Wednesday, May 18, 2011

Different Composting Methods

There are many different composting methods via which organic material can be converted to compost. The type of composting method that you decide you use will depend upon the quantom of waste that you generate and the ammount of land that you have avaliable. A list of different composting methods is listed below for your understanding:

Home Composting

   Home Composting programs take two distinct forms. The first employs home composters, usually plastic bins or barrels with a capacity of about 200 liters. These are supplied to homeowners, often on a subsidized basis, and should be accompanied by instructions on what and how to carry out home composting.  Additional support can be provided by telephone hot lines and by volunteer programs in which experienced home composters provide assistance and advice to beginners. Although home composting programs are feasible only in suburban areas, they are very effective because waste is diverted at source and no pickup or treatment by the municipal system is required.

 Central Composting Facilities
Even with a successful composting program, a central composting facility can make a valuable contribution to waste reduction. The central facility can service apartment buildings, business and neighborhoods where home composters are not feasible; in addition, it can treat leaves in the fall and Christmas trees in winter. Incentives should be developed to ensure that landscaping firms, significant generators of yard wastes, drop off their wastes at the central facility.

      An important part of planning a central composting facility is obtaining regulatory permits, including communicating with local groups that may be affected by the facility. A relatively large parcel of land is required, and this is often located at the municipal landfill; land is available, garbage/recycle trucks come there anyways, infrastructure such as weigh scales and woods shredder is available, and the final compost can be used for landfill cover if no other markets are available.

      The processing of organic materials prior to composting includes shredding to break bags, reduce size of materials such as Christmas trees and large wood pieces, and ensure a relatively uniform material; and sorting to remove contaminants such as plastic bags.

      Composting facilities, though a relatively low technology, still require careful planning and resources. Generally, three basic systems are used; the windrow, static pile, and in-vessel methods ( Tchobanoglous et al., 1993 ).The windrow and static pile  methods are the most popular license they require minimal capital investment and the decomposition process occurs aerobically ( in the presence of oxygen ). In aerobic composting ( versus anaerobic composting, in the absence of oxygen ) far less odor is generated, and temperatures reach higher levels, generally in the 40  to 60 C range, which not only kill most pathogens but also destroy weed seeds.

 Windrow  Composting.        This is one of the oldest and simplest methods of composting. A typical windrow system consists of long rows of organic material, about 1.8 to 2.1 meters high and 4 to 5 meters wide at the base. Actual dimensions vary and depend largely on the equipment available to place and manipulate the piles.

To ensure aerobic conditions and maintain temperatures, the windrow are turned at regular intervals, usually once or twice a week. A moisture content of 50% to 60% must be maintained. Although bulldozers and front-end loaders can be used, specialized turning machines have been developed that are more efficient and can add water at the same time. Proper aeration is important because it prevents anaerobic conditions, which lead to odor. A temperature of at least 55  should be maintained for a minimum of two weeks to ensure destruction of pathogens. The composting period lasts about four or five weeks; the compost is usually cured for an additional two to eight weeks to ensure that it is completely stabilized.

 Aerated static pile composting.        This method can be used to compost a wide variety of organic materials, including yard wastes and separated municipal waste. The materials are laid out in long piles similar to windrows. A layer of screened compost is often placed on top of the pile to control odor and provide insulation. A network of perforated piping is either placed at the bottom of the pile or embedded in the flooring below the pile. Air is introduced by blowers into each pile through the pipe network so that aerobic decomposition occurs. Airflow rates are controlled to maintain the temperature  at the desired level. In modern facilities, all or most of the system is enclosed to allow better processing and odor control. Although the method needs more complex equipment than windrow composting, it does not require turning the material, it minimizes odors, and it provides better control of the process.

 In-vessel composting.           In this method, the materials to be composted are enclosed in a container or vessel.  Vessels of various shapes are used, but they are generally of two basic types: plug flow or dynamic. In the former, the materials move through the vessel without agitation; in the later, the materials are agitated or mixed during the composting. Air and water are added to the vessels in a well-controlled manner. Typical in-vessel composting systems are shown schematically in Figure 5.6, and an actual system is shown in Figure 5.7. Detention (processing) times in in-vessel composters are about 1 to 2 weeks, followed by a 4- to 12-week curing period. In-vessel composters are gaining popularity because they offer good process and odor control, shorter composting time, and lower labor costs, and they can deal with food wastes. In particular, they can be set up in cities to service facilities such as hospitals or large office complexes.

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