Waste Water is water that has been used. It could be used by residences, businesses and industries in a community. It includes substances such as human waste, food scraps, oils, soaps, and chemicals. It also includes storm runoff. Although some people assume that the rain runs down the street during a storm is fairly clean, it isn’t.
We consider wastewater treatment as water use because it is also interconnected with the other uses of water. It is the process of removing contaminants for waste water both runoff and domestic. It includes physical, chemical and biological processes to remove physical, chemical and biological wastes.
The site where waste water is processed before it is discharged back to the environment is called a Waste Water Treatment Plant (WWTP). Waste Water Treatment comprises of Preliminary, Primary, Secondary, and Tertiary Treatment.
The Preliminary treatment is the first step in waste water treatment. It includes screening out, grinding up or separating debris to protect the pumping and other equipment in the treatment. The treatment equipments such as bar screens, comminuters (a large version of garbage disposal) and grit chamber are used as the waste water first enters a treatment plant. The scattered debris are usually disposed in a landfill.
In Primary treatment, the different influent sewage water is strained to remove all large objects that are deposited. It removes the materials that can be easily collected from the raw wastewater and disposed of.
Many plants have sedimentation stage where the sewage is allowed to pass slowly through large tanks, commonly called “primary clarifiers” or “primary sedimentation tanks”. Waste Water are stored there for several hours. It allows particles to settle to the bottom and greases to float to the top. Its main purpose is to produce both a generally homogenous liquid capably of being treated biologically and a sludge that can be separately treated or processed.
Secondary treatment is designed to substantially degrade the biological content of the sewage. Sewage microorganisms are cultivated and added to the wastewater. The microorganisms absorb organic matter from sewage as their food supply. Secondary treatment is classified as fixed film system, suspended film system and lagoon system.
Fixed film systems grow microorganisms on substances such as rocks, sand or plastic. It includes trickling filter and rotating biological contactors where the biomass grows on media in and the sewage passes over its surface.
In Suspended film system- such as activated sludge, the biomass is well mixed with the sewage and can be operated in a smaller surface. It stir and suspend microorganisms in wastewater.
Lagoon systems are shallow basins which hold the waste water for several months to shallow basins which hold the waste water for several months to allow for the natural aeration and microorganisms in the waste water to renovate sewage.
The Final or tertiary treatment focuses on removal of disease causing organisms for efficient quality before it is discharged to the receiving environment. Treated wastewater can be disinfected by adding chlorine or by using ultraviolet light. High levels of chlorine may be harmful to aquatic life in receiving streams. Treatment systems often add a chlorine-neutralizing chemical to the treated wastewater before the discharge.
Advanced treatment is necessary in some treatment system to remove nutrients from wastewater. Chemicals are sometimes added during the treatment process to help settle out or strip out phosphorus or nitrogen. Some examples of nutrient removal system include coagulant addition for phosphorus removal and air stripping for ammonia removal.
Why should we treat waste water? Much of the water used by homes, industries and businesses must be treated before it is released back to the environment. It may harm the marine life and us too.
Sources:
http://ohioline.osu.edu/aex-fact/0768.html
http://ga.water.usgs.gov/edu/wuww.html
http://en.wikipedia.org/wiki/Sewage_treatment
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