Compost

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Compost 

 

Community-level composting in a rural area in Germany

 

Backyard composter

 

Compost (/ˈkɒmpɒst/ or /ˈkɒmpoʊst/) is organic matter that has been decomposed in a process called composting. This process recycles various organic materials otherwise regarded as waste products and produces a soil conditioner (the compost). 

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

Home compost barrel

 

Materials in a compost pile

 

Food scraps compost heap

 

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

Composting can destroy some pathogens or unwanted seeds, those that are destroyed by temperatures above 50 °C (122 °F).^{[citation needed]} Unwanted living plants (or weeds) can be discouraged by covering with mulch/compost.

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.

Industrial composting systems are being installed to treat organic solid waste and recycle it rather than landfilling it. It is one example of an advanced waste processing system. Mechanical sorting of mixed waste streams combined with anaerobic digestion or in-vessel composting is called mechanical biological treatment. It is increasingly being used in developed countries due to regulations controlling the amount of organic matter allowed in landfills. Treating biodegradable waste before it enters a landfill reduces global warming from fugitive methane; untreated waste breaks down anaerobically in a landfill, producing landfill gas that contains methane, a potent greenhouse gas.

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

Industrial-scale composting can be carried out in the form of in-vessel composting, aerated static pile composting, vermicomposting, or windrow composting.

Vermicomposting

Worms in a bin being harvested

Main article: Vermicompost

 

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.

Vermicomposting can also be applied for treatment of sewage sludge.

Composting toilets

Composting toilet with a seal in the lid in Germany

 

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 Hotel in Amsterdam

 

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.

Many countries such as Wales and some individual cities such as Seattle and San Francisco require food and yard waste to be sorted for composting (San Francisco Mandatory Recycling and Composting Ordinance).

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

Compost Basket

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.

Resource recovery

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Resource_recovery 

 

Resource recovery is using wastes as an input material to create valuable products as new outputs. The aim is to reduce the amount of waste generated, thereby reducing the need for landfill space, and optimising the values created from waste. Resource recovery delays the need to use raw materials in the manufacturing process. Materials found in municipal solid waste, construction and demolition waste, commercial waste and industrial wastes can be used to recover resources for the manufacturing of new materials and products. Plastic, paper, aluminium, glass and metal are examples of where value can be found in waste.

Resource recovery goes further than just the management of waste. Resource recovery is part of a circular economy, in which the extraction of natural resources and generation of wastes are minimised, and in which materials and products are designed more sustainably for durability, reuse, repairability, remanufacturing and recycling. Life-cycle analysis (LCA) can be used to compare the resource recovery potential of different treatment technologies. Resource recovery can be enabled by changes in government policy and regulation, circular economy infrastructure such as improved 'binfrastructure' to promote source separation and waste collection, reuse and recycling, innovative circular business models, and valuing materials and products in terms of their economic but also their social and environmental costs and benefits. For example, organic materials can be treated by composting and anaerobic digestion and turned into energy, compost or fertilizer. Similarly, wastes currently stored in industrial landfills and around old mines can be treated with bioleaching and engineered nanoparticles to recover metals such as Lithium, Cobalt and Vanadium for use in low-carbon technologies such as electric vehicles and wind turbines.

Resource recovery can also be an aim in the context of sanitation. Here, the term refers to approaches to recover the resources that are contained in wastewater and human excreta (urine and feces). The term "toilet resources" has come into use recently. Those resources include: nutrients (nitrogen and phosphorus), organic matter, energy and water. This concept is also referred to as ecological sanitation. Separation of waste flows can help make resource recovery simpler. Examples include keeping urine separate from feces (as in urine diversion toilets) and keeping greywater and blackwater separate in municipal wastewater systems.

Materials used as a source

Solid waste

Steel crushed and baled for recycling

 

Recycling is a resource recovery practice that refers to the collection and reuse of disposed materials such as empty beverage containers. The materials from which the items are made can be reprocessed into new products. Material for recycling may be collected separately from general waste using dedicated bins and collection vehicles, or sorted directly from mixed waste streams. 

The most common consumer products recycled include aluminium such as beverage cans, copper such as wire, steel food and aerosol cans, old steel furnishings or equipment, polyethylene and PET bottles, glass bottles and jars, paperboard cartons, newspapers, magazines and light paper, and corrugated fiberboard boxes. 

PVC, LDPE, PP, and PS (see resin identification code) are also recyclable. These items are usually composed of a single type of material, making them relatively easy to recycle into new products. The recycling of complex products (such as computers and electronic equipment) is more difficult, due to the additional dismantling and separation required. 

The type of recycling material accepted varies by city and country. Each city and country have different recycling programs in place that can handle the various types of recyclable materials.

Wastewater and excreta

Valuable resources can be recovered from wastewater, sewage sludge, fecal sludge and human excreta. These include water, energy, and fertilizing nutrients nitrogen, phosphorus, potassium, as well as micro-nutrients such as sulphur and organic matter. There is also increasing interest for recovering other raw materials from wastewater, such as bioplastics and metals such as silver. Originally, wastewater systems were designed only to remove excreta and wastewater from urban areas. Water was used to flush away the waste, often discharging into nearby waterbodies. Since the 1970s, there has been increasing interest in treating the wastewater to protect the environment, and efforts focused primarily on cleaning the water at the end of the pipe. Since around the year 2003, the concepts of ecological sanitation and sustainable sanitation have emerged with the focus on recovering resources from wastewater. As of 2016, the term "toilet resources" came into use, and encouraged more attention to the potential for resource recovery from toilets.

The following resources can be recovered:

• Water: In many water-scarce areas there are increasing pressures to recover water from wastewater. In 2006, the World Health Organization, in collaboration with the Food and Agriculture Organization of the United Nations (FAO) and the United Nations Environment Program (UNEP), developed guidelines for safe use of wastewater. In addition, many national governments have their own regulations regarding the use of recovered water. Singapore for example aims to recover enough water from its wastewater systems to meet the water needs of half the city. They call this NEWater. Another related concept for wastewater reuse is sewer mining.
• Energy: The production of biogas from wastewater sludge is now common practice at wastewater treatment plants. In addition, a number for methods have been researched regarding use of wastewater sludge and excreta as fuel sources.
• Fertilizing nutrients: Human excreta contains nitrogen, phosphorus, potassium and other micronutrients that are needed for agricultural production. These can be recovered through chemical precipitation or stripping processes, or simply by use of the wastewater or sewage sludge. However, reuse of sewage sludge poses risks due to high concentrations of undesirable compounds, such as heavy metals, environmental persistent pharmaceutical pollutants and other chemicals. Since the majority of fertilizing nutrients are found in excreta, it can be useful to separate the excreta fractions of wastewater (e.g. toilet waste) from the rest of the wastewater flows. This reduces the risk for undesirable compounds and reduces the volume that needs to be treated before applying recovered nutrients in agricultural production.

Other methods are also being developed for transforming wastewater into valuable products. Growing Black Soldier Flies in excreta or organic waste can produce fly larvae as a protein feed. Other researchers are harvesting fatty acids from wastewater to make bioplastics.

Organic matter

An active compost heap.

 

Disposed materials that are organic in nature, such as plant material, food scraps, and paper products, can be recycled using biological composting and digestion processes to decompose the organic matter. The resulting organic material is then recycled as mulch or compost for agricultural or landscaping purposes. In addition, waste gas from the process (such as methane) can be captured and used for generating electricity and heat (CHP/cogeneration) maximising efficiencies. The intention of biological processing is to control and accelerate the natural process of decomposition of organic matter. 

There is a large variety of composting and digestion methods and technologies varying in complexity from simple home compost heaps, to small town scale batch digesters, industrial-scale enclosed-vessel digestion of mixed domestic waste (see mechanical biological treatment). Methods of biological decomposition are differentiated as being aerobic or anaerobic methods, though hybrids of the two methods also exist.

Anaerobic digestion of the organic fraction of municipal solid waste (MSW) has been found to be more environmentally effective, than landfill, incineration or pyrolysis. Life cycle analysis (LCA) was used to compare different technologies. The resulting biogas (methane) though must be used for cogeneration (electricity and heat preferably on or close to the site of production) and can be used with a little upgrading in gas combustion engines or turbines. With further upgrading to synthetic natural gas it can be injected into the natural gas network or further refined to hydrogen for use in stationary cogeneration fuel cells. Its use in fuel cells eliminates the pollution from products of combustion. There is a large variety of composting and digestion methods and technologies varying in complexity from simple home compost heaps, to small town scale batch digesters, industrial-scale, enclosed-vessel digestion of mixed domestic waste (see mechanical biological treatment). Methods of biological decomposition are differentiated as being aerobic or anaerobic methods, though hybrids of the two methods also exist.

Recovery methods

In many countries, source-separated curbside collection is one method of resource recovery.

Australia

In Australia, households are provided with several bins: one for recycling (yellow lid), another for general waste (usually a red lid) and another for garden materials (green lid). The garden recycling bin is provided by the municipality if requested. Some localities have dual-stream recycling, with paper collected in bags or boxes and all other materials in a recycling bin. In either case, the recovered materials are trucked to a materials recovery facility for further processing. 

Municipal, commercial and industrial, construction and demolition debris is dumped at landfills and some is recycled. Household disposal materials are segregated: recyclables sorted and made into new products, and unusable material is dumped in landfill areas. According to the Australian Bureau of Statistics (ABS), the recycling rate is high and is "increasing, with 99% of households reporting that they had recycled or reused within the past year (2003 survey), up from 85% in 1992". In 2002–03 "30% of materials from municipalities, 45% from commercial and industrial generators and 57% from construction and demolition debris" was recycled. Energy is produced is part of resource recovery as well: some landfill gas is captured for fuel or electricity generation, although this is considered the last resort, as the point of resource recovery is avoidance of landfill disposal altogether.

Sustainability

Resource recovery is a key component in a business' ability to maintaining ISO14001 accreditation. Companies are encouraged to improve their environmental efficiencies each year. One way to do this is by changing a company from a system of managing wastes to a resource recovery system (such as recycling: glass, food waste, paper and cardboard, plastic bottles etc.)

Education and awareness in the area of resource recovery is increasingly important from a global perspective of resource management. The Talloires Declaration is a declaration for sustainability concerned about the unprecedented scale and speed of environmental pollution and degradation, and the depletion of natural resources. Local, regional, and global air pollution; accumulation and distribution of toxic wastes; destruction and depletion of forests, soil, and water; depletion of the ozone layer and emission of "green house" gases threaten the survival of humans and thousands of other living species, the integrity of the earth and its biodiversity, the security of nations, and the heritage of future generations. Several universities have implemented the Talloires Declaration by establishing environmental management and resource recovery programs. University and vocational education are promoted by various organizations, e.g., WAMITAB and Chartered Institution of Wastes Management. Many supermarkets encourage customers to use their reverse vending machines to deposit used purchased containers and receive a refund from the recycling fees. Brands that manufacture such machines include Tomra and Envipco. 

In 2010, CNBC aired the documentary Trash Inc: The Secret Life of Garbage about waste, what happens to it when it's "thrown away", and its impact on the world.

Extended producer responsibility

Extended producer responsibility (EPR) is a pricing strategy that promotes integrating all costs associated with a given product throughout its life cycle. Having the market price also reflect the "end-of-life disposal costs" encourages more accuracy in pricing. Extended producer responsibility is meant to impose accountability over the entire lifecycle of products, from production, to packaging, to transport and disposal or reuse. EPR requires firms that manufacture, import and/or sell products to be responsible for those products throughout the life and disposal or reuse of products.

Ammonium nitrate

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Ammonium_nitrate 

 

Ammonium nitrate

Names
IUPAC name Ammonium nitrate
Identifiers
CAS Number	6484-52-2
3D model (JSmol)	Interactive image
ChEBI	CHEBI:63038
ChEMBL	ChEMBL1500032
ChemSpider	21511
ECHA InfoCard	100.026.680
EC Number	229-347-8
PubChem CID	22985
RTECS number	BR9050000
UNII	T8YA51M7Y6
UN number	0222 – with > 0.2% combustible substances 1942 – with ≤ 0.2% combustible substances 2067 – fertilizers 2426 – liquid
CompTox Dashboard (EPA)	DTXSID2029668
InChI[show]
SMILES[show]
Properties
Chemical formula	NH4NO3
Molar mass	80.043 g/mol
Appearance	colorless
Density	1.725 g/cm3 (20 °C)
Melting point	169.6 °C (337.3 °F; 442.8 K)
Boiling point	approx. 210 °C (410 °F; 483 K) decomposes
Solubility in water	Endothermic 118 g/100 ml (0 °C) 150 g/100 ml (20 °C) 297 g/100 ml (40 °C) 410 g/100 ml (60 °C) 576 g/100 ml (80 °C) 1024 g/100 ml (100 °C)[1]
Magnetic susceptibility (χ)	-33.6·10−6 cm3/mol
Structure
Crystal structure	trigonal
Explosive data
Shock sensitivity	very low
Friction sensitivity	very low
Detonation velocity	2500 m/s
Hazards
Main hazards	Explosive, Oxidizer
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H201, H271, H319
GHS precautionary statements	P220, P221, P271, P280, P264, P372
NFPA 704 (fire diamond)	0 1 3 OX
Lethal dose or concentration (LD, LC):
LD50 (median dose)	2085–5300 mg/kg (oral in rats, mice)
Related compounds
Other anions	Ammonium nitrite
Other cations	Sodium nitrate Potassium nitrate Hydroxylammonium nitrate
Related compounds	Ammonium perchlorate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Ammonium nitrate is a chemical compound with the chemical formula NH₄NO₃. It is a white crystalline solid consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is predominantly used in agriculture as a high-nitrogen fertilizer. Global production was estimated at 21.6 million tonnes in 2017.

Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction. It is the major constituent of ANFO, a popular industrial explosive which accounts for 80% of explosives used in North America; similar formulations have been used in improvised explosive devices.

Many countries are phasing out its use in consumer applications due to concerns over its potential for misuse. Accidental ammonium nitrate explosions have killed thousands of people since the early 20th century.

Occurrence

Ammonium nitrate is found as the natural mineral gwihabaite – the ammonium analogue of saltpetre – in the driest regions of the Atacama Desert in Chile, often as a crust on the ground or in conjunction with other nitrate, iodate, and halide minerals. Ammonium nitrate was mined there in the past, but virtually 100% of the chemical now used is synthetic.

Production, reactions and crystalline phases

The industrial production of ammonium nitrate entails the acid-base reaction of ammonia with nitric acid:

HNO₃ + NH₃ → NH₄NO₃

Ammonia is used in its anhydrous form (a gas) and the nitric acid is concentrated. The reaction is violent owing to its highly exothermic nature. After the solution is formed, typically at about 83% concentration, the excess water is evaporated off to leave an ammonium nitrate (AN) content of 95% to 99.9% concentration (AN melt), depending on grade. The AN melt is then made into "prills" or small beads in a spray tower, or into granules by spraying and tumbling in a rotating drum. The prills or granules may be further dried, cooled, and then coated to prevent caking. These prills or granules are the typical AN products in commerce.

The ammonia required for this process is obtained by the Haber process from nitrogen and hydrogen. Ammonia produced by the Haber process can be oxidized to nitric acid by the Ostwald process. Another production method is a variant of the nitrophosphate process:

Ca(NO₃)₂ + 2 NH₃ + CO₂ + H₂O → 2 NH₄NO₃ + CaCO₃

The products, calcium carbonate and ammonium nitrate, may be separately purified or sold combined as calcium ammonium nitrate. 

Ammonium nitrate can also be made via metathesis reactions:

(NH₄)₂SO₄ + Ba(NO₃)₂ → 2 NH₄NO₃ + BaSO₄

NH₄Cl + AgNO₃ → NH₄NO₃ + AgCl

Reactions

As ammonium nitrate is a salt, both the cation, NH₄⁺, and the anion, NO₃⁻, may take part in chemical reactions. 

Solid ammonium nitrate decomposes on heating. At temperatures below around 300 °C, the decomposition mainly produces nitrous oxide and water:

NH₄NO₃ → N₂O + 2H₂O

At higher temperatures, the following reaction predominates.

2NH₄NO₃ → 2N₂ + O₂ + 4H₂O

Both decomposition reactions are exothermic and their products are gas. Under certain conditions, this can lead to a runaway reaction, with the decomposition process becoming explosive. See § disasters for details. Many ammonium nitrate disasters, with loss of lives, have occurred.

The red–orange colour in an explosion cloud is due to nitrogen dioxide, a secondary reaction product.

Crystalline phases

A number of crystalline phases of ammonium nitrate have been observed. The following occur under atmospheric pressure.

Phase	Temperature (°C)	Symmetry
(liquid)	(above 169.6)
I	169.6 to 125.2	cubic
II	125.2 to 84.2	tetragonal
III	84.2 to 32.3	α-rhombic
IV	32.3 to −16.8	β-rhombic
V	below −16.8	tetragonal

Both the β-rhombic to α-rhombic forms are potentially present at ambient temperature in many parts of the world but have a 3.6% difference in density. As a result, this phase transition and attending change of volume, with the practical consequence that ammonium nitrate formed as solid rocket motor propellant develops cracks. For this reason, phase stabilized ammonium nitrate (PSAN) which incorporates metal halides as stabilisers has been investigated.

Applications

Fertilizer

Ammonium nitrate is an important fertilizer with NPK rating 34-0-0 (34% nitrogen). It is less concentrated than urea (46-0-0), giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that it is more stable and does not rapidly lose nitrogen to the atmosphere.

Explosives

Ammonium nitrate is an ingredient in certain explosives. Examples of explosives containing ammonium nitrate include:

• Astrolite (ammonium nitrate and hydrazine rocket fuel)
• Amatol (ammonium nitrate and TNT)
• Ammonal (ammonium nitrate and aluminum powder)
• Amatex (ammonium nitrate, TNT and RDX)
• ANFO (ammonium nitrate and fuel oil)
• DBX (ammonium nitrate, RDX, TNT and aluminum powder)
• Tovex (ammonium nitrate and methylammonium nitrate)
• Minol (explosive) (ammonium nitrate, TNT and aluminum powder)
• Goma-2 (ammonium nitrate, nitroglycol, Nitrocellulose, Dibutyl phthalate and fuel)

Mixture with fuel oil

ANFO is a mixture of 94% ammonium nitrate ("AN") and 6% fuel oil ("FO") widely used as a bulk industrial explosive. It is used in coal mining, quarrying, metal mining, and civil construction in undemanding applications where the advantages of ANFO's low cost and ease of use matter more than the benefits offered by conventional industrial explosives, such as water resistance, oxygen balance, high detonation velocity, and performance in small diameters.

Terrorism

Ammonium nitrate-based explosives were used in the Sterling Hall bombing in Madison, Wisconsin, 1970, the Oklahoma City bombing in 1995, the 2011 Delhi bombings, the 2011 bombing in Oslo, and the 2013 Hyderabad blasts. 

In November 2009, the government of the North West Frontier Province (NWFP) of Pakistan imposed a ban on ammonium sulfate, ammonium nitrate, and calcium ammonium nitrate fertilizers in the former Malakand Division – comprising the Upper Dir, Lower Dir, Swat, Chitral, and Malakand districts of the NWFP – following reports that those chemicals were used by militants to make explosives. Due to these bans, "Potassium chlorate – the stuff that makes safety matches catch fire – has surpassed fertilizer as the explosive of choice for insurgents."

Niche uses

Ammonium nitrate is used in some instant cold packs, as its dissolution in water is highly endothermic. It also was used, in combination with independently explosive "fuels" such as guanidine nitrate, as a cheaper (but less stable) alternative to 5-aminotetrazole in the inflators of airbags manufactured by Takata Corporation, which were recalled as unsafe after killing 14 people.

A solution of ammonium nitrate with nitric acid called Cavea-b showed promise for use in spacecraft as a more energetic alternative to the common monopropellant hydrazine. A number of trials were carried out in the 1960s but the substance was not adopted by NASA.

Safety, handling, and storage

Numerous safety guidelines are available for storing and handling ammonium nitrate. Health and safety data are shown on the safety data sheets available from suppliers and from various governments.

Pure ammonium nitrate does not burn, but as a strong oxidizer, it supports and accelerates the combustion of organic (and some inorganic) material. It should not be stored near combustible substances. 

While ammonium nitrate is stable at ambient temperature and pressure under many conditions, it may detonate from a strong initiation charge. It should not be stored near high explosives or blasting agents. 

Molten ammonium nitrate is very sensitive to shock and detonation, particularly if it becomes contaminated with incompatible materials such as combustibles, flammable liquids, acids, chlorates, chlorides, sulfur, metals, charcoal and sawdust.

Contact with certain substances such as chlorates, mineral acids and metal sulfides, can lead to vigorous or even violent decomposition capable of igniting nearby combustible material or detonating.

Ammonium nitrate begins decomposition after melting, releasing NO
x , HNO₃, NH
₃ and H₂O. It should not be heated in a confined space. The resulting heat and pressure from decomposition increases the sensitivity to detonation and increases the speed of decomposition. Detonation may occur at 80 atmospheres. Contamination can reduce this to 20 atmospheres.

Ammonium nitrate has a critical relative humidity of 59.4%, above which it will absorb moisture from the atmosphere. Therefore, it is important to store ammonium nitrate in a tightly sealed container. Otherwise, it can coalesce into a large, solid mass. Ammonium nitrate can absorb enough moisture to liquefy. Blending ammonium nitrate with certain other fertilizers can lower the critical relative humidity.

The potential for use of the material as an explosive has prompted regulatory measures. For example, in Australia, the Dangerous Goods Regulations came into effect in August 2005 to enforce licensing in dealing with such substances. Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse. Additional uses such as education and research purposes may also be considered, but individual use will not. Employees of those with licenses to deal with the substance are still required to be supervised by authorized personnel and are required to pass a security and national police check before a license may be granted.

Health hazards

Health and safety data are shown on the material safety data sheets, which are available from suppliers and can be found on the internet.

Ammonium nitrate is not hazardous to health and is usually used in fertilizer products.

Ammonium nitrate has an LD₅₀ of 2217 mg/kg, which for comparison is about two-thirds that of table salt.

Disasters

Ammonium nitrate decomposes, non-explosively, into the gases nitrous oxide and water vapor when heated. However, it can be induced to decompose explosively by detonation. Large stockpiles of the material can also be a major fire risk due to their supporting oxidation, a situation which can easily escalate to detonation. Explosions are not uncommon: relatively minor incidents occur most years, and several large and devastating explosions have also occurred. Examples include the Oppau explosion of 1921 (one of the largest artificial non-nuclear explosions), the Texas City disaster of 1947, the 2015 Tianjin explosions in China, and the 2020 Beirut explosion.  Ammonium nitrate can explode through two mechanisms:

• Shock-to-detonation transition. An explosive charge within or in contact with a mass of ammonium nitrate causes the ammonium nitrate to detonate. Examples of such disasters are Kriewald, Morgan (present-day Sayreville, New Jersey), Oppau, and Tessenderlo.
• Deflagration to detonation transition. The ammonium nitrate explosion results from a fire that spreads into the ammonium nitrate (Texas City, TX; Brest; West, TX; Tianjin; Beirut), or from ammonium nitrate mixing with a combustible material during the fire (Repauno, Cherokee, Nadadores). The fire must be confined at least to a degree for successful transition from a fire to an explosion.