Concrete septic tank deterioration. Due to poor venting?

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Old 06-27-19, 03:59 PM
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Concrete septic tank deterioration. Due to poor venting?

So, after fixing a section of my vent stack section I got fascinated with the whole design of newer code systems, and then that led me to more reading.

I found some articles that suggest concrete septic tank deterioration is caused by H2S gas, and poor venting through to the vent stack can be a significant contributor to this problem. Is that true? I noticed my tank, which is only 20+ years old and it looks like it is starting to deteriorate. I also noticed in my basement there is a slight sag in my main line to the tank; thanks to a previous plumber. I have no issues with flushing, no gurgling sounds, etc, and I have intended to fix this sag for no other reason other than it should be done right. Maybe this sag and the effluent its holding is reducing the venting capacity of this pipe.

I realize a bad concrete mix can also be an issue but this has got me wondering.
 
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Old 06-27-19, 05:12 PM
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I've heard/read the gas venting thing as well and I don't buy it. After all, the gas is always present in the tank. Venting back up the main drain line and out the house's vent system doesn't remove the gas from the tank. Hydrogen sulfide is almost always at saturation level inside the tank. If it doesn't vent out through the house's vent system it will leak out through the tank's lids or out through the leach field. I personally believe it has more to do with the quality of the concrete and age.
 
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Old 06-28-19, 03:28 AM
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Yeah. Frankly I'd like to buy an air pump and convert my tank to aerobic operation. There seem to be a lot more advantages than disadvantages with that.

Or, with a short intake vent on a tank, and the long vent stack in the warm house, would stack 'chimney' effect create a steady flow of air into the tank and better exhausting out through the vent stack? However I am in Canada where it gets as low as -20c so maybe having an air vent into a tank is simply asking for trouble.
 
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Old 06-28-19, 03:50 AM
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In Canada I would avoid introducing air into the tank if possible. It would be helpful during summer but in winter it could end up cooling it. Whether or not the increased activity of aerobic bacteria can offset the slowing affect of cold I don't know. Either way I wouldn't bother with a vent. A septic tank without a vent has been proven millions of times to work well. Aerobic with a pump is the only thing I would consider but it comes with expense and added maintenance and don't forget that your aeration diaphragm is at the bottom of 6' of poo juice. Not fun to work on in the middle of winter. There is a reason traditional septic is used so often. It's inexpensive and almost bulletproof when operated properly (no grease or oil).
 
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Old 06-28-19, 03:54 AM
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Thanks Pilot Dane, well said.
 
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