What is Composting ? and Types of Composting Process
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Composting is a microbiological conversion of organic residues of plant and animal origin to manure rich in humus and nutrients by various micro-organisms including bacteria, fungi and actinomycetes in the presence of oxygen . During the process it releases by products such as carbon dioxide, water and heat .
Type of Composting Process
- PILE / WINDROW COMPOSTING
- STATIC (ACTIVE/PASSIVE) COMPOSTING
- IN – VESSEL COMPOSTING
- Vermicomposting is a modified and specialized bio-oxidative process of composting which uses earthworms to convert organic wastes into high quality compost .
- Unlike other composting process vermicomposting is not an exothermic process. In this process, the organic matter containing major fraction of nutrients are converted into more available forms known as vermicast.
- Initially the substrate is broken into small fragments for ingestion, thereby it enters into gizzard of earthworms where mincing of the substrate occurs. This mincing helps in increasing the surface area of the substrate and facilitate microbial action.
- During vermicomposting, the earthworm body is report to act as a bio-filter that can purify and also disinfect and detoxify solid wastes . Apart from production of compost of high nutrient rich, vermicomposting has also proved to more efficient in removing pathogens, as they are eliminate as soon entering the food chain of earthworms .
- Windrow composting involves aerobic bioconversion of organic matter to stable compost with release of heat, water vapor and CO2, in which the pile composting can be used only for small quantities of input materials.
- However the windrow composting allows large quantities of materials to be composte, having a geometrical shape ranging from 2 to 4 m wide and 2 to 3 m high at the starting of composting process .
- These types of systems usually acquire a trapezoidal shape, depending on the nature of raw material used for composting. Before forming the windrow, the material is shredded and screened to 3 to 9 cm, with moisture content adjusted to 50-60%. Usually, the windrows are turned twice in a week so that temperature is maintain at 55oC and the process is accomplished in 3-4 weeks.
- Furthermore for curing, the compost is allowed without turning for another 3-4 weeks for the degradation of residual organics.
STATIC (ACTIVE/PASSIVE) COMPOSTING
- Static composting is similar to windrow system in which the raw material is laid in parallel rows, with no restrictions to the size and shape of the compost . But reports state that windrow and static composting are two different processes, in which the material to be compost is agitate manually in the windrow system to introduce oxygen and regulate temperature, whereas in static piles, air is blown through the mass.
- Active aerated systems are the improved form of windrow , which has accelerate degradation and better control over the entire process . Hence aeration plays a critical role in composting as it supplies oxygen for the system and it removes CO2, moisture and excess heat as a result of microbial degradation.
- Static pile (active and passive) is operate by placing them over a network of pipes connected to air blowers that delivers air in and out of the system.
- The waste material use for the system is mix all together in one large pile and these piles are suitable only for high organics such as yard trimming and biodegradable MSW (Municipal Solid Waste ).
- These types of system are effective in substantially reducing the mass and volume of the material being transported to the landfills.
- Passive and active aeration systems produce the same compost quality with similar results , while the maintenance and operation costs differs with the methodology adopted.
- One more advantage of the contain pile over static pile is that the material width size reducing with height due to sliding of material along the angle of repose. As the materials are loaded between the walls, with the decomposition the materials will be gradually slide down. Covering the roof of the contain pile system could also be beneficial in odor contamination.
- Rotary drum composter are one of the first types of In-vessel composting system design with engineering systems that are completely different from other conventional methods practiced earlier.
- A common feature of these types of system is that large amount of waste material can be decompose within an enclose space in shorter time under control process.
- Therefore, drum method of vegetable waste is an efficient and promising technique with its decentralize processing of the material, as it provides agitation, aeration and uniform mixing of the compost material to produce a stabilize end product with high quality .
- In such systems aeration is optimize by various force aeration and mechanical turning devices. Since the time of the compost is drastically reduce when compare with other methods, this methodology can be successfully use.
- There are many reports on the application of drum composting on vegetable waste in combination with many wastes such as cattle manure, tree leaves and saw dust.
- A maximum of 70% reduction in the volume of the input can be achieve in vessel process of household wastes with high quality when compared to other reactors test.
- The final compost can also be use as a soil conditioner by improving the quality of the soil and supplying basic nutrients to the plants . Drum provides complete mixing of the material for better degradation organic matter as reported by many authors.
- There is always a major concern on C/N ratio of the material being added to the compost and this C/N ratio plays crucial part in the compost. Since the composting is fully dependent on microbial activity, if there is any improper supply of carbon and nitrogen sources it will greatly affect the quality of the end product.