Centennial Water District(breadcrumbs are unavailable)

Wastewater Treatment

Where does wastewater come from?

  • Homes– human and household waste from toilets, sinks, baths and drains.
  • Industry, schools and businesses– chemicals and other waste from factories, food-service operations, airports, shopping centers, etc.
  • On average, each person in the United States contributes 50 to 100 gallons of wastewater daily.

How do treatment plants protect our water?

  • Removes solids– This includes everything from rags and sticks to sand and smaller particles found in wastewater.
  • Reduces organic matter and pollutants– Helpful bacteria and other microorganisms are used to consume organic matter in wastewater. The bacteria and microorganisms are then separated from the water.
  • Restores oxygen– Treatment facilities help ensure the water returned back to our lakes or rivers has enough oxygen to support life.

How does a wastewater treatment plant work?

Wastewater treatment usually takes place in two steps:

Primary treatment removes 40 to 50 percent of the solids. Sanitary sewers carry wastewater from homes and businesses to the treatment plant. Bar screens let water pass, but not trash. The trash is collected and properly disposed. A grit chamber is a large tank that slows down the flow of water. This allows sand, grit, and other heavy solids to settle at the bottom for removal later.

Secondary treatment completes the process, so that 85 to 90 percent of the pollutants are removed. A secondary sedimentation tank allows the microorganisms and solid wastes to form clumps and settle. Some of this mixture, called activated sludge, can be mixed with air again and reused in the aeration tank. A disinfectant, such as chlorine, is usually added to the wastewater before it leaves the treatment plant. The disinfectant kills disease-causing organisms in the water. After treatment, the water can be returned to nearby waterways. It can also be used on land for agriculture and other purposes.

What is sludge?

Sludge can be a useful byproduct of treated wastewater. Sludge may be treated, or thickened, to remove some of its water, then be further processed by stabilization. Raw sludge is allowed to decompose in digester tanks. In some cases, special chemicals are used for stabilization. Stabilized sludge has no odor and is free of disease-causing organisms.

Some nontoxic sludge can be safely used as:

  • Soil conditioner to improve the soil for crops in some areas of the nation. Sludge can also improve the soil for lawns, fields and parks.
  • Using certain processes, sludge can also be used to produce methane gas. The methane can then be burned to supply energy for a small power plant or for other purposes.
  • If it can’t be safely used, sludge must be buried in approved landfills or burned using special technology to prevent air pollution.

Who operates treatment plants?

The daily treatment plant operation is conducted by highly trained and certified operators. It requires:

  • A plant manager/superintendent to ensure the plant has enough money, trained personnel and equipment to conduct business.
  • Maintenance personnel to prevent mechanical failures and solve equipment problems.
  • Plant operators who know how to properly treat wastewater before discharging it into the environment. After a thorough training and exam process, operators are licensed through state standards.

Are there any special challenges in treating wastewater?

  • Nutrients- Phosphorus, nitrogen, and other chemical nutrients found in wastewater can damage lakes and rivers. These nutrients need to be turned into less harmful substances, or removed before being released into the environment.
  • Toxic chemicals- Sometimes wastewater contains hazardous chemicals from industry, pesticides, etc. Controlling these chemicals may require pretreatment of wastewater by industries and the use of advanced (tertiary) treatment methods at the wastewater treatment plant.
  • Water infiltration- Water entering the treatment system through cracks or joints in sewer lines or storm drains places an extra burden on a facility.
  • Changes in water flow- The amount and kind of wastewater entering a treatment plant can change quickly. Plant operators must be ready to respond to these changing conditions.