3. Free cultures: mechanisms at play

Free-culture" purification mechanisms are based on the growth of a bacterial culture that is predominantly, but not exclusively, aerobic. Oxygen is supplied by different sources, depending on the plant. Extensive free-culture systems are processes that reproduce and intensify certain self-purification mechanisms that occur naturally in aquatic environments.

Self-purification, which we will examine in greater detail, is the process by which an aquatic ecosystem, such as a river or lake, naturally breaks down the biological pollutants present in the water, without recourse to artificial treatment facilities.

Various mechanisms involved in the self-purification of wastewater in aquatic environments are at play in extensive free-range cultivation.

• Dilution

  When wastewater...