Transform organic waste into nutrient-rich soil while reducing landfill waste, conserving resources, and improving plant health. Composting is a natural process that involves the controlled decomposition of organic matter by microorganisms. It offers a sustainable and environmentally friendly way to manage waste and enhance soil fertility.
Composting was first documented in the early Roman Empire detailing rudimentary piling of decaying organic matter that would decompose ready for the following planting season. Modernisation began in the 1920’s as a tool for organic farming. The first transfer station for the recycling or organic resource materials was set up in Weis, Austria in 1921.
Compost is commonly a mixture of decomposing plant and food waste, recycled organic materials and manure by aerobic methods. It is used as a plant fertiliser to improve soils physical, chemical and biological properties. The mixture is rich in plant nutrients and organisms like bacteria, protozoa, nematodes and fungi. Compost improves soil fertility in a range of settings, gardens, horticulture, agriculture and farming. Compost increases humic acid in the soil acting as a conditioner and fertiliser reducing the need for chemical fertilisers, suppressing pathogens and degradation associated with soil.
As a simple description composting is gathering a mixture of green waste and brown waste. Green waste – leaves, grass and food waste are rich in nitrogen. Brown waste – stalks, paper and wood chips are rich in carbon. Composting can be a multistage process requiring measured inputs of water, nitrogen and carbon rich materials. Decomposition is can also be aided by shredding and aeriation by turning the materials in open piles commonly known as ‘windrows’. Fungi, earthworms and bacteria break down the organic material into heat, carbon dioxide and ammonia.
Composting provides an excellent environmental alternative to landfilling organic matter due to the reduction in methane emissions usually associated with anaerobic breakdown of organic matter in landfills. Offering additional environmental and economic benefits.
Composting requires four important component materials.
Active management of the composting pile is required to maintain sufficient heat (54-71c) and moisture levels allowing microorganisms to heat up the materials. Carbon to nitrogen ratios of 25:1 creates greater efficiency in breaking down the materials while retaining greater heat produces compost more quickly at a ratio of 30:1. Above this level nitrogen is starved and below 15 too much ammonia is produced.
Organisms are present in composting to help break down the organic materials with the correct mixture of carbon, nitrogen, oxygen and water. Chemical decomposers perform chemical decomposition of the materials while physical decomposers process the waste materials by grinding, tearing, chewing and digesting.
Chemical Decomposers – depending on the phase of composting, thermophilic or mesophilic, bacteria process carbon and nitrogen while excreting nitrogen, phosphorus and magnesium.
Mesophilic bacteria raise the temperature through the break down of materials through oxidation of the organic materials. Thermophilic bacteria thrive at higher temperature ranges (40-60c). Actinomycetota break down heavier materials like paper and bark in which larger organic molecules like lignin and cellulose are present. Also making carbon, nitrogen and ammonia available for plant digestion.
Fungi such as molds and yeasts also help break down larger lignin and cellulose molecules that bacteria cannot. While Protozoa contribute to the break down of organic matter and consume bacteria and fungi.
Physical Decomposers – such as ants creating nests, beetles and grubs feeding on decaying materials, earthworms secreting nutrients, flies add bacteria, millipedes, snails and slugs all contribute to the process.
If optimal conditions are met from the ingredients for composting the materials will go through 3 phases:
The time required to compost materials depends on the volume of materials, the granularity of the materials, mixing and aeriation. Larger amounts of materials can reach higher temperatures and remain in thermophilic stages for days or weeks. Hot composting is usually the preferred method for larger scale municipal or agricultural operations.
Cold composting takes much longer to complete. Smaller piles, usually made from household and garden wastes over longer periods. Aeriation by turning is generally not necessary unless waterlogged or from continual compaction.
Due to the higher temperatures achieved in hot composting pathogens are generally killed off making the compost suitable for use. Temperatures in which the pathogens die depends on the temperature, the type of pathogen and the pH level. It is advised that for compost that has not attained a thermophilic phase sufficient personal protective equipment (PPE) is used.
The activity of composting has multiple benefits throughout the supply chain. It reduces wastes, these wastes are often sent to landfill, which can cause harmful methane gas when buried. Composting sequesters carbon in the soil and added compost. Compost are recycled materials that can aid in soil enrichment. Adding organic matter, increasing nutrient content and biodiversity of microbes. Conserves and reduces water use and runoff. Improves plant growth and crop yield. Reduces the reliance on chemical fertilisers. Small scale operations tend to keep waste and compost local, so no additional footprint is associated with the recycling process. Promotes local food production. There is an economic benefit in creating green focused employment. Reduction in the logistics costs of waste removal and disposal.
Compostable materials or feedstock can include a range of residual, agricultural and commercial organic waste streams. Household food, garden or ‘yard’ waste can be collected for large-scale municipal operations or local community-based composting projects.
Organic Solid Waste – commonly described as green and brown waste and includes food waste, grass and garden wastes and fresh leaves. Animal By Products (ABP) can also be composted as nitrogen sources.
Brown organic wastes such as dried vegetation and wood materials, leaves, straw, woodchips, branches, logs, pine needles, sawdust and wood ash, paper and plain cardboard are carbon sources.
Animal Manure & Bedding – manure is a carbon source while bedding, straw and sawdust are great carbon sources. Sources of manure should be mixed with relevant carbon sources as can contain varying degrees of nitrogen.
Human Waste – or ‘Humanure’ in the context of composting as it is nutrient-rich organic materials high in nitrogen. Liquid human waste is high in phosphorus helping plants to convert sunlight into energy by photosynthesis.
Solid human waste can be collected in composting toilets or sewage sludge after appropriate treatment in sewage treatment centres. Capable design and treatment is necessary due to health risks posed by bacteria, viruses and contaminants such as pharmaceutical compounds. Urine can be used directly as does not contain the types of pathogens or contaminants in human solid waste.
Human Bodies – Human Composting, natural organic reduction or terramation has been a long standing practice. A rapid process has been developed where the human remains are encased in organic matter until thermophilic microbes decompose the body in as little as 1-2 months.
In-Vessel Composting
Describes the process of composting that takes place in a building or container. Systems can consist of tanks or bunkers where the airflow can be controlled. Air circulation can be injected from tubes under pressure and discharge filtered. Temperature and moisture is monitored by probes to optimise aerobic decomposition. This can also refer to aerated static pile composting when piles of compost are covered.
Aerated Static Pile Composting
Refers to a number of methods used to biodegrade organic materials using an optimum mixture or ingredients. This could be in windrows, open or covered or in containers. Aerated systems are usually operated by larger organisations processing large amounts of feedstocks.
Windrow Composting
Largely present in agricultural settings, windrow composting is the practice of piling organic waste matter like animal manure and crop residues into long piles and rows. The process is aerobic so known as Open Windrow Composting.
Composting Toilets
A composting toilet is a dry toilet that treats human waste by the natural decomposition of the organic matter usually by bacteria and fungi in controlled aerobic conditions. Sawdust, coconut coir or peat moss can be added after use to create optimal aerobic conditions helping with the creation and ratio of carbon to nitrogen. Longer retention within the unit kills of pathogens through mesophilic composting.
Vermicompost – Worm castings is the end product of the breakdown of organic matter by earthworms. Castings have less contaminants and higher level of saturated nutrients.
Black Soldier Flies – Larvae are able to rapidly consume large amounts of human waste. The compost contains large amounts of nutrients and can be used for further biogas production, traditional composting or vermicomposting.
Bokashi – From Japanese origin, Bokashi is a process that converts food waste and organic matter by fermentation rather than decomposing. This occurs by a special bacteria, applied directly to soil and has little waste, emissions or leachate and almost all input carbon and nutrients can be received back into the soil.
Co-Composting – Is a technique that processes solid organic waste with dewatered fecal sludge or sewage sludge.
Anaerobic Digestion – Is larger scale treatment of organic and food waste. It is combined with mechanical sorting to separate organic and food waste materials from packaging before adding to an anaerobic chamber where materials decompose. The key by products of biogas and the nutrient rich digestate from the process can be further treated for clean energy a soil enrichment fertiliser.
Agriculture & Gardening
Compost can be distributed mechanically to a wide range of industrial crops by spreading approximately a thin layer (25mm) of the recycled organic materials into the soil. This also helps greatly with soil erosion. In countries where composting is established it is often subsidised, so distribution is common-place and cheaper.
In smaller scale crops and often in green houses where temperature and moisture are under greater control, compost is applied as a top soil in rows. Compost is often a mix utilised to grow seedlings. The mix of nutrients can be managed according to the application required. Immature compost may contain phytotoxins and partially decomposed lignin so is not generally used for seedling maturation.
Compost Tea
Is made from the leachate from compost then fermented and applied to the soil. Similar to compost the mixture can be aerated. Adding to crops has proven to be beneficial by improved organic matter, nutrients and microbes while having an positive effect on plant pathogens and soil diseases.
Compost Extract
Are generally non-brewed or unfermented extracts from the compost leachate and a re mixed with a range of liquids to suit application requirements.
Commercial Sales of Compost
Compost is sold for a wide range of agriculture and garden uses in bags via garden centres and focused outlets. There are many different types of bagged compost designed for multiple aspects of planting requirements.
Compost Regulations
There are a range of processes and product guidelines across Europe. In the UK large composting facilities are governed by environmental permitting standards that stipulate capacity of operations. In the USA 26 States now require compost to be processed according to EPA Federal standards. The US Composting Council offers a voluntary paid for certification scheme and access to composts laboratory test showing a range of nutrients and contents. Food and garden waste collection is becoming increasingly common as the affects of methane are well documented in decamping organic waste, especially in landfill.
