After 2 years I had my 8 year old septic tank pumped out for the second time. When we looked inside we found that the area above the outlet had concrete deterioration. Whatever happened ate through about 1/2 to 1 inch of the concrete. Doing some research I read about the lack of oxygen can cause a form of acid which can do this.

Is this correct, and will an aerator system resolve the problem?

1 Answer 1


There are several forms of acidic (sulpheric mainly) conditions causing concrete to decompose, external and internal.

External acid can be caused by sulpher in the ground water.

Anaerobic bacteria can indeed cause hydrogen sulphide gas which then can cause sulpheric acid. High levels can quickly destroy a septic tank.

Aeration of the sludge effluent changes the chemistry to aerobic bacteria and stops the formation of HS gas.

Update The phenomenon of HS gas formation leading to concrete deterioration is known as Crown Rot. Anecdotally, this has been linked to several sources. High vegetable matter (from garbage disposer use) and high levels of sulpher in well water. Active venting does seem provide benefits in reducing the HS gas. (thanks to Capt. P).

  • It's me, Capt. Pedantic again. Sludge is actually the indigestible material at the bottom, there is no point aerating that, you want to leave it undisturbed. You want to aerate the sewage above that layer. I wonder if simply venting the tank would help, if it is not already. One should strongly desire to avoid the mechanical complexity of an aeration system unless completely necessary.
    – bcworkz
    Apr 5, 2013 at 18:43
  • Like any economic decision, only the OP can decide if a tank replacement in x years is a better decision than the expense of an aeration system.
    – HerrBag
    Apr 5, 2013 at 19:17

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