Composting Organisms
Mary Stromberger
Assistant Professor, Soil Microbiology
Dept. Soil and Crop Sciences, CSU
Composting of organic wastes
I have always looked upon decay as being just as wonderful and rich
an expression of life as growth.
-- Henry Miller, The Wisdom of the Heart
The what and why of composting
Compost biota and their activities
Vermicomposting
The What and Why of Composting
Composting = biological decomposition
and stabilization of organic substrates
Under biologically-produced thermophilic
temperatures
Produces a final product that is stable, free of
pathogens and plant seeds and can be
beneficially applied to land
Reduce waste volume
Promote plant productivity and soil quality
Eliminate pathogens, deleterious
organisms, and weed seeds
Sanitize organic wastes
Humus-like
Organic matter
Organic residues
Air
Decomposition
processes
Heat
Gases
(e.g.,CO2, NH3)
Water
Microbial
biomass
Compost Biota
Fauna
Protozoa
Decomposer microorganisms
Bacteria
Actinomycetes
Fungi
Fauna
Important in the
beginning of compost
process
Grind coarse materials
into smaller bits
(communition)
Increases surface
area:volume ratio
Improves access of
microbes to organic
substrates
Protozoa
Active in the early
phases of composting
Process smaller bits
of organic matter
Prey upon microbial
populations
Regulates numbers
Recycles nutrients
Bacteria
Single-celled
prokaryotes
Smallest living
organisms
Most numerous group
in compost
Responsible for most
of the decay and heat
generation in compost
Nutritionally diverse
Actinomycetes
Filamentous bacteria
Produce geosmin
Degraders of
cellulose,
hemicellulose and
lignin
Important during the
thermophilic and
cooling stages
Fungi
Multicellular
eukaryotes
Include mushrooms,
molds and yeasts
Usually filamentous
Decomposers of
complex plant
polymers
cellulose,
hemicellulose and
lignin
Overview of the compost process
Mesophilic
Phase
Thermophilic
Phase
20 - 40C
A few days
Temp.
40 - 65C, as high as 80C
A few days to several months
Time
Curing
Phase
Cooling and maturation
Several months
Stage 1: Mesophilic Stage
Bacteria and Fungi are key players
Fauna and protozoa also important
Decomposition of readily available
substrates
Sugars, proteins and starch
Excess energy is released as heat,
causing pile temperature to increase
Stage 2: Thermophilic Stage
Heat-loving bacteria, actinomycetes and
fungi are key players
Heat intolerant organisms go dormant or
are destroyed
Human and plant pathogens
High temperatures accelerate breakdown
of proteins, fats, and complex polymers
Microorganisms Associated with Compost Piles
Mesophilic Stage
Thermophilic Stage
Bacteria
108 cells g-1
Pseudomonas, Bacillus,
Flavobacterium, Clostridium
109 cells g-1
Bacillus, Thermus
Actinomycetes
104 cells g-1
Streptomyces
108 cells g-1
Streptomyces,
Micropolyspora,
Thermoactinomyces,
Thermomonospora
Fungi
106 fungi g-1
Alternaria, Cladosporium,
Aspergillus, Mucor,
Humicola, Penicillium
107 fungi g-1
Aspergillus, Mucor,
Chaetomium, Humicola,
Absidia, Sporotrichum,
Torula (yeast),
Thermoascus
Zonation of temperatures
per
a
tem
era
Inner
Thermophilic zone
es
tur
ole
r
mp
r te
Co
ole
Edges of pile support
diverse populations of
thermophilic bacteria,
actinomycetes and fungi
Co
Center of pile is
dominated by the most
heat-tolerant bacteria
(eg., Bacillus)
tur
es
Internal temperatures can
be as high as 70 or 80 C
Cooler temperatures
Importance of turning the pile
per
a
-Aerates the pile
era
tem
mp
r te
Inner
Thermophilic zone
es
tur
ole
r
-Cools the pile
ole
Co
Co
tur
es
-Redistributes
microorganisms
Cooler temperatures
-Speeds up
decomposition
-Allows microbial
succession to reoccur
Stage 3: Curing/Cooling Stage
Mesophilic bacteria, actinomycetes and fungi
are key players
Further chemical and physical changes in the
compost
Decomposition of recalcitrant polymers by
actinomycetes and fungi
Degradation of fermentation products, methane, and
other noxious gases which accumulated earlier in
anaerobic microsites
Reduction of odors and toxic intermediates
Vermicomposting
Composting with
worms and
microorganisms
Eisenia foetida
Aka redworms,
red wriggler
worms, tiger
worms
Thrive on rotting
vegetation,
compost and
manure
Physical effects on compost
Burrowing action of
worms help
aerate the compost
mix substrates
redistribute
microorganisms
Composting time is faster!
Less need to turn the pile!
Biochemical effects on compost
Communition of
organic residues
Enhances microbial
access to substrates
Production of casts
Source of readily
available sugars and
proteins for microbes
Final Words
Composting is a microbial process
Its rate is controlled by factors which affect
microbial activities
Lack of suitable substrates, low moisture
content, non-optimum temperatures, and
poor oxygen diffusion are the most
common rate-limiting factors in
composting
