Home biogas

Hi, all. Wanted to say I have a number of friends in the Seattle, WA permaculture community and wanted to let you all know about home biogas as a integral component in permaculture and let you know that a commercially-available home biogas system was available. Please check out the brief video of our flagship home biogas digester in Eugene, Oregon

http://www.youtube.com/watch?v=oNuL5wAc8vg&feature=youtu.be

or visit our website at http://www.hestiahomebiogas.com

and feel welcome to ask me any questions related to biogas or anaerobic digestion. 100% natural, clean-burning biogas generates more energy than solar panels day or night, rain or shine while producing higher quality fertilizer than compost. Our home digester generates 70 cubic feet of biogas per day, enough to cook 3 meals per day for 10 people or run a 1 kW electric generator at full load for 3 hours or power a 200-watt 55-inch flat screen TV for 15 hours per day our of 12-15 lbs. of completely ordinary household and garden waste.

I do have a few questions.

I assume you can put things like table scraps, grass clippings, garden weeds etc in one of these. The thing is I can't see one family having 12-15 lbs of vegetable scraps just from cooking a meal (even if you add in the leftovers) 12-15 lbs seems like a lot of mass. I can see that some weeks you may hit pay dirt and come up with 100 lbs one day and some weeks you may fall short. How important is the regular 12 lbs as day feeding?

If I heard right this is a 2 cubic yard digester. If This was your dedicated fuel supply for a regular cook range and oven (my wife is going to have to have real appliances) and a standard gas hot water heater. would this put out enough for daily use of those two appliances?

How does it work in winter when temps fall below freezing slowing down you bacterial digestion?

Ray

Thanks, Ray. No worries, these are common questions. Odds are everybody has 12-15 lbs. of organic waste within easy walking distance of their home, a friend with animals, a restaurant, etc. The composition of the waste is a factor as well, bakery/brewing waste is very productive and needs much less. For those who don't have the time to mess with it, Hestia offers 40 lb. bags of biogas mix for $2.99, so a monthly supply is available for $40-45. Bags of commercial compost would do almost the same thing with something to adjust pH periodically. Grass is not good to use directly, as it floats and causes a crust problem, however, it produces the most gas of any organic matter per lb. and should not be ignored. We recommend silaging grass for later use.

Our digesters are heated and have a heat exchanger that can circulate either hot water from your existing water tank or free-standing heater to avoid hard freezing. However, it is a popular misconception anaerobic digesters need 80-100 degree temps to operate. Ours operate just fine at 50 F and so will yours. It could easily be made into an "Arctic" installation with the use of strawbales for insulation and have it covered with a greenhouse or hoop house and operate year-round in the coldest climates.

We chose 2 cu.m. as this is a sufficient amount of gas for home cooking or light electric generation and some light on-demand hot water. However, it would not be sufficient for home heating and general hot water, which would require a gasifier. However, if a gasifier was used for wintertime heating and electric, waste heat from the heat exchanger and generator could be utilized to heat the biogas digester in a very nice synergistic relationship.

I do have tons of grass clippings I fill a 3 cubic yard compose bin with grass in a bout four cuttings. So I could let it compost down a while before putting it in the digestor.

When you talk about a gassifier are you talking about using a wood gassifier to run the water heater and the digester to run the cook stove so you are running two different systems or are you talking about something different. I guess what I don't understand is how the gas water heater would be different than the cook stove other than maybe the volume of fuel needed and the addition of a thermocouple to turn the fuel on an off as it cycles.

Thanks for the info.

Ray

PS> one more thing caught my attention. You mentioned bakery waste. SO you can put breads and pastas in this as well as vegetable matter? That would change everything as far as getting enough to feed the system.

Ray, gasifiers and biogas can be used to work together for wintertime energy. Gasifiers produce far more energy (heat and electricity) and can use annually renewable waste such as pellets from twigs, leaves, straw, etc. however, they leave only unusable ash as a byproduct. Gasifiers require a considerable heating up period and the producer gas or syngas from gasification contains carbon monoxide and cannot be safely used indoors. Biogas, on the other hand, is an excellent, clean-burning fuel for home cooking and produces excellent, high-quality fertilizer and soil amendment as a byproduct. So lower quality gases such as syngas should be used for heating, while the biogas reserved for cooking and on-demand energy.

Yes, bakery wastes such as doughs, yeasts, bread, etc. make excellent biogas yields/kg. They are of course concentrated grasses---wheat, barley, etc.

Ok forget the clean and unclean for a moment. My water heater is in my home so I would rather burn the clean fuel and manage and run 1 system rather than two. Is there any mechanical reason I could not run a standard hardware store water heater with the methane? Is it just a matter of the amount of methane one can produce? If that is it, seems to me there would be no difference in having a digester and a gassifier on one hand and having two digesters on the other. Why not use the more efficient cleaner burning fuel all around?

Ray

Yes, Ray, the biogas could be burned in either an on-demand or tank water heater. The gas is 600 BTU per cubic foot, so 70 cubic feet per day would be about 42,000 BTU for heating water. Enough to heat 50 gallons of water 100 degrees (in a perfect system, which none are).

The gas needs to have the hydrogen sulfide (H2S) removed prior to indoor use, which can be easily done by filtering the gas through iron filings. At Hestia we are developing inline cartridge filters that will change color when needed to be changed out.

OK so it is a volume thing because 70 cubit ft would be around 525 gallon of gas which seems a heck of a lot to try and produce per day. If the methane has that low of an energy rating does it take longer to cook things on a stove compared to a propane system or natural gas system? IF so is there anything that can be done to increase the btu rating of the methane?

I'm not trying to be a pain Warren. This is all new to me and I'm just trying to get my head wrapped around the practical end of all this.

Ray

No worries, Ray. Very few people in the West have heard of biogas, it's a learning experience for everybody. There is methods of increasing the methane content in biogas, however, a biogas cook stove side-by-side with a natural gas cook stove you are not going to notice the difference in cooking time. There's no need to bother.

The 70 cubic feet (2 cubic meters) of biogas our digesters produce is more than sufficient for daily cooking needs and some light electric generation. Heating and hot water are best suited for a gasifier as there is certain wastes---wood, wood chips, twigs, branches, straw, etc.---that will not digest anaerobically and have a far higher BTU value. However, the importance of biogas slurry (the byproduct of the digester) should not be eclipsed by the excitement over the energy. The best approach is as every permaculturists knows an integrated one.

Warren, I'm interested in the prospect of using grass clippings as a primary feedstock for a digester. Of course, I'll throw in food waste and animal waste from pets. What is required to properly maintain a digester when grass clipping is used as the primary feedstock, and what kind of production can one expect from this source of biomass? NOTE: I totally agree with your emphasis on an "integrated" approach. The fertilizer available from a digester can be valuable.

Ray, I have to agree with Warren that biogas is both safer and more practical for use as a cooking gas as compared to wood gas. Carbon monoxide should never be admitted into a home. Yes, it could be made to work well, but there are inherent dangers that make me cringe.

Marcos, fresh grass can be a little problematic. It has this hard outer coating on it---forget what it's called---that makes it float and slows down the bacteria attacking it. In China they will compost grass in ordinary lasagna compost piles for 1-month in winter and 1-week in summer to break this down. Otherwise it floats in the digesters and causes a crust to form on the surface of the water. We use grass in our home biogas mix, since it yields considerable biogas per lb. however, we silage our grass. So it has been chopped very fine and silaged for six months or more before use.

So, I would recommend putting the grass in a regular compost pile in lasagna layers with your other waste, then putting it in the digester after that outer coating has broken down. i.e. it sinks going into the inlet rather than floating.

This is the biogas system they have in Tamera.



I was wondering if you could run one on donkey poop? It tends to be drier and more fibrous than horse poop, and turns to powder more easily. But as it's already been through a digestive tract, which might make it similar to what you'd get if grass or hay had been sitting in a compost pile for a month, only in finer particles.