Why use composting in carbon farming?
Composting is an aerobic process that reduces or prevents the release of methane during organic matter breakdown.
Methane is 26 times more potent than carbon dioxide as a greenhouse gas and is a significant contributor to global greenhouse gas emissions. Decomposing organic material in anaerobic conditions — by microbes in the absence of oxygen — releases methane into the atmosphere. Anaerobic fermentation is common in landfill and open stockpiles such as manure piles. Global emissions from waste have almost doubled since 1970 and now produce 3% of anthropogenic (human origin) emissions (IPCC 2014). About half of these emissions come from the anaerobic fermentation of solid waste disposal on land.
About 700 000 tonnes of organic waste material was composted in Western Australia in 2012. Each tonne of organic waste disposed of as landfill and broken down by anaerobic fermentation releases about one tonne of carbon dioxide equivalents (CO2-e) of greenhouse gases, mostly in the form of methane.
However, the aerobic process of composting does not produce methane because methane-producing microbes are not active in the presence of oxygen. Composting is one method to reduce methane emissions from organic waste currently stockpiled or sent to landfill. Composting practices that minimise anaerobic conditions and maximise aerobic conditions will be the most effective at reducing greenhouse gas emissions.
In the presence of oxygen and water, microbes, such as bacteria and fungi, use the carbon for energy and decompose the organic wastes. The benefits of this:
- heat, which kills pathogens and seeds, is produced
- the remaining carbon is stable humus that is weed-free and safe to use for agriculture, landscaping, gardening or other purposes.
What can be composted?
Organic wastes that can be composted include agricultural and forestry residue, manure, food processing, kitchen and garden waste, and biosolids (organic solids from treated sewage). Each year, Western Australia produces hundreds of thousands of tonnes of these by-products and wastes and these could be composted for environmental and soil health benefits.
At a local scale, there are 2 potential benefactors from composting to avoid methane production: waste disposal agencies who wish to avoid methane emissions from the anaerobic fermentation of waste, and farmers and horticulturalists who can use the composted products for agricultural benefits.
The composting procedure
Composting at a commercial scale has multiple steps and is a closely monitored process with temperature regulation and measured inputs of water, air, and the correct balance of carbon-rich and nitrogen-rich materials. Aerobic microbes convert the inputs into stabilised carbon for the soil, with by-products of heat, carbon dioxide and water.
Commercial facilities use a range of technologies to aerate the material, from tractor-drawn and self-propelled windrow turners to sophisticated aerated systems with automated controls.
Who are the major composters?
A 2012 national survey identified 126 organic reprocessing facilities, which receive about 5.5 million tonnes of organic waste each year from commercial, industrial and municipal sources. In Western Australia, there are about 30 facilities which predominantly feature open-air composting in windrows. There are also at least four facilities where continuous aerobic composting conditions are maintained by forcing air into the pile.
The clean energy regulator of Australia maintains an Emissions Reduction Fund Register for those seeking Australian carbon credit units. In 2013 there were 205 claims across all approved Carbon Farming Initiative methodologies (now covered under the Emissions Reduction Fund) and five of these claims were for composting-related methodologies.
Commercial composters, such as C-Wise and councils (e.g. the Southern Metropolitan Regional Council), have established large-scale composting facilities and have access to the Emissions Reduction Fund methodologies for claiming carbon credits from the mitigation of methane production.
Carbon benefits of composting
Carbon credits can be claimed for avoiding methane production using composting under the following Emissions Reduction Fund methodologies (emissions avoidance of landfill and alternative waste treatment):
- avoided emissions from diverting legacy waste from landfill through a composting alternative waste technology
- diversion of legacy waste to an alternative waste treatment facility
- enclosed mechanical processing and composting alternative waste treatment.
The industry association, Australian Organics Recyclers Association, is pursuing opportunities for farmers to share the benefits of using recycled organic products to improve soil performance and reduce the carbon footprint.
Applying compost to agricultural land improves soil productive capacity by:
- increasing soil buffering capacity and moisture holding capacity
- adding a source of organic matter that stimulates biological activity
- improving retention of soil fertiliser
- boosting the pool of nutrients
- providing a liming effect on the soil
- improving soil structure.
Compost reduces the need for applications of fertiliser, water, herbicide and pesticide, and it reduces soil erosion. Additionally, carbon sequestration increases directly through the compost material and indirectly through increased biomass of plant root systems.
Risks from using compost
- There may be increased water repellence of the soil from a buildup of soil organic carbon.
- Compost may be a possible source of fungal and other diseases to humans.
As livestock systems intensify, the amount of biodegradable waste increases and it must be disposed of in a way that does not harm the environment. Farmers can compost animal manures and agricultural waste to avoid or reduce harm to the environment.
The Rural Industries Research and Development Corporation estimates that managing animal manure in effluent lagoons (anaerobic fermentation) accounts for about 3% of Australia’s greenhouse gas emissions. Composting organic agricultural waste offers a solution to this problem while providing economic benefits.
Benefits of on-farm composting
- reduces the risk of spreading pathogens, parasites and weed seeds associated with directly applying manure to the land
- produces a stable product from composting farm organic wastes, such as manures, bedding and feed waste that can be used to improve and maintain soil quality and fertility
- can be used as an alternative depot site for community and industrial green waste
- reduces the need for applications of water, herbicide, pesticide, and purchased fertiliser
- eliminates the carbon footprint associated with transporting composted material to off-site destinations.
In 2016, there were 20 on-farm composting facilities in Australia, including 3 in Western Australia.
Carbon trading now happens through the Emissions Reduction Fund. One risk to potential carbon credit acquisition is the uncertainty of a future carbon price.
The process of composting materials causes greenhouse gas emissions from transport energy used to collect raw material and deliver the compost end-product, and from energy and water used in the composting process.
Inefficient composting processes can result in anaerobic (rather than aerobic) conditions which produces methane and nitrous oxide. Incomplete processing can allow pathogens and weed seeds to survive. Poor process control can lead to the risk of nuisance odours and complaints.
The Australian Government compiled case studies in the report, Solutions for waste management in regional and remote Australia. The case study of the City of Mandurah, Water Corporation and local on-farm composting operation, C-Wise, illustrates the successful recycling of 100% of the green waste and biosolids from a regional city for local economic and environmental benefit.
The technology used was based on design, simplicity, process control, cost of production, and energy and greenhouse gas savings. The process provides a technique that can be used by regional communities, feedlots, farmers and others to effectively process organic wastes.
Mandurah has a population over 65 000. All of its green waste and biosolids are recycled into organic-based fertiliser by composting on a local farm. This fertiliser is used by other farmers to build soil biology and performance at the same time as developing more resilient farming systems.
Each year, over 6000 tonnes of greenhouse gas emissions are being saved using this composting practice. The methodology has been adopted by several communities around Australia.
People and groups working in this space in Australia
- Australian Organic Recyclers Association
- Local producers who are members of the industry association can be found on the ‘Find a Composter’ website
- Waste Management Association of Australia
In Europe, in the 10 years from 2001 to 2011, composting of municipal waste increased from 10% to 15%, with Austria leading the way by composting 34% of its municipal waste. A critical part of this achievement was introducing separate collection bins for green waste for recycling and composting. Consequently, in a country of 8.5 million people, about 1.5 million tonnes of greenhouse gas emissions are avoided each year.
Most of the municipal waste in large waste-producing countries is used for landfill. In the United States, about 8.5% of municipal waste is composted, which represents an increase of 20% since the year 2000. This composting provides an annual benefit of mitigating more than 168 million tonnes of greenhouse gas emissions which is comparable to the annual emissions from more than 33 million passenger vehicles. Conversely, Japan disposes of only about 2% of its municipal solid waste as landfill; about 4% is composted and the rest of it is incinerated.
- Regional councils
- Intensive animal production systems, including piggeries, dairy and beef feedlots
- Generators of green waste, including households, community groups and industry
- Compost users, including farmers, horticulturalists and gardeners
Sources of information
Some examples and information sources
The Australian Organics Recycling Association (AORA) is a national body that raises awareness of the benefits of recycling organic resources. AORA is an advocate for the broader organics resource recovery and beneficial reuse industries.
The ‘Compost for Soils’ website is a free, independent source of information about using compost in agricultural systems. The website has fact sheets and case studies on the commercial use of compost in vegetable, vine, tree and broadacre crops.
The Waste Management Association of Australia (WMAA) supports sustainable waste and resource management across Australia. The WMAA branch in Western Australia has a special interest group called Compost WA.
Several regional local government councils, such as the Southern Metropolitan Regional Council and the Mindarie Regional Council, have pooled resources to develop advanced, large-scale systems to process organic waste.
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