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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:
* Carbon
* Nitrogen
* Oxygen (in the case of aerobic composting)
* 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, which produce
disagreeable odors. Degradation under anaerobic conditions is
called anaerobic digestion.)
Environmental science
Environmental technology
* Air pollution control
* Air pollution dispersion modeling
* Alternative energy
* Biofuel
* Composting
* Ecoforestry
* Energy conservation
* Environmental design
* Future energy development
* Green building
* Hydrogen technologies
* Recycling
* Renewable energy
* Renewable energy development
* Remediation
* Solid waste treatment
* Sustainable energy
* Sustainable development
* Waste water treatment
* Water purification
* Waste management
The goal of a composting system:
The 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 composting:
Given 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:
* 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 (choose vegetarian horse manure, cow manure,
llama manure, etc.)
* 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 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 techniques:
There are a number of different techniques for composting
all employing the two primary methods of aerobic composting:
* Active (or hot) composting allows aerobic bacteria to thrive,
kills most pathogens and seeds, and rapidly produces usable
compost. Aerobic bacteria produce less odour and fewer
destructive green house gases than their anaerobic counterparts.
In addition, they are usually faster at breaking down material
and the faster material is broken down, the faster compost is
created for your garden.
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.
* Passive (or cold) composting lets nature take its course in a
more leisurely manner and leaves many pathogens and seeds
dormant in the pile.
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 composting:
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.
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 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.
Worm Composting:
Recycling the organic waste of a household into compost
allows us to return badly needed organic matter to the soil. In
this way, we participate in nature's cycle, and cut down on
garbage going into burgeoning landfills. Worm composting or
Vermicomposting is a method for recycling food waste into a
rich, dark, earth-smelling soil conditioner. The great advantage
of worm composting is that this can be done indoors and
outdoors, thus allowing year round composting. It also provides
apartment dwellers with a means of composting. The worm then
excretes a soil-nutrient material called worm castings. This is
why wise farmers have historically wanted to have healthy worm
populations living in their fields. Worms are at the bottom
level of the food chain but are critical to healthy soil. In a
nutshell, worm compost is made in a container filled with
moistened bedding and redworms. Add your food waste for a period
of time, and the worms and micro-organisms will eventually
convert the entire contents into rich compost. Some good
gardeners have developed a radical composting product, made
through a brewing process which runs distilled water through Red
Wiggler worm castings. The nutritious elements and
microorganisms of the castings are captured in a concentrated
liquid form, named worm tea. By using worm tea on your plants
and gardens, you put healthy microorganisms back into the soil
where they thrive and multiply, creating a much healthier
growing environment for your plants.
Industrial composting:
Industrial 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 America (the size of 14 NHL rinks).
Other ingredients:
Some 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. |
