These are the most common types of systems. Effluent is settled in a septic tank and then disposed of into trenches or beds. The septic tank pre-treats the wastewater before it goes to the land application system. Three main things happen in the septic tank:
•Solids settle to the bottom of the tank and form a layer of sludge.
• Lighter wastes such as fat and grease float to the surface and form a scum layer.
• Bacteria, which live in the septic tank, help break down the solid wastes and reduce the volume of sludge collecting in the bottom of the tank.
It is important to remember that:
•Septic tanks do not remove nutrients.
•The wastewater is not disinfected and because it is highly infectious it must be applied to land below ground level where bacteria can digest the pollutants and pathogens.
•A poorly operated and maintained septic tank will allow excessive solids to pass to the land application system causing it to clog. This will result in health hazards and a need for expensive reinstatement of the absorption area.
•Desludging of the septic tank is required every 3-5 years depending on use.