Composting - Turned Windrow
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Technology
Turned Windrow
Date Introduced in the market
Composting is an ancient technology. While farm equipment has been used for compost turning as early as the 1930s, specialized compost turning equipment became available in the 1970s.
Maturity of the technology
The technology is commercially available. Turned windrow composting is the most commonly used on-farm composting method.
Type of energy that can be produced
No energy can be captured from a turned windrow composting system.
Typical applications
This technology is suitable for farms that cannot efficiently use all the manure nutrients they generate on their land base, organic farms requiring product composting or farms where spreading raw manure is not allowed.
Payback and benefits
The most important benefit of on-farm composting is the production of marketable compost products that allow farms to sell manure nutrients. Other benefits include a reduction in the volume of a farm’s organic waste. This in turn enhances the farm’s waste handling and storage capacity. The stabilization of nutrients during the composting process also minimizes environmental risks following their application on the land.
Composting produces a plant growth-enhancing soil conditioner that reduces the requirements for fertilizers and pesticides. The use of compost is routinely accepted by organic farming certification programs.
Tipping fees for processing off-farm can help to offset processing costs. It can be assumed that a well-managed composting operation processing 10 000 tonnes of off-farm waste per year would cover its annualized processing costs and generate a profit.
Expertise, skills and training required for the design, installation and operation of composting facilities
Operators of composting systems must become familiar with the principles of the composting process. This includes an understanding of feedstock properties (particle (particle size, porosity), the carbon to nitrogen (C/N) ratio and the composting process itself (optimal moisture content, bulk density, temperature, active composting, curing, etc.). The necessary knowledge and skills can be obtained from other operators and through experience. For larger composting operations, participation in a training course on composting is recommended. The coordinates of schools and companies that provide training courses can be readily found on the Internet.
The involvement of professionals in the design and layout of the composting site is recommended. The technical support they provide can include extension services or the services of technology providers. In come cases, a literature review may suffice.
Site preparation can generally be done by the farmer. The sloping pad for large-scale composting projects be designed by engineers and its construction should be carried out by qualified contractors.
Operating and maintaining turned windrow systems requires familiarity with the compost turning equipment and the requirements of the composting process as described above.
Operational and maintenance requirements
The major time requirement for operating a turned windrow system involves turning the compost usually once or twice weekly. Turning equipment capacity ranges from 50 to over 500 cubic meters per hour depending on equipment size. Other activities include blending products, building the windrow, monitoring temperatures, and screening and curing the final compost. Maintenance requirements apply to the compost turner, loaders an to maintaining the integrity of the composting pad.
BOS and labour requirements
Equipment input. On small operations, a farm loader is sufficient for turning the windrows. For larger operations, a specialized windrow turner is recommended. A grinder may be required for breaking down larger and bulky materials. The production of saleable product requires a screener.
Construction input. An appropriate site for the windrows must be constructed (impermeable pad, sloped to facilitate leachate collection).
Labour input. Labour is required to operate the compost turner, building windrows, monitoring compost temperature and screening the final product.
The process output should be a pathogen-free, safe product with soil fertility-enhancing properties.
Relatively efficient large-scale composting operations require on average one labour-hour for every 6 tonnes of incoming feedstock material or approximately one full-time worker per 10,000 tonnes, year in and year out. However, for lower volumes, for material processed after the active phase or for slightly putrescible material with low odour potential, composting operations can be considered as second priority job that can wait, particularly during the curing phase.
Feedstocks
Feedstock material input. Feedstocks include manure and bulking agents, which may include straw, woody waste, corn stover, or yard trimmings.
Almost all on-farm, and most off-farm waste of plant or animal origin can be processed. Off-farm waste, however, often requires extra attention to comply with health and safety regulations. Generally, a single type of organic waste does not present all the required characteristics for efficient composting. That is why it is necessary to mix different feedstock materials in order to obtain optimal moisture content, porosity and nutrient ratio. Accordingly, wet, high-nitrogen feedstock such as manure must be combined with dry, bulky and high-carbon amendments that include straw, woody waste, corn stover, or yard trimmings, as mentioned above.
Managing the feedstocks
The composition of some manure allows the use of windrow composting without further processing. Liquid manures such as hog manure or dairy manure will require liquid-solid separation before composting the solid fraction. Poultry manures may require addition of carbon in the form of straw or woody waste to reduce ammonia emissions.
Record keeping and quality assessments are critical to ensure the cost effectiveness and environmental safety of the composting process. This includes keeping various types of records:
- Material flow records: total and seasonal quantity and quality of input and output material (on-farm and off-farm resources, distribution or application of compost material);
- Composting process records: temperature and turning frequency;
- Compost quality records: results of compost testing for pathogens and trace metals (but only if intended for off-farm uses in most cases).
- Process parameters, i.e. usually only temperature, should be monitored every 3 to 4 days during the initial composting phase. Material flow should be recorded upon occurrence. Compost quality testing, if the compost is intended for sale, is typically carried out at every 1,000 tonnes or yearly.
System dimensions
There are no minimum or maximum feedstock volume restrictions on the composting system. However, it may be difficult to justify the expenses for systems processing less than 500 tonnes per year. Available space, economic and environmental considerations may limit the use of turned windrow technology. Other composting technologies such as in-vessel or aerated static pile systems should be considered when waste volumes are high (>2,000 tonnes per year), available space is limited, in high rainfall areas, or near residential areas.
Performance per installed unit
For turned windrow composting, windrow size ranges from 3 to 5 meters (10 to 18 ft) wide by 1.5 to 2.0 meters (5 to 7 ft) high. Windrow length depends on volume and site layout, and often ranges from 20 m to 100 m.
The width and height of windrows is typically dictated by the size of the windrow turning equipment. For this type of composting, the creation of a chimney effect, where hot air in the windrow rises to the top and cold air is drawn in through the sides, is critical. The capacity of compost turners ranges from 50 to over 500 cubic meters per hour. The required space capacity for active turned windrow composting ranges from 0.6 m3 of composting material per square meter of composting area for a small tractor-pulled windrow turner, to 1.1 m3 per sq meter for a large self-propelled compost turner. This amounts to 1.2 to 2.2 cubic meters of material per square meter of composting area per year, assuming a 6-month composting period.
The active composting phase typically results in a volume reduction of 20% to 30 % depending on the feedstock material, processing conditions and time. Total approximate volume reduction, from incoming feedstock material to a saleable compost product, i.e. including a refinement by screening, is approximately 50%.
Costs per unit and system
Equipment cost
For small composting operations (<2,000 tonnes per year), the composting process can be completed with existing farm loaders.
For larger composting operations (>5,000 tonnes per year) specialized equipment is recommended. Costs for windrow compost turners range from $20,000 for a small tractor-pulled compost turner to over $500,000 for a large self-propelled turner. Turning costs range from $ 5to $9 per cubic meter assuming weekly turning, depending on the size of turner and the volume of material to be composted.
Site preparation
Costs for site preparation depend on the area, local topography, soil, type of pad and environmental requirements, and can range from under $1 to up to $20 per square meter.
Total cost
Total initial investment costs can be less than $20,000, with no site preparation and the use of available on-farm machinery, to $1,000,000 and more for special equipment and engineered site preparation.
Example
For a farm processing 2,000 tonnes (approx. 3,200 cubic meters) of manure annually investment costs typically range between $40,000 to $200,000, resulting in annualized production costs per tonne of compost between $35 and $70.
System performance limitations and potential problems
Composting manure in a turned windrow system typically requires moisture content of 50-60% and a bulk density of 500 to 750 kg per cubic meter. This means that liquid manures require liquid-solid separation before composting the solids. On the other hand, dry, high- nitrogen content manures such as poultry litter may require additional moisture and carbon.
Outdoor turned windrows are strongly impacted by climatic conditions. This calls for particular attention to moisture and temperature management. Odours may bother neighbours making it advisable to avoid windrow turning at certain times of the day or in certain climatic conditions. Leachate may also be a source of environmental concern but can be avoided by a proper site layout (surface sloping, containment structures such as berms, ditches and impermeable pads). Outdoor turned windrows are not recommended in high rainfall areas because of the large amount of leachate that may be result, as well as poor composting performance due to excess moisture.
Warranties and system life expectancy
The life expectancy of properly maintained machinery and pads ranges between 10 and 20 years.
Potential synergy with other energy systems
Turned windrow composting can be used for processing the solid portion of manure produced from an anaerobic digestion process.
Links to other sources of information
http://www.compost.org/
US Composting Council
http://www.compostingcouncil.org/index.cfm
Composting website of the Cornell University, Ithaca, NY
http://www.css.cornell.edu/compost/Composting_Homepage.html
British Columbia Ministry of Agriculture composting handbook
http://www.agf.gov.bc.ca/resmgmt/publist/300series/382500-0.pdf
On-farm composting handbook
by Robert Rynk (editor), 1992, available from the Northeastern Regional Agricultural Engineering Service, Ithaca, NY. (www.nraes.org)
Compost Software
Co-Composter
Free excel spreadsheet developed by Cornell University that can be downloaded at
http://compost.css.cornell.edu/CoCompost.html
Compost Recip-ez®
Compost planning spreadsheet from Pike Agri-Lab Supplies that can be purchased at
www.pikeagri.com
FORCE3©
Composting formulation software developed by the Centre de Recherche Industrielle Quebec that can be purchased at
www.criq.qc.ca/en/0202_envir/force3.html
Compost Wizard
Spreadsheet windrow composting operation program that can be purchased
www.compostwizard.com
Technology supplier sources
Composting Council of Canada
http://www.compost.org/
US Composting Council
http://www.compostingcouncil.org/index.cfm
BioCycle Magazine
http://www.jgpress.com/
Modern composting technologies.
by Chiumenti, Alessandro et al., 2005, available fromBioCycle, JG Press, Inc.
Recommended steps for the project development process
- Conduct a literature review focusing on on-farm composting (see other sources of information).
- Before contacting extension services or technology providers, be sure to have the following information:
a) Approximate yearly/weekly amount and composition/properties of organic waste material to be composted;
b) For manure composting, access to off-farm material that can be used as bulking agent and carbon source (for example, wood shavings)
c) The intended end-use of the compost product (ex: on-farm application or sale) and whether or not there is a market;
d) The projected location of the composting site:
i. Presence of neighbours insisting on odour control measures;
ii. Nearby surface water and distance to water table.
- Contact local extension services to obtain the following information:
a) Farms in your area that already use composting technologies;
b) Programs promoting composting;
c) Legislation affecting composting at the composting site (provincial legislation and regional bylaws).
- Contact technology providers.
Modified: 03-31-2008
