Think of treatment in three key phases:
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Primary Treatment (The Physical Removal): This is the first line of defense. Wastewater enters the plant and flows through large screens to remove bulky items like sticks, rags, and plastic. It then enters a grit chamber to settle out sand and coffee grounds. Finally, the water sits in large circular tanks called primary clarifiers, where heavier organic solids (sludge) settle to the bottom and are scraped away for further processing.
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Secondary Treatment (The Biological Breakdown): The now clearer water still contains dissolved organic pollutants and harmful microbes. In this biological phase, the water is moved to aeration tanks where oxygen is pumped in. This encourages the rapid growth of beneficial aerobic bacteria, which consume the organic matter as food. The water then flows to secondary clarifiers, where these bacterial masses (now called activated sludge) settle out.
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Tertiary Treatment (The Polishing Stage): This advanced stage is for final "polishing" to meet strict environmental standards. It often involves disinfection using chlorine or ultraviolet (UV) light to kill any remaining pathogens. Other processes can remove specific nutrients like nitrogen and phosphorus that cause algal blooms, or use filters to remove any final suspended particles.
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