Final answer:
Sewage treatment involves primary, secondary, and tertiary treatments to remove solids, decompose organic materials, and further purify the sewage before discharge or reuse.
Step-by-step explanation:
In a wastewater treatment plant, the treatment of wastewater or sewage is a crucial process that occurs in various phases to ensure that the water can be safely returned to the environment or reused. The sewage treatment process involves the primary, secondary, and tertiary treatments, each targeting different contaminants and serving separate functions within the overall system.
In the primary phase, sewage undergoes pre-treatment to remove coarse solids and materials such as sand and gravel through screening. Following this, it is stored in a settling basin to allow organic solids, fat, and grease to separate from the liquid. The sludge settles at the bottom, and oil and other lighter substances rise to the top. These layers are removed, and the liquid proceeds to the next phase.
The secondary treatment involves aerobic bacterial decomposition of the organic solids remaining in the sewage. During this stage, microorganisms break down the organic material into a more stable form. The goal is to significantly reduce the biological oxygen demand of the wastewater, making it less harmful to the environment when released.
Tertiary treatment provides an additional level of refinement. Here, nutrients like nitrogen and phosphorus may be removed, and the water undergoes further filtration to eliminate additional impurities. Disinfection also occurs in this stage, often through the use of chlorine, ozone, ultraviolet light, or bleach, to eradicate residual pathogens.
The processed water can then be discharged into local water bodies, such as rivers, or it can be reused for other purposes including irrigation, habitat preservation, or artificial groundwater recharge. Special handling of the concentrated organic solids, now referred to as sludge, is also required, and it may undergo additional processing such as anaerobic digestion, which can produce methane as a renewable energy source.
Proper sewage treatment is essential for protecting public health and the environment from the various pollutants present in untreated sewage. With the knowledge of these three treatments, it is possible to improve the quality of our fresh water and tackle the water pollution crisis.