Solar Power isn't Feasible!

Solar Power isn't Feasible!
This cartoon was on the cover of the book "SolarGas" by David Hoye. It echoes the Sharp Solar slogan "Last time I checked nobody owned the sun!"

Thursday, July 2, 2009

Archaic Wisdom: Working with Bacteria to Make a Better World

They've been with us since the beginning, predating the arrival of human beings on Earth by not millions but billions of years. And they will be here for billions of years after we've gone. After everyone and everything else is gone.

They were the first and they will be the last, the alpha and the omega.

They are the Archaea -- a kingdom unto themselves, the kingdom of prokaryotic bacteria whose sheer numbers even today create a biomass that dwarfs that of all other living creatures combined, and may contain more biodiversity than all other kingdoms combined. Their kingdom contains the extremophiles -- bacteria that thrive in extreme environments -- from the subzero temperatures of the arctic to the hottest of hot springs, from corrosive surface pools of sulfuric acid to the deepest volcanic vents on the ocean floor, and possibly even other planets or their moons . And this Archaic Kingdom contains the creatures Methanobrevibacter smithii and Methanosphaera stadtmanae, which live benignly within us, in the human gut.

Over half of the known species are methanogenic -- turning organic material into methane gas -- CH4. And therein lies the rub.

The methanogenic Archaea, in our world of accelerating climate change, are a Janus-faced coin. On the one hand they are responsible for the climate changing methane released by billions of belching/farting cows and other livestock, by fetid swamps, and bloated rice paddies and agricultural-waste polluted wetlands, by decaying landfills and, most notably, by the "time-bomb" tundra -- the organic material under the melting permafrost that threatens a catastrophic release of greenhouse gases as the ice thaws. Methane in the atmosphere is considered to be a greenhouse gas 25 times as potent as CO2.

On the other hand, the methanogenic Archaea provide an unprecendented opportunity to create net-climate-neutral fuel supplies for our homes, restaurants, businesses, factories and vehicles. Harnessed, the methanogenic areas of the planet that are causing concern could drastically reduce our dependency on the real greenhouse-gas culprits -- fossil fuels; created de novo in our cities and agricultural areas, specially desinged biogas digestors could eliminate waste and pollution and create rich organic fertilizer as well as power our homes, farms, businesses and industries with clean fuel.

To explore the more sanguine of these possibilities, Solar CITIES, which has implemented Dr. Anand Karve's India ARTI home biogas solution in Cairo, Egypt, is teaming up with arctic ecologist Dr. Katey Walter, who studies the "Methane Time Bomb" in Alaska and Siberia, to see if there is a way to harness the power of the Archaea at the household and community level for temperate zones that experience cold winters.

Household and community level solutions are necessary, Solar CITIES maintains, because it can be assumed that the enthalpy of the fossil fuels that must be consumed in the process of collecting, compacting, transporting and disposing of urban organic wastes, primarily from kitchens, restaurants and markets, is actually greater than the amount recoverable from their transformation into biogas. A quick thought experiment suggests that the net amount of greenhouse gas offset by the creation and use of biogas must be less than the amount produced in transporting the feedstock to the bacteria in a centralized production facility: imagine that your city had no more fossil fuels available and that you had to power the garbage trucks that collect your waste purely from the energy contained within the garbage you produce. If this were the case garbage collection would most likely grind to a standstill (or people would return to using donkey-carts, as the Zabaleen of Cairo do).

This assumption, of course, could potentially be at least partially obviated if every home had an "insinkerator" type waste disposal unit installed that allowed liquid effluent to flow to a biogas facility. In California we have long experience with the environmental benefits of garbage disposal units, which use less than 50 cents worth of household electricity consumption and less than 1% of household water consumption to operate per year. When piped to the sewer system they can use natural gravity flows to send a slurry of food waste to the water treatment plant where it can be easily turned into biogas. Still, many communities do not have such systems. Also, in Europe, for example, it is still very difficult to find garbage disposal units (they have been in the UK since at least 1965, and can now be found in Spain, where they are called "trituradores de desperdicios de comida" and in Italy, where they are known as "dissipatori di rifiuti"; in Germany, they are called "Kuchenabfallentsorger", but they are new to the market, hard to find and very expensive, and plumbers still question whether their connection is allowed. )

However, where natural gravity flows are not available, the energy consumption associated with pumping large volumes of wastewater to a treatment facility, and the energy costs associated with then purifying, storing and delivering gas back to households and other end users reduces the efficiency of the system and its potential to relieve the greenhouse gas burden. (Culhane, in his home in Germany, is convinced that the amount of methane his food-waste produces each day would probably not even be enough to run the 750 Watt Inskinkerator or the 350 Watt Sump Pump (which delivers the food slurry to the digestor) and still leave enough useful gas left over for cooking or other utilities. Fortunately they have photovoltaics to do the job of running the appliances).

From a distributed energy point of view, it makes the most sense to use the waste in-situ, at the point of its creation. Since methanogenic bacteria are self-reproducing, and merely require an anaerobic container to do their work, each household and business could maximize the energetic efficiency of the process by directly converting the slurry produced by a sink-mounted waste disposal unit into methane (in a digestor on the roof, on the porch, under the stairs or in the basement) which would offset a certain percentage of the gas provided by the municipality. In this "household offset model", methane produced from farms, factories, wholesale markets, and sewage treatment plants would be piped into houses, supplying perhaps 75 to 90 % of the household's needs (primarily water and space heating when solar and ground-source heat-pump supplies are unavailable) while the household's own waste would offset 10 to 25% of the household's energy demand (primarily for cooking heat). Household generated methane contains about 40% carbon dioxide, but it burns cleanly and well and does not need any expensive and energy intensive purification.

This is indeed the model being pursued by ARTI in India, where thousands of home-scale biodigestors have been installed. But the limitations of cold weather production have so far have apparently discouraged such thoughts for the temperate zone.

How archaic is the use of the Archaea-based technology?

Before I left for Pune, India last January to learn from Dr. Karve how to build the ARTI urban biogas digestors, I took a taxi cab from the Zabaleen neighborhood of Cairo to the airport and got into a conversation with the driver, a thickly bearded man dressed in a traditional balady galabaya, about solar energy and biogas. When I mentioned to him that I was headed to India to learn about biogas he said, "why go all the way to India? I am from the oases of southern Egypt and in my village we have been using biogas forever. Many of the fellahin know that if you take your garbage and throw it in a ditch, cover it with straw and mud and put a bamboo pipe in it you can get usable gas that you can burn. It works until the winter cold sets in. Only people in the city forget these things..."

I began to wonder if biogas isn't perhaps one of the oldest technologies humans have exploited since the dicovery of fire by Homo erectus.

Nothing new under the sun?

At the recent National Geographic Emerging Explorers Symposium in Washington D.C. (June 7th through 13th, 2009) Katey Walter and Solar CITIES' T.H. Culhane shared their ideas for collaboration in a panel discussion after their presentations. Culhane had shown video clips and images of the household biodigestors he and his wife Sybille have built on rooftops in Cairo and on their own porch in Germany, and Walter, who has become famous with her videos and images of lighting the methane that is dangerously building up beneath arctic lakes also showed images of Scandinavian households that have been harnessing and producing biogas for domestic use for hundreds of years.

In the discussion that followed, we mused about the possibility that human beings might actually have been using biogas since time immemorial. Certainly bacteria have been transforming the wastes humans generated into methane since we first appeared on the planet. And people have been very observant about both combustible material and bacterial processes since long before civilization began -- in fact, the ancient and highly developed arts of fermentation that led to the invention of bread, dairy products and alcoholic spirits prove that Homo sapiens have been well aware of how to harness the generative properties of various species of microbes for at least 10,000 years.

So how is it that the generation of biogas from offal is now considered a "new" bio-technology?

Actually it isn't. Biogas use is documented going back 2,000 to 3,000 years in the Chinese literature, is documented from the 10th Century BC in Assyria, was well known in Persia during the 1500's and was being used on a municipal scale to light the street lamps of Exeter in England in 1895.

One of the answers for why we hear so little about its past importance could be the north/west/temperate zone bias of modern civilization. Southern/eastern/tropical peoples may have been using biogas all along, but their solutions may have been marginalized or erased when they encountered hegemony from northern colonizers who were only familiar with burning wood and charcoal; in any event biogas depends on a stable place for biomass-accumulation and digestion and in the diaspora that follow conquest, displaced people with insecure land tenure would have found it easier to scavenge for woody material wherever they happened to be. They would have then forgotten this earlier technology.

Culhane pointed out from his personal experience that one of the limitations of small-scale biogas production in northern temperature zones like Germany was the winter temperatures stopping the metabolism of the thermophilic bacteria. Many biogas industries, finding it hard to keep temperatures in the appropriate range, stopped using thermophils for this reason and switched to mesophiles. The bacteria now used in most biogas systems are the mesophiles found in the guts of animals and they do best at body temperature. In industrial biogas facilities, like the nearby Imbrahm Recycling plant in Kettwig, which collects the kitchen waste from restaurants all over the area to produce biogas for electricity and heating, a portion of the heat generated from the gas is sacrificed to keep the digestors near 37 degrees Celsius.

But Walter's observations of snowy Scandinavian household biogas digestors that predate the industrial revolution and the discoveries of coal and oil opens up a whole new world of possibilities. The trick in the arctic circle is the use of a complete different group of methanogenic species -- the "psychrophiles" or "cryophiles" -- "cold-loving" bacteria.

It is these extreme members of the Archaea -- these "extremophiles" who can thrive and produce biogas beneath the ice -- that make it now possible to conceive of a north temperate biogas-based society that can efficiently produce energy from garbage all year long. Dr. Walter's studies of the arctic bio-gas producing bacteria have shown that their peak output occurs at 25 degrees Celsius, but they remain healthy and active below the freezing temperature. This high range of viability makes them ideal for systems that experience winter temperature fluctuations from 0 to 15 C; it is supposed that they would also do well in the bottom of digestor tanks in the summertime where, due to thermal stratification, temperatures can easily remain as low as 25 degrees even when the top of the tank reaches 40 or more.

But lest one believe that psychrophils only have potential for winter biogas production it is worth noting that this week here in Essen, Germany, in mid-July, the average daytime temperature has been highs of 16 degrees and lows of 13 degrees with a couple of days peaking at 24 degrees. Our biogas system, which prefers temperatures of 37 degrees, has given us very poor performance this summer with the temperatures being at the bottom of the mesophiles range. But Katey's bacteria are at their best at this European summer temperature range.

What the Walter-Anthonys and the Fruetel-Culhanes have decided to do is to start using psychrophiles and mesophiles together in the same digestor, much in the same way the Chinese (and now development agencies) have done "stereo-breeding" of different species of fish in the different temperature zones of aquaculture tanks to improve productivity. The cold loving bacteria will occupy the colder bottom strata, while the mesophiles will occupy the upper, warmer parts of the tanks thermocline. It might even be possible to populate the top region of the digestor with thermophiles and have "a bacteria for all seasons". Theoretically, if the tank is designed correctly, the psychorophiles will dominate in the winter and the mesophiles (and possibly some thermophiles?) in the summer, but both will hang on during the periods when the temperatures are not optimal for them by occupying the parts of the tank most suitable to their metabolism. And together they will keep the system producing gas all year round. In this way, it is surmised, the winter energy costs for keeping a biogas digestor at the appropriate temperature can be reduced, hopefully to the point where it makes sense to depend on biogas and obviate the need for fossil fuels. (It would also obviate the need for external garbage disposal, since all the other household wastes would remain clean and easily recyclable, and it would eliminate most need for composting, which tends to shut down in the winter time; the biogas digestors would produce liquid fertilizer all year). The key is finding the right combination of bacterial species that can work together across different temperature regimes.

Archaea-ic diversity to the rescue

So much hype is made about "genetic engineering" and the creation of "new organisms" that can "do man's bidding" that we tend to forget that during nearly 4 billion years of evolution the Earth's own microbes have come up with solutions to almost every environmental challenge we can imagine. So spectactularly successful have the Earth's micro-organisms been -- even anticipating the spread the of certain environmental threats -- that some researchers now talk about the possibility of bacteria forming the equivalent of "neural networks" and having some kind of "bacterial intelligence". One researcher particularly active in this field is Israel's Eshel Ben-Jacob, whose 1997 paper "Bacterial wisdom, Godel's theorem and creative genomic webs" has become a favorite among astrobiologists. Another researcher looking into the possibility that micro-organisms express a kind of collective intelligence is Zann Gill, whose book "If Microbes Begat Mind" was presented at the NASA Ames Research Center . In the realm of literary fiction, the idea of microbes forming a kind of swarm mind is the subject of Frank Schatzing's well-researched techno-thriller "The Swarm" and Greg Bear's sci-fi parable "Blood Music". Nebula Award nominee Raymond Gallun's Bioblast pays homage to Altmann's 1886 discovery of the bacterial nature of our mitochondria (Richard Altmann, a German pathologist, studied mitochondria in the 1890s and was the first scientist to theorize about their role in energy production). And in the film world the concept of bacterial symbiosis aiding us in the next step of human evolution is found in such movies as the little known but deep-thinking Alice Krige thriller "Habitat" (Krige, who was also in Dinotopia, is best known to sci-fi fans as the Borg Queen in Star Trek: First Contact) and in Star Wars, where the explanation George Lucas gives us for "The Force" is to be found in bacterial symbionts called "Midi-Chlorians" (both the name and the concept are based on the role mitochondria play in providing energy or "life-force" to our cells; the connection is spelled out by Nick Lane in his book "Power, Sex, Suicide: Mitochondria and the Meaning of Life" on page 5 ).

Whether the subjects of speculation or fiction, in the realm of fact the Archaea must be considered our distant but direct ancestors, that is to say, our (albeit genderless) forefathers and foremothers. Lynn Margulis' theory of Endosymbiosis goes so far as to hypothesize that our own eukaryotic cells are the result of a symbiosis between prokaryotic microbes, and others have suggested that "we are the chimeric product of the fusion of the two main branches of ancient Life, the bacteria and the Archea." We often think of bacteria as food spoiling competitors, disease causing parasites or even flesh-eating predators, but as any beer-lover, wine-connoisseur, cheese-aficianado or probiotic yoghurt, kombucha, sauerkraut, kimche or kefir eater can tell you, bacterial symbionts play a tremendously important role in our well-being. And if you ask a cow or any other ungulate, who depend on bacteria to eat grass, or a termite, who needs bacteria to digest wood, they would tell you life without bacteria would be impossible.

It may well be that it is the invisible Archaea that connect us all in the web of life, a thought that can take all almost spiritual proportions.

Regardless of how one views the Archaea specifically or bacteria in general, it would be hard to contest the notion that if we are looking for an effective and efficient way to terraform our planet away from the impending climate crisis, we could hardly do better than to harness the very creatures that created the biospheric life support system we depend on in the first place. Without having to engage in any bioengineering or gene-tinkering at all, we can most likely find bacteria capable of transforming our wastes into raw materials that are climate friendly.

Working with, instead of against, the bacteria who share our planet, may be the wisest thing we can do to prevent catastrophic climate change. Metaphorically you can be sure that when Noah heard the call to save biodiversity from the great flood, he listened to this Archaic wisdom too - in the stomachs of every creature on the Ark, the Archaea also hitched a ride.

What we propose

Solar CITIES and Katey Walter propose a series of controlled field experiments operating on several continents and in several climates throughout the year for the next three years.

Dr. Anand Karve, inventor of the ARTI Urban Biogas Digestors that we build in Egypt, discussed with Culhane a need for more experimentation with cold climate digestors. One of the limitations he experiences in India is that the cold season production of biogas can be reduced by 50%. Since a 1000 liter system (the size most suitable to households in weight and size) produces roughly 2 hours of cooking gas each day from the normal kitchen waste produced by a family of 4, the winter reduction to one hour or less of fuel can be limiting and either discourage use or force families to supplement with other fuels which may damage health and environment. In colder climates the winter shut down of gas production may stop families from using biogas altogether.

Dr. Katey Walter's Arctic pscychrophiles may hold the key to improved performance in cold conditions.

We propose the following phased experiment (subject to modification):

Phase I: Home testing in Germany

1) Dr. Walter ships some of the bacterial-laden mud she has collected from bio-active Arctic lakes in Alaska and Siberia to Solar CITIES in Germany.

2) We build three identical small scale digestors in the backyard, one containing only the psychrophiles from the arctic, one containing only the normal mesophiles from German livestock, and one containing a mix of the two. Total cost of construction: 600 Euro ( 200 Euro per digestor).

3) We feed each digestor the same amount of feedstock each day, noting the ambient temperature, the temperature of the feedstock and the temperature of the digestor, and measure the volume of gas produced each day.

Phase II: Field testing in Egypt

1) In preparation for the chilly winter in Cairo we build a similar set up there, in the garbage recycling Zabaleen area, to be monitored by Solar CITIES coordinator Hana Fathy. This will show us if the yields are sufficiently enhanced to make it worth while using psychrophiles in the slums of sub-tropical areas with cold winters (ambient temperature 10 to 15 degrees C) as a waste management solution. (Costs: Construction -- 2000 dollars -- 1000 for the digestors, 1000 for coordinator/engineer Hanna Fathy to build, operate and monitor the digestors for six months. Travel -- 2000 dollars for Solar CITIES coordinators T.H. Culhane and Sybille Fruetel and for Katey Walter to travel to Cairo)

2) Based on the results of the German and Cairo experiments, after determining the viability of systems containing mesophiles and psychrophiles, we work on improved designs to maximize the productivity of the bacteria associations.

Phase III: Field testing in Tanzania

1) Working with fellow National Geographic Emerging Explorer and Ethnobotanist Grace Gobbo we build identical systems in Tanzania at or near The Jane Goodall Institute at the Gombe Reserve to determine whether or not biogas can be an effective solution to that part of the deforestation problem caused by the collection of cooking fuel. Although Gombe is considered a tropical location, temperatures in July can be as low as 11 degrees C, with an average minimum of 19 degrees. The goal is to discourage any regress to the use of wood fuel in this critical habitat during colder times. Grace shared with us that the the chimpanzee populations are very threatened because of habitat destruction but ironically even the scientific research stations and park protection facilities use fossil fuels, wood and charcoal for cooking and heating and have a hard time disposing of their waste, thus providing an example to visitors that only exacerbates the very problem they are struggling to solve. A viable year-round biogas system (coupled with solar energy systems) could mitigate and even solve many of these problems, particularly as the Goodall Institute acts as a catalyst for regional change.
Estimated Costs: Construction of 2500 liter biogas digestor: 500 dollars, construction of local solar water heater: 500 dollars, Travel to Gombe for Sybille, T.H., Katey and Solar CITIES coordinator and biogas/solar construction engineer Hanna Fathy, 4000 dollars).

Phase IV: Field Testing in Minnesota, U.S.

1) At the farm of Katey and her husband Peter Anthony we work together to build a 2500 liter digestor so they can monitor performance at home and see how the system works through the cold northern winters. The results of this rural home-scale development will help determine the viability for the U.S. home market.
Estimated Costs: 600 dollars for digestor construction materials. 1000 dollars if free local labor unavailable and a Solar CITIES member must be flown in.

Phase V: Learning from Scandanavian Households

1) To prepare for our Artic Circle Home Biogas Initiative we visit households in Scandanavia that Katey has identified using Biogas and examine the systems and their efficacy. Costs: 5000 dollars for 4 airfares and lodging.

Phase VI: Field Testing in the Arctic Circle

1) Alaska: Extending the experience from Katey's farm we take the concept up to her research site in Alaska and introduce the concept to the Inuit villages. There we build 3 systems -- 1 1000 liter system, one 2000 liter system and 1 3000 liter system to seed the idea in local communities and to see if different volumes affect performance (just as large fish like sharks, though technically poikilotherms, exhibit homeothermic characteristics because their size keeps their internal temperature warmer than their surroundings, it may be assumed that larger biogas tanks maintain a higher temperature in their centers that could affect the bacterial production. This would be tested in this phase of the experiment. Estimated Costs: 1000 dollars for the materials to construct the digestors; 1000 dollars for testing equipment to monitor and log internal temperatures, 4000 dollars for airfares.

2) Siberia: With experience from the Alaska initiative we move on to Katey's field site in Siberia to introduce the system's there. With what we learn from the Alaska experiment we concentrate on building the optimal sized biogas systems and do so for three families so that we can begin creating a culture of biogas use. Cost: 1000 dollars for materials, 4000 dollars for airfares.

Phase VII: Comparing notes with ARTI India

With systems in place and in use by households in Essen, Cairo, Gombe, Minnesota, Alaska and Siberia we should be able to gather useful data on the utility of household digestors using a combination of mesophiles and psychrophiles. The final phase of the experiment would be to share microbes and ideas with Dr. Karve and his team in India.

1) We would bring Dr. Anand Karve and his daughter Dr. Pria Karve to one of the Arctic Circle locations and to Cairo to share their expertise. (Cost of flights and lodging and per diem estimated at 5000 dollars)

2) We would bring Solar CITIES coordinator Hanna Fathy, the Culhanes and Walters to Pune, India to share results and establish an on-going research collaboration. (Estimated cost of flights and lodging estimated at 4000 dollars).

This itinerary puts the low side of the budget at about 40,000 dollars for materials and airfare, without including lodging (except in the case of Phase V and Phase VII it is assumed that we can find free lodging with colleagues), meals and incidentals and equipment (excluding Phase VI).
10,000 additional dollars are estimated to be needed for laboratory equipment so that all of the systems can be rigorously tested and performance data for the bacteria under different design regimes can be gathered.

Why work with couples and families?

The household is the primary unit of reproduction in our economy and families are fundamental. But until now households have not been seen as primary units of energy production. Nor have they been conceived of as the most effective solution to the climate change problem. We know that households around the world are considered to be part of the problem -- families are conceived of as "consumers" and the rate of forms of consumption we engage in to satisfy our family needs and desires are said to be the major factors damaging our life supporting ecosystem.

Our proposal is to make energy production and waste management household level solutions. We seek to turn consumers into "prosumers" by making biogas digestors a family affair. We seek to make the use of methanogenic bacteria a part of daily domestic life. This is not an outlandish idea -- when famed Physicist Freeman Dyson spoke at the TED conference, the first thing he talked about was the future of biotechnology, saying

...we should follow the model that has been so successful with the electronic industry: that what really turns computers into a great success in the worldas a whole is toys. As soon as computers became toys, when kids could come home and play with them, then the industry really took off. And that has to happen with Biotech.
There's a huge community of people in the world who are practical biologists, who are dog breeders, pigeon breeders, orchid breeders, rose breeders -- people who handle biology with their hands, and who are dedicated to producing beautiful things, beautiful creatures: plants, animals, pets. These people will be empowered with biotech, and that will be an enormous positive step to acceptance of biotechnology. That will blow away a lot of the opposition. When people have this technology in their hands, you have a do it yourself biotech kit, grow your own --grow your dog, grow your own cat... Just buy the software, you design it. I won't say anymore, you can take it on from there. It's going to happen, and I think it has to happen before the technology becomes natural becomes part of the human condition,something that everybody's familiar with and everybody accepts."

In this "coming to a home near you" future, the idea of people having "useful pet bacteria" shouldn't seem odd. We've been carrying them around in our body since birth, and having them in our homes as climate change solutions, energy providers and waste managers could seem completely normal to the next generation.

To start that process going, Sybille and T.H. Culhane in their home in Germany and Katey Walter and Peter Anthony in their home in Minnesota, along with Hanna and Sabah Fathy in their home in Cairo will be the methanogenic families taking the first steps toward the biotechnology future that Dyson envisions. We hope to share our experiences with other families around the world and usher in a domestic revolution, now playing in a kitchen near you!

To learn more about Solar CITIES solar and biogas work in Egypt, watch this ABC News Spot on "Green Tech in Garbage City", by Ben Barnier, here:

To learn more about Katie Walter's work on arctic biogas from permafrost, watch this newsspot here:


Anonymous said...

Hi T.H.-

I thought there was a link to a schematic of how to build a biogas digestor, but now I don't see it. The schematic I saw was written in German, not English. Maybe I was dreaming...;)

p.s. This is the first time I've ever "blogged."

T.H. Culhane said...

Hi Katey,
Welcome to the blogosphere! Now we just have to get you on the Nat Geo Emerging Explorers facebook group! :)
The diagram in German you saw was a how-to for building our solar hot water system design, created in the digital realm by our German intern Connie Koeck who just graduated from Freiburg U. (solar capital of Europe) when she was in Cairo working with Hanna learning how to build them. For a design of the ARTI India biogas digestor, which we have implemented, go to Cheers, T

T.H. Culhane said...

The design for the type of digestor we build is from ARTI, and you can see one here:
I bought their how-to video and learned from that but it is surprisingly simple -- the video just confirmed how simple it was (so simple that I wonder why everybody doesn't do it).
Basically any two tanks will do -- the smaller inverted and placed inside the larger. Germany is a terrible place to find materials so my digestor isn't very good -- I had to use a 500 liter rain water collection tank for the bacterial slurry and a 300 liter rain water tank for the gas holder; because it is taller than the 500 liter tank that led to 100 liters worth of dead space in the collection tank. It thus took longer to fill with gas and when it did, there was no way to remove that top 100 liters of gas. I have since disassembled the system, and foam-glued styrofoam in the 100 liter space so that now when using the gas the collection tank's gas area is emptied -- but it means I only get 200 liters of gas when full. However, if I had started with a 200 liter tank it also would have given me dead space at the top. The trick is to try to find two tanks that fit pretty well inside each other when the top tank is upside down.

T.H. Culhane said...

Here in Germany the rain water tanks are conical cylinder and that makes them really awful to use because the mouth of the top cone won't go very far down the bottom, larger cone. In Cairo we use perfectly cylindrical water tanks, like they do in India. The 1000 liter tank is on the bottom and the 750 liter tank on top. We'd get even better performance if we could find a 900 liter tank, but they don't exist in Cairo. I would have built a similar system in Germany but it is almost impossible to come by 1000 liter cylinder tanks. All they sell in normal markets is cubical tanks.

T.H. Culhane said...

It is possible to design a system that does not have one tank in another -- I have seen it done. In that case you can use any type of tank as the reactor and use a pipe to take the gas to another container that fills with gas. The trick is then to get the gas out. What I've seen done in these household systems is they place a third tank, filled with water, above the gas collection tank, with a connection pipe to the bottom of the gas collection tank. The gas enters the collection tank from about 2/3rd up. The collection tank must be completely sealed. Then as the collection tank fills with gas it forces the water out and up into the water tank above. As you use the gas, the water pressure from the tank above displaces the gas and forces it into your kitchen. I don't use this system because it means buying 3 tanks, more pipes and plumbing supplies (which is some of the most expensive stuff) and building a stand for the water tank. Also it is very very hard for us to find tanks that seal well. Remember, we are doing things in ghettoes with the poorest of the poor, so we go for the cheapest practical solution, using found materials.

You asked, Katey, about building systems in basements, under stairs, in the home where it can stay warm. We started doing that in Cairo but the family had concern about smell. The smell isn't bad (it smells like a horse stall in a farm) but nobody wants that it their house. I would prefer to build in basements because methane is lighter than air and water can fall by gravity from the insinkerator to the basement or ground floor -- much more practical. The solution is either a three tank sealed system such as I described above or simply sealing the two-tank telescoping system that we build with plastic bags that can expand and contract as the gas collector tank rises and falls. Another idea I have is to house the rising and falling collection tank in another upside down larger tank (i.e. you would have a 1000 liter tank on the bottom, an inverted 750 liter tank on top doing the telescoping, and cover that with another inverted 1000 liter tank which you seal with tape. We just don't do that again because of money. But all these ideas would work.

Ideally we would do what India is doing and get microfinancing for small entrepreneurs and craftspeople to build systems designed to work perfectly. In India many small scale business make fiberglass biogas digestors for homes. The telescoping is perfectly aligned in a housing so no odor can go anywhere (but let me say the odor is NOT a problem really -- we have a completely open system and even on the hottest days we have no flies, no smell (unless you put your nose next to it) -- and when I removed all the straw from the initial manure inoculation when I was redoing the tanks the farm smell went away completely.

But there is a lot to be done.

In India they recommend black 1000 liter and 750 liter water tanks because the sun heats them up and assists in keeping the temps up where the bacteria like them, and holds the heat at night til the sun comes up again. White tanks would not do that. If the ambient temp falls to 15, as it does in Cairo even in the summer, you spend many hours still getting the tanks up to a productive temp in the day. So black tanks in a sunny area are best. Your idea of keeping them inside is great; don't know if they would help keep the house warm because of the exothermia, but the thermal mass would CERTAINLY help.

So much to do and think about and innovate.
It is an exciting journey, all the more so with the extremophiles on our side!!

T.H. Culhane said...

What I'm doing to increase surface area for the bacteria to live on, after reading Dr. Karve's recent discussion group posts, is hanging mosquito netting (weighted with a metal bar on the bottom and with a styrofoarm float on the top) inside the tank. Supposedly bacteria don't like to work while they are freefloating, so Karve now suggests that giving them a substrate to grow on is best - the bottom and sides of the tank provide too little surface area.

That also may address your question about the stereo breeding. With mosquito netting suspended in the tanks from top to bottom the temperature gradients should determine who ends up colonizing which strata of the netting. As for feeding, I would imagine that the ground up food will go into suspension and foat around the whole tank. German pros use mixers but we can't use them in ours because it would mix oxygen into the water (the pros have airtight systems, ours are open to the air on top, like a swamp). We could make pipes that feed into the bottom , the center and the top of the tank but it might be overkill! Probably best to first see how identical bottom fed tanks with different mixes of bacteria compare.

One thing, by the way, I forget to put in the budget was the materials cost for building 4 new systems to do the testing -- it would be about a thousand bucks for four basic systems (about 250 each here in Germany when all is said and done given the exchange rate).

If we want to use monitoring equipment that would be extra -- maybe we can get loaner equipment (temp probes, data loggers, microscopes, assays -- that's your department -- I haven't worked in a lab since college!)

Let the dialog continue!
(I'll post a youtube video soon that shows our system here).