poo power

[StressMan79]

how much power (heat) does your septic tank put out? the reason I ask is I am pouring my own septic tank, and building up the walls with cement block...
so I was thinking, would it be worth it to put Pex in the slab-bottom of the tank (almost 50 sq ft), then run this in a closed loop into the radiant floor system in the house.
Anyway, if it puts out 3 watts, and I might be able to capture 1 W, this would not be worth it, but if it were more like 100 x that much, I may consider...
-Peter

[JD]

Peter,
I see where you're going but I don't think you would get much heat from your septic tank. The heat generated in, say, a compost pile is due to the aerobic (with oxygen) bacteria digesting the solids. A septic tank is primarily an anaerobic (without oxygen) digester and does not produce much heat. If you're interested in capturing waste heat, and you have a compost pile, here are just a few links that I dug up. There are plenty more if you search for compost heating.
http://www.motherearthnews.com/Renewable-Energy/1981-07-01/DIY-Water-Heating-Compost.aspx
http://www.motherearthnews.com/Modern-Homesteading/1980-05-01/Compost-Heat-Experiment.aspx
http://www.magicsoil.com/Heat/index.htm

[loghousenut]

Not only the heat put out but, more importantly, you may want to capture the heat that went into the septic tank in the form of hot water going down the drain....................... OK, I'm just gonna sit back and watch this discussion progress to the point that someone insulates their sewer pipe between the house and the septic tank hahahahahhahahaaaahhhhhh.
PS, I know it's a serious topic. Go for it Peter.

[Bronco]

Peter are you going to coat the inside of your tank with something to keep seepage in ?
Jim

[StressMan79]

is not that large of a concern, as solid concrete is a pretty good filter...
However, I will cast a slab and then build the walls with dry stacked block, then fill a few of the holes with CC +rebar for strength and use Surface Bonding Concrete to "seal" the tank. I may use two coats on the inside.
Probably more interesting, I will form up a lid on the ground, put bar in it and make some access ports with plastic barrels, and lift this into place with the telehandler.
I'll document this completely for the community.
-Peter

[rreidnauer]

Not only the heat put out but, more importantly, you may want to capture the heat that went into the septic tank in the form of hot water going down the drain....................... OK, I'm just gonna sit back and watch this discussion progress to the point that someone insulates their sewer pipe between the house and the septic tank hahahahahhahahaaaahhhhhh.
PS, I know it's a serious topic. Go for it Peter.

How dare you make fun of what I'll will be doing?!?!? (OK, not quite insulating the sewer horizontals, but....) They do make (and I will be using) drain-water heat recovery devices. http://gfxtechnology.com/

[donjuedo]

http://gfxtechnology.com/


Rod,

I gave that site a cursory glance, but don't see what I'm looking for. How much heat energy is to be recovered, and what it the cost?


Peter

[rreidnauer]

Depends on which model you go with and flow rates. http://www.gfxtechnology.com/EFF.pdf displays efficiency graphs. http://gfxtechnology.com/contents.html#selection lists prices and other comparison specs.

[Captn]

In a conventional field system I can tell you that that area of the yard always was clear of snow first and it had to get down well below freezing before snow would stick in that area. You have hot water from washing, dishwasher, etc as well as the microbes doing their little dance ...

Thomas Elpel talks about building a Chicken Coop over his Septic tank with a removable cover over one walled off section so he could add chicken waste to the tank. The tank produces a slight positive pressure from the methane produced ...

The Heat from the process kept the chickens warm, the methane would run a cooking stove?

Just another example of the inexaustable power of poo ......

[Perry525]

Perry525
It is important to understand how a septic tank works. The microbes from our gut continue their work in the septic, turning our waste into mainly methane and carbon dioxide gases, and others, this process creates heat. If you take away the heat they create as part of the process, then they slow down the conversion, when they get cold the conversion stops. These microbes prefer a temperature of 95f, to work at maximum efficiency. If you remove part of their heat in your experiment, a greater part of your waste will not be converted to gasses, the septic will fill and your costs will rise, via the emptying process.

[donjuedo]

Perry525,
That makes sense. I suppose you could insulate the tank, and only remove heat when the temp is above 95F.

I wonder, though, how many watts are we talking about, per person flushing?

Peter

[Tyofwa]

Looking through a book I have on self-reliance, there are really detailed designs for constructing methane capturing systems for animal and human waste. The methane digester will enable the production of enough methane per day from the following sources:
1 chicken: 300BTU - 1/2CF methane
1 human: 600BTU - 1CF methane (enough to boil a pot of water)
1 cow: 4800BTU - 8CF methane
1 pig: 5400BTU - 9CF methane
It affirms the earlier statement that the digestion process work best closest to the temparatures of the body, and recommends insulating the main tank for best effeciency. The book is "The Self Sufficient Life" by John Seymour.


Hope that helps!
/Ty

[Eco Island]

wow thats alot of methane from a pig compared to cow or human.In my mind I figured a cow would produce more.
I read an article about a farm that gets all its power from the the cow poo.

[houndog1970]

Perry525
It is important to understand how a septic tank works. The microbes from our gut continue their work in the septic, turning our waste into mainly methane and carbon dioxide gases, and others, this process creates heat. If you take away the heat they create as part of the process, then they slow down the conversion, when they get cold the conversion stops. These microbes prefer a temperature of 95f, to work at maximum efficiency. If you remove part of their heat in your experiment, a greater part of your waste will not be converted to gasses, the septic will fill and your costs will rise, via the emptying process.

so would it be possible to run insulated pipes in the ground through the top of the tank allowing the inside temp to heat the pipe, and have it natrually flow upward into the house? Or have some small 12v fans pull the air through the pipes slow enough so as to not change the temp of the pipes enough to change the temp in the tank and disrupt natures process? Im not scientific enough to figure out all the mathmatecal equasions involved but seems like it could work. I havent checked ed's link yet to see what pipes he was referring to either.

[rckclmbr428]

more then once I stuck my arms elbow deep in the manure pile to warm my hands when we had horses, that stuff puts out some serious heat when you get a pile the size of a small house...

[happyquilter]

And then the discussion stopped.... lol!