Understanding Solid Waste Composting

February 15, 20220

Composting is one of the essential technologies for Solid Waste Management (SWM). Any organic material that can be biologically decomposed is compostable. Composting processes include

  • In-vessel composting
  • Open windrow composting
  • Covered windrow composting
  • Aerated static pile composting
  • Vermicomposting
  • Biomineralization

Impact on the environment

Improper waste management is detrimental to human health. It causes the outbreak of various diseases and a reduction in life expectancy. It generates greenhouse gases like methane gas and nitrous oxide, which significantly contributes to the depletion of the ozone layer, increasing the impact of climate change. Gases like Hydrogen sulfide are also released into the air. These substances are toxic to human lives. Wastes that find their way into rivers, streams, and oceans can be disruptive, lowering the pH and causing toxicity to the aquatic animals and humans that use the water. Wastes dumped indiscriminately breed disease vectors and are an ugly sight. Crop productivity is reduced from metals like iron and radioactive wastes present in the water and toxic to soil organisms and plants.

Understanding composting

Decomposition of organic materials is aided by microorganisms like bacteria, fungus, actinomycetes, and bigger creatures such as insects and earthworms. Microorganisms break down organic materials and create carbon dioxide, water, heat, and humus, a reasonably stable organic end product when they begin to degrade the organic material.

‘Mesophilics are microorganisms that grow between 20-45°C. They reproduce by breaking down carbon and nitrogen. This metabolic activity raises the temperature to 40-45° C between two to eight days and lowers the pH of the mixture due to the production of organic acids.

In the thermophilic phase, or ‘sanitation’ phase, the temperature rises over 45° C. Mesophilic microorganisms are replaced by the thermophiles (which proliferate at temperatures between 45-70° C). Thermophiles break down more complex carbon sources, like cellulose and lignin. As a result, nitrogen transforms into ammonia, and the pH of the mixture becomes alkaline.

The cooling stage begins once the carbon and nitrogen have been consumed. The temperature is lowered to 40-45° C. Mesophilics appear again and decompose the remaining cellulose and lignin. Also, the pH drops again slightly.

In the maturation stage, the mixture must stay at room temperature. A series of secondary reactions are produced at this time that triggers condensation and polymerization of the humus. The resulting product at the end of this period is called compost.

C:N ratio

A C:N ratio of 30:1 is good for the composting process. When composting materials low in C:N, air cannot permeate, resulting in anaerobic conditions and odor generation and nitrogen loss in the form of ammonia gas. A high C:N ratio inhibits microorganism activity resulting in a sluggish pace of decomposition. Greens, including grass clippings, kitchen vegetable waste, and manure, are compost ingredients with high nitrogen concentrations. Sawdust, dried leaves and hay are examples of high carbon materials. It is preferable to thoroughly mix the components for the composting process. If the pile remains stacked, composting will take longer.


Aeration is required for a quick odor-free breakdown in high temperature aerobic composting. Aeration can also help to reduce the initial moisture level of composting materials. Aerobic organisms that decompose leaves, grass clippings, and other yard waste into compost must breathe air to survive. Introducing oxygen into the central region accelerates material breakdown and maintains a high temperature, resulting in a hot composting process. Hot composting is an effective method for killing weed seeds, plant pests, and pathogens. Turning the heap, laying it on a series of pipes, or adding bulking agents like wood chips and shredded newspaper all assist in aeration. However, care must be taken not to supply too much oxygen since this might dry out the pile and inhibit the composting process.

Moisture content

Moisture is another important component in microorganisms metabolic activity as microbial cells are entirely reliant on water for their metabolic processes. The moisture level of composting materials should be kept between 40 and 60 percent. Moisture in compost originates from either the original water provided or the metabolic water created by the microorganism activity. Excess water inhibits oxygen diffusion, which, in turn, lowers the metabolic activity of the organisms. Organic molecule digestion by bacteria is only conceivable after the organic molecules have been dissolved in water. Moisture levels fall as the composting process progresses.

pH and Oxygen

Oxygen is also critical during the composting process. When organisms oxidize carbon to make energy, the oxygen present is depleted, and gases are produced. Without sufficient oxygen, the composting process becomes anaerobic, and gases (methane, carbon dioxide, and ammonia) are created, resulting in the formation of disagreeable smells. The composting rate is also affected by the pH of the materials being composted. Alkaline pH is optimum for composting – when the pH is acidic, composting is exceedingly sluggish because the bacteria are killed.

Particle size

Optimal composting conditions are often reached when the particle size of the material is between 1 and 2 inches in diameter. This size has a larger surface area, which facilitates microbial activity and the composting process. The rate of aerobic breakdown rises as particle size decreases. On the other hand, extremely tiny particles may obstruct oxygen circulation within the pile, so reducing the composting process. Additionally, tiny particle size enhances moisture retention and reduces airspace, delaying the composting process. Organic compounds with a rough texture, a high lignin content, or a hard texture degrade slowly. For example, hard, textured leaves degrade at a far slower pace than soft, textured ones. Thorny leaves may take longer to decompose due to the physical barrier produced by the thorns. Leaves with a high lignin content may have a leathery or harsh texture.

Odor control

Composting odors are caused by the release of hydrogen sulphide or ammonia during the decomposition process. Most of the time, odor is caused by the metabolic pathway of degrading organisms that dominate the system or due to higher moisture content.

T1B Compost Aid is an all-natural product, 100% safe and easy to use. It contains a culture of cellolocytic and lignolytic microorganisms and offers a faster and more effective composting of organic waste. The product includes strains that do not putrefy throughout the decomposition process. The biochemical pathways chosen by our bacteria would be different compared to generic bacteria. These helpful ensures no or minimum ammonia and hydrogen sulphide are produced during the composting process minimizing odor. It generates high heat during the process, thus helping in controlling pathogens and weeds. It is effective under a wide range of environmental conditions and provides excellent quality of final compost.

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