Wastewater Dangers

• There are numerous hazards associated with residential and industrial wastewater. Organisms feeding on material in the wastewater can cause illness in people and animals. Chemicals in the wastewater can degrade or destroy natural habitats. Recreational areas lose their value when pollution enters the water system. In some cases, contamination is below the level that an average person could detect. However, many of the pathogens in wastewater are dangerous even in minute quantities.
  
  

Physical Disinfection

• Filters and screens are physical methods of cleaning wastewater. In septic systems, certain soils surround the tank and naturally cleanse the discharged water. Clay or sand slow the progress of the wastewater, allowing for bacteria and other microorganisms to consume pathogens. Boiling is another method for disinfecting wastewater. On a large scale, however, boiling becomes inefficient. None of these physical disinfection methods alone are enough to return water to pristine quality.
  
  

Chlorination

• Chemical disinfection has been the wastewater treatment method of choice since the early 20th century. Chlorine is effective at killing most bacteria, viruses and protozoa that pose risks to human health. The drawback to chlorine as a disinfectant is that it must be removed before treated water is released -- chlorine is itself toxic to life. Even low concentrations of the chemical can prove deadly for marine life. Sodium bisulfite added to the water will remove any chlorine residue.
  
  

Ultraviolet Radiation

• The same radiation that leads to suntanned skin can be harnessed to disinfect wastewater. Ultraviolet lamps immersed in dirty water kill virtually all harmful organisms. Ultraviolet radiation is at least as effective as chlorine as a disinfectant, and it leaves no toxic residue. Cost is the only prohibiting factor preventing ultraviolet radiation's large-scale use. For small treatment facilities with limited budgets, chlorine is still the most economical solution for wastewater disinfection.
  
  

Ozone

• Recently, ozone has begun to get attention as a wastewater disinfection method. Ozone is a gas composed of three oxygen atoms. It's highly energetic, having the ability to tear apart most microorganisms. Ozone also leaves no residue in the water. In fact, ozone increases the oxygen content of water, a beneficial side-effect of disinfection. Despite its advantages, ozone as a disinfectant is not yet cost-competitive with either chlorine or ultraviolet radiation. Some larger facilities in the United States are experimenting with ozone as an additional tool in their treatment process.