Food  Yeast from a Biogas Digester Filled with Farm Waste

           The biogas reactor is an unlikely but good source of nutritious protein.
 
                Yeast is a good food source :

                1) because it has a complete amino acid profile meaning that it
                    has the building blocks of a complete protein.
                2) because it is manageable in that it can be retrieved from the
                         bioreactor solution.

                     3) because it grows rapidly as by a million fold in three days.

                     4) because it grows on precisely those intermediate chemical
                         products made in the biogas reactor by naturally occurring
                         organisms before the gas-generating organisms take over.

                      5) because poultry and fish eat it and thrive on it.

                      6) because the process is simple and depends only upon
                          organisms that occur naturally in decomposing waste in
                          a standard biogas digester.

                  Explanation :   Yeast prefer to live on sugar but will do well on
                                      a variety of other sources of nutrition.

                                    A) Their second preference is amino acids which are
                                        the building blocks of protein.

                                    B)  Some yeast do well on acetic acid (vinegar).

                                    C)  Many yeast  nourish themselves on peptides.

                                    D) Monosaccharides  are forms of sugars  which
                                         are good food for yeast to grow on.

            The Astonishing Thing is That All of
            The  Above Nutrients are Found in a
             Common, Ordinary Biogas Digester
         During  Certain Periods of its Operation.

              ( Monosaccharides, peptides and amino acids are all found in the first
                 period when the waste is first broken down chemically.)

               ( Acetic acid is found in the second period.)

                ( Remember that all of these are good food for yeast and the yeast
                  can multiply by the millions in a few days.  -- So if one begins with
                   a one pound cake of yeast, and if everything goes right, he should
                   have a million pounds of  excellent chicken feed in a few days --
                   provided of course that there was enough saccharides, peptides and
                   amino acids from his digester to feed all of these yeast.)

                 **  The periods referred to above relate to the fact that there are
                       three periods that take place in a biogas digester in the course of
                       conversion of waste to methane. 1) In the first  period waste is
                           converted to  monosaccharides, peptides and amino acids.
                           2) In the second period the products of the first period are con-
                       verted to acetic acid.  In the third  period acetic acid is con-
                       verted to methane gas. All periods depend on anaerobic conditions.
                       That is to say they must be carried out in a sealed container that
                        does not allow the continual admission of air.
                 **  Thus if the process is  stopped after the first or second period,
                       and before gas is vigerously evolved, the products of the biogas
                       digester will provide good nourishment for yeast.

         The Big Question then for the experiment is:
           Small print --->  How long does it take the digester to convert waste into monosaccharides,
                 The catch                peptides and amino acids ?  At this point only an astute biogas digester
                                                          operator knows.

           But there are a few difficulties, namely:

                   1) When yeast is multiplying to make more yeast, it needs air to
                       grow. So it is necessary to let air into the biogas generator after
                       the period in which the monosaccharides, peptides and amino
                       acids are formed. Nothing is free ! It means one must be willing
                       to sacrifice biogas for food.

                    2) But that is not the only problem. All of those natural organisms
                        that produced the yeast food in the first period must be sterilized
                        in order not to kill the yeast when the yeast is added at the end of
                        the first or second period. The problem is how to sterilize all of
                        the messy material in the biogas generator before adding yeast.

                             Possible solutions:
                                   a) Use the solar water tank heater to sterilize by heating
                                       the digester to 180 degrees F.
                                   b) If one has electricity or a car generator, use acid shock
                                       systems described earlier.
                                   c) Drain off small amounts of the liquid at a time and
                                       boil it. Then, when cooled, add the yeast

                                                                      or

                                   d) Bubble air through the digester at the end of the first
                                       period. Since the bacteria at work in the first period
                                       were anerobic and can function only in conditions
                                       without air, the presence of air  would at least greatly
                                       weaken them and thus let the yeast with their own
                                       defenses take over. It has to be worth a try for the
                                       sake of  a great yeast harvest.

               Alternative :      In place of  using biogas  products  at the end of the
                                    first period, use biogas digester products from the sec-
                                    cond period. In the second period acetic acid is formed
                                    and is used to feed yeast in place of monosaccharides,
                                    peptides and amino acids. The procedure is the same in
                                    so far as admitting air to the biogas generator takes
                                    place. But the admission of air and the insertion of yeast
                                    take place at a later time after a longer period of diges-
                                    tion. Acetic acid is also an acceptable nutrient for yeast.

                 Harvesting  Yeast from the Biogas Digester

                 1. Drain the fluid - yeast  mixture from the digester and  filter out
                          the coarse fiber.  Next, filter the yeast and fine fiber from
                          from the water and dry the yeast.  Use the unrefined raw
                          yeast and remaining fiber as feed for poultry and fish.