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Paola RicordTechnical Description: Septic Tanks

St. Clair College

Technical Description: Septic Tanks

Introduction and General Description

A septic tank is a private sewage disposal system also known as on-site water treatment system. It is used to treat the wastewater coming from your house and move it into the soil and groundwater environment. They are out of sight and when maintain properly odorless. Septic tanks are used in rural areas or in places where the municipal sewage services are not available.

The septic tank is a watertight box, usually made of concrete, fiberglass or polyethylene with a pipe coming from your house and a pipe going to the underground soil. It’s made out of four major parts: the house sewer drain pipe, the septic tank and the drainfield.

Water flows from the house sewer pipe to the septic tank, the septic tank holds the wastewater long enough so that liquids and solids can separate. Once they separate they form three layers, which are called: scum (oil and greases lighter than water), clarified water and sludge (solids at the bottom). The clarified water comes out through the drainfield and the soil acts as a natural filter.

Description and Function of the Parts

Sewer drain pipe

All the wastewater that exits the house through a pipe and eventually to the septic tank.

The septic tank

The septic tank collects all the discharges from the sewer drain pipe and provides the needed time for wastes to settle or float. They are broken in three layers, the bottom layer:

the heavy solids that settle to the bottom of the tank where they are broken down by bacteria and forms sludge. The top layer: the lighter solids, fats and grease, partially decompose and rise to the surface to form a layer called scum (that helps with the decomposition of solid materials). The middle layer: partially treated wastewater after the separation process.

Compartments and a T-shaped outlet in the septic tank prevent the sludge and scum from leaving the tank and traveling into the drainfield area. Eventually the only layer that makes it to the drainfield is the middle layer, which is the treated water.

Drainfield

Is a system of trenches and distribution pipes that are surrounded by clear stone and gravel. The drainfield needs to be in a location where the soil is permeable so that the soil can adsorb the water coming from the septic tank. The drainfield must be properly sized, constructed and maintained to assure satisfactory operation and long life. The wastewater exits the septic tank and is deposit into the drainfield for further treatment by the soil. The soil acts as a natural filter by removing harmful bacteria, viruses, and nutrients. The partially treated wastewater is pushed along into the drainfield for further treatment every time new wastewater enters the tank.

Summary and Operating Description

The septic tank holds wastewater from the home that comes though a pipe called sewer drain pipe until solids settle at the bottom of the tank (the sludge layer or bottom) and lighter waste, such as oil, rises to the top to form the scum layer. Between the two layers lies clarified water, which flows into an outlet pipe (T shaped pipe) and is gradually dissipated through a drain field where the soils acts as a natural filter. Bacteria in the septic tank naturally break down organic waste matter and slow the accumulation of the sludge layer. The sludge layer sitting at the bottom needs to be pump out every 3 to 5 years.

The wastewater comes from the sewer drain pipe goes into the septic tank and clear water comes out of the septic tank through a T-shaped pipe and to the drainfield which transfers the clarified water to the soil so the soil can finish treating the water by deleting bacteria and germs.

Operating cycle: you flush your water closet or other domestic appliance the wastewater travels through the pipe called sewer drain pipe, the waste water goes into the septic tank. The septic tank holds the wastewater long enough so the liquids and solids are able to separate, after the separation process they are divided in three layers called the scum, the sludge and clarified water. The clarified water leaves the septic tank through a T shaped pipe and goes into the drainfield. The drainfield moves the water through perforated pipes surrounded by clear stone so they can be transferred to the soil. The soil acts as a natural filter and finishes treating the water.

Reference List

http://www.who.int

http://www.alcamservices.com

www.septicleanse.com

https://www.health.ny.gov