Compost and Composting: 

Compost: Compost is the final product of the composting process. It is a stabilized, humus-rich, granular material with an earthy, odorless scent. The composting process involves the microbial decomposition of organic matter, which passes through various stages before it becomes a stable product that can be applied to soil. When compost is mature, it can be stored without producing foul odors or attracting insects.

• Characteristics of Mature Compost:
  • Stable and odorless
  • Granular and humus-rich
  • Free from further decomposition
  • Can be directly applied to the soil
  • Contains beneficial nutrients that support plant growth

Immature Compost: Immature compost, when applied directly to soil, can lead to temporary nitrogen deficiency in the soil. This phenomenon, called nitrogen immobilization, occurs because microorganisms in the immature compost consume available nitrogen during decomposition. While this effect is temporary, it can affect plant growth in the early stages of soil amendment.

Composting: Composting is a natural, biological process that involves the decomposition of organic matter by microorganisms under controlled aerobic conditions (requiring oxygen). The result is the transformation of organic material into a relatively stable humus-like substance, known as compost. Various microorganisms like bacteria, fungi, and invertebrates play a role in breaking down the organic matter.

Process of Composting: The efficiency of composting depends on several factors, including:

• Oxygen: Needed for aerobic decomposition
• Temperature: Affects the rate of microbial activity
• Moisture: Essential for microbial survival and activity
• Material disturbance: Aerates the pile and accelerates decomposition
• Organic matter content: Influences the composition of the final product
• Microbial populations: Their size and activity determine the rate of decomposition

Types of Microorganisms Involved in Composting:

• Psychrophiles: Microorganisms that thrive in cold temperatures
• Mesophiles: Thrive in moderate temperatures
• Thermophiles: Heat-loving microorganisms that work in high-temperature environments

Composting generally begins in the mesophilic temperature range (moderate temperatures) and moves to the thermophilic range (high temperatures) as decomposition intensifies. As decomposition progresses, various organisms, including insects and earthworms, assist in the process.

What Happens During Composting: Composting begins immediately when raw materials are mixed, and oxygen and easily degradable components are consumed by microorganisms. The temperature rises due to the microbial activity, typically reaching 120-140°F (49-60°C) in the initial stages. The active composting phase lasts for several weeks, after which the temperature begins to drop as the process slows down. During this period, compost continues to stabilize and mature.

Loss of Nitrogen: During composting, nitrogen is lost as gaseous ammonia in a process called volatilization, which may affect the nutrient balance in the compost.

Stages of Composting:

The composting process can be broken down into three main stages:

1. Mesophilic Stage:

• • This is the initial phase of composting, where the temperature remains below 45°C.
  • Microorganisms multiply and break down easily available carbohydrates in the raw materials.
  • The pH of the composting material starts to decrease as acids are produced, and the pile becomes more active.

2. Thermophilic Stage:

• • This stage follows the mesophilic phase, and the temperature rises to 50-65°C in the center of the pile.
  • Thermophilic bacteria (heat-loving microbes) degrade the organic matter vigorously.
  • Key processes during this stage include:
    • Reduction of particle size: Organic material becomes more finely broken down.
    • Pathogen destruction: Higher temperatures (above 55°C) kill pathogens, fly larvae, and weed seeds.
    • Degradation of complex materials: Organic material is broken down into simpler substances.

3. Curing Stage:

• • This is the final stage, where stability is achieved in the compost.
  • Growth of actinomycetes and fungi is enhanced, which aids in the digestion of hemicelluloses (complex carbohydrates).
  • The curing stage is essential for developing the disease-suppressive properties of the compost, making it safer for soil application and reducing the risk of transmitting plant diseases.

Methods of Composting

1. Indore Method; This method was developed by Howard and Wad in 1931 at Indore, Madhya Pradesh. It is one of the most popular methods of composting in India.

• Process:
  • Waste materials such as plant residues, animal waste, street refuse, and other organic matter are collected.
  • These materials are chopped into small pieces for quicker decomposition.
  • The material is then laid in layers of 10-15 cm thickness in pits or heaps. The heap should be about 1 meter wide, 1 meter deep, and of any convenient length.
  • Cow dung is mixed with soil to moisten the material and maintain moisture levels of around 50%. Water is sprinkled to achieve the required moisture content.
  • The compost pile is covered with a thin layer of soil (2-3 cm) to keep moisture and protect it from harsh environmental conditions.
  • The composting material undergoes aerobic decomposition, where oxygen is used by microorganisms to break down organic material.
  • After the compost pile has been set up, it is turned periodically (3-4 times) to ensure aeration and proper decomposition. This turning helps speed up the composting process by increasing oxygen supply to microorganisms.

• Advantages:
  • Produces nutrient-rich compost that improves soil fertility.
  • It is a relatively simple method and can be used for small to medium-scale composting.

• Limitations:
  • The process requires substantial labor due to frequent turning.
  • The composting site should be well-maintained to prevent rainwater stagnation, which can interfere with the process.
  • The method can be impractical for large-scale composting due to its high labor and time demands.
  • There can be significant nutrient loss, especially in the initial stages when nitrogen and organic matter degrade.

2. Bangalore Method: Introduced by Acharya in 1939, this method is also called “Hot Fermentation” and was used initially to compost town refuse and night soil.

• Process:
  • This method involves using trenches, typically located on the outskirts of cities, to dispose of waste materials, including night soil (human waste) and town refuse (organic waste).
  • A layer of town refuse (approximately 15 cm thick) is placed in the trench.
  • Night soil is then added in a 5 cm thick layer on top of the refuse, and this alternating layering continues until the trench is filled.
  • The final layer placed on top is town refuse.
  • The entire compost heap is left undisturbed for 3 to 4 months to decompose. No turning or watering is required.
  • Decomposition occurs largely under anaerobic (low oxygen) conditions, which is a slower process compared to aerobic decomposition. However, anaerobic decomposition results in less nitrogen loss.
  • High temperatures develop in the lower layers due to bacterial activity, speeding up the breakdown of organic materials.

• Advantages:
  • The method works well for areas with limited water and labor resources, as there is no need for turning or frequent watering.
  • The compost produced is rich in nutrients and ready in 3-4 months.

• Limitations:
  • Handling night soil can be unhygienic and may lead to the spread of diseases if not handled carefully.
  • If not managed well, the method could cause health hazards, particularly if flies and pests breed in the compost.
  • Decomposition is slower compared to aerobic methods.

3. Coimbatore Method

• Process:
  • In this anaerobic method, crop residues and farm wastes are filled into pits that are 2 meters wide, 4 meters long, and 1 meter deep.
  • Each layer of waste is spread with a slurry of cow dung (5 cm thick) to encourage microbial activity.
  • Rock phosphate (1 kg per layer) is applied to reduce nitrogen loss, which is a common issue in composting.
  • Layers of crop residue, cow dung slurry, and rock phosphate are added alternately until the pile reaches a height of 0.5 meters.
  • The pile is then covered with soil to prevent rainwater from entering and to maintain temperature levels within the pile.
  • After 35-40 days, the material is turned to make it aerobic, allowing the composting process to proceed more efficiently.
  • After about 4-5 months, the compost will be ready for use.

• Advantages:
  • This method helps preserve nitrogen and increases the nutrient content of the compost.
  • Suitable for areas with limited water resources as it requires minimal turning and watering.

• Limitations:
  • Requires a well-organized pit system, and monitoring moisture levels is crucial for success.
  • Can take several months to produce compost.

4. Mechanical Compost Plants

• Process:
  • This method is more suitable for larger cities or towns where large-scale composting of city refuse is needed.
  • The refuse (organic waste) is first passed through a primary grinder to break it down into smaller pieces. Non-compostable materials such as plastic, rubber, stones, and glass are removed.
  • The refuse is then kept in a pre-fermentation yard for 7-10 days to undergo aerobic decomposition, which reduces weight, volume, and moisture content and kills harmful pathogens.
  • The partially fermented waste is then passed through a secondary grinder and a vibrating sieve to remove any remaining non-decomposable material.
  • Finally, the processed material undergoes further fermentation for 3-4 weeks, after which it is ready to be used as compost.

• Advantages:
  • It is quicker than the Bangalore trench method and is more hygienic because it eliminates issues such as foul odors and fly breeding.
  • The process is automated, reducing the labor required.

• Limitations:
  • The initial investment cost for setting up mechanical compost plants can be high.
  • Requires a consistent supply of organic waste, and the process can be energy-intensive.

NADEP Method

• Process:
  • In this method, a pit of size 15 feet by 6 feet by 6 feet (L x W x H) is created using bricks.
  • The pit’s walls have small holes for aeration to improve the process of decomposition.
  • The pit is filled with layers of rural waste (8 inches), farmyard manure (4 inches), and soil (4 inches). The layers are built alternately.
  • Moisture levels of about 60-70% are maintained to facilitate decomposition.
  • The NADEP method is known for its simplicity and cost-effectiveness.

• Advantages:
  • Cost-effective and easy to manage, making it suitable for small farms and rural areas.
  • Can be handled with minimal resources, making it accessible in areas with limited infrastructure.

• Limitations:
  • The pit size needs to be adequate, and maintaining moisture levels is essential for successful composting.
  • Some labor is required to manage the materials and ensure proper layering.

Other Methods of Composting

• Barkley Method: Developed in 1953 at the University of California. Known as the “Two Weeks Method,” it is designed for fast composting in a very short period, but it’s not widely practiced in India.
• Windrow Method: Developed in Connecticut, USA, this method uses long rows (windrows) of composting material, which are regularly turned. It is suitable for large-scale municipal composting operations.
• Beccari Process: Commonly used in Italy, France, and the USA, this method uses alternating layers of organic materials, which are composted anaerobically to produce nutrient-rich compost.
• Indore Process of USA: This is a refined version of the original Indore method, designed by Wiley in 1976. It aims to improve the efficiency of the traditional Indore process by refining techniques and ensuring better compost quality.