- Septic system design - USGS
A septic system is like a small sewage treatment plant attached to a building, typically a private dwelling. The sewage system receives all the dirty water from the building – everything that goes down the drain or is flushed down the toilet – removes all the solids from the water, cleanses it of disease-causing organisms, filters it, and returns it to the local environment.
Nature has a system for cleaning water and removing solids and bacteria. For example, water flowing through bogs and marshes is rendered clean through filtration and the activities of plants, microscopic organisms, and other species. Septic systems are the same: they take advantage of the natural activities of microbial species, and the filtering capacity of the soil, to cleanse wastewater.
Septic tank design
In typical septic systems, wastewater leaving the home is deposited in the septic tank, a holding tank where solids settle out and form a layer of thick sludge on the bottom of the tank. Some substances in wastewater float, and these accumulate at the top of the septic tank in what is commonly referred to as the scum layer. Between the scum and the sludge, there is a layer of relatively clean water – the clear zone.
In the septic tank, anaerobic bacteria (bacterial that grow in the absence of oxygen) begin the process of breaking down organic material and removing potentially harmful organisms from the water. Any gas produced escapes through a ventilation pipe.
The septic system drain field
While sludge and scum are trapped in the septic tank, water from the clear zone can move along into the septic field (or drain field). The drain field is built with perforated pipe laid down on porous material that allows water to percolate through.
Water flowing through the pipes escapes into the porous material and either evaporates or filters down through the soil. In the process, aerobic bacteria help to remove any remaining organic material and harmful organisms. By the time the water returns to a body of water or water course in the environment, it is clean.
There are different septic system designs to address a variety of different circumstances. When the conditions are difficult, a septic system can be designed by an engineer to meet wastewater treatment requirements.
Sources:
- Canada Mortgage and Housing Corporation. “Your Septic System.” cmhc-schl.gc.ca Accessed Feb 01, 2011
- Columbia County Health Department. “How Does a Septic System Work?” Florida Department of Health doh.state.fl.us Accessed Feb 01, 2011
Rosemary Drisdelle - Rosemary Drisdelle has been published many times as a nonfiction writer and several times as a poet. Her first book, Parasites: Tales of ...
