Domestic Wastewater Treatment Methods For Purifying Water
The subject of wastewater treatment encompasses two major types, that of industrial and domestic treatment. Water needing to be treated from domestic sources first undergoes two steps in the decontamination process. The third process, called tertiary treatment, may be followed by disinfection. Many other processes are involved, but these are the principal steps in treating water.
Water contaminated to such a degree that it needs to be significantly treated originates from two main sources. Water coming from a commercial enterprise or industry comes under the heading of industrial waste. The other main source of contaminated water comes from domestic sources, and includes runoff, or excess surface water, and sewage, or water contaminated from domestic household use. Both come under the general heading of sewage treatment.
Sewage is waste material carried in water from domestic sources such as from washing and laundry, from the kitchen sink that is associated with food preparation, and that carrying urine and feces. All of these types contain infectious organisms, including bacteria, viruses, spores and disease causing proteins called prions. Sewage must be treated before being released to the environment as it may cause disease, contamination of rivers, lakes or ground water, or harm to plants and animals due to toxicity.
The first step in treating sewage is termed the primary stage. This consists mainly of releasing the water into tanks for a time where the solid waste may sink to the bottom and the resulting sludge is scraped or pumped off into a separate facility to be treated. Oils and grease are simultaneously allowed to rise to the surface where they are removed using various processes. The primary stage is called sedimentation.
Next is the secondary stage, in which the sludge is treated by aerating it to mix in oxygen, which is necessary so biological processes involving bacteria breaking down the contaminants and binding the remains into solids can occur. These secondary facilities are categorized as either fixed film or suspended growth systems. Fixed film types use a combination of filtration and collecting the solids on a growth medium. Suspended growth methods mix microbes with the sludge so flocculation, the process of forming the waste into solids, can occur.
The tertiary stage is for further improvement of the quality of the water. This is done with a combination of techniques such as sand filtration to remove the leftover contaminants, and lagooning. Lagoons are storage ponds whose purpose is to allow final settling of solids, and reeds and other aquatic plants are allowed to grow to remove any remaining particles. Excess nitrogen and phosphorus are also removed.
The final stage is disinfection, in which substances are added to the water to destroy the remaining microorganisms. Using methods like ozone, chlorine, or ultraviolet light, the water is disinfected enough to release it into the environment. Chlorine is the most common, but may be a health hazard. Ultraviolet is very effective for killing bacteria, but some may remain due to solids in the water. Ozone is the safest, but most expensive approach.
Many other processes are involved before and during wastewater treatment. There are pretreatment steps to screen out larger objects, and grit and grease removal. Finally the treated sludge may be superheated to kill the remaining pathogens and the result is used to manufacture fertilizer pellets for farming.
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Category: Home Management
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