Septic tanks contain bacteria that grow best in oxygen-poor conditions.
These bacteria carry out a portion of the treatment process by converting
most solids into liquids and gases. Bacteria that require oxygen thrive in
the drain field and complete the treatment process begun in the septic
tank. If the septic tank is working well, the waste water which flows out
the tank is relatively clear, although it still has an odor and may carry
disease organisms. It should flow only into the drain field, never onto
the ground surface or into Florida waters.
A septic system, properly installed and
is a good way to treat wastewater and to protect groundwater quality when
municipal sewer service is not available. A typical septic system
consists of two major parts, the septic tank and drain field.
Waste from toilets, sinks, washing machines and showers enters the
tank, which is a holding tank generally made of pre-cast concrete or
fiberglass and is sized according to the estimated wastewater flow from a
given-sized residence or business.
The septic tank separates the wastewater into three general components --
solids or "sludge", floatable or the "scum layer", and a
zone of relatively clear water. Anaerobic bacteria (able to live in an
oxygen-free environment) perform the first treatment of the wastewater,
generating gas that is vented through the vent stack of the building's
plumbing, and breaking the solids into a liquid form. The oxygen-free
conditions inside the septic tank also deactivate some of the disease germs
that are found in sewage.
From the septic tank, the liquid portion of the wastewater flows into the
which is generally a series of perforated pipes or slotted panels that are
usually surrounded by a layer of gravel, tire chips, or other lightweight
materials such as Styrofoam pieces. The drain field provides secondary
treatment of the sewage by allowing aerobic (oxygen-using) bacteria to
continue deactivating the disease germs that remain in the wastewater.
The drain field also provides filtration of the wastewater as gravity draws the
water downwards through the soil layers. In addition, evaporation of
water occurs through the layer of soil covering the drain field.
In some areas where soil types such as clay layers or bedrock exist, or in
areas where there is a shallow seasonal high water table, septic systems must
be elevated above the ground surface ("mounded" systems). This
ensures the wastewater has sufficient permeable or unsaturated soil in order
to provide adequate filtration before the remaining wastewater reaches the
groundwater table and the underlying aquifer.
In other areas, such as flood zones near rivers or other bodies of water,
traditional septic systems may not be sufficient to treat the wastewater.
In these cases, advanced wastewater treatment systems that "aerate"
or add oxygen to the wastewater may be required. Other advanced
wastewater treatment systems may have chlorinating chambers or peat moss-based
filtration chambers which neutralize the disease germs before they can reach