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!"

Monday, November 9, 2009

There are more than 22 million urban household biogas digesters worldwide. 8 of them are in Egypt.

(Photos by T.H. Culhane, Hanna Fathy, Sybille Culhane and Mike Rimoin
Special thanks to Thomas and Nicole Szartowicz for helping to fund the Solar CITIES biogas initiative.)

Photo: Rural systems traditionally use animal manure as the feedstock for biogas digesters, leading people in cities to think they can not take advantage of this simple, clean and effective renewable energy solution.

Photo: As it turns out, the city is the best place for biogas digesters due to an abundance of energy rich kitchen wastes which Dr. Anand Karve of ARTI India estimates produces 400 to 800 times the amount of biogas as animal wastes.

There are more than 20 million small-scale urban biogas digesters in cities in China, and more than 2 million in cities in India. And now, thanks to our Solar CITIES associates and supporters we now have 8 in Egypt, 5 of them in some of the poorest sections of inner city Cairo.

O.K., comparatively speaking 8 is nothing.

But when one is measuring environmental progress at the household level it is hard to beat China and India -- they've had government policies aimed at supporting "appropriate technology" for decades and their cultures contain an entrepreneurial spirit when it comes to enviro-tech that is hard to beat because the household demand in the face of poverty and environmental degradation is huge. A more fair comparison would be with the number of known urban household biodigesters in Germany: 1. It's on our porch. And this is in a country that is one of the kings of biogas production (we should know -- our neighbor in the next town, Imbrahm, has a 1 million Euro facility that processes all the restaurant waste from the surrounding cities to produce millions of Kw of electricity and hot water every year).
Small scale urban bio-digesters are uncommon in the "developed world" if they can be found at all (try to find one in America!). And in developing countries biogas facilities have been largely a rural phenomenon, relying on animal wastes. So 8 small-scale CITY digesters in Egypt appearing within the last 8 months isn't such a bad figure when you consider that Egypt still faces the greatest barrier to the deployment and acceptance of renewable energy systems:

Grossly distorted energy prices due to terribly targeted subsidies.

There, I said it. Energy is too cheap in Egypt and throughout the Middle East/North Africa region. It doesn't matter how much sunshine, wind, biomass or garbage there is in a country if it costs multiples more to turn it into useful energy than it does to simply plug into the grid, the pipe or the bottle.

So the 8 small-scale biodigesters we've built in Egypt, particularly the 5 in the urban core of Cairo, represent an indomitable vision on the part of the early adopters who have decided to integrate these unusual climate change and poverty alleviation solutions on their roofs and into their lifestyles, and we celebrate them!

You can celebrate them too -- by visiting the visionaries struggling to prepare greater Cairo for a greater future. You can see them on a "Solar CITIES Green Technology tour", get to know the families and their stories and even pitch in to Cairo's climate solutions initiative by helping build more renewable energy systems, donating time, expertise, money or materials. Each biogas system costs about 150 dollars for materials. With your support the 8 existing systems can turn into 80, and then 800 ( which we could easily achieve within a little more than two years if we built one per day, which is all it takes) and then 8000 and then 800,000. When we reach a million biogas roofs (and a million solar roofs),we will be well on our way to slowing and then stopping climate change. And because biogas systems eliminate organic waste (turning it into useful clean cooking gas and liquid fertilizer) we will have eliminated the filthy organic garbage problem plaguing Cairo (particularly now that the pigs have been slaughtered due to unfounded Swine Flu fears).

Can you tell me how to get... how to get to Biogas Street?

Photo: Culhane checks with the children of building 72 in Darb Al Ahmar, where Solar CITIES built one of its first hand-made solar hot water systems, to see what they think about the new biogas initiative.

Here's where the 5 inner city systems are located:

Photo 1: The location of the biogas systems shown in Google Earth (download .kmz file here)

Photo 2: The same part of Cairo with street names from Google Maps.

1. Musa's ARTI India style Biogas System
For GPS freaks:
Latitude 30° 1'52.69"N
Longitude 31°16'20.55"E
Altitude: about 12 meters. You'll have to climb some stairs.
For people who still use taxis:
Just under the bridge on El Muqattam Road in Zurayib (aka Shari'a El Furn) on the right before you get to the Zabaleen Recycling School (made famous by Musa and Adham and others in the award winning film "Garbage Dreams").

(Photos: Musa with his rooftop system, T.H. and Watson fellow Kelley Maby helping to build the system).

2. Garbage Association NGO's ARTI India style Biogas System
For GPS freaks:
Latitude: 30° 1'55.70"N
Longitude: 31°16'24.38"E
Altitude: less than 1 meter. It's basically on the ground, really easy to reach. You can also see the first Solar CITIES solar hot water system on the roof of the school opposite.
For people who still use taxis:
Up El Muqattam Road from Musa's also on the right in the garage opposite the famous Zabaleen Recycling School, at the foot of the stairs of the building owned by the Garbage Association NGO, one of the oldest NGO's in the area. See Ishaq, the director, for details.

3. Roh El Shabab (Spirit of Youth) NGO's ARTI India style Biogas System
For GPS freaks:
Latitude: 30° 2'4.44"N
Longitude: 31°16'32.18"E
Altitutude: about 9 meters, up two flights of stairs, on the roof. It is next to a single panel Solar CITIES hot water system that is the first to use pressed recycled plastic bags for the collector box.
For people who still use taxis:
If you can get the driver to continue down El Muqattam road (no easy task, because of prejudice and the fact that the roads are muddy and impassable in the winter) tell him to drop you off on the corner of the road leading up to the St. Samaan Monastery. Both systems are visible from that road, so if you can't find the building (which is tucked away on the next side street on the right), climb up the road to the monastery 100 meters and look down on your right. You will see them.

Photo: Biologist and AUC graduate Ahmed Droubi gets his first taste of loading a biogas digester with bacteria, using cow dung on the first day. After this no further animal manure is needed.

Photo: Culhane puts a 1/2" valve on the gas collector, which we call "the plastic cow's anus", to seal it so that it can start fermenting.

Photo: Culhane, working into the night and filthy as usual, points out the finished systems at Roh El Shabab -- a solar hot water system that uses pressed recycled plastic bags for its collector box and a recycled plastic shampoo barrel as its hot water tank (right) and biogas digester run on organic garbage (left).

4. Hanna Fathy's Solar CITIES home office and Biogas System in Manshiyet Nasser's Zabaleen community
Hanna is a co-founder of Solar CITIES Egypt and works as a renewable energy expert at the Sekem Farm.
For GPS freaks:
Latitude: 30° 2'4.48"N
Longitude: 31°16'22.72"E
Altitude: about 18 meters. You have to climb a flight of stairs from the main street (Shari'a Warshaw) to Hanna's street and then climb 5 flights of stairs in his house to get to the roof. You will also see his three panel home-made Solar HW system. Since this is the home office of Solar CITIES in Cairo you will also be able to enjoy a cup of biogas tea. Hanna speaks fluent English and Arabic and gives Solar CITIES tours as a way of earning extra income to reinvest in his renewable energy experiments.
For people who still use taxis: Forget it. A taxi won't take you to Hanna's house. It is accessible by foot. Get the taxi to drop you off at Kubry Manshiyet Nasser (on Google Maps it is called Kubry AlBageah) and cross El Seka Al Hadied (the railroad track). Climb up Shari'a Al Warsha (known on Google Maps as El Mahgar) past the welder's workshops (where we weld our solar hot water heaters). Look for an imposing garbage strewn staircase leading up between buildings and climb it, then turn left, pass the donkeys on your left and bear right with the road. About 4 iron doors down is Hanna's place. If you get lost go back to Shari'a Al Warsha (El Mahgar) and go down to the welding shop next to the plumbing supply shop. Ask Isa (Arabic for "Jesus") the copper welder who does all Solar CITIES hot water systems how to locate Hanna Fathy. He will help you. There should be a Solar CITIES sign on the door.

Photo: Innoventor Hanna Fathy illuminates his biogas system for nighttime tourists visiting from Canada using a large LED lamp powered by a 9 volt battery, all scavenged from the garbage.

Photo: Innoventors Ayman Fathy and T.H. Culhane run a converted 4 stroke 6.5 HP Engine Electric generator on the biogas produced from yesterday's kitchen garbage.

In this video clip Solar CITIES Egypt director Hanna Fathy, MBA Student and Solar CITIES intern Mike Rimoin and  Solar CITIES co-founder T.H. Culhane run a 6.5 HP 3 Kw electric generator for five minutes on biogas. The engine could have run much longer  (we think up to half an hour) on a full tank but we didn't have that amount of gas to work with.  Ultimately, though, the water vapor in the gas made it very hard to start the engine and we ended up breaking the reciprocal starter spring. (To do:  find a way to dry the gas before sending it to the genset. Best would be also to have an automatic rather than pull start.)

Photo: Foreign visitors on the Solar CITIES tour marvel at how much gas a small family can produce each day from just the food waste they would otherwise throw out each day. This tank is filled with 750 liters of biogas, which produces about 2 hours of cooking on a small stove (every 10 cm represents approximately 75 liters), offsetting between 25% and 50% of the household's gas use just from using the garbage.

Photo: Hanna and Sabah and Christiano already have a Solar Hot Water System so they can keep their biogas system operating at capacity in the winter.

5. Hussain Sulaiman El Farag's Solar CITIES home office and Biogas System in Darb Al Ahmar
Hussain is a co-founder of Solar CITIES Egypt and is a craftsman producing small scale renewable energy systems.
For GPS freaks:
Latitude: 30° 2'27.19"N
Longitude: 31°15'36.57"E
Altitude: about 12 meters. You have to climb a couple of flights of stairs. You will also be rewarded by the sight of Cairo's first space saving solar HW system that hangs off the roof rather than taking space on the roof. Hussain and his brother Hamdi and family have a small metal workshop on the ground floor where they have begun to manufacture hand-made Solar Hot Water systems for sale to villas outside of Cairo. Very entrepreneurial, they also sell the liquid fertilizer from the biogas system to rooftop gardeners and florists for 1 LE per jerry can.
For those who insist on taxis: Take a taxi to Bab Zuela (driver enters at Bab Al Khalq next to the jail off Port Said street on Ahmed Maher street which turns into Darb Al Ahmar street) then ask the driver to continue on Darb Al Ahmar street bearing right as it turns into Darb Al Gadeed at the old mosque. Just before Darb Al Gadeed becomes Al Tabana street turn left and zig zag into Zara El Nawa El Kabeer street. The house has a metal gate and is the second house on your left. Across from it is a garage space where Hussain parks his car. There should be a Solar CITIES sign on the door.

Photo: Ever the entrepreneur, Hussain fills 10 liter jerry cans with the effluent liquid fertilizer his system produces each day and sells them to gardeners for 1 LE (20 cents) each.

Photo: Hussain puts flower planters on top of the digester as weights to increase the pressure pushing the gas down to his stove in his apartment below. Culhane discusses the need to build a cage support to hold the gas collector stable.

Photo: Culhane explains the hybrid solar and biogas systems to a group of visitors from the Aga Khan Trust for Culture.

Photo: One of Hussain's innovations was to mount his solar panels on the roof wall so that he has more space for visitors on the roof.

Photo: Hussain cleverly puts coils of iron wire into the biogas stove to increase its heat output and retention.

Photo: Biogas gas tea being prepared for Solar CITIES tour guests at Hussain's.
012 422 8748

Systems 6, 7 and 8: Sekem Environmental Science Center and Vocational Training School, Bilbaes (See Previous Post)

Latitude: 30°22'51.90"N
Longitude: 31°39'53.81"E

Hanny Fathy, Solar CITIES "Green Collar Jobs" Coordinator and Trainer, Coptic Christian Community, Cairo Egypt.


Mahmoud Dardir, Solar CITIES Associate, Abu Nimrus Environmental Science Center, Cairo Egypt

Moustafa Hussain, Solar CITIES Associate, Aga Khan Trust for Culture, Muslim Community, Darb El Ahmar, Cairo Egypt

Mustafa Hussein vocational trainer mobil 2010-720-1983
web site
Hussein Soliman Farag, Solar CITIES Associate, Solar HW and Biogas System Manufacturer Darb El Ahmar, Cairo Egypt

012 422 8748

Sunday, November 8, 2009

New designs for cold-season biogas digesters

Outside of Cairo, Egypt, at the Sekem Farm and Vocational Training Center in Bilbaes, Solar CITIES was invited this past month (October 2009) to build and test our new biogas digester designs in anticipation of our upcoming Blackstone Ranch/National Geographic Emerging Explorer's Innovation Grant, to be conducted in partnership with Dr. Katey Walter in Alaska, Germany, Egypt, Israel, Tanzania, Botswana, and Rwanda (among other places!).

During this preparatory pre-grant phase we built 4 different digester designs in order to experiment with different locally available materials.

Digester 1: (A success)

We started with a traditional ARTI India biogas digester as a control, but made some modifications to bring the cost down and improve winter performance. The typical ARTI household kitchen waste digester uses two cylindrical black plastic water tanks, a 1000 liter tank to hold the bacterial-food-slurry (LE 330 = 60 dollars) in Sabtiya Market in Cairo) and a 750 liter tank (LE 270 = 50 dollars) to hold the gas as it is created. This is a "telescoping" digester, so named because the smaller top tank, inverted and placed into the larger tank, rises and falls ("telescopes") as gas is produced and used.

Preparing the tanks is a fairly simple procedure. The top of the 1000 liter tank is simply cut off, making an open barrel. One can prepare the 750 liter tank one of two ways. The traditional ARTI way is to remove the screw lid and cut holes in the top of the tank, leaving the supports intact. This is done so that the gas collector has some extra weight in a center-down direction, making it unnecessary to use bricks or other weights when using the gas for cooking. We've also experimented with simply cutting the top off, exactly as we do with the larger tank, and it seems to work fine and is a lot quicker and simpler. This was our first modification.

The second modification we made was the reduction of the inlet feedpipe size from 4 inches to 2 inches. Since 4" and 3" PVC fittings are quite expensive, and most urban dwellers have access to a food blender, we felt that the larger sizes were unnecessary. In Germany, thinking like a sacred cow, we decided to try to make the "throat" size the same as that of a small ungulate and found 2" to work quite well if the food was properly ground up with water. And whereas the cost of a 4" tank connector is LE 85 (about 17 dollars) and a 3" connector LE 35 (about 7 dollars) because demand is relatively low relative to supply, a 2" connector can be found for as little as LE 6.50 ($1.30). So the cost savings are considerable. Food merely has to be fluid enough with small enough particle sizes that it won't clog up the "throat". We also used 2" connectors for the drain on the bottom (2" valves are much less expensive than 3 or 4" valves!) and a 1" plastic Zahran connector for the fertilizer-overflow outlet (since this is digested solids in a fairly homogeneous liquid matrix). For the gas outlet we use a 1/2" plastic Zahran connector. These simple modificatons reduced the cost of construction by nearly 300 LE (half the average monthly salary in our communities) -- from about LE 1000 to LE 700, putting the digester in the range of many more families.

One note: One has to be VERY careful with the cheap blenders on the Egyptian market -- do not overload with food and avoid fibrous material -- we burned ours out within two days of use and lost our LE 125 investment. Better, perhaps to buy a more expensive blender (next category starts at LE 250) but then the loss would be higher too if it burns out. The best thing is to get Egypt to start importing and then manufacturing heavy duty kitchen waste disposal units like the Insinkerator.

The third modification we made to the traditional ARTI design was to increase the surface area available to the bacteria for the reaction. We always put broken bricks -- the kinds with holes in them (much more surface area) on the bottom of the tank, but this time we asked the students to make strips of waste cloth and sew styrofoam floats to the top and then tie small rocks to the bottom and insert 10 of these into the tank. These act as hanging vertical strips that bacteria can colonize.

The final modification we made was to wrap the digester tank with cheap black polyethylene irrigation pipe to act as a heat exchanger, connected to the hot water tank from our solar hot water system. The hot water flows down the coils under gravity from the elevated Hot Water tank and is pulled by thermosiphon into the bottom of the solar collector. The digester can then be covered with insulation.

Photo left: Irrigation tube surrounds the digester to be heated by solar hot water for elevated winter performance. Photo right: CREATING YOUR OWN SACRED COW: According to ARTI India's Dr. Anand Karve, when constructing a biogas digester, it helps to "think like a Sacred Cow" -- cows don't eat manure, and the bacteria in their stomachs don't eat manure either -- they make manure. When creating a biogas digester all you are really doing is building an artificial cow as a home for the bacteria. The bottom barrel is the cow's stomach, the top inverted barrel is the cow's intestines. A funnel is the cow's mouth into which you put "chewed up food" (food waste in a blender) and water, and the 2 " pvc tube is her throat. The liquid fertilizer outlet is her urethra; when you give her water she expunges the equivalent amount of fertile tea. The gas outlet on top of the intestines is the cow's anus. When the intestines fill with gas you open the valve and she farts clean climate friendly biogas!

Digester 1 is the simplest and least expensive or complicated biogas digester you can build. Besides the addition of the heating coils and a covering of insulation, winter performance can be improved by building a cage to hold the gas collection tank and covering the whole thing with a sheet of black plastic and then a sheet of clear plastic. Nonetheless these digester designs are open to the environment and experience heat loss and, while suitable for subtropical zones such as Egypt, would not be suitable for north temperate zones in Europe, the U.S., Canada or Alaska.

Digester 2: (A failure)

Digester 2 was an attempt to use the same materials as digester 1 but create a sealed digester with a water jacket. The 1000 liter tank, instead of being the cow's stomach, filled with slurry, was simply turned into a heatable water bath. The 750 liter tank was placed right side up this time and configured as the cow's stomach. The gas collection was to be achieved in a separate vessel, a common square 1000 liter plastic water tank, which was to be pressurized by a similar tank above it. The liquid in the "water jacket" was connected to the solar heater, creating a "bath" for the inner tank. Since the liquid is not in contact with the slurry in the smaller tank it could conceivably be mixed with anti-freeze (ethylene glycol) for cold climate application, or the fluid could be a thin vegetable oil based substance.

The concept was rather good but unfortunately we were unable to seal the screw-on lid of the 750 liter tank so that it would remain water or gas tight. We tried using large rubber gaskets, grease and even an enormous amount of silicone. Eventually all sprung leaks. This is due to the poor thread design of these water tanks. They are not meant to be completely water tight and the lids do not screw on tightly.

This was a great frustration and disappointment to us, but inspired another idea:

Digester 3: An Imminent Success

(Photos not yet available)

Instead of using the cylindrical tanks to produce the gas and the square tank as a gas collector, we've decided to repurpose the materials in the other direction -- the square tank is now the sealed digester. We cut and turn the 750 liter tank upside down, placing it into the 1000 liter tank, exactly like the ARTI digester design, only this time the 1000 liter cylindrical tank contains NO slurry, only water (with anti-freeze). The gas from the square tank is piped into the upper tank, which is the typical gas storage container that rises and falls in typical telescoping fashion. The big difference is that only gas and anti-freeze containing water are found in this open telescoping part of the system so it doesn't matter how cold they get. The bacteria stay nice and warm in the well insulated square production tank which is heated by adding solar heated water along with the food slurry.

Digester 3 would be useful in cold climate countries because it is simple to build (almost identical to the ARTI design in simplicity of gas storage and retrieval and because the gas production vessel is sealed it could be kept indoors (in the basement, under a stairwell or in a shed) while the gas collection vessel could be located outside since it would not be disturbed by cold weather. Retrieving the gas could be done using bricks or some other weight source in the typical way (Hanna and Hussain use planters to beautify the systems).

Digester 4: The Tower of Power Water Displacement System -- A Qualified Success

Digester 4's design, which is more complicated, comes from the unpleasant fact that the typical cylindrical water tanks, ubiquitous in developing countries, are very difficult to find in developed lands, and are very very expensive when they can be found. We have built telescoping digesters in Germany using 500 liter and 300 liter cylindrical rain water barrels, but finding larger sizes is very difficult. It thus became necessary to create a system that uses the easy to find and relatively cheap square cage-mesh 1000 liter plastic water tanks which come on a pallete and can be found almost everywhere. In Germany we can get them for as little as 60 Euro.

In Cairo these sorts of tanks are also extant everywhere, costing about the same price (300 LE), so we decided to purchase a black one (photo below, right) and make it the actual digestor, and pipe the gas to a separate gas collection tank made of the same material.

There are two problems with a rigid tank as gas collector. The first is the question "what will the gas be displacing?". In the telescoping system the gas collector is immersed in a water slurry and so is filled with that liquid. The gas lifts the collection vessel out of the water, and as the gas is used it descends back into the water. The water thus helps push the gas out of the tank. With a separate rigid tank you have to decide what should be in the tank, and how you will get it out. If you start with air, since methane is lighter than air, you could theoretically push the air out of the bottom. But the gas and the air will tend to mix, and this would creates either an explosive mixture when lots of gas is present (biogas is generally safe because it is already a mix of 60 % methane and 40% carbon dioxide; it becomes flammable when it combines with air) or a mix of gases too dilute to to much work (when little gas is present). The second is the question "what will replace the gas in the tank as you use the gas?" Air creates the same problems already stated.

Water is the logical choice for a medium to be displaced by the gas. Unfortunately for the gas collection phase water is heavy and gas is light. This means that if the water tank is above the gas production vessel , the water will tend to push the gas back into the production tank. Fortunately for the gas use phase water is heavy and gas is light. This means that a water tank above the gas collection vessel will push the gas out of the tank for pressurized use.

The devil is in the details, designing a system with the tanks and their inputs and outputs at the right relative heights. With no previous systems to go by, we had to design our water displacement systems from scratch. And because it took 3 weeks from the loading of the bacterial starter material (cow manure in this case) until first flammable methane production (which is when you start feeding the system exclusively kitchen waste) we had to build a system that would allow us to test various hypotheses about heights and placements that would be ready when the gas first came.

What we did first was to build a three story tall gas collection/water-displacement-and-replacement system. The bottom two tanks would serve as gas collection vessels. Both were completely filled with water. The gas would be piped to either one of the two tanks -- the white tank on the bottom in the picture, or the white tank in the middle of the picture, and would enter from the top portion of the front of the tank. Our experience in Germany on our porch with the ARTI style open digester, with the telescoping collector kept still by a pile of bricks, was that since methane is lighter than air, it prefers to rise. Rather than displace water from a tank at the same height as the digester, it simply forced water up and out of the open digester itself. Fearing a similar result we put a valve on the outflow pipe of the sealed digester and made the food intake pipe wide (back to 4" PVC!) and tall. And we mounted one of the collection tanks ABOVE the gas production vessel. This way we had our bases covered. The bottoms of either of the tanks could be variably connected to a one inch polypropylene pipe coming from the bottom of the top tank, which we left empty. This one inch pipe had a valve on it at the bottom, before it entered the gas collector.

Photos: The three story "power of tower" was used for several weeks of testing. It was determined that a three story system was un-necessary and ineffective and that a two story system would work better.

In front of the 1 inch pipe, coming from a T, we placed a swinging door check valve and a half-inch rubber hose going up to the top of the top tank. We filled this hose with a column of water all the way to the top. The theory was that as gas pressure built up in the collection tank in would force the water down inside the tank. This would then push water through the check valve and cause the column of water to spill over into the top tank. As the gas filled the collection tank the displaced water, in turn, would fill the top tank. When the gas collection tank was full with gas the top tank would be filled with the water displaced. To use the gas we would simply open the valve on the 1 inch pipe connecting them and the water pouring into the bottom of the lower tank would force the gas up and out and into the kitchen. The cycle would repeat itself as we produced more gas.

The devil, as we've noted, is in the details. When the black square collection vessel started producing gas we found that it didn't have the pressure necessary to force water out of the middle tank and up into the top tank. Instead the water, even though coming from the top of the gas collection tank, forced its way back into the gas production vessel. To solve this problem we installed a check valve at the outlet of the gas production vessel but found that most of the time the water pressure was greater than the gas pressure and it kept most of the gas stuck in the gas production vessel (though some did make it up to occupy the very top of gas collection vessel, which we found out when we opened it and did a flame test -- it created a small but surprising explosion, which I call "doing a Katey Walter".)

Photo: Solar CITIES intern and MBA student Mike Rimoin experiments with the placement of a check valve.

We then moved the check valve to the top of the gas collection vessel and found this did improve the amount of gas going into the tank but it still wasn't fast enough for practical use. By contrast, when we put the hose into the top of the bottom collection tank, the gas bubbled in fairly vigorously. And because the inlet to the collection vessel was near the same height as the outlet from the gas production vessel, no water would back up into the gas production tank. It appeared that by keeping the slurry overflow valve shut and loading the feed inlet pipe with water, a positive pressure was created that pushed the gas into collection tank. It also appeared that some of that pressure was able to push displaced water up and into the water collection/pressure tank. However as we left Egypt we didn't get full results on how effective the recycling system works.

Photo shows the construction and placement of the water displacement system described above. The student is shown filling the water tube before placing it into the top tank.

Nonetheless, it appears that this system will work and could have broad application in temperate and cold climates. As shown in the picture below, the final configuration is to have the gas production tank (the ground mounted black square tank to the left, which is filled with slurry and gets the food waste) connected to the top of the sealed gas collection tank (also ground mounted and thus at the same height). This bottom of this collection vessel is connected to an identical tank mounted above it in two ways: 1) a one inch (green polypropylene) pipe with a valve connect it to the bottom of the top tank. 2) a half inch hose with a check valve connected to a T and filled with water connects it to the top of the top tank. To the left of the system is our polythylene heat absorber and plastic tank solar hot water system to provide the hot water needed to keep the reaction going in winter. The black production vessel still needs to be insulated, and the system should be fairly complete. The gas collection vessel does not need to be insulated and can be filled with water containing anti-freeze for cold-climate performance.

Photo: After much testing, we finally hit upon a recycling water displacement design that seems to work. One of its advantages is that the water displacement/gas collection tanks can be filled with a fixed quantity anti-freeze and the sealed digester can be insulated and kept warm by adding solar heated water when it is fed. The system requires three 1000 liter (1 ton) tanks which cost about 60 Euro each (about 90 dollars), so the base cost with plumbing is about 350 to 400 dollars. The solar heater adds another 300 to 400 dollars to the price. It is hoped that the use of psychrophilic bacteria will obviate the need for a solar heater.