Truly, there is no better cleanser and renovator than living earth. A cleanser, because clay particles in the soil act as electrostatic filters capable of adsorbing virus pathogens before they can migrate; a renovator, because microorganisms, as they work, transform harmful microbes into carbon dioxide and soil nutrients, and produce antibiotics in the bargain.
Oxygen is critical to the absorption field and the creatures in it. Aerobic bacteria — those that thrive in a well-aerated environment — are far better suited to the chore of recycling effluent than are the anaerobic varieties. Without sufficient oxygen, aerobic bacteria and the protozoa that feed on them fall dormant or die. At this point, anaerobic bacteria, fungi and yeasts will take over.
The anaerobic organisms work more slowly and give off less heat. They also process waste material differently than the aerobic variety, creating acids and methane rather than the sugars and fixed nitrogen beneficial to the soil. Under these conditions, ferrous sulfide forms and bonds with algae and dead bacteria to make a layer of insoluble gum, called the organic mat , that clogs soil pores and restricts drainage. This clogging mat exists in limited measure under aerobic conditions and is important to the system as a natural filter. But when it spreads out of control in unhealthy soil, the field will ultimately fail to do its job.