From Wikipedia, the free encyclopedia
Community-level composting in a rural area in Germany
Compost is rich in nutrients. It is used, for example, in
gardens,
landscaping,
horticulture,
urban agriculture and
organic farming. The compost itself is beneficial for the land in many ways, including as a soil conditioner, a
fertilizer, addition of vital
humus or
humic acids, and as a natural
pesticide for soil.
Compost is useful for erosion control, land and stream reclamation, wetland construction, and as landfill cover.
At the simplest level, the process of composting requires making a heap of wet organic matter (also called
green waste), such as leaves, grass, and food scraps, and waiting for the materials to break down into
humus
after a period of months. However, composting can also take place as a
multi-step, closely monitored process with measured inputs of water,
air, and carbon- and nitrogen-rich materials. The
decomposition
process is aided by shredding the plant matter, adding water and
ensuring proper aeration by regularly turning the mixture when open
piles or "windrows" are used.
Fungi,
earthworms and other
detritivores further break up the material.
Aerobic bacteria and fungi manage the chemical process by converting the inputs into heat,
carbon dioxide, and
ammonium.
Fundamentals
Materials in a compost pile
Composting is an
aerobic method (meaning that it requires the presence of air) of decomposing organic solid wastes. It can therefore be used to recycle organic material. The process involves decomposition of organic material into a
humus-like material, known as compost, which is a good
fertilizer
for plants. Composting requires the following three components: human
management, aerobic conditions, and development of internal biological
heat.
Composting organisms require four equally important ingredients to work effectively:
- Carbon — for energy; the microbial oxidation of carbon produces the heat, if included at suggested levels. High carbon materials tend to be brown and dry.
- Nitrogen — to grow and reproduce more organisms to oxidize
the carbon. High nitrogen materials tend to be green (or colorful, such
as fruits and vegetables) and wet.
- Oxygen — for oxidizing the carbon, the decomposition process.
- Water — in the right amounts to maintain activity without causing anaerobic conditions.
Certain ratios of these materials will provide microorganisms to work
at a rate that will heat up the pile. Active management of the pile
(e.g. turning) is needed to maintain sufficient supply of oxygen and the
right moisture level. The air/water balance is critical to maintaining
high temperatures 130–160 °F (54–71 °C) until the materials are broken
down.
The most efficient composting occurs with an optimal carbon:nitrogen ratio of about 25:1.
Hot container composting
focuses on retaining the heat to increase decomposition rate and
produce compost more quickly. Rapid composting is favored by having a
C/N ratio of ~30 or less. Above 30 the substrate is nitrogen starved,
below 15 it is likely to outgas a portion of nitrogen as ammonia.
Nearly all plant and animal materials have both carbon and
nitrogen, but amounts vary widely, with characteristics noted above
(dry/wet, brown/green).
Fresh grass clippings have an average ratio of about 15:1 and dry
autumn leaves about 50:1 depending on species. Mixing equal parts by
volume approximates the ideal C:N range. Few individual situations will
provide the ideal mix of materials at any point. Observation of amounts,
and consideration of different materials as a pile is built over time,
can quickly achieve a workable technique for the individual situation.
Microorganisms
With
the proper mixture of water, oxygen, carbon, and nitrogen,
micro-organisms are able to break down organic matter to produce
compost.
The composting process is dependent on micro-organisms to break down
organic matter into compost. There are many types of microorganisms
found in active compost of which the most common are:
- Bacteria- The most numerous of all the microorganisms found in compost. Depending on the phase of composting, mesophilic or thermophilic bacteria may predominate.
- Actinobacteria- Necessary for breaking down paper products such as newspaper, bark, etc.
- Fungi- molds and yeast help break down materials that bacteria cannot, especially lignin in woody material.
- Protozoa- Help consume bacteria, fungi and micro organic particulates.
- Rotifers- Rotifers help control populations of bacteria and small protozoans.
In addition,
earthworms
not only ingest partly composted material, but also continually
re-create aeration and drainage tunnels as they move through the
compost.
Phases of composting
Three years old household compost
Under ideal conditions, composting proceeds through three major phases:
- Mesophilic phase: An initial, mesophilic phase, in which
the decomposition is carried out under moderate temperatures by
mesophilic microorganisms.
- Thermophilic phase: As the temperature rises, a second,
thermophilic phase starts, in which the decomposition is carried out by
various thermophilic bacteria under higher temperatures (50 to 60 °C
(122 to 140 °F).)
- Maturation phase: As the supply of high-energy compounds
dwindles, the temperature starts to decrease, and the mesophiles once
again predominate in the maturation phase.
Slow and rapid composting
There are many proponents of rapid composting that attempt to correct
some of the perceived problems associated with traditional, slow
composting. Many advocate that compost can be made in 2 to 3 weeks.
Many such short processes involve a few changes to traditional methods,
including smaller, more homogenized pieces in the compost, controlling
carbon-to-nitrogen ratio (C:N) at 30 to 1 or less, and monitoring the
moisture level more carefully. However, none of these parameters differ
significantly from the early writings of compost researchers,
suggesting that, in fact, modern composting has not made significant
advances over the traditional methods that take a few months to work.
For this reason and others, many scientists who deal with carbon
transformations are skeptical that there is a "super-charged" way to get
nature to make compost rapidly.
Both sides may be right to some extent. The bacterial activity in
rapid high heat methods breaks down the material to the extent that
heat-sensitive pathogens and seeds are destroyed,
and the original feedstock is unrecognizable. At this stage, the
compost can be used to prepare fields or other planting areas. However,
most professionals recommend that the compost be given time to cure
before using in a nursery for starting seeds or growing young plants.
An alternative approach is anaerobic fermentation, known as
bokashi.
It retains carbon bonds, is faster than decomposition, and for
application to soil requires only rapid but thorough aeration rather
than curing. It depends on sufficient carbohydrates in the treated
material.
Pathogen removal
Materials that can be composted
Composting is a process used for
resource recovery. It can
recycle an unwanted by-product from another process (a
waste) into a useful new product.
Organic solid waste (green waste)
A large compost pile that is steaming with the heat generated by
thermophilic microorganisms.
Composting is a process for converting decomposable organic materials into useful stable products. Therefore, valuable
landfill
space can be used for other wastes by composting these materials rather
than dumping them on landfills. It may however be difficult to control
inert and plastics contamination from
municipal solid waste.
Co-composting is a technique that processes organic solid waste together with other input materials such as dewatered
fecal sludge or
sewage sludge.
Animal manure and bedding
On many farms, the basic composting ingredients are animal
manure
generated on the farm and bedding. Straw and sawdust are common bedding
materials. Non-traditional bedding materials are also used, including
newspaper and chopped cardboard. The amount of manure composted on a
livestock farm is often determined by cleaning schedules, land
availability, and weather conditions. Each type of manure has its own
physical, chemical, and biological characteristics. Cattle and horse
manures, when mixed with bedding, possess good qualities for composting.
Swine manure, which is very wet and usually not mixed with bedding
material, must be mixed with straw or similar raw materials. Poultry
manure also must be blended with carbonaceous materials - those low in
nitrogen preferred, such as sawdust or straw.
Human waste and sewage sludge
Human waste
can be added as an input to the composting process since human excreta
is a nitrogen-rich organic material. It can be either composted
directly, as in
composting toilets, or indirectly (as
sewage sludge), after it has undergone treatment in a
sewage treatment plant.
Feces contain a wide range of microorganisms including bacteria,
viruses and parasitic worms and its use in home composting can pose
significant health risks.
Urine can be put on compost piles or directly used as fertilizer.
Adding urine to compost can increase temperatures and therefore
increase its ability to destroy pathogens and unwanted seeds. Unlike
feces, urine does not attract disease-spreading flies (such as
houseflies or
blowflies), and it does not contain the most hardy of pathogens, such as
parasitic worm eggs.
Uses
Compost can be used as an additive to soil, or other matrices such as
coir and
peat, as a
tilth improver, supplying humus and nutrients. It provides a rich
growing medium as absorbent material (porous). This material contains moisture and soluble minerals, which provides support and
nutrients. Although it is rarely used alone, plants can flourish from mixed
soil,
sand, grit, bark chips,
vermiculite,
perlite, or
clay granules to produce
loam.
Compost can be tilled directly into the soil or growing medium to boost
the level of organic matter and the overall fertility of the soil.
Compost that is ready to be used as an additive is dark brown or even
black with an earthy smell.
Generally, direct seeding into a compost is not recommended due to the speed with which it may dry and the possible presence of
phytotoxins in immature compost that may inhibit germination, and the possible tie up of nitrogen by incompletely decomposed lignin. It is very common to see blends of 20–30% compost used for transplanting
seedlings at
cotyledon stage or later.
Compost can be used to increase plant immunity to diseases and pests.
Composting technologies
Various
approaches have been developed to handle different ingredients,
locations, throughput and applications for the composted product.
Industrial-scale
Vermicomposting
Worms in a bin being harvested
Vermicompost is the product or process of organic material degradation using various species of worms, usually
red wigglers,
white worms, and
earthworms,
to create a heterogeneous mixture of decomposing vegetable or food
waste (excluding nitrogen-rich meat or dairy and fats or oils), bedding
materials, and vermicast. Vermicast, also known as
worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by
species of earthworm.
Composting toilets
A
composting toilet collects human excreta. These are added to a compost heap that can be located in a chamber below the toilet seat.
Sawdust and straw or other carbon rich materials are usually added as well. Some
composting toilets do not require water or electricity; others may. If they do not use water for flushing they fall into the category of
dry toilets. Some composting toilet designs use
urine diversion,
others do not. When properly managed, they do not smell. The composting
process in these toilets destroys pathogens to some extent. The amount
of pathogen destruction depends on the temperature (mesophilic or
thermophilic conditions) and composting time.
Composting toilets with a large composting container (of the type
Clivus Multrum
and derivations of it) are popular in United States, Canada, Australia,
New Zealand and Sweden. They are available as commercial products, as
designs for self builders or as "design derivatives" which are marketed
under various names.
Black soldier fly larvae
Black soldier fly (
Hermetia illucens) larvae are able to rapidly consume large amounts of organic material when kept at around 30 °C.
Black soldier fly larvae can reduce the dry matter of the organic waste
by 73% and convert 16–22% of the dry matter in the waste to biomass. The resulting compost still contains nutrients and can be used for
biogas production, or further traditional composting or
vermicomposting The larvae are rich in fat and protein, and can be used as, for example, animal feed or
biodiesel production. Enthusiasts have experimented with a large number of different waste products.
Bokashi
Bokashi is not composting as defined earlier, rather an alternative technology. It
ferments (rather than decomposes) the input organic matter and feeds the result to the
soil food web (rather than producing a soil conditioner). The process involves adding
Lactobacilli to the input in an airtight container kept at normal room temperature. These bacteria ferment
carbohydrates to
lactic acid, which preserves the input. After this is complete the preserve is mixed into soil, converting the lactic acid to
pyruvate, which enables soil life to consume the result.
Bokashi is typically applied to
food waste
from households, workplaces and catering establishments, because such
waste normally holds a good proportion of carbohydrates; it is also
applied to other organic waste by supplementing carbohydrates. Household
containers ("bokashi bins") typically give a batch size of 5–10
kilograms (11–22 lb), accumulated over a few weeks. In horticultural
settings batches can be orders of magnitude greater.
Inside
a recently started bokashi bin. Food scraps are raised on a perforated
plate (to drain runoff) and are partly covered by a layer of bran
inoculated with Lactobacilli
Bokashi offers several advantages:
- Fermentation retains all the original carbon and energy. (In
comparison, composting loses at least 50% of these and 75% or more in
amateur use; composting also loses nitrogen, a macronutrient of plants, by emitting ammonia and the potent greenhouse gas nitrous oxide.)
- Virtually the full range of food waste is accepted, without the exclusions of composting. The exception is large bones.
- Being airtight, the container inherently traps smells, and when
opened the smell of fermentation is far less offensive than
decomposition. Hence bokashi bins usually operate indoors, in or near
kitchens.
- Similarly the container neither attracts insect pests nor allows them ingress.
- The process is inherently hygienic because lactic acid is a natural bactericide and anti-pathogen; even its own fermentation is self-limiting.
- Both preservation and consumption complete within a few weeks rather than months.
- The preserve can be stored until needed, for example if ground is frozen or waterlogged.
- The increased activity of the soil food web improves the soil texture, especially by worm action - in effect this is in-soil vermicomposting.
The importance of the first advantage should not be underestimated: the mass of any
ecosystem depends on the energy it captures. Plants depend upon the soil ecosystem making nutrients available within
soil water.
Therefore, the richer the ecosystem, the richer the plants. (Plants can
also take up nutrients from added chemicals, but these are at odds with
the purpose of composting).
Other systems at household level
Hügelkultur (raised garden beds or mounds)
An almost completed Hügelkultur bed; the bed does not have soil on it yet.
The practice of making raised garden beds or mounds filled with rotting wood is also called
hügelkultur in German. It is in effect creating a
nurse log that is covered with soil.
Benefits of
hügelkultur garden beds include water retention and warming of soil. Buried wood acts like a
sponge as it decomposes, able to capture water and store it for later use by crops planted on top of the
hügelkultur bed.
Compost tea
Compost teas are defined as water extracts leached from composted materials.
Compost teas are generally produced from adding one volume of compost
to 4–10 volumes of water, but there has also been debate about the
benefits of aerating the mixture.
Field studies have shown the benefits of adding compost teas to crops
due to the adding of organic matter, increased nutrient availability and
increased microbial activity. They have also been shown to have an effect on plant pathogens.
Worm Hotels
Worm Hotels accommodate useful worm in ideal conditions.
Related technologies
Organic ingredients intended for composting can also be used to generate
biogas through
anaerobic digestion. This process stabilizes organic material. The residual material, sometimes in combination with
sewage sludge can be treated by a composting process before selling or giving away the compost.
Regulations
There are process and product guidelines in Europe that date to the
early 1980s (Germany, the Netherlands, Switzerland) and only more
recently in the UK and the US. In both these countries, private trade
associations within the industry have established loose standards, some
say as a stop-gap measure to discourage independent government agencies
from establishing tougher consumer-friendly standards.
The USA is the only Western country that does not distinguish
sludge-source compost from green-composts, and by default in the USA 50%
of states expect composts to comply in some manner with the federal EPA
503 rule promulgated in 1984 for sludge products.
Compost is regulated in Canada and Australia as well.
Examples
Edmonton Composting Facility
Large-scale composting systems are used by many urban areas around the world.
- The world's largest municipal co-composter for municipal solid waste (MSW) is the Edmonton Composting Facility in Edmonton, Alberta, Canada, which turns 220,000 tonnes of municipal solid waste and 22,500 dry tonnes of sewage sludge per year into 80,000 tonnes of compost. The facility is 38,690 m2 (416,500 sq ft) in area, equivalent to 4½ Canadian football fields, and the operating structure is the largest stainless steel building in North America.
- In 2006, Qatar awarded Keppel Seghers Singapore, a subsidiary of Keppel Corporation, a contract to begin construction on a 275,000 tonne/year anaerobic digestion
and composting plant licensed by Kompogas Switzerland. This plant, with
15 independent anaerobic digesters, will be the world's largest
composting facility once fully operational in early 2011 and forms part
of Qatar's Domestic Solid Waste Management Centre, the largest
integrated waste management complex in the Middle East.
- Another large municipal solid waste composter is the Lahore Composting Facility in Lahore,
Pakistan, which has a capacity to convert 1,000 tonnes of municipal
solid waste per day into compost. It also has a capacity to convert
substantial portion of the intake into refuse-derived fuel
(RDF) materials for further combustion use in several energy consuming
industries across Pakistan, for example in cement manufacturing
companies where it is used to heat cement kilns. This project has also been approved by the Executive Board of the United Nations Framework Convention on Climate Change for reducing methane emissions, and has been registered with a capacity of reducing 108,686 tonnes carbon dioxide equivalent per annum.
- Kew Gardens in London has one of the biggest non-commercial compost heaps in Europe.
- Compost is used as a soil amendment in organic farming.
- Within an EU project conducted in Portugal and Spain, organic
compost has been successfully used to revive degraded landscapes by
improving the quality of soil.
Commercial composts
The
term “compost” can also refer to potting mixes which are bagged up and
sold commercially in garden centres and other outlets.
This may include composted materials such as manure and peat, but is
also likely to contain loam, fertilisers, sand, grit, etc. Varieties
include multi-purpose composts designed for most aspects of planting,
John Innes formulations
[48],
growbags, designed to have crops such as tomatoes directly planted
into them. There are also a range of specialist composts available, e.g.
for vegetables, orchids, houseplants, hanging baskets, roses,
ericaceous plants, seedlings, potting on etc.
History
Composting as a recognized practice dates to at least the early Roman Empire, and was mentioned as early as
Cato the Elder's 160 BCE piece
De Agri Cultura.
Traditionally, composting involved piling organic materials until the
next planting season, at which time the materials would have decayed
enough to be ready for use in the soil. The advantage of this method is
that little working time or effort is required from the composter and it
fits in naturally with agricultural practices in temperate climates.
Disadvantages (from the modern perspective) are that space is used for a
whole year, some nutrients might be leached due to exposure to
rainfall, and disease-producing organisms and insects may not be
adequately controlled.
Composting was somewhat modernized beginning in the 1920s in Europe as a tool for
organic farming. The first industrial station for the transformation of urban organic materials into compost was set up in
Wels, Austria in the year 1921. Early frequent citations for propounding composting within farming are for the German-speaking world
Rudolf Steiner, founder of a farming method called
biodynamics, and
Annie Francé-Harrar, who was appointed on behalf of the government in
Mexico and supported the country 1950–1958 to set up a large humus organization in the fight against erosion and
soil degradation.
In the English-speaking world it was
Sir Albert Howard who worked extensively in
India on sustainable practices and
Lady Eve Balfour
who was a huge proponent of composting. Composting was imported to
America by various followers of these early European movements by the
likes of
J.I. Rodale (founder of Rodale Organic Gardening), E.E. Pfeiffer (who developed scientific practices in biodynamic farming),
Paul Keene (founder of Walnut Acres in Pennsylvania), and
Scott and
Helen Nearing (who inspired the
back-to-the-land movement
of the 1960s). Coincidentally, some of the above met briefly in India -
all were quite influential in the U.S. from the 1960s into the 1980s.
Society and culture
Terminology
The term "composting" is used worldwide with differing meanings.
"Humanure" is a
portmanteau of
human and
manure, designating human excrement (
feces and
urine)
that is recycled via composting for agricultural purposes. The term was
first used in 1994 in a book by Joseph Jenkins that advocates the use
of this
organic soil amendment. The term humanure is used by compost enthusiasts in the United States but not widely used elsewhere.
Because the term "humanure" has no authoritative definition it is
subject to various uses. News reporters may use the term also for
sewage sludge or
biosolids.
Bonn, Germany
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