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What Do Water Treatment Plants Do?

A water treatment plant treats sewage and stormwater runoff so it can safely be returned to the environment. The cleaning process removes solid particles such as plastics, fabric and organic waste. A water treatment plant uses bacteria to naturally process some of the waste and restore oxygen to the water. The water is recirculated into our waterways.

  1. Screening

    • Screening is the initial filtration process when wastewater reaches the treatment plant. This includes getting garbage and organic material such as wood, rocks and plants, and even dead animals out of the water. This is the first step of a water treatment plant. The water flows in through sewers and pipes. Screens on the pipes allow water to pass but traps larger solid objects.

    Settling

    • The water then flows into one of two settling tanks. A settling tank is a still basin that allows the sediment and sludge in wastewater to settle on the bottom of the pool. Scrapers and skimmers clear the sludge from the bottom and the scum from the tops of the settling tanks. Treatment plant operators control the flow of water from control rooms and take samples to maintain the quality of treatment. The primary water then flows to the next stage of treatment.

    Aeration

    • Aeration is a process that gets dissolved gasses and chemicals out of wastewater by exposing them to air. The air is pumped through the water. Wastewater contains toxins and harmful organic matter such as hydrogen sulfide from human excrement. As the organic matter decays, it uses oxygen. Feeding it oxygen allows it to decay faster as helpful bacteria devour the organic matter. During the process, the "grit" or sand, coffee grounds and other small grains settle to the bottom and are collected.

    Killing Bacteria

    • A chlorine contact tank is used to kill the remaining bacteria in the water. Chlorine is used to treat the water but most of it is gone by the time the bacteria are gone. If residual chlorine exists, it is neutralized using other chemicals. It is important to remove the chlorine from the water because it is harmful to fish, plants, other aquatic life and humans.

    Sludge

    • The sludge collected from the water treatment process is stored in digestions tanks for up to a month. These tanks are heated and encourage bacteria to dissolve the solid waste. As the bacteria break down the waste, they reduce its volume, odor and toxicity. During this step, methane gas is produced, which can be used as fuel to power much of the treatment plant's operations. The remaining solids can be used in soil as fertilizer.

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