Composting provides a safe means of waste management, utilizing microorganisms to degrade complex materials into organic and inorganic by-products.
DR PRIYADARSHINI PILLAI
Composting plays a crucial role in agriculture and the recycling of farm wastes. However, the lengthy composting duration poses a challenge, particularly in the presence of materials that take longer to decompose, especially during co-composting. The addition of activators to raw materials can enhance the nutritional quality of compost. Furthermore, slow-mineralizing degradable organic materials should be assessed for their potential benefits in perennial or biennial crop production. Incorporating organic sources of viricides, fungicides, anti-nematodes, and antibacterial can also enhance compost quality. Lastly, extending the composting duration proves beneficial. Inadequate waste management practices have adverse effects on human health, causing air pollution, water contamination, and ozone layer depletion due to burning, thereby exacerbating climate change. Common conventional methods, such as burning, ocean disposal, waterway dumping, and roadside dumping, lead to insect infestations, offensive odours, visual pollution, and contribute to global warming. Organic waste transformation occurs through either aerobic or anaerobic processes, resulting in the formation of compost or biogas and biofertilizers, respectively. Composting provides a safe means of waste management, utilizing microorganisms to degrade complex materials into organic and inorganic by-products. These by-products, enriched with unique 'humic-like' compounds, differentiate compost from native soil, coals, and peats. Ultimately, composting serves as an environmentally friendly method to transform various degradable wastes into beneficial biofertilizers and soil amendments.
The composting process offers significant advantages over landfilling as a waste disposal method, particularly in safeguarding underground water from pollution. Composting reduces the presence of pathogenic microbes and chemical pollutants found in waste, ensuring human safety. Beneficial microbes present in compost absorb persistent organic pollutants (POPs) and endocrine-disrupting residues (EDRs) remaining in the soil during composting. The application of compost improves agricultural productivity and enhances soil organic matter content, thereby contributing to food security. Moreover, compost finds utility in bioremediation, plant disease and weed control, pollution prevention, erosion control, landscaping, and wetland restoration. Composting also enhances soil biodiversity while reducing environmental risks associated with synthetic fertilizers. Unlike natural and uncontrolled decomposition, composting is initiated and managed under controlled environmental conditions. However, challenges exist, including longer maturation time, offensive odour, prolonged mineralization, thermotolerant pathogens, and nutrient deficiencies, which have hindered the widespread adoption of composting in sustainable agriculture. Therefore, it is crucial to assess the advantages and disadvantages of composting compared to synthetic fertilizers. Further research is needed to explore odour-trapping techniques, rapid pathogen and heavy metal detection methods, and the use of specific nutrient-rich activators, antibacterial, antifungal, antiviral, and anti-nematode agents. While composting offers numerous benefits, it also poses challenges related to climate change, carbon dioxide emissions, oxygen depletion, and offensive smells. Regulations governing composting practices have been established globally to address health impacts. To improve composting, two key areas requiring attention are temperature regulation and oxygen flow control, which directly influence microbial activity. Monitoring and optimizing the temperature for specific microbial functions and ensuring sufficient oxygen supply to minimize anaerobic activity are crucial. By addressing these concerns, composting can become an effective and sustainable waste management solution.
Waste and its Effects
Waste is any unwanted solid, liquid, or gaseous substance Poorly managed wastes have adverse effects on humans, animals, plants, and the environment. About 50% of wastes generated is organic, thus, the proper management of organic wastes will drastically reduce the volume of pollution arising from improper waste management.
Wastes affect the environment leading to severe hazardous impact on lives. Humans and animals alike are affected by these adverse effects, which can cause disease outbreak, reduction in life expectancy, and unsafe environment. Some wastes may rot, but those that do not will smell and generate methane gas, which significantly contributes to the greenhouse effect. The environmental and health impacts of wastes will be described subsequently. Wastes pollute the air, water, and soil. Air pollution includes odour, smoke, and dust. When solid wastes are burnt, greenhouse gases such as carbon dioxide and nitrous oxide are released, these lead to ozone layer depletion and greenhouse effect . Hydrogen sulfide and methane are also released into the air. These substances are toxic to human lives.
It is reported that approximately 1400 people die daily due to water and water-related problems/disease. Wastes that find their way into water bodies such as rivers, streams, and oceans can have a disruptive influence on the water bodies by lowering the pH and causing toxicity to the aquatic inhabitants and humans that use the water.
Composting and its impacts
Composting is important for several reasons.
Waste Reduction: Composting provides a sustainable solution for managing organic waste. By diverting organic materials such as food scraps, yard trimmings, and agricultural residues from landfills, composting helps reduce the volume of waste that would otherwise contribute to landfill congestion and greenhouse gas emissions.
Soil Enrichment: Compost is a valuable soil amendment that improves soil health and fertility. It enhances soil structure, increases water-holding capacity, and promotes nutrient retention. Compost also introduces beneficial microorganisms to the soil, enhancing its overall biological activity and supporting plant growth.
Nutrient Recycling: Composting allows for the recycling of nutrients found in organic waste. As organic materials break down during composting, their nutrients are transformed into forms that plants can readily absorb. These nutrients are then reintroduced to the soil, closing the nutrient cycle and reducing the need for synthetic fertilizers.
Environmental Protection: Composting plays a crucial role in environmental protection. By diverting organic waste from landfills, composting helps reduce the production of methane, a potent greenhouse gas that contributes to climate change. Additionally, compost-amended soils have the capacity to sequester carbon, mitigating the impacts of carbon dioxide emissions.
Water Management: Compost-amended soils have improved water-holding capacity and drainage, reducing the risk of soil erosion and water runoff. By enhancing soil structure and reducing water runoff, composting helps protect water quality by minimizing the leaching of pollutants into groundwater and surface water bodies.
Sustainable Agriculture: Compost provides a natural and sustainable alternative to synthetic fertilizers, reducing the reliance on chemical inputs in agriculture. It promotes soil biodiversity, supports beneficial microorganisms, and contributes to long-term soil health, thereby fostering sustainable farming practices.
Circular Economy: Composting exemplifies the principles of a circular economy by transforming organic waste into a valuable resource. It closes the loop by returning organic matter back to the soil, completing the cycle of natural nutrient replenishment and promoting a more sustainable and resource-efficient approach to waste management.
Composting Methods
There are different composting methods, with each method having its advantages and disadvantages. Therefore, the method that best suits the goal of the researcher and the type of material to be composted dictates the composting method to be adopted. Some of the composting methods are enumerated below.
Indian Bangalore Composting: The Indian Bangalore composting method was developed at Bangalore in India . The method is majorly recommended for the composting of night soil and refuse. The composting is carried out by digging trenches or pits about one meter deep where organic residues and night soil are put in alternate layers . The pit is finally covered with a 15–20 cm thick layer of refuse. The materials are left in the pit without turning or watering for three months. During this period, there is a reduction in the volume of the materials, and more night soil and refuse are placed on top in alternate layers and covered with mud or earth to prevent loss of moisture and breeding of flies. This type of composting takes about six to eight months to obtain the finished product . This method is laborious and expensive to support.
Vessel Composting: In-vessel composting refers to any type of composting conducted in an enclosed area such as a container, building, or vessel. In-vessel methods depend on a variety of forced aeration and mechanical turning techniques to enhance the composting process . This method is labour-intensive and expensive.
Windrow Composting: Windrow composting is conducted by placing raw materials in long narrow piles or windrows, which are turned regularly. The mixing of the materials allows aeration into the setup. A typical windrow composting set up should start from 3 feet in height for dense materials like manures and 12 feet high for fluffy materials like leaves. It is difficult, and costly to support, but it is rapid and retains heat.
Vermicomposting: The term refers to the use of earthworms for composting degradable organic matters [64]. Earthworms can degrade practically all kinds of organic matter by feeding on them. They can eat their body weight per day. For example, earthworms that weigh 0.1 kilogram can eat 0.1 kilogram of residue per day. The excreta of the worms—termed “castings”—are rich in nitrate, as well as available forms of phosphorus, potassium, calcium, and magnesium, which improve soil fertility The existence of earthworms in the soil promotes bacterial and actinomycetes growth.
Static Composting: This is a traditional method of composting where wastes are composted aerobically using passive aeration (little and infrequent turnings or static aerations like perforated poles or pipes). This method is time-consuming, though it is a simple way of composting, which has low operational and capital costs compared to vermicomposting, windrow, vessel, and Indian Bangalore composting. This method simply involves the formation of a pile of raw materials and has a low requirement of labor and equipment. Aeration is based mainly on the passive movement of air through the pile, thereby degrading the organic matter slowly.
Sheet Composting: Sheet composting release the benefit of decayed organic material without building a composting pile. In this method, organic matters such as leaves, garden debris, grass clippings, weeds, and vegetative food are thinly spread directly onto the soil as a mulch. The organic materials are then tilled in with a hoe, spade or garden fork and left to decay there, rather than in a heap or container. One or more layers of organic material(s) are spreads over the growing area, watered thoroughly and left to decompose until planting time. More layers of organic materials are placed at the bottom layers decompose thoroughly . The method is cheap and straightforward.
Indian Indore Composting
Indian Indore method involves a mixture of raw materials such as plant residues, animal dung, and urine, earth, wood ash, and water. All organic wastes available on a farm such as weeds, stalks, stems, fallen leaves, pruning, chaff, fodder leftovers are made into a layer about 15-cm-thick until the heap is about one and a half meters high. The heap is cut into vertical slices of about 20–25 kg for the night rest. The bedding is taken to the composting pits and filled layer by layer within a week. Enough quantity of water is sprinkled over the materials in the pit to wet them. Moisturizing of the compost is done only three times throughout the whole period of composting. The moisturizing is done on the fifteenth day after stacking the compost pit, on the next 15 days after the first moisturizing and finally after one month after the first moisturizing. This method is labour-intensive and time-consuming. It is also prone to flies, and pest disturbances and wind can lead to loss of nutrients .
Berkley Rapid Composting: This is a fast-composting method. Here, materials compost faster if the size is between 0.5–1.5 inches in size. Soft, succulent tissues do not need to be chopped in very small pieces because they decompose rapidly. The harder the tissues, the smaller they need to be chopped to enhance decomposition. Once a pile is started, nothing should be added because it takes a certain length of time for the initial materials to break down, and anything added has to start from the initial breakdown stage—thus lengthening the decomposition time for the whole pile.
Factors that affect composting process
Microorganisms and Insects: Microorganisms, mostly aerobic bacteria, and insects further speed the composting process. An open bottom on the compost pile allows these organisms to move into the pile from the soil below. You can also add a commercial compost starter or two or three shovel-fulls of healthy garden soil to introduce these organisms to the pile. Earthworms, centipedes, millipedes and springtails are some of the insects that aid the composting process.
Moisture and Aeration: Compost materials and the organisms that break them down both need moisture and oxygen to work. An evenly moist compost pile feels as damp as a wrung-out sponge. The pile may require watering during dry periods to ensure it remains moist throughout. Turning the pile once a week provides additional aeration and ensures all materials are moist, which speeds the composting process. Overly wet piles will break down slowly, so it may be necessary to cover the pile with a tarp during wet, rainy weather.
Temperature: The pile warms as the composting process accelerates. A rapidly composting pile usually reaches temperatures between 90 and 140 degrees Fahrenheit, which also provides the optimum temperatures for most microorganisms to survive. Providing the right materials, moisture level and aeration helps the pile heat up and maintain these temperatures. During cold weather, especially in winter, composting may slow if the temperature in the pile begins to drop, but it quickly speeds up as temperatures warm in spring and summer. Adding more nitrogen materials to a pile can help raise the temperature if it drops and the composting process slows.
Carbon-Nitrogen Ratio: and nitrogen are two elements that are essential to decomposition. All organic matter contains both carbon and nitrogen in differing amounts, and getting the right mixture often takes some practice. Green materials such as grass clippings are high in nitrogen but low in carbon. Brown materials, such as wood chips, contain more carbon. This is called the C:N ratio. The tiny microorganisms use carbon as an energy source, while nitrogen helps with protein synthesis. While the ideal C:N ratio is around 30 to 1 (About 3-1/2 pounds of green materials to 100 pounds of brown materials), decomposition still occurs at different ratios. Not enough nitrogen will slow the process down, while too much nitrogen will cause the formation of unpleasant ammonia gas.
Oxygen and pH: The presence of oxygen is important during the composting process. When organisms oxidize carbon for energy formation, the oxygen present is used up, and gases are produced. Without adequate oxygen, the composting process will become anaerobic, and gases (methane, carbon dioxide, and ammonia) will be produced, leading to the production of undesirable odours. The pH of the materials that are composted affects the composting rate. Alkaline pH has been reported to be best for composting. When pH is acidic, composting is very slow because the microorganisms are destroyed.
Inadequate waste management practices pose risks to both the environment and human well-being. However, there is a growing global focus on improving environmental and human health through safer waste management methods. Composting, as a form of organic fertilizer, holds great promise in achieving this objective. By shifting from chemical fertilizers to compost, significant benefits can be realized, including reduced release of toxic chemicals into the environment. Nonetheless, there is still a need to raise awareness about the potential of composting technology to ensure its widespread adoption by farmers. To enhance composting practices, several recommendations are proposed to drive its improvement and effectiveness.
Dr Priyadarshini Pillai is a professor of Botany; undertakes researches and promotes environmental activities that are sustainable.
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