Process involves in wastewater treatment

There are four  main steps that have been practiced over the year

Preliminary treatment
Primary treatment
Secondary treatment (or biological treatment)
Tertiary treatment

The above four steps are sufficient to treat the wastewater.
Preliminary treatment involves separating the floating impurities (like Wood, dead body, plastics, etc) from the wastewater

To remove these types of impurities we use large size of screens and the process is called screening.
 

After the screening process wastewater passes through the grid chamber.
Grit chambers are used to remove grit present in the wastewater like gravel, sand, broken glass, fragments of metal, and inorganic solids. It prevents damage to the pumps, and to prevents their accumulation in sludge digesters.

Primary treatment
In primary treatment, we have to remove fine small particle that is silt that couldn't extract from about process. to remove the silt particle we are going to use a sedimentation tank 
Feature of sedimentation tank
Sedimentation tank- sedimentation of solid wastes
It removes almost 60%-70% of fine particles
The colloidal and soluble organic content of wastewater is not removed in this tank
to remove the colloidal particle we have the flocculation method
know about the flocculation method click here

Secondary treatment (biological treatment)
In secondary we remove organic content and pathogens that are dissolved in the wastewater. it can be done in three ways.
Aerobic treatment 
Aerobic treatment is a biological process that uses oxygen to decompose the organic matter and remove other pollutants like nitrogen and phosphorus. It converts organic matter into carbon dioxide and new biomass. During aerobic treatment, oxygen is continuously required so forced air from an air blower or compressor is mixed with the wastewater. The aerobic bacteria feed on the waste in this water and aerobic treatment takes place.
Anaerobic treatment
​Anaerobic digestion is a process in which microorganisms convert organic matter into biogas in the absence of oxygen. It is an energy-efficient process that is typically utilized to treat high-strength industrial wastewater that is warm and contains high concentrations of biodegradable organic matter (measured as BOD, COD, and/or TSS). An anaerobic system can be used for pretreatment prior to discharging to a municipal wastewater treatment plant or before polishing in an aerobic process
facultative treatment
It is a shallow pond consisting of an aerobic zone close to the surface and a deeper, anaerobic zone. AS algae grow on the surface, they produce oxygen, which is consumed by aerobic bacteria in the middle of the pond degrading the BOD. In the lower zones of the pond, anaerobic digestion takes place.