Septic Tanks for On-Site Systems and Enviornmental Concerns

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Tutor

Environmental Science

8th October 2008

Septic Tanks for On-Site Systems and Environmental Concerns

Introduction

The disposal wastes is critical since improper handling may result in pollution of both terrestrial and aquatic environments and more critical , disease outbreaks . It is therefore imperative that waste disposal , particularly sewage disposal be done in a manner that causes less damage to the different ecosystems . While many populated areas such as towns and cities are served by municipal sewer lines (Alth , Alth and Duncan , 1991 )1 , this is not possible in

rural areas where there is sparse population as it would not only be expensive to construct the sewer line but it would also be underused . Therefore , since rural areas are not served by sewer lines , homeowners must establish subsurface sewage discharge systems in the form of an individual family unit waste treatment tanks . Such systems are known as septic tanks (Alth , Alth and Duncan , 1991

Structure and function of septic tank systems

Septic tank systems comprise an underground tank and a seepage or drain channel that function together to ensure that household wastewater is cleansed (Alth , Alth and Duncan , 1991 . The septic tank is watertight (does not allow entry of water from any other channel except the source and is designed to separate solids from liquids (Massey , 1998 )1 It is estimated that in each 100 gallons of wastewater there is 0 .75 pound of solids (Massey , 1998 . Therefore , once the wastewater gets into the septic tank , the heavier portions of waste settle to the bottom while less dense particles and grease rise to the top

To be efficient , the tank should hold the wastewater for at least 24 hours (Massey , 1998 . This long span (retention time ) gives bacteria ample time to break down most of the solids . Bacterial activity is very vital in that bacteria convert the solid wastes into gases and liquids that are not as deleterious as the solids would be (Massey , 1998 Figure 1 below shows a structure of the septic system and specifically where the wastes settle for digestion

Source : Insect '1

Once the solids have been digested , any new entry of sewage into the tank causes the accumulated gases to move up through the drainage vent pipes into the atmosphere through ventilation located above the roof of the building . Further , as new sewage gets into the tank , an equal amount of digested sewage is forced through the outlet into the drainage (drain ) field (Figure 2 . A connection to a drainage field can be a subsurface system of made of pen joints or pierced pipes fixed below the outlet . As the effluent (waste ) moves through the perforated regions , it is oxidized and therefore evaporates (Massey , 1998

Figure 2 : Illustration of the drain field

4Source : Miller , 2007

At the end of bacterial digestion , tiny amounts of solids remain at the tank 's bottom as sludge , whereas lighter undigested materials settle at the surface of the liquid as scum . While the septic tank can last for between 15 to...