| Experiments Home |
|
| Botany |
|
|
| Compost & Composting |
|
|
|
|
  |
|
|
 The Orchid Grower A Juvenile Science Adventure Novel |
|
|
Compost & Composting K-12 Experiments
Compost
Compost is the aerobically decomposed remnants of organic materials (those with plant and animal origins). Compost is used in gardening and agriculture as a soil amendment, and commercially by the landscaping and container nursery industries. It is also used for erosion control, land/stream reclamation, wetland construction, and as landfill cover (see compost uses). Compost is also used as a seed starting medium generally mixed with a small portion of sand for improved drainage.
Compost ingredientsGiven enough time, all biodegradable material will compost. However, not all compost feedstocks are appropriate for backyard composting. Most backyard systems will not reach high enough temperatures to kill pathogens and deter vermin, so pet droppings, non-vegetarian animal manure, meat scraps, and dairy products are best left to operators of high-rate, thermophylic composting systems. Certain substances should not be composted by the average homeowner, as they require more sophisticated systems, competent management, and more efficient, cost-competitive, environmentally sound technology. British composting standardThe British Composting Association[1] worked to establish an industry standard for the composts, the BSI PAS 100 certified by the British Standards Institute. The specification covers the entire process; from raw materials and production methods, through quality control and lab testing ensuring certified composts are quality assured traceable safe and reliable.[2] Compost types and ingredients
See alsoReferences
Composting is the process of producing compost through aerobic decomposition of biodegradable organic matter. The decomposition is performed primarily by aerobes, although larger creatures such as ants, nematodes, and oligochaete worms also contribute. This decomposition occurs naturally in all but the most hostile environments, such as within landfills or in extremely arid deserts, which prevent the microbes and other decomposers from thriving. Composting can be divided into the two areas of home composting and industrial composting. Both scales of composting use the same biological processes, however techniques and different factors must be taken into account. Composting is the controlled decomposition of organic matter. Rather than allowing nature to take its slow course, a composter provides an optimal environment in which decomposers can thrive. To encourage the most active microbes, a compost pile needs the correct mix of the following ingredients: Decomposition happens even in the absence of some of these ingredients, but not as quickly or as pleasantly. (For example, vegetables in a plastic bag will decompose, but the absence of air encourages the growth of anaerobic microbes, which produce disagreeable odors. Degradation under anaerobic conditions is called anaerobic digestion.)
The goal of a composting systemThe goal in a composting system is to provide a healthy environment and nutrition for the rapid decomposers, the bacteria. The most rapid composting occurs with the ideal carbon to nitrogen ratio of between 25 and 30 to 1 by dry chemical weight. In other words, the ingredients placed in the pile should contain 25 to 30 times as much carbon as nitrogen. For example, grass clippings average about 19-to-1 and dry autumn leaves average about 55-to-1. Mixing equal parts by volume approximates the ideal range. Commercial-grade composting operations pay strict attention to this ratio. For backyard composters, however, the charts of carbon and nitrogen ratios in various ingredients and the calculations required to get the ideal mixture can be intimidating, so many rules of thumb exist to guide composters in approximating this mixture. Materials for compostingGiven enough time to die, all biodegradable material will compost. However, not all compost feedstocks are appropriate for backyard composting. Most backyard systems will not reach high enough temperatures to kill pathogens and deter vermin, so pet droppings, non-vegetarian animal manure, meat scraps, and dairy products are best left to operators of high-rate, thermophylic composting systems. Certain substances should not be composted by the average homeowner, as they require more sophisticated systems, competent management, and more efficient, cost-competitive, environmentally sound technology. These substances include non-vegetarian animal manures and bedding, by-products of food production and processing, restaurant grease and cooking oils, and residuals from the treatment of wastewater and drinking water. Composting will also break down petroleum hydrocarbons and some toxic compounds for recycling and beneficial reuse. The use of composting for such purposes is most commonly referred to as a form of bioremediation. High-carbon sources provide the cellulose needed by the composting bacteria for conversion to sugars and heat, while high-nitrogen sources provide the most concentrated protein, which allow the compost bacteria to thrive. Some ingredients with higher carbon content:
Some ingredients with higher nitrogen content:
Poultry manure provides lots of nitrogen but little carbon. Horse manure provides both. Sheep and cattle manure don't drive the compost heap to as high a temperature as poultry or horse manure, so the heap takes longer to produce the finished product. Mixing the materials as they are added increases the rate of decomposition, but it can be easier to place the materials in alternating layers, approximately 15 cm (6 in) thick, to help estimate the quantities. Keeping carbon and nitrogen sources separated in the pile can slow down the process, but decomposition will occur in any event. Greasy food waste and wastes from meat, dairy products, and eggs should not be used in household compost because they tend to attract unwanted vermin and they do not appropriately decompose in the time required. However, eggshells are a good source of nutrients for the compost pile and the soil although they typically take more than one year to decompose. If recycling of meat and dairy products is desirable, Bokashi is a suitable alternative, which uses fermentation. However, even in Bokashi, liquids like milk and oil should not be used. Manure from non-vegetarian animals should never be used, and neither should human or pet waste. Composting techniquesThere are a number of different techniques for composting all employing the two primary methods of aerobic composting:
Pasteurisation in a hot compost (such as the Compost Oven) will occur in any garden compost bin if the temperature reaches above 55 °C (131 °F) for three or more days. To achieve it, you need to keep your garden compost bin warm, insulated and damp since this encourages the cultivation of actinomycetes, a vital bacteria in the pasteurisation process. Naturally created pasteurised soil through heat in the garden compost is very valuable for the composting gardener since it is both expensive and complicated to pasteurise material and adding chemicals to compost to produce the pasteurisation effect makes the compost less healthy.
Cold composting is the type of composting done in most domestic garden compost bins where temperatures never reach above 30 °C (86 °F). Cold composting is typically people placing their kitchen scraps in the garden compost bin and forgetting about them. In this circumstance, a garden compost bin becomes a storage container for scraps and has a very high moisture content which means it turns quite anaerobic and smelly. This type of composting generates significant adverse green house gas emissions. When composting this way, a gardener can improve the process by adding some wood chip or small pieces of bark, leaves, twigs or a combination of these materials through the mixture. This material helps to improve drainage and airflow. Composting systems are also either enclosed (home container composting, industrial in-vessel composting) or in piles (industrial windrow composting). Home compostingHome composters use a range of techniques varying from extremely passive composting (throw everything in a pile in a corner and leave it alone for a year or two) to extremely active (monitoring the temperature, turning the pile regularly, and adjusting the ingredients over time) and combinations of both. Some composters use mineral powders to absorb smells, although a well-maintained pile seldom has bad odors. Microbes and heating the pileAn effective compost pile is kept about as damp as a well wrung-out sponge. This provides the moisture that all life needs to survive. Bacteria and other microorganisms fall into a variety of groups in terms of what their ideal temperature is and how much heat they generate as they do their work. Mesophilic bacteria enjoy midrange temperatures, from about 20 to 40 °C (70 to 110 °F). As they decompose the organic matter, they generate heat, and the inner part of a compost pile heats up the most. The heap should be about 1 m (3 ft) wide, 1 m (3 ft) tall, and as long as is practicable. This provides a suitable insulating mass to allow a good heat build-up as the material decays. The ideal temperature is around 60 °C (140 °F), which kills most pathogens and weed seeds and while providing a suitable environment for thermophilic (heat-loving) bacteria, which are the fastest acting decomposers. The centre of the heap can get too warm, possibly hot enough to burn a bare hand. If this fails to happen, common reasons include the following:
The solution is to add material, if necessary, and/or to turn the pile to aerate it. Depending on how quickly the compost is required, the heap can be turned one or more times to bring the outer layers to the inside of the heap and vice versa, as well as to aerate the mixture. Adding water at this time helps keep the pile as damp. One guideline is to turn the pile when the high temperature has begun to drop, indicating that the food source for the fastest-acting bacteria (in the center of the pile) has been largely consumed. When the temperature stops rising after the pile has been turned, there is no further advantage in turning the pile. When all the material has turned into dark brown or nearly black crumbly matter, it is ready to use. Industrial compostingIndustrial composting systems are being increasingly installed as an alternative form of waste management to landfill along with other advanced waste processing systems. The industrial composting or anaerobic digestion can be combined with mechanical sorting of mixed waste streams and is given the term mechanical biological treatment. Industrial composting helps prevent global warming by treatment of biodegradable waste before it enters landfill. Once this waste is landfilled it breaks down anaerobically producing landfill gas that contains methane, a potent greenhouse gas. Most commercial and industrial composting operations use active composting techniques. This ensures a higher quality product and produces results in the shortest time (see compost windrow turner). The greatest control, and therefore the highest quality, is generally achieved by composting inside an enclosed vessel which is monitored and adjusted continuously for optimal temperature, air flow, moisture, and other parameters. See In-vessel (also en-vessel). Large scale composting systems are used by a few urban centers around the world. Co-composting is a technique which combines solid waste with de-watered bio-solids. The world's largest co-composter is in Edmonton, Alberta, Canada, which turns 220,000 tonnes of residential solid waste and 22,500 dry tonnes of biosolids per year into 80,000 tonnes of compost using a facility 38,690 square metres in size (equivalent to 8 football fields). The aeration building alone is the largest stainless steel building in North American (the size of 14 NHL rinks). Other ingredientsSome users like to put special materials and activators into their compost. Adding commercially available Effective MicroorganismsTM helps to keep the balance between "good" and "bad" bacteria. A light dusting of agricultural lime (not on the animal manure layers) can curb excessive acidity that can slow down the fermentation. Seaweed meal can provide a ready source of trace elements. Finely pulverized rock (rock flour or rock dust) can also provide needed minerals, as opposed to clay (which is trace mineral-poor and/or leached rock dust). Animal manure should only be collected from vegetarian animals, such as horses, cows, sheep, llamas, etc. Pet waste, human waste, and non-vegetarian animal waste should not be used in the average compost heap. Human waste can be collected by composting toilets (in this case, human feces). However, such compost is usually not used as a fertilizer for plants that are directly edible (e.g., salad crops). Most composting toilets do not allow for the thermophilic activity needed to completely kill off the pathogens and bacteria. However, if these high temperatures are reached, there is no danger of contamination, and the resulting compost can be safely used on food crops. Most composts heaps are unable to reach those temperatures. Composting toilets should only be used as a way to reduce waste in the environment, not as a fertilizer; in the case that they are used with crops, they should only use human waste for non-food crops, or with careful filteration, food based crops. See also
External links
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia articles "Compost" and "Composting" |
