Septic Tank Air Pump - Necessary?

Roxburgh_rose

I have lived in houses with septic tanks for the last 30 years - either brick built or plastic tank and rarely had issues with them. The house I've recently purchased has a plastic septic tank with an air pump. I've never had an air pump before. Does anyone have advice on whether they are really necessary? Most of the information I can find online is from air pump suppliers so, remarkably, suggest they're essential! Thanks :-) 

Strummer22

Is it actually a septic tank, or a sewage treatment plant (STP)? A septic tank would probably discharge to a soakaway, whereas as STP results in a cleaner effluent and might discharge to water. 

Roxburgh_rose

Strummer22 said:

Is it actually a septic tank, or a sewage treatment plant (STP)? A septic tank would probably discharge to a soakaway, whereas as STP results in a cleaner effluent and might discharge to water. 

It's definitely a septic tank. It discharges to a soakaway running down the adjacent field. Ultimately the soakaway would drain to a burn but that's ~500m away 

Strummer22

I would not know for sure, but I guess if it has an air pump, then running the air pump is necessary for optimum operation. I've got an STP which is clearly designed to be aerated so I've not had to think about this issue previously.

From brief reading around the issue, aeration makes the breakdown of sewage more effective. An anaerobic system will have a larger treatment volume and soakaway to account for the slower treatment process. Not using the air pump would potentially compromise the system and result in rapid sludge build up and/or minimally-treated sewage discharging into the soakaway. Lovely.  

Section62

Roxburgh_rose said:

Strummer22 said:

Is it actually a septic tank, or a sewage treatment plant (STP)? A septic tank would probably discharge to a soakaway, whereas as STP results in a cleaner effluent and might discharge to water. 

It's definitely a septic tank. It discharges to a soakaway running down the adjacent field. Ultimately the soakaway would drain to a burn but that's ~500m away 

The septic tank process is anaerobic, hence the name 'septic'.  I.e. it shouldn't need to have excess air added.

However, the decomposition of waste is incomplete in the anaerobic process, which is why if you want to discharge to a watercourse the effluent needs to undergo a second aerobic treatment to reduce the biochemical oxygen demand (BOD) below the maximum permitted by the discharge consent.

What I was taught about sewage treatment processes was that reducing the introduction of air prior to the completion of the anaerobic process was the goal because you want the anaerobic bacteria to thrive to do their work on the effluent.... but maybe the people selling these air pumps have made some new scientific discovery which turns that logic on its head?

Roxburgh_rose

Strummer22 said:

 

Not using the air pump would potentially compromise the system and result in rapid sludge build up and/or minimally-treated sewage discharging into the soakaway. Lovely.  

No wonder the field is so green 

Roxburgh_rose

Section62 said:

What I was taught about sewage treatment processes was that reducing the introduction of air prior to the completion of the anaerobic process was the goal because you want the anaerobic bacteria to thrive to do their work on the effluent.... but maybe the people selling these air pumps have made some new scientific discovery which turns that logic on its head?

That was my understanding too. But 'scientific discoveries' that miraculously result in sales of more stuff must trump your actual knowledge and my basic Googling  .  Maybe I'll risk turning it off and see what happens...

Kiran

So I was under the same impression as others, that septic tanks were anerobic in operation. Having googled it there is also an aerobic septic tank method. I found this info which gives you the low down and pros vs cons etc.

Anaerobic Septic System Explained & Differences Between Aerobic Septic System | Septic Tank Pro

Section62

Kiran said:

So I was under the same impression as others, that septic tanks were anerobic in operation. Having googled it there is also an aerobic septic tank method. I found this info which gives you the low down and pros vs cons etc.

Anaerobic Septic System Explained & Differences Between Aerobic Septic System | Septic Tank Pro

That American site is best ignored - you were right the first time that septic tanks are anaerobic.

The wording they use is confused and misleading - what it describes as an aerobic 'septic tank' is what we would call a secondary treatment system.