science project

chuck satterlee · Post by **chuck satterlee** » Mon Oct 21, 2002 9:17 am

hello, I am also building an anaerobic digester with my daughter for her science
project.I plan to use a one gallon container and chicken manure as we have 8 chickens in a coop.I plan to use the flame
we produce to heat a thrmoelectric module
and power some lights and a small motor.but as yet I do not have a design for a simple
digester. could you please give me an idea
on how to go about this.do I need more in the jar than just manure and water? how long should it take to produce methane?
I know im asking alot so thanks for any info you can give me. chuck

Post by **Bob** » Tue Oct 22, 2002 8:21 am

Whoa! Interesting as a science project, but don't expect to get too much electricity from 8 chickens...

Did you check out the amount of biogas you can get from 8 chickens, using my digester calculator? It looks like maybe about 3 cu ft/day biogas (2 cu ft methane), say about 1,800 Btu/day (at 900 btu/cu ft methane), or about ~500 watts/day (@ 3.413 btu/watt gross heat value).

I plan to use a one gallon container and chicken manure as we have 8 chickens in a coop.

I'd suggest something more like a 5-gallon container.

I plan to use the flame we produce to heat a thrmoelectric module and power some lights and a small motor.

This TE generator, for example, requires 53 cu ft of natural gas/day (@ 1,000 btu/cu ft) to generate 15 watts (I assume they mean continuously for 24 hrs). Assuming you could generate 2 cu ft/day of methane, it looks like you could run it flat out for about 1 hr/day.

... but as yet I do not have a design for a simple digester. could you please give me an idea on how to go about this.

See Shadows' "mini-digester?" topic for some ideas...

do I need more in the jar than just manure and water?

(Again, check out the calculator). Chicken manure, by itself, is too high in nitrogen, and should have some carbon added -- say, leaves, shredded paper, etc. This will also help buffer it.

how long should it take to produce methane?

Under ideal conditions, you could start producing methane in a couple of weeks. This would take careful monitoring of temperature and pH, and a good viable 'seed'.

chuck satterlee · Post by **chuck satterlee** » Wed Oct 23, 2002 6:07 am

Thanks bob for your quick response and good information. The electricity that we plan to produce, will not need to be on that large of a scale we will only be powering some small LEDs, for the visual display, just to show how we use the methane for a practical purpose. The test that we plan to perform that will acually constitute the science project will be to use the chicken manure and other biomatter available on our property to see what highest concentration of methane we can produce. We will try three different mixtures in one gallon containers and then use a meter to test for the concentration of methane. I am a mechanical contractor by trade and work with gas companys and suppliers so i should be able to borrow the meter necissary as well as get some help with a safe flame nozzle then once we determain which mixture has produced the best ratio of methane we will recreate this in a 5 gallon container and hopefully produce enough methane to power our lights for a short period of time.The power module that we are going to use is a HZ-2 bought from http://www.hi-z.com/ I think I have come up with a fair design with a 5 gallon water jug but I am not shur how much water to use with the organic material to get a true result I will have to weigh the chicken manure the same in all three containers as well as the three different materials that I add, grass clipings,decaying leaves and I have not come up with the third yet.Any ideas? When you say a good seed material do you mean the chicken manure? Do I have to add anythind else? I will use a small heater to keep the temperature at 95 F. thanks again..

nathan_lamothe · Post by **nathan_lamothe** » Wed Oct 23, 2002 4:52 pm

what about table scraps as your third material? should be easy to come by... potatoe peels, carrot peels, lettuce, whatever.

I wonder if cooked makes any difference to the digestion efficiency? Bob?

Post by **Bob** » Thu Oct 24, 2002 2:58 pm

"I will have to weigh the chicken manure the same in all three containers as well as the three different materials that I add, grass clipings,decaying leaves and I have not come up with the third yet. Any ideas?"

kitchen scraps -- as Nathan suggests? Assuming that you're doing this for more than just a science fair project -- i.e. that you want to solve a real-world waste disposal problem and turn it into an asset, what do you have on hand? You said you want to see which material(s) produce the most biogas. That suggests that (1) you want to know exactly what your 'recipe' is composed of, and (2) you need to hold all the other parameters -- i.e. temperature, quantity of feedstock material, seed material, pH, etc.-- constant. Then you'll be able to say with some confidence that any differences in gas production between one batch and the next are due solely to the differences in composition.

Whatever you select, you will want to know at least the TS (total solids), and, ideally, at least some idea of the C:N ratio. You should get the best results from a recipe that is about 30:1. This table from Cornell U gives C:N ratios for a number of common raw materials, and this page describes how to do the calculations. (My online calculator uses the same method, but doesn't have as great a selection of materials. (Maybe it's time to add to it.)

To determine TS of each material, weigh a wet sample, heat it in a 220degF oven until all the moisture is evaporated, then weigh it again. The easiest way to do that would be to use a pyrex or other oven-safe container, weigh the empty container first, weigh it again with the wet material in it, then weigh it again after you have driven off all the moisture.

"When you say a good seed material do you mean the chicken manure?"

Yes. More detail when I get some more time...

btw, thanks for the pointer to hi-z, Chuck. I've had a longstanding interest in thermoelectric generators. It looks like the technology has progressed since the last time I looked -- or at least the availability and price of OEM components has. Here is another site that might be of interest -- a consumer product with heat sink, mount and electrical connections already made. I like their thinking. Thermoelectric generators are only about 2-3% efficient (for all practical purposes, at the temps we are using), but if you're already burning that hard-earned gas for light and heat...

Post by **Bob** » Thu Oct 24, 2002 3:09 pm

"I wonder if cooked makes any difference to the digestion efficiency?

I would guess that, to the extent that heating breaks down cell walls, it would be more 'bio-available'. But there probably isn't a completely straightforward answer. It probably depends a lot on the material.

chuck satterlee · Post by **chuck satterlee** » Fri Oct 25, 2002 4:50 am

WOW! thanks for all the info guys I will be sure to post our results. IT seems like I have more tests to do than we can include in the science project but we will still continue on because this is such a cool topic. I am very intersted in the possibility of using TE generators to reclaim so much lost energy in the form of heat. Just imagine an oven that was lined on the inside with TE generators, while cooking your food you could be charging banks of high capacity batteries that could supply some of the power you use in your home.Even if the oven you are using is electric you would still be recapturing energy that would otherwise be lost.And realocating it for other tasks.Again thanks Bob and Nathan for all your input.. Chuck

Laurel · Post by **Laurel** » Mon Oct 28, 2002 3:50 am

Hello Everyone,

I have been reading about your projects to generate methane. I was just thinking that you might want to get a good inoculum to help start the process going. Methanogens have a long doubling time, so it would take weeks or months to build up enough biomass to see any gas-producing activity. What you could do is go to your nearest swamp and dig up some black mud from the bottom. Stir in a little of that into your waste mixture. If there is sulfate in your waste, you will make some H2S first by sulfate reduction. When the sulfate is gone, the methanogens will kick in.

(And if you happen to have a swamp nearby, you can have some fun with swamp gas. You can collect the gas by covering the surface of the water with a large inverted funnel with your thumb over the hole. Stomp around to release the gas, and when you're ready, release your thumb and light the gas. It helps if you have some friends around, and it's more fun at dusk. They do this every year at the Microbial Diversity course in Woods Hole...)

Post by **Bob** » Wed Oct 30, 2002 9:44 am

Hi Laurel,

Thanks for the info. Think I'll go out & stomp around in a swamp with a funnel & some matches this weekend. Fun.

Another thought regarding seeding: Diversity. The term "methanogen" doesn't apply to a particular organism or species, but to bazillions of different organisms--about as many as there are different types of food for them to eat.

It's like as if you had an aquarium with thousands of different kinds of fish in it, a few of each. The fish that will multiply the fastest--and eventually come to dominate the population--will depend on what you feed it. The rest will die out, or just eke out a marginal existence waiting for the day when the diet changes and their chance might come.

Try to gather anaerobic cultures from a variety of sources, the more the better. They can be found in swamps, in the digestive systems of insects and animals, in sewage lagoons, in wet rotting garbage, garden soil, etc. They have even been found in "wetwood"--the darker colored heartwood at the core of the trunks of older (decaying) trees. Cottonwoods, in particular. These may be best suited for decomposing wood wastes.

But the main idea is diversity. (Something Laurel can speak to with authority -- as a microbial ecologist. Nice to see you here, Laurel.)