Treatment 101

Wastewater treatment/reclamation facilities:

  • Remove solids – everything from rags and plastics to sand and smaller particles found in wastewater;
  • Reduce organic matter and pollutants – naturally occurring helpful bacteria and other microorganisms consume organic matter in wastewater and are then separated from the water; and,
  • Restore oxygen – the treatment/reclamation process ensures that the water put back into our rivers or lakes has enough oxygen to support life.

Wastewater treatment/reclamation basically takes place in three stages:

  1. Primary treatment, which removes 40-60% of the solids.
  2. Secondary treatment, which removes about 90% of the pollutants and completes the process for the liquid portion of the separated wastewater.
  3. Solids Processing or Sludge Management, which treats and disposes of biosolids.


Follow along with the captions beneath the pictures below to take a virtual photo tour of a Boone County Regional Sewer District Wastewater Treatment Plant.

  • Treatment Tour 1

    1. Bar Screen

    Primary Treatment - Upon arrival via the sewer collection system, the wastewater is sent through a bar screen, which removes large solid objects such as sticks and rags. All the collected debris from the bar screen is disposed of at a sanitary landfill or recycled.

  • Treatment Tour 2

    2. Equalization (EQ) Basin

    Flow continues from the bar screen to the equalization (EQ) basin. The flow rate of the incoming raw wastewater from the plant's service area's collection system varies throughout the day. The EQ basin absorbs the surges in flow and allows us to pump at one constant flow rate throughout the day, making it easier for an operator to maintain stable plant operation.

  • Treatment Tour 3

    3. Aeration Tank

    Secondary Treatment - Secondary treatment is a biological treatment process that removes dissolved organic material from wastewater. The wastewater from the EQ basin flows by gravity into an aeration tank. Here it is mixed with solids containing micro-organisms that use oxygen to consume the remaining organic matter in the wastewater as their food supply. The aeration tank uses air bubbles to provide the mixing and the oxygen, both of which are needed for the micro-organisms to multiply. Watch a video of microscopic ciliated protozoa.

  • Treatment Tour 4

    4. Clarifier

    After leaving the aeration tank, the liquid mixture, composed of solids with micro-organisms and water, is sent to the clarifier. Here the solids settle to the bottom where some of the material is sent to the solids handling process, and some is recirculated to replenish the population of micro-organisms in the aeration tank to treat incoming wastewater.

  • Treatment Tour 5

    5. Digester or Sludge Storage Basin

    Solids Processing - Primary solids from the EQ basin and secondary solids from the clarifier are sent to the digester or sludge storage basin. During this process, micro-organisms use the organic material present in the solids as a food source and convert it to by-products such as methane gas and water. Digestion results in a 90% reduction in pathogens and the production of a wet soil-like material called "biosolids."

  • Treatment Tour 6

    6. Excess Biosolid or Sludge Removal

    The District removes excess biosolids or sludge from its treatment facilities and transports the material to the City of Columbia. The City has a sludge management program and bills the District for taking care of the treatment and disposal of the sludge the District’s plants produce.

  • Treatment Tour 7

    7. Ultraviolet Disinfection

    Some permits require more treatment especially when the reclaimed water will be returned to a waterway that is used for recreational activity such as fishing and swimming. Many of the District's plants disinfect the effluent to kill harmful bacteria before releasing the effluent into receiving waters. Although there are many methods available to kill these micro-organisms, chlorine and ultraviolet disinfection are used most widely. If chlorination is the method used at a particular facility, the water must be dechlorinated to remove residual chlorine. Following disinfection and dechlorination, the treated wastewater can be returned to the receiving waters from which it came. The flow is conveyed to an outfall and discharged through a series of diffusers into a surface water body or stream.