Everyone knows that in areas where a municipal sewer is not available we must install a septic tank, however very few people have any real understanding of how the home septic waste treatment process actually works. While we principally think only in terms of the tank itself, in truth the tank only performs 1/3 of the actual waste treatment process.

Typically a septic tank is divided into two chambers, the sediment chamber and the digester. As the waste enters the sediment chamber any heavy non-digestible wastes settle to the bottom of the tank. It is also in the first chamber where biodegradable solids such as fecal matter or the bits and pieces from the garbage disposal break down into liquid slurry, which then passes through the baffles into the digester compartment. While there certainly is a high level of sewer gas in the upper portion of the sediment compartment, nonetheless, it does receive some atmospheric air from the house vents and sewer line; therefore there is a small percentage of oxygen in the first compartment atmosphere.

The baffle between the first and second compartment extends well below the normal liquid level of the tank so there is no path for atmospheric air to enter the digester chamber, thus any available space between the top surface of the liquid and the tank top is filled with a toxic soup of sewer gas. (Methane, hydrogen sulfide, sulpher-dioxide, and carbon dioxide) In the digester chamber there is a active colony of anaerobic bacteria (bacteria which thrive in the absence of oxygen) that consume most of the biodegradable material leaving a gray water which then discharges into the leachfield.

The leachfield lines are buried fairly shallow, which allows a small amount of oxygen from the atmosphere to permeate the soil and enter the pipes. The oxygen kills any of the anaerobic bacteria that happened to be carried over into the leachfield, while at the same time another colony of aerobic bacteria (bacteria which thrive in oxygen) consume the final fragments of biodegradable material in the gray water. The water then leaches into the surrounding soil through the holes in the leachfield pipe. At this point the water has a high concentration of nitrogen and other elements that are natural nutrients to vegetation thus we are required to have a sod covering over the leachfield so that the grass will consume the nutrients leaving only water.

In some areas where there is a high water table or where the leachfield is in the close proximity of a stream there is the risk that some of the graywater could be carried into the water shed before the total process is complete. In this case they may require that the tank be equipped with a chlorinator.

In its simplest form the chlorinator is a PVC pipe that is connected to the leachfield line and runs vertically up to the surface with a threaded cap on top like a cleanout. About once a month the cap is removed and you drop in large tablets or pucks of chlorine similar to those used in swimming pools, which are then absorbed into the water.

In areas where the soil will not pass a perk test for a leachfield they are now installing an aerated septic tank system. These systems have a 3-compartment tank. The sediment compartment, the digester, and an aerated compartment that takes the place of the leach field. In this type of system you have a small air compressor that supplies air to injector nozzles in the bottom of the tank. In most jurisdictions the aerated septic systems are required to have a chlorinator and the liquid discharged from the final stage may be discharged directly into the surface watershed or storm sewers.

Thx for the info. Can I just use the same 3" tabs that I use for my pool? OR is there some "special" type of tablet to use? If so, where do I purchase?

My personal experience with the chlorinators has only been during the initial installation phase so I am not certain what the requirements are.

I would suggest you call your local health department and ask them if your pool chlorine will work.