Briefly describe Pretreatment, Primary Treatment and Secondary Treatment for
municipal wastewater.
https://en.wikipedia.org/wiki/Sewage_treatment We are not going to do your work for you.
Pretreatment, primary treatment, and secondary treatment are essential steps in the process of treating municipal wastewater.
1. Pretreatment:
The purpose of pretreatment is to remove large solids and debris from the wastewater before it enters the treatment plant. This step is crucial in order to protect the equipment and infrastructure of the wastewater treatment plant from damage. It generally involves three main processes:
a) Screening: Wastewater flows through screens that trap large objects such as plastics, rags, and branches.
b) Grit Removal: The wastewater then goes through a grit chamber where sand, gravel, and other heavy particles settle to the bottom.
c) Primary Sedimentation: In this step, the wastewater is allowed to sit in large tanks, allowing suspended solids to settle to the bottom. This process helps in removing a significant portion of suspended solids and organic matter.
2. Primary Treatment:
Primary treatment involves the physical separation of suspended solids and the reduction of organic matter in the wastewater. This step is achieved through the use of sedimentation tanks or clarifiers, where the velocity of the wastewater is reduced. This decrease in velocity allows suspended solids and organic matter to settle at the bottom of the tank. The settled solids, known as primary sludge, are removed and further processed separately. Primary treatment does not effectively remove dissolved pollutants or nutrients from the wastewater.
3. Secondary Treatment:
Secondary treatment is designed to remove dissolved and colloidal organic matter, as well as nutrients such as nitrogen and phosphorus from the wastewater. It mainly relies on biological processes in which microorganisms break down the remaining organic matter. There are two commonly used methods for secondary treatment:
a) Activated Sludge Process: This process involves mixing the wastewater with a large population of aerobic microorganisms in a tank. As the microorganisms consume the organic matter, they form a floc-like mass known as activated sludge. The wastewater is then aerated to provide sufficient oxygen for the microorganisms to thrive. Afterwards, the activated sludge is separated from the treated wastewater in a settling tank, and a portion of it is returned to the treatment process as "seed sludge."
b) Trickling Filters: This process includes allowing wastewater to trickle over a medium, such as rocks or plastic materials, which are then colonized by microorganisms. As the wastewater passes through the filter, the microorganisms attached to the medium break down the organic matter.
After secondary treatment, the wastewater typically undergoes disinfection to kill any remaining pathogens before being discharged into receiving water bodies or reused for various purposes.
In summary, pretreatment removes large solids and debris, primary treatment focuses on physical separation, and secondary treatment uses biological processes to break down organic matter and remove dissolved pollutants.