Composting: stages & factors affecting

1. Composting: stages and factors
Sankrita Gaonkar
Assistant Professor in Botany
sankrita002@gmail.com

2. Contents
• Composting
• Stages of composting
• Factors affecting composting
• References

3. Composting
• Definition - Decomposition of organic matter under aerobic conditions into
humus-like substances and minerals by the action of microorganisms
combined with chemical and physical reactions.
• Organisms in composting require adequate amounts of macro- and micro-
nutrients, oxygen, and water.
• Compost stabilizes nutrient content of manures and other organic materials
and releases nutrients slowly, minimizing nutrient loss and potential
environmental contamination.
• Mature batch of compost will take 6 to 8 months.

4. • Composting is predominantly an aerobic or oxygen-requiring process in which
microorganisms consume oxygen while feeding on the organic matter. In doing so,
they produce carbon dioxide, water, heat, other gaseous by-products, and compost.
• As soon as the appropriate raw materials and water are mixed and brought together in
a pile, composting process starts. In the presence of oxygen, microorganisms consume
and start decomposing the organic matter.
• The major group of microorganisms that participate in composting are bacteria, fungi
and actinomycetes.

5. What Microbes Need?
• Carbon (sugars) fuels their metabolism
• Nitrogen (protein) makes enzymes used in decay process
• Moisture transports and supports life functions
• Oxygen
• Hospitable environment

6. Microorganisms Involved in the Composting Process:
Bacteria - Responsible for most of decomposition and heat generation in
compost – Bacillus, Pseudomonas, and Arthrobacter.
Fungi - Break down tough organic debris (Cellulose, hemicellulose, lignin)
• Can decompose materials too dry, acidic, or low in nitrogen for bacterial
activity – Aspergillus, Penicillium, Fusarium, and Trichoderma
Actinomycetes - Degrade cellulose, lignin, chitin, proteins - Some species
in thermophilic phase, others in curing phase

8. Three temperature stages of composting:
1. Mesophilic (20° – 45 °C)
2. Thermophilic (45° – 60 °C)
3. Mesophilic or curing (<45 °C)
4. Maturation phase (20 – 30 °C)

9. 1. Mesophilic
• Bacteria break down cellulose into glucose (sugars, protein, starch)
• Makes temperatures in pile rise
• Produce endospores as pile heats up
• Endospores – tough coating, resists heat, drying, UV radiation, chemicals,
can survive next, hotter phase then return to active state when cool again
2. Thermophilic
• Thermophilic bacteria, fungi take over
• Heat-intolerant microbes go dormant
• Pathogens destroyed
• Complex carbohydrates fully broken down
• Some proteins are decomposed
• Hemicelluloses (more resistant) decay
Endospore

10. 3. Mesophilic or curing
• Mesophilic microbes return to active state
• Proteins and carbs diminish
• Metabolic activity decreases
• Temperatures in pile drop
• Lignin (most resistant plant component) decayed by actinomycetes, fungi
• Physical decomposers support microbes
• Matter gets exposed to bacteria as arthropods forage
• Allows microbial populations to increase Earthworms, mites, spiders, ants,
snails, sow bugs, slugs, nematodes, springtails, centipedes, etc

11. 4. Maturation Phase
• During maturation phase the temperature of the compost pile drops to
the ambient temperature
• During this phase condensation of carbonaceous compounds and
polymerization occurs, which further helps in formulation of fulvic and
humic acids.

12. Factors affecting composting process
1. Aeration (Oxygen)
2. Carbon source
3. Moisture
4. Temperature
5. Carbon-nitrogen (C:N) ratio
6. pH
7. Particle size
8. Surface area

13. Aeration
• Composting is an aerobic process and adequate ventilation should be maintained to
allow respiration of microorganisms that release carbon dioxide (CO2)
• aeration also helps in reducing compaction or water filling in the compost material.
Moisture
• water present in the raw material is used by the microorganisms for transportation of
nutrient and energy through their cell membranes.
• 55% - ideal moisture
Carbon source
• For energy
• High carbon materials tend to be brown and dry

14. Temperature
• Ambient temperature has a wide range of variation depending on the phase of
the process.
• Composting begins at ambient temperature that can rise up to 65 °C with no
need of human intervention (external heating). While, during maturation
phase the compost pile attains the ambient temperature.
pH
• The composting pH depends on the source materials and varies in each phase
of the process (from 4.5 to 8.5
• The pH is a determinant factor for microorganisms’ survival and the various
group of microorganisms have their optimal pH range for growth and
multiplication. Most bacterial activity occurs at pH 6.0-7.5, while most fungal
activity occurs at pH 5.5 to 8.0. The ideal range is from 5.8 to 7.2.

15. C:N ratio
• The C:N ratio changes according to the parent material used for composting.
• The C:N ratio varies throughout the composting process, with a continuous
reduction from 35:1 to 15:1.
Particle size
• The ideal size of the parent materials for composting is 5 to 20 cm.
• Affects the aeration and moisture retention of the compost pile
Surface area
• More the surface area, faster the decomposition

16. References
• Kawai K and Gamaralalage PJ. 2020. CCET guideline series on
intermediate municipal solid waste treatment technologies: Composting.
United Nations Environment Programme.
• Graves RE. 2000. Environmental Engineering National Engineering
Handbook. Chapter 2-Composting. National Produdction Services, Fort
Worth, Texas.
• Meena AL , Karwal M, Dutta D and Mishra RP. 2021. Composting: Phases
and Factors Responsible for Efficient and Improved Composting.
Agriculture and Food: Newsletter, 3:85-90.