Composting: stages & factors affecting

Composting: stages & factors affecting

1. Composting: stages and factors Sankrita Gaonkar Assistant Professor in Botany [email protected]

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

7. 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)

8. 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

9. 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

10. 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.

11. 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

12. 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

13. 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.

14. 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

15. 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.