and compressed to remove any organic matter
put into screening bins and sent to landfill
sedimentation
following the pre-treatment, the water moves on to a clarifier or settling tank
under very calm conditions, sewage solids settle to the bottom of the tank
Not all of the solids are removed in the primary clarifier
-very small, light particles take too long to settle.
The solids collected at the bottom of the tank which are called primary sludge are then pumped from the tank for treatment elsewhere in the plant
Activated Sludge
removes nutrients and remaining solids through bacterial decomposition
uses naturally occurring biological processes
The level of oxygen in the wastewater is changed at different stages
- to produce aerobic & anaerobic environment
These two environments cause different bacterial communities to thrive
different 'communities' of bacteria remove different 'pollution' components from the water during the treatment processes
Those bacteria that require oxygen to convert food into energy are called aerobic
those that will perish in the presence of oxygen are anaerobic
facultative anaerobes may thrive in either the presence or absence of oxygen
Typically aerobes, which can degrade pollutants 10-100 times faster than anaerobes, are utilized most frequently in this treatment process
Clarifier
Just clean water is left
Some of the solids collected in the secondary clarifier are sent back to the aeration tank for re-treatment
The excess (waste activated sludge) is pumped to another location in the plant for further treatment.
The clean water that flows out the top of the clarifier is sent along for disinfection
the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment
removes remaining inorganic compounds, and substances, such as the nitrogen and phosphorus
Bacteria, viruses and parasites, which are harmful to public health, are also removed at this stage