It's gas. Natural gas. Truly natural gas. Not the fossil fuel that is named to fool us. It doesn't contribute to global warming, if that's what you are worried about. But it is gas. It is flammable. It burns. You can hurt yourself, sure. Singe your eyebrows, that kind of thing. Treat it the way you would treat the gas from any gas oven.
I mean REALLY safe?
No one in our world wide network has ever reported any life threatening accidents with home scale biogas. The tanks we work with can't explode if that is what you are thinking, because they are filled with water. Water and dung. They store very little gas, and it isn't under any particular pressure.
Solar CITIES demonstrated the safety of INDOOR biogas in an unventilated room at Mercy College for over a year.
We actually started with a small biogas system in my upstairs bathroom in Germany, using my babies diaper waste as starter material (solved that problem! "Who wants to change the baby's diaper?"
"I do, I do"!).
The feedstock then became the uneaten baby food.
See https://www.youtube.com/watch?v=kFOapalN5uA for the first flame test inside in 2010
Our three IBC system that we developed at the SEKEM farm in Egypt in 2010 was implemented indoors in a favela of Sao Paulo, Brazil, by Paulo Mellett in 2014.
Are there commercial preparations or do I have to do it myself?
We think the microbes that make biogas from food and/or toilet wastes are truly special but the fact is they are ubiquitous. They are found everywhere! You can source them from almost any animal manure (including your own 'humanure' -- we started systems on our baby's diaper wastes) and even from most lake and pund muds (we started a system on some sediment Culhane brought back from Mount Everest Base Camp!). So don't be fooled by anyone telling you you need to buy special cultures. You CAN use septic assist products (we've used RidX, for example, as it has cellulase, lipase, protease and amylase in addition to live microbes), but that is your call. We generally get ours by going to a stable and collecting horse manure. We've followed cows and pigs around their paddocks and we've even spent time in Botswana scurrying behind herds of elephants. Everything worked great except the elephant poo in Botswana. We aren't sure why. But people have started systems on dog poo, cat litter and alpaca poo. Give it a try. Just remember -- you want a CONSORTIUM of microbes, not a single species. So this isn't like making beer or yoghurt exactly. It is an ecology you are creating!
Silly rabbit! Trix are for kids AND biodigesters. In fact, breakfast cereals are BETTER suited for biodigesters than human beings. Just make sure the tank doesn't go acid. Don't overfeed cereals... or carrots for that matter. Overloading carbs and fats makes things go sour.
Is it a hassle? Should I be discouraged?
Discouraged? Never! Hassle? The answer ranges from "not at all" to "Not comparatively" ! It depends how you design and set up your system, and how you feed it, but the short answer is "it is easier to run and keep running a home biogas system than it is to keep doing things the way you were doing them before."
For me, using home biogas for more than 5 years, there is really only one minor hassle -- bringing the biogas stove into the kitchen each time I want to use it and then going on the porch to turn on the gas. It takes me all of 3 minutes. What a hassle! :) And that is simply because when we remodelled the apartment we didn't think to put a hole for the gas pipe to the kitchen. We plumbed the kitchen sink and insinkerator food waste grinder to a sump pump under the bathtub because we wanted to use the greywater in the garden -- this was in 2008 before we knew how easy it was to do home biogas. So we were set for effortlessly getting the feedstock into the digester when we built it on our porch in 2009. But we didn't antcipate the ease with which we could get our own biogas into the kitchen, because we didn't know that a 1000 liter water tank on the porch could produce enough gas to cook anywhere from a half hour to 2 hours each day. Had we known we would have made a simple penetration from the porch to the kitchen and put a tube in it that we could connect to the stove and to the hose going to the digester.
So now getting the digester fed is easy!! We scrape our plates and dishes into the sink, throw our banana peels and avocado skins and seeds and everything organic into the sink and press a button. The in-sink food grinder sends it with a trickle of warm water to the sump pump which pumps it into the digester tank automatically. The overflow (a nutrient rich liquid fertilizer that comes out everytime we put ground up food in) goes automaticaly into a 100 liter storage tank and the overspill from that goes down the drain to the sewer system automatically. That way we have liquid compost tea to use in our porch garden and any excess we don't have to think about.
So feeding the system is much much much easier than the old tradition of taking out the garbage! Now THAT used to be a hassle -- we used to have to throw our sloppy icky plate scrapings and cuttings and food scraps into the garbage can, which gets really stinky and gooky. When it was full we had to tie the bag and carry it two flights down the stairs and out to the bin by the street (a distance 3 to 4 times as far as simply going on the porch to turn on the gas). If garbage pickup didn't come, vermin would. On hot days the garbage would stink up the street. The roar of the garbage truck disturbed our sleep and the fumes from the diesel poisoned our children's lungs.
THAT was indeed a hassle.
Now we never have to take out the garbage. Our garbage bin fills up with recyclable plastic, metal, glass and paper only. We can let it sit as long as we want and then take it in a leisurely fashion to the recycling center. When we have enough we can get cash back.
In apartment buildings in Egypt where we have installed home biogas systems on the roof, many families don't have a food grinder and most don't have a pump to get the food waste to the roof. In these cases the family has to take the organic garbage up to the roof (usually a flight or two of stairs up) and grind it up and pour it in the digester. Some people use a blender in the kitchen, others pound it in a mortar and pestle, some chop it with a knife. In Indian cities they usually leave the food waste for a day or too in a bucket of warm water in the sun and when it softens mash it with their fingers before pouring it in. It all depends on the design of the digester. If it has a wide enough feeding tube, like the Puxin (Chinese) and Flexi (Kenyan) and Hestia (US) systems then you can dump the food waste in unground. We tend to build systems with 2 inch pipes that are connected to the food grinder so everything can be automatic. It is a matter of cost and preference.
Either way you slice it (grind it?) the hassle of a non-automated system isn't much greater than taking out the garbage in the first place. You walk to your digester instead of your garbage bin or your compost pile. And it is a whole lot easier than composting (with biogas there is no turning, layering, shoveling or other maintainance that compost aficianados put themselves through to make sure the pile stays aerobic -- biogas is anaerobic, so no worries there! And biogas systems produce a nutrient rich LIQUID fertilizer, so it is much easier to use the end product).
For anybody who composts biogas is a slam dunk, literally, as you just dunk the food waste in the tank and leave it there. Nature does the rest. Folks like me, who have been composting for several decades, and taking out garbage for decades before that, simply don't feel like going to the trouble anymore now that we have home biogas. We shudder at the thought of having to "deal with" organic residuals and long to be home with our biogas systems when we visit friends who still aren't part of the movement, watching them deal with a stinky garbage bag or hard to maintain compost bin.
With biogas you can say goodbye to all of that hassle and discomfort.
And if you run the plastic hose from the gas storage of the digester to your kitchen stove in a permanent fashion you've got it made in the shade. Just turn on the gas when you need it (again depending on the design there will be simple considerations for getting the gas to the stove -- in a floating dome system like the ARTI India system, the gas is under pressure from the floating drum so you don't have to do anything to get it to flow. Same with the Puxin 4, 6 and 10 cubic meter systems and the Solar CITIES 3 IBC systems or IBC/ARTI hybrids and the Hestia Home Biogas and Eco-gas Israel systems. For systems where gas storage is in a PVC holding bag or rubber inner tube or air mattress you need a way to push the gas out of the bag. Some people put boards or bricks or heavy blankets on the baloon to push the gas out, which is a "hassle" that takes about 60 to 120 seconds of your time. We use a Chinese biogas pump (they sell for about $60). It is like an aquarium pump. The only hassle there is that you have to remember to turn it on. It has a switch. You walk over and press the switch. That's how tough it is. Should you be discouraged?
People keep talking about "food waste" and "toilet waste" and that makes me think "eeew, stinky". There must be a big "eeew factor" to this technology. I don't even like to compost because things are rotting in there and there are bugs. What about biogas?
Funny you should say that. I mean really funny, as in it makes me laugh. I used to think biogas would have to be stinky too, because it was my job as a kid to take out the garbage and it made me want to vomit. Bleccccchh! Now I recoil when I am in households that still throw their food scraps away, with all the odors and the inevitable flies, and long to be home or in a sensible place where all the food waste is sent to a biogas system.
Why is a biogas system cleaner?
Think of your own stomach and intestines. They are filled with rotting food stuff most of the time. In effect, to be indelicate about it, you are "full of sh!t"!
The reason you don't smell is because you mostly keep it contained in your body (I say mostlly because everybody farts, except those who are liars and say they don't). Biogas systems can actually be less smelly than people because we capture the biogas (which is, effectively, fart gas) in an airtight tank, chamber or balloon, and when we burn it it has no smell at all.
Like with our answer to the maintainance question this one can also be answered "it depends on the design"; our IBC systems are completely sealed so there is no smell possibility at all. That is why we have built them in basements of residential homes in New York. But even the open systems, like the ARTI India and other floating drum digesters, don't have an objectional smell. On rooftops in Cairo where we have built them, even on the hottest stillest day you can't smell much of anything unless you go and stick your nose right up at the gap between the gas holder and the digester tank. And the smell you get there isn't unpleasant. It doesn't stimulate your gag reflex, it doesn't have the objectionable smell of carnivore or omnivore crap. It smells, if anything, like a barn. Like horses and cows. And only when you are sticking your nose in it really close. This is because the digesting material is under water at all times and the odors don't rise.
There are times when it can smell a bit -- if you overfeed the system and it goes acid, the slurry can smell sour. Again you wouldn't really notice unless you were right next to the system, but if you put your nose to the fertilizer effluent when the tank has gone acid you can tell it has an acrid odor to it and you know you should stop feeding and it needs to be pH balanced to work well again.
The liquid fertilizer, when you use it on your garden, does smell like fertilizer -- again, like dung. If that bothers you there is a simple solution -- aerate it. We use biogas slurry in my mother's tower garden in her apartment in New York. When we pour it in directly the area around the tower smells a bit like dung. But because the tower garden is aeroponic and rains the slurry through every fifteen minutes, picking up lots of oxygen, the smell disappears completely in just a few hours. Some people run the output of their digester through a bucket that has an aquarium air stone bubbling through it (I do this too). Within 4 to 6 hours all smells are pretty much gone and the liquid has a slightly musty neutral soil smell.
I am talking here about indoor biogas systems. Out in the garden or on the roof or porch you would hardly know the system is there, open or sealed. Certainly the sealed systems are undetectable by the human nose (and must be by other noses too because we rarely if ever see insects around them -- they don't seem to attract flies and they certainly don't get noticed by rats, mice, dogs, cats, possums, birds or any other wildlife or possible "vermin". So in that sense they are much much much superior to compost bins -- in composting we are told not to throw in fats and oils and meat and such because they would create odors and attract vermin. With a biogas system you can throw EVERYTHING in!!
Look ma, no smell!
If there is an objectionable odor it means you didn't design your system right. And even then, as I've mentioned, the smell isn't a bad one, just the same smell of fertilizer you get when you put fertilizer on your plants that you erroneously spent your hard earned money on from a home and garden shop, not knowing you could make your own from your very own garbage!
Since summer of 2014 several startup companies around the world are beginning to offer home biogas systems for sale. This of course has been the case for a decade or more in China and India, but the rest of the world is starting to catch up. If you are in Kenya check out Flexi-biogas systems from Simply Logic. If you are in the Middle East check out the Teva Gas system from Eco-gas Israel and the modified ARTI systems from "the Biogas People" in Cairo. Green Elephant/Green Box in Pune India will have a home system soon that may be available internationally and in South Africa there is the "Little Green Monster". In the United States of America we are working with Hestia Home Biogas out of Eugene Oregon and Seattle Washington whose unique rotomolded 2 cubic meter systems are now on the market and sold on the West and East Coasts with distribution out of Brooklyn.
Most 2 cubic meter systems that are made of rotomolded plastic cost in the range of $1500 to $3000 and produce enough gas to cook for between 2 and 4 hours a day. The Flexi systems from Kenya, made from UV stabilized flexible bags, are the least expensive, about $500 for the kit.
If you want to build one yourself, check out our education section. It's rather simple really! Just do it!
Is it really the same as "fart gas"?
You had to ask!
Well, yes it is. As Culhane's Biogas song goes, "It's the same gas as the gas we pass!".
Seriously though, biogas is a mixture of methane (CH4) 60 to 70%, carbon dioxide (CO2) 30 to 40% and sniffable amounts of H2S (that makes it safe because you know if there is a leak, right?). It can be dropped in in place of so called "natural gas" but has less heat content per unit volume. But that doesn't make much of a difference in any practical sense for the home user since it is free (once you have paid for the digester).
It can be made from almost any organic foodstuff that animals would eat and from the resultant poo that animals make when they are done eating. The ideal way to make biogas in our opinion is from food scraps -- the wasted parts of plants and animals that you don't eat and that you would throw away anyway.
But to Solar CITIES Biogas is something else:
Biogas is solar energy. More precisely it is STORED SOLAR ENERGY.
In effect, biogas is a solar battery. But it is far more reliable, durable and usable than any other form of stored sunshine because biogas "never loses its charge". It can be kept in storage until needed for... well, for millions if not billions of years. Try to do that with a battery!
Plants and animals, of course, are also forms of stored solar energy, but they don't last. They grow for a while, storing sunshine along the way, but then they die, and when they decay most of that energy is lost to entropy pretty quickly. But when we turn those dead animal and plant parts, with the help of living microbes, into biomethane, and we store that biologically derived methane, that energy is held in place in a stable form until we need it. And since methane is lighter than air, unlike batteries it is really easy to transport.
Of course biogas is a gas so it takes up a lot of volume (remember Avogadro's number? 22.4 liters per mole, and a mole of methane is only 16 grams so even without the CO2 content, which is 44 grams per mole and makes up roughly 35%, it's a lot of space for something so light). But it doesn't have to be transported in big baloons (although we do carry it around like that sometimes), it can easily be piped. Just like so-called "natural gas".
And yes, it can be compressed (again just like CNG) but we generally don't do that at the home scale because you have to remove the CO2 first and it is still fairly expensive to do that relative to the economies of scale. So we tend to use biogas as a local way to store the solar energy in organic chemical bonds and use it where we generate it.
Because biogas stores sunshine so well we believe it is the best solar solution. We capture it whenever the sun shines (even on cloudy days) because plants use the sunshine to grow. Then we create comfortable conditions for the archaea and the bacteria to turn dead parts of plants and the animals that feed on them into useful energy that is available 24/7, 365 days a year.
So that is the bottom line -- BIOGAS IS SOLAR ENERGY. And that is why we are so interested in it in Solar CITIES.
Surely "the government"/"multi-national corporation"/"military-industrial complex"/"my anxious mother" ain't gonna let "we the people" get away with building our own perfect clean home energy/in-situ waste management/free fertilizer solution, right? What are the regs?
"Regulations? We don neet no stinkin' regoooolaaaations!"
But seriously folks...
As of this date (September 2014) we aren't aware of any regulations concerning small scale (10m3 and under) biodigesters specifically. The regulations would probably fall under those written for home septic tanks, home water storage tanks and possibly home use of Natural Gas and LPG bottles. When an urban planner came to our house we showed him our system and his reaction was "it's a full tank of dirty water". He then saw that the overflow discharge went right down the drain to the sewer system. We had used up all the gas when he arrived. All he saw from that part of the system was a plastic barrel submerged in another plastic barrel filled with water and an empty pvc bag. Remember that you are storing unpressurized gas in flexible containers over or near water. They can't explode because there isn't any air in them and they don't contain enough gas nor occupy enough rigidity to pose a danger. And you use it up every day. When you go away, you don't feed the system so it produces almost no gas. In the event that it produces more gas than you can store, the overage simply burps out in little pulses or "farts" and can not be ignited. Biogas is lighter than air so it disperses and disappears almost immediately. We have never been able to get small gas leaks or burps to ignite.
No doubt as our movement goes forward somebody will try to regulate it. We will have to stay one step ahead of them and demonstrate the safety, efficacy and value of this solution to waste and energy problems in the world. For now all we can say is "it is much much much much much much much safer than all the alternatives you are currently using." Tell them that. Show them that.
What can't you use biogas for, really?
It makes a hell of a whoopee cushion!
But seriously (as if talking about the gas that propels flatulence can ever be taken that seriously!) ...
Biogas can be used straight up for COOKING, LIGHTING GAS LAMPS, and running gas REFRIGERATION (like the Dometic that Culhane has at home in Germany). With a simple modifaction you can turn most gasoline engines into "trifuel engines" and run your genset on gasoline, propane, natural gas or biogas. You can use biogas with on demand gas heaters for showers or baths or dishwashing hot water. You could run your car, bus or truck or tractor off it (though you would have to find a way to compress and store it, like they do in Sweden).
Essentially you can use biogas for exactly the same things that people use natural gas for.
And why? Because biogas IS natural gas. It is in fact the only true NATURAL GAS -- the other being fossil fuel ('natural' in the prosaic sense, but hardly environmentally friendly in terms of extraction and net CO2 contribution).
There used to be natural gas air conditioners sold in the 1950s until the price of NG got too high. Now that we have biogas and also because the price of NG has gone down again, yes, you could run air conditioners on biogas.
So there -- there is very little we can't do with biogas. In some places they not only run taxis and buses off the stuff (like in the aforementioned Sweden) but run thousands and thousands of homes and businesses, creating both electricity and hot water using co-generation (this occurs in both the US and Germany among many other places!).
So what are you waiting for? Once you start producing your own biogas it is free energy, made from garbage. Go for it!
How much food waste do I have to add to make my digester useful and how long do I have to wait? I'm a busy guy, and I eat out a lot!
The general rule of thumb is that every liter of digester volume yields its same volume in gas after 24 hours at body temperature. That is an ideal that is rarely met. But theoretically the typical 1000 liter (275 gallon) home digester should make 1 cubic meter (1000 liters, 275 gallons) of biogas in a day or so after being fed. The amount of food that usually yields that volume of gas is about a bucket's worth, a bucket being between 20 and 25 liters (5 gallons or so). We use buckets because people have them and most people were instructed to dislike math. We gotta deal with that reality. Bucketfulls are easier to remember.
So we say a bucket of ground up food waste (mixed with warm water) poured in a 1 cubic meter digester (IBC tanks are cubes so they make it easy to visualize) should be able to fill another IBC with gas.
The problem is usually temperature. Most biodigesters seem to have slurry in them normalizing at about 20 C. These only produce about 100 to 300 liters of gas a day. At 25 you start topping 300. At 30 C you may be looking at 500 liters of gas. At 35 to 37 (98.6 Fahrenheit -- body temperature) you may see the theoretical 1000 liters that will enable you to cook for about 2 hours on a single burner.
Look, the microbes came from the guts of an animal and are optimized at mammalian body temp. So if you make them happy they will produce. The curve is nonlinear though -- they produce a LOT more at 37 C than they do at 30 C. At 15 C they get really sluggish. Warren Weisman at Hestia Home Biogas gets production down at 13 C. But the higher the temp the faster the gas comes out, that is for sure.
Our rule of thumb is: "every 100 liters of gas should give you 15 minutes cooking time on a single burner on medium flame" -- the kind most of us cook on. So don't sweat it if you are at 20 C and you are only getting 100 liters a day -- you can still cook breakfast until you figure out your best way of keeping the tank warm.
Meanwhile, a bucket of food waste isn't that hard to come up with. Just don't overfeed. If you do it will go acid (go sour) with indigestion. Then you will need to feed it an antacid (Sodium carbonate is good, Sodium hydroxide faster) and maybe reinnoculate with fresh bacteria. Try RidX or go back to fresh manure. Then start feeding again slowly.
How does temperature affect all this?
Here is a chart that David House, author of the Biogas Handbook, came up with, featured in his blog at Mother Earth News. It does a great job of breaking it down for you based on temperature:
"95 degrees Fahrenheit/35 degrees Celsius: 100 percent
• 85 degrees Fahrenheit/30 degrees Celsius: 68 percent
• 75 degrees Fahrenheit/24 degrees Celsius: 46 percent
• 65 degrees Fahrenheit/18 degrees Celsius: 32 percent
• 55 degrees Fahrenheit/13 degrees Celsius: 21 percent
• Colder than 55 degrees Fahrenheit: zero percent"
He says, "Just to keep it simple so as far as temperature is concerned, we’ll call the rate of biogas production at 95 degrees “100 percent,” and compare other (lower) temperatures to that. Every time Mother Nature drops the temperature by as little as 10 degrees, the rate of the production of biogas also drops, pretty steeply, by about a third. (See the table above)"
Do different feedstocks give different amounts of biomethane?
Yup. They do. Here is a chart created by David William House, author of "The Biogas Handbook":
David House writes,
"Freshly cut grass clippings can ultimately produce better than 1½ cubic feet of biogas per dried pound. By contrast, the same dry weight of cow manure, under the same conditions, will produce less than a quarter of that. If you’re lucky enough to have enough of what the Bavarians call “residual fats,” then the comparable pound will produce 24 times the amount of biogas as the cow manure. So like I said: different substrates produce different amounts of biogas. In spades"
How much biogas do I need to make my life better?
Once again, we turn to a chart from David House's Biogas Handbook:
"The chart asumes two critical things: first, that you are digesting food waste, and second, that the digester is at body temp. Given just those two assumptions, it shows you how many 1-gallon buckets of food waste you need to be able to get the outcome you want— and what size of digester you’ll need too. Simple. Clear. Ready? Here it is:
Food waste power!
We also make use of the advice found in the Chinese Biogas Manual (I purchased it from Knowledge Publications)
What benefits are there to using psychrophilic ('cold loving' or 'cryophilic') microbes in biodigesters, where do I get them, and how do I use them?
Psychrophilic or 'cold loving' microbes don't really love the cold, they just do much much better at low temperatures than "mesophilic" (medium temperatue loving) and certainly than "thermophilic" (heat loving) microbes. They operate from as low as 0 C (some report as low as -4 C!) to 25 C. They actually prefer 25 C (room temperature) to the colder temperatures so I would say we should re-brand them "ambiophilic" or "Zimmerphilic" microbes. The point is that they have a lower temperature range at which they can metabolize, due to some glycol like or anti-freeze like properties in their membranes. That said, they don't produce a huge amount of gas below 10 C and as with most methanogens, the curve is nonlinear meaning you get substantially more gas at 25 C than at 10 C and lots lots more than at 5 C or of course 0 C. That's just the physics of it. Everything slows down in the cold.
That said, given that most unmixed biogas systems (and that includes most of the small scale systems from 1 to 10 m3) have a thermocline in them with the coldest area being the bottom of the tank and the warmest up at the top. That is how water stratifies when left to settle (think of a pond or a pool). The top of the tank can be a toasty 40 C and the bottom can be as cold as 10 C and you could put your hand in and feel the point at which it goes from burning you to chilling you. It is abrupt, with rarely any gradation.
Because of this, we recommend putting BOTH psychrophiles and mesophiles in your digester.
The psychrophiles should establish themselves in the colder lower regions and the mesophiles in the warmer upper regions (we also recommend putting in a lot of vertical surface area, like what we call "microbe motels" or "microbial fuel rods" so they can seek out their own best temperature regime.)
You can try innoculating with thermophiles too, but they are finicky and don't handle temperature changes well. They way survive in areas where it constantly stays over 40 C, and they give LOTS of gas, but you will have a hard time taming them we think. The mesophiles are the most tolerant to temperature changes.
But since the bottoms of tanks do usually stay at or well below 25 C, it is good to have the psychrophiles in there, chumming along. They may not make a LOT of gas, but they will constantly be doing it so they are kind of an insurance policy, and they seem to play well with the mesophiles (maybe they even engage in gene transfer, who knows?).
Where do I get my psychrophiles?
You can get psychrophiles from pond muck, usually from duck ponds (I call it "duck muck") or lake sediments, anywhere where the water has stayed under 25 C all year (as most freshwater water bodies do) and where animals, particularly migrating birds, have sat and shat. I got some from Lake Eyak in Alaska (in Cordova) and from the thermokarst lakes north of Fairbanks. I also brought some back from a little pond on the trail by Mount Everest Base Camp. These critters were very well adapted to cold weather, needless to say. But still they didn't produce noticibly more gas than the ones I got from our local Ententeich (duck pond) in Essen, Germany. Or from the duck pond at 145 Palisades near Curious on Hudson Bookstore in Dobbs Ferry NY. Some speculate that these extremophiles are all the same, spread on the feet of migatory birds all over the planet.
The point is that you don't need to go very far to get methane producing psychrophiles. Katey Walter Anthony from U Fairbanks got some from the hippo wallows in the Okavanga Delta when she visited the biogas systems we built there. Anywhere you stick a stick in the mud and bubbles come up you can be pretty sure you have psychrophiles.
It isn't a bad idea to have active pond or lake muck in your digester regardless. Put them in any time and let them settle to the bottom. Also add mesophiles from any manure source (even human) any time. The key to a healthy digester is biodiversity. Keep adding sources of methanogens of any philia, and let them sort it out. That is our advice.
How much would you feed a 1m3 system (like the IBC tanks you guys build)? A 10 cubic meter system (like the Puxin you guys build?)
We tend to think in buckets, 5 gallon (20 liter) paint buckets. That is something everybody in the world can relate to.
Figure about 1 bucket per cubic meter each day. That is, if you filled a bucket with food waste. If you grind it you are adding water as you grind, but because it grinds up and occupies less space and you then add water you are still talking about a bucket (because generally when you grind with water you end up with a bucket having about 50/50 food particles to water).
So a 10 cubic meter system generally takes up to 10 buckets of food waste a day safely (without getting indigestion). That equals about a 55 gallon oil drum worth of food ( or a 200 liter blue barrel like you find all over the world).
This isn't going to be exact, as what you feed will have an effect. If it is mostly fats, which produce fatty acids, you may want to add less (going acid is what we worry about). If it is mostly sugars or carbs it may also go acid. If it is a balanced meal type of food waste then you are okay and may even exceed the 1 bucket per cubic meter of tank space rule.
Another rule has been (although this was developed for manures) 1:40, i.e. 1/40th of the volume of the tank. But for a 1000 liter tank that still amounts to no more than 25 liters of waste material, so the general rule still holds.
Most biogas people agree with the aerobic compost folks that the ideal is to have feedstock that has the typical C:N ration of anywhere between 20:1 and 30:1. 25:1 is pretty darn good. That means it would probably be good if you have some nitrogen rich foods (animal and/or plant proteins) and some carbon rich foods (leafy stuff, even brown leaves, some say even charcoal; coffee grounds should work well).
Don't make the mistake of putting in straight sugar or straight white flour or starch -- we've done that and rapidly made the tank go acid.
How do I recover from an acid event , a.k.a. "digester souring"?
Add sodium hydroxide or potassium hydroxide (lye), usually as crystals is better (be careful; they don't call it "caustic soda" for nothing -- wear gloves and eye protection, and don't do it with good clothes on as it will eat through them!).
I have also had success with sodium carbonate (washing powder). In fact, I have had success feeding my digester 10 kg of sugar with 5 kg of sodium carbonate mixed in. Three times. This doesn't mean it will always work, but it did for me, thrice!
I've also buffered my pH and brought it back with sodium bicarbonate (baking soda). It took more of it than the sodium carbonate, and lots lots more than the sodium hydroxide.
We don't have exact figures yet... we are still tinkering and experimenting at the home scale!
Let us know what results you get!
Be patient with the bounce back. I have seen it take a coupld of weeks and I have seen it take a couple of days (for that matter I've seen biodigesters bounce back to a neutral pH after getting to an acidic 4 just by sitting unfed for several weeks. But it seems that the tanks that bounce back are the onces with the most internal surface area and lots of internal carbon, like straw and leaves and gravel mixed in -- ones that just had starter manure didn't recover -- perhaps the microbes had fewer places to hide and recover...)
I want to buy or make my own gas storage bag. I'm aware from your website that I can get them from Puxin or make them out of PVC tarp or .45 mil EPDM pond liner or roofing membrane. How big do I make them to get a known quantity of gas?
Puxin bags set the standards. Here are their measurements, from
PUXIN biogas storage bag
Used to store the excess biogas every day, with 1 to 200 cubic meter capacity
Catalogue of PUXIN biogas Storage Bag
1. Biogas Storage Bag for family Size biogas plant
PVC, Size:1.5*1.2M Thickness 0.6mm
PVC, Size:1.5*2.2M Thickness 0.6mm
PVC, Size:1.5*2.8M Thickness 0.6mm
PVC Thickness 0.6mm
PVC Thickness 0.6mm
PVC Thickness 0.6mm
2. Biogas Storage Bag for medium and large size biogas plants
Materials:Red Mud reinforced plastics
Thickness 1.0mm. The size and shape can be customized.
I may not be able to use all the gas I produce at times and can't store it. I've read that methane is 28 times stronger than CO2 as a greenhouse gas and that cow farts and belches are possible contributors to climate change. How do I keep my bioidgester from being a part of the problem rather than the solution?
The methane released (actually only averaging 65% of the biogas by volume) is ultimately non-anthropogenic in the sense that it is the decay product of organic decomposition that has been going on as part of the carbon cycle for millions of years.
It is NOT fossil derived and, like the gases we emit from our own bodies and that of all animals and from the roots of plants and from septic tanks and ponds and lakes and streams and swamps and oceans and forests, most of it is decomposed by methanotrophic microbes who render it back into CO2 and water for the uptake by other organisms (mostly plants) to create more structured carbon which becomes food and food waste and toilet wastes again.
That humans now collect those naturally produced bubbles of CH4 and use them is actually a good thing in that they offset the use of fossil fuels and can contribute to reducing global warming. But if we didn't collect them and burn them (turning them immediately into CO2 and water through combustion) they would be broken down anyway.
The ontribution of domestic biogas to global warming is nil to none.
When people talk about cows belching so much methane that they are a contributor they are talking about unnaturally dense CAFO (Concentrated animal feedlot operations) supported by fossil fuels to concentrate so many animals and grow so much carbon rich food which would have never occurred in a balanced ecosystem. It is only because of the fossil inputs that animal populations can make so much methane.
One could argue that human population is similarly concentrated unnaturally, but this goes on whether we use a biodigester to make it or simply release our organic waste into the "waste stream". And it would be another argument for the wisdom capturing the gas and using it; either way you get the biogas, usually just bubbling out the anus of the person or animal, or bubbling through the leach field, or the land fill or in the garbage can or compost bin. The trick is to somehow get the methane oxidized, and that can be done by burning or by harnessing methanotrophs.
Here is the abstract of an article on methanotrophs;
And here is an article on methane oxidation in rice paddies.
The rice paddy article gives the best clue of how to avoid methane release from your biodigester if you aren't storing or using it:
"Methane-oxidizing bacteria (methanotrophs) are abundant in the oxidized floodwater-soil interface and in the rice rhizosphere. They sequentially oxidize methane to carbon dioxide via methanol, formaldehyde, and formate. Oxygen is essential for the growth of methanotrophs, but the required partial pressure may be low (Cicerone and Oremland 1988). Methane oxidation greatly limits diffusion of methane to the atmosphere. Up to 60% of the methane produced during a rice growing season may be oxidized before it reaches the atmosphere (Holzapfel-Pschorn et al. 1986, Sass et al. 1991). Ammonium ion inhibited methane oxidation in studies with pure cultures of methanotrophs (Hyman and Wood 1983, Whittenbury et al. 1970). Field experiments have revealed no significant effect of ammonium ions, probably because of their immediate uptake by rice plants.
Rice plants supply atmospheric oxygen to the roots for respiration via a special vascular system, the aerenchyma. The aerenchyma has its own openings at the leaf sheath (Nouchi et al. 1991), and the gas supply to and from the roots is independent of transpiration and stomatal gas exchange. Oxygen diffusion from rice roots constitutes an important part of the roots' oxidizing power, aside from enzymatic hydrogen peroxide production. Because of the abundance of methane-oxidizing bacteria present in the rhizosphere, the rhizophere's potential for methane oxidation is high.
De Bont et al. (1978) counted ten times more methane-oxidizing bacteria in the rhizosphere than in the bulk anaerobic soil and one-third more than in the oxidized soil-water interface. They found significant increases in methane emission by the rice cultivar IR36 when methane oxidation was suppressed with acetylene at the soilwater interface. However, acetylene had only a small effect on emission rates when applied to the rhizosphere. De Bont and his colleagues concluded that the use of oxygen by reduced substances and microbes other than methanotrophs at the region of the root-soil interface exceeds the supply of oxygen by the root. Consequently, the aerobic zone surrounding the root of IR36 is too thin to oxidize the diffusing methane, or the rhizosphere is for the most part anaerobic. Nevertheless, variability in root-oxidizing power of rice cultivars is high, and the impact of roots on methane oxidation merits further study.
Methane fluxes in rice fields
Methane is released from anaerobic wetland soils to the atmosphere through diffusion of dissolved methane, ebullition of gas bubbles, and via plants that, like rice, develop aerenchyma tissue. Large portions of methane formed in an anaerobic soil may remain trapped in the flooded soil. Entrapped methane may be oxidized to carbon dioxide when the floodwater is drained during the rice growing season or when the soil dries at the end of or after the rice growing season. But large amounts of entrapped methane may escape to the atmosphere immediately after the floodwater recedes (Denier van der Gon et al. 1992).
The low solubility of methane in water limits its diffusive transport in the flooded soil, and most methane is oxidized to carbon dioxide via methanol, formaldehyde, and formate as it passes the aerobic soil-water interface. The release of methane by diffusion through the wet soil column is negligible in clayey soil, but it may become significant in sandy soils in which bigger pores between soil particles prevail. Most rice soils have high clay contents. Soil fauna, especially aquatic earthworms (Tubificidae), increase emission through diffusion and ebullition when they dig into the topsoil. At the same time, oxidation of methane is enhanced. In deepwater rice fields, diffusing methane may only be oxidized in the upper water column, because the soil-water interface and the lower water column may be anaerobic."
So if you decide you can't currently capture and use the biogas your digester makes, we can follow the natural cycle and work with methanotrophs.
Again, we are talking about extremely small volumes in any case and therefore not a problem, but if you wanted to be sure not to have ANY impact on methane accumulation in the atmosphere and can't burn the gas your digester makes, our suggestion is that you mimic the rhizosphere and allow the methanotrophs to decompose your biogas.
Simply run your biogas hose through a layer of rhizome rich soil. Get a container, fill it with loose biologically active soil or compost and put some weed seeds in there. Let things sprout. Run your gas tube into the bottom of the container and let nature do the rest! Case closed!
I have an arduino with an SD card shield reading the ds18b20 temperature probes in my digestors with a time stamp from an RTC. How do I get that data off the card and into the computer for analysis?
1) Turn off the power to the Arduino (or simply unplug)
2) carefully remove the SD card by pushing in until you hear a click and feel the bounce back, then pull it out, noting the wires (maybe take a picture) in case you accidentally disconnect something.
3) put the SD card in your computer and open the file. Hit save as and change the name from Datalog.txt to KathyBorgNov22Datalog.txt (This will enable us to keep backups of the old data each week and the arduino will start a new log called simply datalog.txt when it powers up again)
4) Hit "save as" again and save the KathyBorgNov22Datalog.txt file to your computer.
5) Upload this txt file to the files section of the group.
6) Replace the SD card in the arduino carefully.
7) Power it up.
If you want to make SURE it is recording well again, then before you power up the board connect it instead to your laptop and launch the Arduino program. Go to "Tools:Port" and select the port it says your arduino is connected to (just make sure it is checked and not grey).
Then go to Tools:Serial Monitor and open the serial monitor. In a few seconds it will hopefully tell you the SD card has been initialized and spit out some temp values. You can then close the program, unplug the Arduino from the computer and plug it back into power and it should record for another week. This should really be done weekly.
Is HomeBiogas certified for risk and safety?
Okay, I've got my domestic dragon. How do I care for it?
First keep in mind, its an animal, not a machine. It has a stomach. It can be overfed.
It will then get indigestion.
It will then stop making methane.
You will be able to tell because the gas won't light (it will be increasingly just CO2). The effluent will begin to smell sour (acidic). Your nose will tell you.
At that point you must stop feeding food waste. That will only sour it further. And you should give the poor dragon's stomach some antacid. I suppose you could drop a roll of TUMS in... lots of rolls of TUMS, but that would get expensive! You could use baking soda (sodium bicarbonate, from Arm and Hammer, the same stuff you may put in your refrigerator to keep it from smelling, just be careful, it tends to fizz and froth like your kid's science fair volcano and gets messy). You can use sodium carbonate (Arm and Hammer Washing Powder), that doesn't fizz like the bicarbonate. You can use sodium hydroxide (drain cleaner pellets or fluid). How much? Well, you have to add a little at a time until you get the pH back to neutral.
And then you can ALWAYS add more manure. Manure is a good thing. It reinocculates with methanogenic microbes. It helps balance the pH. It adds some energy that won't sour the tank. Some manures have indigestible stuff that the microbes can live on. You can add manures whenever you want, with impunity. Just know that the more you add the more fertilizer overflow you will have to take care of.
So how do you take care of your dragon?
The rule of thumb for the appropriate 30 to 40 day hydraulic retention time of the solids you put in is to feed the tank no more than 1/40th of its volume. So for a 1000 liter IBC tank you wouldn't put in more than a 25 liter bucket of food waste (mixed food waste and water, usually at about a 50:50 ratio, but since food already is mostly water this is hard to calculate. Just grind up about a bucket worth of food at a consistency that you can easily pour in).
In practical terms this means about one 5 gallon paint bucket filled with a slurry of food waste per day per 1 ton tank. Do the math if you have a larger tank or a smaller tank. 1/40th the volume.
You can always feed less with no problem. In fact the tanks can go months and months with no feeding at all. Mine have recovered for over half a decade from up to half a year of complete neglect and 6 total freezing events. Just know that when you start feeding again, take it slow (like start with a cup or two a day and work your way up to that full bucket) so it doesn't get indigestion as the microbes recover from their slumber. So there is no minimum on feeding. And you can always put in manure at any time. Did we already say that?
You can wait a week and feed your digester only once a week but you can't feed it a full week's worth of food in one go. It is a stomach. Of an animal. An artificial animal to you, but to the microbes who live in your tank well, they think they are still in the cow or horse they came from. Go easy. They can handle about a bucket every 24 hours or so. And it really helps if it is warm.
Don't shock your microbes. They hate getting hot and bothered and then cold and bothered and then hot and bothered. Try to keep their home a constant 20C to 40C averaging 25 to 30. Body tempertature is ideal but hard to acheive in practicality. The tank size helps... they buffer temperature swings a bit.
Do warm water feeding. Keep your tanks well insulated. Heat as necessary. Try to make the microbes happy.
Every time you feed you will get an equivalent amount of liquid organic fertilizer out. Use it with your aeroponics or hydroponics or in your garden or on your grass and trees and shrubs, or simply let it go down the drain. Or you can capture it and use it to grind up the next batch of food and recycle it back into the tank. Give it to your neighbor to start their biodigester. Collect 1000 liters of it and make another 1000 liter digester that will start right away. Oh the possibilities!
There isn't much maitainance to do with the gas. Store it in a gas bag or an air mattress or a floating drum or whatever you want (inner tubes from trucks or tractors stack nicely). Use it whenever you have enough (enough is usually 500 liters which gives you an hour of cooking or so; a tractor inner tube can usually store 60 to 80 liters).
The gas can be stored for millions of years. It won't go bad. Yeah... its natural gas. (Well, that depends on how long your storage bladder lasts, but you could technically keep moving it from storage balloon to storage balloon for the next million years or so...)
If you don't feed the tanks they will stop producing gas, so if you go away, you don't have to worry. Just leave about 1000 liter bag attached to collect what the last bucket of food waste you put in creates if you fed it just before leaving the house. If it makes a little more it will safely burp out the other side (the slurry out tube). And since the CO2 part (30% or so) is heavier than air and falls and the methane part (70% or so) is lighter and floats away and disperses quickly, you are okay.
There isn't much cleaning to do if the system is working right. Occasionally you may find that you didn't grind your food well and some of it floats up and clogs the pipes. So remove the top of the pipe where the fitting is (we don't glue them for this reason) and shove a stick down and unclog it.
If you used a ton of manure with a lot of straw in it you may get a scum layer on top after a few months that impedes the gas from getting out. In that case you may have to open up the IBC lid (unscrew it), reach in and shovel out the scum layer and reseal it. No biggy. We've done it several times. No, there is no worry that while you open the tank you can get hurt. Just don't lick your fingers.
Hope that helps you understand the feeding an maintainance of your dragon.
Journalist's Questions about the Mission
You are giving lectures about energy, clean technologies, reducing environmental pollution
and saving methods. Your works in Cairo are really impressive. However, each country has
different conditions and most of the time; the one that works for a location is not convenient
for the other. In the context of these works, what do you think about the difference between
cultures and social structure of a society? Can you give us a couple of examples concerning
As a sustainable development professional and environmental science
professor focusing on how to help us reach our UN Millennium goals I
constantly reflect on the distinction between “techne” (knowledge that
is immutable, universal and transferable) and “metis” (knowledge that is
ever changing, intensely local and can't be replicated elsewhere). As a
National Geogaphic Explorer I confront the distinctions on a first hand
basis through my travel to as many as 10 different countries every year.
For example we don't all have the same access to sunlight, to wind, to
sources of heating or cooling, to fresh water, to wood and rock and
fertile soil. And we can't always rely on importation of vital resources
from outside. To create a sustainable situation we have to find solutions
based on what is available and reliable using our metis. But at the same
time our knowledge of the physical, chemical and biological constants of
nature enable us to take certain materials and environments anywhere
and create new technologies that can simplify our lives. The area where
techne and metis meet that I focus on is in the universals that we all
share as human beings. The fundamental one for me, besides my
observation that the same proportions of human kindness, curiosity,
compassion and genius are found everywhere, is that we all have food
waste and toilet waste, and we all have the good microbes that can
transform them into fuel and fertilizer. These constants have been
ignored as a fundamental solution to our problems and because of this
created terrible problems – diseases, pollution, deforestation, and loss of
soil fertility chief among them. But now that we know through our own
study and experience that organic wastes can be fairly easily transduced
into constant renewable energy and soil which can be used to cook,
light, heat, refrigerate, and generate electricity in quantities enough to
meet our baseline needs, I am a lot more confident that the other
solutions that depend on unique local characteristics and resources can
guarantee a high quality life for people anywhere.
You’ve been to Turkey before. From your point of your, what are the main differences in
Turkey? Thus, on which topics should we focus more about energy saving and actions to
reduce environmental pollution?
Turkey impresses me each time I visit with its dedication to creating a
healthy progressive environment; I was delighted to see a growing
number of solar electric panels, solar hot water systems and wind farms
as we travelled through the country. I loved seeing the commitment
Turks make to planting and nurturing trees and in Cappadocia I was
impressed by the celebration of creating beautiful architecture out of
materials and shapes unique to the local landscape. Turkey is blessed
with a large coastline, great sunshine and wind, many mountains, fast
flowing streams and rivers and the land and both landscape diversity and
cultural diversity to experiment with the many solutions that will get us
through the 21st century safely. The new paradigm of decentralized,
distributed energy and resources and waste treatment is well suited for
a country like Turkey with such a rich and diverse heritage, and with easy
access to the markets and ideas of both East and West. In a world that
desperately needs decentralized solutions, Turkey's central geographic
position gives it a unique opportunity to connect all the dots and offer
the world a new model of systems integration. Most impressive for me
was the amout of activity going on around various scales of biogas
systems. In Ankara at the University we were given a great tour of the
laboratory of Kursad Fendoglu who is doing experiments in small scale
anaerobic digestion from food waste, combined with an innovative algae
reactor creating a closed loop industrial ecology system where the
output of one process fed the input of another. We also learned that
their team was building large scale commercial systems. We've stayed in
touch via our facebook group “Solar CITIES Biogas Innoventors and
Practitioners” and are linked up with many of the students and faculty
we met on the last tour so we are excited to see how Turkey is
progressing in this field.
As a Google Science Fair judge for the past 4 years I've also had the
pleasure of working with Turkish high school student Elif Bilgin from
Istanbul who, at 16, invented a way to turn banana peels into a durable
bio-plastic. This kind of innovation is in the cultural DNA of this ancient
yet post-modern land. It is clear that Turkey could emerge as a leader
in these fields and be the bridge that demonstrates to both Europe and
Asia how effective environmental sustainability can be once all organic
wastes are transformed into fuel and fertilizer and even plastics.
Can you describe your project in one sentence so I can tell my teacher... or my mom... or the relevant authorities?
We are closing the loop by transforming "food-waste-to-fuel-and-fertilizer-to-food-and-cooking again" at the home and community scale.
The name of our signature project that makes this magic accessible to EVERYONE is "The Solar CITIES DIY IBC Biodigester for Homestead Ecosystems"
What seems to be the problem here? And why do you think your rag-tag army of capeless-crusaders can solve it?
We strive to tackle and solve the "metabolic rift" problem -- the ecological crisis caused by linear cradle to grave resource mining and transformation with non-equilibrium capital accumulation and entropic dispersion engendered by the division between town and country. That's just a fancy way of saying that as long as energy and fertility are being mined in one place ("the countryside"), utilized in another ("the town" or "the city"), and disposed of as waste products in another ("the landfill", "the dump", "the river", "the ocean") , the result is inevitable impoverishment and system collapse. The rift between the sources or "cradle" of energy and food production, and their destination or "grave" as waste materials, destroys the chance for a living metabolism of recycling that would ensure sustainability. Still, this problem is actually quite easy to deal with, particularly at the local level (it can also be scaled up). An "industrial ecology" approach treats all outputs from one system as an input to another in a semi-closed loop (open to solar input).
We are successfully using "Do it Yourself" Biogas systems based on readily obtainable and inexpensive IBC plastic shipping containers to close the rift and want to share the solution as widely as possible.
What´s innovative? Why does the world need it? On what technology or method is it based?
People used to think that biogas systems needed to be big, were difficult and needed experts to construct, needed to be outdoors, and needed a lot of animal manure to work.
None of this is true.
In our work in Solar C3ITIES (Connecting Community Catalysts Integrating Technologies for Industrial Ecology Solutions) we have demonstrated in dozens of countries from Botswana to Alaska, in both rural and urban homes, and at Mercy College New York and in other Universities and private homes (increasingly indoors, in families' basements!), that it is yawningly easy to take one of those ubiquitous used IBC shipping container tanks (1000 liter polypropylene International Bulk Containers) that are found in every country in the world and a couple of uniseals or bulkhead fittings and some plastic pipes and create in just a few hours a really effective, really low cost, easy to build biodigester.
These home scale biodigesters, using the principle of anaerobic fermentation, can turn almost all organic residues (food scraps and all kitchen wastes, including all the meat and grease and fat and bones and toilet wastes and animal droppings that cities won't let you compost, everything except for woody material like branches) safely and efficiently into useful, reliable cooking fuel (biogas) that can also be stored for use in emergency generators, gas lamps or refrigerators. Each IBC produces between an hour and two hours of cooking gas per day from a daily input of approximately one bucket of ground up food scraps.
The systems, using 24 hour anaerobic fermentation of these wastes, also produce a liquid compost -- an NPK rich compost tea, that can be directly used with hydroponics and vertical aeroponic gardens as the sole source of fertilizer, ensuring that nutritious food can be grown right in the city and other areas where there is no available land for agriculture.
The IBCs can be used in a modular fashion, used in series and parallel, increasing the amounts of waste consumed and gas and fertilizer produced. Our research, living with home biogas and biofertilizer produced this way for the past six years, has proven its effectiveness. We are closing the metabolic rift and we want to get the word out, make this simple solution open source and available and empower others to do this as quickly as possible.
(choose a maximum of three)
renewable energy production
energy efficiency & monitoring
goods & household products
construction & housing
agriculture & food
mobility & vehicles
circular economy & waste reduction
biomaterials & bioconstruction
production & fabrication tools
Do you need CNC machines, 3D Printers, wood, metal, tape etc.?
Our needs are small:
Some used IBC tanks with intact lids. A drill with appropriately sized hole saws. Plumbing materials (pipes, valves, elbows, Ts and fittings). Black paint. Insulation materials. Gravel or stones. About 100 kg of some kind of animal manure as a starter inoculant to introduce the microbes. That's it. We've done this in remote villages in Africa and in the streets of Istanbul and everywhere in between. This ain't rocket science; we just need it to take off!
Give us links to pictures, sketches, plans, designs or other forms of documentation of your most advanced prototype, project or idea
Give us links of your blog, profiles or other references you would like to share with us
Go to Tamera Solar Village Test Field in Portugal or come to Mercy College or the home of Kathy and Ed Puffer in Tilson NY or the Rockefeller Mud Creek Farm in Hudson NY and see for yourself!
Or, click on our maps here at these websites, click on the location point and then go visit for real (the above mentioned locations are on the map):
Or read about us here:
And read about us in National Geographic here:
Journalist's Question about the People
In other words "if it is so damn good, and so damn easy, why isn't everybody doing it?"
Simple ignorance. Unfamiliarity. Fear. Laziness. Aversion to working with 'wastes'. Information assymetry. Myths, disinformation, risk aversion, a Zeitgeist of apathy, disbelief, defeatism, lack of trust, lack of experimentation, systemic patron-client discouragement, bad public policy, lack of incentives, withholding of key information motivated by a desire for profit and personal gain. All psychological, none technological or material.
Is the HomeBiogas system from Ecogas Israel safe for use in MY home?
Yes, it is safe.
Since this is a commercial system that has been deployed in many countries and tested for years for safety in people's homes and gardens and schools, it has the CE rating and government approvals for safety standards in Israel and the US.
HomeBiogas has a team dedicated to answering questions for new users, so we don't have to try and reinvent anything; the system is just new to the US so people are unfamiliar with it.
Basically it is a "sealed liquid compost bin" rather than a machine. It is always filled with water and hence can never pose a fire hazard. The compost it produces, which is a liquid compost tea, is odorless and bacteria free thanks to a chlorine sterilizing disk at the output side. It doesn't attract any flies or vermin, unlike solid compost bins.
The amount of biogas that slowly bubbles out during warm days when fed, can only reach a certain volume, is contained within the flexible bag above the water reservoir and is under such low pressure that it represents no bursting hazard. It contains no air so it is not flammable except when lit at a stove, and it can not explode.
If a saboteur were to puncture the bag and light it deliberately it would flare off in a few seconds. If a flaming arrow was shot into the bag it would flare off in a few seconds. And since the bag is made of flexible plastic, if a saboteur were to inject air from a scuba tank into the gas bag and try to plunge a flaming spear into the bag the plastic would simply rupture and the gas would flare off in seconds. There would be no explosion and no noise other than a slight "whoosh" even in this most extreme of unlikely scenarios. We've been doing home biogas indoors in New York and Pennsylvania for 3 years and can't find a way to make the systems even remotely dangerous. Outdoors the risk is essentially near zero, by the laws of biology, chemistry and physics. The only risk posed would come from deliberately drinking the compost tea perhaps or by deliberately lighting the gas in one's face or sticking one's hand in the stove. We routinely bring full bags of biogas into our classrooms and cook eggs and bacon and pancakes with the gas, and have had fire inspector approval for this in several states.
In Alaska in a high school the fire marshall gave his approval saying, "even if you set the system on fire deliberately, it would be self-extinguishing due to the full bladder of water beneath the small quantity of biogas, which itself is 30% carbon dioxide which acts as a flame extinguisher and ensures the biomethane portion never accumulates... the biomethane almost instantly disperses when not captured and directed to the stove. Even a stove left on poses no hazard. And the regulated flame on an active stove only lasts two hours from each bucket of food waste fed, which occurs at most once a day. If lit, it is thus more like a pilot light with a limited supply of gas. The gas runs out quickly if the valve is opened, posing no risk. If it is not fed, it won't produce gas at all. So it is very easy to control.
It also takes about three weeks to start bubbling any gas out when first filled with liquid and inoculant. So once it is set up it won't do anything for nearly a month. Then the gas bubbles from the liquid bag into the gas bag at a rate of a few bubbles every 5 seconds or so. If the gas bag is full and people kept feeding it (which they would not) then it would bubble out the overspill so slowly that it would be almost undetectable and certainly could not pose a hazard (think of it like a pond which itself is a biodigester, releasing little bubbles of biogas every 5 or 10 seconds. Our bodies actually do the same thing. These can not be easily ignited and certainly pose no hazard, as many children have discovered trying to light flatulence.)
HomeBiogas can supply more thorough information and will send you results from the many installations in homes in Israel and elsewhere. I just thought it would be nice to give you my analysis after my own many years of use. I allow my children to play around mine because I feel it is so safe and so much better than our previous compost bins or garbage bins. We put one in our house because it eliminated rather than created problems.
I hope that as more and more people install these simple systems around the world you will find an opportunity to walk around a homebiogas system and see it and get a sense of what it is all about rather than just using pictures and your imagination. It is lightweight when it is unfilled with water and when first set up completely inactive so it can be easily carried around to different locations by a couple of people so you can see where you might want to place it in or around your home before committing and filling it with water. You don't have to make quick decisions with this system; you can set it up and move it about and can get people in your family, neighborhood or community to actually see and touch this exciting new problem solving appliance to get everyone comfortable and get total buy-in before you commission it with innoculant and put it into service. Once it is filled it will weigh about 700 kilograms, so you don't have to worry about somebody walking away with it, but if you want to move it you can always drain it conveniently and put it in a more suitable location.
At some point they will be as ubiquitous as washing machines and garbage cans (and a whole lot better!).
Thanks for taking the time to meet with us the other day and brainstorm and I look forward to more problem solving with you!
T.H. Culhane, Ph.D.
What are the triple bottom line benefits of biogas?
For sustainability efforts to be considered viable they need to pass the "triple bottom line test".
The triple bottom line means that a project can demonstrate benefits that are social, environmental and financial.
We believe that biogas projects can easily satisfy these criteria.
Biogas systems create jobs. Digesters employ people with design and construction and maintainance skills across sectors -- from architects and planners to builders and plumbers and electricians. The digesters need to be sited, permitted, built, inspected, operated and maintained. Because they generate energy and fertilizer for decades and never run out of feedstock, they provide a perpetual source of employment.
Biogas systems involve interdisciplinary expertise. Job training and retraining for the biodigester sector builds capacity in STEM (Science Technology Engineering and Math) subjects with emphasis on careers in chemistry and biochemistry, microbiology, informatics, and economics.
Biodigester systems trump most other solutions on the environmental axis. In one fell swoop a well maintained biodigester can:
- Extremely reduce or eliminate the need for firewood or charcoal. With this one benefit we eliminate many of the causes of deforestation at the margins, completely eliminate indoor air pollution and smoke from fires (which claim up to 4 million lives a year, particularly the lives of women and children, while blackening homes and utensils with soot), and significantly reduce the amount of time women must spend collecting biomass, allowing more time for child rearing, education and microenterprise activities. The unparalleled safety of biogas (rarely able to create explosions, non-sparking, easy to extinguish) means much greater safety for families and drastically reduced potential for burns or for fires to get out of control.
- Extremely reduce or eliminate the threat or nuisance of vermin and disease causing animals. Biodigesters do not attract wildlife, neither bears, feral dogs, cats, coyotes and other problemaitic mammals, nor flies or other insects. As such they solve almost all of the problems associated with poorly maintained compost bins and trash receptacles. Maintained properly they are odor free (when covered); at worst they smell like cow or horse manure (a barn smell or a swamp smell) . They do not elicit the "gag reflex" or nausea response.
- Extremely reduce the threat of pathogenic microbes. Properly maintained, and particularly when coupled with aerobic post processing, they elminate 98 to 99% of most disease causing bacteria, even when fed fecal material.
- Invulnerable to fluctuating gas prices. Biodigesters produce a reliable amount of gas when fed the proper amount, and will do so in perpetuam. When fed approximately one fortieth of their volume, the digesters kept at body temperature (about 37 C) can produce their tank volume in uncompressed gas. Each 5 degrees or so lower than that they produce approximately half that volume. But if frozen or unfed they simply hibernate and can be quickly revived. Since food and animal wastes are always being produced, the digester can operate indefinitely and is thus a robust source of clean renewable energy.
- Produce no smoke or carbon monoxide. Biogas burns clean, releasing only CO2 and water vapor that adds no net carbon to the atmosphere. This makes biodigesters a good weapon in the arsenal against climate change.
- Produce an NPK (nitrogen, phosophorous, pottasium) and micronutrient rich liquid fertilizer or "anaerobic compost tea" that is microbially active or "prebiotic". Biodigesters enable us to create new food from food waste by transforming the "garbage" into a slurry that can be used for hydroponics, aeroponics, rooftop and urban gardens and for soil formation in marginal areas. The use of bioidgesters to transduce urban organic wastes into "liquid soil" creates the possibility to "close the cycle" and enable cities and communities to produce their own nutritious food in situ without the need for arable land or costly fertilizers.
These are just a few of the chief environmental benefits associated with the biodigestion of organic waste. Both the fertilizer and the gas can be stored indefinitely, so they can be seen as forms of "solar batteries" to help ensure we can create true solar cities.
Reduces waste haulage which costs money. Saves money by recycling wastes.
Lowered tipping fees by diverting organics from landfill
Lower waste collection expenses (labour costs reduced by more than 50%), waste transport costs reduced by up to 50% (trucking, rail),