Israel’s Biogas Production Plant

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Biogas production takes place in these two Insulated digestion chambers.
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[2] Pumps force the farm waste slurry through heat exchangers.
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Cattle at this feedlot supply the raw materials

Early last year, two of MOTHER EARTH NEWS’ editors visited Israel as part of a solar tour sponsored by this magazine and Michigan’s Jordan College. That Mideast nation, even though oil-poor, does receive an abundance of sunshine … which is widely used to supplement more conventional energy sources. But, while the Israeli people are maintaining their position in the vanguard of solar development, they are continuing to look into the potential of other alternative forms of power as well. In fact, the Kefar Gil’adi kibbutz–on Israel’s northern frontier–incorporates what may very well be the largest thermophilic biogas production plant in the world!

Biogas (composed largely of methane, carbon dioxide, and a bit of water vapor) is processed from organic waste. Closely related to natural gas, the “scavenged” fuel can be used to power stoves, heaters, lamps, refrigerators, and internal combustion engines.

Israel’s methane gas project has been an ongoing affair for nearly two years. Initial research was carried out on a 35-cubic-foot digester … then two 350-cubic-foot experimental plants were built. Finally, in August of 1979, a 7,063-cubic-foot biogas “factory” was put into operation. Though it’s not completed yet (the plant is actually a practical “working” research project), the system has been producing gas on a regular basis all through its “debugging” phase.

A Simple Process…

The people responsible for the success of the biogas project don’t look at the plant as merely a source of energy. Instead, they take a wholistic approach. The operation started with a 500-head cattle feedlot–where disposal of waste was a concern–and, in effect, converted that “problem” into usable energy … enough to replace about half a ton of fuel oil a day. That, of course, Is all well and good, but the researchers are also feeding the spent manure (after it’s been “degassed”) to fish being raised in the farm’s breeding ponds … and then using the fish for human consumption!

Actually, the gas generation process isn’t too complicated: Waste from the cattle shed is scraped into a concrete trench with a front-end loader and is taken–via conveyor belt–to a pit where it’s mixed with water and thoroughly ground up by a mechanical macerator until the material is in the form of a homogeneous slurry … which is particularly high in solids by normal biogas production standards.

At this point, the undigested mixture is pumped through a series of heat exchangers–where it’s warmed to 131°F using methane-fed gas jets–and on into two insulated, steel digestion chambers totaling over 7,000 cubic feet in volume. (The use of two tanks rather than one makes the digestion process somewhat more flexible.) Each day, a small percentage of fresh manure material is added to the vessels to replace the slurry that has been digested.

…And Increased Production

Normally, the rule of thumb for biogas plant output is approximately one cubic foot of biogas per cubic foot of digester per day. However, the Israeli system can produce nearly five volumes of gas per volume of generator in the same amount of time … a phenomenon which can be attributed partly to the fact that the kibbutz members utilize a more concentrated slurry solution, but is mainly a result of the thermophilic digestion system used (which operates at temperatures in the 130°F range, as opposed to the more common mesophilic digestion method that requires only about 95°F).

Of course, there’s a price to pay for this greater gas output in that [1] it costs more–and takes more energy–to preheat the slurry, [2] there is additional equipment involved (which, of course, increases the chance of breakdown), and [3] the gas-producing thermophilic bacteria are notably less hardy than their mesophilic counterparts, and thus a fairly constant environment must be maintained in order to insure their survival.

There’s More to Come

At present, the inventive Israelis have nearly completed the “working-in” period and are ready to give some serious consideration to several problems that have been discovered in the process … one of which involves the agitation of digesting slurry (the present design allows for some partially dissolved material to be displaced before it’s completely exhausted). In addition, new ideas–such as the use of solar collectors, rather than gas burners, to preheat the slurry–are currently being investigated.

But even more interesting is the proposed utilization of the spent manure. Although the experimenters are already using the leftovers from the digestion process as fish feed and fertilizer, the Middle Easterners are planning to continue testing the digested material as livestock feed (so far, it constitutes 20% of the kibbutz’s cattle staple). They will also evaluate its use as animal bedding, as a solid fuel, and even–in a compressed form–as a construction material (similar to fiberboard). They intend to further research the chemical composition of the methane product in hopes of extracting sizable quantities of carbon dioxide vapor for use in on-farm greenhouses, as well.

Needless to say, the Israelis’ search for viable alternatives to petroleum is a matter of survival as well as curiosity. But even under such pressing circumstances, they’re doing an excellent piece of work which–in the future–will come to the aid of people everywhere!

EDITOR’S NOTE: For the second year, MOTHER EARTH NEWS and Jordan College are sponsoring a solar tour to Israel (from February 19 to March 3, 1981) that will give participants a chance to see what that energy-conscious nation is doing to promote alternatives to petroleum.

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