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 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.



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.

Contact:

cghannaschaap@hotmail.com

+20.(0)12.1827315

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.

hussfarag@yahoo.com

012 182 7315

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.

cghannaschaap@hotmail.com

+20.(0)12.1827315

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

khamasino2006@yahoo.com

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

moustafahussain@yahoo.com

Mustafa Hussein vocational trainer mobil 2010-720-1983
web site http://www.mustafahusein.blogspot.com

Hussein Soliman Farag, Solar CITIES Associate, Solar HW and Biogas System Manufacturer Darb El Ahmar, Cairo Egypt

hussfarag@yahoo.com

012 182 7315

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.

A low-cost solar heater using ubiquitous black polyethylene irrigation pipes? Why didn't I think of that?!

An effective solar hot water system that can be made using some cheap plastic irrigation tube, scissors, hose clamps and a screw driver. Nothing could be simpler.

"Why didn't I think of that?" you might ask yourself.
Actually you probably did!
And no doubt you've had many many different thoughts about how to innovate our way out of this mess of climate change, pollution, poverty, injustice and discomfort. So many great green ideas are floating around these days, and lots of them will probably work and work well.
The real question we often ask ourselves at Solar CITIES when we have such ideas is "why didn't we implement it?"
And when we reach that point, that half-way place between vision and reality, particularly when it comes to simple, obvious ideas, we feel a sudden urge to get empirical, and DO something.

Photo: A traditional ARTI India biogas digester wrapped in polyethylene pipe as a heat exchanger connected to the solar hot water system. Once insulated, this should keep the digester warm in the winter months.

This month, in Cairo, we stuck ourselves with the task of creating a cheap solar hot water system to improve our biogas digester's performance in the winter months (the mesophilic bacteria we use don't like temperatures below 20 C and all but shut down at 15 C).
At home in Germany we built a solar hot water system for our biogas digester out of an old steel radiator (painted black in a wooden box covered with glass) but these radiators, ubiquitous in Europe, don't exist in Egypt. And the normal Solar CITIES solar hot water systems we build in Cairo cost a lot because of the huge expense and difficulty of copper pipes (both the raw material and the welding). The marginal benefits of laying out a few thousand Egyptian pounds to heat the bacteria so they would increase their output seemed to outweigh the costs and impose an acceptance barrier for most Egyptian families who can't even afford solar hot water for their own bathing.

Was there a way to radically reduce the costs without sacrificing performance?

Photo: The basic parts of this inexpensive but effective do-it-yourself solar hot water system: cheap rolls of 1/2 inch black polyethylene irrigation pipe (thin-walled, 80 LE for 400 meters) and plastic T's, plumbing adaptors and hose clamps.

Photo: To cut the plastic pipe, which has a tendency to curl, to uniform length, we use a piece of aluminum window frame.

In California we are very familiar with black plastic heat-exchangers used for solar heating swimming pools; in the summer everything black gets hot, and water flowing through black plastic pipes is no exception. But these solar pool heaters are specialty products, factory molded to provide the maximum surface area, are far too expensive for the average Egyptian, and in any event do not work in the winter when exposure to the cold air and wind quickly removes all the heat. What we needed was something that would heat up quickly during the short winter days when the sun was out and transfer that heat to the water in an insulated tank to then flow into the heat exchanger around the biogas system. And it had to be cheap.

Some great papers by Iranian and Kuwaiti researchers in Tehran suggested that black polypropylene did in fact have good heat transfer properties and would be suitable for solar hot water systems, but we couldn't find a description of how to make it, and we found little published on the use of polyethylene. (See "An experimental evaluation of copper, steel and polypropylene tubes in solar water heaters with thermosyphonic flow" by M. R. Riazi¹ , J. Razavi², A. Sadeghi² and A. Javaheri in Applied Solar Energy Volume 45, Number 1 / March, 2009). In any case, in Cairo we couldn't find suitable thin walled polypropylene. But we could find polyethylene drip irrigation pipe everywhere.

Bolstered by the graphs and data in Riazi et al., our decision was thus to try to simply get out and do something -- to go into the field and build a collector by hand, replacing the copper pipes in our normal Solar CITIES solar hot water system with the cheapest black polyethylene irrigation tubes we could find but otherwise keep the design exactly the same as we have always done things. This way, if the experiment failed, we could always salvage all the other parts (the galvanized box, the aluminum heat absorber, the glass, the polypropylene plumbing and fitting and the recycled plastic water tanks and float valves) and throw in the copper pipes and still have a solar hot water system (albeit a more expensive one).

This is part of the nature of the Solar CITIES ethos: when experimenting, try to make everything modular and re-usable (re-purposable) so that if one idea fails the net loss is low. Since we are very poor relative to Western Standards (yet relatively wealthy by the standards of the Egyptain poor) we are learning to understand how those less wealthy in this world think while having the flexibility to do experimentation.

Photo: Instead of being imprisoned by the old way of thinking, we've now learned that we can radically cut costs by replacing the expense and labor of using welded copper with plastic irrigation hose.

Photo: The Culhane's cousin Heni, visiting from Germany, shows how lightweight the new plastic heat exchanger is.


What we learned this month in Cairo is that a solar collector made from black polyethylene irrigation pipe inside the glass topped box instead of copper works very well indeed, producing hot water over 45 degrees Celsius even on cold (but bright sunny) days.

Photo: Comparison of a copper heat exchanger with a same sized polyethylene heat exchanger. The one on the left costs about 500 LE, the one on the right about 30 LE.

Photo: Two people can assemble the heat exchanger in less than an hour with scissors and screw drivers. No welding required!


Even better, such a system can be made by children, since it involves no welding. Instead the heat exchanger "shabaka" (matrix) can be made with scissors and a screw driver and hose clamps and plastic T's. This way, the students at the Sekem Environmental Science Center (with whom we are partnering) can learn how to build fully functional solar hot water systems that they can take home to their families, and, in the future, if they want to learn welding and go to the extra expense of buying copper, can simply replace the plastic shabaka with a copper one for improved performance and durability. In this way school kids can learn real skills without having to always build "toys" or "little models" that have no immediate practical value.

Photo: To get the galvanized steel for the box on the micro-buses from Cairo to Bilbaes, we had to cut it into four pieces and reassemble in the field with rivets.

Photo: Sekem students assemble a do-it-yourself portable solar hot water system in the field.

Photo: The experiments in Egypt this month were generously sponsored by the Julius-Stursberg-Gymnasium in Germany.

It is true that the plastic heat exchanger is relatively delicate and is prone to springing tiny leaks if not constructed properly (i.e. if the hose clamps aren't tightened properly and one isn't careful about putting stress on it during assembly). But the total cost of the plastic heat exchanger is merely 30 LE for each box, as opposed to 500 to 600 LE for the copper (425 for the copper itself, about 100 or more for the drilling and welding, to say nothing of the difficulty), and broken plastic T's can be fairly easily replaced. In any event, if it does leak a little it has no effect on the collector -- plastic doesn't rust or create a galvanic response that would degrade the aluminum absorber so no permanent damage is done while waiting for a repair. And when using the panel to heat a biogas digester, slight water dripping and lowered performance isn't a disaster.

Photo: Solar CITIES Egypt Director Hanna Fathy and Sekem vocational student Salah put the glass on the box containing the polyethylene heat exchanger.

The neat thing is that we've found this low-cost do-it-yourself solar heater works just fine for domestic water heating too -- a good entry level solar hot water system for those who want to get into the game and understand how to build and use solar energy infrastructure.

Photo: As is typical for developing countries where quality assurance is a problem, the glass, delivered in three pieces, supposedly 60cm by 80 cm, for easy transport, was not properly cut, so Hanna and Salah have to carefully chip it to the right size with pliers before assembling the box.

Photo: Veteren Sekem teacher Yvonne Floride and Renewable Energy project manager Martin Haagen observe Culhane, Fathy and the students constructing the low-cost plastic solar hot water and biogas systems.

Photo: Hanna checks for leaks while a proud Salah poses in front of the completed system.

I know you've probably thought about doing this too -- building stuff out of the cheapest materials around that your intuition tells you will probably work, to help solve global problems on the local level. The question is "what are you going to do about it?" May we suggest you jump into the game, and as the Nike commercial says, "Just do it?" The devil is in the details, but in this case we've found a relatively simple success! Give it a try!

Photo: Solar CITIES Egypt Director Hanna Fathy and Solar CITIES co-founder T.H. Culhane stand in front of their irrigation-pipe solar heater and solar heated cold-season biogas digester system.

Photo: Fathy and Culhane assemble a traditional copper heat-exchanger next to the polyethylene system for comparison and performance testing. The goal is to see if we can abandon using copper altogether and still get good efficiencies during the winter months with a system that uses plastic pipes and plastic storage tanks.

Culhane's "Melodic-Mnemonics": Science Education through Music Video

On October 1st, 2009 in Geneva Switzerland, Melody Dialouge.org will host an

International Forum on Music as a Catalyst for Environmental Awareness

"Under the patronage of UNESCO and the United Nations Environment Programme (UNEP) and with the support of the Swiss National Commission for UNESCO, the Association Melody for Dialogue among Civilizations (www.melodydialogue.org) is organising a two-part programme with the theme "Music for a Green Planet".

One is an International Forum to be held at Geneva’s International Conference Centre (CICG). High-level participants will explore the relationship between music, the environment and sustainable development. It will focus on the potential of music and musical dialogue to heighten awareness of environmental issues – such as water, the oceans, forests, energy and climate change. This Forum will be followed by the second part of the programme, an innovative multi-cultural concert at Geneva’s prestigious Victoria Hall".

As we prepare to participate as speakers at this exciting "Melody Dialouge" Conference we are pausing to review how we got started in this business of using music to teach science:








The video above was the first Melodic-Mnemonic song I wrote during my first year as a science teacher at Crenshaw High School in South Central Los Angeles back in 1989.

The lyrics can be obtained here if you want to sing it with your own students, kids or medical school friends: http://melodic-mnemonics.blogspot.com/2009/09/cytoplasm-blues.html

Why did I pick this topic? Because an understanding of "the lives of a cell" (to quote the title of one of my favorite books by Lewis Thomas which I read in high school -- or rather, in spite of high school!) seemed fundamental to all of our understandings of how our ecosystems and our environment works. As Lewis Thomas wrote,

"I have been trying to think of the earth as a kind of organism, but it is no go. I cannot think of it this way. It is too big, too complex, with too many working parts lacking visible connections. The other night, driving through a hilly, wooded part of southern New England, I wondered about this. If not like an organism, what is it like, what is it most like? Then, satisfactorily for that moment, it came to me: it is most like a single cell."


I didn't write the song to "teach" cell biology to my students, rather I wrote the song because I was in love with the book, in love with the topic, in love with biology, in love with life. I felt there was no better way to celebrate my love of science than to use the artistic side of my brain to express how I was learning to see the world.


I actually started this trend in 1985 when I was at Harvard and was inspired by Stephen J. Gould when he came into class and sang the geologic eras as a close-harmony acapella song accompanied by a tape of his singing group doing the doo-wop. And Tom Lehrer's song about "The Periodic Table" was played for us in Chemistry Class by Nobel Prize winner Dudley R. Herschbach who was also my house master at Harvard's Currier House.


My very first song for science was thus written for my Harvard Senior thesis in Biological Anthropology in 1985, called "A Talking Seal? Get Outta Here". It accompanied a music video that Steve Sessions and I made of Hoover, the Talking Seal -- the only known mammal to spontaneously reproduce human speech.

My second science music video was "The Classification Rap", which was aired on Beverly Hills Community Television from 1990 to 1995 and may have been seen by a few hundred people, but now, thanks to "youtube" has been seen in the past two years by more than 30,000 viewers and is used in schools all over the world. From the emails I get each month on my youtube account I've learned that kids are being inspired by this to make their own songs to help them and their friends learn science. It is certainly fun communicating and interacting with science students around the world this way, decades after I have formally left the class room.


But the Cytoplasm Blues, my very first attempt at this when I moved to "the 'hood" to start tackling the "inner city school problem" evolved during my first month teaching when I brought in a guitar and, in a Burl Ives fashion, tried to explain through a call and response song how to think of "the lives of a cell" and what went on within the cell membrane, using easily understandable metaphors. The call and response theme worked well in place of "rote memorization" -- by getting the students to use a time honored Cab Calloway type technique they seemed to enjoy the repetition that goes with memorization much more.


Of course back in 1989 we didn't have things like "video projectors" and "Power-Point" and other visual multi-media easily available, so I would write all the vocabulary on the blackboard and put up posters and diagrams of cells and organelles around the room. Then I would get out my guitar and get some of my students to literally stand on the tables with me (in a Robin Williams, 'carpe diem' Dead Poets Society kind of way!) , holding diagrams of cells they themselves had made and start the call and response song. Using "Drama in Education", acting out the story of the "lives of a cell", gave the students a kinesthetic, whole-body-whole-mind, multiple intelligence feel for the subject matter.

Culhane and his students at Crenshaw High School, South Central L.A. in 1989 act out the "lives of a cell" in "The Cytoplasm Blues"

The experience led us to become one of the NASA/McGraw Hill/Business Week "Challenger 7" Teaching Fellows. McGraw Hill Published Culhane's lesson plan for teachers around the country to replicate (click on scanned pages to enlarge. You can also download the entire document as a pdf at http://solarcities.eu/Articles/TouchingTheFuture.pdf):

Each Challenger 7 fellow (Barbara Durrett, Tom Greene, Bonnie Price, Thomas H. Culhane, Terry Thode, Helen Martin and Marc Sacerdote, shown above with McGraw Hills Charlotte Frank and Richard Morgan) were invited to visit the halls of congress and received a 3,000 dollar award for educational excellence from first lady Barbara Bush.

At the time we called our Melodic-Mnemonics Science Education through Music and Video Program "Bio-Rhythms" because we were teaching biology through Rhythm And Poetry (RAP) and music. Later we expanded to cover all areas of the environmental curriculum.

The method we use now in workshops around the world is very similar 20 years later except that the technology has caught up with the vision. Students can record music and video on their laptops and download the images -- which we used to painstakingly scan from their textbooks -- from the internet and then share their "self-made educational materials" with the world on youtube.

The simplest way to do a melodic-mnemonic is what we show in the Cytoplasm Blues video:

1) Record the song onto your laptop and put it in the audio track of your video editing program, or as an audio file in Powerpoint.
2) Type the lyrics into PowerPoint (or OpenOffice.org's Impress (freeware!) or any equivalent presentation software.)
3) Browse the web for the appropriate images to illustrate the lyrics and concepts (or, better yet, shoot pictures or video of your own diagrams, drawings, models or live action illustrations!) and put them onto the appropriate slides.
4) Export the slides as a series of .jpg or .png images.
5) Arrange the slides according to the beat in the video program so that they flow with the music.
6) Export your video for youtube.

This is the first step toward creating a melodic-mnemonic music video. Once you have done this what you have, in effect, is a "storyboard" of what you can then turn into a real music video.
The next step is to go out into the field and shoot your band and your singers performing the song, and shoot all your "B-roll" footage of the subjects being discussed in the song and then edit them in to replace the slides and make your own MTV style video!

In this way, the science textbook can truly be "brought to life!"

At the time, back in 1989, when this was much harder to do, and we still had to get training and work in our community access television studios to be able to do this stuff, we teachers realized that the technology was on the thresh-hold of becoming something everybody could use and afford.

I made a speech to the school that our class turned into a really cheesy over-the-top (but still sincere) poor-quality video while learning to edit and composite music.




The script, the philosophy of which we stand by even more vehemently 20 years later, was as follows:


"Once upon a time, school was boring. But that was before "Bio-Rhythms". Bio Science Education Through Music Video. Feel the Beat."

"Now who says school shouldn't be a three-ring circus, huh?

"You see anybody buying tickets to get into biology these days?

"But all that is going to change and let me tell you why:

"Over the past 40 years, ever since the advent of the electric guitar, the technologies of music and television production have changed the way we learn. There was simply no way that high school could compete.

"Now let's face facts folks, you would have rather been home watching television and listening to the radio, right?

"But today, the means of production have fallen into the hands of the masses. And that means that the same technology that the entertainment industry was using to woo kids away from their studies, is now affordable by even the most poorly paid professionals in our country -- I'm referring to the American Teacher.

"Today, with a little bit of creativity and enthusiasm the classroom can be turned into a production workshop, a place where students and teachers from every discipline can put their subject knowledge to use, creating not "busy work", but a product that they can be proud of.

"Now I teach science in the inner city, but our approach can be applied to all areas and all curricula, turning our children from idle consumers into active producers, having fun and learning at the same time, that's what "Bio-Rhythms" is all about.

"All of our children are capable of creative genius. The education problem isn't with them; the challenge is for us to teach them in the ways they learn best...

"Bio-Rhythms: Isn't it time all of our children got turned on to science?"





We would like to think that when we and our colleagues were "touching the future" twenty years ago, we were inspiring a new generation of young people who themselves may now be teachers or parents or both, to use a holistic approach to science education that puts music and video and art firmly into the science curriculum, merging left and right brain together to make science and learning about how to face the challenges of our environment as fun and empowering as it is important.




More examples of our music videos can be found at http://melodic-mnemonics.blogspot.com

Biogas Water Heating Trial 1

The first video clip shows the heating of 2 liters of water with biogas for 18 minutes. We see the full unthrottled six brick flame and the throttled flame.





The second video clip shows the spreadsheet calculations for determining how much of a smaller quantity of hot water must be added to a larger quantity of cold water to get bath temperature water.


Graph shows the temperature curve for heating 2 liters of water with tonights biogas using 6 bricks for pressure, but restricting the pressure using the stove valve . X-axis is time in minutes, Y-axis is temperature in degrees C. We will replicate this with the valve wide open, giving a higher flame but a shorter burn,  to see if this makes much of a difference.



One of the questions I often get is, "cooking with biogas is all fine and good, but what about using it to heat bathing water? Does it produce enough?"

Tonight I started experimenting with this.

We had two sunny days in Germany this weekend with average daytime temperatures between 18 and 20 degrees and tonight were able to use the biogas for 18 minutes.

We decided to put 2 liters of water in a cooking pot (about what you would use to cook spaghetti) and see how hot it would get (water heating is a very energy intensive process). In 18 minutes it reached 84 degrees. It might have gotten hotter if we had remembered to cover the pot earlier -- we only put the cover on after 11 minutes, so we lost a lot of heat to the room!

Originally I wanted to see how long it would take to boil 2 liters of water for a pot of spaghetti using my biogas, but when I ran out of gas after 18 minutes having reached a temperature of 84 degrees -- not hot enough to finish the spaghetti -- rather than throw the water out I changed my plan and decided to see how much bath temperature water (between 32 and 40 degrees) this 2 liters of 84 degree water might give me.

I have created a table in Excel (note: you can use "Calc", OpenOffice.org's Open Source Spreadsheet if you don't want to spend the money on Excel!) called “how to get water to bath temperature” for the families I have been working with in Cairo. It uses the common physics formula for mass and temperature showing that the final or “total” Temperature of a body of water (Tt) is equal to an initial mass of water multiplied by its temperature plus the mass of a second body of water that is added to it multiplied by its temperature, divided by the sum of the two masses.

Tf = ((m1*T1)+(m2*T2))/(m1+m2)
Variables Values Calculations Formulas Description

I had previously calculated what it would take to heat 40 liters of water for a bath (the amount I usually use, which is twice what most under-capitalized Egyptians use in the "poor communities.") The formula showed that if you boiled 10 liters of water and added 30 liters of cold tap water you could take a 40 liter hot bath (at 38.5 C, hotter than your body temperature, so it would feel hot).

m1 30 30.0 (m2*(Tt-T2))/(T1-Tt) mass of water one, the bathtub
m2 10.5 10.5 (m1*(T1-Tt))/(Tt-T2) mass of water two, the water you are going to add
T1 17 17.0 ((Tt*(m1+m2)-m2*T2)/m1) temperature of water one, the bathtub
T2 100 99.9 (Tt*(m1+m2)-m1*T1)/m2 temperature of water two, the water you are boiling
Tt 38.5 38.5 ((m1*T1)+(m2*T2))/(m1+m2) Final total temperature desired


I algebraically manipulated the equation on the spreadsheet so that one could plug in any of the variables to get any of the other unknowns and demonstrated it to the families. We noticed that the average rule of thumb was that you can take a bucket of water at pipe temperature (average 17 degrees celsisus) and add roughly 1/3 of a bucket of boiling water and get it up to the required 38.5 degrees for a bath or clothes washing. This mathematical explanation satisfied the families, who claimed they already knew the principle of this, boiling about a third of the quantity of water on the stove to prepare a bath. This home grown appreciation of an alternative way to get hot washing water is not captured in most attribute tables. As has been reported for India, many residents in Cairo may be exercising a preference for effectively boiling water using biomass or low cost waste materials, defying the modernist assumption of a linear “energy ladder” (see Gupta, forthcoming, Amacher 1993, Barnes 2002, Arnold 2006, Pohekar 2006) Thus, the status quo, if properly explored, may be very revealing!

In our recent experiment shown in the video we heated 2 liters of water with biogas for 18 minutes and got it to 84 degrees.
By the time we went to add it to 5 liters of tap water (at 17 degrees) it had dropped to 82. The theoretical temperature we should have gotten according to the formula was 35.57 degrees:

Spreadsheet formula:
A2 =((B2*C2)+(D2*E2))/(B2+D2)
where A2 is the cell with the final temperature, B2 contains the biogas heated mass, C2 the temperature reached, D2 the larger tap water mass, E2 the temperature of the cold tap water.

T final Mass 1 Temp 1 Mass 2 Temp 2
35.57 2 82 5 17

We recorded a fluctuating 33 to 32 degrees, still very comfortable for a bath, and attribute the difference to losses from pouring and mixing (losses to the air and to the walls of the bucket) and possible inaccuracies of the measuring device. The bottom line is that it was still plenty warm for a bath.

Given that we can get an hour to two hours of biogas from the 1000 liter digestors we build in Cairo, it should be no problem each day to heat enough bathing water for one or two or more people. The average Cairene in my sample used a 20 liter bastila for bathing and heating about 5 liters on the stove to about 90 degrees, mixing it with 15 liters of cold tap water at about 17 degrees, achieving roughly the same temperature as in our experiment. The formula shows it equaling 35.25 degrees C.

T final Mass 1 Temp 1 Mass 2 Temp 2
35.25 5 90 15 17


In 20 minutes of biogas heating we could have gotten the 2 liters up to 90 degrees. This implies that 50 minutes of heating would raise 5 liters to that temperature. On good biogas production days, even with 90 to 100 minutes of gas one should be able to double that amount and provide 2 20 liter baths.

Is it worth it? The India experience is that the biogas is better utilized for cooking, and most families who have biogas digesters still use propane bottles for heating water for bathing. Nonetheless people don't always eat at home, and it is useful to see if it is worth trying to heat bathing water with gas that, after all, came from kitchen scraps. My feeling is that it definitely is.

Further experiments have to be done to determine whether or not it is best to use the biogas to heat the whole 20 liters to bath temperature or heat a smaller quantity to near boiling and add it to 15 liters of cold tap water. There are pros and cons to both, and they are experienced daily by the enterprising Egyptians who heat their bath water on the stove using bottled gas (60 % of Manshiyet Nasser's Zabaleen and 25% of Darb Al Ahmar are in this category).

Placing 20 liters of water on a stove can break the stove and many elderly people and young people can not lift the 20 liters, particularly without spilling. On the other hand, the larger quantity of water never gets hot enough to be dangerous. 5 liters heated to near boiling is lighter in weight, so it can be heated much easier on the stove, but it is very dangerous to carry; spilling causes scalds that puts many people in the hospital every year. Heating 2 small batches of 2.5 liters (a spaghetti pot worth of water) would be safer, but while waiting for the second 2.5 liters to heat one would lose much of the heat in the first batch. If one has a two burner stove one could heat two batches of 2.5 liters simultaneously but many families have only one burner.

What will weigh in here is the efficiency of heating large versus small quantities of water, given that biogas is in limited supply each day. Certainly families using biogas can supplement with bottled gas when needed, but we would like to have the data for the times when fossil derived natural gas is either too expensive or is simply unavailable.

مخمرات البيوجاز

تتكون آساسا من حيز مناسب يسمح بتوفير ظروف الهضم الاهوایي وتحقيق الظروف المناسبة لنشاط الكائنات الدقيقة وبحخم يكفى كمية المخلفات المتوفرة بعد خلطها بامائ بالنسبة المطل،بة مع إمكانية تجميع وتخزين الغاز المنتج لسحبة عند الحاخة للاستجدام مع توفير وسيلة مناسبة لإدخال المادة العصوية بالقدر و الشكل المطلوب وكذا وسيلة لإخراخها بعد التخمير آو الهظم لضمان استمرار العملية بكفاءة والمخموات تتفاوت في آحجامها حسب كمية المخلفات المتاحة او كمية الغاز المطلوبة كما آنها تختلف من ناحية التصميم فمنها البسيط (منخفض الانتاجية) ومنها المصمم بطريقة توفر آفضل ظروف التخمير لزيادة الانتاجية (شكل ١ - آ ب ج) مخمر بيوغاز هند ي الطراز  و مخمر بيوغاز صيني الطراز   شكل رقم ١ - ٣ بعض مخمرات البيوجاز المنزلية البسسيطة< 

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