Some composters promote the importance of
special inocula (bacterial activators), supposedly
containing several pure strains of laboratory
organisms or other biological factors essential
to decompose organic matter and fix nitrogen.
They call them "enzymes," "hormones,"
"preserved living organisms," "activated
factors," "biocatalyst," etc.
In fact, several commercial composting processes
are built around the use of some special
inoculum, often known only to its discoverer
and proponent, who claim it to be fundamental
to the successful operation of the process.
The need for inocula has always been debatable,
and most composting studies have strongly
indicated that they are unnecessary.
Bacteria are always present in every bit
of organic matter, whether manure, vegetable
waste, leaves, and can be eliminated only
by drastic sterilization methods. So it makes
sense that inocula is not necessary for the
composting process. In any case, the number
of bacteria is rarely a limiting factor in
composting because, provided the environmental
factors are appropriate, the indigenous bacteria,
which are much better adapted when forms
attenuated under laboratory conditions, multiply
rapidly. Thus the rate of composting is governed
simply by the environmental conditions.
The vast number of enzymes involved in decomposition,
as well as the difficulty and expense involved
in isolating and synthesizing them would
make composting with enzymes highly impractical
even if satisfactory preparations were available.
The addition of enzymes to raw compostable
materials is unnecessary because bacteria
synthesize efficiently and rapidly all the
enzymes required. The term "hormones"
is popularly used to designate the growth
factors and vitamins needed by bacteria or
other organisms. Organic matter usually contains
all the growth factors needed for normal
growth. Also, growth factors and vitamins
can be produced by microorganisms and will
undoubtedly be produced in sufficient quantities
in a mixed microbial population to meet normal
The terms "biocatalyst" and "activated
factors" are applied to various biological
materials that are supposed to activate and
accelerate decomposition and stabilization
of organic material. Experimental investigations
with sludge digestion and activated-sludge
treatment of sewage indicated that biocatalyst
did not affect either of these processes.
In some cases the "activator" usually
supplied some material that was lacking in
the compost. For example, straw or paper,
which does not contain the necessary biological
nutrients, is not decomposed readily alone,
but if nitrogen and phosphorus are added,
the straw and paper will serve as the source
of carbon for decomposition.
Using horse manure, compost material, normal
soils, and special commercially prepared
bacterial cultures in the composting of mixed
garbage and refuse was investigated. Similar
materials were composted with and without
these different inocula, and although rich
in bacteria, none of the inocula accelerated
the composting process or improved the final
product. There was no significant difference
in the temperature curves or in the chemical
analyses of the material at different intervals
during the composting period. Inocula failed
to alter the composting cycle because the
indigenous microbial population was adequate.
There have been some interesting recent research
studies suggesting that special preparations
made from specific plant and other substances
used in producing compost on Biodynamic farms
can make a difference in the composting process.
In these studies, Biodynamic treated composts
maintained an average 3.4 degree C higher
temperature throughout the 8 week active
composting period, and reached maturity faster
than the control compost.
On the whole, though, when the environment
is appropriate, varied indigenous (originating
in a particular region) biological population
will multiply rapidly and composting happens.
Microbial inoculation would be useful only
if the biological population in any emerging
environment were unable to develop sufficiently
rapidly, or take full advantage of the capacity
of the environment to support the increase
in numbers. In such a case, a time lag would
occur which could be overcome by supplementing
the initial indigenous population to the
refuse. However, no such time lag has been
observed in these experiments or in composting
the usual materials that contain a large
indigenous bacterial population.
Some groups of organisms in the mixed microbial
population apparently remain inactive until
the environment is satisfactory for their
growth, emerging to perform a role in the
succession of steps in the stabilization
process. Since the process is dynamic and
any individual group of organisms can survive
a wide environmental range, one population
may begin to emerge when another is still
flourishing and yet another is disappearing.
Hence, when any group of bacteria is capable
of multiplying at a rate equal to that of
its developing environment, any addition
of similar organisms as an inoculum would
The best inoculum a home composter could
use would be a shovelful of their own already
finished compost, which would contain the
microorganisms present for their specific
Successful compost operations that donít
use special inocula in the Netherlands, New
Zealand, South Africa, India, China, the
USA, and a great many other places, provide
convincing evidence that inocula and other
additions are not essential in composting.