Renewable energy


Wednesday, February 02, 2005

More news from the Philippine biodigester

I have managed to test a few carbon based feedstocks as we last discussed.
They are:
1. lawn-mower grass cuttings from the greens of a nearby golf course
2. shredded sweet potatoes (yams) - from waste bin in vegetable market
3. shredded potatoes - from waste bin in vegetable market
4. sliced tomatoes - from waste bin in vegetable market
5. pressed coconut meat - from a native cake bakeshop

The sliced tomatoes and pressed coconut meat did not appear to produce biogas.d(When fed to a working biodigester, biogas output continued to decline as if no feedstock was added.)

Worse, the pressed coconut meat floats and may be floating inside the digester impeding digestion.

With the grass cuttings, gas production did not drop. In fact, there was a small noticeable increase for a few days.

The yams and potatoes, however, gave a surge in biogas production for a few days. Yams and potatoes (apparently, vegetables that cause one to fart) are good for biogas production.

In all instances, approximately 5 % feedstock by volume was added once and production was observed for two weeks.

I plan to repeat the tests and validate the results.
I have also been keeping track of the listserv forum. The composting of biomass wastes before using it as feedstock is a good idea specially for wastes that tend to float.

Returning from a vacation, we passed a little remote-community that had signs saying they were using biogas. We stopped, interviewed two users and examined their set-ups. Though they invested heavily when their digesters were built in 2001, they are very happy to have them now that LPG prices have almost tripled.

I was able to track down one of the technicians who happily reported that he has built 41 digesters ranging from 5 to 10 m3 since 2000 -- with funding assistance from UNDP.

It was great to find that community with home-type or family-type biodigesters. The find affirms that biogas WORKS!

My biodigester which only costs about 80 % today for what they paid for in 2001 continues to appear to be a great idea for the Philippines. The DOST tech I mentioned above agrees and plans to try my units in his next projects.

The 10 m3 HDPE units installed in our farm are now full of biogas. We are going to test burning the biogas when I go there tomorrow.

I also have a couple of relatives interested in 10 m3 units for their farms. This is getting interesting.


  • Since you're subscribed to listserv as you mentioned, try looking up all references to A. D. Karve's digester from the STOVES and DIGESTION lists. (There's one good compilation of Karve's correspondence in STOVES.) He's reporting significant starch to methane conversion in his units. His model involves two cylinders, one telescoping into the other. The larger cylinder is the fermenter, the smaller one the gas holder. His first units have a 400 liter capacity. To start, he primes the fermenter initially with 10 kg of cattle dung mixed with water. (This will be the source of methanogenic bacteria.) Then he waits for gas to accumulate in the holder which takes days. Once combustible gas is had, he starts feeding starch- and sugar-rich stock to the fermenter - 1 kg in the morning and 1kg at night. Karve claims 800 liters of gas from 1kg of starch. He has reported success from "flour of cereal grains, flour of a whole lot of seeds collected from various tree species, leftover food, sugarcane juice, macerated whole sugarcane, oilcakes of edible as well non-edible oilseeds, pulp of papaya, bananas, mangoes, rotten onions, macerated tubers of potato, tapioka, sweet potato, taro etc." Elsewhere, he also mentions canna, nutgrass, arums, dioscoreas, spoilt fruit juice, flour swept from the floor of a flour mill. He also suggests sorghum. Quite versatile, this one. He's reporting the most promising results from oilcakes of non-edible oilseeds. Karve explains: "Because of the residual oil and the high protein content of the oilcake, its calorific value is much greater than that of starch from cereal grains, rhizomes or tubers." Very encouraging news.

    A Biomass Watcher

    By Anonymous Anonymous, at 10:19 PM  

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