Biology of composting is one of the subtopic of composting. In this slide cover chemical and physical decomposers that were needed during composting.

1. Submitted by:
Anu Shree Varshney

2.  Composting is the biological decomposition or breakdown of
organic material by bacteria and other organisms.
 Bacteria are the primary decomposing organism, but there are
many others, including fungi, actinomycetes, worms and beetles.
These organisms bring about decomposition by feeding on organic
material. The result is compost or humus, a dark, nutrient-rich soil
conditioner.
 There can be physical decompostion by the physical decomposers
or there can be chemical decomposition by chemical decomposers.

3. CHEMICAL DECOMPOSERS
(Microscopic organisms such as bacteria, fungi, and actinomycetes
decompose organic material through a process of chemical decomposition)

4. 1. B ACTERIA:
 Bacteria are responsible for most of the decomposition
and heat generation in compost.
 There are many different kinds of bacteria at work in the
compost pile. Each type needs specific conditions and the
right kind of organic material.
(i) Psychrophilic bacteria :
 Psychrophiles are a type of extremophile.
 Bacteria that decompose organic material at temperatures
below freezing.
 They work best at around 55°, they continue to work
down to 0°F.
 As they work, they give off small amounts of heat.
 If conditions are good like plenty of oxygen, moisture, and
nitrogen this heat will be enough to set the stage for the
next group of bacteria, the “mesophylic,” or middle range
temperature bacteria.
Psychrophilic bacteria

5. (ii) Mesophilic bacteria :
 Their working temperature range is generally between
70°Fto 100°F.
 Mesophilic bacteria include hydrogen-oxidizing, sulfur-
oxidizing, nitrifying, and nitrogen-fixing bacteria.
 Mesophilic microorganisms break down sugars,
fats, starches and proteins releasing heat.
 Resistant to long carbon chain containing
compound.
 When the pile temperature rises above 100º F, the
mesophilic bacteria begin to die off or move to the outer
part of the heap. They are replaced by heat-loving
thermophilic bacteria.
iii) Thermophilic bacteria:
 Thermophilic bacteria thrive at temperatures
ranging from 113°F to 160°F.
 Thermophilic bacteria continue the decomposition
process, raising the pile temperature 130°F to
160°F.
 As the thermophilic bacteria decline and the
temperature of the pile gradually cools off, the
mesophilic bacteria again become dominant.
Mesophilic bacteria
Thermophilic bacteria

6. 2. Actinomycetes:
 Organisms that resemble fungi but actually are
filamentous bacteria.
 After bacteria, actinomycetes are the second
most abundant micro-organism in your compost
pile.
 Their enzymes enable them to chemically break
down tough debris such as woody stems, bark,
or newspaper.
 They give compost its pleasant earthy smell.
 They are especially important in the formation
of humus - organic matter that has reached the
final state of decomposition.
 As well, actinomycetes liberate carbon and
nitrogen, making these important nutrients
available to plants.
Actinomycetes in composting

7. 3.Fungi:
 Fungi are smaller in number than bacteria
or actinomycetes, but larger in body mass.
 Like actinomycetes, fungi are present
during the final stages of composting,
 Fungal species are numerous during both
mesophilic and thermophilic phases of
composting.
 They prefer moderate temperatures 70-
75°F , although a few forms can live as
high as 120°F. During higher temperature
they live on outer layer of compost
 They can attack organic residues that are
too dry, acidic, or low in nitrogen for
bacterial decomposition.
 Fungi are also the only organisms that can
break down lignin, the gluey substance
found in woody materials.
 They work at a pH of 5.5-7.0, slightly more
acid than the bacteria.
Actively growing Fungal
Mycelium in Compost

8. PHYSICAL DECOMPOSERS
(Physical Decomposers are macro level organism.They are more active in the
later, mature stages of the composting process, when temperatures are
dropping but decomposition is not yet complete. Macro-decomposers
ingest food physically, by grinding, chewing, sucking, digesting, and
churning.It include centipedes, worms, beetles, and springtails etc ).

9. 1.Worms:
 If bacteria are the champion microscopic decomposers,
then the heavyweight champion is doubtlessly the
earthworm.
 As soil or organic matter is passed through an earthworm’s
digestive system, it is broken up and neutralized by
secretions of calcium carbonate from calciferous glands
near the worm’s gizzard.
 Once in the gizzard, material is finely ground prior to
digestion. Digestive intestinal juices rich in hormones,
enzymes, and other fermenting substances continue the
breakdown process.
 The matter passes out of the worm’s body in the form of
casts, which are the richest and finest quality of all humus
material.
2. Centipedes
 They are third-level consumers, feeding on soil
invertebrates of their size or larger.
 This means they are unwelcome in a worm bin as they
may attack and kill the worms.
Earth Worms in Composting

10. 3. Ants:
 Ants prey are the first level consumers, and may
benefit the composting process by bringing fungi
and other organisms into their nests.
 Ants feed on a variety of material, including aphid
honeydew, fungi, seeds, sweets, scraps, other
insects, and sometimes other ants.
 Ants can make compost richer in phosphorus and
potassium by moving minerals around as they work.
4. Millipedes:
 Millipedes have wormlike segmented bodies, with
each segment having two pairs of walking legs
(except the front few segments).
 Millipedes feed on moist decaying plant matter,
helping break down the contents of your compost
pile. Millipedes in composting

11. 5.Fflies:
 Flies are two-wing insects that feed on almost any kind of organic material.
 Although flies are not often a problem associated with compost piles, you can
control their numbers by keeping a layer of dry leaves or grass clippings on top of
the pile.
 Also, bury food scraps at least eight to twelve inches deep into the pile.
6.Snails and slugs :
 Snails have a spiral shell with a distinct head and retractable foot.
 Slugs do not have a shell and are somewhat bullet shaped with antennae on their
front section.
 They feed primarily on living plant material, but they will also attack plant debris.
 Look for them in finished compost before using it, as they could do damage to your
garden if they move in.