Q&A
What happens after they clean out your septic tank? Well, it’s complicated.
CreditVictoria RobertsQ. When septic tanks get emptied, what happens to the contents?
A. The tank of a home septic system should be emptied every few years by a licensed contractor, usually with a vacuum truck. The target is the sludge at the bottom called septage, mostly human waste that the useful bacteria in the septic tank have not been able to digest.
In the United States, there are government standards for licensed septage processing facilities, public and private. The waste may be treated with municipal wastewater and discharged. Or septage may be processed separately in a dedicated facility, undergoing several stages of treatment. The end product may be buried, burned or spread on fields as fertilizer.
[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]
In the many places where the waste becomes fertilizer, it is treated to stabilize it and greatly reduce the disease-causing bacteria it carries. Lime is used to cut the acid content, and aerobic and anaerobic bacteria digest the septage further.
Substances like sawdust may be added as the material is composted, much like a garden compost heap. The heat generated during composting helps kill harmful bacteria and can produce burnable gases.
The stabilized septage is spread on the surface of agricultural land, plowed under it, or injected below the surface.
