Methane Digester for village households

Digester design and construction info

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BRIAN
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Methane Digester for village households

Postby BRIAN » Sat Mar 10, 2007 1:44 pm

Hey Everybody,

I am a design student that is currently working on a human powered project, and the concept I have come up with is a methane digesting unit for villages in Rwanda, particularly household units. I want to utilize a methane digester to take care of the household's human waste and also supplement it with their livestock waste, to provide methane for cooking and sanitation purposes as well as using the fertilizer by- product for agriculture reasons. I was also thinking about using the fertilizer by- product as a fuel source, by drying it out and forming "brickets" for burning.

I have done some research on biomas digesters but would like to talk to someone knowledgeable about these systems to get a better understanding of the possibilities and limitations to design around. This site by far has been the best resource I have come across fro these systems.

Thanks,

Brian

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Bob
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Postby Bob » Sun Mar 11, 2007 11:06 am

Hi Brian,

Sounds like a great project -- and worthy goal. Can you say more about the specific local conditions?

My initial guess, without knowing more, is that something like this simple inexpensive design from Francisco Aguilar might be most appropriate. Where my two-stage system is relatively inexpensive here, it might be beyond the reach of your clientele. It also depends on availability of plastic tanks that might be difficult or expensive to obtain in Rwanda.

(Just guessing...)

BRIAN
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Joined: Sat Mar 10, 2007 1:26 pm
Location: Pasadena, CA

village household biodigester

Postby BRIAN » Sun Mar 11, 2007 2:55 pm

Hey Bob,

Thanks for the reply. The conditions will be rural area's with ample rain fall, very hot humid conitions. The fanily size I'm anticipating will use this system will be 4-5 persons. The cattle they have will either be goat or oxen, cows, probably one or two per household. I want to design this thing from the ground up, basing it off existing units but also incorporating a toilet mechansim that is connected to the storage tank. Also I want to make this as easily operated as possible, especially when it comes to collecting the fertilizer. Part of this project involves a humanitarian foundation that supplies impoverished communities with bicycles for transportation. What we have to do is utilize bicycle components and create human powered systems for third world problems. I was thinking to incorporate bicycle cranks and gears for a macerating device, also a stirring device, and possibly pump mechanisms for waste retrieval. Like I said before I have been doing research on these systems but I am not sure what is posible and imposible. Thanks for your time and help, I really appreciate it.

Brian


P.S. Is it possible to turn the leftover sludge into fuel brickets by drying it out?

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Bob
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Postby Bob » Fri Mar 16, 2007 11:23 am

Also I want to make this as easily operated as possible, especially when it comes to collecting the fertilizer.

I agree, that that is a key issue. It sounds like you will want to have two input sources here -- toilet(s) for human waste, and some sort of tank or barrel that you can stir and add water to, for the animal wastes.

My own inclination would be to first try to find ways to reduce or eliminate the requirement for maceration, stirring, pumping, transport, etc. as much as possible -- i.e. all those things that add cost, complexity and moving parts subject to failure. For example, does the toilet have to be water flush, or can it be located directly on top of the digester, fed via a drop chute?

P.S. Is it possible to turn the leftover sludge into fuel brickets by drying it out?

Possible, but using it for fertilizer would probably be a better use for it. The N content is far more valuable than the C content.

farmer
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Postby farmer » Sun Feb 17, 2008 6:29 am

HI Bob,

The link you provided above is inactive. Any thoughts?

My initial guess, without knowing more, is that something like this simple inexpensive design from Francisco Aguilar


Thanks!
farmer

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Bob
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Postby Bob » Sun Feb 17, 2008 5:34 pm

I found it again at:

http://crat.africa-web.org/Biogas/technology.htm

(it's hard to keep up with link-rot...)

farmer
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Postby farmer » Mon Feb 18, 2008 6:03 am

Hi Bob,

Thanks a million for tracking that down!

How do you think this would do in temperate climates? I am envisioning building an insulated house for the bag, then looping radiant heat tubing around the base of the bag to keep it around 90F...

After reading your posts about two stage digesters, I sketched out a modified plug flow design using an inner tube for both chambers, first chamber sized for 3 days HRT, second chamber sized for 9 days HRT. Add a loop of aerater tubing to the second chamber...

I have some heat "mats" that are made for warming greenhouse seedling trays. I think the inner tube design will fit nicely on a long heat mat. Just enough to play with to help me get a grasp on the concept.

Do you think the two stage bag idea is worth the trouble, or will a single horizontal bag do OK on its own?

Thanks!
farmer

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Bob
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Postby Bob » Fri Feb 29, 2008 4:01 pm

How do you think this would do in temperate climates? I am envisioning building an insulated house for the bag, then looping radiant heat tubing around the base of the bag to keep it around 90F...

I guess that all depends on the ambient temperatures (which will determine how much of a building you have to build around it, and how well it has to be insulated). And, after all is said and done, if the added cost and complexity is compensated for by the value of the end products (e.g. fuel gas, fertilizer, avoided cost of other sanitation methods, etc.)

I have some heat "mats" that are made for warming greenhouse seedling trays. I think the inner tube design will fit nicely on a long heat mat. Just enough to play with to help me get a grasp on the concept.

If you are talking about a small test digester, that should work fine -- if you add a way to thermostatically control the process temperature (not just the temperature of the heat mat itself). I've successfully used industrial heating products from Omega for that. But if you are talking about a production digester, I don't think you could ever get enough heat value from the gas to offset the cost of heating it with electricity.

Do you think the two stage bag idea is worth the trouble, or will a single horizontal bag do OK on its own?

It's hard to say without seeing specific details. But gut feeling is to just keep it simple. That is one of the primary advantages of the simple bag design.

farmer
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Getting there

Postby farmer » Sat Mar 01, 2008 1:13 pm

Thanks Bob. Simple is attractive to me too. I just want to use the electric heat mats to start my first "pet" digester... hot water seems to make more sense for the production unit we hope to build.

I've got the housing for the inner tube built, now just need to fit it with insulation and get the bag seeded etc...

More soon!
Farmer


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