Making Compost at Home, Primer


Home Composting is not a new technology and it has been practiced for many years around the world, as a simple and low cost solution to manage household organic waste at source. In Sri Lanka, different set-ups of household composting units can be found and it has been more popularized in some areas. Compost offers several benefits such as enhanced soil fertility and soil health-thereby increased agricultural productivity, improved soil biodiversity, reduced ecological risks and a better environment.

Home composting is now being encouraged as a means of reducing the organic waste being discarded and sent to the landfills. In Sri Lanka, organic fraction of Municipal Solid Waste (MSW) contributes 70 – 90% of total waste stream in many municipalities. These organic substances are bulky to handle and contributes for numerous liquid and gaseous emissions that deteriorate dumpsite environments. A good home composting programs can significantly reduce the quantity of organic waste adding to the mainstream (>50%) and subsequent emissions upon final disposal. Valuable products (compost) are produced while reducing the costs incurred for collection, transportation and final disposal at dumpsite.

Community participation has been a vital component in most successful integrated solid waste management (ISWM) programs. Home composting encourages the community involvement on waste management activities and it facilitates easy transferring of source separation concepts to the people. Home based composting compared to the compost produced from mixed waste is of high quality as the waste does not get contaminated with hazardous materials. The separated inorganic materials need less effort for cleaning before recycling. Therefore, household composting has been identified as an option to enhance the economic conditions of urban poor people through home-gardening and selling of compost and/or recyclables.

There are various technical options available as household level composting systems that vary from simple pit /heap methods to complex bin or rotating drum designs. Traditional composting methods (pit, heap, Jeewakotu) have been common practices in many rural/sub-urban areas with different kinds of organic matters. Most urban dwellers prefer bin composting system due to its convenience and as it has less impact an aestheticism with their very limited space.

The Composting Process

Composting is a natural biological process that carried out under controlled aerobic (requires oxygen) or anaerobic conditions. Anaerobic composting is not common due to its slow degradation rate and odorous intermediate products. Aerobic composting is widely used and in this process, various microorganisms, including bacteria and fungi, break down organic matter into simpler substances. The effectiveness of the composting process is dependent upon the environmental conditions present within the composting system i.e. oxygen, temperature, moisture, material disturbance, substrate conditions.

The essential elements required by the composting microorganisms are Carbon, Nitrogen
(represent by C: N ratio), Oxygen and Moisture. If any of these elements are lacking, or if they are not provided in the proper proportion, the microorganisms will not flourish and will not provide adequate heat. A composting process that operates at optimum performance will convert organic matter into stable compost that is odor and pathogen free, and a poor breeding substrate for flies.

In addition, it will significantly reduce the volume and weight of organic waste as the composting process converts much of the biodegradable component to gaseous carbon dioxide and water. Composting is relatively simple to manage and can be carried out on a wide range of scales in almost any indoor or outdoor environment and in almost any geographic location. It has the potential to manage most of the organic material in the waste stream including kitchen waste, leaves and yard wastes, farm waste, animal manure, paper products, sewage sludge etc.

So composting has been a vital component in many integrated waste management plans that is developing worldwide.

Optimum conditions for composting

Oxygen / aeration

If there is insufficient oxygen, a different set of anaerobic microorganism dominates the degradation process and produce odorous intermediate products such as methane, organic acids and hydrogen sulphide. A constant supply of oxygen will give the aerobic microorganisms an advantage over the anaerobic micro-organisms. Approximately a 5% minimum concentration of oxygen is required within the pore spaces in the media.

Aeration is the process of providing oxygen into the composting material. This will also provide a platform to remove water vapor, gases and excess heat trapped within the material. Aeration is common practice with high rate large scale composting facilities.

Moisture content

Moisture supports the metabolic processes of the micro-organisms. Water is the medium for chemical reactions. Biological activity ceases below 15% moisture content and in theory activity is optimal when materials are saturated. Generally moisture content of between 40% and 65% should be maintained. At moisture content of below 40%, micro-organism activity will continue but at a slower rate and above 65% water will displace much of the air in the pore spaces of the composting material. This will limit the movement of air and lead to anaerobic conditions.

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