Humanure toilet vs biogas digester?

This forum is so much more active than the Biogas forum. And that has me flummoxed. For most situations, I can't think of a single advantage to composting humanure without harvesting the methane off of it first. So, I am curious why more of you in this forum aren't incorporating a methane digester into your designs. Are there some glaring disadvantages that I haven't considered? Please enlighten me.

2 main reasons this is not done more:

1. you need warmth for methane production (tank should always be 90F or better for max production). In the case of a flushing toilet to digester setup, you should really have hot water in the toilet.

2. you need a lot of manure to make any amount of methane. For a family of 4, you'll need a cow and a few pigs. The humanure is so little in volume, it wouldn't make a big difference.

So, if you have a digester already, then throw in your humanure. If you don't, then just building a digester for your human waste will not be worth it.

Hmm.. I get what you are saying. But I still think there is a disproportionate lack of interest in biogas. I can think of easy solutions to the issues you raised:

1) If I am not mistaken, the digestion process generates a lot of its own heat, so the ambient air temp requirements aren't any different than making compost. Additionally, the digester should be insulated and use a black top, ideally located in a greenhouse or built with a cold frame around it. For water flushing, one could easily use a solar thermal toilet tank, achieved with some basic carpentry and plumbing knowledge.
2) For a family with a very small yard, the situation for composting toilets would be equally as difficult as biogas. But for anyone with enough land to run chickens and have a decent sized garden, there is plenty of biomass available to harvest methane. The advantages for biogas only increase from there. Have a cow? Anyone with a couple acres of pasture should really prioritize a biogas setup. At least, that is how I see it. But no one seems to actually be doing this on an appropriate scale, so maybe I am really missing something. (And most of rural China and India?)

Daniel Bowman wrote:Hmm.. I get what you are saying. But I still think there is a disproportionate lack of interest in biogas.

This is mainly because cooking gas/fuel is very cheap, so biogas is really used in the developing areas of the world, vs the US. In the US, you have digesters on factory farms in the north, where they have cheap sources of bulk feedstock and high fuel demands, making the operation financially feasible.

Daniel Bowman wrote:1) If I am not mistaken, the digestion process generates a lot of its own heat, so the ambient air temp requirements aren't any different than making compost.

You are mistaken, it does not generate enough heat to self maintain. While it will still perform in cooler temps, it will not do so very efficiently. Big digesters in the midwest often freeze, due to poor design.

There are lots of easy ways to heat a digester, and of course insulation is necessary. But, the problem is that if you are putting in cold water from a toilet every few hours, you are working against yourself. You are right, though, this is something that can be overcome, but you must first realize it is an issue.

Daniel Bowman wrote:2) For a family with a very small yard, the situation for composting toilets would be equally as difficult as biogas. But for anyone with enough land to run chickens and have a decent sized garden, there is plenty of biomass available to harvest methane.

It depends. You can harvest methane from one chicken dropping, but that doesn't mean it is enough to meet your needs. You need a LOT of chickens to produce enough methane to supply the cooking fuel for even one person. For a family of four, you really need a cow AND some pigs to have enough manure to make it work. even one pig produces several times the manure of that whole family in a day.

Have a cow? Anyone with a couple acres of pasture should really prioritize a biogas setup.

Why? You will basically have to pen up that cow in a small area or follow her around all day to collect the biomass.

And that's the rub with methane from manure, and one of the reasons you don't see it more in permaculture setups. It is less labor to just let the animals shit in the fields, rather than collect their manure and move it to a digester, and then move it to the fields.

Biogas has its place, and that place is where there are lots of confined animals and a biomass/manure problem.

Daniel Bowman wrote:But no one seems to actually be doing this on an appropriate scale, so maybe I am really missing something. (And most of rural China and India?)

yeah, it is bigger in tropical climates in developing regions. Tropical, because of the temp requirement, and developing, because of the financial side. Most people in those situations are using dung or wood for cooking, so they are moving to gas, and at a relatively low cost of doing so. They are only using biogas for cooking, so their requirements are very low, and they can get by with a dozen pigs or so as their source of biomass.

Thanks for the thorough response! Makes my day to see such a good reply. But, even though your overall view is critical, my optimist's spin on it is: Simple designs are entirely possible, even if they are mostly nonexistent, for integrating (warm) flush toilets and (passively) heating a biogas plant in temperate N. hemisphere regions (maybe zone 6 and above). Also, my experience with pastured cows is that if you pen them up in a barn at night, there is still a fair amount of manure in the morning. Especially if you are a lazy farmer, who doesn't exactly rise at dawn. Also pigs put their manure in a single spot, as do llamas. Maybe the case for chickens is overstated, maybe even for a whole cow. But let's say you have a couple acres of pasture and some additional subprime forage land. Not so far-fetched for a lot of permies, I should hope. If you kept a handful of pigs, a couple llamas and zero to a few cows, even if all are on pasture during the day, you would have enough biomass for a small neighborhood or intentional community. Especially when you add to that weeds and hedge trimmings, kitchen scraps and humanure. Even without all that, there is (at least one) example of a functional biogas plant. In Eugene, OR there is the one digester that I know of in our area. It is an unheated 600 gallon tank which is fueled entirely on kitchen scraps, weeds and humanure, generating the cooking fuel for community meals for everybody. I think they have around 20+ poop-contributing people living there, but no animals. Regarding your point about cheap fuel.. I would have to offer the counter example of rainwater catchment that gets quite a lot of fanfare by permies. Water is even cheaper than cooking fuel. But folks latch onto the idea for a variety of reasons (morals, self-reliance, etc.) even when there is little compelling ROI. In the age of fracking and LNG pipelines and all the dirty sources of energy, I don't see replacing propane or natural gas as any less significant a lifestyle modification than tapping into the municipal water system or pulling from an aquifer or getting off the grid, even if all of these have a ROI of a few decades or more... folks still do it for other reasons. Biogas shouldn't be any different, in my opinion, but it seems far less popular than these other practices. Anyway.. I would love to get more feedback on these thoughts. My apologies to the moderator for posting in the composting toilets forum.

We've been thinking and reading a lot about this too: biogas digesters for a cold area, using cow manure and possibly human manure. Here's what I've found out:

Biogas digesters are, or can be, extremely low tech. However, someday you might have to repair or clean it out. If it's cow manure, nobody in India minds. If it's human manure, nobody in India will want to go near it when it's disassembled, much less crawl inside of it to repair a leak! Would you?

In India, where biogas used a lot, I've been told that the general rule of thumb is that three or four cows produce enough biogas for a family, if the cows are home all day. If it's only nighttime barn collection, more would be needed. I've been told that it takes a lot of humans, maybe a dozen or more, to equal one cow in biogas manure output.

Anaerobic decomposition doesn't produce heat. The digesters perform best at very warm temps like above 30C, they digest slowly at normal warm temps like 25 - 30C, and pretty much stop somewhere below 25C. For us, even with a solar greenhouse, we'd have a hard time keeping a tank above 20C all winter, especially if adding cold flush-water. Which would mean that the human manure would move through the tank for months and come out at the end entirely undecomposed into the slurry pond. Not so bad for cow manure, but a problem if it's human manure...

Pathogens are destroyed easily by the heat of aerobic decomposition, but a human gut is anaerobic, and a biodigester is ideally about body temp, so apparently pathogens might be happy in there and make it through to the output.

One friend who visited a few biogas installations said the only one that smelled like sh*t was the only one that included human manure. but I wonder if this had to do with different filters in different installations, so I don't know if that's a real problem.

The biogas digesters I've seen, and I think this is common, you throw some cow pies and water in the inlet tank and stir them with a stick till they are the right consistency of pudding, and then you let them down into the tank. I don't mind doing that with cow manure, but human poop...?

We already use two large solar cookers and have two to four cows, so we're thinking we'll put in a biogas tank anyway as a learning experience and to put a dent in our use of LPG cooking gas. We waver between feeling optimistic about adding toilets to the biogas (we've got 40+ people most of the time). My feeling is we should start with just cow manure for a few years and then see how smoothly it runs before deciding whether to add toilets.

Daniel Bowman wrote:Thanks for the thorough response! Makes my day to see such a good reply. But, even though your overall view is critical, my optimist's spin on it is: Simple designs are entirely possible, even if they are mostly nonexistent, for integrating (warm) flush toilets and (passively) heating a biogas plant in temperate N. hemisphere regions (maybe zone 6 and above).

You are completely right with that. It is possible and doable, folks just need to know the obstacles before getting going. Start doing the math with it, and figure out what you need, based on your fuel use, and then see if you can make it work in your situation.

Daniel Bowman wrote:Also, my experience with pastured cows is that if you pen them up in a barn at night, there is still a fair amount of manure in the morning.

Most people who pasture cows do not put them up at night, but if you do, yes you will get some manure. You'll need more cows than someone who just has them penned up, but it can work.

Daniel Bowman wrote:Also pigs put their manure in a single spot, as do llamas.

If pigs are in a pasture, they will have several toilet areas, but you can certainly collect it. If you have more than a pig or two, that will be a major chore on any space bigger than an acre. (15 lbs of manure per pig per day)

If you kept a handful of pigs, a couple llamas and zero to a few cows, even if all are on pasture during the day, you would have enough biomass for a small neighborhood or intentional community. a few pigs, a cow or 2 would produce enough biomass MAYBE for a family's cooking. I think you are underestimating the amount of material needed per unit of gas produced. Still, even though they are producing the biomass, the problem is not production of manure, it is collection of manure and transport to the digester. If you are just collecting that they give at night, then you need double the amount of animals as a system with animals confined.

I'm not saying this can't work, I'm just saying by adding a digester in the loop of a permaculture setup (where animals are not confined) adds significant labor for little payoff. It may work fine in your situation, and if you can make it work, all the more power to you!

In Eugene, OR there is the one digester that I know of in our area. It is an unheated 600 gallon tank which is fueled entirely on kitchen scraps, weeds and humanure, generating the cooking fuel for community meals for everybody. I think they have around 20+ poop-contributing people living there, but no animals.

I think you'll find that they are actually adding a significant amount of vegetable matter to make it work, and/or their gas needs are very low. Humans just don't produce that much manure (.5 lb a day), so the contribution of humanure to the digester is insignifcant compared to their other feedstock.

I bet all of the humanure produced by that place is still less than what one sow or cow produces in a day. And you'd need many cows and/or sows to cook for that population.

Water is even cheaper than cooking fuel.

Well, that depends. I have lived on rain catchment for over 12 years, and water is not cheaper than fuel in my area. In fact, my options for water (other than rain catchment) are expensive. Wells cost $20K+, hauling water would be cheap for the water, expensive for the transportation, etc, etc. Each situation is different. The ROI for rain catchment is quite different in the Chihuahuan Desert (where there isn't a lot of water) compared to Oregon (where there is more).

I agree with you in that biogas should be more popular. In my own situation, we have some livestock (rabbits, pigs, chickens) and we use a humanure toilet. Still, we don't produce enough manure to have enough gas to cook with. We could allocate space to growing crops for gas production (cattails, azolla, weeds, etc?), but it doesn't really work for us in a financial sense right now.

There is another issue that pops up when you start doing this, as well. We currently use LPG (that's what's available here). So, to use biogas as a fuel, we have to change the ports on the stove (not a big job). If we don't produce enough biogas one day for cooking, then it is difficult to have a backup. We can't easily just switch back to LPG for a day. So, it makes sense to include some long term "rainy day" storage of biogas as well. Biogas is bulky to store, unless you compress it to very high pressures.

Another thing to mention is that solar cooking and cooking with wood are both a lot better than LPG or LNG, but have much better ROIs than biogas. They don't work in every climate (like biogas), but can be part of the overall reduction in cooking fuels.

In India, where biogas used a lot, I've been told that the general rule of thumb is that three or four cows produce enough biogas for a family, if the cows are home all day. If it's only nighttime barn collection, more would be needed. I've been told that it takes a lot of humans, maybe a dozen or more, to equal one cow in biogas manure output.

I think this is a significant point that needs to be stressed. It takes a lot of manure to feed a digester. Cows produce dozens of lbs of manure a day. A human produces less than 1 lb. That makes a big difference.

Pathogens are destroyed easily by the heat of aerobic decomposition, but a human gut is anaerobic, and a biodigester is ideally about body temp, so apparently pathogens might be happy in there and make it through to the output.

the best way to deal with this would be to aerobically compost the effluent with carbon material. Alternatively, run it through an earthworm bed before using.

i really appreciate everything that's been mentioned, and there is another point i have been considering in my own question of whether to build a digester or not--and that is the different organisms needed for the anaerobic vs the aerobic --theoretically most plants prefer aerobic bacteria, so whatever happens, what with the need to raise the temps to kill pathogens, it would seem to be necessary to eventually follow up on biogass with aerobic composting, which might require a second round of carboniferous material to be added (since methane is a carbon chain being removed from the pile)

i don't have actual experience with this, but the whole humanure composting thing is still a bit of an experiment so anyone with actual experience would be good to hear from--also, anyone who has actually tested final outputs for pathogens from the anaerobic system

You can keep the digester warm using the Jean Pain method by surrounding the digester tank with decomposing compacted wood chips. A big compost pile will keep it hot even in winter. The compost pile Jean Pain was using heated a hot water heater for his home and kept a digester warm to supply bio gas for cooking in his kitchen.

You can look at this video:
https://www.youtube.com/watch?v=bVCaczil4W4

Jacques Gauthier,

I think Jean Pain was... not entirely accurate in his reports. The video is misleading at best. See http://www.appropedia.org/Talk:Jean_Pain_system.

Oof, very interesting!

I 1st wanted biogas.
Then I thought it was too difficult
...and turned to a compost toilet.

Then I was told about a family in the Canary (our summers are usually under 30ºC)
doing all their cooking only with the familly toilet!
So I turned back to the methan production idea...

How can a familly produce enough for their cooking use?
I was told by the friend who visited them than the only little "problem" was the "fart smell" just when lightening.
(the smell would stop as soon as the gas was on)

That bad!!!

http://completebiogas.com/workshops.html]

Information not easily found elsewhere is clearly presented in this book. For example, the small scale use of human wastes to produce biogas is thoroughly examined:

“The American toilet gives us an end product which is neither suitable for use in a small-scale generator, nor safe to dispose of into the environment. Not only will it fail to give us biogas, but it kills aquatic life and spreads disease.

“One way out of this dilemma is to ignore the toilet and produce biogas using only kitchen wastes. Therefore access to the waste water from an existing sink (via modifications under the sink), or the addition of a special sink, used only for kitchen garbage, may be a better answer. (A garbage disposal, if carefully used to avoid introduction of excess water, is a definite plus.) Besides, for one or two people, the added biogas from toilet wastes will probably not amount to a great deal.”

“‘But,’ you may protest, ‘I want to make biogas from my food’ (i.e., after it has been eaten). So be it. But not with an average toilet hooked into the system, or only with a great deal of well-shredded dry substrate in the bargain, if an average toilet is used.

“Assuming you use your toilet, you will need a minimum of 200 liters of generator volume per flush per day (assumes a 10-day HRT), and you should add between 1 and 1.8 kilograms (2.2 to 4 pounds; TS weight) of well-shredded substrate materials (such as leaves or kitchen wastes) per flush— if you can.

“In other words, minimum generator volume of ten times the toilet waste volume per day, plus added materials to bring the total solids up to between 5% and 9%…”

Chapter 50: Home Wastes Generator, pg. 209

“…One adult on an ordinary diet will produce from 100 to 250 grams of feces per day. On a vegetable diet, an adult will produce from 300 to 400 grams per day. (Respectively, 0.22 to 0.55, and 0.66 to 0.88 pounds per day.) Feces are usually neutral to slightly alkaline in pH, 24% to 27% TS (dry weight), with a C/N of 6 to 10, nitrogen 4% to 6% of TS, VS is 85% of TS. Normal values for urine are 1 to 1.6 liters volume per day, average pH 6.0, 4% to 6% TS, with a C/N of 0.8, nitrogen 15% to 18% of TS, VS is 72% of TS. (That’s 1.06 to 1.69 quarts volume produced daily.) Every liter of urine weighs about 1,020 grams. Every quart of urine weighs about 2.9 pounds.”

Chapter 16: Manure Substrates, pg. 68

The link needs a slight correction. This works:

http://completebiogas.com/workshops.html

The book it links to looks great and I wanna buy it!

I'm interested in this too.

I have a wheely bin (240 litre plastic container) based compost loo system. It's poo & sawdust mix. We separate urine and then would just leave the bin to breakdown over 18months before emptying it.

I have been thinking perhaps once the bin is full I could fill it almost to the top with water, then tape a bag over the top with a pipe to a floating collector tank.

How much methane would 150 litres of poo give me?

Not all biodigesters need to be hot. The bacteria in Alaskan lakes also produce methane.

"1,000 litre digester using psychrophiles harvested from "mud from a frozen lake in Alaska has produced 200–300 litres of methane per day, about 20 to 30% of the output from digesters in warmer climates." http://energy-alaska.wdfiles.com/local--files/psychrophiles-for-generating-heating-gas/Cordova%20Project%20Final%20Report.pdf

I just found this thread, and I feel like I should mention something that hasn't come up. While a household sized digester (or vapor-tight septic system, which is basicly the same thing) is unlikely to yield enough to provide that same household with it's daily cooking energy needs alone, that's not a necessary requirement for making use of said biogas. If the biogas is cleaned and scrubbed (i.e. steps have been taken to remove the H2S & CO2 in the gas stream) then whatever biogas the digester can produce can be consumed by an off-grid home that uses traditional propane appliances simply by 'downblending' the propane stream after the final regulator with another regulator (with propane pressure settings) and a restrictor & anti-backflow to keep the biogas percentage in the mainline low. Propane appliances are typically capable of quite a bit of variation in the heating capacity of the gas, so it's unlikely that a 9 to 1 propane to biogas ratio would even be noticable to the typical end user.

However, this does require some quality 'scrubbing' of the gas, because even a little H2S in the stream will destroy the metalic internals of propane devices rather quickly. So if downblending of the main house's gas line bothers you (or your homeowner's insurance policy) then simply design some good gas storage into your digester setup, and plumb the output to dedicated devices. For example, you could have an outdoor kitchen (which you would want anyway if you lived anywhere in the South without air conditioning) and you could cook on the outdoor stove when you knew you had enough biogas to make it work, or everyday during the summertime with a downblending setup and a 20# portable propane tank to make up the difference. The digester might not work well during the colder months, but you're not going to be using the outdoor kitchen during those times anyway. The biogas could be dedicated towards a radiant heater in the chicken coop, a gaslight for the back deck, or a gas log in the outdoor fire ring; or with sufficent storage volume, dedicated to a small genset converted to gas to recharge the house batteries after a long run of cloudy days. The downblending trick can also be applied to a single device that's otherwise still on the house's main propane lines, by adding anti-backflow 'stop-cock' valves in the lines leading to that particular device; so a single propane device that uses quite a bit of propane (I'm thinking about an absorption refrigerator or an old type storage water heater) all summer long could make good use of the biogas while the digester can make it; and the propane service can automaticly take up the slack when the biodigester is too cold or underfed to make enough to matter. In this case, only one device might need to be adjusted/modified to work with the variation in energy density of the mixed gases (if at all) and the additional risk of early failure due to H2S corrosion is limited to a single device.

I'll admit that I haven't yet tried my own theories here, but I intend to build a 3 IBC tote digester & storage volume system this fall, mostly for field testing. I have zero chance of getting my wife on board using the humanure system, even if I thought I had time for the additional chores that would involve; so a future change out of the septic system (in the event of a catastrophic failure of the current system) is a more likely event. I'm going to be using diakon radishes for my feedstock, that I have growing as a cover crop in my garden space anyway. If my testing works out, I might just build myself an outdoor kitchen populated with propane devices; as well as plant more radishes and some sugar beets specificly as feedstock for my digester.

@ Sam Na; the sawdust in a biodigester might be a bad plan. Litigocellulose does not break down without oxygen, so the sawdust portion would have to be half rotten to go into a digester anyway.

H2S and metalic pipes ?
Does this mean that copper gas conducts cannot be used in any biogas system?
Then what should be used? Plastic?

About what you say for sawdust and Litigocellulose, does this mean that no lignified material can be used at all?
I think about small branches or old weeds even...

No, Xisca, it doesn't mean that. H2S will produce sulfuric acid under certain conditions, which will damage iron/steel components over time. However, the volume of H2S is rather small, less than 1% of the total gas volume, and would take some time even if no attempts to mitigate the damage occurs. But it's important to keep the possibility in mind, if you intend to port biogas to a sensitive piece of equipment. Ironicly, the H2S can be used to reverse oxidation on most metals, if done in such a manner that any sulfuric acid produced as a result is nutralized. If H2S gas (what we have) is passed slowly over oxidized metals (such as tarnished silver, green copper or rusted iron) the H2S will "steal" the oxygen atoms away from the metals, leaving behind H2O (water) and a mixture of elemental sulfur and sulfuric acid. So, in theory, we can use the H2S gas to keep our silverware shiny; or to eat the rust off of those old well pump parts.

So yes, you can use copper tubing or pipes in a biogas system, but I would suspect that the copper pipes will not last as long as the plastic in service.

Lignified materal does no harm in a biogas digester, but it does take up space. Probably better to burn your sticks in your woodstove or rocket stove.

To me, the best application would be as a way to light/heat a green house,especially one where animals overwinter.
You would have your feed stock in the form of manure, plant prunings and bedding. I doubt the light would benefit the plants much, but it might help the laying of the hens.
Burning the gas in a turkey fryer under a 55 gallon drum of water could be a good way to store the heat, or you could pipe it into the feed tube/ batch box of a rocket stove.
Of course the deep litter method might do just as well to provide heat.

In fact, maybe using biogas for heat is a mistake. Biogas for electrical generation and light might make more sense. Of course wood gas does the same, and if you run a charcoal gasifier,the setup is simple,plus the storage medium is stable and has multiple uses...
Maybe biogas is just not worth messing with?

I wish that the humanure digesters didn't stink so much, they could be a good way for urbanites to do humanure composting without an open bin.
My open bin compost,sans manure of any kind, earned me a visit from the man.
My closed container compost is what stank like hell! Go figure...



I like a design in which the gas digester is separate from the container-floating-in-a-container-of-liquid storage. Supposedly, this lessens the stink.

This has answered so many questions and raised so many more. Currently we use a humanure bucket system but have tossed around the idea of biogas. Thanks for the wealth of knowledge you folks have shared. As usual, an hour on premies is like week in a textbook and class. Hats off to you all.

The reason why I never bothered with trying to produce biogas from my composting toilet is due to the fact that it takes 1000 lbs of human waste produces about 0.6 cubic meters of biogas (enough cooking fuel for about 1 to 2 persons). A family of four makes ~4lbs of waste per day, it would take a better part of a year to collect enough to put into a digester. It just is not worth the effort.

Like many things if you had a large enough supply it would make sense to have a dedicated human waste digester but the gain in production would not warrant adding human waste to a home bio digester when you consider the problems it would add. Compost it or vermiculture it and leave the digesting to other materials.

Forgive me if I'm resuming a topic that has been quiet for almost a year, and also forgive me if I say something ignorant (still have to understand alla the information I got so far).

I'm trying to figure out the best way to handle humanure and organic waste in my future permacultural setup. I read the humanure handbook and I thought this was the way to go.
A few days ago I came across this product and it seems it's able to:

digest 6l of food scraps or (/and?) 15l of animal manure each day

get 5 to 10 liters of fertilizer each day

get 200l of gas from 1l of food scraps (or 2-3 hours of cooking gas per day if at maximum load)

store 400l of gas, after which the gas is released in the atmosphere.

work well in places where the average day/night temp is above 17°C/66°F (you can put it in a greenhouse if it's well ventilated)

I still have to make all the calculations (my organic waste productions and the temperatures I can operate with), but I would like to ask you if you think it could be feasible to use it also as a humanure digester (I imagine by taking out my compost toilet bucket every day to homebiogas, and forgetting about the compost pile), just to have another renewable source of energy for cooking.

Thanks for the attention!

While I imagine that it could digest human waste, I would be concerned with the pathogen content of the resulting fertilizer. Assuming that the total time the material is in the digester is less than a month, I do not think that it would be enough time for harmful pathogens to run their course. And at 66ºF, that isn't sufficient enough heat to kill them either. As per the Humanure handbook, you either need sufficient time or temperature to make the end product safe and this would give you neither. And as per my above post, the biogas you would get from adding your own waste to the digester really wouldn't be worth the effort. Especially considering that you are talking about emptying the bucket everyday rather than waiting for them to get full, the increased risk of exposure to fresh human feces just doesn't seem worth it.

That HomeBiogas digester seems like a really great product and I'd be interested in it for all the things they designed it to digest, but I would not want to put Humanure into that system.

Thank you Tom, you confirmed my worries.
Better to stick to the humanure handbook and buld a good compost pile then!

On the topic of that biogas digester, I started looking into that design, and I found a half dozen very similar digesters for sale on alibaba.com for significantly less. At that price, I'm almost inclined to buy one just to see if it works...

Thank you everyone. I know this post started a long time ago but I am only looking into this now. I am off grid and using human manure as per the handbook. We struggle in winter for keeping batteries charged, not much sun for solar. Looking at ways to run a greenhouse we want to build next spring etc. The biogas Digester seems like great way to add to our system. Sounds like a lot of work though to get enough fuel. Also need a way to keep it from freezing. This thread has helped to understand and answer all the questions I had.

I will share one idea for those of you who do want to go the way of biogas as to fuel and chicken poop. In our coop we have what is called a poop tray. It sits under the roost. At night our chickens sit up on the roost and poop on to the tray. The poop tray we have is actually designed so we can also lift it up and clean underneath it so we do not find it a problem and only positive results. Anyway, it is a way to use the poop instead of wasting it. We use a drywall trowel to scrape off the poop 2-3 times a week but it would only take a couple minutes to do it daily to add to a biogas unit.

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Is there any one who have experience to work on Boigas production from human toilet. If yes, please share your idea in here.

Suppose we don't try to use the methane for any productive purpose, but just want to burn it to prevent it getting into the atmosphere. My understanding is that the resulting carbon dioxide would be a less potent greenhouse gas. Is that possible?

Honestly, I would instead make sure that my humanure decomposition is aerated. Methanogenic bacteria live in an oxygen-free environment. If you pump oxygen into the system, oxygen-loving bacteria will thrive and decompose your manure.

What I take from this, after years of posts, is that humanure really isn't the best return on investment in a number of cases. It's taken off in India (the first book I read on the subject was a Mother Earth News booklet on the "new" developments in India, circa 1970-something) because there's a lot of livestock manure for use, and because they don't have a glut of natural gas.

I don't think I would concentrate on biogas. I think I would make sure that my system employs at least one method of ensuring that pathogens die completely, either passive or assisted (solar and air movement) dessication, or hot composting, or both.

If I needed to make a burnable gas out of biomass, I think I would build a charcoal retort that would supply a burner with woodgas. I get cooking fuel and biochar, and the manure stays out in the paddock where it belongs, except for the human variety, which would get special attention in a humanure setup as I have detailed.

No muss, no fuss, no accidentally contaminating you or your food with human fecal pathogens.

-CK

@Chris Kott: I think I'm asking the opposite question. I want to compost humanure and NOT get methane, but deal with any methane that I do get by not releasing it into the atmosphere, where it's a powerful greenhouse gas. But it sounds like (a) not much methane can be made from the manure of a few humans, even if you try, and (b) that will be much less or negligible if the pile is aerobic. Does that sound right?

Yes, that sounds right to me.

@Chris Kott: Thanks for the info.

First we need to divide between continuous and discontinuous systems. Discontinuous systems are filled, digest and emptied. Lot of work. Pretty useless for a toilet.
Continuous systems are usually filled with water so that the entire environment is anaerobic. One the one side something goes in, while the same amount gets out on the other side.

So a flush toilet that comes with water is ideal because if you want to get the shit into the system water is the ideal transport medium.
The digestion process is not exothermic. It needs to get on temperature to function properly.

With the humanure of one family you are not getting far. There is not that much energy left in humanur. If you can combine it with compostable non-lignin containing material you will get far better results.
In my opinion humunur in a biogas system is always just an addition to the other stuff that you are feeding in when we talk family scale digesters.