Compost

Related Topics:
Compost :: Compost_Gin :: Compostela_Valley :: Composting :: Composting_Toilets

Compost is the 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.)

Composting

Compost is the means by which organic matter is recycled in its environment. Compost is also used as a seed starting medium generally mixed with a small portion of sand for improved drainage.

Composting is the common name for the decomposition of organic matter under aerobic conditions. The decomposition is performed primarily by microbes, 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 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:

Carbon
Nitrogen
Oxygen (from the air)
Water

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 that produce disagreeable odors, degradation under anaerobic conditions is called anaerobic digestion.)

There are a variety of methods of composting. In the home this is often done in a composting bin or a simple compost heap at the bottom of the garden. Industrial methods of composting include:

Decomposers

All guidelines for building compost piles are written with the goal of creating the proper environment for a decomposing ecosystem in mind. The most effective decomposers are bacteria and other microorganisms. Also important are fungi, protozoa, and actinobacteria (or actinomycetes). These bacteria are often seen as white filaments in decomposing organic matter. At a macroscopic level, earthworms, ants, snails, slugs, millipedes, sow bugs, springtails, and other organisms consume and break down the organic matter. Centipedes and other predators feed upon these decomposers.

Compost ingredients

Given 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 animal manures, pet droppings, meat scraps, and dairy products are best left to operators of high-rate, thermophylic systems. Only through the employment of more sophisticated systems and with competent management is composting an efficient, cost-competitive, environmentally sound technology to recycle not only animal manures and bedding, but also the 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.

The goal in a compost pile 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.

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:

Dry, straw-type material, such as cereal straws
Autumn leaves
Sawdust and wood chips
Some paper and cardboard (such as corrugated cardboard or newsprint with soy-based inks)

Some ingredients with higher nitrogen content:

Green plant material (fresh or wilted) such as crop residues, hay, grass clippings, weeds
Animal manures
Fruit and vegetable trimmings
Seaweeds
Used Coffee grounds

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. 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.

Composting techniques

There are two primary methods of aerobic composting:

Active (or hot) composting, which allows the most effective decomposing bacteria to thrive, kills most pathogens and seeds, and rapidly produces usable compost
Passive (or cold) composting, which lets nature take its course in a more leisurely manner and leaves many pathogens and seeds dormant in the pile

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).

Home 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.

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 being 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).

Microbes and heating the pile

An 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 heap is too wet, thus excluding the oxygen required by the compost bacteria
The heap is too dry, so that the bacteria do not have the moisture needed to survive and reproduce
There is insufficient protein (nitrogen-rich material)

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.

Other ingredients

Some users like to put special materials and activators into their compost. 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).

The animal manure part of compost source materials 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, there is research that shows that if these high temperatures are reached, there is no danger of contamination, and the resulting compost can be safely used on food crops.

Composting systems

External Links

Composting Guide Info, articles, tips, and more on compost.
Composting for Beginners
UC Davis - Project Compost

Gourt Home::Gourt :: Compost