Aerobic biological decomposition and stabilization under conditions which allow development of thermophilic temperatures as a result of biological heat, with a final product sufficiently stable for storage and beneficial soil application.
|Best Available Technique:
The main objective is to obtain a stable product with low moisture content and being free of pathogens and seeds. The significant reduction of mass (water evaporation) reduces substantially transport costs.
|Level of complexity
|Typical technology combinations||
Composting can be a downstrem processing, following separation of liquids. Adding bulking agent, composting.
Illustration of on farm composting (first to third columns) and centralized composting of solid cattle manure, Juncosa, Spain (fourth column).
Waggon for placing separation solids in windrows at Iowa cattle farm.
|Theroetical fundamentals and process description
||Compost is obtained through a thermophilic aerobic degradation process of the organic matter, followed by a curing phase where temperature slowly decreases and complex organic macromolecules are produced (fulvic and humic acids).|
In the first stage (decomposition), exothermic reactions produce an increase of temperature of the composting matrix above 50ºC (55-70ºC). Aerobic conditions must be assured in order to enable the reaction. Mechanical turning of the piles, as well as forced aeration are commonly used. The high temperatures, together with aeration, leads to a high rate of water evaporation. Water must be provided and maintained to a certain level to avoid microbes inhibition. In a second stage, curing is produced. Complex organic matter is degraded and humic and fluvic acids are produced. Temperature slowly decreases till room temperature. The whole process lasted between 8 to 16 weeks.
Adequate initial conditions of the composting matrix: Moisture content: 40-65%, C/N ratio: 25-35. Porosity (AFP: Air Filled Porosity): 30-60%.
Solid manures usually need the addition of bulking agent (e.g. well-chopped straw) in order to have appropriate C/N ratio, structure and porosity. When applied to slurries a previous mechanical separation is necessary.
Composting of liquid manures requires abundant bulking agent, in order to absorb the water and have an adequate C/N ratio.
Effects on air (emissions):
Tiquia et al. (2002) found from trials with composting pig manure in Iowa, USA the following results:
The impacts of composting on the loss of weight, carbon and crop nutrients, especially N and P, has been the subject of many trials and studies, including the abovementioned results of Tiquia et al. (2002) that documents the massive losses of crop nutrients and the high production of grenhouse gases during the process.
- A mass loss during composting of 27-57%, highest in turned windrows (47-57%), compared to not turned windrows (27-43%). The mass loss is due to evaporation of water, but also losses of cabon (C) as a result of the oxidative processes, as well as loss of plant nutrients, N, P and K.
- The loss of C was similarly highest in the turned windrows (50 to 63%) compared to the unturned windrows (30–54%). C is especially lost as CO2, meaning that for instance 10 tonnes manure with a C content of 10% (fresh weight) during composting would produce up to 3.7 tonnes CO2, considering the atomic weight of C and O. However, some C is due to anaerobic zones also lost as methane (CH4) emissions, which is a much stronger greenhouse gas than CO2.
- The loss of N was also high, measured to between 37 and 60% of the initial N. N is during composting lost via both leaching, runoff and evaportation, the latter in form of ammonia (NH3) and laughing gas (N2O) emissions.
- Phosphorus (P) and potassium (K) losses were 23 to 39% and 20 to 52% of the initial P and K, respectively, while the sodium (Na) loss was between 32–53% of the initial Na. The main losses of these nutrients happened in the form of leaching and runoff.
Flotats et al. (2011) concluded on basis of literature reviews the following magnitude of greenhouse gas production during the composting process:
|g/kg VS degraded
||8.1 - 13
||0.047 - 0.176
|CO2eq (g/kg VS degraded)
||271 - 418
||22 - 83
The use of close systems (tunnels), or semi-permeable membranes, as well as efficient aeration, can reduce emissions, but would alos make the composting process even more costly.
Effects on water/soil (and management):
- According the above concerning environmental effects, up to 60% of the nitrogen (N) and 39% of the phosphorus (P) in the initial material is lost during composting. The phosphorus is mainly lost via runoff and a minor parts as leaching, and it is therfore polluting waters and resulting in eutrophication.
- Part of the considerable loss of N during composting happens as leaching and runoff. Sommer (2001) indicates the N loss via leacing to be around one fifth of the entire N loss.
- Organic matter stabilization, pathogens and seeds removal, and odour abatement (during the thermophilic phase).
- Due to the huge loss of crop nutrients during composting, the fertilising value of compost is low and resulted in poor yields of barley (Sommer, 2001).
- Volume and weigh reduction: 40-50%
- Conversion of ammonia to NO3 and organic nitrogen (40 – 70%)
- Concentration of nutrients and heavy metals (due to water evaporation)
- Organic matter stabilization, pathogens and seeds removal, and odour abatement.
Net energy consumption - explanation:
The guidance consumptions of the possible machineries used in a composting plant are:
Energy consumption (KWhel/t)
|Shredding and crushing
|Container composting (11 days)
|Waste gas purification of 11 days intensive composting
|Conversion of the secondary maturing stage windrows in door composting, every 14 days for 8 weeks
|Waste gas purification (8 weeks)
Reagent 1 - explanation:
- Bulking agent in different proportions
- Water: 250-650 L/t manure
- Possible use of inoculum to start up the process, or chemical agents to reduce odour emission
Composting can be applied at farm scale (exists many experiences), but composting in centralized plants could benefit of scale economy.
|Economic indicators (Economic figures are rough indications, which cannot be used for individual project planning)||
- Turner machinery (windrow composting): 30,000 € (100 m3/h) / 100,000 € (1,000 – 1,500 m3/h)/ 180,000 (2,500 m3/h)
- Tractor: 50,000 €
- Mixers: 20,000- 50,000 € (10-100 m3/h)
- Drum sieve: 70,000 (100 m3/h)
Full plant (investment cost):
- Turned windrow composting plant (2,000 t/y manure + 1,360 t/y sawdust): 35,000 – 100,000 € (depending on the buildings or covers constructed)
Operational costs - explanation:
As a guidance: 20€/ton
Quantifiable income - text:
Sales of compost (guidance price): 15 - 30 €/t
Non economically quantifiable benefits:
Favours closing the nutrient cycle, consequently the consumption of fossil fuels used to synthesize chemical fertilizers is reduced.
- Ahn, H.K., Mulbry, W., White, JH.W., Kondrar, S.L. (2011) Pile mixing increases greenhouse gas emissions during composting of dairy manure. Bioresource Technology 102: 2904-2909.
- Barrington, S. Choinière, D., Trigui, M., Knight, W. (2002). Effect of carbon source on compost nitrogen and carbon losses. Bioresource Technology 83: 189-194.
- CBMI (2010). Best available Technologies for manure treatment- For intensive rearing of pigs in batic sea region EU member states. Baltic Sea 2020. pp. 103
- de Guardia, A., Mallard, P., Teglia, C., Marin, A., Le Pape, C., Launay, M., Benoist, J.C., Petiot, C. (2010). Comparison of five organic wastes regarding their behaviour during composting: Part 2, nitrogen dynamic. Waste Management 30: 415 – 425
- Flotats, Xavier, Henning Lyngsø Foged, August Bonmati Blasi, Jordi Palatsi, Albert Magri and Karl Martin Schelde. 2011. Manure processing technologies. Technical Report No. II concerning “Manure Processing Activities in Europe” to the European Commission, Directorate-General Environment. 184 pp.
- Hao, X., Chang, C., Larney, F. J., Travis, G.R. (2001) Greenhouse gas emissions during cattle feedlot manure composting. J. Environ. Qual. 30: 376-386
- Levasseur P. (2004) Traitement des effluents porcins. Guide Pratique des Procédés. Institut Technique du Porc. pp.36
- Sommer, S. G. 2001. Effect of composting on nutrient loss and nitrogen availability of cattle deep litter. European Journal of Agronomy Volume 14, Issue 2, March 2001, Pages 123-133
- Tiquia, S.M, T.L. Richard & M.S. Honeyman. 2002. Carbon, nutrient, and mass loss during composting. Nutrient Cycling in Agroecosystems 62: 15–24, 2002.
- Zhu, N. (2007). Effect of low initial C/N ratio on aerobic composting of swine manure with rice straw. Bioresource Technology 98: 9-13
|Real scale installation references
Many full scale plants at farm level as well as centralized plants. E.g.:
- Composting Plant Juncosa de les Garrigues (Catalunya, Spain)
|Examples of suppliers