The Septic Tank, Septic Tank Additives and the Pirana

Its been a month or more since I've left a blog for anyone who discovers this site to read. Due to the economic down turn changes in my schedule have taken up most if not all of my time. But as Jack Nicholson is famous for saying, "He's back!!!!!!"

Here is a subject that may be common knowledge (or not?). The subject is frequently asked in two questions: Is it a good idea to put in additives into my septic tank on a monthly basis? When my septic system is nearing failure, should I start putting additives into my septic tank? Here's how I answer these questions.

No one can say with absolute certainty when a disposal field will fail. The only judgments anyone can make are based on the averages that have consistently been observed over the years for disposal field life expectancy. 20 to 25 years is the most common time frame.

When a disposal field is nearing failure due to age, or there are early indications that failure is imminent, putting bacteria, enzymes and chemical additives into a septic tank on a monthly basis by the homeowner, hoping to extend the life of the disposal field, is not a good idea. Putting additives monthly during the life of a septic system is even a less good idea. It is not possible to stop people from doing so, therefore the EHDs don't make prohibitions about doing it. They rightfully recommend against it however. Here's why.

The ultimate purpose of a septic tank is to sequester and thus remove bio-solids from the waste stream by separation into sinkable and floatable solids through intestinal bacteria activity within the septic tank. This is commonly called "primary treatment". The intestinal bacteria in your solid waste don't digest the organic material in the septic tank (they didn't in your intestines so how can they in a septic tank?) but they break apart molecules making up the solids into solids that can sink to the bottom of the tank forming what is called sludge and this allows solids that can now float or rise to the surface of the effluent to form a solids layer called scum. This removes between 70 and 90 percent of the solids you just put into water to take them out of your house by gravity. To do this most effectively, there is a minimum retention time for the effluent to remain in the septic tank. This is why you have to pump your septic tank; to remove these sequestered solids so the retention time for liquid to remain in the septic tank stays within the design limits. Eventually solids take up space and reduce the liquid capacity of the septic tank, reducing retention time. What people are doing with the additives they put into their tank every month is short circuit the sequestration process.

The bacteria, enzymes and chemicals additives breakdown and solubilize some of these sequestered solids and allow them to leave the septic tank (where they belong) and travel in suspension within the effluent to the disposal field. There these solids form a congealed sludge and can potentially decrease the functional life of the disposal field. People feel better and believe they are doing something powerful for themselves by having to pump their septic tank less frequently. The reality is different. They aren't removing solids from the system, they are merely moving them to another area of the system, the disposal field. The potential for decreasing the functional life of the disposal field is more problematic and could be more costly than saving some pumping costs. Homeowners putting these products into a septic tank are potentially damaging the most expensive aspect of their septic system...the life of the disposal field.

If you are willing to pay for a highly over priced disposal field replacement, then my comments about these additives are not germane to you. But if you want to make certain that you are not doing anything to compromise the potential functional life of your disposal field, then you are well advised not to put these bacteria, enzyme and chemical additives into the septic tank. Allow the tank to provide the sequestration as its designed to do and pay for periodic pumping. Pumping is cheap compared to the potential for early disposal field replacement.

Thanks for stopping by.