Is Anaerobic Sewage Treatment Exothermic?

In summary, this is a conversation about a sewage treatment plant that is looking at ways to reduce the amount of heat that is needed to digest the waste. They are considering insulating the tanks that the waste is put in, and also buying a bunch of generators to capture the waste heat and use it to heat the tanks. They are also considering burning the waste methane to generate electricity, but they don't know how much gas is currently being used for that.
  • #1
russ_watters
Mentor
23,126
10,302
And if so, how much heat is produced?

Ok, so here's the problem. We are working with a generator salesman who is trying to sell a bunch of generators to a sewage treatment plant to capture the waste methane and burn it to make electricity. Great idea. The complication is that currently *some* of the methane produced is used to fire boilers to heat the crap to its optimal temperature of 95F for digestion. And we don't know how much gas is currently used for that, so we don't know if we can completely eliminate it (we will recover some of the waste heat from the generators for that purpose, but the efficiency is low).

We're also considering insulating the digester tanks (outdoor concrete tanks 175 feet in diameter) to reduce the need for heating them, but if we insulate them and they produce heat, we'll kill the bacteria.

We have numbers for the methane that is currently being burned-off and for the gas being produced, but they don't match: they are often burning as waste (not in the boilers) more than they produce. This could be because the production numbers are methane only and the burning (flaring) is methane + carbon dioxide, but we don't know those proportions either.

I know aerobic digestion produces heat, but I don't know about anaerobic. Anyone have any insights...?
 
Biology news on Phys.org
  • #2
This reference might be useful:

http://www.cropgen.soton.ac.uk/publication/14_MC%20Process%20Calculations.pdf [Broken]

Unfortunately, it doesn't answer you question, but it provided a simple heat balance.
My feeling however is that the heat balance is not subtantially influenced by the reactions taking place.
 
Last edited by a moderator:
  • #3
Well, the fact that it talks about heat loss and heat input without mentioning biochemical heat production implies that it isn't a significant factor...

Thanks for the link.
 
  • #4
Russ, you need to see case-studies, as the amount of methane (and other combustible gases) will vary wildly with the quality of the feed effluent, the temperature at which it is digested and the type of feed-system and mixing and the configuration of the reaction vessel. The vendor has to pony up, here. No consultant should have to predict the efficiency of such a system based on the (probably vastly inflated) claims of a sales-person. Good luck getting good data, though. The vendors will not refer you to their failures, only to their successes. Been there.
 
  • #6
turbo-1 said:
Russ, you need to see case-studies, as the amount of methane (and other combustible gases) will vary wildly with the quality of the feed effluent, the temperature at which it is digested and the type of feed-system and mixing and the configuration of the reaction vessel. The vendor has to pony up, here. No consultant should have to predict the efficiency of such a system based on the (probably vastly inflated) claims of a sales-person. Good luck getting good data, though. The vendors will not refer you to their failures, only to their successes. Been there.
My issue isn't quite that bad. For starters, this is an existing water treatment plant and they know they are burning off a lot of gas that they could be using to generate electricity (they just don't exactly know how much), so there is a definite upside and a very short payback. The system we are designing will have all the controls necessary to run the existing boilers to keep the digesters warm if the turbines don't put out enough heat for that. So the primary risk is buying 12 turbines and having only 6 run at a time because the gas is needed to fire the boilers. That would piss off the client...

Insulating the tanks could be a secondary project that could be done after a year of datalogging.
 

1. Is anaerobic sewage treatment exothermic?

Yes, anaerobic sewage treatment is exothermic. This means that it produces heat as a byproduct of the biological reactions that take place during the treatment process.

2. How does anaerobic sewage treatment produce heat?

During anaerobic treatment, microorganisms break down organic matter in the absence of oxygen. This process releases energy, which is converted into heat. Additionally, the mixing and agitation of the sewage in the treatment tank also contributes to the increase in temperature.

3. Can the heat produced in anaerobic sewage treatment be utilized?

Yes, the heat produced in anaerobic sewage treatment can be harnessed and used for various purposes. It can be used to heat buildings, produce electricity, or even to heat the sewage itself to maintain optimal treatment conditions.

4. Is the heat produced in anaerobic sewage treatment harmful?

No, the heat produced in anaerobic sewage treatment is not harmful. It is a natural byproduct of the treatment process and is not toxic. However, if the temperature in the treatment tank gets too high, it can affect the efficiency of the treatment process.

5. How is the temperature controlled in anaerobic sewage treatment?

The temperature in anaerobic sewage treatment is controlled through various methods such as adjusting the flow rate of the sewage, using cooling systems or heat exchangers, and monitoring the temperature regularly. This ensures that the treatment process is efficient and the microorganisms are not harmed by extreme temperatures.

Similar threads

Replies
4
Views
3K
Replies
9
Views
2K
  • Chemistry
Replies
4
Views
5K
  • Sci-Fi Writing and World Building
Replies
21
Views
851
  • General Engineering
Replies
4
Views
2K
  • DIY Projects
Replies
23
Views
4K
Replies
8
Views
2K
Replies
13
Views
10K
Replies
152
Views
4K
Back
Top